全文获取类型
收费全文 | 3101篇 |
免费 | 51篇 |
国内免费 | 20篇 |
专业分类
化学 | 2085篇 |
晶体学 | 36篇 |
力学 | 48篇 |
数学 | 550篇 |
物理学 | 453篇 |
出版年
2022年 | 26篇 |
2021年 | 24篇 |
2020年 | 35篇 |
2019年 | 28篇 |
2018年 | 25篇 |
2017年 | 35篇 |
2016年 | 44篇 |
2015年 | 35篇 |
2014年 | 56篇 |
2013年 | 151篇 |
2012年 | 146篇 |
2011年 | 164篇 |
2010年 | 96篇 |
2009年 | 107篇 |
2008年 | 213篇 |
2007年 | 194篇 |
2006年 | 169篇 |
2005年 | 139篇 |
2004年 | 138篇 |
2003年 | 123篇 |
2002年 | 136篇 |
2001年 | 46篇 |
2000年 | 48篇 |
1999年 | 34篇 |
1998年 | 27篇 |
1997年 | 30篇 |
1996年 | 60篇 |
1995年 | 28篇 |
1994年 | 38篇 |
1993年 | 27篇 |
1992年 | 40篇 |
1991年 | 22篇 |
1990年 | 18篇 |
1989年 | 31篇 |
1988年 | 29篇 |
1987年 | 25篇 |
1986年 | 19篇 |
1985年 | 47篇 |
1984年 | 47篇 |
1983年 | 29篇 |
1982年 | 55篇 |
1981年 | 54篇 |
1980年 | 35篇 |
1979年 | 38篇 |
1978年 | 46篇 |
1977年 | 27篇 |
1976年 | 30篇 |
1974年 | 22篇 |
1973年 | 34篇 |
1972年 | 18篇 |
排序方式: 共有3172条查询结果,搜索用时 406 毫秒
11.
The central observation of this paper is that if εn random arcs are added to any n‐node strongly connected digraph with bounded degree then the resulting graph has diameter 𝒪(lnn) with high probability. We apply this to smoothed analysis of algorithms and property testing. Smoothed Analysis: Recognizing strongly connected digraphs is a basic computational task in graph theory. Even for digraphs with bounded degree, it is NL‐complete. By XORing an arbitrary bounded degree digraph with a sparse random digraph R ∼ 𝔻n,ε/n we obtain a “smoothed” instance. We show that, with high probability, a log‐space algorithm will correctly determine if a smoothed instance is strongly connected. We also show that if NL ⫅̸ almost‐L then no heuristic can recognize similarly perturbed instances of (s,t)‐connectivity. Property Testing: A digraph is called k‐linked if, for every choice of 2k distinct vertices s1,…,sk,t1,…,tk, the graph contains k vertex disjoint paths joining sr to tr for r = 1,…,k. Recognizing k‐linked digraphs is NP‐complete for k ≥ 2. We describe a polynomial time algorithm for bounded degree digraphs, which accepts k‐linked graphs with high probability, and rejects all graphs that are at least εn arcs away from being k‐linked. © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 2007 相似文献
12.
Details are given of a new method allowing an exact calculation of the spontaneous magnetization in the corner as well as along the edge at an arbitrary distance of the corner for a rectangular planar Ising ferromagnet. 相似文献
13.
A well-known problem of prediction in linear regression models is to find a confidence interval for the random value of the dependent variable when the values of the independent variables are given. Such a situation may arise in economic quality control models when the independent variables are costly inputs and the dependent variable is some measure of quality or production. In such a circumstance, an important control objective may be to find values for the inputs that will maximize the lower limit of the prediction confidence interval for a fixed budget, or alternatively, to minimize the cost of the inputs for a fixed lower limit of the confidence interval. In this paper, we shall show that global optima can be found using known algorithms. The special case of simple linear regression is discussed and an illustrative example is provided. 相似文献
14.
Robert Andreu Gerard Lligadas Joan Carles Ronda Marina Galià Virginia Cádiz 《Journal of polymer science. Part A, Polymer chemistry》2007,45(21):4965-4973
A new oxazolidine derivative was obtained from phenol, 2‐amino‐2‐methylpropane‐1,3‐diol and paraformaldehyde. The reaction of this novel oxazolidine diol with phenylisocyanate lead to a urethane model compound which can be polymerized thermally by oxazolidine ring opening to give a Mannich bridge structure. Linear segmented polyurethanes were prepared by reaction of different ratios of oxazolidine diol and commercial polyethylenglycol (Mw ~ 400) with 4,4′‐methylenbis (cyclohexylisocyanate) (HMDI, 90% isomers mixture). The polyurethanes were thermally characterized and crosslinked by oxazolidine ring opening to obtain materials which showed improved thermal stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4965–4973, 2007 相似文献
15.
We study the structure of the most common type of Riemannian submersions, namely those whose fibers are given by the orbits
of an isometric group action on a Riemannian manifold. Special emphasis is given to the case where the ambient space has nonnegative
curvature.
The first author was supported by research grant MTM2004-04794-MEC. Most of this work was done during a visit of the second
author to Madrid, financed in part by funds of the aforementioned grant. 相似文献
16.
Gerard Lallement 《Semigroup Forum》1989,38(1):371-374
Communicated by N. Reilly 相似文献
17.
Remco van der Hofstad Gerard Hooghiemstra Piet Van Mieghem 《Random Structures and Algorithms》2002,20(4):519-539
In this paper we study the covariance structure of the number of nodes k and l steps away from the root in random recursive trees. We give an analytic expression valid for all k, l and tree sizes N. The fraction of nodes k steps away from the root is a random probability distribution in k. The expression for the covariances allows us to show that the total variation distance between this (random) probability distribution and its mean converges in probability to zero. © 2002 Wiley Periodicals, Inc. Random Struct. Alg., 20: 519–539, 2002 相似文献
18.
19.
20.
Gerard Walschap 《Journal of Geometric Analysis》1992,2(4):373-381
We prove a rigidity theorem for Riemannian fibrations of flat spaces over compact bases and give a metric classification of compact four-dimensional manifolds of nonnegative curvature that admit totally geodesic Riemannian foliations. 相似文献