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   54279篇
  免费   10291篇
  国内免费   19185篇
化学   41154篇
晶体学   2160篇
力学   3967篇
综合类   1904篇
数学   8664篇
物理学   25906篇
  2024年   117篇
  2023年   558篇
  2022年   1950篇
  2021年   1986篇
  2020年   1936篇
  2019年   1912篇
  2018年   1787篇
  2017年   2611篇
  2016年   2013篇
  2015年   2757篇
  2014年   3416篇
  2013年   4408篇
  2012年   4400篇
  2011年   4821篇
  2010年   4738篇
  2009年   4905篇
  2008年   5515篇
  2007年   4994篇
  2006年   4725篇
  2005年   4090篇
  2004年   3160篇
  2003年   2204篇
  2002年   2237篇
  2001年   2274篇
  2000年   2392篇
  1999年   1371篇
  1998年   798篇
  1997年   600篇
  1996年   561篇
  1995年   571篇
  1994年   528篇
  1993年   511篇
  1992年   463篇
  1991年   328篇
  1990年   330篇
  1989年   326篇
  1988年   218篇
  1987年   217篇
  1986年   154篇
  1985年   139篇
  1984年   140篇
  1983年   97篇
  1982年   82篇
  1981年   94篇
  1980年   59篇
  1979年   78篇
  1978年   26篇
  1977年   21篇
  1965年   19篇
  1959年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Introduction In the previous studies on the oxidation reaction,peroxydisulfate was widely used as an oxidizingagent.1-5 One of the advantages of this oxidant lies in itsstability in a wide range of pH values. The reaction be-tween Fe(CN)5L3- (L=N-aromatic heterocyclic li-gands) and S2O8 2- has been proved to proceed throughan outer-sphere electron transfer mechanism.5 For a re-action [(Eq. (1)] to be under an outer-sphere mechanismthe steps involved are the formation of a reactant …  相似文献   
142.
The polyacrylic acid functionalized polystyrene nanospheres were synthesized and self-assembled into irregular, densely packed monolayers in non-aqueous media. The polymer nanoparticles were chemically adhered to substrates. The morphologies of the resulting films were investigated. The impact of the volume fraction of alcohol in the mixed solvents on the particle adsorption and fabrication of nanosphere assembled films was examined.  相似文献   
143.
A new cobalt(Ⅱ) complex with tridentate ligand 2, 6-bis (benzimidazol-2-yl)pyridine has been synthesized by microwave irradiation method and characterized by elemental analysis,electrochemical and spectral methods. The binding of the complex with calf thymus DNA has also been investigated by absorption and fluorescence spectra.  相似文献   
144.
As photosensitizer for solar cell, a new ruthenium (Ⅱ) complex with four ester groups had been synthesized, in which a phenol substituted by {[(2-hydroxy-5-tert-butylbenzyl)(pyridyl-2-methyl)amino]methyl} is covalently linked to ruthenium (Ⅱ) tris-bipyridine. The structures of the new compounds were confirmed by NMR and ESI-MS spectra. The electrochemical and photochemical properties were also studied.  相似文献   
145.
The first intramolecular charge transfer transition based on 2-ureido-4[1H]-pyrimidinone binding module was reported.  相似文献   
146.
The adsorption of asymmetrical triblock copolymers from a non-selective solvent on solid surface has been studied by using Scheutjens-Fleer mean-field theory and Monte Carlo simulation method on lattice model. The main aim of this paper is to provide detailed computer simulation data, taking A8-kB20Ak as a key example, to study the influence of the structure of copolymer on adsorption behavior and make a comparison between MC and SF results. The simulated results show that the size distribution of various configurations and density-profile are dependent on molecular structure and adsorption energy. The molecular structure will lead to diversity of adsorption behavior. This discrepancy between different structures would be enlarged for the surface coverage and adsorption amount with increasing of the adsorption energy. The surface coverage and the adsorption amount as well as the bound fraction will become larger as symmetry of the molecular structure becomes gradually worse. The adsorption layer becomes thicker with increasing of symmetry of the molecule when adsorption energy is smaller but it becomes thinner when adsorption energy is higher. It is shown that SF theory can reproduce the adsorption behavior of asymmetrical triblock copolymers. However, systematic discrepancy between the theory and simulation still exists.The approximations inherited in the mean-filed theory such as random mixing and the allowance of direct back folding may be responsible for those deviations.  相似文献   
147.
The relation of the isoelectric point (IEP) and the point of zero net charge (PZNC) of the hydrotalcite-like compounds was discussed. It was found that the IEP does not equal to the PZNC and the IEP is higher than the PZNC. The structural positive charges existing in the HTlc,which cause the difference between the IEP and the PZNC. The effects of the structural positive charges of the HTlc on its IEP and PZNC are the same as the specific adsorption of metal cations.  相似文献   
148.
A Glaser coupling reaction of terminal alkynes in the presence of nickel chloride withoutany organics and bases in hot water has been developed, which produces the correspondinghomo-coupling products in good yields.  相似文献   
149.
An unusual reductive ring-opening reaction of phthalimide with sodium hydride in anhydrous DMF was observed for the first time. The presumed mechanism was described in detail.  相似文献   
150.
李治平 《数学进展》2003,32(3):257-268
晶体微观结构是晶体材料在特定物理条件下其多个能量极小平衔态在空间形成的某种微尺度的规则分布.几何非线性的连续介质力学理论可以用能量极小化原理来解释晶体微观结构的形成,并用Young测度来刻画平衡态各变体在空间的概率分布.定性的理解与定量地分析和计算晶体材料的微观结构对于发展和改进高级晶体功能材料,如形状记忆合金、铁电体、磁至伸缩材料等,有重要的意义.本文回顾了近年来晶体微观结构数值计算方面的最新进展.介绍了计算晶体微观结构的几种数值方法及有关的数值分析结果。  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