首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   8089篇
  免费   1139篇
  国内免费   1425篇
化学   7540篇
晶体学   127篇
力学   422篇
综合类   158篇
数学   338篇
物理学   2068篇
  2024年   20篇
  2023年   133篇
  2022年   563篇
  2021年   569篇
  2020年   415篇
  2019年   345篇
  2018年   295篇
  2017年   416篇
  2016年   466篇
  2015年   423篇
  2014年   532篇
  2013年   780篇
  2012年   609篇
  2011年   574篇
  2010年   409篇
  2009年   539篇
  2008年   537篇
  2007年   448篇
  2006年   396篇
  2005年   358篇
  2004年   292篇
  2003年   225篇
  2002年   196篇
  2001年   134篇
  2000年   127篇
  1999年   122篇
  1998年   103篇
  1997年   99篇
  1996年   73篇
  1995年   60篇
  1994年   52篇
  1993年   58篇
  1992年   58篇
  1991年   37篇
  1990年   22篇
  1989年   30篇
  1988年   32篇
  1987年   17篇
  1986年   20篇
  1985年   20篇
  1984年   10篇
  1983年   7篇
  1982年   7篇
  1981年   4篇
  1980年   3篇
  1979年   7篇
  1976年   3篇
  1973年   2篇
  1971年   2篇
  1957年   1篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
饮食中微量元素砷的分布规律与人体健康关系   总被引:3,自引:1,他引:2  
采用催化动力学光度法测定了六大类(共三十种)样品中的总砷含量,探讨了砷在食品中的分布规律,建立了砷在人体中的安全系效和积累系效的效学评价公式,用于评价砷与人体健康的关系,这对人们选择食物有一定的指导意义。  相似文献   
42.
采用MTT比色法对体外培养的肿瘤细胞进行细胞毒作用实验,验证槲寄生蛋白注射液体外抗肿瘤效果.并且鉴定这种检测方法的有效性。实验结果表明槲寄生蛋白注射液有一定的体外抗肿瘤效果;MTT比色法是一种可用的体外细胞毒作用检测法,为新药品的开发提供了实验依据。  相似文献   
43.
用光谱技术研究了水溶液中氧氟沙星(OFLX)和左氟沙星(LVFX)与人血清白蛋白相互作用的机制.荧光猝灭法测得的结果表明反应的结合常数为KOFLX=0.482×105L@mol-1,KLVFX=0.529×105L@mol-1,结合位点数nOFLX=0.72,nLVFX=0.74.按照Fōorster非辐射能量转移理论得到药物-蛋白之间的结合距离分别为rOFLX=2.94nm,nVFX=2.85 nm.实验结果说明OFLX与LVFX在体内与蛋白结合直到运输到受体部位这一环节基本相同.  相似文献   
44.
In this article a new technique was developed to fabricate scaffolds with a unique microstructure by solid–liquid separation in combination with particulate-leaching. Firstly, the effects of polymer concentration, quenching temperature on the porous morphology and the mechanical property of obtained scaffolds during solid–liquid separation have been investigated. Then, salt granules as porogen were introduced into the solid–liquid phase separation to produce the unique pore structure of the scaffold. The pore diameter of the scaffold could be controlled with the particulate size and the wall of pores possessed special microstructure, which enhanced the pore interconnectivity. The cell culture results confirmed that a good interconnectivity of the scaffold prepared by the improved solid–liquid separation was useful for nutrition transportation and cell proliferation. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
45.
Total syntheses of the peptide enamide natural products terpeptin and aspergillamides A and B are reported. An oxidative decarboxylation-elimination protocol is employed to construct the indolic enamide moiety. Unambiguous stereochemical assignment of (−)-terpeptin is accomplished by synthesis of all possible stereochemical analogues. Select compounds have been evaluated in cell cycle inhibitor assays which show that the natural amino acid configuration of terpeptin has the most potent inhibitory activity.  相似文献   
46.
