期刊文献+
共找到190,483篇文章
< 1 2 250 >
每页显示 20 50 100
Design and analysis of a class of redundant collaborative manipulators with 2D large rotational angles 认领
1
作者 Xiaodong JIN Yuefa FANG +1 位作者 Dan ZHANG Xueling LUO 《机械工程前沿:英文版》 SCIE CSCD 2020年第1期66-80,共15页
The parallel spindle heads with high rotational capability are demanded in the area of multi-axis machine tools and 3D printers.This paper focuses on designing a class of 2R1T(R:Rotation;T:Translation)parallel spindle... The parallel spindle heads with high rotational capability are demanded in the area of multi-axis machine tools and 3D printers.This paper focuses on designing a class of 2R1T(R:Rotation;T:Translation)parallel spindle heads and the corresponding collaborative 5-axis manipulators with 2-dimension(2D)large rotational angles.In order to construct 2D rotational degrees of freedom(DOFs),a platform with 2D revolute joints is proposed first.Based on the constraint screw theory,the feasible limbs that can be connected in the platform are synthesized.In order to provide constant rotational axis for the platform,a class of redundant limbs are designed.A class of redundant 2R1T parallel spindle heads is obtained by connecting the redundant limbs with the platform and the redundant characteristics are verified by the modified Grübler-Kutzbach criterion.The corresponding 5-axis collaborative manipulators are presented by constructing a 2-DOF series translational bottom moving platform.The inverse kinematics and the orientation workspace as well as the decoupling characteristics of this type of 2R1T parallel spindle heads are analyzed.The results show that these manipulators have large 2D rotational angles than the traditional A3/Z3 heads and can be potentially used in the application of multi-axis machine tools and the 3D printers. 展开更多
关键词 parallel mechanism redundant mechanism large rotational angles machine tools 2R1T spindle head collaborative manipulator
Priori information analysis of optocoupler accelerated degradation experiment based on failure mechanism verification test 认领
2
作者 Xuan-gong Zhang Xi-hui Mu +1 位作者 Jing Feng Hui-zhi Li 《Defence Technology(防务技术)》 SCIE EI CAS CSCD 2020年第2期392-400,共9页
The optocoupler is a weak link in the inertial navigation platform of a kind of guided munitions.It is necessary to use accelerated storage test to verify the storage life of long storage products.Especially for small... The optocoupler is a weak link in the inertial navigation platform of a kind of guided munitions.It is necessary to use accelerated storage test to verify the storage life of long storage products.Especially