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   431544篇
  免费   4734篇
  国内免费   1315篇
化学   222645篇
晶体学   7039篇
力学   19690篇
综合类   12篇
数学   49671篇
物理学   138536篇
  2021年   3527篇
  2020年   3875篇
  2019年   4270篇
  2018年   5702篇
  2017年   5875篇
  2016年   8408篇
  2015年   4951篇
  2014年   8101篇
  2013年   19862篇
  2012年   15030篇
  2011年   18239篇
  2010年   13143篇
  2009年   12880篇
  2008年   16295篇
  2007年   16231篇
  2006年   15216篇
  2005年   13585篇
  2004年   12493篇
  2003年   11105篇
  2002年   11023篇
  2001年   12917篇
  2000年   9621篇
  1999年   7616篇
  1998年   6422篇
  1997年   6288篇
  1996年   5946篇
  1995年   5298篇
  1994年   5062篇
  1993年   4983篇
  1992年   5549篇
  1991年   5701篇
  1990年   5464篇
  1989年   5386篇
  1988年   5199篇
  1987年   5291篇
  1986年   5025篇
  1985年   6488篇
  1984年   6648篇
  1983年   5511篇
  1982年   5879篇
  1981年   5445篇
  1980年   5444篇
  1979年   5694篇
  1978年   5832篇
  1977年   5740篇
  1976年   5753篇
  1975年   5456篇
  1974年   5266篇
  1973年   5485篇
  1972年   3756篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
Fullerene deuteride was obtained by the reaction of deuterium with solid palladium fulleride C60Pd4.9 under fairly mild conditions. The compound was identified by FD-MS, UV-Vis and IR spectroscopies, and TLC.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 483–484, February, 1996  相似文献   
992.
4-Vinylcyclohexene (VCH) and cyclooctadiene (COD) were investigated as termonomers in EPDM (ethylene/propylene/diene) synthesis by using rac-ethylenebis (1-η5-indenyl) zir-conium dichloride ( 1 ) as a catalyst precursor. Homopolymerizations of VCH, vinylcycloh-exane and cyclohexene were compared. The parameter Kπκp, which is the apparent rate constant for Ziegler-Natta polymerization, is about the same for VCH and vinylcyclohexanebut is 10 times smaller for cyclohexene. Therefore, the linear olefinic double bond is more active than the cyclic internal double bond. VCH reduces ethylene polymerization rate but not propylene polymerization rate in copolymerizations. In terpolymerizations, VCH tends to suppress ethylene incorporation especially at elevated polymerization temperature and Lowers the polymer MW by about two-fold. COD has very low activity as a termonomer. © 1995 John Wiley & Sons, Inc.  相似文献   
993.
994.
The equilibrium and rate of solvent extraction of zinc chloride complexes from HCl solutions into benzene solutions of tributyl phosphate (TBP) have been studied. The extracted species are discussed in the light of the results. The extraction was found to be first order with respect to both Zn(II) and TBP, and zero order for HCl. The rate-controlling steps are discussed and the rate constants for these reactions are calculated.  相似文献   
995.
In this paper we find conditions guarantee that irregular boundary value problems for elliptic differential-operator equations of the second order in an interval are fredholm. We apply this result to find some algebraic conditions guarantee that irregular boundary value problems for elliptic partial differential equations of the second order in cylindrical domains are fredholm. Apparently this is the first paper where the regularity of an elliptic boundary value problem is not satisfied on a manifold of the dimension equal to dimension of the boundary. Nevertheless the problem is fredholm and the resolvent is compact. It is interesting to note that the considered boundary value problems for elliptic equations in a cylinder being with separating variables are noncoercive.  相似文献   
996.
We show that Abelian gauge theories in 2+1 space-time dimensions with the introduction of a topological Chern-Simons term can be quantized with the use of the symplectic formalism. The consistency of our results are verified by the agreement with the ones from the Dirac case.  相似文献   
997.
The application of some recently proposed algebraic multilevel methods for the solution of two-dimensional finite element problems on nonuniform meshes is studied. The locally refined meshes are created by the newest vertex mesh refinement method. After the introduction of this refinement technique it is shown that, by combining levels of refinement, a preconditioner of optimal order can be constructed for the case of local refinement along a line. Its relative condition number is accurately estimated. Numerical tests demonstrating the performance of the proposed preconditioners will be reported in a forthcoming paper.  相似文献   
998.
999.
1000.
T. Shevchenko Kiev University, 252022 Kiev, Pr. Akad. Glushakova, 6, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 3, pp. 192–196, May–June, 1995.  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