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   428篇
  国内免费   56篇
  完全免费   15篇
  数学   499篇
  2018年   11篇
  2017年   3篇
  2016年   5篇
  2015年   2篇
  2014年   16篇
  2013年   7篇
  2012年   16篇
  2011年   29篇
  2010年   20篇
  2009年   42篇
  2008年   40篇
  2007年   38篇
  2006年   38篇
  2005年   30篇
  2004年   29篇
  2003年   23篇
  2002年   29篇
  2001年   15篇
  2000年   16篇
  1999年   16篇
  1998年   22篇
  1997年   15篇
  1996年   9篇
  1995年   7篇
  1994年   7篇
  1993年   4篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1989年   2篇
  1987年   1篇
  1985年   1篇
  1977年   1篇
  1972年   1篇
  1971年   1篇
排序方式: 共有499条查询结果,搜索用时 46 毫秒
1.
卷积算子的交换子   总被引:10,自引:0,他引:10       下载免费PDF全文
利用Fourier变换估计和对算子的局部性质做精细的分析,建立与一类卷积算子交换子相关的一些算子的LP有界性结果.作为这些结果的应用,得到了与球平均算子交换子相关的离散极大算子以及一类低维集上奇异积分算子交换子等的LP有界性.  相似文献
2.
单位阶跃函数在广义Fourier变换中的屏蔽效应   总被引:9,自引:0,他引:9  
付立志 《大学数学》2007,23(3):149-151
对u(t)在广义傅氏变换的作用进行了探讨,并给出了半屏、翻掩、隐匿、零点对应和对称等相关定理.  相似文献
3.
分块K—循环Toeplitz矩阵求逆的快速付氏变换法   总被引:8,自引:1,他引:7  
1算法描述及推导 Toeplitz矩阵及Toeplitz系统的求解在谱分析、线性预测、误差控制码、自回归滤波器设计等领域内起着重要的作用~[1-3],而分块Toeplitz矩阵在计算机的时序分析、自回归时序模型滤波中也经常出现~[4]。对一般Toeplitz矩阵求逆,其算术复杂性为O(n~2)~[5]-[6],其中n为Toepleitz矩阵的阶,而K-循环Toeplitz矩阵的求逆,其算术复杂性可降为O(nlog_2n),本文提供了mn附分块K-循环Toeplitz矩阵求逆的一种快速付氏变换算法,其算术复杂性为O(mnlog_2mn).  相似文献
4.
This paper reviews the Fourier-series method for calculating cumulative distribution functions (cdf's) and probability mass functions (pmf's) by numerically inverting characteristic functions, Laplace transforms and generating functions. Some variants of the Fourier-series method are remarkably easy to use, requiring programs of less than fifty lines. The Fourier-series method can be interpreted as numerically integrating a standard inversion integral by means of the trapezoidal rule. The same formula is obtained by using the Fourier series of an associated periodic function constructed by aliasing; this explains the name of the method. This Fourier analysis applies to the inversion problem because the Fourier coefficients are just values of the transform. The mathematical centerpiece of the Fourier-series method is the Poisson summation formula, which identifies the discretization error associated with the trapezoidal rule and thus helps bound it. The greatest difficulty is approximately calculating the infinite series obtained from the inversion integral. Within this framework, lattice cdf's can be calculated from generating functions by finite sums without truncation. For other cdf's, an appropriate truncation of the infinite series can be determined from the transform based on estimates or bounds. For Laplace transforms, the numerical integration can be made to produce a nearly alternating series, so that the convergence can be accelerated by techniques such as Euler summation. Alternatively, the cdf can be perturbed slightly by convolution smoothing or windowing to produce a truncation error bound independent of the original cdf. Although error bounds can be determined, an effective approach is to use two different methods without elaborate error analysis. For this purpose, we also describe two methods for inverting Laplace transforms based on the Post-Widder inversion formula. The overall procedure is illustrated by several queueing examples.  相似文献
5.
