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   558013篇
  免费   6312篇
  国内免费   2135篇
化学   279421篇
晶体学   6742篇
力学   28019篇
综合类   8篇
数学   87986篇
物理学   164284篇
  2020年   3488篇
  2019年   3727篇
  2018年   14177篇
  2017年   13870篇
  2016年   12839篇
  2015年   5946篇
  2014年   8005篇
  2013年   22065篇
  2012年   19880篇
  2011年   29875篇
  2010年   18640篇
  2009年   18906篇
  2008年   24682篇
  2007年   26880篇
  2006年   18380篇
  2005年   17646篇
  2004年   16380篇
  2003年   15119篇
  2002年   14030篇
  2001年   15003篇
  2000年   11582篇
  1999年   9219篇
  1998年   7617篇
  1997年   7440篇
  1996年   7390篇
  1995年   6692篇
  1994年   6393篇
  1993年   6334篇
  1992年   6782篇
  1991年   6606篇
  1990年   6135篇
  1989年   5969篇
  1988年   6324篇
  1987年   5901篇
  1986年   5651篇
  1985年   8048篇
  1984年   8226篇
  1983年   6744篇
  1982年   7166篇
  1981年   7141篇
  1980年   6828篇
  1979年   7146篇
  1978年   7184篇
  1977年   7139篇
  1976年   7144篇
  1975年   6790篇
  1974年   6730篇
  1973年   6915篇
  1972年   4403篇
  1971年   3444篇
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
1.
Journal of Fluorescence - This report describes a combined immunofluorescence and fluorescence viability stain applied as one staining solution for rapid detection of live Legionella...  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.
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   
4.
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   
5.
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   
6.
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   
7.
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   
8.
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   
9.
Sun  J.  Yuan  H. 《Experimental Mechanics》2021,61(3):565-580
Experimental Mechanics - Temperature gradients significantly affect the material fatigue process. A reliable and robust test procedure is needed for quantifying the effects of temperature gradients...  相似文献   
10.
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   
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