全文获取类型
收费全文 | 25694篇 |
免费 | 758篇 |
国内免费 | 816篇 |
专业分类
化学 | 4743篇 |
晶体学 | 875篇 |
力学 | 498篇 |
综合类 | 76篇 |
数学 | 18014篇 |
物理学 | 3062篇 |
出版年
2023年 | 91篇 |
2022年 | 170篇 |
2021年 | 199篇 |
2020年 | 219篇 |
2019年 | 633篇 |
2018年 | 645篇 |
2017年 | 439篇 |
2016年 | 435篇 |
2015年 | 400篇 |
2014年 | 766篇 |
2013年 | 1455篇 |
2012年 | 779篇 |
2011年 | 1620篇 |
2010年 | 1648篇 |
2009年 | 1866篇 |
2008年 | 2012篇 |
2007年 | 1930篇 |
2006年 | 1542篇 |
2005年 | 1130篇 |
2004年 | 1080篇 |
2003年 | 894篇 |
2002年 | 725篇 |
2001年 | 551篇 |
2000年 | 489篇 |
1999年 | 522篇 |
1998年 | 471篇 |
1997年 | 388篇 |
1996年 | 533篇 |
1995年 | 471篇 |
1994年 | 466篇 |
1993年 | 397篇 |
1992年 | 312篇 |
1991年 | 197篇 |
1990年 | 184篇 |
1989年 | 186篇 |
1988年 | 125篇 |
1987年 | 126篇 |
1986年 | 133篇 |
1985年 | 189篇 |
1984年 | 123篇 |
1983年 | 93篇 |
1982年 | 114篇 |
1981年 | 106篇 |
1980年 | 89篇 |
1979年 | 57篇 |
1978年 | 72篇 |
1977年 | 70篇 |
1976年 | 62篇 |
1975年 | 17篇 |
1974年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Regularity of multiwavelets 总被引:7,自引:0,他引:7
The motivation for this paper is an interesting observation made by Plonka concerning the factorization of the matrix symbol associated with the refinement equation for B-splines with equally spaced multiple knots at integers and subsequent developments which relate this factorization to regularity of refinable vector fields over the real line. Our intention is to contribute to this train of ideas which is partially driven by the importance of refinable vector fields in the construction of multiwavelets. The use of subdivision methods will allow us to consider the problem almost entirely in the spatial domain and leads to exact characterizations of differentiability and Hölder regularity in arbitrary L p spaces. We first study the close relationship between vector subdivision schemes and a generalized notion of scalar subdivision schemes based on bi-infinite matrices with certain periodicity properties. For the latter type of subdivision scheme we will derive criteria for convergence and Hölder regularity of the limit function, which mainly depend on the spectral radius of a bi-infinite matrix induced by the subdivision operator, and we will show that differentiability of the limit functions can be characterized by factorization properties of the subdivision operator. By switching back to vector subdivision we will transfer these results to refinable vectors fields and obtain characterizations of regularity by factorization and spectral radius properties of the symbol associated to the refinable vector field. Finally, we point out how multiwavelets can be generated from orthonormal refinable bi-infinite vector fields. 相似文献
82.
Kehe Zhu 《Integral Equations and Operator Theory》1998,31(3):371-387
The paper deals with two closely related questions about the Bergman space of the unit disk. First, we investigate a special class of invariant subspaces of the Bergman space, namely, invariant subspaces induced by certain Hankel operators. We show that such spaces always have the co-dimension 1 or 2 property; and we determine exactly when such a space has the co-dimension 1 property. Second, we introduce the notion of inner spaces in the Bergman space and give several characterizations of when an inner space is maximal.Research supported by the National Science Foundation 相似文献
83.
S. A. Denisov 《Integral Equations and Operator Theory》2002,42(2):166-173
We consider the Krein systems. For the set of Stummel class coefficients, we establish the criterion in terms of these coefficients for the system to satisfy the Szegö-type estimate on the spectral measure. 相似文献
84.
85.
Sans résumé
相似文献
相似文献
86.
Summary We prove convergence and error estimates in Sobolev spaces for the collocation method with tensor product splines for strongly elliptic pseudodifferential equations on the torus. Examples of applications include elliptic partial differential equations with periodic boundary conditions but also the classical boundary integral operators of potential theory on torus-shaped domains in three or more dimensions. For odd-degree splines, we prove convergence of nodal collocation for any strongly elliptic operator. For even-degree splines and midpoint collocation, we find an additional condition for the convergence which is satisfied for the classical boundary integral operators. Our analysis is a generalization to higher dimensions of the corresponding analysis of Arnold and Wendland [4]. 相似文献
87.
Properties of nonparametric estimators of autocovariance for stationary random fields 总被引:1,自引:0,他引:1
Summary We introduce nonparametric estimators of the autocovariance of a stationary random field. One of our estimators has the property that it is itself an autocovatiance. This feature enables the estimator to be used as the basis of simulation studies such as those which are necessary when constructing bootstrap confidence intervals for unknown parameters. Unlike estimators proposed recently by other authors, our own do not require assumptions such as isotropy or monotonicity. Indeed, like nonparametric function estimators considered more widely in the context of curve estimation, our approach demands only smoothness and tail conditions on the underlying curve or surface (here, the autocovariance), and moment and mixing conditions on the random field. We show that by imposing the condition that the estimator be a covariance function we actually reduce the numerical value of integrated squared error. 相似文献
88.
The problem of nonparametric stationary distribution function estimation by the observations of an ergodic diffusion process is considered. The local asymptotic minimax lower bound on the risk of all the estimators is found and it is proved that the empirical distribution function is asymptotically efficient in the sense of this bound. 相似文献
89.
Intense multi- and single-line laser operation is reported from semiconductively preionised atomic fluorine lasers employing an optimised capacitor transfer excitation circuitry. The performance and spectral characteristics of these lasers are discussed and compared to the characteristics of previously described atomic fluorine lasers. The efficiency of one of these lasers described, at optimum conditions, is reaching a value as high as 0.14%. To the best of our knowledge, this is the highest efficiency reported up date, for an atomic fluorine laser. 相似文献
90.
In this paper we generalize to coisotropic actions of compact Lie groups a theorem of Guillemin on deformations of Hamiltonian
structures on compact symplectic manifolds. We show how one can reconstruct from the moment polytope the symplectic form on
the manifold.
Received: 21 March 2006 相似文献