全文获取类型
收费全文 | 2846篇 |
免费 | 647篇 |
国内免费 | 136篇 |
专业分类
化学 | 72篇 |
力学 | 206篇 |
综合类 | 30篇 |
数学 | 2241篇 |
物理学 | 604篇 |
无线电 | 476篇 |
出版年
2024年 | 7篇 |
2023年 | 95篇 |
2022年 | 74篇 |
2021年 | 129篇 |
2020年 | 216篇 |
2019年 | 211篇 |
2018年 | 175篇 |
2017年 | 216篇 |
2016年 | 175篇 |
2015年 | 122篇 |
2014年 | 210篇 |
2013年 | 252篇 |
2012年 | 195篇 |
2011年 | 183篇 |
2010年 | 113篇 |
2009年 | 113篇 |
2008年 | 150篇 |
2007年 | 128篇 |
2006年 | 131篇 |
2005年 | 122篇 |
2004年 | 115篇 |
2003年 | 96篇 |
2002年 | 85篇 |
2001年 | 53篇 |
2000年 | 51篇 |
1999年 | 41篇 |
1998年 | 26篇 |
1997年 | 22篇 |
1996年 | 23篇 |
1995年 | 11篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1936年 | 4篇 |
排序方式: 共有3629条查询结果,搜索用时 968 毫秒
171.
172.
173.
174.
175.
176.
177.
New numerical techniques are presented for the solution of a two-dimensional anomalous sub-diffusion equation with time fractional derivative. In these methods, standard central difference approximation is used for the spatial discretization, and, for the time stepping, two new alternating direction implicit (ADI) schemes based on the L1 approximation and backward Euler method are considered. The two ADI schemes are constructed by adding two different small terms, which are different from standard ADI methods. The solvability, unconditional stability and H1 norm convergence are proved. Numerical results are presented to support our theoretical analysis and indicate the efficiency of both methods. 相似文献
178.
In order to utilize the space of an input plane efficiently and make the optical structure more flexible, an image displacement measurement based on phase-encoded reference joint fractional transform correlator (PER-JFrTC) is proposed. We use a random phase mask to encode the reference image and overlay it with the target image forming the input image. Joint power spectrum (JPS) of the input image is obtained by Fourier transform and the resultant is encoded by the same phase mask. Then a fractional Fourier transform with an order p is applied to the phase-encoded JPS (PJPS), resulting in a correlation output with a sharp cross-correlation peak, which includes the displacement information between the reference and the target image. Contrast to displacement measurement based on traditional joint transform correlator (JTC), PER-JFrTC can use the space of the input plane efficiently and reduces the influence of the auto-correlation. Also the position of cross-correlation peak can be fixed arbitrarily according to the fractional order p as well as the optical set-up can be more flexible and easier to implement. Results based on digital computation show that PER-JFrTC could detect the displacement accurately and verify our proposal. A possible optical set-up is suggested. 相似文献
179.
Ion-acoustic waves in plasma of warm ions and isothermal electrons using time-fractional KdV equation
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Sayed A. El-Wakil Essam M. Abulwaf Emad K. El-Shewy Abeer A. Mahmoud 《中国物理 B》2011,20(4):40508-040508
The ion-acoustic solitary wave in collisionless unmagnetized plasma consisting of warm ions-fluid and isothermal electrons is studied using the time fractional KdV equation. The reductive perturbation method has been employed to derive the Korteweg-de Vries equation for small but finite amplitude ion-acoustic wave in warm plasma. The Lagrangian of the time fractional KdV equation is used in a similar form to the Lagrangian of the regular KdV equation with fractional derivative for the time differentiation. The variation of the functional of this Lagrangian leads to the Euler-Lagrange equation that gives the time fractional KdV equation. The variational-iteration method is used to solve the derived time fractional KdV equation. The calculations of the solution are carried out for different values of the time fractional order. These calculations show that the time fractional can be used to modulate the electrostatic potential wave instead of adding a higher order dissipation term to the KdV equation. The results of the present investigation may be applicable to some plasma environments,such as the ionosphere plasma. 相似文献
180.
以超混沌Chen系统和超混沌Lorenz系统为例,研究了慢时变参数超混沌系统的反同步问题.首先利用主动控制的思想,消去超混沌系统中的非线性部分,然后基于Lyapunov稳定性理论,合理地选取参数自适应控制律,很好的解决了时变参数的参数摄动问题,从而实现了两个超混沌系统的反同步.在此基础之上,又进一步研究了分数阶超混沌系统,使用滑模控制方法对其进行控制,理论上分析了该方法的可行性.数值模拟实验进一步验证了所提出方法的有效性.
关键词:
超混沌
分数阶
自适应
滑模 相似文献