全文获取类型
收费全文 | 10179篇 |
免费 | 945篇 |
国内免费 | 1471篇 |
专业分类
化学 | 6033篇 |
晶体学 | 67篇 |
力学 | 793篇 |
综合类 | 136篇 |
数学 | 3287篇 |
物理学 | 2279篇 |
出版年
2024年 | 24篇 |
2023年 | 123篇 |
2022年 | 245篇 |
2021年 | 252篇 |
2020年 | 336篇 |
2019年 | 293篇 |
2018年 | 303篇 |
2017年 | 338篇 |
2016年 | 353篇 |
2015年 | 304篇 |
2014年 | 437篇 |
2013年 | 636篇 |
2012年 | 477篇 |
2011年 | 571篇 |
2010年 | 515篇 |
2009年 | 574篇 |
2008年 | 652篇 |
2007年 | 715篇 |
2006年 | 630篇 |
2005年 | 569篇 |
2004年 | 442篇 |
2003年 | 435篇 |
2002年 | 481篇 |
2001年 | 353篇 |
2000年 | 299篇 |
1999年 | 260篇 |
1998年 | 289篇 |
1997年 | 203篇 |
1996年 | 225篇 |
1995年 | 185篇 |
1994年 | 175篇 |
1993年 | 145篇 |
1992年 | 124篇 |
1991年 | 89篇 |
1990年 | 66篇 |
1989年 | 56篇 |
1988年 | 49篇 |
1987年 | 47篇 |
1986年 | 44篇 |
1985年 | 45篇 |
1984年 | 32篇 |
1983年 | 19篇 |
1982年 | 38篇 |
1981年 | 42篇 |
1980年 | 26篇 |
1979年 | 26篇 |
1978年 | 21篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
23.
In this paper, we study the linearization of the Cauchy problem and the mixed problem for the system of Grad--Hermite moments in nonequilibrium thermodynamics in the neighborhood of the equilibrium state. Stability conditions for solutions of the Cauchy problem are proved as a generalization of the classical Hermite--Biller theorem on stable polynomials. For the mixed problem, we prove an analog of the Vishik--Lyusternik theorem on small singular perturbations of general elliptic problems. The last observation allows us to introduce the Shapiro--Lopatinskii condition, which implies the well-posedness of the mixed problem. 相似文献
24.
A Variable Neighborhood Search for the Multi Depot Vehicle Routing Problem with Time Windows 总被引:6,自引:0,他引:6
Michael Polacek Richard F. Hartl Karl Doerner Marc Reimann 《Journal of Heuristics》2004,10(6):613-627
The aim of this paper is to propose an algorithm based on the philosophy of the Variable Neighborhood Search (VNS) to solve Multi Depot Vehicle Routing Problems with Time Windows. The paper has two main contributions. First, from a technical point of view, it presents the first application of a VNS for this problem and several design issues of VNS algorithms are discussed. Second, from a problem oriented point of view the computational results show that the approach is competitive with an existing Tabu Search algorithm with respect to both solution quality and computation times. 相似文献
25.
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.
26.
林诒勋 《高校应用数学学报(英文版)》2003,18(3):361-369
§ 1 IntroductionThe cutwidth problem for graphs,as well as a class of optimal labeling and embed-ding problems,have significant applications in VLSI designs,network communicationsand other areas (see [2 ] ) .We shall follow the graph-theoretic terminology and notation of [1 ] .Let G=(V,E)be a simple graph with vertex set V,| V| =n,and edge set E.A labeling of G is a bijec-tion f:V→ { 1 ,2 ,...,n} ,which can by regarded as an embedding of G into a path Pn.Fora given labeling f of G,th… 相似文献
27.
构造一个求解椭圆型边值问题的多子域D—N交替算法,导出对应的容度方程和等价的迭代法,证明算法的收敛性。 相似文献
28.
Govindarajan Sankar A. Sultan Nasar 《Journal of polymer science. Part A, Polymer chemistry》2007,45(8):1557-1570
A series of substituted N‐methylaniline‐blocked polyisocyanates based on 4,4′‐methylenebis(phenyl isocyanate) and poly(tetrahydrofuran) were prepared and characterized thoroughly with FTIR, 1H NMR, and 13C NMR spectroscopy methods. Compared with unsubstituted N‐methylaniline, a blocking agent with an electron‐releasing substituent at the para position took a shorter time, whereas those with an electron‐releasing substituent at the ortho position or an electron‐withdrawing substituent at the ortho and para positions took longer times for the blocking reaction. The thermal dissociation reactions of blocked polyisocyanates were carried out with an FTIR spectrophotometer attached to hot‐stage accessories under dynamic and isothermal conditions. The dynamic method was used to determine the deblocking temperature, and the isothermal method was used to calculate the deblocking kinetics and activation parameters. The cure times of blocked polyisocyanates with hydroxyl‐terminated polybutadiene were also determined. The deblocking temperatures, the results of cure‐time studies, and the kinetic parameters revealed that the thermal dissociation of the N‐methylaniline‐blocked polyisocyanates was retarded by electron‐donating substituents and facilitated by electron‐withdrawing substituents. The action of N‐methylanilines as blocking agents for isocyanate was explained by the formation of a four‐center, intramolecularly hydrogen‐bonded ring structure during the thermal dissociation of the blocked polyisocyanates. The formation of such a hydrogen‐bonded ring structure was confirmed and supported by variable‐temperature 1H NMR studies and entropy parameters, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1557–1570, 2007 相似文献
29.
We discuss differential equations with nonlinear boundary conditions. We formulate sufficient conditions under which problems
with deviating arguments have quasisolutions or solutions. To obtain the results, we apply the method of monotone iterations. 相似文献
30.
A. V. Gavrilov 《Siberian Mathematical Journal》2007,48(1):56-61
We study the double exponential map which is a composition of a special form of two exponential maps on a manifold with connection. We relate this map and the composition of covariant derivations as well as the composition of pseudodifferential operators on these manifolds. 相似文献