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   550619篇
  免费   7441篇
  国内免费   3716篇
化学   284503篇
晶体学   7909篇
力学   27310篇
综合类   204篇
数学   70059篇
物理学   171791篇
  2021年   5846篇
  2020年   6301篇
  2019年   7039篇
  2018年   9106篇
  2017年   9287篇
  2016年   12625篇
  2015年   7195篇
  2014年   11575篇
  2013年   25047篇
  2012年   20126篇
  2011年   23708篇
  2010年   17675篇
  2009年   17514篇
  2008年   22056篇
  2007年   21770篇
  2006年   19753篇
  2005年   17549篇
  2004年   16205篇
  2003年   14582篇
  2002年   14444篇
  2001年   15164篇
  2000年   11788篇
  1999年   9220篇
  1998年   8014篇
  1997年   7885篇
  1996年   7377篇
  1995年   6614篇
  1994年   6642篇
  1993年   6283篇
  1992年   6618篇
  1991年   7092篇
  1990年   6736篇
  1989年   6612篇
  1988年   6437篇
  1987年   6225篇
  1986年   5964篇
  1985年   7490篇
  1984年   7824篇
  1983年   6580篇
  1982年   6854篇
  1981年   6354篇
  1980年   6032篇
  1979年   6522篇
  1978年   6751篇
  1977年   6636篇
  1976年   6591篇
  1975年   6308篇
  1974年   6134篇
  1973年   6429篇
  1972年   4710篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
We have synthesized 5-alkyl(alkoxy)-2-(o-lzydroxy-p-alkoxyphenyl)pyrimidines and considered the effect of the OH group on the inesomorphism. We have found that in binuclear o-hydroxyarylpyrimidines, an ortho OH group forming an intramolecular hydrogen bond increases Tmp, inhibits the appearance of nematic properties, and promotes the appearance of a smectic A.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 30, No. 1, pp. 90–92, January, 1994.  相似文献   
42.
By changing the conditions of the electrohydraulic treatment of aqueous plant heterodisperse systems comparatively high degradation of the lignin component of plant tissue has been achieved. In addition to free monosaccharides, their reduced forms have been detected in the aqueous phase. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 795–798, November–December, 1994.  相似文献   
43.
44.
The influence of sunflowerseed and cottonseed oils and also of fractions of normal and oxidized triacylglycerols isolated from them on cytochrome P-450 from rat liver microsomes has been investigated.  相似文献   
45.
6-Halogeno-1,3-benzodioxane analogs of chalcones have been synthesized by various methods. Flavanone and flavone analogs of silandrin and hydnocarpin have been obtained from them. The structures of the new flavonoids have been shown by their PMR spectra.  相似文献   
46.
The electron-impact mass spectra of a number of phenylpropanoids and iridoid glycosides containing a phenylethanoid fragment in their structure have been studied. This has revealed features of the formation of fragments of 4-hydroxyphenylethyl and 3,4-dihydroxyphenylethyl alcohols and also of fragments of phenylethylamine and indolylethylamine derivatives present in the structures of the compounds investigated.  相似文献   
47.
Some features of the kinetics of the hydrolysis of apple protopectin have been studied on the basis of an analysis of monosaccharide residues of the pectin substances and determinations of characteristic viscosity. It has been shown that the fine regulation of the physicochemical parameters of the hydrolysis of protopectin leads to the formation of pectin substances with different properties.  相似文献   
48.
49.
The phsicochemical indices and the fatty-acid and triacylglycerol compositions of cottonseed and palm oils, of cottonseed oil hydrogenate, and of compositions based on them have been determined with the aid of IR and UV spectroscopies, GLC analysis, and chemical transformations. The compositions and amounts of the main classes of lipids in the initial oils and the hydrogenate have been studied. It has been found that in the process of hydrogenation the amount of oxygenated components falls. The work was conducted with the financial support of the Uzbek Fund for Fundamental Investigations.  相似文献   
50.
Institute of Botany, Academy of Sciences of the Republic of Azerbaidzhan, Baku. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 291–292, March–April, 1994.  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