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   330157篇
  免费   3483篇
  国内免费   929篇
化学   165089篇
晶体学   5376篇
力学   15579篇
综合类   7篇
数学   38665篇
物理学   109853篇
  2021年   3132篇
  2020年   3348篇
  2019年   3769篇
  2018年   5221篇
  2017年   5450篇
  2016年   7393篇
  2015年   4177篇
  2014年   7068篇
  2013年   15962篇
  2012年   12441篇
  2011年   14905篇
  2010年   11070篇
  2009年   10953篇
  2008年   13311篇
  2007年   13253篇
  2006年   12203篇
  2005年   10561篇
  2004年   9866篇
  2003年   8707篇
  2002年   8700篇
  2001年   10405篇
  2000年   7671篇
  1999年   5977篇
  1998年   4985篇
  1997年   4826篇
  1996年   4494篇
  1995年   3872篇
  1994年   3838篇
  1993年   3715篇
  1992年   4101篇
  1991年   4308篇
  1990年   4098篇
  1989年   4008篇
  1988年   3781篇
  1987年   3918篇
  1986年   3685篇
  1985年   4631篇
  1984年   4687篇
  1983年   3887篇
  1982年   3977篇
  1981年   3699篇
  1980年   3652篇
  1979年   3915篇
  1978年   3908篇
  1977年   3913篇
  1976年   3882篇
  1975年   3681篇
  1974年   3618篇
  1973年   3650篇
  1972年   2606篇
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
961.
We study a model procedure to solve the incompressible Navier-Stokes equations on the flow inside contraction geometry. The governing equations are expressed in the primitive variable formulation. A rectangular computational plane is arises by elliptic grid generation technique. The numerical solution is based on a technique of automatic numerical generation of a curvilinear coordinate system. By transformed the governing equation into computational plane. The time dependent momentum equations are solved explicitly for the velocity field using the explicit marching procedure, the continuity equation is applied at each grid point in the solution of pressure equation, while the successive over relaxation (SOR) method is used for the Neumann problem for pressure. We will apply the technique on several irregular-shape.  相似文献   
962.
Ridge-waveguide InGaAsN triple-quantum-well strain-compensated lasers grown by metal organic chemical vapor deposition were fabricated with pulsed anodic oxidation. The laser’s output power reached 145 mW in continuous-wave mode at room temperature for a 4-?m -stripe-width laser. Continuous-wave single longitudinal mode operation was maintained at a high injection current level with a wavelength of 1287.3 nm at room temperature. Single longitudinal mode operation at 1317.2 nm was achieved at twice the threshold current at 100 °C. The band gap of InGaAsN in the quantum wells at different temperatures was calculated and compared to the measured temperature-dependent laser wavelength.  相似文献   
963.
Numerical solutions to three systems of integrable evolutionary equations from the Toda lattice hierarchy are analyzed. These are the classical Toda lattice, the second local dispersive flow, and the second extended dispersive flow. Special attention is given to the properties of soliton solutions. For the equations of the second local flow, two types of solitons interacting in a special manner are found. Solutions corresponding to various initial data are qualitatively outlined.  相似文献   
964.
Experimental data demonstrate that a study of accelerated aging can enable prognostication of the working capacity and storage life of polymeric formulations used in aircraft components on the basis of changes in thermogravimetric constants of these polymeric formulations.  相似文献   
965.
The effect of the paste molding pressure on the physicomechanical and texture characteristics of catalysts was studied. An indirect criterion is suggested to evaluate the molding pressure in industrial extruders, whose optimal value ensures good physicomechanical properties of the catalysts and kinetic control over the catalyzed reaction. The results obtained were verified in paste molding on various industrial extruders, and this enabled the optimal choice of the molding equipment.  相似文献   
966.
967.
The systematics of hyperfine magnetic fields at sp impurities on the Z-sites in Co based Heusler alloys are investigated. New TDPAC measurements of Cd hyperfine fields are reported.  相似文献   
968.
A high-performance liquid chromatographic procedure was developed for the quantitation of homoharringtonine in plasma. Harringtonine was used as an internal standard, and 1 ml of sample was required. The single-step extraction with dichloromethane resulted in almost 100% recovery for homoharringtonine and harringtonine. Analysis was performed on a reversed-phase CN column with amperometric detection. Chromatography was completed in 12 min. At an oxidation potential of +1.0 V, the detection limit was 1 ng/ml at a signal-to-noise ratio of 2. The mean analytical recovery for homoharringtonine was 99.5%. The within-run precision and between-run precision were both less than 11%. The method is equally applicable for plasma or serum, and it has been demonstrated to be applicable for study of the pharmacokinetics of homoharringtonine in patients suffering from acute non-lymphocytic leukaemia.  相似文献   
969.
970.
We use the spectral ballistic imaging technique to measure the impulse response of a Fabry–Pérot etalon with less than 0.2 ps temporal resolution. The results show excellent agreement with the theoretical predictions and negligible noise. Comparison to the Kramers–Kronig method along with its limitations is also presented. PACS 42.65.Re; 07.60.Ly; 42.30.Kq  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