全文获取类型
收费全文 | 14384篇 |
免费 | 1077篇 |
国内免费 | 1061篇 |
专业分类
化学 | 1373篇 |
晶体学 | 20篇 |
力学 | 784篇 |
综合类 | 136篇 |
数学 | 3521篇 |
物理学 | 3178篇 |
综合类 | 7510篇 |
出版年
2024年 | 30篇 |
2023年 | 99篇 |
2022年 | 210篇 |
2021年 | 174篇 |
2020年 | 281篇 |
2019年 | 296篇 |
2018年 | 272篇 |
2017年 | 409篇 |
2016年 | 419篇 |
2015年 | 452篇 |
2014年 | 777篇 |
2013年 | 823篇 |
2012年 | 753篇 |
2011年 | 879篇 |
2010年 | 640篇 |
2009年 | 903篇 |
2008年 | 992篇 |
2007年 | 1185篇 |
2006年 | 1040篇 |
2005年 | 848篇 |
2004年 | 778篇 |
2003年 | 623篇 |
2002年 | 556篇 |
2001年 | 459篇 |
2000年 | 443篇 |
1999年 | 372篇 |
1998年 | 304篇 |
1997年 | 310篇 |
1996年 | 230篇 |
1995年 | 179篇 |
1994年 | 153篇 |
1993年 | 115篇 |
1992年 | 86篇 |
1991年 | 78篇 |
1990年 | 70篇 |
1989年 | 68篇 |
1988年 | 77篇 |
1987年 | 47篇 |
1986年 | 15篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 13篇 |
1980年 | 4篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1957年 | 3篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Durand William A.Pham Ngoc Dinh 《Journal of Mathematical Analysis and Applications》2003,282(1):95-106
An electromagnetic diffraction problem in a wedge shaped region is reduced to a system of coupled functional difference equations by means of Sommerfeld integrals and Malyuzhinets theorem. By introducing an integral operator it is shown that the solutions of this system of functional equations can be defined in terms of integral representations whose kernels are solutions of a singular integral equation of Cauchy-Carleman type for which an explicit solution is given. 相似文献
72.
Jonatan Lenells 《Journal of Mathematical Analysis and Applications》2007,325(2):1468-1478
We use the inverse scattering transform to show that a solution of the Camassa-Holm equation is identically zero whenever it vanishes on two horizontal half-lines in the x-t space. In particular, a solution that has compact support at two different times vanishes everywhere, proving that the Camassa-Holm equation has infinite propagation speed. 相似文献
73.
74.
By introducing an imaginary space transform curvature ρs, a complex space called Riemannian space is constructed, in which the light propagating in free space has the trajectory
of straight line while propagating. Moreover, this curvature couples with that of the wave front of the paraxial beam ρw, and therefore a complex curvature ρc is constructed, which can be employed to investigate the behavior of the light transmission and to generalize the ABCD law.
Project supported by the National Hi-Tech Inertial Confinement Fusion Committee, the Guangdong Natural Science Foundation
the Postdoctoral Foundation of Guangdong and National Postdoctoral Foundation of China. 相似文献
75.
G. Mastroianni 《Numerical Algorithms》1995,10(1):113-126
The author gives some upper and lower bounds for the generalized Christoffel functions related to a Ditzian-Totik generalized weight. As an application, an error estimate of Gauss quadrature formula inL
1-weighted norm is derived.Dedicated to Prof. Luigi Gatteschi on the occasion of his 70th birthdayWork sponsored by MURST 40%. 相似文献
76.
P. W. Hemker 《Advances in Computational Mathematics》1995,4(1):83-110
We introduce a multigrid algorithm for the solution of a second order elliptic equation in three dimensions. For the approximation of the solution we use a partially ordered hierarchy of finite-volume discretisations. We show that there is a relation with semicoarsening and approximation by more-dimensional Haar wavelets. By taking a proper subset of all possible meshes in the hierarchy, a sparse grid finite-volume discretisation can be constructed.The multigrid algorithm consists of a simple damped point-Jacobi relaxation as the smoothing procedure, while the coarse grid correction is made by interpolation from several coarser grid levels.The combination of sparse grids and multigrid with semi-coarsening leads to a relatively small number of degrees of freedom,N, to obtain an accurate approximation, together with anO(N) method for the solution. The algorithm is symmetric with respect to the three coordinate directions and it is fit for combination with adaptive techniques.To analyse the convergence of the multigrid algorithm we develop the necessary Fourier analysis tools. All techniques, designed for 3D-problems, can also be applied for the 2D case, and — for simplicity — we apply the tools to study the convergence behaviour for the anisotropic Poisson equation for this 2D case. 相似文献
77.
THENBELCANDNWELCCLASSESOFLIFEDISTRIBUTIONS¥CAOJINHUA;WANGYUEDONG(InstituteofAppliedMathematics,ChineseAcademyofScience,Beijin... 相似文献
78.
A new method for rotation and brightness invariant pattern recognition was proposed by applying multiple circular harmonic expansions to the joint transform correlator. The amplitudes of the multiple orders of circular harmonic expansions made from a detecting image were synthetically modified to respond to the same auto-correlation peaks. These modified circular harmonic expansions were arranged in the input plane as reference patterns together with an arbitrary target pattern, and the correlation signals between them were calculated in the subtracted joint transform correlator. The fraction of the correlation-peak intensities between the target and the references were extracted as a new discrimination parameter. This new parameter performs pattern recognition under rotation and brightness invariance with good discriminability. Its high discriminability has been proved in computer simulations using the face image patterns of many individuals. 相似文献
79.
熊国华 《北京大学学报(自然科学版)》2002,38(3):315-317
利用环上的特殊非线性函数,提出构造参数为(4q\+2,q(2q-1),q(q-1))的Hadamard差集的新途径. 相似文献
80.
Lina Hemmingsson 《Numerical Algorithms》1994,7(2):375-389
In this report we consider block-tridiagonal systems with Toeplitz blocks. Each block is of sizen×n consisting ofn
c×n
c matrices as entries, and there arem×m blocks in the system. The solution of those systems consists of 2n
c
m modified sine transforms and an intermediate solution ofn block-tridiagonal systems. Symmetries in the data vectors are exploited such that one modified sine transform can be computed in terms of one Fourier transform of half the length of the original one, hence requiringO(2.5nlog2
n) operations. Similarly, we only have to solve (n+1)/2 of the intermediate systems due to symmetry.This work was supported by the Swedish National Board for Industrial and Technical Development, NUTEK, under contract No. 89-02539 P. 相似文献