全文获取类型
收费全文 | 17262篇 |
免费 | 2741篇 |
国内免费 | 994篇 |
专业分类
化学 | 1659篇 |
晶体学 | 172篇 |
力学 | 2508篇 |
综合类 | 196篇 |
数学 | 6459篇 |
物理学 | 10003篇 |
出版年
2024年 | 43篇 |
2023年 | 133篇 |
2022年 | 247篇 |
2021年 | 298篇 |
2020年 | 391篇 |
2019年 | 303篇 |
2018年 | 324篇 |
2017年 | 512篇 |
2016年 | 574篇 |
2015年 | 435篇 |
2014年 | 856篇 |
2013年 | 1101篇 |
2012年 | 978篇 |
2011年 | 1031篇 |
2010年 | 843篇 |
2009年 | 987篇 |
2008年 | 1196篇 |
2007年 | 1305篇 |
2006年 | 1209篇 |
2005年 | 1057篇 |
2004年 | 890篇 |
2003年 | 930篇 |
2002年 | 709篇 |
2001年 | 636篇 |
2000年 | 560篇 |
1999年 | 529篇 |
1998年 | 439篇 |
1997年 | 392篇 |
1996年 | 272篇 |
1995年 | 247篇 |
1994年 | 208篇 |
1993年 | 193篇 |
1992年 | 155篇 |
1991年 | 123篇 |
1990年 | 125篇 |
1989年 | 72篇 |
1988年 | 72篇 |
1987年 | 68篇 |
1986年 | 65篇 |
1985年 | 81篇 |
1984年 | 64篇 |
1983年 | 35篇 |
1982年 | 48篇 |
1981年 | 49篇 |
1980年 | 28篇 |
1979年 | 35篇 |
1978年 | 49篇 |
1977年 | 34篇 |
1976年 | 22篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
81.
We have presented an investigation of the induced focusing in Kerr media of two laser beams, the pump beam and the probe beam,
which could be either Gaussian or elliptic Gaussian or a combination of the two. We have used variational formalism to derive
relevant beam-width equations. Among several important findings, the finding that a very week probe beam can be guided and
focused when power of both beams are well below their individual threshold for self-focusing, is a noteworthy one. It has
been found that induced focusing is not possible for laser beams of any wavelength and beam radius. In case both beams are
elliptic Gaussian, we have shown that when power of both beams is above a certain threshold value then the effective radius
of both beams collapses and collapse distance depends on power. Moreover, it has been found that induced focusing can be employed
to convert a circular Gaussian beam into an elliptic Gaussian beam. 相似文献
82.
Differentiation of functions w.r.t. finite atomless measures with compact support on the real line is introduced. The related harmonic calculus is similar to that of the classical Lebesgue case. As an application we obtain the Weyl exponent for the spectral asymptotics of the Laplacians w.r.t. linear Cantor-type measures with arbitrary weights. 相似文献
83.
基于正弦灰度变换的X光图像增强 总被引:11,自引:0,他引:11
介绍了灰度变换法的几种形式 ,提出了一种正弦非线性变换法 ,对三幅数字X光医学图像进行了处理 ,获得了令人满意的对比度增强效果 ,证明该方法有效而实用 相似文献
84.
Alex Hellsten 《Archive for Mathematical Logic》2006,45(6):705-714
We extract some properties of Mahlo’s operation and show that some other very natural operations share these properties. The weakly compact sets form a similar hierarchy as the stationary sets. The height of this hierarchy is a large cardinal property connected to saturation properties of the weakly compact ideal. 相似文献
85.
Many recent algorithmic approaches involve the construction of a differential equation model for computational purposes, typically
by introducing an artificial time variable. The actual computational model involves a discretization of the now time-dependent differential system, usually
employing forward Euler. The resulting dynamics of such an algorithm is then a discrete dynamics, and it is expected to be
“close enough” to the dynamics of the continuous system (which is typically easier to analyze) provided that small – hence
many – time steps, or iterations, are taken. Indeed, recent papers in inverse problems and image processing routinely report
results requiring thousands of iterations to converge. This makes one wonder if and how the computational modeling process
can be improved to better reflect the actual properties sought.
In this article we elaborate on several problem instances that illustrate the above observations. Algorithms may often lend
themselves to a dual interpretation, in terms of a simply discretized differential equation with artificial time and in terms
of a simple optimization algorithm; such a dual interpretation can be advantageous. We show how a broader computational modeling
approach may possibly lead to algorithms with improved efficiency.
AMS subject classification (2000) 65L05, 65M32, 65N21, 65N22, 65D18 相似文献
86.
87.
This paper describes the performance and simulation of a compact integrated optical processor for the real-time reconstruction of two-dimensional images in airborne stripmap synthetic aperture radar applications. The functional behavior of the processor is explained in some detail. The design criteria are briefly given. The simulation step allowed the main processor characteristics and properties to be identified. A number of comparisons were obtained in airborne SAR mission scenarios between the predictions of the optical device and those achieved by the modern electronic digital approach, based on the wavefront reconstruction method by matched filtering. 相似文献
88.
89.
Linear complexity and linear complexity profile are important characteristics of a sequence for applications in cryptography
and Monte-Carlo methods.
The nonlinear congruential method is an attractive alternative to the classical linear congruential method for pseudorandom
number generation.
Recently, a weak lower bound on the linear complexity profile of a general nonlinear congruential pseudorandom number generator
was proven by Gutierrez, Shparlinski and the first author. For most nonlinear generators a much stronger lower bound is expected.
Here, we obtain a much stronger lower bound on the linear complexity profile of nonlinear congruential pseudorandom number
generators with Dickson polynomials. 相似文献
90.