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   311222篇
  免费   1849篇
  国内免费   366篇
化学   145884篇
晶体学   4822篇
力学   17302篇
综合类   4篇
数学   43034篇
物理学   102391篇
  2021年   3504篇
  2020年   3846篇
  2019年   4686篇
  2018年   6674篇
  2017年   6864篇
  2016年   8560篇
  2015年   3946篇
  2014年   7561篇
  2013年   13236篇
  2012年   11111篇
  2011年   12842篇
  2010年   10645篇
  2009年   10647篇
  2008年   12026篇
  2007年   11819篇
  2006年   10468篇
  2005年   9020篇
  2004年   8679篇
  2003年   8026篇
  2002年   8254篇
  2001年   7791篇
  2000年   6171篇
  1999年   4564篇
  1998年   4321篇
  1997年   4200篇
  1996年   3807篇
  1995年   3354篇
  1994年   3418篇
  1993年   3453篇
  1992年   3458篇
  1991年   3850篇
  1990年   3841篇
  1989年   3844篇
  1988年   3586篇
  1987年   3663篇
  1986年   3358篇
  1985年   3905篇
  1984年   4128篇
  1983年   3530篇
  1982年   3726篇
  1981年   3398篇
  1980年   3174篇
  1979年   3675篇
  1978年   3730篇
  1977年   3901篇
  1976年   3968篇
  1975年   3701篇
  1974年   3543篇
  1973年   3710篇
  1972年   3186篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
941.
A series of 7-carboxy-3-R-1,5-dinitro-3-azabicyclo[3.3.1]non-6-enes was synthesized by reduction of 3,5-dinitrobenzoic acid with sodium borohydride followed by Mannich reaction with formaldehyde and primary amines. The mechanism of decomposition under electron impact of the 3-azabicyclo[3.3.1]nonane was established. Enthalpies of formation of compounds synthesized were calculated by semiempirical PM3 method.  相似文献   
942.
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   
943.
Kinetic regularities of hydrogenation, oxidation with oxygen, and condensation of allyl alcohol in the presence of colloid palladium in situ were revealed. A mechanism of the reactions was proposed.  相似文献   
944.
945.
946.
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   
947.
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   
948.
949.
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   
950.
We propose a new approach to obtaining composites of the intercalation type based on polyaniline and V2O5. We have determined the characteristics of these composites using x-ray diffraction, IR spectroscopy, and EPR. We show that the compounds obtained exhibit stable redox properties in aqueous and aprotic electrolytes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 6, pp. 361–364, November–December, 1995.We would like to express our thanks to V. G. II'in for help in carrying out the x-ray phase investigations. This work was made possible with the partial support of the International Science Foundation (grant N U6B000).  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