横观各向同性饱和地基的三维动力响应   总被引:5,自引:1,他引:4  
王小岗  黄义 《应用数学和力学》2005,26(11):1278-1286
首先引入位移函数,将直角坐标系下横观各向同性饱和土Biot波动方程转化为2个解耦的六阶和二阶控制方程;然后基于双重Fourier变换,求解了Biot波动方程,得到以土骨架位移和孔隙水压力为基本未知量的积分形式的一般解,并用一般解给出了饱和土总应力分量的表达式.在此基础上系统研究了横观各向同性饱和半空间体的稳态动力响应问题,考虑表面排水和不排水两种情况,得到了半空间体在任意分布的表面谐振荷载作用下,表面位移的稳态动力响应,文末给出了算例.  相似文献
6.
关于粗糙奇异积分算子的一点注记   总被引:5,自引:0,他引:5  
马丽  王卫红 《数学研究》2008,41(3):287-294
研究R^n上一类沿多项式曲线的奇异积分算子,在一些相当弱的尺寸条件下建立了这些算子的L^p有界性.  相似文献
7.
The linear complexity of sequences is one of the important security measures for stream cipher systems. Recently, in the study of vectorized stream cipher systems, the joint linear complexity of multisequences has been investigated. By using the generalized discrete Fourier transform for multisequences, Meidl and Niederreiter determined the expectation of the joint linear complexity of random N-periodic multisequences explicitly. In this paper, we study the expectation and variance of the joint linear complexity of random periodic multisequences. Several new lower bounds on the expectation of the joint linear complexity of random periodic multisequences are given. These new lower bounds improve on the previously known lower bounds on the expectation of the joint linear complexity of random periodic multisequences. By further developing the method of Meidl and Niederreiter, we derive a general formula and a general upper bound for the variance of the joint linear complexity of random N-periodic multisequences. These results generalize the formula and upper bound of Dai and Yang for the variance of the linear complexity of random periodic sequences. Moreover, we determine the variance of the joint linear complexity of random periodic multisequences with certain periods.  相似文献
8.
Generalized Fourier transform on an arbitrary triangular domain   总被引:4,自引:0,他引:4  
In this paper, we construct generalized Fourier transform on an arbitrary triangular domain via barycentric coordinates and PDE approach. We start with a second-order elliptic differential operator for an arbitrary triangle which has the so-called generalized sine (TSin) and generalized cosine (TCos) systems as eigenfunctions. The orthogonality and completeness of the systems are then proved. Some essential convergence properties of the generalized Fourier series are discussed. Error estimates are obtained in Sobolev norms. Especially, the generalized Fourier transforms for some elementary polynomials and their convergence are investigated. This work was supported by the Major Basic Project of China (No. G19990328) and National Natural Science Foundation of China (No. 60173021).  相似文献
9.
Generalized intersection bodies   总被引:4,自引:0,他引:4  
We study the structures of two types of generalizations of intersection-bodies and the problem of whether they are in fact equivalent. Intersection-bodies were introduced by Lutwak and played a key role in the solution of the Busemann–Petty problem. A natural geometric generalization of this problem considered by Zhang, led him to introduce one type of generalized intersection-bodies. A second type was introduced by Koldobsky, who studied a different analytic generalization of this problem. Koldobsky also studied the connection between these two types of bodies, and noted that an equivalence between these two notions would completely settle the unresolved cases in the generalized Busemann–Petty problem. We show that these classes share many identical structural properties, proving the same results using integral geometry techniques for Zhang's class and Fourier transform techniques for Koldobsky's class. Using a functional analytic approach, we give several surprising equivalent formulations for the equivalence problem, which reveal a deep connection to several fundamental problems in the integral geometry of the Grassmann manifold.  相似文献
10.
横观各向同性弹性层点力解   总被引:3,自引:0,他引:3  
本文根据弹性层状结构的传递矩阵法思想,由横观各向同性弹性力学基本方程,导出了含应力和位移两类变量的混合方程,利用Fourier变换和文献[7]的位移函数通解,以及计算机代数软件,得到了横观各向同性层的点力解,这个点力解可直接退化到各同性情形的解.  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