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   304947篇
  免费   4468篇
  国内免费   1049篇
化学   150321篇
晶体学   4069篇
力学   15230篇
综合类   7篇
数学   59836篇
物理学   81001篇
  2021年   2088篇
  2020年   2307篇
  2019年   2480篇
  2018年   12944篇
  2017年   12676篇
  2016年   10805篇
  2015年   4422篇
  2014年   5220篇
  2013年   11613篇
  2012年   13312篇
  2011年   20881篇
  2010年   12863篇
  2009年   12905篇
  2008年   16326篇
  2007年   18205篇
  2006年   9606篇
  2005年   9855篇
  2004年   9194篇
  2003年   8590篇
  2002年   7301篇
  2001年   6559篇
  2000年   5115篇
  1999年   3827篇
  1998年   3242篇
  1997年   3069篇
  1996年   3102篇
  1995年   2679篇
  1994年   2685篇
  1993年   2597篇
  1992年   2864篇
  1991年   2720篇
  1990年   2645篇
  1989年   2544篇
  1988年   2504篇
  1987年   2500篇
  1986年   2366篇
  1985年   3123篇
  1984年   3157篇
  1983年   2704篇
  1982年   2921篇
  1981年   2698篇
  1980年   2666篇
  1979年   2760篇
  1978年   2768篇
  1977年   2634篇
  1976年   2734篇
  1975年   2621篇
  1974年   2562篇
  1973年   2763篇
  1972年   1755篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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   
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 Analytical Chemistry - The present development involved a flow injection strategy using a mini-column of multiwalled carbon nanotubes and fluorescent detection (λex of 283 nm,...  相似文献   
5.
Meccanica - In this work we study, from the numerical point of view, a one-dimensional thermoelastic problem where the thermal law is of type III. Quasi-static microvoids are also assumed within...  相似文献   
6.
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   
7.
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   
8.

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   
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.

In this paper, we design a Branch and Bound algorithm based on interval arithmetic to address nonconvex robust optimization problems. This algorithm provides the exact global solution of such difficult problems arising in many real life applications. A code was developed in MatLab and was used to solve some robust nonconvex problems with few variables. This first numerical study shows the interest of this approach providing the global solution of such difficult robust nonconvex optimization problems.

  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