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   663795篇
  免费   7390篇
  国内免费   1936篇
化学   335904篇
晶体学   10083篇
力学   31898篇
综合类   19篇
数学   90583篇
物理学   204634篇
  2021年   4962篇
  2020年   5517篇
  2019年   6076篇
  2018年   13360篇
  2017年   13697篇
  2016年   14233篇
  2015年   7871篇
  2014年   11472篇
  2013年   27584篇
  2012年   23752篇
  2011年   33896篇
  2010年   23006篇
  2009年   22877篇
  2008年   30589篇
  2007年   32683篇
  2006年   22004篇
  2005年   23986篇
  2004年   20397篇
  2003年   18300篇
  2002年   16872篇
  2001年   17942篇
  2000年   13776篇
  1999年   10725篇
  1998年   8988篇
  1997年   8718篇
  1996年   8464篇
  1995年   7634篇
  1994年   7539篇
  1993年   7426篇
  1992年   8113篇
  1991年   8223篇
  1990年   7834篇
  1989年   7684篇
  1988年   7742篇
  1987年   7534篇
  1986年   7105篇
  1985年   9318篇
  1984年   9660篇
  1983年   7692篇
  1982年   7914篇
  1981年   7857篇
  1980年   7385篇
  1979年   7885篇
  1978年   8124篇
  1977年   7925篇
  1976年   7939篇
  1975年   7303篇
  1974年   7291篇
  1973年   7340篇
  1972年   5201篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
Cavitation erosion is caused in solids exposed to strong pressure waves developing in an adjacent fluid field. The knowledge of the transient distribution of stresses in the solid is important to understand the cause of damaging by comparisons with breaking points of the material. The modeling of this problem requires the coupling of the models for the fluid and the solid. For this purpose, we use a strategy based on the solution of coupled Riemann problems that has been originally developed for the coupling of 2 fluids. This concept is exemplified for the coupling of a linear elastic structure with an ideal gas. The coupling procedure relies on the solution of a nonlinear equation. Existence and uniqueness of the solution is proven. The coupling conditions are validated by means of quasi‐1D problems for which an explicit solution can be determined. For a more realistic scenario, a 2D application is considered where in a compressible single fluid, a hot gas bubble at low pressure collapses in a cold gas at high pressure near an adjacent structure.  相似文献   
72.
73.
A two‐step synthesis of structurally diverse pyrrole‐containing bicyclic systems is reported. ortho‐Nitro‐haloarenes coupled with vinylic N‐methyliminodiacetic acid (MIDA) boronates generate ortho‐vinyl‐nitroarenes, which undergo a “metal‐free” nitrene insertion, resulting in a new pyrrole ring. This novel synthetic approach has a wide substrate tolerance and it is applicable in the preparation of more complex “drug‐like” molecules. Interestingly, an ortho‐nitro‐allylarene derivative furnished a cyclic β‐aminophosphonate motif.  相似文献   
74.
75.
Russian Journal of General Chemistry - Hybrid liquid crystal systems with different ratios of the components have been prepared on the basis of 5,5′-di(heptadecyl)-2,2′-bipyridine...  相似文献   
76.
77.
78.
Palladium nanoparticle‐incorporated metal–organic framework MIL‐101 (Pd/MIL‐101) was successfully synthesized and characterized using X‐ray diffraction, nitrogen physisorption, X‐ray photoelectron, UV–visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL‐101 and high stability of nano‐size palladium particles. Pd/MIL‐101 nanocomposite was investigated for the Sonogashira cross‐coupling reaction of aryl and heteroaryl bromides with various alkynes under copper‐free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
79.
We study the full counting statistics of transport electrons through a semiconductor two-level quantum dot with Rashba spin–orbit (SO) coupling, which acts as a nonabelian gauge field and thus induces the electron transition between two levels along with the spin flip. By means of the quantum master equation approach, shot noise and skewness are obtained at finite temperature with two-body Coulomb interaction. We particularly demonstrate the crucial effect of SO coupling on the super-Poissonian fluctuation of transport electrons, in terms of which the SO coupling can be probed by the zero-frequency cumulants. While the charge currents are not sensitive to the SO coupling.  相似文献   
80.
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