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   346304篇
  免费   3530篇
  国内免费   1046篇
化学   177153篇
晶体学   5885篇
力学   15512篇
综合类   7篇
数学   40411篇
物理学   111912篇
  2021年   2638篇
  2020年   2941篇
  2019年   3290篇
  2018年   4321篇
  2017年   4305篇
  2016年   6436篇
  2015年   3915篇
  2014年   6241篇
  2013年   15624篇
  2012年   11975篇
  2011年   14434篇
  2010年   10183篇
  2009年   10088篇
  2008年   13309篇
  2007年   13279篇
  2006年   12670篇
  2005年   11345篇
  2004年   10578篇
  2003年   9402篇
  2002年   9151篇
  2001年   10499篇
  2000年   7998篇
  1999年   6204篇
  1998年   5106篇
  1997年   5035篇
  1996年   4667篇
  1995年   4389篇
  1994年   4224篇
  1993年   4027篇
  1992年   4597篇
  1991年   4532篇
  1990年   4415篇
  1989年   4166篇
  1988年   4221篇
  1987年   4252篇
  1986年   3961篇
  1985年   5200篇
  1984年   5476篇
  1983年   4654篇
  1982年   4891篇
  1981年   4702篇
  1980年   4577篇
  1979年   4771篇
  1978年   4898篇
  1977年   4840篇
  1976年   4939篇
  1975年   4688篇
  1974年   4633篇
  1973年   4895篇
  1972年   3176篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
201.
The yields and fatty acid compositions of the free lipids and lipids weakly and strongly bound to proteins from seeds of cottonplant varieties resistant and susceptible to verticillium wilt have been determined and the changes in these indices in the seeds of the infected plants have been measured. It has been established that the seeds of healthy plants of the two varieties are similar in the qualitative compositions of the lipids and fatty acids but differ with respect the amounts of lipids in them bound with protein in different ways and with respect to the amounts of the individual fatty acids. The observed changes in the lipid and fatty-acid compositions depend on the degree of resistance of the variety to wilt.  相似文献   
202.
On the basis of the results of acid hydrolysis, chromatographic analysis of the hydrolysates, and a study of IR spectra, it has been established that the suspended particles liberated under the action of electrohydraulic shocks on heterodisperse water—plant systems consist of small fragments of the lignocarbohydrate complex of the plant tissue.  相似文献   
203.
204.
205.
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   
206.
207.
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   
208.
209.
The main directions of fragmentation and the EI of six pseudoguaianolides related to carpesiolin have been studied. It has been established that acylation of the OH group at C-6 suppresses the selective breakdown of the guaiane skeleton, while the simultaneous presence of AcO groups at C-2 and C-4 favors the formation of a number of characteristic ions. The hydrogenation of the exomethylene group has no appreciable influence on direction of fragmentation.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 530–535, July–August, 1993.  相似文献   
210.
The synthesis has been effected of alkyl anabasinoprop-2-yl and alkyl piperidinoprop-2-yl methylphosphonothionates. It has been shown by1H,13C and31P NMR spectroscopies that the anabasine derivatives exist in solution as four diastereomeric forms. The kinetics of the interaction of the compounds synthesized with two types of cholinesterases has been studied.A. S. Sadykov Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent, Fax 627071. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 70–74, January–February, 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