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   154420篇
  免费   1607篇
  国内免费   398篇
化学   83196篇
晶体学   2034篇
力学   6749篇
综合类   7篇
数学   15619篇
物理学   48820篇
  2020年   1133篇
  2019年   1207篇
  2018年   1504篇
  2017年   1466篇
  2016年   2518篇
  2015年   1577篇
  2014年   2459篇
  2013年   6387篇
  2012年   5006篇
  2011年   6353篇
  2010年   4335篇
  2009年   4354篇
  2008年   5775篇
  2007年   5857篇
  2006年   5494篇
  2005年   5088篇
  2004年   4492篇
  2003年   3927篇
  2002年   3932篇
  2001年   4358篇
  2000年   3345篇
  1999年   2608篇
  1998年   2262篇
  1997年   2216篇
  1996年   2008篇
  1995年   1923篇
  1994年   1911篇
  1993年   1738篇
  1992年   2018篇
  1991年   2133篇
  1990年   1936篇
  1989年   1930篇
  1988年   1872篇
  1987年   1763篇
  1986年   1704篇
  1985年   2216篇
  1984年   2346篇
  1983年   1912篇
  1982年   2092篇
  1981年   1977篇
  1980年   1898篇
  1979年   2039篇
  1978年   2207篇
  1977年   2082篇
  1976年   2125篇
  1975年   2027篇
  1974年   2082篇
  1973年   2065篇
  1972年   1358篇
  1971年   1213篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
21.
22.
We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs).  相似文献   
23.
24.
25.
In this work, a series of 2-chalcogenylindoles was synthesized by an efficient methodology, starting from chalcogenoalkynes, including a previously unreported tellurium indole derivative. For the first time, these 2-substituted chalcogenylindoles were obtained in the absence of metal catalyst or base, under thermal conditions only. In addition, the results described herein represent a methodology with inverse regioselectivity for the chalcogen functionalization of indoles.  相似文献   
26.
27.
The European Physical Journal E - The isothermal gas adsorption of two hexane isomers (n-hexane and cyclohexane) in the mesopores of MCM-41 silica have been investigated by small angle neutron...  相似文献   
28.
Investigated is the dependency of the crack tip opening displacement (CTOD) on the local microstructure of the heat affected zone in high-strength low-alloy (HSLA) microalloyed steel. Since the initiation of the crack tip location could not be controlled in fatigue, any possible correlation between heat iput in welding and fracture toughness could be smeared. Modified CTOD data are defined; they show that the fracture resistance of the weld joint decreased as the heat input increased.  相似文献   
29.
Residual effects of an initial bolus of gadolinium contrast agent have been previously demonstrated in sequential dynamic susceptibility contrast MR experiments. While these residual effects quickly reach a saturation steady state, their etiology is uncertain, and they can lead to spurious estimates of hemodynamic parameters in activation experiments. The possible influence ofT1effects is now investigated with experiments in whichT1weighting is varied as well as with serial regionalT1measurements. Little evidence for significant residualT1effects is found, suggesting instead that susceptibility effects underlie these observations. An initial saturation dose of contrast agent minimizes this effect.  相似文献   
30.
The investigation of the 1s HFS provides a good possibility for testing QED effects in a combination of a strong electric and magnetic field. Here, we report about the laserspectroscopic measurements of the ground state hyperfine splitting in 207Pb81+. To handle this M1-transition in the infrared optical regime with its long lifetime, we developed a new detection technique using a bunched ion beam. For the observation of fluorescence light, a new mirror system is adapted to the emission characteristics from an ion beam at relativistic velocities. This revised version was published online in July 2006 with corrections to the Cover Date.  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