全文获取类型
收费全文 | 29725篇 |
免费 | 4179篇 |
国内免费 | 3022篇 |
专业分类
化学 | 16089篇 |
晶体学 | 276篇 |
力学 | 1355篇 |
综合类 | 187篇 |
数学 | 2297篇 |
物理学 | 8479篇 |
无线电 | 8243篇 |
出版年
2024年 | 114篇 |
2023年 | 690篇 |
2022年 | 843篇 |
2021年 | 1123篇 |
2020年 | 1068篇 |
2019年 | 1014篇 |
2018年 | 875篇 |
2017年 | 915篇 |
2016年 | 1237篇 |
2015年 | 1296篇 |
2014年 | 1495篇 |
2013年 | 1992篇 |
2012年 | 2286篇 |
2011年 | 2379篇 |
2010年 | 1621篇 |
2009年 | 1667篇 |
2008年 | 1863篇 |
2007年 | 1752篇 |
2006年 | 1574篇 |
2005年 | 1310篇 |
2004年 | 1013篇 |
2003年 | 913篇 |
2002年 | 856篇 |
2001年 | 676篇 |
2000年 | 645篇 |
1999年 | 686篇 |
1998年 | 613篇 |
1997年 | 563篇 |
1996年 | 608篇 |
1995年 | 513篇 |
1994年 | 546篇 |
1993年 | 378篇 |
1992年 | 326篇 |
1991年 | 311篇 |
1990年 | 214篇 |
1989年 | 166篇 |
1988年 | 143篇 |
1987年 | 107篇 |
1986年 | 106篇 |
1985年 | 100篇 |
1984年 | 69篇 |
1983年 | 62篇 |
1982年 | 47篇 |
1981年 | 31篇 |
1980年 | 33篇 |
1979年 | 21篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1974年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
Mai Lu Paul J. Leonard Duo-Wang Fan Fu-Yong Xu 《Journal of Infrared, Millimeter and Terahertz Waves》2004,25(10):1469-1479
In this paper, the cutoff characteristic of rectangular-shaped microshield transmission line has been analysed by edge element method. Dependence of cutoff wavelengths on the thickness of metallic signal strip, dielectric constant of dielectric substrate and the width of the rectangular-shaped ground conductor are presented in tabular form. Numerical results in this paper have important values in design of rectangular-shaped microshield lines in microwave and millimeter wave integrated circuits. 相似文献
152.
A near-optimal multiuser detector for DS-CDMA systems using semidefinite programming relaxation 总被引:1,自引:0,他引:1
A multiuser detector for direct-sequence code-division multiple-access systems based on semidefinite programming (SDP) is proposed. It is shown that maximum likelihood (ML) detection can be carried out by "relaxing" the associated integer programming problem to a dual SDP problem, which leads to a detector of polynomial complexity. Computer simulations that demonstrate that the proposed detector offers near-optimal performance with considerably reduced computational complexity compared with that of existing primal-SDP-relaxation based detectors are presented. 相似文献
153.
In this paper, a new vectorial boundary element method is introduced and applied to the modal analysis of dielectric waveguides with piecewise homogeneous refractive indexes. The procedure, which is free of spurious modes, determines the full field distribution from the longitudinal fields at the refractive index boundaries. Singular kernels are evaluated through series solutions while the electric field discontinuity at corners is accommodated through either a grid refinement technique or a semianalytic approach. Our formalism generates propagation constants and modal field distributions for several representative refractive index profiles with far higher accuracy than standard finite-difference or finite-element procedures. 相似文献
154.
信息技术的发展及其在军事领域的应用,改变了未来战争的作战方式,使其在作战理念、作战手段、作战空间以及作战实施方面呈现出不同于传统作战方式的特点。本文对信息时代的作战特点进行了分析总结,并在此基础上对加强我军信息化建设途径进行了探讨。 相似文献
155.
156.
Sergiy V. Rosokha Jian Jiang Lu Sergey M. Dibrov Jay K. Kochi 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):o464-o466
The title compound, C6H2N6O10·2C2H4Cl2, forms layered stacks of pentanitroaniline molecules, which possess twofold symmetry. The voids between these stacks are occupied by dichloroethane molecules, which reside near a 2/m symmetry element and display pseudo‐inversion symmetry. The C atoms in one of the two solvent molecules are threefold disordered. In the pentanitroaniline molecule, considerable distortion of the benzenoid ring, coupled with the short C—N(H2) bond and out‐of‐plane NO2 twistings, point to significant intramolecular `push–pull' charge transfer at the amino‐ and nitro‐substituted (ortho and para) positions, as theoretically quantified by natural bond orbital analysis of the π‐electron density. 相似文献
157.
158.
A numerical simulation is performed to investigate the flow induced by a sphere moving along the axis of a rotating cylindrical container filled with the viscous fluid. Three‐dimensional incompressible Navier–Stokes equations are solved using a finite element method. The objective of this study is to examine the feature of waves generated by the Coriolis force at moderate Rossby numbers and that to what extent the Taylor–Proudman theorem is valid for the viscous rotating flow at small Rossby number and large Reynolds number. Calculations have been undertaken at the Rossby numbers (Ro) of 1 and 0.02 and the Reynolds numbers (Re) of 200 and 500. When Ro=O(1), inertia waves are exhibited in the rotating flow past a sphere. The effects of the Reynolds number and the ratio of the radius of the sphere and that of the rotating cylinder on the flow structure are examined. When Ro ? 1, as predicted by the Taylor–Proudman theorem for inviscid flow, the so‐called ‘Taylor column’ is also generated in the viscous fluid flow after an evolutionary course of vortical flow structures. The initial evolution and final formation of the ‘Taylor column’ are exhibited. According to the present calculation, it has been verified that major theoretical statement about the rotating flow of the inviscid fluid may still approximately predict the rotating flow structure of the viscous fluid in a certain regime of the Reynolds number. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
159.
160.
通过理论分析和实验研究液晶分子附着能和液晶盒间隙对响应时间(τ0)的影响。用液晶盒有效间隙法和表面动力学方程法两种方法推出分析公式,由这两种方法推出的结果是一致的。实验数据与简化方程τ0-dx基本拟合(其中d是液晶盒的间隙,x是指数)。在两种极端的(极大或极小)附着能极限下,指数x分别接近2和1。这个结论有助于优化液晶显示器件的应用。 相似文献