全文获取类型
收费全文 | 4715篇 |
免费 | 345篇 |
国内免费 | 321篇 |
专业分类
化学 | 1267篇 |
晶体学 | 9篇 |
力学 | 408篇 |
综合类 | 83篇 |
数学 | 2400篇 |
物理学 | 1214篇 |
出版年
2024年 | 4篇 |
2023年 | 59篇 |
2022年 | 78篇 |
2021年 | 118篇 |
2020年 | 102篇 |
2019年 | 138篇 |
2018年 | 104篇 |
2017年 | 178篇 |
2016年 | 189篇 |
2015年 | 147篇 |
2014年 | 224篇 |
2013年 | 351篇 |
2012年 | 292篇 |
2011年 | 225篇 |
2010年 | 218篇 |
2009年 | 309篇 |
2008年 | 281篇 |
2007年 | 312篇 |
2006年 | 249篇 |
2005年 | 210篇 |
2004年 | 178篇 |
2003年 | 193篇 |
2002年 | 220篇 |
2001年 | 150篇 |
2000年 | 119篇 |
1999年 | 104篇 |
1998年 | 97篇 |
1997年 | 87篇 |
1996年 | 70篇 |
1995年 | 65篇 |
1994年 | 51篇 |
1993年 | 40篇 |
1992年 | 24篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1989年 | 22篇 |
1988年 | 18篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1975年 | 5篇 |
1973年 | 2篇 |
排序方式: 共有5381条查询结果,搜索用时 171 毫秒
51.
Andreas Spillner 《Mathematical Logic Quarterly》2006,52(1):29-36
We study the problem of tiling a polyomino P with as few squares as possible such that every square in the tiling has a non‐empty intersection with the boundary of P . Our main result is an algorithm which given a simply connected polyomino P computes such a tiling of P . We indicate how one can improve the running time of this algorithm for the more restricted row‐column‐convex polyominoes. Finally we show that a related decision problem is in NP for rectangular polyominoes. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
52.
Li Changjun; Li Zheng; Evans David J.; Zhang Tie 《IMA Journal of Numerical Analysis》2003,23(4):581-592
Golub et al. (2001, BIT, 41, 7185) gave a generalizedsuccessive over-relaxation method for the augmented systems.In this paper, the connection between the SOR-like method andthe preconditioned conjugate gradient (PCG) method for the augmentedsystems is investigated. It is shown that the PCG method isat least as accurate (fast) as the SOR-like method. Numericalexamples demonstrate that the PCG method is much faster thanthe SOR-like method. 相似文献
53.
ZHANG Shu-min 《数学季刊》2004,(2)
In the paper, we prove that the complement of Tm(1,4,m - 6)(m > 10) is chromatically unique if and only if m ≠5k(k ≥ 2). 相似文献
54.
A time‐marching formulation is derived from the space–time integrated least squares (STILS) method for solving a pure hyperbolic convection equation and is numerically compared to various known methods. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
55.
Transmission fluctuation spectrometry (TFS) is a method for the analysis of particle size distributions based on the statistical fluctuations of a transmission signal. Complete information on the PSD and particle concentration can be retrieved by a special transformation of the transmission signal, whereby the expectancy of the transmission square (ETS) is determined after the signal has been subjected to a procedure of spatial and temporal averaging. By varying the averaging parameters over a wide range, a spectrum of ETSs is obtained and introduced into a linear equation system, which yields the PSD. In the experimental realization presented here, variable temporal averaging is realized in the frequency domain with a series of low pass filters at different cutoff frequencies while spatial averaging inevitably occurs as the particles pass through a focused Gaussian beam of finite cross section. Experimental results on spherical particles (glass beads) and non‐spherical particles (SiC) are presented. The PSDs are resolved in 30 intervals within a particle size range from 1–1000 μm, employing a modified Chahine inversion algorithm. So far, the measurements are limited to moderate particle concentrations. Some influences affecting the measurements, especially for higher particle concentrations, are discussed in detail. 相似文献
56.
This study presents a method of adaptive identification of parameters describing Sugeno fuzzy inference system in presence of bounded disturbances while maintaining the readability and interpretability of the fuzzy model during and after identification. This method do not require any a priori knowledge of a bound on the disturbance and noise and of a bound on the unknown parameters values. The method can be used for the robust and adaptive identification of slowly time varying nonlinear systems using fuzzy inference systems. The suggested method was used to build a fuzzy expert system that approximates the functional relationship between physical fitness and some of the measurable physiological parameters by their real measurements and opinion (human-experiences) of a medical expert. 相似文献
57.
Jorge Rivera-Noriega 《Proceedings of the American Mathematical Society》2004,132(5):1321-1331
An extension of an inequality of J. B. Garnett (1979), with improvements by B. E. J. Dahlberg (1980), on an approximation property of harmonic functions is proved. The weighted inequality proved here was suggested by the work of J. Pipher (1993) and it implies an extension of a result of S. Y. A. Chang, J. Wilson and T. Wolff (1985) and C. Sweezy (1991) on exponential square integrability of the boundary values of solutions to second-order linear differential equations in divergence form. This implies a solution of a problem left open by R. Bañuelos and C. N. Moore (1989) on sharp estimates for the area integral of harmonic functions in Lipschitz domains.
58.
In this paper, based on known crystal structures of square pyramid (SP) and trigonal bipyramid (TBP) penta coordinated phosphorus compounds containing amino acid side chains, such as amino, carboxyl, hydroxyl or thiol, a software for survey the P(5)-structure of phosphorylated proteins was derived. By this software, it was found that 382 of 398 phosphorus related kinases (96%) from current PDB could go through the penta-coordinated phosphorus transition state or intermediate. 相似文献
59.
60.
The frequency or dispersion relation for the least‐squares mixed formulation of the shallow‐water equations is analysed. We consider the use of different approximation spaces corresponding to co‐located and staggered meshes, respectively. The study includes the effect of Coriolis, and the dispersion properties are compared analytically and graphically with those of the mixed Galerkin formulation. Numerical solutions of a test problem to simulate slow Rossby modes illustrate the theoretical results. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献