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   468964篇
  免费   4008篇
  国内免费   1307篇
化学   236064篇
晶体学   7473篇
力学   23621篇
综合类   17篇
数学   56782篇
物理学   150322篇
  2021年   4302篇
  2020年   4563篇
  2019年   5304篇
  2018年   7403篇
  2017年   7591篇
  2016年   10327篇
  2015年   5666篇
  2014年   9731篇
  2013年   21701篇
  2012年   16842篇
  2011年   20127篇
  2010年   15226篇
  2009年   15318篇
  2008年   18408篇
  2007年   18276篇
  2006年   16651篇
  2005年   14570篇
  2004年   13649篇
  2003年   12174篇
  2002年   12193篇
  2001年   14155篇
  2000年   10482篇
  1999年   8095篇
  1998年   6825篇
  1997年   6731篇
  1996年   6229篇
  1995年   5455篇
  1994年   5504篇
  1993年   5281篇
  1992年   5898篇
  1991年   6189篇
  1990年   5836篇
  1989年   5852篇
  1988年   5557篇
  1987年   5691篇
  1986年   5345篇
  1985年   6794篇
  1984年   6951篇
  1983年   5770篇
  1982年   5806篇
  1981年   5586篇
  1980年   5344篇
  1979年   5887篇
  1978年   5833篇
  1977年   6015篇
  1976年   5990篇
  1975年   5654篇
  1974年   5545篇
  1973年   5659篇
  1972年   4142篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
981.
The influence exerted by the length exerted by the conjugation chain in 4-hydroxybenzylidenealkanones on the generation of the third harmonic by complexes of these chromophores with aliphatic polyamidine was studied.  相似文献   
982.
983.
984.
Carbamoylformhydroxymoyl chlorides were synthesized by the reactions of carbamoylformamide oximes with sodium nitrite in the presence of hydrochloric acid, and their reactivities were examined.  相似文献   
985.
Orlov  I. S.  Moiseeva  A. A.  Butin  E. P.  Egorov  M. P. 《Russian Chemical Bulletin》2002,51(10):1961-1962
An unusual reaction of diaminogermylene and diaminostannylene with sterically hindered phenols which leads to the formation of stable phenoxyl radicals in high concentrations was found. The reaction mechanism was proposed. Amides [(Me3Si)2N]2E (E = Ge, Sn) were investigated electrochemically.  相似文献   
986.
Russian Chemical Bulletin - The monomer [Cr3O(OCOCH=CH2)6]OH was produced by reaction of acrylic acid with fresh chromium hydroxide. This monomer was investigated by a number of physicochemical...  相似文献   
987.
988.
An investigation was carried out of the spectral-luminescent and acid-base properties at the stage of formation of the hydrogen bond and during the protonation of compounds with annelated aromatic and heterocyclic rings, obtained by introduction of bridging groups -CH=CH- (I), -CH=N- (II) and -CO-N(CH3)-(III) in the 4- and 2-positions of the molecules of 4-substituted derivatives of 2,5-diphenyloxazole. The nature of the reaction center was estabished, and an analysis was carried out of its sensitivity to the electronic influence of the substituents, and the reasons for the observed differences in the properties of compounds of various reaction series are discussed. A comparative analysis of the fluorescent properties of the neutral and protonated forms of the oxazole derivatives studied was made and the conclusion that the generation is possible of laser emission by the protonated forms of compounds of the reaction series (I) was confirmed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 4, pp. 343–349, July–August, 1992.  相似文献   
989.
990.
A polarization variant of an intracavity laser spectrometer based on the competition of beams in an argon ion laser, radiating a number of narrow lines in the 275 to 529 nm spectral range, is proposed and described for the spectral analysis of liquid samples, having broad absorption bands, mainly biomolecules in solutions. By careful optimization of the operating conditions, a procedure has been established that results in a minimal measurable absorbance decreased up to 10(-5) units of optical density. The examined spectrometer provides a wide dynamic range of analysis. A determination of trace contents of amino acids in methanol were carried out.  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