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   246593篇
  免费   2627篇
  国内免费   843篇
化学   125170篇
晶体学   3097篇
力学   11136篇
综合类   1篇
数学   28358篇
物理学   82301篇
  2020年   2007篇
  2019年   2290篇
  2018年   2984篇
  2017年   2918篇
  2016年   4326篇
  2015年   2771篇
  2014年   4359篇
  2013年   11062篇
  2012年   8221篇
  2011年   10237篇
  2010年   7289篇
  2009年   7146篇
  2008年   9423篇
  2007年   9338篇
  2006年   8858篇
  2005年   7979篇
  2004年   7412篇
  2003年   6512篇
  2002年   6439篇
  2001年   7334篇
  2000年   5642篇
  1999年   4461篇
  1998年   3754篇
  1997年   3585篇
  1996年   3259篇
  1995年   3087篇
  1994年   3077篇
  1993年   3167篇
  1992年   3261篇
  1991年   3410篇
  1990年   3136篇
  1989年   3078篇
  1988年   3109篇
  1987年   3064篇
  1986年   2878篇
  1985年   3946篇
  1984年   4145篇
  1983年   3299篇
  1982年   3537篇
  1981年   3475篇
  1980年   3349篇
  1979年   3495篇
  1978年   3578篇
  1977年   3509篇
  1976年   3619篇
  1975年   3302篇
  1974年   3280篇
  1973年   3324篇
  1972年   2327篇
  1971年   1919篇
排序方式: 共有10000条查询结果,搜索用时 31 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