全文获取类型
收费全文 | 14624篇 |
免费 | 2193篇 |
国内免费 | 889篇 |
专业分类
化学 | 2446篇 |
晶体学 | 163篇 |
力学 | 2815篇 |
综合类 | 232篇 |
数学 | 6734篇 |
物理学 | 5316篇 |
出版年
2024年 | 23篇 |
2023年 | 137篇 |
2022年 | 290篇 |
2021年 | 274篇 |
2020年 | 412篇 |
2019年 | 348篇 |
2018年 | 318篇 |
2017年 | 478篇 |
2016年 | 498篇 |
2015年 | 348篇 |
2014年 | 632篇 |
2013年 | 982篇 |
2012年 | 731篇 |
2011年 | 748篇 |
2010年 | 727篇 |
2009年 | 802篇 |
2008年 | 893篇 |
2007年 | 979篇 |
2006年 | 931篇 |
2005年 | 917篇 |
2004年 | 774篇 |
2003年 | 759篇 |
2002年 | 625篇 |
2001年 | 550篇 |
2000年 | 496篇 |
1999年 | 468篇 |
1998年 | 354篇 |
1997年 | 345篇 |
1996年 | 239篇 |
1995年 | 207篇 |
1994年 | 164篇 |
1993年 | 169篇 |
1992年 | 129篇 |
1991年 | 123篇 |
1990年 | 101篇 |
1989年 | 59篇 |
1988年 | 78篇 |
1987年 | 62篇 |
1986年 | 61篇 |
1985年 | 68篇 |
1984年 | 63篇 |
1983年 | 29篇 |
1982年 | 42篇 |
1981年 | 54篇 |
1980年 | 33篇 |
1979年 | 38篇 |
1978年 | 47篇 |
1977年 | 36篇 |
1976年 | 22篇 |
1971年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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
92.
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
93.
94.
A. A. Dokukin 《Computational Mathematics and Mathematical Physics》2006,46(5):914-918
To validate approximate optimization schemes for estimate calculation algorithms (ECAs), it is necessary to compute the optimal height, which cannot be done in a reasonable amount of time. A variety of samples are built for which the optimal height of the ECAs is known by construction. 相似文献
95.
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
96.
条件愈苦,意志愈坚 --记王淦昌早年的科研活动 总被引:1,自引:0,他引:1
文章介绍了中国物理学家王淦昌早期的科研工作,特别是在抗日战争时期的科研成绩.王淦昌早期的科研贡献并不是在先进的实验仪器上,在条件优裕的实验室内完成的,而是在实验设备缺乏,科学文献不足等极端困难的环境中完成的.从王淦昌身上,可以看到那个时代中国优秀科学家脚踏实地、执志若金的奋斗精神. 相似文献
97.
98.
In this paper, we discuss the viscosity solutions of the weakly coupled systems of fully nonlinear second-order degenerate parabolic equations and their Cauchy-Dirichlet problem. We prove the existence, uniqueness and continuity of viscosity solution by combining Perron's method with the technique of coupled solutions. The results here generalize those in Proc. London Math. Soc. 63 (1991) 212-240 and Comm. Partial Differential Equations 16 (1991) 1095-1128. 相似文献
99.
The motion of a particle in the field of an electromagnetic monopole (in the Coulomb–Dirac field) perturbed by an axially symmetric potential after quantum averaging is described by an integrable system. Its Hamiltonian can be written in terms of the generators of an algebra with quadratic commutation relations. We construct the irreducible representations of this algebra in terms of second-order differential operators; we also construct its hypergeometric coherent states. We use these states in the first-order approximation with respect to the perturbing field to obtain the integral representation of the eigenfunctions of the original problem in terms of solutions of the model Heun-type second-order ordinary differential equation and present the asymptotic approximation of the corresponding eigenvalues. 相似文献