for small sample products,it is very important to obtain prior information for the design and implementation of accelerated degradation test.In this paper,the optocoupler failure mechanism verification test is designed and the experimental results are analyzed and the prior information is obtained.The results show that optocouplers have two failure modes,one is sudden failure and the other is degradation failure;the maximum temperature stress of optocoupler can’t exceed 140℃;the increase of leakage current of optocoupler is caused by movable ions contaminating the LED chip.The surface leakage current is proportional to the adsorption amount.The increase of leakage current makes p-n junction tunneling effect occur which LEDs the failure of the optocoupler.The lifetime distribution model of the optocoupler is determined by the failure physics.The lifetime of the optocoupler is subject to the lognormal distribution.The degeneracy orbit of the optocoupler leakage current is described by a power law model.The estimated values of the orbital parameters are initially calculated and the parameters of its life distribution function are deduced.The above information lays a good foundation for the optimization design and data processing of the accelerated degradation experiment. 展开更多
关键词 Priori information Failure mechanism Failure mechanism verification test Accelerated degradation
在线阅读 免费下载
Application of nanoparticles in cast steel:An overview 认领
3
作者 Feng Qiu Tian-shu Liu +5 位作者 Xin Zhang Fang Chang Shi-li Shu Hong-yu Yang Qing-long Zhao Qi-chuan Jiang 《中国铸造:英文版》 SCIE 2020年第2期111-126,共16页
The innovative and environmentally friendly methodologies for comprehensively enhancing the performances of high-strength steels without damage to plasticity,toughness and heat/corrosion/fatigue resistance are being d... The innovative and environmentally friendly methodologies for comprehensively enhancing the performances of high-strength steels without damage to plasticity,toughness and heat/corrosion/fatigue resistance are being developed.In recent years,nanoparticles elevate the field of high-strength steel.It is proposed that nanoparticles have the potential to replace conventional semi-coherent intermetallic compounds,carbides and alloying to optimize the steel.The fabrication process is simplified and the cost is lower compared with the traditional methods.Considerable research effort has been directed towards high-performance cast steels reinforced with nanoparticles due to potential application in major engineering.Nanoparticles are found to be capable of notably optimizing the nucleation