全文获取类型
收费全文 | 17165篇 |
免费 | 1669篇 |
国内免费 | 1473篇 |
专业分类
化学 | 12331篇 |
晶体学 | 152篇 |
力学 | 84篇 |
综合类 | 76篇 |
数学 | 5484篇 |
物理学 | 2180篇 |
出版年
2024年 | 23篇 |
2023年 | 312篇 |
2022年 | 285篇 |
2021年 | 319篇 |
2020年 | 518篇 |
2019年 | 618篇 |
2018年 | 678篇 |
2017年 | 367篇 |
2016年 | 599篇 |
2015年 | 666篇 |
2014年 | 930篇 |
2013年 | 1453篇 |
2012年 | 903篇 |
2011年 | 1114篇 |
2010年 | 980篇 |
2009年 | 1136篇 |
2008年 | 1162篇 |
2007年 | 1110篇 |
2006年 | 928篇 |
2005年 | 716篇 |
2004年 | 675篇 |
2003年 | 607篇 |
2002年 | 595篇 |
2001年 | 396篇 |
2000年 | 344篇 |
1999年 | 328篇 |
1998年 | 310篇 |
1997年 | 206篇 |
1996年 | 227篇 |
1995年 | 264篇 |
1994年 | 234篇 |
1993年 | 182篇 |
1992年 | 173篇 |
1991年 | 91篇 |
1990年 | 87篇 |
1989年 | 73篇 |
1988年 | 73篇 |
1987年 | 47篇 |
1986年 | 47篇 |
1985年 | 64篇 |
1984年 | 59篇 |
1982年 | 61篇 |
1981年 | 52篇 |
1980年 | 40篇 |
1979年 | 52篇 |
1978年 | 43篇 |
1977年 | 32篇 |
1976年 | 37篇 |
1975年 | 23篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
21.
We consider normal ≡ Gaussian seemingly unrelated regressions (SUR) with incomplete data (ID). Imposing a natural minimal set of conditional independence constraints, we find a restricted SUR/ID model whose likelihood function and parameter space factor into the product of the likelihood functions and the parameter spaces of standard complete data multivariate analysis of variance models. Hence, the restricted model has a unimodal likelihood and permits explicit likelihood inference. In the development of our methodology, we review and extend existing results for complete data SUR models and the multivariate ID problem. 相似文献
22.
The moduli space of torus sextics with the configuration of singularities {A2+A5+2E6} has two connected components. We compute the fundamental groups π1(CP2−C) for sextics C in both components and study their differences. 相似文献
23.
A. M. Vinogradov 《Acta Appl Math》1989,15(1-2):3-21
The main notions and results which are necessary for finding higher symmetries and conservation laws for general systems of partial differential equations are given. These constitute the starting point for the subsequent papers of this volume. Some problems are also discussed. 相似文献
24.
Yevhen Zelenyuk 《Topology and its Applications》2006,153(14):2382-2385
We introduce the notion of a partially selective ultrafilter and prove that (a) if G is an extremally disconnected topological group and p is a converging nonprincipal ultrafilter on G containing a countable discrete subset, then p is partially selective, and (b) the existence of a nonprincipal partially selective ultrafilter on a countable set implies the existence of a P-point in ω∗. Thus it is consistent with ZFC that there is no extremally disconnected topological group containing a countable discrete nonclosed subset. 相似文献
25.
26.
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
27.
F. Balibrea 《Topology and its Applications》2006,153(12):2092-2095
Recently, Forti, Paganoni and Smítal constructed an example of a triangular map of the unite square, F(x,y)=(f(x),g(x,y)), possessing periodic orbits of all periods and such that no infinite ω-limit set of F contains a periodic point. In this note we show that the above quoted map F has a homoclinic orbit. As a consequence, we answer in the negative the problem presented by A.N. Sharkovsky in the eighties whether, for a triangular map of the square, existence of a homoclinic orbit implies the existence of an infinite ω-limit set containing a periodic point. It is well known that, for a continuous map of the interval, the answer is positive. 相似文献
28.
Chuanming Zong 《Monatshefte für Mathematik》2002,134(3):247-255
In this article we study the simultaneous packing and covering constants of two-dimensional centrally symmetric convex domains.
Besides an identity result between translative case and lattice case and a general upper bound, exact values for some special
domains are determined. Similar to Mahler and Reinhardt’s result about packing densities, we show that the simultaneous packing
and covering constant of an octagon is larger than that of a circle.
(Received 17 January 2001; in revised form 13 July 2001) 相似文献
29.
Kunyu Guo 《Journal of Functional Analysis》2004,213(2):380-411
This paper mainly concerns defect operators and defect functions of Hardy submodules, Bergman submodules over the unit ball, and Hardy submodules over the polydisk. The defect operator (function) carries key information about operator theory (function theory) and structure of analytic submodules. The problem when a submodule has finite defect is attacked for both Hardy submodules and Bergman submodules. Our interest will be in submodules generated by polynomials. The reason for choosing such submodules is to understand the interaction of operator theory, function theory and algebraic geometry. 相似文献
30.
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