全文获取类型
收费全文 | 14389篇 |
免费 | 1070篇 |
国内免费 | 1062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 | 7509篇 |
出版年
2024年 | 30篇 |
2023年 | 98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 0 毫秒
41.
根据W变换和Delta函数的定义,讨论了函数f(x)的线性函数af(x) b的W变换和函数Ⅱi-1^n,(x)的W变换问题,并推广了W变换的线性性质,得到了几个进一步的结果. 相似文献
42.
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
43.
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
44.
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
45.
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
46.
安韶君 《中山大学学报(自然科学版)》2002,41(5):11-14
图视密码学方案最初由Naor和Shamir在 1994年欧洲密码学会议上提出 ,但像素扩展太大 ,生成分存图像太大。采用小波变换对分存图像进行压缩 ,有效地降低了分存图像规模。 相似文献
47.
基于小波变换的运动汽车阴影分割 总被引:3,自引:0,他引:3
利用在阴影区域内的点所接受环境光强与汽车的相对位置关系,结合多分辨率小波分析,提出了一种新的基于小波变换的运动汽车阴影分割方法.该方法不需要知道光源的方向,也不需要车体的彩色信息;对背景的纹理也没有要求,适用于复杂纹理背景下任何颜色的汽车阴影分割.实验表明,该方法定位准确、速度快、抗噪能力强. 相似文献
48.
Bernard Bialecki 《Numerical Algorithms》1994,8(2):167-184
Cyclic reduction and Fourier analysis-cyclic reduction (FACR) methods are presented for the solution of the linear systems which arise when orthogonal spline collocation with piecewise Hermite bicubics is applied to boundary value problems for certain separable partial differential equations on a rectangle. On anN×N uniform partition, the cyclic reduction and Fourier analysis-cyclic reduction methods requireO(N
2log2
N) andO(N
2log2log2
N) arithmetic operations, respectively. 相似文献
49.
50.
对广泛应用的Lagrange方程的动力学本质做了探讨,指出在引入速度变换矩阵后,Lagrange方程实际上是牛顿第二定律的一种表示方式;由于引入了速度变换矩阵,Lagrange方程可以方便地在任意的坐标系中建立,对动力学问题的求解提供了一个途径。 相似文献