全文获取类型
收费全文 | 4122篇 |
免费 | 553篇 |
国内免费 | 412篇 |
专业分类
化学 | 144篇 |
晶体学 | 6篇 |
力学 | 329篇 |
综合类 | 93篇 |
数学 | 2643篇 |
物理学 | 806篇 |
无线电 | 1066篇 |
出版年
2024年 | 7篇 |
2023年 | 45篇 |
2022年 | 58篇 |
2021年 | 76篇 |
2020年 | 80篇 |
2019年 | 105篇 |
2018年 | 92篇 |
2017年 | 132篇 |
2016年 | 167篇 |
2015年 | 135篇 |
2014年 | 224篇 |
2013年 | 307篇 |
2012年 | 259篇 |
2011年 | 279篇 |
2010年 | 236篇 |
2009年 | 263篇 |
2008年 | 283篇 |
2007年 | 326篇 |
2006年 | 272篇 |
2005年 | 252篇 |
2004年 | 188篇 |
2003年 | 206篇 |
2002年 | 156篇 |
2001年 | 128篇 |
2000年 | 112篇 |
1999年 | 97篇 |
1998年 | 77篇 |
1997年 | 92篇 |
1996年 | 73篇 |
1995年 | 44篇 |
1994年 | 52篇 |
1993年 | 28篇 |
1992年 | 27篇 |
1991年 | 36篇 |
1990年 | 21篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 19篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1981年 | 11篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1972年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有5087条查询结果,搜索用时 15 毫秒
1.
2.
This paper solves the problem of the duration of the total eclipseof a satellite of a body, provided that (a) the body is sphericalin shape and the mass distribution inside the body is sphericallysymmetrical; (b) the satellite is a very small object; (c) thesatellite's orbit around a body is circular and the satellitecan pass through the centre of its shadow; (d) a source of lightis the source of the conical body's shadow (umbra) and it doesnot change its apparent position in the sky; (e) there are noperturbations on the satellite's orbit. The solution presentedrepresents the general discussion of the problem based on utilizationof some parts of the theory of contraction mappings. 相似文献
3.
4.
Transmission of signals, whether on-chip or off-chip, places severe constraints on timing and extracts a large price in energy. New silicon device technologies, such as back-plane CMOS, provide a programmable and adaptable threshold voltage as an additional tool that can be used for low power design. We show that one particularly desirable use of this freedom is energy-efficient high-speed transmission across long interconnects using multi-valued encoding. Our multi-valued CMOS circuits take advantage of the threshold voltage control of the transistors, by using the signal-voltage-to-threshold-voltage span, in order to make area-efficient implementations of 4-PAM (pulse amplitude modulation) transceivers operating at high speed. In a comparison of a variety of published technologies, for signal transmission with interconnects of 10-15 mm length, we show up to 50% improvement in energy for on-chip signal transmission over binary encoding together with higher limits for operating speeds without a penalty in circuit noise margin. 相似文献
5.
曾六川 《高等学校计算数学学报(英文版)》2003,12(1)
The purpose of this paper is to investigate the problem of approximating fixed points of non-Lipschitizian asymptotically pseudocontractive mappings in an arbitrary real Banach space by the modified Ishikawa iterative sequences with errors. 相似文献
6.
给出了Banach空间的一个增算子不动点定理,将这一定理应用到Banach空间的积分-微分方程,给出了一类积分-微分方程的连续可微最大解和连续可微最小解的存在性定理. 相似文献
7.
J. Giroire T. Ha‐Duong V. Moumas 《Mathematical Methods in the Applied Sciences》2005,28(13):1527-1552
This article deals with a boundary value problem for Laplace equation with a non‐linear and non‐local boundary condition. This problem comes from petroleum engineering and is used to obtain an estimation of well productivity. The non‐linear and non‐local boundary condition is written on the well boundary. On the outer reservoir boundaries, we have both Dirichlet and Neumann conditions. In this paper, we prove the existence and uniqueness of a solution to this problem. The existence is proved by Schauder theorem and the uniqueness is obtained under more restricted conditions, when the involved operator is a contraction. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
8.
The problem of investigation of the amplitude and phase structure of a time-varying probing optical signal and the structure of time-varying inhomogeneities of a substance tested by this signal is considered. The analysis is concerned, in particular, with determination of the structure of signals and processes with resolution in the pico- and femtosecond range. The scheme used for the analysis is based on registration of four spatially separated spectra of the studied radiation. The spectra are formed in a four-channel scheme with a twin-wave Michelson interferometer and a spectral device. Modulators based on electrooptical crystals (perovskites) are placed in the channels. The sum spectra are formed: without modulators, with the effect of either of the modulators, and with both of them affecting the radiation. The effect of the studied substance implies either modulating the radiation (in this case it is described by multiplication) or redistributing the radiation (then it is described by convolution). 相似文献
9.
Krzysztof Pawaowski 《K-Theory》1998,13(1):41-55
The paper presents a procedure for constructing smooth actions of finite perfect groups on spheres with fixed point sets having certain prescribed properties (Theorem A); in particular, having any prescribed configuration of Chern and Pontryagin numbers (Corollary C). The main ingredients used are equivariant thickening and equivariant surgery. 相似文献
10.
A Fixed Point Theorem for Multi-valued Composite Increasing OperatorsLiFengyou(李凤友)(DepartmentofMathematics,Tianjin'NormalUni... 相似文献