全文获取类型
收费全文 | 37410篇 |
免费 | 4688篇 |
国内免费 | 4070篇 |
专业分类
化学 | 12846篇 |
晶体学 | 84篇 |
力学 | 2902篇 |
综合类 | 347篇 |
数学 | 22109篇 |
物理学 | 7880篇 |
出版年
2024年 | 98篇 |
2023年 | 449篇 |
2022年 | 567篇 |
2021年 | 858篇 |
2020年 | 1254篇 |
2019年 | 1286篇 |
2018年 | 1107篇 |
2017年 | 1174篇 |
2016年 | 1549篇 |
2015年 | 1406篇 |
2014年 | 2017篇 |
2013年 | 3739篇 |
2012年 | 2049篇 |
2011年 | 2384篇 |
2010年 | 2043篇 |
2009年 | 2592篇 |
2008年 | 2547篇 |
2007年 | 2614篇 |
2006年 | 2325篇 |
2005年 | 1839篇 |
2004年 | 1590篇 |
2003年 | 1550篇 |
2002年 | 1314篇 |
2001年 | 1075篇 |
2000年 | 1061篇 |
1999年 | 929篇 |
1998年 | 784篇 |
1997年 | 721篇 |
1996年 | 503篇 |
1995年 | 348篇 |
1994年 | 322篇 |
1993年 | 228篇 |
1992年 | 223篇 |
1991年 | 161篇 |
1990年 | 146篇 |
1989年 | 112篇 |
1988年 | 103篇 |
1987年 | 81篇 |
1986年 | 73篇 |
1985年 | 120篇 |
1984年 | 137篇 |
1983年 | 71篇 |
1982年 | 108篇 |
1981年 | 97篇 |
1980年 | 92篇 |
1979年 | 78篇 |
1978年 | 72篇 |
1977年 | 49篇 |
1976年 | 50篇 |
1975年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
本文给出Riccati方程及另外一类具有代表性微分方程的亚纯解(n,1)级的上界估计,在一定条件下确立了文[2]中的猜测的正确性。 相似文献
82.
The paper proposes a rational method to derive fairness measures for surfaces. It works in cases where isophotes, reflection lines, planar intersection curves, or other curves are used to judge the fairness of the surface. The surface fairness measure is derived by demanding that all the given curves should be fair with respect to an appropriate curve fairness measure. The method is applied to the field of ship hull design where the curves are plane intersections. The method is extended to the case where one considers, not the fairness of one curve, but the fairness of a one parameter family of curves. Six basic third order invariants by which the fairing measures can be expressed are defined. Furthermore, the geometry of a plane intersection curve is studied, and the variation of the total, the normal, and the geodesic curvature and the geodesic torsion is determined. 相似文献
83.
84.
LIU Hong-Zhun PAN Zu-Liang LI Peng 《理论物理通讯》2006,46(10)
In this article, we will derive an equality, where the Taylor series expansion around ε = 0for any asymptotical analytical solution of the perturbed partial differential equation (PDE) with perturbing parameter ε must be admitted.By making use of the equality, we may obtain a transformation, which directly map the analytical solutions of a given unperturbed PDE to the asymptotical analytical solutions of the corresponding perturbed one. The notion of Lie-B(a)cklund symmetries is introduced in order to obtain more transformations. Hence, we can directly create more transformations in virtue of known Lie-B(a)cklund symmetries and recursion operators of corresponding unperturbed equation. The perturbed Burgers equation and the perturbed Korteweg-de Vries (KdV) equation are used as examples. 相似文献
85.
Johan Helsing 《BIT Numerical Mathematics》2006,46(2):307-323
A sparse mesh-neighbour based approximate inverse preconditioner is proposed for a type of dense matrices whose entries come
from the evaluation of a slowly decaying free space Green’s function at randomly placed points in a unit cell. By approximating
distant potential fields originating at closely spaced sources in a certain way, the preconditioner is given properties similar
to, or better than, those of a standard least squares approximate inverse preconditioner while its setup cost is only that
of a diagonal block approximate inverse preconditioner. Numerical experiments on iterative solutions of linear systems with
up to four million unknowns illustrate how the new preconditioner drastically outperforms standard approximate inverse preconditioners
of otherwise similar construction, and especially so when the preconditioners are very sparse.
AMS subject classification (2000) 65F10, 65R20, 65F35, 78A30 相似文献
86.
87.
Mehdi Dehghan 《Numerical Methods for Partial Differential Equations》2002,18(2):193-202
Developement of numerical methods for obtaining approximate solutions to the three dimensional diffusion equation with an integral condition will be carried out. The numerical techniques discussed are based on the fully explicit (1,7) finite difference technique and the fully implicit (7,1) finite difference method and the (7,7) Crank‐Nicolson type finite difference formula. The new developed methods are tested on a problem. Truncation error analysis and numerical examples are used to illustrate the accuracy of the new algorithms. The results of numerical testing show that the numerical methods based on the finite difference techniques discussed in the present article produce good results. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 18: 193–202, 2002; DOI 10.1002/num.1040 相似文献
88.
本文主要解决奇异非光滑方程组的解法。应用一种新的次微分的外逆,我们提出了牛顿法和不精确牛顿法,它们的收敛性同时也得到了证明。这种方法能更容易在一引起实际应用中实现。这种方法可以看作是已存在的解非光滑方程组的方法的延伸。 相似文献
89.
90.
We investigate an operator renormalization group method to extract and describe the relevant degrees of freedom in the evolution of partial differential equations. The proposed renormalization group approach is formulated as an analytical method providing the fundamental concepts of a numerical algorithm applicable to various dynamical systems. We examine dynamical scaling characteristics in the short-time and the long-time evolution regime providing only a reduced number of degrees of freedom to the evolution process. 相似文献