全文获取类型
收费全文 | 12623篇 |
免费 | 1098篇 |
国内免费 | 818篇 |
专业分类
化学 | 2586篇 |
晶体学 | 23篇 |
力学 | 742篇 |
综合类 | 205篇 |
数学 | 8364篇 |
物理学 | 2619篇 |
出版年
2024年 | 25篇 |
2023年 | 81篇 |
2022年 | 203篇 |
2021年 | 245篇 |
2020年 | 231篇 |
2019年 | 277篇 |
2018年 | 254篇 |
2017年 | 376篇 |
2016年 | 466篇 |
2015年 | 297篇 |
2014年 | 576篇 |
2013年 | 1004篇 |
2012年 | 655篇 |
2011年 | 649篇 |
2010年 | 590篇 |
2009年 | 710篇 |
2008年 | 743篇 |
2007年 | 793篇 |
2006年 | 712篇 |
2005年 | 648篇 |
2004年 | 582篇 |
2003年 | 485篇 |
2002年 | 492篇 |
2001年 | 438篇 |
2000年 | 379篇 |
1999年 | 397篇 |
1998年 | 309篇 |
1997年 | 274篇 |
1996年 | 236篇 |
1995年 | 196篇 |
1994年 | 165篇 |
1993年 | 125篇 |
1992年 | 133篇 |
1991年 | 111篇 |
1990年 | 84篇 |
1989年 | 68篇 |
1988年 | 56篇 |
1987年 | 57篇 |
1986年 | 53篇 |
1985年 | 63篇 |
1984年 | 72篇 |
1983年 | 27篇 |
1982年 | 37篇 |
1981年 | 22篇 |
1980年 | 24篇 |
1979年 | 30篇 |
1978年 | 17篇 |
1977年 | 20篇 |
1976年 | 16篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
We prove that simply connected open manifolds of bounded geometry, linear growth and sublinear filling growth (e.g. finite filling area) are simply connected at infinity. 相似文献
72.
Efficiencies of the maximum pseudolikelihood estimator and a number of related estimators for the case-cohort sampling design in the proportional hazards regression model are studied. The asymptotic information and lower bound for estimating the parametric regression parameter are calculated based on the effective score, which is obtained by determining the component of the parametric score orthogonal to the space generated by the infinite-dimensional nuisance parameter. The asymptotic distributions of the maximum pseudolikelihood and related estimators in an i.i.d. setting show that these estimators do not achieve the computed asymptotic lower bound. Simple guidelines are provided to determine in which instances such estimators are close enough to efficient for practical purposes. 相似文献
73.
This study investigates the robust output tracking problem for a class of uncertain linear systems. The uncertainties are assumed to be time invariant and to satisfy the matching conditions. According to the selected nominal parameters, an optimal solution with a prescribed degree of stability is determined. Then, an auxiliary input via the use of an adapting factor, connected to the nominal optimal control, is introduced to guarantee the robustness and prescribed degree of stability for the output tracking control of the uncertain linear systems. This method is very simple and effective and can reject bounded uncertainties imposed on the states. A maglev vehicle model example is given to show its effectiveness. 相似文献
74.
This paper considers the estimation problem for a trigonometric regression model with the noise specified by the Ornstein–Uhlenbeck
process with unknown parameter. We propose a sequential procedure which ensures a prescribed mean square precision uniformly
in the nuisance parameter. The asymptotic behaviour of the procedure duration mean has been studied.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
75.
Eero Immonen 《Journal of Mathematical Analysis and Applications》2004,300(1):79-101
In this article, we study the effect of the chosen representation of a point value (and point evaluation) on the class of periodic signals realizable using a certain type of infinite-dimensional linear system. By suitably representing the point evaluation at the origin in a Hilbert space, we are able to give a complete characterization of its extensions. These extensions involve a new concept called δ-sequence, the use of which as an observation operator of an infinite-dimensional linear system is studied in this article. In particular, we consider their use in the realization of periodic signals. We also investigate how the use of δ-sequences affects the convergence properties of such realizations; we consider the rate and character of convergence and the removal of the Gibbs phenomenon. As still a further demonstration of the significance of the chosen concept of a point value, we discuss the use of distributional point values in the realization of periodic distributions. The possible applications of this work lie in regulator problems of infinite-dimensional control theory, as is indicated by the well-known internal model principle. 相似文献
76.
77.
Andrew V. Goldberg Michael D. Grigoriadis Robert E. Tarjan 《Mathematical Programming》1991,50(1-3):277-290
Goldfarb and Hao (1990) have proposed a pivot rule for the primal network simplex algorithm that will solve a maximum flow problem on ann-vertex,m-arc network in at mostnm pivots and O(n
2
m) time. In this paper we describe how to extend the dynamic tree data structure of Sleator and Tarjan (1983, 1985) to reduce the running time of this algorithm to O(nm logn). This bound is less than a logarithmic factor larger than those of the fastest known algorithms for the problem. Our extension of dynamic trees is interesting in its own right and may well have additional applications.Research partially supported by a Presidential Young Investigator Award from the National Science Foundation, Grant No. CCR-8858097, an IBM Faculty Development Award, and AT&T Bell Laboratories.Research partially supported by the Office of Naval Research, Contract No. N00014-87-K-0467.Research partially supported by the National Science Foundation, Grant No. DCR-8605961, and the Office of Naval Research, Contract No. N00014-87-K-0467. 相似文献
78.
Miguel A. Arcones 《Annals of the Institute of Statistical Mathematics》1998,50(1):87-117
We consider exact weak and strong Bahadur-Kiefer representations of the least absolute deviation estimator for the linear regression model. The precise behavior of these representations is obtained under minimal conditions. 相似文献
79.
Véronique Cariou 《Computational Statistics》2006,21(2):325-341
Summary Several data can be presented as interval curves where intervals reflect a within variability. In particular, this representation
is well adapted for load profiles, which depict the electricity consumption of a class of customers. Electricity load profiling
consists in assigning a daily load curve to a customer based on their characteristics such as energy requirement. Within the
load profiling scope, this paper investigates the extension of multivariate regression trees to the case of interval dependent
(or response) variables. The tree method aims at setting up simultaneously load profiles and their assignment rules based
on independent variables. The extension of multivariate regression trees to interval responses is detailed and a global approach
is defined. It consists in a first stage of a dimension reduction of the interval response variables. Thereafter, the extension
of the tree method is applied to the first principal interval components. Outputs are the classes of the interval curves where
each class is characterized both by an interval load profile (e.g. the class prototype) and an assignment rule based on the
independent variables. 相似文献
80.
We consider a composite material composed of fibres included in a resin which becomes solid when it is heated up (reaction of reticulation). The mathematical modelling of the cure process is given by a kinetic equation describing the evolution of the reaction of reticulation coupled with the heat equation. In this paper, we are interested in the computation of approximate solutions. We propose a family of discretized problems depending on two parameters (β1, β2) ε [0, 1]2 which split the linear and non‐ linear terms in implicit and explicit parts. We prove the stability and convergence of the discretization for any (β1, β2) ε [½, 1 ] × [0, 1]. We present also some numerical results. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献