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   316866篇
  免费   13661篇
  国内免费   7698篇
化学   162387篇
晶体学   4438篇
力学   17580篇
综合类   313篇
数学   46054篇
物理学   107453篇
  2022年   3461篇
  2021年   3857篇
  2020年   4251篇
  2019年   4129篇
  2018年   12925篇
  2017年   13585篇
  2016年   10106篇
  2015年   5854篇
  2014年   6592篇
  2013年   11392篇
  2012年   15692篇
  2011年   24956篇
  2010年   15700篇
  2009年   15556篇
  2008年   20658篇
  2007年   23601篇
  2006年   9219篇
  2005年   14746篇
  2004年   10244篇
  2003年   9363篇
  2002年   7124篇
  2001年   7095篇
  2000年   5602篇
  1999年   4619篇
  1998年   3442篇
  1997年   3492篇
  1996年   3518篇
  1995年   3061篇
  1994年   2913篇
  1993年   2562篇
  1992年   2944篇
  1991年   2939篇
  1990年   2710篇
  1989年   2558篇
  1988年   2494篇
  1987年   2441篇
  1986年   2234篇
  1985年   2657篇
  1984年   2633篇
  1983年   2096篇
  1982年   2077篇
  1981年   1908篇
  1980年   1884篇
  1979年   2165篇
  1978年   2246篇
  1977年   2117篇
  1976年   2067篇
  1975年   1934篇
  1974年   1906篇
  1973年   1991篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
In this article, we construct and analyze a residual-based a posteriori error estimator for a quadratic finite volume method (FVM) for solving nonlinear elliptic partial differential equations with homogeneous Dirichlet boundary conditions. We shall prove that the a posteriori error estimator yields the global upper and local lower bounds for the norm error of the FVM. So that the a posteriori error estimator is equivalent to the true error in a certain sense. Numerical experiments are performed to illustrate the theoretical results.  相似文献   
3.
4.
The European Physical Journal Special Topics - The removal of suspended particles from the interior of a thermocapillary liquid bridge via a finite-particle-size effect restricting the particle...  相似文献   
5.
6.
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   
7.
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   
8.
9.
10.
We conducted measurements of black carbon(BC) aerosol in Jiaxing,China during autumn from September 26 to November 30,2013.We investigated temporal and diurnal variations of BC,and its correlations with meteorological parameters and other major pollutants.Results showed that hourly mass concentrations of BC ranged from 0.2 to 22.0 μg/m3,with an average of 5.1 μg/m3.The diurnai variation of BC exhibited a bimodal distribution,with peaks at 07:00 and 18:00.The morning peak was larger than the evening peak.The mass percentages of BC in PM2.5 and PM10 were 7.1%and 4.8%,respectively.The absorption coefficient of BC was calculated to be 44.4 Mm-1,which accounted for 11.1%of the total aerosol extinction.BC was mainly emitted from local sources in southwestern Jiaxing where BC concentrations were generally greater than 11 μg/m3 during the measurement period.Correlation analysis indicated that the main sources of BC were motor vehicle exhaust,and domestic and industrial combustion.  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