全文获取类型
收费全文 | 11706篇 |
免费 | 1543篇 |
国内免费 | 908篇 |
专业分类
化学 | 6723篇 |
晶体学 | 122篇 |
力学 | 405篇 |
综合类 | 50篇 |
数学 | 838篇 |
物理学 | 2931篇 |
无线电 | 3088篇 |
出版年
2024年 | 24篇 |
2023年 | 270篇 |
2022年 | 270篇 |
2021年 | 399篇 |
2020年 | 416篇 |
2019年 | 397篇 |
2018年 | 320篇 |
2017年 | 280篇 |
2016年 | 507篇 |
2015年 | 478篇 |
2014年 | 585篇 |
2013年 | 787篇 |
2012年 | 986篇 |
2011年 | 975篇 |
2010年 | 622篇 |
2009年 | 676篇 |
2008年 | 767篇 |
2007年 | 743篇 |
2006年 | 647篇 |
2005年 | 617篇 |
2004年 | 393篇 |
2003年 | 313篇 |
2002年 | 337篇 |
2001年 | 263篇 |
2000年 | 248篇 |
1999年 | 229篇 |
1998年 | 201篇 |
1997年 | 146篇 |
1996年 | 146篇 |
1995年 | 180篇 |
1994年 | 153篇 |
1993年 | 121篇 |
1992年 | 107篇 |
1991年 | 88篇 |
1990年 | 80篇 |
1989年 | 41篇 |
1988年 | 52篇 |
1987年 | 40篇 |
1986年 | 40篇 |
1985年 | 38篇 |
1984年 | 26篇 |
1983年 | 15篇 |
1982年 | 29篇 |
1981年 | 16篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1971年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
81.
Weikai Su Wei Hong ZhengHau Zhu YunYi Wang 《Journal of Infrared, Millimeter and Terahertz Waves》1992,13(12):1925-1941
In this paper, the scattering parameters of a waveguide cross junction loaded with a metallic post in the center are analyzed for the first time by using the Method of Lines. The homogeneous boundary condition of the third kind and curved boundary are introduced in the formulation. Numerical results are in good agreement with the experimental data. The scattering parameters at Ka-band and W-band of the cross junctions loaded with metallic posts of different radii are presented. It is shown from the numerical results that loaded with metallic posts is an effective means for adjusting the network parameters of the waveguide cross junction to satisfy some special requirements in the design of millimeter wave components. 相似文献
82.
Wei-yi SU~ 《中国科学A辑(英文版)》2007,50(7):1005-1014
The Lipschitz class Lipαon a local field K is defined in this note,and the equivalent relationship between the Lipschitz class Lipαand the Holder type space C~α(K)is proved.Then,those important characteristics on the Euclidean space R~n and the local field K are compared,so that one may interpret the essential differences between the analyses on R~n and K.Finally,the Cantor type fractal functionθ(x)is showed in the Lipschitz class Lip(m,K),m<(ln 2/ln 3). 相似文献
83.
用解偏振光强法和差示扫描量热法(DSC)分别研究了聚甲醛和聚甲醛助剂P的等温结晶动力学和非等温结晶动力学。探讨了助剂P对聚甲醛的结晶成核作用。 相似文献
84.
本文从智能网的基本概念入手,论述了利用 ZXJ10程控交换系统为发展智能网业务提供支持功能的技术策略以及分阶段实现的过程,并对各个阶段能够实现的业务作了简要介绍。 相似文献
85.
86.
87.
The kinetic behaviour of aluminum naphthenate/benzene system in the process of gelation and degradation was systematically studied. The results obtained from the kinetic experiments indicated that the gelation stage was in accordance with a kinetic model of an auto-catalytic first-order reaction, and the degradation stage was a simple first-order reaction. The rate constants in these two stages at various temperaturs were measured. And the determined apparent activation energies for the gelation stage and for the degradation stage are 27.5±2.0 and 37.7±2.3 kJ/mol, respectively. 相似文献
88.
89.
The basic structural units of the genome are nucleotides. A single nucleotide polymorphism (SNP) is a mutation at a single nucleotide position. This paper discusses several major problems in SNP data analysis and review some existing solutions in this work. Generally speaking, a rich set of SNP analysis problems are cast in the signal processing framework. Our objective is to offer a state-of-the art review on this topic from a signal processing viewpoint so that researchers in the signal processing field can grasp the important domain knowledge to overcome the barrier between the two fields 相似文献
90.
In this paper, a novel generalization of subspace-based blind channel identification methods in cyclic prefix (CP) systems is proposed. For the generalization, a new system parameter called repetition index is introduced whose value is unity for previously reported special cases. By choosing a repetition index larger than unity, the number of received blocks needed for blind identification is significantly reduced compared to all previously reported methods. This feature makes the method more realistic especially in wireless environments where the channel state is usually fast-varying. Given the number of received blocks available, the minimum value of repetition index is derived. Theoretical limit allows the proposed method to perform blind identification using only three received blocks in absence of noise. In practice, the number of received blocks needed to yield a satisfactory bit-error-rate (BER) performance is usually on the order of half the block size. Simulation results not only demonstrate the capability of the algorithm to perform blind identification using fewer received blocks, but also show that in some cases system performance can be improved by choosing a repetition index larger than needed. Simulation of the proposed method over time-varying channels clearly demonstrates the improvement over previously reported methods. 相似文献