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   26439篇
  免费   3379篇
  国内免费   12701篇
化学   27976篇
晶体学   517篇
力学   1260篇
综合类   720篇
数学   4436篇
物理学   7610篇
  2024年   230篇
  2023年   883篇
  2022年   868篇
  2021年   1009篇
  2020年   898篇
  2019年   1219篇
  2018年   770篇
  2017年   1112篇
  2016年   1257篇
  2015年   1340篇
  2014年   2024篇
  2013年   2159篇
  2012年   2249篇
  2011年   2155篇
  2010年   2103篇
  2009年   2252篇
  2008年   2703篇
  2007年   2464篇
  2006年   2611篇
  2005年   2301篇
  2004年   2533篇
  2003年   1540篇
  2002年   671篇
  2001年   640篇
  2000年   647篇
  1999年   779篇
  1998年   417篇
  1997年   287篇
  1996年   225篇
  1995年   206篇
  1994年   211篇
  1993年   307篇
  1992年   335篇
  1991年   332篇
  1990年   235篇
  1989年   228篇
  1988年   184篇
  1987年   73篇
  1986年   29篇
  1985年   14篇
  1984年   8篇
  1983年   5篇
  1982年   2篇
  1959年   4篇
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
81.
5,6-Dihydro-OSW-1 (1) was synthesized following our previous procedure for the total synthesis of OSW-1. This compound demonstrated slightly stronger potency than that of OSW-1 against the growth of cancer cells.  相似文献   
82.
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   
83.
A mild, regioselective 1, 3-dipolar cycloaddition protocol for the preparation ofphenylselenomethyl isoxazolines through substituted allyl phenyl selenides and nitrile oxides wasreported.  相似文献   
84.
2,5-Disubstituted oxazoles were prepared conveniently by treatment of aromatic α-methyl ketones and nitriles with poly[styrene(iodosodiacetate)] in one-pot process.  相似文献   
85.
The first intramolecular charge transfer transition based on 2-ureido-4[1H]-pyrimidinone binding module was reported.  相似文献   
86.
A facile solid phase synthesis of 2-substituted 1,3-oxazin-6-ones using polymer-supported Meldrum‘s acid has been reported. Reaction of the resin-bound cyclic malonic acid ester with triethyl orthoformate and subsequent double substitution with amide, afforded the corresponding polymer-supported acylaminomethylene cyclic malonic acid ester, which upon thermal treatment led to 1, 3-oxazin-6-ones in good yields and with high purity.  相似文献   
87.
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   
88.
The crystal structures of two potential tumor imaging agents and therapeutic agents -copper(Ⅱ) complexes with salicylidene-tyrosinato Schiff base and nitrogen-donor chelating Lewis base, [Cu(sal-tyr)(bipy)] 1 and [Cu(sal-tyr)(phen)]2CH3OH 2 are presented. Our work is helpful to get deep understanding of novel 64Cu tumor imaging agents and therapeutic agents.  相似文献   
89.
证明了3-正则图的最小平分问题和最小α-分割问题都是NP-完全问题.  相似文献   
90.
钟德寿  贺龙光 《数学进展》2003,32(3):311-318
在这篇文章中,我们讨论了李双代数胚之间的态射,得到了一些李双代数胚之间态射的性质.研究了泊松群胚在泊松流形上的泊松作用,以及这个泊松作用与被作用流形的切李双代数胚到作用泊松群胚的切李双代数胚之间的态射的关系,得到了一些有用的结论。  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