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   300053篇
  免费   1420篇
  国内免费   334篇
化学   138132篇
晶体学   4662篇
力学   16941篇
综合类   3篇
数学   42324篇
物理学   99745篇
  2021年   3133篇
  2020年   3464篇
  2019年   4240篇
  2018年   6261篇
  2017年   6466篇
  2016年   8027篇
  2015年   3576篇
  2014年   6942篇
  2013年   12224篇
  2012年   10250篇
  2011年   11925篇
  2010年   10062篇
  2009年   10204篇
  2008年   11526篇
  2007年   11305篇
  2006年   10057篇
  2005年   8681篇
  2004年   8433篇
  2003年   7827篇
  2002年   8127篇
  2001年   7690篇
  2000年   6085篇
  1999年   4503篇
  1998年   4284篇
  1997年   4139篇
  1996年   3749篇
  1995年   3308篇
  1994年   3367篇
  1993年   3385篇
  1992年   3390篇
  1991年   3802篇
  1990年   3795篇
  1989年   3806篇
  1988年   3552篇
  1987年   3631篇
  1986年   3326篇
  1985年   3859篇
  1984年   4099篇
  1983年   3494篇
  1982年   3699篇
  1981年   3383篇
  1980年   3146篇
  1979年   3635篇
  1978年   3705篇
  1977年   3862篇
  1976年   3936篇
  1975年   3673篇
  1974年   3536篇
  1973年   3696篇
  1972年   3180篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
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   
933.
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   
934.
935.
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   
936.
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   
937.
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   
938.
The molecular structures of the initial compounds and the products of photocyclization involving amino and azomethine groups in perchlorates ofN-amino (1) andN-azomethine (2) derivatives of 2,4,6-triphenylpyridinium cations were studied. Cations1 and2 have an essentially non-coplanar arrangement of the -Ph rings, and the product of photocyclization of2, cation3, is characterized by a flattened structure. It was found that the orientation of the lone electron pair of the N atom with respect to one of the planes of the -Ph rings in molecule1 is more favorable for monocyclization involving the amino group. The structure of molecule2 allows two routes of the photoreaction,viz., O N proton transfer and monocyclization with an -Ph ring. However, the structural features of molecule2 are more favorable for photocyclization.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 296–301, February, 1995.  相似文献   
939.
940.
The quasi-homogeneous model was used to study the “dead zone” in porous catalyst granules of spherical, cylindrical, and platelike shapes for parallel catalytic reaction with the Langmuir-Hinshelwood kinetics that occur under transient or artificially created nonstationary conditions.  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