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   379880篇
  免费   2602篇
  国内免费   1179篇
化学   162248篇
晶体学   4714篇
力学   22199篇
综合类   1篇
数学   74880篇
物理学   119619篇
  2020年   1806篇
  2019年   2066篇
  2018年   18852篇
  2017年   19321篇
  2016年   12284篇
  2015年   3857篇
  2014年   4361篇
  2013年   10487篇
  2012年   14265篇
  2011年   28540篇
  2010年   17522篇
  2009年   17904篇
  2008年   23272篇
  2007年   28100篇
  2006年   8635篇
  2005年   14724篇
  2004年   11226篇
  2003年   10886篇
  2002年   8211篇
  2001年   7437篇
  2000年   5901篇
  1999年   4404篇
  1998年   3776篇
  1997年   3556篇
  1996年   3347篇
  1995年   3107篇
  1994年   3015篇
  1993年   3112篇
  1992年   3182篇
  1991年   3349篇
  1990年   3088篇
  1989年   3053篇
  1988年   3105篇
  1987年   3005篇
  1986年   2838篇
  1985年   3863篇
  1984年   4060篇
  1983年   3233篇
  1982年   3459篇
  1981年   3389篇
  1980年   3294篇
  1979年   3424篇
  1978年   3521篇
  1977年   3371篇
  1976年   3499篇
  1975年   3168篇
  1974年   3174篇
  1973年   3267篇
  1972年   2267篇
  1971年   1865篇
排序方式: 共有10000条查询结果,搜索用时 265 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