全文获取类型
收费全文 | 9165篇 |
免费 | 1012篇 |
国内免费 | 535篇 |
专业分类
化学 | 392篇 |
晶体学 | 3篇 |
力学 | 967篇 |
综合类 | 166篇 |
数学 | 7211篇 |
物理学 | 1973篇 |
出版年
2024年 | 9篇 |
2023年 | 114篇 |
2022年 | 129篇 |
2021年 | 181篇 |
2020年 | 237篇 |
2019年 | 202篇 |
2018年 | 227篇 |
2017年 | 327篇 |
2016年 | 360篇 |
2015年 | 250篇 |
2014年 | 442篇 |
2013年 | 676篇 |
2012年 | 495篇 |
2011年 | 463篇 |
2010年 | 404篇 |
2009年 | 486篇 |
2008年 | 542篇 |
2007年 | 537篇 |
2006年 | 529篇 |
2005年 | 470篇 |
2004年 | 373篇 |
2003年 | 393篇 |
2002年 | 363篇 |
2001年 | 351篇 |
2000年 | 309篇 |
1999年 | 278篇 |
1998年 | 227篇 |
1997年 | 193篇 |
1996年 | 165篇 |
1995年 | 165篇 |
1994年 | 82篇 |
1993年 | 68篇 |
1992年 | 73篇 |
1991年 | 67篇 |
1990年 | 53篇 |
1989年 | 34篇 |
1988年 | 48篇 |
1987年 | 47篇 |
1986年 | 36篇 |
1985年 | 47篇 |
1984年 | 41篇 |
1983年 | 21篇 |
1982年 | 35篇 |
1981年 | 15篇 |
1980年 | 38篇 |
1979年 | 31篇 |
1978年 | 13篇 |
1977年 | 22篇 |
1976年 | 20篇 |
1975年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
71.
Recently, molecular imaging has been rapidly developed to studyphysiological and pathological processes in vivo at the cellularand molecular levels. Among molecular imaging modalities, opticalimaging has attracted a major attention for its unique advantages.In this paper, we establish a mathematical framework for multispectralbioluminescence tomography (BLT) that allows simultaneous studiesof multiple optical reporters. We show solution existence, uniquenessand continuous dependence on data as well as the limiting behaviourswhen the regularization parameter approaches zero or when thepenalty parameter approaches infinity. Then, we propose twonumerical schemes for multispectral BLT and derive error estimatesfor the corresponding solutions. 相似文献
72.
This article studies the inshore-offshore fishery model with impulsive diffusion. The existence and global asymptotic stability of both the trivial periodic solution and the positive periodic solution are obtained. The complexity of this system is also analyzed. Moreover, the optimal harvesting policy are given for the inshore subpopulation, which includes the maximum sustainable yield and the corresponding harvesting effort. 相似文献
73.
Boniface Nkemzi 《Mathematical Methods in the Applied Sciences》2006,29(9):1053-1080
This paper is concerned with the structure of the singular and regular parts of the solution of time‐harmonic Maxwell's equations in polygonal plane domains and their effective numerical treatment. The asymptotic behaviour of the solution near corner points of the domain is studied by means of discrete Fourier transformation and it is proved that the solution of the boundary value problem does not belong locally to H2 when the boundary of the domain has non‐acute angles. A splitting of the solution into a regular part belonging to the space H2, and an explicitly described singular part is presented. For the numerical treatment of the boundary value problem, we propose a finite element discretization which combines local mesh grading and the singular field methods and derive a priori error estimates that show optimal convergence as known for the classical finite element method for problems with regular solutions. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
74.
We study the existence and the continuity properties of the boundary values on the real axis of the resolvent of a self-adjoint operator H in the framework of the conjugate operator method initiated by Mourre. We allow the conjugate operator A to be the generator of a C0-semigroup (finer estimates require A to be maximal symmetric) and we consider situations where the first commutator [H,iA] is not comparable to H. The applications include the spectral theory of zero mass quantum field models. 相似文献
75.
Tristrom Cooke 《Journal of multivariate analysis》2004,89(2):191-383
The quadratic discriminant function is often used to separate two classes of points in a multidimensional space. When the two classes are normally distributed, this results in the optimum separation. In some cases however, the assumption of normality is a poor one and the classification error is increased. The current paper derives an upper bound for the classification error due to a quadratic decision surface. The bound is strict when the class means and covariances and the quadratic discriminant surface satisfy certain specified symmetry conditions. 相似文献
76.
We show that the tensor product B-spline basis and the triangular Bernstein basis are in some sense best conditioned among all nonnegative bases for the spaces of tensor product splines and multivariate polynomials, respectively. We also introduce some new condition numbers which are analogs of component-wise condition numbers for linear systems introduced by Skeel. 相似文献
77.
In this paper, an interior point cutting plane method (IPCPM)is applied to solve optimal power flow (OPF) problems. Comparedwith the simplex cutting plane method (SCPM), the IPCPM is simpler,and efficient because of its polynomial-time characteristic.Issues in implementing IPCPM for OPF problems are addressed,including (1) how to generate cutting planes without using thesimplex tableau, (2) how to identify the basis variables inIPCPM, and (3) how to generate mixed integer cutting planes.The calculation speed of the proposed algorithm is further enhancedby utilizing the sparsity features of the OPF formulation. Numericalsimulations on IEEE 14-300-bus test systems have shown thatthe proposed method is effective. 相似文献
78.
Some previous works show that symmetric fixed- and variable-stepsize linear multistep methods for second-order systems which do not have any parasitic root in their first characteristic polynomial give rise to a slow error growth with time when integrating reversible systems. In this paper, we give a technique to construct variable-stepsize symmetric methods from their fixed-stepsize counterparts, in such a way that the former have the same order as the latter. The order and symmetry of the integrators obtained is proved independently of the order of the underlying fixed-stepsize integrators. As this technique looks for efficiency, we concentrate on explicit linear multistep methods, which just make one function evaluation per step, and we offer some numerical comparisons with other one-step adaptive methods which also show a good long-term behaviour.
79.
用迈克耳逊干涉仪测量气体折射率的误差的研究 总被引:1,自引:0,他引:1
研究在用迈克尔逊干涉仪测量气体折射率时存在的系统和方法误差,提出了误差修正方法。 相似文献
80.
Algorithm for Optimal Triangulations in Scattered Data Representation and Implementation 总被引:2,自引:0,他引:2
Scattered data collected at sample points may be used to determine simple functions to best fit the data. An ideal choice for these simple functions is bivariate splines. Triangulation of the sample points creates partitions over which the bivariate splines may be defined. But the optimality of the approximation is dependent on the choice of triangulation. An algorithm, referred to as an Edge Swapping Algorithm, has been developed to transform an arbitrary triangulation of the sample points into an optimal triangulation for representation of the scattered data. A Matlab package has been completed that implements this algorithm for any triangulation on a given set of sample points. 相似文献