全文获取类型
收费全文 | 121018篇 |
免费 | 8396篇 |
国内免费 | 12642篇 |
专业分类
化学 | 71430篇 |
晶体学 | 1164篇 |
力学 | 2547篇 |
综合类 | 845篇 |
数学 | 13686篇 |
物理学 | 21187篇 |
无线电 | 31197篇 |
出版年
2024年 | 338篇 |
2023年 | 1468篇 |
2022年 | 2653篇 |
2021年 | 2640篇 |
2020年 | 3012篇 |
2019年 | 2979篇 |
2018年 | 2796篇 |
2017年 | 3937篇 |
2016年 | 3969篇 |
2015年 | 3805篇 |
2014年 | 4885篇 |
2013年 | 8283篇 |
2012年 | 8092篇 |
2011年 | 7212篇 |
2010年 | 5782篇 |
2009年 | 7465篇 |
2008年 | 7760篇 |
2007年 | 8276篇 |
2006年 | 7616篇 |
2005年 | 6484篇 |
2004年 | 5896篇 |
2003年 | 4834篇 |
2002年 | 5765篇 |
2001年 | 3459篇 |
2000年 | 3123篇 |
1999年 | 2853篇 |
1998年 | 2560篇 |
1997年 | 2041篇 |
1996年 | 1743篇 |
1995年 | 1674篇 |
1994年 | 1431篇 |
1993年 | 1160篇 |
1992年 | 1072篇 |
1991年 | 757篇 |
1990年 | 599篇 |
1989年 | 556篇 |
1988年 | 398篇 |
1987年 | 319篇 |
1986年 | 285篇 |
1985年 | 235篇 |
1984年 | 246篇 |
1983年 | 144篇 |
1982年 | 219篇 |
1981年 | 185篇 |
1980年 | 205篇 |
1979年 | 189篇 |
1978年 | 171篇 |
1977年 | 127篇 |
1976年 | 111篇 |
1973年 | 71篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
IR LASER BACKSCATTERING FROM AN ARBITRARILY SHAPED DIELECTRIC OBJECT WITH ROUGH SURFACE 总被引:2,自引:0,他引:2
吴振森 《电子科学学刊(英文版)》1993,10(4):298-306
The backscattering of light wave from arbitrarily convex dielectric objects withrough surface is investigated and formulas for calculating the backscattering cross-section of bothcoherent and incoherent fields are obtained.In the infrared wave-band,the influence of the ge-ometry,permittivity and statistical characteristics of the rough surface on LRCS is analyzed,byusing rough sphere and ellipsoids as examples. 相似文献
992.
Michael Bildhauer 《manuscripta mathematica》1998,97(3):389-406
H?lder continuity up to the free boundary is proved for minimizing solutions if they meet the supporting surface in an angle
which is bounded away from zero. The problem is localized by proving the continuity of the distance function, a result which
is also true for stationary points.
Received: 14 April 1998 相似文献
993.
SHIHongju SHIYongji 《半导体光子学与技术》1998,4(4):197-208,234
The liquid crystal televison spatia light modulator(LCTVSLM)characterized is usable in optical processing applications.e.g.,optical pattern recognition,associative memory,optical computing,correlation detection and optical data processing systems.The array performance and real-time optical correlation applications are reviewed. 相似文献
994.
995.
996.
Summary. A third-order accurate Godunov-type scheme for the approximate solution of hyperbolic systems of conservation laws is presented.
Its two main ingredients include: 1. A non-oscillatory piecewise-quadratic reconstruction of pointvalues from their given
cell averages; and 2. A central differencing based on staggered evolution of the reconstructed cell averages. This results in a third-order central scheme, an extension along the lines
of the second-order central scheme of Nessyahu and Tadmor \cite{NT}. The scalar scheme is non-oscillatory (and hence – convergent),
in the sense that it does not increase the number of initial extrema (– as does the exact entropy solution operator). Extension to systems is carried out by componentwise application of the scalar framework. In particular, we have the advantage that, unlike upwind schemes, no (approximate) Riemann
solvers, field-by-field characteristic decompositions, etc., are required. Numerical experiments confirm the high-resolution
content of the proposed scheme. Thus, a considerable amount of simplicity and robustness is gained while retaining the expected
third-order resolution.
Received April 10, 1996 / Revised version received January 20, 1997 相似文献
997.
998.
本文报导了聚4-氨基联苯的电化学合成,测定了它的ESR、IR及紫外可见光谱。聚合物在THF、DMF和DMSO中能全部溶解。界面移动法测得聚4-氨基联苯的DMF饱和溶液中正离子的迁移率为1.48×10~(-8)m~2·S~(-1)·V~(-1)。 相似文献
999.
Recently, with the advent of supercomputers, there has been considerable interest in the use of direct numerical simulation to obtain information about turbulent shear flow at low Reynolds number. This paper presents a pseudospectral technique to solve the full three-dimensional time-dependent Navier-Stokes and advection-diffusion equations without the use of subgrid-scale modelling. The technique has not been previously used for fully developed turbulent channel flow simulation and is based on methods applied in other contexts. The emphasis of this paper is to provide a reasonably detailed account of how the simulation is done rather than to present new calculations of turbulence. The details of an algorithm for turbulent channel flow simulation and the grid and time step sizes needed to integrate through transient behaviour to steady state turbulence have not been published before and are presented here. Results from a Cray-2 simulation of fully developed turbulent flow in a channel with heat transfer are presented along with a critical comparison between experiment and computation. The first- and second-order moments agree well with experimental measurements; the agreement is poor for higher-order moments such as the skewness and flatness near the walls of the channel. Detailed information given about the effects of spatial grid resolution on a computed results is important for estimating the size of the computation required to study various aspects of a turbulent flow. 相似文献
1000.
带有光放大的波分复用技术在光纤通信中的应用 总被引:1,自引:0,他引:1
本文论述了波分复用技术的优点及其应用;介绍了波分复用技术与光纤放大器相结合后的发展概况2;评述了波分复用技术发展中的主要问题及其在当前实用系统中的解决方案和今后的发展方向。 相似文献