全文获取类型
收费全文 | 1842篇 |
免费 | 46篇 |
国内免费 | 80篇 |
专业分类
化学 | 143篇 |
晶体学 | 1篇 |
力学 | 295篇 |
综合类 | 10篇 |
数学 | 1141篇 |
物理学 | 378篇 |
出版年
2024年 | 3篇 |
2023年 | 39篇 |
2022年 | 31篇 |
2021年 | 20篇 |
2020年 | 53篇 |
2019年 | 51篇 |
2018年 | 40篇 |
2017年 | 53篇 |
2016年 | 39篇 |
2015年 | 44篇 |
2014年 | 126篇 |
2013年 | 179篇 |
2012年 | 73篇 |
2011年 | 133篇 |
2010年 | 126篇 |
2009年 | 148篇 |
2008年 | 136篇 |
2007年 | 160篇 |
2006年 | 92篇 |
2005年 | 59篇 |
2004年 | 65篇 |
2003年 | 40篇 |
2002年 | 37篇 |
2001年 | 33篇 |
2000年 | 21篇 |
1999年 | 21篇 |
1998年 | 26篇 |
1997年 | 17篇 |
1996年 | 16篇 |
1995年 | 12篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1968条查询结果,搜索用时 31 毫秒
101.
We present here a systematic study of general boundary value problems on weighted networks that includes the variational formulation of such problems. In particular, we obtain the discrete version of the Dirichlet Principle and we apply it to the analysis of the inverse problem of identifying the conductivities of the network in a very general framework. Our approach is based on the development of an efficient vector calculus on weighted networks which mimetizes the calculus in the smooth case. The key tool is an adequate construction of the tangent space at each vertex. This allows us to consider discrete vector fields, inner products and general metrics. Then, we obtain discrete versions of derivative, gradient, divergence and Laplace-Beltrami operators, satisfying analogous properties to those verified by their continuous counterparts. On the other hand we develop the corresponding integral calculus that includes the discrete versions of the Integration by Parts technique and Green’s Identities. Finally, we apply our discrete vector calculus to analyze the consistency of difference schemes used to solve numerically a Robin boundary value problem in a square. 相似文献
102.
A four-node discrete singular convolution (DSC) method is developed for free vibration analysis of arbitrary straight-sided quadrilateral plates. The straight-sided quadrilateral domain is mapped into a square domain in the computational space using a four-node element. By using the geometric transformation, the governing equations and boundary conditions of the plate are transformed from the physical domain into a square computational domain. Numerical examples illustrating the accuracy and convergence of the DSC method for skew, trapezoidal, rhombic and arbitrary quadrilateral plates are presented. The results obtained by DSC method were compared with those obtained by the other numerical methods. 相似文献
103.
本文利用马尔可夫骨架过程理论研究PERT网络模型,其中网络各弧线的长度是相互独立的随机变量。文中构造了一个马尔可夫骨架过程,利用其向后方程求解随机网络最长路径长度的分布函数。 相似文献
104.
In a recent paper [P. Bates, A. Chmaj, A discrete convolution model for phase transition, Arch. Rational Mech. Anal. 150 (1999) 281-305], a discrete convolution model for Ising-like phase transition has been derived, and the existence, uniqueness of traveling waves and stability of stationary solution have been studied. This nonlocal model describes l2-gradient flow for a Helmholts free energy functional with general range interaction. In this paper, by using the comparison principle and the squeezing technique, we prove that the traveling wavefronts with nonzero speed is globally asymptotic stable with phase shift. 相似文献
105.
106.
M. Calixto J. Guerrero J. C. Sánchez-Monreal 《Journal of Fourier Analysis and Applications》2008,14(4):538-567
Using coherent-state techniques, we prove a sampling theorem for Majorana’s (holomorphic) functions on the Riemann sphere
and we provide an exact reconstruction formula as a convolution product of N samples and a given reconstruction kernel (a sinc-type function). We also discuss the effect of over- and under-sampling.
Sample points are roots of unity, a fact which allows explicit inversion formulas for resolution and overlapping kernel operators
through the theory of Circulant Matrices and Rectangular Fourier Matrices. The case of band-limited functions on the Riemann
sphere, with spins up to J, is also considered. The connection with the standard Euler angle picture, in terms of spherical harmonics, is established
through a discrete Bargmann transform.
相似文献
107.
This paper deals with a new solution technique for approximately solving certain variational problems in elasticity by using discrete optimization techniques that were originally used in information theory. This allows us to easily and approximately solve large deformation buckling problems for slender cantilever beams (including post-buckling behavior) as well as problems where the strain energy function is non-convex.The core idea is to quantize or discretize the variables describing the possible configurations of the body. This, when combined with the fact that the variational problem has an inherent Markov structure allows us to use computationally efficient search techniques based on dynamic programming (equivalent to finding the shortest path in a weighted directed graph) to find optimal solutions within the quantized state space. The results can be used in two ways: (1) directly as a fast approximate solution to the variational problem (2) As a means for finding very good (nearly minimum energy) initial configurations for application of conventional minimization techniques, which might otherwise fail because of a poor starting configurations which are far from the global minimum. We demonstrate both these uses in the paper. 相似文献
108.
Ulrike Bücking 《Geometriae Dedicata》2008,137(1):163-197
A circle pattern is a configuration of circles in the plane whose combinatorics is given by a planar graph G such that to each vertex of G corresponds a circle. If two vertices are connected by an edge in G, the corresponding circles intersect with an intersection angle in (0, π). Two sequences of circle patterns are employed to approximate a given conformal map g and its first derivative. For the domain of g we use embedded circle patterns where all circles have the same radius decreasing to 0 and with uniformly bounded intersection
angles. The image circle pattern has the same combinatorics and intersection angles and is determined from boundary conditions
(radii or angles) according to the values of g′ (|g′| or arg g′). For quasicrystallic circle patterns the convergence result is strengthened to C
∞-convergence on compact subsets.
相似文献
109.
Mireille Bousquet-Mélou Svante Linusson Eran Nevo 《Journal of Algebraic Combinatorics》2008,27(4):423-450
The enumeration of independent sets of regular graphs is of interest in statistical mechanics, as it corresponds to the solution
of hard-particle models. In 2004, it was conjectured by Fendley et al., that for some rectangular grids, with toric boundary conditions, the alternating number of independent sets is extremely simple. More precisely, under a coprimality condition on the sides of the rectangle,
the number of independent sets of even and odd cardinality always differ by 1. In physics terms, this means looking at the
hard-particle model on these grids at activity −1. This conjecture was recently proved by Jonsson.
Here we produce other families of grid graphs, with open or cylindric boundary conditions, for which similar properties hold
without any size restriction: the number of independent sets of even and odd cardinality always differ by 0, ±1, or, in the
cylindric case, by some power of 2.
We show that these results reflect a stronger property of the independence complexes of our graphs. We determine the homotopy
type of these complexes using Forman’s discrete Morse theory. We find that these complexes are either contractible, or homotopic
to a sphere, or, in the cylindric case, to a wedge of spheres.
Finally, we use our enumerative results to determine the spectra of certain transfer matrices describing the hard-particle
model on our graphs at activity −1. These results parallel certain conjectures of Fendley et al., proved by Jonsson in the toric case. 相似文献
110.
In this paper numerical solutions of mixed hyperbolic problems are computed using a discrete eigenfunctions method combined with an implicit difference scheme. This new numerical technique preserves the qualitative properties of the analytic solution due to the Sturm-Liouville structure of the underlying discrete linear boundary-value problem and has computational stability advantages vs other methods. Illustrative examples are included. 相似文献