全文获取类型
收费全文 | 11514篇 |
免费 | 256篇 |
国内免费 | 273篇 |
专业分类
化学 | 1418篇 |
晶体学 | 31篇 |
力学 | 77篇 |
综合类 | 17篇 |
数学 | 9713篇 |
物理学 | 787篇 |
出版年
2023年 | 18篇 |
2022年 | 34篇 |
2021年 | 26篇 |
2020年 | 42篇 |
2019年 | 247篇 |
2018年 | 281篇 |
2017年 | 150篇 |
2016年 | 99篇 |
2015年 | 120篇 |
2014年 | 290篇 |
2013年 | 713篇 |
2012年 | 351篇 |
2011年 | 671篇 |
2010年 | 605篇 |
2009年 | 901篇 |
2008年 | 870篇 |
2007年 | 872篇 |
2006年 | 661篇 |
2005年 | 428篇 |
2004年 | 382篇 |
2003年 | 299篇 |
2002年 | 235篇 |
2001年 | 217篇 |
2000年 | 231篇 |
1999年 | 255篇 |
1998年 | 255篇 |
1997年 | 177篇 |
1996年 | 244篇 |
1995年 | 251篇 |
1994年 | 251篇 |
1993年 | 193篇 |
1992年 | 171篇 |
1991年 | 125篇 |
1990年 | 142篇 |
1989年 | 142篇 |
1988年 | 91篇 |
1987年 | 95篇 |
1986年 | 105篇 |
1985年 | 139篇 |
1984年 | 110篇 |
1983年 | 57篇 |
1982年 | 94篇 |
1981年 | 67篇 |
1980年 | 78篇 |
1979年 | 58篇 |
1978年 | 60篇 |
1977年 | 39篇 |
1976年 | 33篇 |
1975年 | 24篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
The paper provides significant simplifications and extensions of results obtained by Gorsich, Genton, and Strang (J. Multivariate Anal. 80 (2002) 138) on the structure of spatial design matrices. These are the matrices implicitly defined by quadratic forms that arise naturally in modelling intrinsically stationary and isotropic spatial processes. We give concise structural formulae for these matrices, and simple generating functions for them. The generating functions provide formulae for the cumulants of the quadratic forms of interest when the process is Gaussian, second-order stationary and isotropic. We use these to study the statistical properties of the associated quadratic forms, in particular those of the classical variogram estimator, under several assumptions about the actual variogram. 相似文献
12.
Parallel to Cox's [JRSS B34 (1972) 187-230] proportional hazards model, generalized logistic models have been discussed by Anderson [Bull. Int. Statist. Inst. 48 (1979) 35-53] and others. The essential assumption is that the two densities ratio has a known parametric form. A nice property of this model is that it naturally relates to the logistic regression model for categorical data. In astronomic, demographic, epidemiological, and other studies the variable of interest is often truncated by an associated variable. This paper studies generalized logistic models for the two-sample truncated data problem, where the two lifetime densities ratio is assumed to have the form exp{α+φ(x;β)}. Here φ is a known function of x and β, and the baseline density is unspecified. We develop a semiparametric maximum likelihood method for the case where the two samples have a common truncation distribution. It is shown that inferences for β do not depend the nonparametric components. We also derive an iterative algorithm to maximize the semiparametric likelihood for the general case where different truncation distributions are allowed. We further discuss how to check goodness of fit of the generalized logistic model. The developed methods are illustrated and evaluated using both simulated and real data. 相似文献
13.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
14.
15.
Franz-Viktor Kuhlmann 《Advances in Mathematics》2004,188(2):399-424
We consider the Zariski space of all places of an algebraic function field F|K of arbitrary characteristic and investigate its structure by means of its patch topology. We show that certain sets of places with nice properties (e.g., prime divisors, places of maximal rank, zero-dimensional discrete places) lie dense in this topology. Further, we give several equivalent characterizations of fields that are large, in the sense of F. Pop's Annals paper Embedding problems over large fields. We also study the question whether a field K is existentially closed in an extension field L if L admits a K-rational place. In the appendix, we prove the fact that the Zariski space with the Zariski topology is quasi-compact and that it is a spectral space. 相似文献
16.
Dmitri I. Panyushev 《Advances in Mathematics》2004,186(2):307-316
We study Abelian ideals of a Borel subalgebra consisting of long roots. It is shown that methods of Cellini and Papi can be extended to this situation. A uniform expression for the number of long Abelian ideals is given. We also show that there is a one-to-one correspondence between the long Abelian ideals and B-stable commutative subalgebras in the little adjoint representation of the Langlands dual Lie algebra. 相似文献
17.
In this paper we relate the operators in the operator representations of a generalized Nevanlinna function N(z) and of the function −N(z)−1 under the assumption that z=∞ is the only (generalized) pole of nonpositive type. The results are applied to the Q-function for S and H and the Q-function for S and H∞, where H is a self-adjoint operator in a Pontryagin space with a cyclic element w, H∞ is the self-adjoint relation obtained from H and w via a rank one perturbation at infinite coupling, and S is the symmetric operator given by S=H∩H∞. 相似文献
18.
The existence of an attractor for a 2D-Navier-Stokes system with delay is proved. The theory of pullback attractors is successfully applied to obtain the results since the abstract functional framework considered turns out to be nonautonomous. However, on some occasions, the attractors may attract not only in the pullback sense but in the forward one as well. Also, this formulation allows to treat, in a unified way, terms containing various classes of delay features (constant, variable, distributed delays, etc.). As a consequence, some results for the autonomous model are deduced as particular cases of our general formulation. 相似文献
19.
Peter Clifford 《Annals of Combinatorics》2005,9(3):281-291
Motivated by recent results of Stanley, we generalize the rank of a partition λ to the rank of a shifted partition S(λ). We show that the number of bars required in a minimal bar tableau of S(λ) is max(o, e + (ℓ(λ) mod 2)), where o and e are the number of odd and even rows of λ. As a consequence we show that the irreducible projective characters of Sn vanish on certain conjugacy classes. Another corollary is a lower bound on the degree of the terms in the expansion of Schur’s
Qλ symmetric functions in terms of the power sum symmetric functions.
Received November 20, 2003 相似文献
20.
We give a criterion to decide if a given w-homogeneous derivation on A?k[X1,X2,X3] is locally nilpotent. We deduce an algorithm which decides if a k-subalgebra of A, which is finitely generated by w-homogeneous elements, is the kernel of some locally nilpotent derivation. 相似文献