全文获取类型
收费全文 | 315897篇 |
免费 | 1791篇 |
国内免费 | 588篇 |
专业分类
化学 | 144471篇 |
晶体学 | 5015篇 |
力学 | 18089篇 |
综合类 | 12篇 |
数学 | 47876篇 |
物理学 | 102813篇 |
出版年
2021年 | 2252篇 |
2020年 | 2254篇 |
2019年 | 2819篇 |
2018年 | 11294篇 |
2017年 | 11916篇 |
2016年 | 8807篇 |
2015年 | 3336篇 |
2014年 | 4949篇 |
2013年 | 10036篇 |
2012年 | 11727篇 |
2011年 | 20099篇 |
2010年 | 13544篇 |
2009年 | 13869篇 |
2008年 | 17946篇 |
2007年 | 20907篇 |
2006年 | 8008篇 |
2005年 | 12311篇 |
2004年 | 9304篇 |
2003年 | 8969篇 |
2002年 | 7205篇 |
2001年 | 6885篇 |
2000年 | 5255篇 |
1999年 | 3874篇 |
1998年 | 3260篇 |
1997年 | 3275篇 |
1996年 | 3155篇 |
1995年 | 2709篇 |
1994年 | 2788篇 |
1993年 | 2652篇 |
1992年 | 2986篇 |
1991年 | 3096篇 |
1990年 | 3017篇 |
1989年 | 3045篇 |
1988年 | 3000篇 |
1987年 | 3004篇 |
1986年 | 2813篇 |
1985年 | 3493篇 |
1984年 | 3609篇 |
1983年 | 2977篇 |
1982年 | 2974篇 |
1981年 | 2950篇 |
1980年 | 2668篇 |
1979年 | 3127篇 |
1978年 | 3083篇 |
1977年 | 3210篇 |
1976年 | 3249篇 |
1975年 | 2986篇 |
1974年 | 2909篇 |
1973年 | 3082篇 |
1972年 | 2342篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
An exponentially fitted special second-order finite difference method is presented for solving singularly perturbed two-point boundary value problems with the boundary layer at one end (left or right) point. A fitting factor is introduced in a tri-diagonal finite difference scheme and is obtained from the theory of singular perturbations. Thomas Algorithm is used to solve the system and its stability is investigated. To demonstrate the applicability of the method, we have solved several linear and non-linear problems. From the results, it is observed that the present method approximates the exact solution very well. 相似文献
982.
A theorem on the existence of a G-representation and a differential-geometric criterion of the kinematic integrability for nonlinear differential equations
from the Λ2-G-classes is proved. Examples of zero-curvature representations and metrics for some equations of mathematical physics are
presented.
__________
Translated from Fundamental’naya i Prikladnaya Matematika (Fundamental and Applied Mathematics), Vol. 11, No. 1, Geometry,
2005. 相似文献
983.
Ch. Tsitouras 《Numerical Algorithms》2007,44(3):291-307
Runge–Kutta (RK) pairs furnish approximations of the solution of an initial value problem at discrete points in the interval
of integration. Many techniques for enriching these methods with continuous approximations have been proposed. Here we construct
C
1 continuous, eighth and ninth order interpolation methods for a recently appeared RK pair of orders 9(8). These interpolants
share a very small leading truncation error making them suitable for use at quadruple precision, i.e. 32–33 decimal digits
of accuracy. Extended numerical results justify our effort. 相似文献
984.
The photogyrotropic properties of several mordant yellow azo dyes in gelatin and polymer matrices that are in the normal state or exposed to circularly polarized light are investigated. A model explanation for the experimental data is given. 相似文献
985.
986.
987.
988.
The aim of this paper is to highlight the added value of the generalized Gouy phase shift introduced by Siegman. Although suited for optical systems study, including those more complex than free space, we note that it did not meet the use that it deserves so far. The analysis of the whole of the ideas and analytical approaches associated to the important concept of the Gouy phase proves its effectiveness.
Usually, the resonance condition is systematically built on the basis of the equivalent empty cavity. Unfortunately, this approach does not cover some of the useful parameters of the real resonator. By means of the generalized Gouy phase and the self-consistent complex parameter q, we derive here a new approach for the calculation of the resonance condition for the real cavity. Moreover, the use of the generalized Gouy phase clearly simplifies the study of resonators, while making it possible to avoid the use of the Huygens’ Fresnel integral. 相似文献
989.
990.
I. P. Raevskii L. A. Reznichenko M. P. Ivliev V. G. Smotrakov V. V. Eremkin M. A. Malitskaya L. A. Shilkina S. I. Shevtsova A. V. Borodin 《Crystallography Reports》2003,48(3):486-490
(Na, K)NbO3 crystals with a perovskite structure and a KNbO3 content up to 40 mol % were grown from flux with the use of the solvent NaBO2. The dielectric measurements of the crystals grown revealed phase transitions that had never been observed before in ceramic samples. 相似文献