behavior and precipitate process.The prominently optimized microstructure configuration and performances of cast steel can be acquired synchronously.In this review,the lattice matching and valence electron criterion between diverse nanoparticles and steel are summarized,and the existing various preparation methods are compared and analyzed.At present,there are four main methods to introduce nanoparticles into steel:external nanoparticle method,internal nanoparticle method,in-situ reaction method,and additive manufacturing method.These four methods have their own advantages and limitations,respectively.In this review,the synthesis,selection principle and strengthening mechanism of nanoparticles in cast steels for the above four methods are discussed in detail.Moreover,the main preparation methods and microstructure manipulation mechanism of the steel reinforced with different nanoparticles have been systematically expatiated.Finally,the development and future potential research directions of the application of nanoparticles in cast steel are prospected. 展开更多
关键词 NANOPARTICLES high-performance steel strengthening mechanism preparation method microstructure manipulation mechanism
Novel method of constructing generalized Hoberman sphere mechanisms based on deployment axes 认领
4
作者 Xuemin SUN Yan-An YAO Ruiming LI 《机械工程前沿:英文版》 SCIE CSCD 2020年第1期89-99,共11页
This study proposes a method of constructing type II generalized angulated elements(GAEs II)Hoberman sphere mechanisms on the basis of deployment axes that intersect at one point.First,the constraint conditions for in... This study proposes a method of constructing type II generalized angulated elements(GAEs II)Hoberman sphere mechanisms on the basis of deployment axes that intersect at one point.First,the constraint conditions for inserting n GAEs II into n deployment axes to form a loop are given.The angle constraint conditions of the deployment axes are obtained through a series of linear equations.Second,the connection conditions of two GAEs II loops that share a common deployable center are discussed.Third,a flowchart of constructing the generalized Hoberman sphere mechanism on the basis of deployment axes is provided.Finally,four generalized Hoberman sphere mechanisms based on a fully enclosed regular hexahedron,arithmetic sequence axes,orthonormal arithmetic sequence axes,and spiral-like axes are constructed in accordance with the given arrangement of deployment axes that satisfy the constraint conditions to verify the feasibility of the proposed method. 展开更多
关键词 deployable mechanism type II generalized angulated elements Hoberman sphere mechanism deployment axes constraint conditions
