全文获取类型
收费全文 | 15748篇 |
免费 | 446篇 |
国内免费 | 439篇 |
专业分类
化学 | 1937篇 |
晶体学 | 70篇 |
力学 | 136篇 |
综合类 | 13篇 |
数学 | 13291篇 |
物理学 | 1186篇 |
出版年
2023年 | 36篇 |
2022年 | 42篇 |
2021年 | 68篇 |
2020年 | 102篇 |
2019年 | 356篇 |
2018年 | 365篇 |
2017年 | 231篇 |
2016年 | 162篇 |
2015年 | 179篇 |
2014年 | 360篇 |
2013年 | 880篇 |
2012年 | 555篇 |
2011年 | 883篇 |
2010年 | 794篇 |
2009年 | 1112篇 |
2008年 | 1221篇 |
2007年 | 1254篇 |
2006年 | 963篇 |
2005年 | 642篇 |
2004年 | 575篇 |
2003年 | 502篇 |
2002年 | 294篇 |
2001年 | 309篇 |
2000年 | 302篇 |
1999年 | 314篇 |
1998年 | 292篇 |
1997年 | 227篇 |
1996年 | 308篇 |
1995年 | 332篇 |
1994年 | 323篇 |
1993年 | 276篇 |
1992年 | 208篇 |
1991年 | 114篇 |
1990年 | 129篇 |
1989年 | 127篇 |
1988年 | 114篇 |
1987年 | 148篇 |
1986年 | 118篇 |
1985年 | 189篇 |
1984年 | 145篇 |
1983年 | 100篇 |
1982年 | 162篇 |
1981年 | 146篇 |
1980年 | 124篇 |
1979年 | 105篇 |
1978年 | 130篇 |
1977年 | 116篇 |
1976年 | 111篇 |
1975年 | 30篇 |
1974年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
21.
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
22.
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
23.
Andrei K. Lerner 《Archiv der Mathematik》2005,85(6):538-543
We show that the Hardy-Littlewood maximal operator and a class of Calderón-Zygmund singular integrals satisfy the strong type
modular inequality in variable Lp spaces if and only if the variable exponent p(x) ∼ const.
Received: 15 September 2004 相似文献
24.
25.
26.
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
27.
Paulo D. Cordaro 《Advances in Mathematics》2004,184(1):89-118
Taking as a start point the recent article of Meziani [7], we present several results concerning the normalization of a class of complex vector fields in the plane which degenerate along a real curve. We mainly deal with operators with finite regularity and analyze both the local situation as well as the case of normalization near a circle. Some related questions (e.g., on semi-global solvability and on the normalization of a class of generalized Mizohata operators) are also discussed. 相似文献
28.
Reduced rank regression assumes that the coefficient matrix in a multivariate regression model is not of full rank. The unknown rank is traditionally estimated under the assumption of normal responses. We derive an asymptotic test for the rank that only requires the response vector have finite second moments. The test is extended to the nonconstant covariance case. Linear combinations of the components of the predictor vector that are estimated to be significant for modelling the responses are obtained. 相似文献
29.
Ya. I. Kurys’ N. S. Netyaga V. G. Koshechko V. D. Pokhodenko 《Theoretical and Experimental Chemistry》2007,43(5):334-342
A guest-host nanocomposite based on electroconducting polyaniline doped with 12-phosphotungstic acid and V2O5 as well as its bifunctional analog containing not more than 5 mass% nanosized platinum were obtained. A study was carried
out on the structure of these nanocomposites, their redox characteristics, and electrocatalytic activity in the reduction
of oxygen. These nanocomposites were found to display catalytic properties in the electrochemical reduction of oxygen, while
the presence of even a slight amount of nanosized platinum in the bifunctional composite leads to a significant increase in
its electrocatalytic activity.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 307–314, September–October, 2007. 相似文献
30.
Abstract. We propose a general approach to deal with nonlinear, nonconvex variational problems based on a reformulation of the problem
resulting in an optimization problem with linear cost functional and convex constraints. As a first step we explicitly explore
these ideas to some one-dimensional variational problems and obtain specific conclusions of an analytical and numerical nature. 相似文献