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   534282篇
  免费   6044篇
  国内免费   1673篇
化学   289955篇
晶体学   8048篇
力学   22817篇
综合类   19篇
数学   61329篇
物理学   159831篇
  2021年   4233篇
  2020年   4752篇
  2019年   5062篇
  2018年   6365篇
  2017年   6245篇
  2016年   9891篇
  2015年   6413篇
  2014年   9653篇
  2013年   24109篇
  2012年   18417篇
  2011年   22725篇
  2010年   15711篇
  2009年   15254篇
  2008年   20665篇
  2007年   20689篇
  2006年   19376篇
  2005年   17607篇
  2004年   16257篇
  2003年   14330篇
  2002年   14104篇
  2001年   15753篇
  2000年   11898篇
  1999年   9486篇
  1998年   7926篇
  1997年   7685篇
  1996年   7481篇
  1995年   6767篇
  1994年   6520篇
  1993年   6356篇
  1992年   7132篇
  1991年   7183篇
  1990年   6856篇
  1989年   6760篇
  1988年   6742篇
  1987年   6641篇
  1986年   6303篇
  1985年   8245篇
  1984年   8438篇
  1983年   6784篇
  1982年   7131篇
  1981年   6951篇
  1980年   6600篇
  1979年   7009篇
  1978年   7282篇
  1977年   7078篇
  1976年   7023篇
  1975年   6559篇
  1974年   6453篇
  1973年   6608篇
  1972年   4552篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
An infinite row of periodically spaced, identical rigid circularcylinders is excited by an acoustic line source which is parallelto the generators of the cylinders. A method for calculatingthe scattered field accurately and efficiently is presented.When the cylinders are sufficiently close together, Rayleigh–Blochsurface waves that propagate energy to infinity along the arrayare excited. An expression is derived which enables the amplitudesof these surface waves to be computed without requiring thesolution to the full scattering problem.  相似文献   
103.
Self broadened widths of seven lines of ozone between 75 and 120 GHz have been measured at room temperature. The variation with temperature of the self-broadening parameter for three of these lines has been studied in the range 245–292°K.  相似文献   
104.
The complete set of self-consistent parameters of nominally undoped LiNbO3 crystals of congruent composition that describe the electro-optic, piezoelectric, elasto-optic, elastic, and dielectric response has been determined by numerically evaluating available measurements. The parameters were determined at room temperature and consist of the low-frequency clamped dielectric constants εS ij, elastic stiffness constants at constant electric field CE ijkl, piezoelectric stress coefficients eijk, elasto-optic constants at constant electric field pE ijkl, and clamped electro-optic coefficients rS ijk. It is shown that the complete set is required for calculating the effective electro-optic coefficients and dielectric constants in photorefractive applications of LiNbO3. Received: 4 January 2002 / Revised version: 1 February 2002 / Published online: 14 March 2002  相似文献   
105.
The statistical characteristics of conditional time before ruin of an insurance company, including the distribution function of conditional time and its moments are examined.  相似文献   
106.
We discuss some variant superfield representations which can arise by the replacement of some of the usual fields in a multiplet with p-form gauge fields.  相似文献   
107.
Off-the-shell anomalous factors of the two-body Coulomb transition matrices appear in the integral form of the Faddeev second-order nuclear-electronic amplitude, for proton-hydrogen charge transfer scattering in a typical nlmnlm′ transition. A symmetric-impulse approximation (SIA) is applied to eliminate these factors and an induction method is proposed to analytically calculate the remaining integrals. The nuclear-electronic amplitude is derived for the general case, and for totally symmetric collisions, in terms of generalized hypergeometric functions of two variables, F 4, and of one variable, 3 F 2, respectively. The angular distribution of the second-order nuclear-electronic charge transfer amplitude shows the Thomas mechanism as a peak or a hump for symmetric and asymmetric collisions. There also exists a peak in the forward angular distribution of the second-order nuclear-electronic amplitude, which partly cancels the kinematic peak in the angular distribution of the charge transfer differential cross sections.  相似文献   
108.
109.
110.
The thermal and dielectric behaviors of poly(vinylidene fluoride-trifluoroethylene) copolymers near the ferroelectric-to-paraelectric phase transition are investigated for samples with 20, 25, 30, and 40 mol% trifluoroethylene (TrFE). The data suggest that the transition becomes continuous for a particular composition near 50 mol% TrFE. Experimental data are sensitive to thermal history (kinetics of crystallization, and kinetics and cycling over the structural transition). It is found that several anomalies are present at the structural change, and in particular the 30 mol% TrFE sample shows the most marked anomalies. These phenomena can be attributed to defects, but another possibility would be the existence of an intemediate supplementary phase. Both hypotheses are discussed.  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