Phthalonitrile Resins Derived from Vanillin: Synthesis, Curing Behavior, and Thermal Properties 认领
5
作者 Yue Han Dong-Hao Tang +4 位作者 Guang-Xing Wang Ya-Nan Sun Ying Guo Heng Zhou Wen-Feng Qiu 《高分子科学:英文版》 SCIE CAS CSCD 2020年第1期72-83,I0007共13页
Vanillin was used as sustainable source for phthalonitrile monomer synthesis, and allyl/propargyl ether moieties were introduced to improve the processability at the minimal cost of thermal properties. The synthesis r... Vanillin was used as sustainable source for phthalonitrile monomer synthesis, and allyl/propargyl ether moieties were introduced to improve the processability at the minimal cost of thermal properties. The synthesis route was optimized to minimize side-reactions and simplify post-processing, and the monomers were obtained in high purity and good yields. The curing behavior, mechanism, and processability of the monomers were studied, and the thermal properties of cured polymers were evaluated. Of the two monomers, the allyl ether-containing one exhibited a wide processing window of 185 °C, and was mainly cured into phthalocyanine and linear aliphatic structures through self-catalytic curing process. Also, the glass transition temperature was higher than 500 °C. In contrast, the propargyl ether-containing monomer could only be partially cured, and heat resistance was found to be compromised. Compared with traditional petroleum-based phthalonitrile resins, the biobased monomers could be cured without the addition of catalysts, and improvement in processability was achieved at no cost of thermal performances. 展开更多
关键词 ALLYL ETHER CURING mechanism PHTHALONITRILE Thermal properties VANILLIN
金属有机框架材料UTSA-74高效去除水溶液中的砷 认领
6
作者 余文婷 张慧 +2 位作者 孙玉珍 吴昊 罗明标 《应用化学》 CAS CSCD 北大核心 2020年第2期205-210,共6页
利用水热法合成金属有机框架材料UTSA-74,并用它同时去除水中的As(Ⅴ)和As(Ⅲ)。批次实验结果表明,在低质量浓度情况下(~1 mg/L),UTSA-74对As(Ⅴ)的去除率高达95%。对As(Ⅲ)的去除率达85%。经拟合,本实验符合拟二级动力学及Freundlich... 利用水热法合成金属有机框架材料UTSA-74,并用它同时去除水中的As(Ⅴ)和As(Ⅲ)。批次实验结果表明,在低质量浓度情况下(~1 mg/L),UTSA-74对As(Ⅴ)的去除率高达95%。对As(Ⅲ)的去除率达85%。经拟合,本实验符合拟二级动力学及Freundlich等温吸附模型。本文还探究了共存离子(如Cl^-、NO3^-、PO4^3-)干扰影响,结果表明PO4^3-的存在会抑制吸附的进行,可能是由于竞争吸附位点所致。此外,本文对吸附后的材料进行洗脱(0.1 mol/L NaOH),将洗脱后的UTSA-74材料再次进行吸附探究,反复3次,其去除率仍可达70%左右。为探究其中机理,本文通过X射线衍射(XRD)、扫描电子显微镜(SEM)、红外光谱(IR)对吸附前后材料进行表征,结果表明吸附过程中可能形成了Zn—O—As,以此促进吸附反应的进行。综上所述,UTSA-74可以作为一种处理砷的新型吸附剂,具有一定的实用价值。 展开更多
关键词 去除 UTSA-74 机理
在线阅读 下载PDF
Study of Mechanisms of CO and NO2O xidation on Zn–CNT(6,0) and Zn–BNNT(6,0),Mn–B38N38 and Mn–C76 认领
7
作者 曾智文 李翔 +1 位作者 张复兴 NAJAFI Meysam 《结构化学》 SCIE CAS CSCD 2020年第1期41-47,2共8页
