全文获取类型
收费全文 | 14349篇 |
免费 | 1072篇 |
国内免费 | 885篇 |
专业分类
化学 | 10652篇 |
晶体学 | 141篇 |
力学 | 397篇 |
综合类 | 66篇 |
数学 | 2504篇 |
物理学 | 2546篇 |
出版年
2023年 | 143篇 |
2022年 | 260篇 |
2021年 | 414篇 |
2020年 | 436篇 |
2019年 | 377篇 |
2018年 | 335篇 |
2017年 | 328篇 |
2016年 | 622篇 |
2015年 | 577篇 |
2014年 | 676篇 |
2013年 | 1023篇 |
2012年 | 1175篇 |
2011年 | 1362篇 |
2010年 | 936篇 |
2009年 | 794篇 |
2008年 | 1045篇 |
2007年 | 1030篇 |
2006年 | 880篇 |
2005年 | 748篇 |
2004年 | 654篇 |
2003年 | 445篇 |
2002年 | 404篇 |
2001年 | 197篇 |
2000年 | 150篇 |
1999年 | 158篇 |
1998年 | 93篇 |
1997年 | 104篇 |
1996年 | 109篇 |
1995年 | 80篇 |
1994年 | 68篇 |
1993年 | 62篇 |
1992年 | 58篇 |
1991年 | 38篇 |
1990年 | 44篇 |
1989年 | 31篇 |
1988年 | 28篇 |
1987年 | 41篇 |
1986年 | 28篇 |
1985年 | 47篇 |
1984年 | 43篇 |
1983年 | 30篇 |
1982年 | 23篇 |
1981年 | 19篇 |
1980年 | 15篇 |
1979年 | 22篇 |
1978年 | 18篇 |
1977年 | 13篇 |
1975年 | 12篇 |
1974年 | 12篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
Juan Nieto 《Journal of Mathematical Analysis and Applications》2004,291(2):716-726
In this paper we study the stability of the following nonlinear drift-diffusion system modeling large population dynamics ∂tρ+div(ρU−ε∇ρ)=0, divU=±ρ, with respect to the viscosity parameter ε. The sign in the second equation depends on the attractive or repulsive character of the field U. A proof of the compactness and convergence properties in the vanishing viscosity regime is given. The lack of compactness in the attractive case is caused by the blow-up of the solution which depends on the mass and on the space dimension. Our stability result is connected, depending of the character of the potentials, with models in semiconductor theory or in biological population. 相似文献
33.
Juan Gonzá lez-Meneses Luis Paris 《Transactions of the American Mathematical Society》2004,356(1):219-243
We show that Vassiliev invariants separate braids on a closed oriented surface, and we exhibit a universal Vassiliev invariant for these braids in terms of chord diagrams labeled by elements of the fundamental group of the surface.
34.
Using Lagrange's multiplier rule, we find upper and lower bounds of the energy of a bipartite graph G, in terms of the number of vertices, edges and the spectral moment of fourth order. Moreover, the upper bound is attained in a graph G if and only if G is the graph of a symmetric balanced incomplete block design (BIBD). Also, we determine the graphs for which the lower bound is sharp. 相似文献
35.
Gabriela Jeronimo Teresa Krick Juan Sabia Martín Sombra 《Foundations of Computational Mathematics》2004,4(1):41-117
We present a bounded probability algorithm for the computation of the
Chowforms of the equidimensional components of an algebraic variety. In particular,
this gives an alternative procedure for the effective equidimensional decomposition
of the variety, since each equidimensional component is characterized by its Chow
form.
The expected complexity of the algorithm is polynomial in the size and the geometric
degree of the input equation system defining the variety. Hence it improves (or
meets in some special cases) the complexity of all previous algorithms for computing Chow forms. In addition to this, we clarify the probability and uniformity aspects,
which constitutes a further contribution of the paper.
The algorithm is based on elimination theory techniques, in line with the geometric
resolution algorithm due to M. Giusti, J. Heintz, L. M. Pardo, and their collaborators.
In fact, ours can be considered as an extension of their algorithm for zero-dimensional
systems to the case of positive-dimensional varieties. The key element for dealing
with positive-dimensional varieties is a new Poisson-type product formula. This
formula allows us to compute the Chow form of an equidimensional variety from a
suitable zero-dimensional fiber.
As an application, we obtain an algorithm to compute a subclass of sparse resultants,
whose complexity is polynomial in the dimension and the volume of the input
set of exponents. As another application, we derive an algorithm for the computation
of the (unique) solution of a generic overdetermined polynomial equation system. 相似文献
36.
We consider the generalization of the classical P||Cmax problem (assign n jobs to m identical parallel processors by minimizing the makespan) arising when the number of jobs that can be assigned to each processor cannot exceed a given integer k. The problem is strongly NP-hard for any fixed k > 2. We briefly survey lower and upper bounds from the literature. We introduce greedy heuristics, local search and a scatter search approach. The effectiveness of these approaches is evaluated through extensive computational comparison with a depth-first branch-and-bound algorithm that includes new lower bounds and dominance criteria. 相似文献
37.
Models, describing relativistic particles, where Lagrangian densities depend linearly on both the curvature and the torsion of the trajectories, are revisited in D=3 space forms. The moduli spaces of trajectories are completely and explicitly determined using the Lancret program. The moduli subspaces of closed solitons in the three sphere are also determined. 相似文献
38.
Piotr Winiarek Juan Carlos Q. Colmenares Elbieta Fedoryska 《Reaction Kinetics and Catalysis Letters》2004,81(2):333-339
Transformations of diphenylmethane were investigated in a flow system in the presence of alumina and silica-alumina modified
with boron trifluoride at atmospheric pressure and elevated temperatures. Hydrogen transfer reaction was observed on addition
of tetralin to the substrate stream.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
39.
Manuel Ritoré Cé sar Rosales 《Transactions of the American Mathematical Society》2004,356(11):4601-4622
We study the problem of existence of regions separating a given amount of volume with the least possible perimeter inside a Euclidean cone. Our main result shows that nonexistence for a given volume implies that the isoperimetric profile of the cone coincides with the one of the half-space. This allows us to give some criteria ensuring existence of isoperimetric regions: for instance, local convexity of the cone at some boundary point.
We also characterize which are the stable regions in a convex cone, i.e., second order minima of perimeter under a volume constraint. From this it follows that the isoperimetric regions in a convex cone are the euclidean balls centered at the vertex intersected with the cone.
40.
We present a general risk model where the aggregate claims, as well as the premium function, evolve by jumps. This is achieved by incorporating a Lévy process into the model. This seeks to account for the discrete nature of claims and asset prices. We give several explicit examples of Lévy processes that can be used to drive a risk model. This allows us to incorporate aggregate claims and premium fluctuations in the same process. We discuss important features of such processes and their relevance to risk modeling. We also extend classical results on ruin probabilities to this model. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献