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   257979篇
  免费   2559篇
  国内免费   1106篇
化学   127273篇
晶体学   3163篇
力学   12976篇
综合类   18篇
数学   30623篇
物理学   87591篇
  2020年   2020篇
  2019年   2320篇
  2018年   3904篇
  2017年   3960篇
  2016年   4732篇
  2015年   2877篇
  2014年   4507篇
  2013年   10790篇
  2012年   8796篇
  2011年   10305篇
  2010年   7449篇
  2009年   7426篇
  2008年   9267篇
  2007年   9284篇
  2006年   8701篇
  2005年   10535篇
  2004年   9895篇
  2003年   7893篇
  2002年   6533篇
  2001年   7478篇
  2000年   5651篇
  1999年   4457篇
  1998年   3766篇
  1997年   3600篇
  1996年   3225篇
  1995年   3095篇
  1994年   3024篇
  1993年   3143篇
  1992年   3263篇
  1991年   3431篇
  1990年   3207篇
  1989年   3154篇
  1988年   3130篇
  1987年   3071篇
  1986年   2896篇
  1985年   3951篇
  1984年   4163篇
  1983年   3310篇
  1982年   3555篇
  1981年   3474篇
  1980年   3379篇
  1979年   3524篇
  1978年   3644篇
  1977年   3583篇
  1976年   3731篇
  1975年   3399篇
  1974年   3443篇
  1973年   3468篇
  1972年   2527篇
  1971年   2109篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
1.
Kinetics and Catalysis - A new ruthenium(II) cage complex with polar terminal groups in the apical substituents has been synthesized; the molecular design of the complex contributes to the...  相似文献   
2.
Russian Journal of General Chemistry - Aminophosphabetaines, i.e., isobutyl {[alkyl(dimethyl)ammonio]methyl}phosphonates with higher alkyl substituents at the nitrogen atom, were obtained by a...  相似文献   
3.
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   
4.
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   
5.
Journal of Experimental and Theoretical Physics - The surface current density of charge carriers in two-dimensional doubly periodic n-type semiconductor superlattices in an external magnetic field...  相似文献   
6.
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   
7.
Journal of Applied Spectroscopy - Three simple, sensitive, precise, and rapid spectrophotometric methods are developed and optimized for the assay of vardenafil in pharmaceutical formulations. The...  相似文献   
8.
Russian Journal of General Chemistry - Tungstophosphatozincates with the Keggin anion structure Kt5[PW11O39Zn(H2O)]?nH2O, Kt = Rb+, Cs+, (CH3)4N+; (C2H5)4N+ were synthesized. Their...  相似文献   
9.
Journal of Optimization Theory and Applications - Direct optimization of many-revolution spacecraft trajectories is performed using an unconstrained formulation with many short-arc, embedded...  相似文献   
10.
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