The abilities and performances of Mn–C76,Mn–B38N38,Zn–CNT(6,0)and Zn–BNNT(6,0)to the oxidation of NO2 and CO are investigated.The oxidation reactions of NO2 and CO through the Langmuir-Hinshelwood(LH)and Eley-Ride... The abilities and performances of Mn–C76,Mn–B38N38,Zn–CNT(6,0)and Zn–BNNT(6,0)to the oxidation of NO2 and CO are investigated.The oxidation reactions of NO2 and CO through the Langmuir-Hinshelwood(LH)and Eley-Rideal(ER)mechanisms by theoretical methods are examined.The most stable intermediates of oxidation reactions of NO2 and CO on Mn–C76,Mn–B38N38,Zn–CNT(6,0)and Zn–BNNT(6,0)are obtained from thermodynamics view point.In the LH pathway,Mn–C76,Mn–B38N38,Zn–CNT(6,0)and Zn–BNNT(6,0)catalysts are deactivated via the second NO2 and CO molecules.In the ER pathway,the second NO3 and CO2 molecules are separated.Finally,the Mn–C76,Mn–B38N38,Zn–CNT(6,0)and Zn–BNNT(6,0)are proposed to oxidize NO2 and CO molecules with high performances at room temperature. 展开更多
关键词 NO2 CO2 CATALYST MECHANISM NANO MN and ZN
在线阅读 下载PDF
竞技健美操腕关节损伤的机制、治疗及预防 认领
8
作者 黄志欣 《体育科技文献通报》 2020年第5期49-50,共2页
腕关节是竞技健美操运动员在长期的训练和比赛中出现损伤的部位,这种损伤的治疗方法多种多样,它的治疗与预防也需要建立在对其损伤机制了解的基础上。本文通过文献资料法,梳理近年来竞技健美操项目中关于腕关节损伤的机制、治疗及预防... 腕关节是竞技健美操运动员在长期的训练和比赛中出现损伤的部位,这种损伤的治疗方法多种多样,它的治疗与预防也需要建立在对其损伤机制了解的基础上。本文通过文献资料法,梳理近年来竞技健美操项目中关于腕关节损伤的机制、治疗及预防的研究,并进行总结,给出自己的建议。 展开更多
关键词 腕关节 竞技健美操 机制 治疗 预防
在线阅读 下载PDF
载硫活性炭脱汞性能及其反应机理研究 认领
9
作者 陶君 谷小兵 +1 位作者 李娜 段钰锋 《热能动力工程》 CAS CSCD 北大核心 2020年第2期201-207,共7页
以市售商业载硫活性炭为研究对象,在固定床实验台上进行汞吸附实验,分析吸附温度、入口汞浓度对其脱汞性能的影响,通过表征方法对失活前后吸附剂的物理化学性质进行对比,采用程序升温热脱附实验得到样品中吸附的汞形态,并探究其脱汞机... 以市售商业载硫活性炭为研究对象,在固定床实验台上进行汞吸附实验,分析吸附温度、入口汞浓度对其脱汞性能的影响,通过表征方法对失活前后吸附剂的物理化学性质进行对比,采用程序升温热脱附实验得到样品中吸附的汞形态,并探究其脱汞机理。结果表明:实验样品的适宜脱汞温度为70℃,脱汞效率随着汞浓度的升高而降低;活性炭样品失活后比表面积下降,表面含氧官能团减少,非氧化态硫含量降低,其汞吸附形态以HgS、HgO为主;载硫活性炭样品对汞的吸附脱除主要依靠含氧官能团和含硫官能团的化学吸附作用。 展开更多
关键词 载硫活性炭 脱汞 吸附 失活 机理
重组人白血病抑制因子蛋白对兔椎间盘退变模型髓核细胞凋亡的影响机制 认领
10
作者 穆林 房昕 +2 位作者 龚箭 高迎庆 周强 《中国医院用药评价与分析》 2020年第4期403-406,共4页
目的:探讨重组人白血病抑制因子(leukemia inhibitory factor,LIF)蛋白对兔椎间盘退变模型髓核细胞(nucleus pulposus cells,NPCs)凋亡的影响机制。方法:采用针刺法构建兔椎间盘退变模型,利用磁共振成像观察兔椎间盘退变程度,摘除髓核... 目的:探讨重组人白血病抑制因子(leukemia inhibitory factor,LIF)蛋白对兔椎间盘退变模型髓核细胞(nucleus pulposus cells,NPCs)凋亡的影响机制。方法:采用针刺法构建兔椎间盘退变模型,利用磁共振成像观察兔椎间盘退变程度,摘除髓核组织提取组织蛋白,采用Western Blot法检测髓核组织LIF蛋白表达水平,提取退变NPCs,采用流式细胞术观察不同浓度重组人LIF蛋白对退变NPCs凋亡的影响,采用Western Blot法检测不同浓度重组人LIF蛋白对细胞外基质成分和MAPK-ERK1/2通路蛋白表达的影响。结果:模型组兔的椎间盘高度和信号-噪声比(SNR)明显低于对照组,差异均有统计学意义(P<0.05);模型组兔髓核组织中LIF蛋白表达水平明显高于对照组,差异有统计学意义(P<0.05);针刺2周、4周及8周,各组兔髓核组织中LIF蛋白表达水平比较,差异有统计学意义(P<0.05);0、10、20、50及100 ng/ml重组人LIF蛋白处理的退变NPCs凋亡率比较,差异有统计学意义(P<0.05);0、10、20、50及100 ng/ml重组人LIF蛋白处理的退变NPCs中Aggtecan蛋白、Ⅱ型胶原及p-ERK1/2蛋白表达水平比较,差异有统计学意义(P<0.05)。结论:兔椎间盘退变髓核组织中LIF蛋白呈高表达,其可能通过激活ERK1/2通路促进细胞外基质合成达到抑制NPCs凋亡作用,重组LIF在延缓椎间盘退变方面显示出了良好前景。 展开更多
