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   405428篇
  免费   3831篇
  国内免费   1382篇
化学   212787篇
晶体学   5037篇
力学   17882篇
综合类   7篇
数学   46852篇
物理学   128076篇
  2020年   3430篇
  2019年   3936篇
  2018年   5305篇
  2017年   5170篇
  2016年   7394篇
  2015年   4414篇
  2014年   7164篇
  2013年   17881篇
  2012年   13195篇
  2011年   16261篇
  2010年   11605篇
  2009年   11499篇
  2008年   15261篇
  2007年   15356篇
  2006年   14406篇
  2005年   13047篇
  2004年   11861篇
  2003年   10650篇
  2002年   10545篇
  2001年   11655篇
  2000年   9067篇
  1999年   6989篇
  1998年   5989篇
  1997年   5838篇
  1996年   5159篇
  1995年   4735篇
  1994年   4791篇
  1993年   4833篇
  1992年   5127篇
  1991年   5313篇
  1990年   5014篇
  1989年   4984篇
  1988年   4940篇
  1987年   4842篇
  1986年   4566篇
  1985年   6221篇
  1984年   6502篇
  1983年   5204篇
  1982年   5646篇
  1981年   5491篇
  1980年   5205篇
  1979年   5507篇
  1978年   5696篇
  1977年   5671篇
  1976年   5729篇
  1975年   5278篇
  1974年   5335篇
  1973年   5443篇
  1972年   3774篇
  1971年   3237篇
排序方式: 共有10000条查询结果,搜索用时 156 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.
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   
3.
Journal of Structural Chemistry - The structures of Ni(II), Cu(II), and Zn(II) complexes with anions of 2,5-pyrrolyl-disubstituted nitronyl nitroxide (L1) and iminonitroxide (L2) diradicals (HL1 is...  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.
Russian Journal of Applied Chemistry - Recent achievements in the field of the development of preparation methods and study of structure and properties of epoxy nanocomposites with metal-containing...  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