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   433940篇
  免费   3534篇
  国内免费   1172篇
化学   208978篇
晶体学   5800篇
力学   21982篇
综合类   4篇
数学   60287篇
物理学   141595篇
  2020年   2771篇
  2019年   3069篇
  2018年   11540篇
  2017年   12221篇
  2016年   9435篇
  2015年   4390篇
  2014年   6025篇
  2013年   15180篇
  2012年   15166篇
  2011年   24853篇
  2010年   16219篇
  2009年   16208篇
  2008年   22193篇
  2007年   25078篇
  2006年   12711篇
  2005年   17122篇
  2004年   13364篇
  2003年   12357篇
  2002年   10518篇
  2001年   11732篇
  2000年   8913篇
  1999年   6773篇
  1998年   5291篇
  1997年   5294篇
  1996年   4810篇
  1995年   4543篇
  1994年   4489篇
  1993年   4394篇
  1992年   4990篇
  1991年   5149篇
  1990年   4816篇
  1989年   4770篇
  1988年   4783篇
  1987年   4698篇
  1986年   4385篇
  1985年   5804篇
  1984年   6018篇
  1983年   4781篇
  1982年   4970篇
  1981年   4795篇
  1980年   4675篇
  1979年   5062篇
  1978年   5268篇
  1977年   5080篇
  1976年   5162篇
  1975年   4712篇
  1974年   4707篇
  1973年   4844篇
  1972年   3290篇
  1971年   2705篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
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   
2.
Chromatographia - We developed a simple, rapid, ecological RP-HPLC method for the estimation of Pitavastatin (PIT), Fenofibrate (FEN), and their impurities in a novel fixed dose combination. We...  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.
Mechanics of Composite Materials - Carbon fiber (CF)/ polyamide (PA6) composites are one of the most promising thermoplastic materials for automobile applications. However, the interfacial...  相似文献   
5.
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   
6.
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   
7.
Journal of Structural Chemistry - Atomic and electronic structures of cyclic organosilicon compound 9,9,10,10-tetraethynyl-9,10-dihydrodisilaanthracene are studied by the density functional theory....  相似文献   
8.
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   
9.
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   
10.
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   
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