关键词 重组人LIF蛋白 兔椎间盘退变模型 髓核细胞凋亡 机制
在线阅读 下载PDF
塞来昔布对食管癌EC109细胞凋亡及机制的影响 认领
11
作者 赵梦瑶 李思源 +3 位作者 肖志伟 蔺茹君 赵晓伟 李军 《广州医药》 2020年第1期10-13,共4页
目的利用分析各种浓度环氧化酶-2(COX-2)特异度抑制剂塞来昔布对食管癌EC109细胞系的作用,进而对COX-2蛋白表达的影响及对细胞凋亡能力的作用,进一步探讨塞来昔布对食管癌细胞凋亡的作用及机制。方法使用0μmol/L、20μmol/L、60μmol/L... 目的利用分析各种浓度环氧化酶-2(COX-2)特异度抑制剂塞来昔布对食管癌EC109细胞系的作用,进而对COX-2蛋白表达的影响及对细胞凋亡能力的作用,进一步探讨塞来昔布对食管癌细胞凋亡的作用及机制。方法使用0μmol/L、20μmol/L、60μmol/L、100μmol/L四个浓度的塞来昔布处理EC109细胞24 h,酶联免疫吸附剂测定(ELISA)法测定COX-2蛋白表达;流式细胞仪测定EC109细胞凋亡情况。结果与0μmol/L塞来昔布组比较,20μmol/L、60μmol/L、100μmol/L塞来昔布组EC109细胞内COX-2蛋白表达不断降低(1.581±0.116;1.226±0.089,0.846±0.076,0.521±0.082)(P<0.05);而细胞凋亡率逐步上升(1.700±0.557,13.400±1.735,18.766±1.301,28.100±1.997)(P<0.05)药物浓度依赖于梯度。结论塞来昔布是一种COX-2抑制剂,可能以浓度梯度的形式抑制COX-2蛋白的表达,从而促进EC109细胞的凋亡。 展开更多
关键词 食管癌 塞来昔布 细胞 机制 凋亡
在线阅读 免费下载
NLR比值在2型糖尿病慢性肾脏疾病中的意义 认领
12
作者 修贤杰 张萍 陈光 《广东化工》 CAS 2020年第7期120-120,106,共2页
2型糖尿病合并慢性肾脏疾病较为常见,作为2型糖尿病的主要并发症之一,慢性肾脏疾病的出现不仅会加重糖尿病病情,降低患者的生活水平,还会对进一步威胁患者的健康乃至生命安全。中性粒细胞/淋巴细胞比值(NLR)是评价2型糖尿病慢性肾脏疾... 2型糖尿病合并慢性肾脏疾病较为常见,作为2型糖尿病的主要并发症之一,慢性肾脏疾病的出现不仅会加重糖尿病病情,降低患者的生活水平,还会对进一步威胁患者的健康乃至生命安全。中性粒细胞/淋巴细胞比值(NLR)是评价2型糖尿病慢性肾脏疾病的重要指标,通过对NLR比值的计算能够在一定程度上了解和掌握2型糖尿病合并慢性肾脏疾病的病情,进而对预后的改善起到积极的作用。 展开更多
关键词 中性粒细胞 淋巴细胞 慢性肾脏疾病 意义 机制
在线阅读 下载PDF
锰系锂离子电池正极材料的锰溶解及沉积机理研究进展 认领
13
作者 李文博 李世友 +2 位作者 耿彤彤 彭峰峰 梁有维 《硅酸盐学报》 EI CAS CSCD 北大核心 2020年第1期73-78,共6页
锰溶解是造成锰基正极材料性能恶化的重要因素之一,它不仅直接引起电极活性材料的损失,还会随着锰的迁移而在负极表面进行沉积,进而引发一系列的副反应,造成电池容量的不可逆损失。总结了锰系锂离子电池正极材料的锰溶解及沉积机理,分... 锰溶解是造成锰基正极材料性能恶化的重要因素之一,它不仅直接引起电极活性材料的损失,还会随着锰的迁移而在负极表面进行沉积,进而引发一系列的副反应,造成电池容量的不可逆损失。总结了锰系锂离子电池正极材料的锰溶解及沉积机理,分析了其对电池性能的影响,提出了抑制锰溶解及沉积的方法,并对锰基正极材料的发展进行了展望。 展开更多
关键词 锂离子电池 锰基正极材料 锰溶解 锰沉积 机理
Mn2NiO4 spinel catalyst for high-efficiency selective catalytic reduction of nitrogen oxides with good resistance to H2O and SO2 at low temperature 认领
14
作者 Fengyu Gao Xiaolong Tang +3 位作者 Honghong Yi Shunzheng Zhao Wenjuan Zhu Yiran Shi 《环境科学学报:英文版》 SCIE EI CAS CSCD 2020年第3期145-155,共11页
Mn-Ni oxides with different compositions were prepared using standard co-precipitation(CP) and urea hydrolysis-precipitation(UH) methods and optimized for the selective catalytic reduction of nitrogen oxides(NOx) by N... Mn-Ni oxides with different compositions were prepared using standard co-precipitation(CP) and urea hydrolysis-precipitation(UH) methods and optimized for the selective catalytic reduction of nitrogen oxides(NOx) by NH3 at low temperature.Mn((2))Ni(1)Ox-CP and Mn(2)Ni(1)Ox-UH(with Mn:Ni molar ratio of 2:1) catalysts showed almost identical selective catalytic reduction(SCR) catalytic activity,with about 96% NOx