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   633784篇
  免费   6734篇
  国内免费   2203篇
化学   311947篇
晶体学   8886篇
力学   31131篇
综合类   9篇
数学   105505篇
物理学   185243篇
  2020年   3467篇
  2019年   3683篇
  2018年   19866篇
  2017年   20295篇
  2016年   15238篇
  2015年   6764篇
  2014年   7944篇
  2013年   23019篇
  2012年   23030篇
  2011年   38877篇
  2010年   23662篇
  2009年   23862篇
  2008年   32578篇
  2007年   37203篇
  2006年   18498篇
  2005年   23974篇
  2004年   19266篇
  2003年   17683篇
  2002年   14941篇
  2001年   14928篇
  2000年   11660篇
  1999年   9109篇
  1998年   7531篇
  1997年   7321篇
  1996年   7315篇
  1995年   6684篇
  1994年   6314篇
  1993年   6188篇
  1992年   6803篇
  1991年   6748篇
  1990年   6325篇
  1989年   6169篇
  1988年   6412篇
  1987年   6078篇
  1986年   5858篇
  1985年   8270篇
  1984年   8477篇
  1983年   6938篇
  1982年   7558篇
  1981年   7449篇
  1980年   7210篇
  1979年   7301篇
  1978年   7551篇
  1977年   7319篇
  1976年   7403篇
  1975年   6993篇
  1974年   6945篇
  1973年   7330篇
  1972年   4411篇
  1971年   3318篇
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
41.
42.
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   
43.
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   
44.
45.
46.
47.
We summarize the results of our recent work on Bäcklund transformations (BTs), particularly focusing on the relation between BTs and infinitesimal symmetries. We present a BT for an associated Degasperis–Procesi (aDP) equation and its superposition principle and investigate the solutions generated by applying this BT. Following our general methodology, we use the superposition principle of the BT to generate the infinitesimal symmetries of the aDP equation.  相似文献   
48.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant.  相似文献   
49.
50.
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