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   8125篇
  免费   355篇
  国内免费   320篇
化学   4209篇
晶体学   152篇
力学   167篇
综合类   34篇
数学   2488篇
物理学   1750篇
  2023年   24篇
  2022年   64篇
  2021年   53篇
  2020年   116篇
  2019年   150篇
  2018年   134篇
  2017年   152篇
  2016年   153篇
  2015年   126篇
  2014年   176篇
  2013年   279篇
  2012年   195篇
  2011年   380篇
  2010年   295篇
  2009年   534篇
  2008年   413篇
  2007年   446篇
  2006年   388篇
  2005年   396篇
  2004年   530篇
  2003年   464篇
  2002年   432篇
  2001年   321篇
  2000年   276篇
  1999年   208篇
  1998年   174篇
  1997年   176篇
  1996年   204篇
  1995年   162篇
  1994年   206篇
  1993年   160篇
  1992年   135篇
  1991年   80篇
  1990年   62篇
  1989年   64篇
  1988年   55篇
  1987年   70篇
  1986年   56篇
  1985年   47篇
  1984年   44篇
  1983年   13篇
  1982年   38篇
  1981年   41篇
  1980年   48篇
  1979年   67篇
  1978年   53篇
  1977年   52篇
  1976年   37篇
  1974年   13篇
  1973年   18篇
排序方式: 共有8800条查询结果,搜索用时 640 毫秒
51.
The likelihood method is developed for the analysis of socalled regular point patterns. Approximating the normalizing factor of Gibbs canonical distribution, we simultaneously estimate two parameters, one for the scale and the other which measures the softness (or hardness), of repulsive interactions between points. The approximations are useful up to a considerably high density. Some real data are analyzed to illustrate the utility of the parameters for characterizing the regular point pattern.  相似文献   
52.
We formulate the super-KMS condition suggested by Connes and Kastler, in the context of entire cyclic cohomology of quantum algebras. We show that the Chern character of Jaffe, Lesniewski, and Osterwalder — associated by Kastler to a super-KMS functional — satisfies the entire growth condition. Hence, a super-KMS functional defines a cocycle for the entire cyclic cohomology of quantum algebras.Supported in part by the National Science Foundation.  相似文献   
53.
The master equation for a complex chemical reaction cannot always be reduced to a simpler master equation, even if there are fast and slow individual reaction steps. Nevertheless the elimination of intermediates can be carried out with the help of the-expansion. This is illustrated with a well-known complex reaction: the dissociation of N2O5. It is shown that the intrinsic fluctuations in the N2O5 decay are larger than those implied by the master equation suggested by the macroscopic rate law.  相似文献   
54.
7-氮杂-3,6-二氧杂-二环[3.3.0]辛-2-酮类化合物合成的新方法   总被引:1,自引:0,他引:1  
5-甲氧基-2-(5H)-呋喃酮与氮酸硅烷基酯通过1,3-偶极环加成反应可以为7-氮杂-4-甲氧基-3,6-二氧杂-二环[3.3.0]辛-2-酮类化合物提供新的合成途径。通过元素分析、IR、^1HNMR、^13CNMR、MS等波谱分析进行了结构表征。  相似文献   
55.
The recent development of asymmetric Baeyer—Villiger oxidation of prochiral and racemic ketones is briefly summarized, focusing on the regio- and stereocontrol of the oxidation attained by regulating the stereoelectronic demand in the step of rearrangement of the Criegee intermediate.Based on the report presented at the International Conference Modern Trends in Organoelement and Polymer Chemistry dedicated to the 50th anniversary of the A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences (Moscow, May 30–June 4, 2004).Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1784–1794, September, 2004.  相似文献   
56.
Summary Irradiation of solutions of excess cyclohexene and 2-acetyl-5,5-dimethyl-1,3-cyclohexanedione (1), and 3-acetyl-1,5,5-trimethyl-2,4-pyrrolidinedione (4) results mainly in the formation of 1,5-diones2 and5. These originate from intermediate cycloadducts of cyclohexene and theexo-enols of the cyclic 1,3-diketones. The yields decrease with increasing polarity of the solvent. In solution2 and5 are in equilibrium with the cyclic hemiacetales3 and6.
  相似文献   
57.
58.
The reaction of styrene and -methylstyrene with P in aprotic polar solvents in the presence of KOH affords diorganylphosphinous acids.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1680–1681, September, 1994.  相似文献   
59.
The reaction of organomagnesium compounds (OMC) containing alkyl radicals of normal structure with -olefins, resulting in the formation of alkenylorganomagnesium compounds and accompanied by hydride transfer was discovered and systematically investigated. A scheme providing for the formation of zirconacyclopentane complexes was proposed for the mechanism of the reaction.Institute of Organic Chemistry, Ural Branch, Russian Academy of Sciences, 450054 Ufa. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1187–1196, May, 1992.  相似文献   
60.
A series of ethyl(phenyl) 6-amino-2,3,6-trideoxy--D-glucopyranosides (amino=piperidino (Pip), pyrrolidino (Pyr), azetidino (Az), Bu2N) have been prepared from tri-O-acetyl-D-glucal to obtain catalysts for asymmetric synthesis and the starting compounds for the syntheses of other bidentate ligands.Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 45–52, January, 2000.  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