conversion at 750 C and-99%in the temperature range from 100 to 250℃.X-ray diffraction(XRD) results showed that Mn(2)Ni(1)Ox-CP and Mn(2)Ni(1)Ox-UH catalysts crystallized in the form of Mn2NiO4 and MnO2-Mn2NiO4 spinel,respectively.The latter gave relatively good selectivity to N2,which might be due to the presence of the MnO2 phase and high metal-O binding energy,resulting in low dehydrogenation ability.According to the results of various characterization methods,it was found that a high density of surface chemisorbed oxygen species and efficient electron transfer between Mn and Ni in the crystal structure of Mn2NiO4 spinel played important roles in the high-efficiency SCR activity of these catalysts.Mn(2)Ni(1)Ox catalysts presented good resistance to H2O or/and SO2 with stable activity,which benefited from the Mn2NiO4 spinel structure and Eley-Rideal mechanism,with only slight effects from SO2. 展开更多
关键词 Mn-Ni OXIDES SPINEL structure Low-temperature SCR H2O and SO2 RESISTANCE Eley-Rideal mechanism
急性外伤性硬脑膜下血肿快速消散的病理、机制及相关因素探讨 认领
15
作者 杜海平 李刚 《创伤外科杂志》 2020年第4期264-266,共3页
目的探讨急性外伤性硬脑膜下血肿(TASDH)快速消散的病理、机制,分析其相关因素,为临床治疗提供指导。方法回顾性分析2017年1月—2019年2月山东大学齐鲁医院神经外科TASDH患者12例,男性10例,女性2例;年龄15~51岁,平均35.8岁。观察患者入... 目的探讨急性外伤性硬脑膜下血肿(TASDH)快速消散的病理、机制,分析其相关因素,为临床治疗提供指导。方法回顾性分析2017年1月—2019年2月山东大学齐鲁医院神经外科TASDH患者12例,男性10例,女性2例;年龄15~51岁,平均35.8岁。观察患者入院时GCS评分、症状体征、头颅CT检查及诊断治疗情况,初步探讨血肿快速消散的机制。结果患者入院时平均GCS评分(11.7±2.2)分;平均血肿量18.2 mL。血肿呈断线样低高或等高混杂密度5例,较薄边缘呈锐利窄弧带样7例;中线移位7例,平均6.8mm,中线无移位5例;伴轻度脑挫裂伤2例,伴线性颅骨骨折4例;脑萎缩2例。伤后12h内消散3例,12~24h消散6例,24~72h消散3例;患者平均住院15.8d,出院3个月门诊随访,除1例偶有轻度头疼,近记忆力差的后遗症外,其余11例预后良好,无明显后遗症。结论部分TASDH患者经非手术治疗后血肿伤后12~72h消散,多数患者预后良好,可避免手术造成不必要的损伤。但在非手术治疗期间应根据病情变化行CT监测。 展开更多
关键词 颅脑损伤 硬脑膜下血肿 快速消散 机制
在线阅读 下载PDF
介词“照”的语法化探析 认领
16
作者 王义洁 《现代语文》 2020年第3期26-36,共11页
汉语中许多介词的产生,都是动词语法化的结果。“照”由“照射”义动词引申为“比照”义动词后,又进一步虚化为介词。介词“照”有作依据介词、时间介词、方向介词、对象介词、比较介词五种用法。“照”的依据介词用法、方向介词用法和... 汉语中许多介词的产生,都是动词语法化的结果。“照”由“照射”义动词引申为“比照”义动词后,又进一步虚化为介词。介词“照”有作依据介词、时间介词、方向介词、对象介词、比较介词五种用法。“照”的依据介词用法、方向介词用法和比较介词用法来源于动词“照”的“比照”义,“照”的时间介词用法由依据介词“照”虚化而来,“照”的对象介词用法则来源于方向介词“照”的功能扩展。“照”由动词语法化为介词的动因有语义层面的词义扩大及语义感染、句法层面的连动式结构、语用层面的口语交际及方言推动。 展开更多
关键词 “照” 介词 语法化 路径 动因 机制
在线阅读 下载PDF
Task allocation based on profit maximization for mobile crowdsourcing 认领
17
作者 Hou Yinglin Cheng Weiqing 《中国邮电高校学报:英文版》 EI CSCD 2020年第1期26-37,共12页
