全文获取类型
收费全文 | 7836篇 |
免费 | 1073篇 |
国内免费 | 274篇 |
专业分类
化学 | 458篇 |
晶体学 | 77篇 |
力学 | 2997篇 |
综合类 | 112篇 |
数学 | 2449篇 |
物理学 | 3090篇 |
出版年
2024年 | 11篇 |
2023年 | 62篇 |
2022年 | 133篇 |
2021年 | 190篇 |
2020年 | 209篇 |
2019年 | 165篇 |
2018年 | 162篇 |
2017年 | 228篇 |
2016年 | 235篇 |
2015年 | 201篇 |
2014年 | 308篇 |
2013年 | 508篇 |
2012年 | 402篇 |
2011年 | 479篇 |
2010年 | 351篇 |
2009年 | 437篇 |
2008年 | 473篇 |
2007年 | 528篇 |
2006年 | 519篇 |
2005年 | 443篇 |
2004年 | 364篇 |
2003年 | 361篇 |
2002年 | 332篇 |
2001年 | 311篇 |
2000年 | 266篇 |
1999年 | 225篇 |
1998年 | 206篇 |
1997年 | 164篇 |
1996年 | 143篇 |
1995年 | 125篇 |
1994年 | 100篇 |
1993年 | 85篇 |
1992年 | 78篇 |
1991年 | 52篇 |
1990年 | 55篇 |
1989年 | 23篇 |
1988年 | 20篇 |
1987年 | 32篇 |
1986年 | 30篇 |
1985年 | 27篇 |
1984年 | 23篇 |
1983年 | 10篇 |
1982年 | 20篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 15篇 |
1973年 | 5篇 |
排序方式: 共有9183条查询结果,搜索用时 125 毫秒
991.
Abstract Seabirds breeding on islands are vulnerable to introduced predators, such as rats and cats, and the removal of such predators is generally viewed as a priority for seabird conservation and restoration. However, multiple invasive mammal species interacting may generate unexpected outcomes following the removal (eradication) of one species. Generally these indirect interactions are not well understood or demonstrated. We propose and study a prey (seabird)‐mesopredator (rat)‐superpredator (cat) model, taking into account the juvenile stages in the prey population, in order to direct conservation management for seabird conservation. We give a more biologically realistic differential system than those studied before (Courchamp et al. [1999] ; Fan et al. [2005] ), in particular for long‐lived seabird species. We present a theoretical study and show existence and uniqueness of a positive solution as well as a qualitative study of the equilibria that may appear. Because standard numerical methods, usually implemented in scientific softwares, can fail to give the right biological approximations ( Anguelov et al. [2009] ), we propose a reliable algorithm that preserves most of the qualitative properties of the continuous system, using the theory of nonstandard finite difference methods. Finally, we use biologically realistic parameters available for the representative Barau's petrel (Pinet et al. [2008] ), an endemic species from Réunion island, to present numerical simulations that support the theoretical study. Cats play the major role in seabird prey population dynamics. Seasonality in seabird breeding delays but does not prevent extinction. In all scenarios, cat control (or preferably eradication) is imperative to prevent extinction of vulnerable long‐lived seabirds, like the Barau's petrel. 相似文献
992.
Hossein Aminikhah 《Numerical Methods for Partial Differential Equations》2010,26(6):1291-1299
In this article, an analytic approximation to the solution of Blasius equation is obtained by using a new modification of homotopy perturbation method. The Blasius equation is a nonlinear ordinary differential equation which arises in the boundary layer flow. The comparison with Howart's numerical solution shows that the new homotopy perturbation method is an effective mathematical method with high accuracy. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2010 相似文献
993.
结合某市的艾滋病现状给出了相应的传染病动力学模型,研究了其平衡点的稳定性,讨论了流行病的阈值,并对不同的说服率、不同的因病死亡率、不同的传染率分别进行了数值模拟,对该市艾滋病的预防和控制给出了理论上的指导和建议. 相似文献
994.
995.
996.
997.
实例说明用第一类换元积分法或分部积分法求解几个典型不定积分,其被积函数含有根式a2-x2或x2±a2. 相似文献
998.
Francisco Rus 《Applied mathematics and computation》2010,217(6):2788-2797
Four numerical methods with first- to fourth-order of accuracy have been developed for the time integration of the Rosenau-Hyman K(2, 2) equation. The error in the solution and the invariants for the propagation of one-compacton, and the stability in collisions among compactons have been studied using these methods. Numerically-induced radiation has also been characterized by means of wavefront velocity and wavefront amplitude, showing that the self-similarity of the radiation wavepackets observed in the numerical results is a consequence of the time-stepping method. Among the four methods studied in this paper, the best results in terms of accuracy, computational cost, and stability have been obtained by means of using the second-order time integration method. 相似文献
999.
S. V. Ludkovsky 《Mathematical Methods in the Applied Sciences》2010,33(9):1148-1173
The article is devoted to Gaussian quasi‐measures and Feynman integrals on infinite‐dimensional spaces with values in the octonion algebra. Their characteristic functionals are studied. Products and convolutions of characteristic functionals and quasi‐measures are investigated. Theorems about properties of octonion‐valued Gaussian quasi‐measures and Feynman integrals are proved. Applications of the Feynman integration over octonions to quantum mechanics and partial differential equations are outlined. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
1000.