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   413469篇
  免费   5236篇
  国内免费   1996篇
化学   229255篇
晶体学   5922篇
力学   16621篇
综合类   67篇
数学   48495篇
物理学   120341篇
  2020年   3733篇
  2019年   4108篇
  2018年   5282篇
  2017年   5257篇
  2016年   7713篇
  2015年   4915篇
  2014年   7331篇
  2013年   17640篇
  2012年   14248篇
  2011年   17306篇
  2010年   12249篇
  2009年   11909篇
  2008年   16231篇
  2007年   16402篇
  2006年   15369篇
  2005年   13996篇
  2004年   12481篇
  2003年   11118篇
  2002年   10907篇
  2001年   11550篇
  2000年   9074篇
  1999年   6725篇
  1998年   5685篇
  1997年   5711篇
  1996年   5575篇
  1995年   4771篇
  1994年   4895篇
  1993年   4778篇
  1992年   5151篇
  1991年   5202篇
  1990年   4954篇
  1989年   4863篇
  1988年   4712篇
  1987年   4624篇
  1986年   4571篇
  1985年   5964篇
  1984年   6157篇
  1983年   5030篇
  1982年   5498篇
  1981年   5222篇
  1980年   4821篇
  1979年   5192篇
  1978年   5477篇
  1977年   5481篇
  1976年   5488篇
  1975年   5105篇
  1974年   5227篇
  1973年   5354篇
  1972年   3938篇
  1971年   3257篇
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
1.
Kinetics and Catalysis - The catalytic properties of a nickel phosphide catalyst supported on silica gel in the reductive amination of carbonyl compounds were studied in a flow reactor using...  相似文献   
2.
Yang  T. L.  Kao  C. L.  Kuo  C. E.  Yeh  H. C.  Li  W. J.  Li  H. T.  Chen  C. Y. 《Chemistry of Natural Compounds》2022,58(5):825-827
Chemistry of Natural Compounds - A novel bibenzyl derivative, hydrangchinenin (1), was isolated from the stems of Hydrangea chinensis Maxim. (Hydrangeaceae). Its structure was determined on the...  相似文献   
3.
Journal of Structural Chemistry - The structures of Ni(II), Cu(II), and Zn(II) complexes with anions of 2,5-pyrrolyl-disubstituted nitronyl nitroxide (L1) and iminonitroxide (L2) diradicals (HL1 is...  相似文献   
4.
Mechanics of Composite Materials - Carbon fiber (CF)/ polyamide (PA6) composites are one of the most promising thermoplastic materials for automobile applications. However, the interfacial...  相似文献   
5.
Journal of Structural Chemistry - A new polymorph of the [ReCl3(MeCN)(PPh3)2] complex is synthesized and characterized by single crystal X-ray diffraction (XRD). Its recrystallization from the...  相似文献   
6.
Nitrene transfer reactions have emerged as one of the most powerful and versatile ways to insert an amine function to various kinds of hydrocarbon substrates. However, the mechanisms of nitrene generation have not been studied in depth albeit their formation is taken for granted in most cases without definitive evidence of their occurrence. In the present work, we compare the generation of tosylimido iron species and NTs transfer from FeII and FeIII precursors where the metal is embedded in a tetracarbene macrocycle. Catalytic nitrene transfer to reference substrates (thioanisole, styrene, ethylbenzene and cyclohexane) revealed that the same active species was at play, irrespective of the ferrous versus ferric nature of the precursor. Through combination of spectroscopic (UV-visible, Mössbauer), ESI-MS and DFT studies, an FeIV tosylimido species was identified as the catalytically active species and was characterized spectroscopically and computationally. Whereas its formation from the FeII precursor was expected by a two-electron oxidative addition, its formation from an FeIII precursor was unprecedented. Thanks to a combination of spectroscopic (UV-visible, EPR, Hyscore and Mössbauer), ESI-MS and DFT studies, we found that, when starting from the FeIII precursor, an FeIII tosyliodinane adduct was formed and decomposed into an FeV tosylimido species which generated the catalytically active FeIV tosylimide through a comproportionation process with the FeIII precursor.  相似文献   
7.
Russian Journal of Applied Chemistry - Recent achievements in the field of the development of preparation methods and study of structure and properties of epoxy nanocomposites with metal-containing...  相似文献   
8.
Russian Journal of Applied Chemistry - A method for the disposal of hydrolysis lignin waste based on its modification with ZnCl2 and FeCl3 and subsequent carbonization at 800°C was proposed....  相似文献   
9.
Russian Journal of General Chemistry - The review article traces the main trends of the synthetic approach to the solution of the problem of overcoming the resistance of pathogenic bacterial...  相似文献   
10.
Numerical Algorithms - In this work, we propose a fractional extension of the one-dimensional nonlinear vibration problem on an elastic string. The fractional problem is governed by a hyperbolic...  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