首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   615篇
  免费   75篇
  国内免费   36篇
化学   55篇
晶体学   2篇
力学   110篇
综合类   4篇
数学   237篇
物理学   318篇
  2024年   3篇
  2023年   5篇
  2022年   5篇
  2021年   6篇
  2020年   13篇
  2019年   12篇
  2018年   17篇
  2017年   29篇
  2016年   15篇
  2015年   20篇
  2014年   24篇
  2013年   63篇
  2012年   33篇
  2011年   25篇
  2010年   35篇
  2009年   28篇
  2008年   25篇
  2007年   36篇
  2006年   34篇
  2005年   35篇
  2004年   23篇
  2003年   35篇
  2002年   19篇
  2001年   20篇
  2000年   13篇
  1999年   16篇
  1998年   17篇
  1997年   20篇
  1996年   11篇
  1995年   13篇
  1994年   7篇
  1993年   5篇
  1992年   3篇
  1991年   8篇
  1990年   6篇
  1989年   6篇
  1988年   4篇
  1987年   7篇
  1986年   4篇
  1985年   9篇
  1984年   2篇
  1983年   1篇
  1982年   2篇
  1981年   5篇
  1979年   2篇
  1978年   2篇
  1976年   1篇
  1975年   1篇
  1936年   1篇
排序方式: 共有726条查询结果,搜索用时 15 毫秒
631.
Abstract

As our reliance on computer networks grows, it becomes increasingly important that we understand the behavior of the traffic that they carry. Because of the speeds and sizes involved, working with traffic collected from a computer network usually means working with large datasets. This article describes our experience with traffic collected from the common channel signaling (CCS) network. I will briefly describe the data and how they are collected and discuss similarities with and differences from other large datasets. Next, I will describe our analysis tools and outline the reasons that they have been found useful. Finally, I will discuss the challenges facing us as we strive for a better understanding of more data from faster networks. Although my emphasis in this article is on the CCS network, it has been my experience that both the problems and the solutions generalize to data from other networks.  相似文献   
632.
We study the two-dimensional eikonal equation ψ x 2 + ψ y 2 = 1/v 2(x, y). We carry out the group analysis of the equation, establish a connection between the group properties and geometric characteristics of the Riemannian space with the metric ds 2 = [dx 2 + dy 2]/v 2(x, y). We select the most important classes of equations and derive some conditions for reducibility of a given equation to an equation of one of those classes. We find a condition for two equations to be equivalent (the theorem of seven invariants). For the equations corresponding to Riemannian spaces of constant curvature, we obtain explicit formulas for the solutions describing the wave front for a point source and also the ray equations.  相似文献   
633.
We investigate the coupled inhomogeneous nonlinear Schrodinger equation by the covariant prolongation structure theory, and obtain its Lax's representation. Moreover, we present the corresponding Riccati equations, Backlund transformation, and one-soliton solution.  相似文献   
634.
The Löwdin natural orbitals (NO) are defined as those orbitals which bring the first-order density matrix of a correlated electron assembly into diagonal form. Another one-particle density matrix with the same diagonal elements is the single-particle idempotent Dirac density matrix generated by the one-body potential of density functional theory. Here, we compare the off diagonal form of γ expanded in terms of the Slater–Kohn–Sham (SKS) orbitals generated by V(r) with the NO expansion of Löwdin for general inhomogeneous electron liquids. In particular, the equation of motion of the correlated γ is corrected from that of γ s , both now containing the one-body potential V(r). To illustrate the theory presented here, we first construct an approximate, albeit accurate, correlated 1DM for the ground state of the He atom and display connections between the resulting NOs and the SKS orbitals. The second example we discuss, but now quite briefly, is that of the inhomogeneous electron liquid in crystalline Si, where the NO expansion is available from the literature.  相似文献   
635.
636.
设Z_n为非对角元素都为非正实数的n阶方阵的集合,令A_k∈Z_n,k∈{1,…,m},给出矩阵Fan积最小特征值的一个新下界,其中p_k>0且and (sum from k=1 to m)1/p_k≥1,这个下界改进了文献中的相关结果.  相似文献   
637.
We develop a kinetic theory of systems with long-range interactions taking collective effects and spatial inhomogeneity into account. Starting from the Klimontovich equation and using a quasilinear approximation, we derive a Lenard–Balescu-type kinetic equation written in angle–action variables. We confirm the result obtained by Heyvaerts [Heyvaerts, Mon. Not. R. Astron. Soc. 407, 355 (2010)] who started from the Liouville equation and used the BBGKY hierarchy truncated at the level of the two-body distribution function (i.e., neglecting three-body correlations). When collective effects are ignored, we recover the Landau-type kinetic equation obtained in our previous papers [P.H. Chavanis, Physica A 377, 469 (2007); J. Stat. Mech., P05019 (2010)]. We also consider the relaxation of a test particle in a bath of field particles. Its stochastic motion is described by a Fokker–Planck equation written in angle–action variables. We determine the diffusion tensor and the friction force by explicitly calculating the first and second order moments of the increment of action of the test particle from its equations of motion, taking collective effects into account. This generalizes the expressions obtained in our previous works. We discuss the scaling with NN of the relaxation time for the system as a whole and for a test particle in a bath.  相似文献   
638.
We propose a new integral equation formulation to characterize and compute transmission eigenvalues in electromagnetic scattering. As opposed to the approach that was recently developed by Cakoni, Haddar and Meng (2015) which relies on a two‐by‐two system of boundary integral equations, our analysis is based on only one integral equation in terms of the electric‐to‐magnetic boundary trace operator that results in a simplification of the theory and in a considerable reduction of computational costs. We establish Fredholm properties of the integral operators and their analytic dependence on the wave number. Further, we use the numerical algorithm for analytic nonlinear eigenvalue problems that was recently proposed by Beyn (2012) for the numerical computation of the transmission eigenvalues via this new integral equation.  相似文献   
639.
In this paper we study time inhomogeneous versions of one-dimensional Stochastic Differential Equations (SDE) involving the Local Time of the unknown process on curves. After proving existence and uniqueness for these SDEs under mild assumptions, we explore their link with Parabolic Differential Equations (PDE) with transmission conditions. We study the regularity of solutions of such PDEs and ensure the validity of a Feynman–Kac representation formula. These results are then used to characterize the solutions of these SDEs as time inhomogeneous Markov Feller processes.  相似文献   
640.
The amplitudes and the excitation profiles of coherent resonant Raman scattering (coherent anti‐Stokes and Stokes Raman scattering (CARS and CSRS)) by impurity centers in crystals and/or molecules in solutions are studied, taking into account the coherence of the excited mode and the inhomogeneity of the environment. The CARS and CSRS excitation profiles can directly be related to one‐photon absorption when using the transform theory known from spontaneous resonant Raman scattering. The enlargement of the amplitude of the active mode reveals itself in an enhancement of the vibrational overtones. At large amplitudes, a splitting in the profiles caused by the contribution of two turning points of a strong coherent vibration is observed. The inhomogeneous broadening is different in the excitation profiles of CARS and CSRS. The overlapping contributions to spectrally narrow and broad transitions lead to Fano peculiarities. The effects are illustrated by model calculations. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号