全文获取类型
收费全文 | 2254篇 |
免费 | 95篇 |
国内免费 | 126篇 |
专业分类
化学 | 55篇 |
力学 | 373篇 |
综合类 | 15篇 |
数学 | 1591篇 |
物理学 | 441篇 |
出版年
2024年 | 3篇 |
2023年 | 45篇 |
2022年 | 36篇 |
2021年 | 27篇 |
2020年 | 59篇 |
2019年 | 53篇 |
2018年 | 41篇 |
2017年 | 59篇 |
2016年 | 45篇 |
2015年 | 55篇 |
2014年 | 133篇 |
2013年 | 198篇 |
2012年 | 97篇 |
2011年 | 170篇 |
2010年 | 169篇 |
2009年 | 178篇 |
2008年 | 158篇 |
2007年 | 179篇 |
2006年 | 125篇 |
2005年 | 88篇 |
2004年 | 82篇 |
2003年 | 55篇 |
2002年 | 60篇 |
2001年 | 42篇 |
2000年 | 34篇 |
1999年 | 36篇 |
1998年 | 42篇 |
1997年 | 41篇 |
1996年 | 27篇 |
1995年 | 15篇 |
1994年 | 12篇 |
1993年 | 14篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 10篇 |
1981年 | 1篇 |
1980年 | 6篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有2475条查询结果,搜索用时 15 毫秒
61.
The present work is intended as a first step towards applying semidefinite programming models and tools to discrete lot-sizing problems including sequence-dependent changeover costs and times. Such problems can be formulated as quadratically constrained quadratic binary programs. We investigate several semidefinite relaxations by combining known reformulation techniques recently proposed for generic quadratic binary problems with problem-specific strengthening procedures developed for lot-sizing problems. Our computational results show that the semidefinite relaxations consistently provide lower bounds of significantly improved quality as compared with those provided by the best previously published linear relaxations. In particular, the gap between the semidefinite relaxation and the optimal integer solution value can be closed for a significant proportion of the small-size instances, thus avoiding to resort to a tree search procedure. The reported computation times are significant. However improvements in SDP technology can still be expected in the future, making SDP based approaches to discrete lot-sizing more competitive. 相似文献
62.
63.
Jinghua YANG 《数学年刊B辑(英文版)》2019,40(2):227-236
In this paper, the author gives the discrete criteria and J\o
rgensen inequalities of subgroups for the special linear group on
$\overline{\mathrm{F}}((t))$ in two and higher dimensions. 相似文献
64.
65.
Discrete fine-scale models, in the form of either particle or lattice models, have been formulated successfully to simulate the behavior of quasi-brittle materials whose mechanical behavior is inherently connected to fracture processes occurring in the internal heterogeneous structure. These models tend to be intensive from the computational point of view as they adopt an “a priori” discretization anchored to the major material heterogeneities (e.g. grains in particulate materials and aggregate pieces in cementitious composites) and this hampers their use in the numerical simulations of large systems. In this work, this problem is addressed by formulating a general multiple scale computational framework based on classical asymptotic analysis and that (1) is applicable to any discrete model with rotational degrees of freedom; and (2) gives rise to an equivalent Cosserat continuum. The developed theory is applied to the upscaling of the Lattice Discrete Particle Model (LDPM), a recently formulated discrete model for concrete and other quasi-brittle materials, and the properties of the homogenized model are analyzed thoroughly in both the elastic and the inelastic regime. The analysis shows that the homogenized micropolar elastic properties are size-dependent, and they are functions of the RVE size and the size of the material heterogeneity. Furthermore, the analysis of the homogenized inelastic behavior highlights issues associated with the homogenization of fine-scale models featuring strain-softening and the related damage localization. Finally, nonlinear simulations of the RVE behavior subject to curvature components causing bending and torsional effects demonstrate, contrarily to typical Cosserat formulations, a significant coupling between the homogenized stress–strain and couple-curvature constitutive equations. 相似文献
66.
《Journal of computational and graphical statistics》2013,22(3):464-486
In recent years, hierarchical model-based clustering has provided promising results in a variety of applications. However, its use with large datasets has been hindered by a time and memory complexity that are at least quadratic in the number of observations. To overcome this difficulty, this article proposes to start the hierarchical agglomeration from an efficient classification of the data in many classes rather than from the usual set of singleton clusters. This initial partition is derived from a subgraph of the minimum spanning tree associated with the data. To this end, we develop graphical tools that assess the presence of clusters in the data and uncover observations difficult to classify. We use this approach to analyze two large, real datasets: a multiband MRI image of the human brain and data on global precipitation climatology. We use the real datasets to discuss ways of integrating the spatial information in the clustering analysis. We focus on two-stage methods, in which a second stage of processing using established methods is applied to the output from the algorithm presented in this article, viewed as a first stage. 相似文献
67.
F. Balibrea Gallego J.L. García Guirao J.I. Muñoz Casado 《Journal of Difference Equations and Applications》2013,19(3-4):289-304
We consider Sturm–Liouville eigenvalue problems of second order with arbitary seperated boundary conditions and perform a suitabl discretization of them. The obtained discrete Sturm–Liouville eigenvalue problems are examined and the asymptotic behavior of their eigenvalue as the norm of the partition tends to zero is investigated. 相似文献
68.
We consider symplectic difference systems involving a spectral parameter, together with the Dirichlet boundary conditions. The main result of the paper is a discrete version of the so-called oscillation theorem which relates the number of finite eigenvalues less than a given number to the number of focal points of the principal solution of the symplectic system. In two recent papers the same problem was treated and an essential ingredient was to establish the concept of the multiplicity of a focal point. But there was still a rather restrictive condition needed, which is eliminated here by using the concept of finite eigenvalues (or zeros) from the theory of matrix pencils. 相似文献
69.
In this article, we deal with the notion of the envelopes of homotopies which is the generalized version of functional envelopes in discrete dynamical systems. We prove the stability for envelopes of homotopies in complete normed algebra and we get the stabilities of the derivation and the extended derivation for the notion in the spaces. 相似文献
70.
《Optimization》2012,61(4):293-316
The paper develops sufficient conditions for controllability and necessary conditions in different forms of the maximum principle for extremal solutions of discrete inclusions. The objective function is assumed to be locally lipschitzian only 相似文献