全文获取类型
收费全文 | 374篇 |
免费 | 30篇 |
国内免费 | 5篇 |
专业分类
化学 | 6篇 |
力学 | 29篇 |
数学 | 315篇 |
物理学 | 59篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 5篇 |
2021年 | 16篇 |
2020年 | 18篇 |
2019年 | 10篇 |
2018年 | 6篇 |
2017年 | 16篇 |
2016年 | 7篇 |
2015年 | 12篇 |
2014年 | 30篇 |
2013年 | 22篇 |
2012年 | 18篇 |
2011年 | 35篇 |
2010年 | 38篇 |
2009年 | 30篇 |
2008年 | 32篇 |
2007年 | 18篇 |
2006年 | 19篇 |
2005年 | 9篇 |
2004年 | 15篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
排序方式: 共有409条查询结果,搜索用时 531 毫秒
391.
Heuristics for the traveling salesman problem (TSP) have made remarkable advances in recent years. We survey the leading methods and the special components responsible for their successful implementations, together with an experimental analysis of computational tests on a challenging and diverse set of symmetric and asymmetric TSP benchmark problems. The foremost algorithms are represented by two families, deriving from the Lin-Kernighan (LK) method and the stem-and-cycle (S&C) method. We show how these families can be conveniently viewed within a common ejection chain framework which sheds light on their similarities and differences, and gives clues about the nature of potential enhancements to today’s best methods that may provide additional gains in solving large and difficult TSPs. 相似文献
392.
From a biological point of view, we consider a prey-predator-type free diffusion fishery model with stage-structure and harvesting. First, we study the stability of the nonnegative constant equilibria. In particular, the effect of harvesting on the stability of equilibria is discussed and supported with numerical simulation. Then, employing the upper and lower solution method, we show that when the wave speed is large enough there exists a traveling wavefront connecting the zero solution to the positive equilibrium of the system. Numerical simulation is also carried out to illustrate the main result. 相似文献
393.
The feasible solutions of the traveling salesman problem with pickup and delivery (TSPPD) are commonly represented by vertex lists. However, when the TSPPD is required to follow a policy that loading and unloading operations must be performed in a last-in-first-out (LIFO) manner, we show that its feasible solutions can be represented by trees. Consequently, we develop a novel variable neighborhood search (VNS) heuristic for the TSPPD with last-in-first-out loading (TSPPDL) involving several search operators based on the tree data structure. Extensive experiments suggest that our VNS heuristic is superior to the current best heuristics for the TSPPDL in terms of solution quality, while requiring no more computing time as the size of the problem increases. 相似文献
394.
This paper is devoted to the study of a three-dimensional delayed system with nonlocal diffusion and partial quasi-monotonicity.
By developing a new definition of upper-lower solutions and a new cross iteration scheme, we establish some existence results
of traveling wave solutions. The results are applied to a nonlocal diffusion model which takes the three-species Lotka-Volterra
model as its special case. 相似文献
395.
主要考虑下面的交通模型的行波解的渐近稳定性.{vt-ux=0 (E)ut+p(v)x=1/ε(f(v)-u+μuxx 其中初始值为 (v,u)(x,0)=(v0(x),u0(x))→(v±,u±),v±>0,as x→±∞.(Ⅰ)在允许流函数f不是凹函数以及初始值在无穷远处的极限不满足平衡方程的条件下,我们得到了稳定性... 相似文献
396.
Bongsuk Kwon 《Journal of Differential Equations》2011,251(8):2226-2261
We investigate stability of multidimensional planar shock profiles of a general hyperbolic relaxation system whose equilibrium model is a system, under the necessary assumption of spectral stability and a standard set of structural conditions that are known to hold for many physical systems. Our main result, generalizing the work of Kwon and Zumbrun in the scalar relaxation case, is to establish the bounds on the Green?s function for the linearized equation and obtain nonlinear L2 asymptotic behavior/sharp decay rate of perturbed weak shock profiles. To establish Green?s function bounds, we use the semigroup approach in the low-frequency regime, and use the energy method for the high-frequency bounds, separately. For the system equilibrium case, the analysis of the linearized equation is complicated due to glancing phenomena. We treat this difficulty similarly as in the inviscid and viscous systems, under the constant multiplicity condition. 相似文献
397.
Xiao Zhang 《Journal of Mathematical Analysis and Applications》2011,373(2):475-484
In this paper, a diffusive predator-prey model with nonlocal delay and stage structure is investigated. By using the cross iteration method and Schauder's fixed point theorem, we reduce the existence of traveling wave solutions to the existence of a pair of upper-lower solutions. Numerical simulations are carried out to illustrate the theoretical results. 相似文献
398.
《Current Applied Physics》2014,14(8):998-1004
In this paper, a study of a stripline dipole antenna on a substrate lens used as a photoconductive detector in a terahertz system is presented. The traveling-wave behavior of the stripline dipole and the influence of the substrate lens are investigated over a broad frequency range up to 5.0 THz. The numerical results show that the lens shape represented by the ratio of the extension length to the lens radius plays an important role in maximizing the antenna gain and radiation spectral bandwidth. The gain response exhibited an increased level of sensitivity to the lens shape as the lens size increased, and this is particularly important in optimizing large substrate lenses. Improvements in the gain level over the entire frequency range of interest were observed as the lens diameter increased. This study provides helpful guidelines in choosing and optimizing a substrate lens designed for a terahertz photoconductive antenna, which is particularly useful for specific applications requiring a miniaturized photoconductive antenna design. 相似文献
399.
400.