全文获取类型
收费全文 | 6204篇 |
免费 | 839篇 |
国内免费 | 397篇 |
专业分类
化学 | 482篇 |
晶体学 | 21篇 |
力学 | 472篇 |
综合类 | 77篇 |
数学 | 3356篇 |
物理学 | 1195篇 |
无线电 | 1837篇 |
出版年
2024年 | 17篇 |
2023年 | 89篇 |
2022年 | 149篇 |
2021年 | 219篇 |
2020年 | 193篇 |
2019年 | 177篇 |
2018年 | 178篇 |
2017年 | 239篇 |
2016年 | 223篇 |
2015年 | 221篇 |
2014年 | 306篇 |
2013年 | 503篇 |
2012年 | 310篇 |
2011年 | 332篇 |
2010年 | 291篇 |
2009年 | 347篇 |
2008年 | 358篇 |
2007年 | 396篇 |
2006年 | 355篇 |
2005年 | 326篇 |
2004年 | 258篇 |
2003年 | 232篇 |
2002年 | 253篇 |
2001年 | 226篇 |
2000年 | 215篇 |
1999年 | 164篇 |
1998年 | 145篇 |
1997年 | 146篇 |
1996年 | 105篇 |
1995年 | 71篇 |
1994年 | 79篇 |
1993年 | 46篇 |
1992年 | 38篇 |
1991年 | 31篇 |
1990年 | 27篇 |
1989年 | 15篇 |
1988年 | 18篇 |
1987年 | 12篇 |
1986年 | 21篇 |
1985年 | 29篇 |
1984年 | 21篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1971年 | 3篇 |
1959年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有7440条查询结果,搜索用时 0 毫秒
31.
本地多点分配业务(LMDS)是近年来在国际上兴起的固定式宽带无线接入技术,具有传输容量大、起始费用低的优点,受到了国内外电信业务经营者的普遍关注.文章介绍了LMDS提供的业务类型、工作频率、系统结构和标准化情况,并将LMDS与有线电视网络、ADSL、MMDS等现有的接入技术进行了比较.文章认为LMDS的商业推广尚需解决信号质量、服务区尺寸、费用等制约因素. 相似文献
32.
M. Iuga G. Steinle-Neumann J. Meinhardt 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(2):127-133
Athermal elasticity for some ceramic materials (α-Al2O3,
SiC (α and β phases), TiO2 (rutile and anatase),
hexagonal AlN and TiB2, cubic BN and CaF2, and monoclinic
ZrO2) have been investigated via density functional theory.
Energy-volume equation-of-state computations to obtain the zero pressure
equilibrium volume and bulk modulus as well as computations of the full
elastic constant tensor of these ceramics at the experimental zero pressure
volume have been performed. The present results for the single crystal
elasticity are in good agreement with experiments both for the aggregate
properties (bulk and shear modulus) and the elastic anisotropy. In contrast,
a considerable discrepancy for the zero pressure bulk modulus of some
ceramics evaluated from the energy-volume fit to the computational zero
pressure volume has been observed. 相似文献
33.
W. Brüggemann K. Fischer H. Jahnke 《Journal of Mathematical Modelling and Algorithms》2003,2(2):153-169
In Part I of this study, we suggest to identify an operations research (OR) problem with the equivalence class of models describing the problem and enhance the standard computer-science theory of computational complexity to be applicable to this situation of an often model-based OR context. The Discrete Lot-sizing and Scheduling Problem (DLSP) is analysed here in detail to demonstrate the difficulties which can arise if these aspects are neglected and to illustrate the new theoretical concept. In addition, a new minimal model is introduced for the DLSP which makes this problem eventually amenable to a rigorous analysis of its computational complexity. 相似文献
34.
Some properties of the bilevel programming problem 总被引:8,自引:0,他引:8
J. F. Bard 《Journal of Optimization Theory and Applications》1991,68(2):371-378
The purpose of this paper is to elaborate on the difficulties accompanying the development of efficient algorithms for solving the bilevel programming problem (BLPP). We begin with a pair of examples showing that, even under the best of circumstances, solutions may not exist. This is followed by a proof that the BLPP is NP-hard.This work was partially supported by a grant from the Advanced Research Program of the Texas Higher Education Coordinating Board. 相似文献
35.
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
36.
在研究排队网络的文献中,G-网络(即推广的排队网络)最近受到了国际学者广泛的关注,它的研究在一定程度上丰富了排队网络的内容.正因为有很多学者投入到此项研究中,新的结果是层出不穷的.本文简短地介绍G-网络近年来的发展. 相似文献
37.
Jinyan Fan 《Computational Optimization and Applications》2006,34(2):215-227
In this paper, we present the new trust region method for nonlinear equations with the trust region converging to zero. The
new method preserves the global convergence of the traditional trust region methods in which the trust region radius will
be larger than a positive constant. We study the convergence rate of the new method under the local error bound condition
which is weaker than the nonsingularity. An example given by Y.X. Yuan shows that the convergence rate can not be quadratic.
Finally, some numerical results are given.
This work is supported by Chinese NSFC grants 10401023 and 10371076, Research Grants for Young Teachers of Shanghai Jiao Tong
University, and E-Institute of Computational Sciences of Shanghai Universities.
An erratum to this article is available at . 相似文献
38.
Howel Tong 《应用数学学报(英文版)》2002,18(2):177-184
Abstract I reflect upon the development of nonlinear time series analysis since 1990 by focusing on five majorareas of development. These areas include the interface between nonlinear time series analysis and chaos,thenonparametric/semiparametric approach,nonlinear state space modelling,financial time series and nonlinearmodelling of panels of time series. 相似文献
39.
We investigate function spaces of generalised smoothness of Besov and Triebel–Lizorkin type. Equivalent quasi-norms in terms
of maximal functions and local means are given. An atomic decomposition theorem for this type of spaces is proved.
Mathematics Subject Classification (2000) 46E35 相似文献
40.
J. Freudenberger 《Discrete Applied Mathematics》2006,154(2):294-304
We consider bounded distance list decoding, such that the decoder calculates the list of all codewords within a sphere around the received vector. We analyze the performance and the complexity of this suboptimum list decoding scheme for the binary symmetric channel. The reliability function of the list decoding scheme is equivalent to the sphere-packing bound, where the decoding complexity is asymptotically bounded by 2nR(1-R). Furthermore, we investigate a decision feedback strategy that is based on bounded distance list decoding. Here, any output with zero or many codewords will call for a repeated transmission. In this case the decoding complexity will be of the order 2nR(1-C), where C denotes the channel capacity. The reliability function is close to Forney's feedback exponent. 相似文献