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   77807篇
  免费   523篇
  国内免费   113篇
化学   41332篇
晶体学   1274篇
力学   3280篇
综合类   1篇
数学   7832篇
物理学   24724篇
  2022年   629篇
  2021年   874篇
  2020年   967篇
  2019年   1104篇
  2018年   1596篇
  2017年   1686篇
  2016年   2149篇
  2015年   1024篇
  2014年   1719篇
  2013年   3269篇
  2012年   2899篇
  2011年   3276篇
  2010年   2643篇
  2009年   2639篇
  2008年   3006篇
  2007年   2874篇
  2006年   2772篇
  2005年   2435篇
  2004年   2241篇
  2003年   2072篇
  2002年   2138篇
  2001年   2235篇
  2000年   1629篇
  1999年   1254篇
  1998年   1129篇
  1997年   1039篇
  1996年   896篇
  1995年   832篇
  1994年   821篇
  1993年   811篇
  1992年   864篇
  1991年   933篇
  1990年   877篇
  1989年   905篇
  1988年   816篇
  1987年   769篇
  1986年   740篇
  1985年   865篇
  1984年   966篇
  1983年   821篇
  1982年   835篇
  1981年   746篇
  1980年   701篇
  1979年   768篇
  1978年   890篇
  1977年   913篇
  1976年   808篇
  1975年   774篇
  1974年   790篇
  1973年   761篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
Protolytic equilibria of hydroxyxanthene dyes, Fluorescein, Eosin, as well as of some relatedcompounds, in ethanol were studied by spectrophotometry. Stepwise ionization and tautomeric equilibriumconstants were determined.  相似文献   
133.
134.
135.
The procedure for studying the nonuniformity of filtration flows in capillary-porous media was developed. Time dependences of local filtration coefficients averaged over the area and their spatial variation during the flow of water and aqueous electrolyte solutions were studied on soil samples of undisturbed structure using tracer method. It was found that the transformation of a pore space structure accompanied with reverse variations in pore sizes occurs because of the action of disjoining pressure in thin films depending on the ion nature. Relaxation times corresponding to the times necessary to attain equilibrium within interlayer gaps of clay minerals were determined. The conclusion was made that if the system volume is constant, the variations in the pore space structure take place because of decrease in the relative fraction of macropores and their sizes.  相似文献   
136.
137.
Inner-sphere replacement of alcohols by imidazole and its derivatives in the complex (acetato)-(tetraphenylporphyrinato)chromium(III) was studied by electronic absorption spectroscopy. The rate constants and activation parameters of the process were calculated. The entering ligand structure was shown to affect the reaction rate, while the alcohol nature (departing ligand) does not influence the kinetic parameters of the process to an appreciable extent. Regression analysis revealed participation of imidazole and ethanol in the rate-determining stages. The kinetic equation for the inner-sphere axial substitution implies interaction of a free alcohol molecule with that coordinated to chromium, followed by replacement of the associate by the heteroring. Mathematical processing of the kinetic data in terms of the proposed solvolytic association-dissociation mechanism gave the rate constants for particular stages of the process and showed an extremal relation between the rate constant and composition of the solvent.  相似文献   
138.
139.
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   
140.
The reaction of carboxymethyl polysaccharides and their ethyl esters with amines was studied with the aim to determine how the structure of the polymeric acylating agent affects the composition of the reaction products.  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