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   413150篇
  免费   2549篇
  国内免费   705篇
化学   198865篇
晶体学   6438篇
力学   22069篇
综合类   5篇
数学   53794篇
物理学   135233篇
  2021年   3826篇
  2020年   4223篇
  2019年   5026篇
  2018年   7191篇
  2017年   7404篇
  2016年   9654篇
  2015年   4723篇
  2014年   8518篇
  2013年   16920篇
  2012年   13828篇
  2011年   16351篇
  2010年   13072篇
  2009年   13265篇
  2008年   15766篇
  2007年   15438篇
  2006年   14160篇
  2005年   12504篇
  2004年   11832篇
  2003年   11003篇
  2002年   11098篇
  2001年   12254篇
  2000年   9395篇
  1999年   7087篇
  1998年   5998篇
  1997年   5947篇
  1996年   5420篇
  1995年   4896篇
  1994年   4917篇
  1993年   4781篇
  1992年   5279篇
  1991年   5675篇
  1990年   5511篇
  1989年   5459篇
  1988年   5224篇
  1987年   5311篇
  1986年   4818篇
  1985年   5817篇
  1984年   6066篇
  1983年   5037篇
  1982年   5214篇
  1981年   4770篇
  1980年   4559篇
  1979年   5279篇
  1978年   5421篇
  1977年   5509篇
  1976年   5541篇
  1975年   5190篇
  1974年   5025篇
  1973年   5169篇
  1972年   4135篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Data were obtained on the composition of products and kinetics of the reaction of SO2 with Ph(R)CN2 (R=Ph, Me) in solutions of isooctane, 1,4-di-oxane, and ethanol at 295 K. A mechanism was proposed for the process in accordance with which the sulfene being formed participates in concurrent reactions with the starting reagents. The relative rate constants for the process stages were determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2496–2500, November, 1990.  相似文献   
993.
Cross-polarization 29Si NMR spectra have been used for aerosil modified by methylchlorosilanes to identify surface organosilicon compounds and their reactions during hydrolysis and methanolysis.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, No. 3, pp. 378–383, May–June, 1986.  相似文献   
994.
995.
996.
Reaction of phenyl-ß-naphthylamines with formaldehyde and acetone in the presence of HCl and nitrobenzene in butanol solution leads to cyclization involving the naphthalene and phenyl rings, and formation of N-aryllepidine salts. 15 lepidine and 5, 6-benzoepidine salts are synthesized and characterized by their UV absorption spectra, as well as by their picrates.For Part LIII see [3].  相似文献   
997.
Conclusions Intermediate formation of 3-oxynaphthenyl-2 radical during oxidation of 3-oxythionaphthene to thioindigo was demonstrated by the inhibitor method. The 1:1 recombination product of this radical and diphenylpicrylhydrazyl was isolated. It is assumed that the postulated oxidation mechanism is general for compounds possessing a methylene group bonded to an electron-donating X group and an electron-accepting C=O group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1168–1170, May, 1970.  相似文献   
998.
Topochemical investigations of peptide systems   总被引:4,自引:0,他引:4  
The basic principles of the topochemical approach to the investigation of the structure-function relation in peptide systems are formulated. This approach makes use of the new possibility of transforming natural peptides, consisting in the modification of the molecule as a whole and utilization of the resultant analogs to elucidate the boundaries of the stereoelectronic complementarity of the biologically active peptide to the corresponding receptor. In particular, on the example of depsipeptide antibiotics and their topochemical analogs the fruitfulness of using such compounds as tools in elucidating the physicochemical basis of functioning of biological membranes is shown. The topochemical principle has also been applied in preparing specific competitive inhibitors of proteolytic enzymes, whose study may shed light on the nature of the forces binding the substrate to the contact site of the corresponding enzyme.  相似文献   
999.
1000.
A new pyridine synthesis has been found by refluxing certain simple secondary car☐amides in HMPA. Thus 2,6-dimethylpyridine, 2-ethyl-6-methylpyridine, 2,3,6-trimethylpyridine, 2-ethyl-3,6-dimethylpyridine, 2-benzyl-6-methyl-3-phenylpyridine, 2-ethyl-3-methyl-5,6,7,8-tetrahydroquinoline and 2-t-butyl-6-methylpyridine were prepared in 15–40% yield.  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