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   328300篇
  免费   2509篇
  国内免费   853篇
化学   150157篇
晶体学   4364篇
力学   17348篇
综合类   2篇
数学   49769篇
物理学   110022篇
  2020年   1928篇
  2019年   2189篇
  2018年   11036篇
  2017年   11786篇
  2016年   7865篇
  2015年   3380篇
  2014年   4259篇
  2013年   10422篇
  2012年   11968篇
  2011年   21557篇
  2010年   13652篇
  2009年   13696篇
  2008年   18961篇
  2007年   22345篇
  2006年   8759篇
  2005年   14101篇
  2004年   10319篇
  2003年   9536篇
  2002年   7601篇
  2001年   7339篇
  2000年   5756篇
  1999年   4330篇
  1998年   3646篇
  1997年   3332篇
  1996年   3299篇
  1995年   3094篇
  1994年   3004篇
  1993年   3094篇
  1992年   3200篇
  1991年   3347篇
  1990年   3114篇
  1989年   3054篇
  1988年   3101篇
  1987年   3005篇
  1986年   2834篇
  1985年   3879篇
  1984年   4067篇
  1983年   3233篇
  1982年   3455篇
  1981年   3402篇
  1980年   3295篇
  1979年   3417篇
  1978年   3522篇
  1977年   3388篇
  1976年   3515篇
  1975年   3179篇
  1974年   3186篇
  1973年   3294篇
  1972年   2273篇
  1971年   1878篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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   
2.
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   
3.
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   
4.
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   
5.
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   
6.
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   
7.
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   
8.
9.
Central European Journal of Operations Research - Sustainability practice within supply chains remains in an early development phase. Enterprises still need tools that support the integration of...  相似文献   
10.
Nonlinear Dynamics - Given a data-set of Ribonucleic acid (RNA) sequences we can infer the phylogenetics of the samples and tackle the information for scientific purposes. Based on current data and...  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