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   453956篇
  免费   3840篇
  国内免费   1269篇
化学   216398篇
晶体学   7386篇
力学   22774篇
综合类   4篇
数学   65370篇
物理学   147133篇
  2020年   2976篇
  2019年   3342篇
  2018年   11723篇
  2017年   12448篇
  2016年   9948篇
  2015年   4645篇
  2014年   6631篇
  2013年   16593篇
  2012年   15830篇
  2011年   25354篇
  2010年   16792篇
  2009年   16804篇
  2008年   22660篇
  2007年   25648篇
  2006年   13374篇
  2005年   17318篇
  2004年   13773篇
  2003年   12640篇
  2002年   10831篇
  2001年   11236篇
  2000年   8673篇
  1999年   6637篇
  1998年   5579篇
  1997年   5431篇
  1996年   5299篇
  1995年   4818篇
  1994年   4730篇
  1993年   4703篇
  1992年   5107篇
  1991年   5158篇
  1990年   4923篇
  1989年   4806篇
  1988年   4827篇
  1987年   4721篇
  1986年   4491篇
  1985年   6021篇
  1984年   6290篇
  1983年   5236篇
  1982年   5501篇
  1981年   5285篇
  1980年   5176篇
  1979年   5459篇
  1978年   5550篇
  1977年   5366篇
  1976年   5514篇
  1975年   5135篇
  1974年   5141篇
  1973年   5354篇
  1972年   3662篇
  1971年   3014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.
Kinetics and Catalysis - The results of studies in the field of synthesis and characterization of layered double hydroxides (LDHs) obtained using solid-phase reactions are summarized. The effect of...  相似文献   
3.
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   
4.
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   
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.

A kinetic study of the effect of thermoheliox (inhalation of a helium and oxygen mixture, 70 °C) on the functional hemodynamics of the human brain by functional magnetic resonance imaging was carried out. The dynamic responses of the BOLD signal were found to be biphasic. An empirical equation describing the first phase of the hemodynamic response to visual stimulus was proposed. It was shown that preliminary inhalation of thermoheliox stimulates the hemodynamic responses by slowing down the vasoconstriction.

  相似文献   
8.
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   
9.
10.
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   
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