全文获取类型
收费全文 | 22477篇 |
免费 | 3806篇 |
国内免费 | 1531篇 |
专业分类
化学 | 2751篇 |
晶体学 | 110篇 |
力学 | 2822篇 |
综合类 | 168篇 |
数学 | 2629篇 |
物理学 | 10638篇 |
综合类 | 8696篇 |
出版年
2024年 | 77篇 |
2023年 | 223篇 |
2022年 | 342篇 |
2021年 | 456篇 |
2020年 | 531篇 |
2019年 | 453篇 |
2018年 | 466篇 |
2017年 | 565篇 |
2016年 | 663篇 |
2015年 | 577篇 |
2014年 | 1046篇 |
2013年 | 1636篇 |
2012年 | 1225篇 |
2011年 | 1481篇 |
2010年 | 1158篇 |
2009年 | 1287篇 |
2008年 | 1342篇 |
2007年 | 1534篇 |
2006年 | 1382篇 |
2005年 | 1382篇 |
2004年 | 1198篇 |
2003年 | 1112篇 |
2002年 | 974篇 |
2001年 | 895篇 |
2000年 | 812篇 |
1999年 | 670篇 |
1998年 | 607篇 |
1997年 | 521篇 |
1996年 | 457篇 |
1995年 | 378篇 |
1994年 | 351篇 |
1993年 | 374篇 |
1992年 | 295篇 |
1991年 | 275篇 |
1990年 | 236篇 |
1989年 | 207篇 |
1988年 | 168篇 |
1987年 | 133篇 |
1986年 | 74篇 |
1985年 | 53篇 |
1984年 | 40篇 |
1983年 | 23篇 |
1982年 | 41篇 |
1981年 | 21篇 |
1980年 | 15篇 |
1979年 | 14篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1973年 | 8篇 |
1971年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
基于WEB的在线答疑系统的设计与实现 总被引:4,自引:0,他引:4
根据登录者的身份,基于WWW技术的在线答疑系统设计为三大模块:学生模块、教师模块和系统管理员模块,它们可分别完成提问、回答和版务管理等功能.还探讨了系统主要的实现技术。 相似文献
13.
14.
Vaidya-Bonner-de Sitter黑洞的量子非热辐射及视界表面引力 总被引:9,自引:2,他引:7
在Vaidya-Bonner-deSitter黑洞时空中,通过研究Hamihon-Jacobi方程,采用tortoise坐标变换,讨论了此黑洞的量子非热辐射及视界表面引力问题. 相似文献
15.
用波导产生倍频波时,如果倍频波进入辐射模区,仍然有相匹配问题。契伦可夫辐射式倍频不是自动地实现相匹配的。相匹配要求导波基波模式场,倍频传输场(自由波),倍频触发场,以及经多次反射透射后的辐射场的迭加形成的总辐射场处于同步的相匹配状态。根据这个相匹配的分析,提出波导契伦可夫相匹配的特有的方法,那就是对波导的模色散进行设计,并指出非对称波导的特有优点,是改变一个边界上的反射相变,即选择不同色散的线性材料作包层,由此可得到相匹配的高效契伦可夫倍频辐射。 相似文献
16.
对非线性叠加效应进行了研究,在Toda晶格中,当两孤立子运动方向相同时,其速度波的振幅的极大值是原来两波振幅之差,两波叠加的最大振幅是原来两波振幅之和。这些结果跟线性波叠加情况是完全不同的。 相似文献
17.
Second-order random wave solutions for interfacial internal waves in N-layer density-stratified fluid
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper studies the random internal wave equations describing the density interface displacements and the velocity potentials of N-layer stratified fluid contained between two rigid walls at the top and bottom. The density interface displacements and the velocity potentials were solved to the second-order by an expansion approach used by Longuet-Higgins (1963) and Dean (1979) in the study of random surface waves and by Song (2004) in the study of second- order random wave solutions for internal waves in a two-layer fluid. The obtained results indicate that the first-order solutions are a linear superposition of many wave components with different amplitudes, wave numbers and frequencies, and that the amplitudes of first-order wave components with the same wave numbers and frequencies between the adjacent density interfaces are modulated by each other. They also show that the second-order solutions consist of two parts: the first one is the first-order solutions, and the second one is the solutions of the second-order asymptotic equations, which describe the second-order nonlinear modification and the second-order wave-wave interactions not only among the wave components on same density interfaces but also among the wave components between the adjacent density interfaces. Both the first-order and second-order solutions depend on the density and depth of each layer. It is also deduced that the results of the present work include those derived by Song (2004) for second-order random wave solutions for internal waves in a two-layer fluid as a particular case. 相似文献
18.
Yoel Shkolnisky Mark Tygert Vladimir Rokhlin 《Applied and Computational Harmonic Analysis》2006,21(3):413-420
Many signals encountered in science and engineering are approximated well by bandlimited functions. We provide suitable error bounds for the approximation of bandlimited functions by linear combinations of certain special functions—the prolate spheroidal wave functions of order 0. The coefficients in the approximating linear combinations are given explicitly via appropriate quadrature formulae. 相似文献
19.
Bruno Lengeler 《Mikrochimica acta》1987,91(1-6):455-475
The synchrotron radiation (SR) emitted by circulating high-energy electrons has extraordinary properties: The light is intensive and bright, it is tunable and highly collimated, and finally, it is linearly polarized. These exceptional properties have initiated a unique revival of many spectroscopies using electromagnetic radiation. The techniques of special concern for materials analysis which are treated in this article are: X-ray absorption, reflection, fluorescence, diffraction and topography. A number of examples will be given in order to illustrate the possibilities of these techniques when SR is used.On leave of absence from Institut für Festkörperforschung, KFA Jülich, D-5170 Jülich, Federal Republic of Germany 相似文献
20.
V. I. Dashkevich 《Journal of Applied Spectroscopy》2002,69(6):862-870
Based on a semiclassical theory, investigations were made of the dynamics and spectral composition of pulsed generation with self-injection of priming radiation from the active part of a three-mirror linear resonator, the passive part of which contains an active loss modulator and serves as the output reflector of the laser. It is shown that there exists a range of resonator parameters at which pulsed lasing has virtually a single frequency irrespective of the detuning of the frequencies of the priming radiation and of the nearest eigenmode of the composite resonator. Considering graphically the phase conditions of generation, it is established that among pulsed lasers with self-injection of priming radiation which are constructed on the basis of three-mirror linear and branched resonators, the most efficient for creating single-frequency generation are those in which the length of the main resonator, where generation of the pulse occurs, is larger than the length of the additional one intended for forming the priming radiation. With an inverse ratio of the lengths of the resonators, the conditions of single-frequency pulsed generation becomes dependent on the priming radiation frequency. 相似文献