全文获取类型
收费全文 | 18103篇 |
免费 | 404篇 |
国内免费 | 443篇 |
专业分类
化学 | 2563篇 |
晶体学 | 94篇 |
力学 | 128篇 |
综合类 | 46篇 |
数学 | 14552篇 |
物理学 | 1567篇 |
出版年
2023年 | 42篇 |
2022年 | 106篇 |
2021年 | 76篇 |
2020年 | 97篇 |
2019年 | 385篇 |
2018年 | 429篇 |
2017年 | 238篇 |
2016年 | 189篇 |
2015年 | 209篇 |
2014年 | 481篇 |
2013年 | 1109篇 |
2012年 | 571篇 |
2011年 | 1129篇 |
2010年 | 909篇 |
2009年 | 1288篇 |
2008年 | 1333篇 |
2007年 | 1333篇 |
2006年 | 1031篇 |
2005年 | 726篇 |
2004年 | 595篇 |
2003年 | 540篇 |
2002年 | 419篇 |
2001年 | 374篇 |
2000年 | 377篇 |
1999年 | 414篇 |
1998年 | 414篇 |
1997年 | 288篇 |
1996年 | 390篇 |
1995年 | 394篇 |
1994年 | 383篇 |
1993年 | 308篇 |
1992年 | 263篇 |
1991年 | 200篇 |
1990年 | 218篇 |
1989年 | 207篇 |
1988年 | 138篇 |
1987年 | 136篇 |
1986年 | 129篇 |
1985年 | 184篇 |
1984年 | 139篇 |
1983年 | 87篇 |
1982年 | 131篇 |
1981年 | 103篇 |
1980年 | 102篇 |
1979年 | 70篇 |
1978年 | 78篇 |
1977年 | 53篇 |
1976年 | 49篇 |
1975年 | 29篇 |
1973年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
Summary. We introduce linear semi-implicit complementary volume numerical scheme for solving level set like nonlinear degenerate diffusion
equations arising in image processing and curve evolution problems. We study discretization of image selective smoothing equation
of mean curvature flow type given by Alvarez, Lions and Morel ([3]). Solution of the level set equation of Osher and Sethian
([26], \[30]) is also included in the study. We prove and estimates for the proposed scheme and give existence of its (generalized) solution in every discrete time-scale step. Efficiency
of the scheme is given by its linearity and stability. Preconditioned iterative solvers are used for computing arising linear
systems. We present computational results related to image processing and plane curve evolution.
Received April 25, 2000 / Revised version received June 11, 2001 / Published online November 15, 2001 相似文献
102.
Sans résumé
相似文献
相似文献
103.
In the framework of ARMA models, we consider testing the reliability of the standard asymptotic covariance matrix (ACM) of the least-squares estimator. The standard formula for this ACM is derived under the assumption that the errors are independent and identically distributed, and is in general invalid when the errors are only uncorrelated. The test statistic is based on the difference between a conventional estimator of the ACM of the least-squares estimator of the ARMA coefficients and its robust HAC-type version. The asymptotic distribution of the HAC estimator is established under the null hypothesis of independence, and under a large class of alternatives. The asymptotic distribution of the proposed statistic is shown to be a standard χ2 under the null, and a noncentral χ2 under the alternatives. The choice of the HAC estimator is discussed through asymptotic power comparisons. The finite sample properties of the test are analyzed via Monte Carlo simulation. 相似文献
104.
Takashi Kishimoto 《Journal of Pure and Applied Algebra》2007,208(1):189-204
Let X?(T,D) be a compactification of an affine 3-fold X into a smooth projective 3-fold T such that the (reduced) boundary divisor D is SNC. In this paper, as an affine counterpart to the work due to S. Mori (cf. [S. Mori, Threefolds whose canonical bundles are not numerically effective, Ann. of Math. 116 (1982) 133-176]), we shall classify (K+D)-negative extremal rays on T. In particular, if such an extremal ray R=R+[C] intersects K non-negatively, we shall describe the log flips and divisorial contractions appearing explicitly. 相似文献
105.
This article introduces and analyzes a p-version FEM for variational inequalities resulting from obstacle problems for some quasi-linear elliptic partial differential
operators. We approximate the solution by controlling the obstacle condition in images of the Gauss–Lobatto points. We show
existence and uniqueness for the discrete solution u
p
from the p-version for the obstacle problem. We prove the convergence of u
p
towards the solution with respect to the energy norm, and assuming some additional regularity for the solution we derive
an a priori error estimate. In numerical experiments the p-version turns out to be superior to the h-version concerning the convergence rate and the number of unknowns needed to achieve a certain exactness of the approximation. 相似文献
106.
In this paper we first give a lower bound on multiplicities for Buchsbaum homogeneous k-algebras A in terms of the dimension d, the codimension c, the initial degree q, and the length of the local cohomology modules of A. Next, we introduce the notion of Buchsbaum k-algebras with minimal multiplicity of degree q, and give several characterizations for those rings. In particular, we will show that those algebras have linear free resolutions. Further, we will give many examples of those algebras. 相似文献
107.
Zero-schemes on smooth complex projective varieties, forcing all elements of ample and free linear systems to be reducible, are studied. Relationships among the minimal length of such zero-schemes, the positivity of the line bundle associated with the linear system, and the dimension of the variety are established. Bad linear spaces are also investigated. 相似文献
108.
C. Foias A. E. Frazho I. Gohberg M. A. Kaashoek 《Integral Equations and Operator Theory》1997,29(4):455-490
The family of all solutions of the three chains completion problem with a prescribed tolerance is described explicitly. It is shown that this family can be parameterized by a natural set of contractive upper triangular operators. As an application all solutions to a suboptimal nonstationary Nehari problem are described. 相似文献
109.
用玻色子组态混合和玻色子表面δ相互作用研究核谱 总被引:2,自引:0,他引:2
用玻色子组态混合波函数和玻色子表面δ相互作用研究了三玻色子核46Ti和54Cr的sdgIBMI的能谱和E2跃迁概率,理论计算结果令人满意,比sdIBMI能拟合出更多的能级和E2跃迁概率,而且它们的误差更小. 说明g玻色子在振动区也起着重要的作用,同时进一步证明了这种玻色子组态混合模型是成功的. 相似文献
110.
R. M. Dudley 《Probability Theory and Related Fields》1994,100(2):175-189
Summary In a separable metric space, if two Borel probability measures (laws) are nearby in a suitable metric, then there exist random variables with those laws which are nearby in probability. Specifically, by a well-known theorem of Strassen, the Prohorov distance between two laws is the infimum of Ky Fan distances of random variables with those laws. The present paper considers possible extensions of Strassen's theorem to two random elements one of which may be (compact) set-valued and/or non-measurable. There are positive results in finite-dimensional spaces, but with factors depending on the dimension. Examples show that such factors cannot entirely be avoided, so that the extension of Strassen's theorem to the present situation fails in infinite dimensions.This research was partially supported by a Guggenheim Fellowship, by National Science Foundation grant DMS 8505550 at MSRI-Berkeley, and other NSF grants 相似文献