In recent years, with the development of smart devices, mobile users can use them to sense the environment. In order to improve the data quality and achieve maximum profits, incentive mechanism is needed to motivate u... In recent years, with the development of smart devices, mobile users can use them to sense the environment. In order to improve the data quality and achieve maximum profits, incentive mechanism is needed to motivate users to participate. In this paper, reputation mechanism, participant selection, task allocation and joint pricing in mobile crowdsourcing system are studied. A user reputation evaluation method is proposed, and a participant selection algorithm(PSA) based on user reputation is proposed. Besides, a social welfare maximization algorithm(SWMA) is proposed, which achieves task pricing with maximizing the interests of all parties, including both task publishers and mobile users. The social welfare maximization problem is divided into local optimization sub-problems which can be solved by double decomposition. It is proved that the algorithm converges to the optimal solution. Results of simulations verify that algorithms PSA and SWMA are effective. 展开更多
关键词 MOBILE crowdsourcing MAXIMUM PROFITS REPUTATION mechanism TASK ALLOCATION
丁酸在幼龄反刍动物中的作用机理及其产品应用的研究进展 认领
18
作者 吴东霖 徐萍 +1 位作者 邵凯 徐明 《动物营养学报》 CAS CSCD 北大核心 2020年第3期1034-1046,共13页
丁酸有促进幼龄反刍动物胃肠道发育、降低腹泻、缓解断奶应激和提高生长性能等生理功能。丁酸产品是在乳和饲料中添加的一类安全、无残留、环保的饲料添加剂。本文总结了丁酸在幼龄反刍动物中的作用机理,并以丁酸产品在乳和饲料中添加... 丁酸有促进幼龄反刍动物胃肠道发育、降低腹泻、缓解断奶应激和提高生长性能等生理功能。丁酸产品是在乳和饲料中添加的一类安全、无残留、环保的饲料添加剂。本文总结了丁酸在幼龄反刍动物中的作用机理,并以丁酸产品在乳和饲料中添加的应用效果为框架,综述了国内外丁酸产品在幼龄反刍动物中应用的研究进展,旨在为丁酸产品的推广应用提供参考。 展开更多
关键词 丁酸 作用机理 应用效果 幼龄反刍动物
在线阅读 下载PDF
试论“为官不为”现象的逻辑机理 认领
19
作者 岳鹏星 吕承文 《宝鸡文理学院学报:社会科学版》 2020年第2期31-37,共7页
懒庸顽劣是“为官不为”现象的集中体现,导致了怠政、懒政、误政等问题。近些年来,尽管国家反腐败的力度日益加大,社会中腐败的势头得到了有力地抑制,但是,这种“为官不为”现象却并未因此消失。从学理上来分析,“为官不为”现象是一种... 懒庸顽劣是“为官不为”现象的集中体现,导致了怠政、懒政、误政等问题。近些年来,尽管国家反腐败的力度日益加大,社会中腐败的势头得到了有力地抑制,但是,这种“为官不为”现象却并未因此消失。从学理上来分析,“为官不为”现象是一种制度性的结果,与政绩考核的制度设计、反腐败的广度及传统政治文化的路径依赖具有密切的关联,这也构成了其产生的逻辑机理。如将个人政绩考核与集体政绩考核辩证统一起来,在加大反腐力度的同时拓宽反腐的广度,与此同时继续开创出全新的现代政治文化,这样才可有效地消除当前存在的“为官不为”现象。 展开更多
关键词 “为官不为” 逻辑 机理
在线阅读 下载PDF
柴胡加龙骨牡蛎汤对急性心肌梗死合并焦虑小鼠血清ACTH及CORT的影响 认领
20
作者 杜泓森 史金玉 +4 位作者 王帅 安莹 靳会会 贾静芸 赵海滨 《世界中医药》 CAS 2020年第2期239-243,共5页
目的:观察柴胡加龙骨牡蛎汤对AMI合并焦虑小鼠血清ACTH及CORT的影响。方法:将30只小鼠随机分为假手术组、AMI组、焦虑组、AMI+焦虑组、中药组,每组6只,以冠脉结扎法合并空瓶刺激法制作复合模型,予柴胡加龙骨牡蛎汤干预14 d。造模结束后... 目的:观察柴胡加龙骨牡蛎汤对AMI合并焦虑小鼠血清ACTH及CORT的影响。方法:将30只小鼠随机分为假手术组、AMI组、焦虑组、AMI+焦虑组、中药组,每组6只,以冠脉结扎法合并空瓶刺激法制作复合模型,予柴胡加龙骨牡蛎汤干预14 d。造模结束后,予行为学及心脏彩超检测,后处死取各组血清检测ACTH及CORT含量。结果:与假手术组比较,AMI组小鼠LVEF和LVFS明显降低,LVEDd及LVESd值明显增加;AMI组及焦虑组小鼠水平和垂直运动得分均降低,开放臂进入次数和停留时间均减少;焦虑组ACTH和CORT含量增加;AMI组仅ACTH含量增多。与AMI+焦虑组比较,AMI组、焦虑组及中药组的LVEF、LVFS升高,LVEDd值明显较低;水平和垂直运动得分均升高;血清ACTH和CORT含量均降低。LVESd值仅AMI组及焦虑组降低;AMI组及中药组的OE%增加、OT%延长,焦虑组仅OT%延长。结论:柴胡加龙骨牡蛎汤抗焦虑、改善AMI预后的疗效机制可能与抑制ACTH和CORT含量的升高有关。 展开更多
关键词 柴胡加龙骨牡蛎汤 AMI合并焦虑 小鼠 血清 疗效 机制 ACTH CORT
在线阅读 下载PDF
上一页 1 2 250 下一页 到第
使用帮助 返回顶部 意见反馈