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   58136篇
  免费   10694篇
  国内免费   19675篇
化学   44768篇
晶体学   2291篇
力学   3864篇
综合类   1945篇
数学   8950篇
物理学   26687篇
  2024年   122篇
  2023年   548篇
  2022年   2020篇
  2021年   2063篇
  2020年   2008篇
  2019年   2048篇
  2018年   1854篇
  2017年   2714篇
  2016年   2152篇
  2015年   2986篇
  2014年   3704篇
  2013年   4705篇
  2012年   4767篇
  2011年   5187篇
  2010年   5095篇
  2009年   5208篇
  2008年   5863篇
  2007年   5295篇
  2006年   5069篇
  2005年   4313篇
  2004年   3347篇
  2003年   2381篇
  2002年   2509篇
  2001年   2397篇
  2000年   2464篇
  1999年   1404篇
  1998年   811篇
  1997年   567篇
  1996年   532篇
  1995年   522篇
  1994年   484篇
  1993年   493篇
  1992年   431篇
  1991年   328篇
  1990年   313篇
  1989年   329篇
  1988年   204篇
  1987年   211篇
  1986年   157篇
  1985年   138篇
  1984年   144篇
  1983年   98篇
  1982年   84篇
  1981年   95篇
  1980年   62篇
  1979年   81篇
  1978年   31篇
  1977年   25篇
  1976年   21篇
  1959年   22篇
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
141.
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   
142.
The first intramolecular charge transfer transition based on 2-ureido-4[1H]-pyrimidinone binding module was reported.  相似文献   
143.
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   
144.
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   
145.
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   
146.
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   
147.
A mono-funtionalised tetraphenylporphyrin (TPP) bearing valine moiety at the phenyl ring was synthesized for photocytotoxicity examination in four steps, starting from regiospecific mono-nitration of TPP at the phenyl ring. The in vitro photocytotoxicitic effect against SPC-Al adenocarcinona cell line was tested.  相似文献   
148.
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   
149.
§ 1. Introduction  InthelaserandplasmaphysicsundertheinteractionofanonlinearcomplexSchr dingerfieldandarealBoussinesqfield ,thedynamicsisdescribedbythefollowingequationsiεt +Δε=nε ,( 1 .1 )ntt -Δn+γΔ2 n-Δf(n) -Δ|ε|2 =0 ,( 1 .2 )whereεrepresentsthecomplexSchr dingerfieldandnrepresentstherealBoussinesqfield .Theseequationshavemanyinterestingproperties,suchasafour parameterfamilyofsolitonso lutionsandLangmuircollapse(see [1— 4]) .Thustheydrawmuchattentionofmanyphysicistandmath…  相似文献   
150.
The distributions of limit cycles of cubic vector fields (P2, Q3) are considered in this paper, where P2 and Q3 are polynomials of x and y of order two and three, respectively. It is possibly seven different distributions of limit cycles given in [1]. We now prove that in which three kinds of distributions are impossible and other four kinds all can be realized by concrete vector fields of (P2,Q3). Some related results are also given.  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