Finite element analysis of fluid flow with moving free surface has been performed in 2‐D and 3‐D. The new VOF‐based numerical algorithm that has been proposed by the present authors (Int. J. Numer. Meth. Fluids, submitted) was applied to several 2‐D and 3‐D free surface flow problems. The proposed free surface tracking scheme is based on two numerical tools; the orientation vector to represent the free surface orientation in each cell and the baby‐cell to determine the fluid volume flux at each cell boundary. The proposed numerical algorithm has been applied to 2‐D and 3‐D cavity filling and sloshing problems in order to demonstrate the versatility and effectiveness of the scheme. The proposed numerical algorithm resolved successfully the free surfaces interacting with each other. The simulated results demonstrated applicability of the proposed numerical algorithm to the practical problems of large free surface motion. It has been also demonstrated that the proposed free surface tracking scheme can be easily implemented in any irregular non‐uniform grid systems and can be extended to 3‐D free surface flow problems without additional efforts. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
47.
In this paper we describe the experimental analysis of a novel ion-exchange polymer metal composite (IPMC) actuator under large external voltage. The experimental analysis is supplemented with a coupled thermodynamic model, which includes mass transport across the thickness of the polymer actuator, chemical reactions at boundaries, and deformation as a function of the solvent (water) distribution. In this paper, the case of large electrode potentials (over 1.2 V) has been analyzed experimentally and theoretically. At these voltage levels, electrochemical reactions take place at both electrodes. These are used in the framework of overpotential theory to develop boundary conditions for the water transport in the bulk of polymer. The model is then simplified to a three-component system comprised of a fixed negatively charged polymeric matrix, protons, and free water molecules within the polymer matrix. Among these species, water molecules are considered to be the dominant species responsible for the deformation of the IPMC actuators. Experiments conducted at different initial water contents are described and discussed in the context of the proposed deformation mechanism. Comparison of numerical simulations with experimental data shows good agreement.  相似文献   
48.
49.
This paper describes numerical modelling of a dual band multi-layered microstrip patch antenna operating at 35GHz on an in-house semi-insulating GaAs substrate. The simulated and measured resonant frequencies at both lower and upper resonant frequencies will be compared to check the accuracy of the different numerical modelling techniques.  相似文献   
50.
The radical terpolymerization of 8‐bromo‐1H,1H,2H‐perfluorooct‐1‐ene with vinylidene fluoride (VDF) and perfluoro(4‐methyl‐3,6‐dioxaoct‐7‐ene) sulfonyl fluoride is presented. Changing the feed compositions of these three fluorinated comonomers enabled us to obtain different random‐type poly[vinylidene fluoride‐ter‐perfluoro(4‐methyl‐3,6‐dioxaoct‐7‐ene) sulfonyl fluoride‐ter‐8‐bromo‐1H,1H,2H‐perfluorooct‐1‐ene] terpolymers containing various sulfonyl fluoride and brominated side groups. Yields higher than 70% were reached in all cases. The hydrolysis of the sulfonyl fluoride group into the ? SO3Li function in the presence of lithium carbonate was quantitatively achieved without the content of VDF being affected, and so dehydrofluorination of the VDF base unit was avoided. These original terpolymers were then crosslinked via dangling bromine atoms in the presence of a peroxide/triallyl isocyanurate system, which produced films insoluble in organic solvents such as acetone and dimethylformamide (which totally dissolved uncured terpolymers). The acidification of ? SO3Li into the ? SO3H function enabled protonic membranes to be obtained. The thermal stabilities of the crosslinked materials were higher than those of the uncured terpolymers, and their electrochemical performances were investigated. According to the contents of the sulfonic acid side functions, the ion‐exchange capacities ranged from 0.6 to 1.5 mequiv of H+/g, whereas the water uptake and conductivities ranged from 5–26% (±11%) and from 0.5 to 6.0 mS/cm, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4566–4578, 2006  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号