全文获取类型
收费全文 | 5854篇 |
免费 | 127篇 |
国内免费 | 34篇 |
专业分类
化学 | 4057篇 |
晶体学 | 88篇 |
力学 | 136篇 |
数学 | 992篇 |
物理学 | 742篇 |
出版年
2022年 | 36篇 |
2021年 | 43篇 |
2020年 | 41篇 |
2019年 | 62篇 |
2018年 | 58篇 |
2017年 | 47篇 |
2016年 | 114篇 |
2015年 | 114篇 |
2014年 | 114篇 |
2013年 | 315篇 |
2012年 | 264篇 |
2011年 | 325篇 |
2010年 | 149篇 |
2009年 | 147篇 |
2008年 | 287篇 |
2007年 | 313篇 |
2006年 | 264篇 |
2005年 | 301篇 |
2004年 | 250篇 |
2003年 | 281篇 |
2002年 | 234篇 |
2001年 | 102篇 |
2000年 | 87篇 |
1999年 | 84篇 |
1998年 | 63篇 |
1997年 | 86篇 |
1996年 | 94篇 |
1995年 | 92篇 |
1994年 | 84篇 |
1993年 | 64篇 |
1992年 | 54篇 |
1991年 | 60篇 |
1990年 | 49篇 |
1989年 | 63篇 |
1988年 | 72篇 |
1987年 | 55篇 |
1986年 | 52篇 |
1985年 | 78篇 |
1984年 | 99篇 |
1983年 | 67篇 |
1982年 | 90篇 |
1981年 | 95篇 |
1980年 | 91篇 |
1979年 | 74篇 |
1978年 | 77篇 |
1977年 | 72篇 |
1976年 | 67篇 |
1975年 | 58篇 |
1974年 | 48篇 |
1973年 | 36篇 |
排序方式: 共有6015条查询结果,搜索用时 0 毫秒
11.
Ioana Dumitriu Alan Edelman 《Annales de l'Institut Henri Poincaré (B) Probabilités et Statistiques》2005,41(6):1083-1099
In this paper we examine the zero and first order eigenvalue fluctuations for the β-Hermite and β-Laguerre ensembles, using tridiagonal matrix models, in the limit as β→∞. We prove that the fluctuations are described by multivariate Gaussians of covariance O(1/β), centered at the roots of a corresponding Hermite (Laguerre) polynomial. The covariance matrix itself is expressed as combinations of Hermite or Laguerre polynomials respectively.We show that the approximations are of real value even for small β; we can use them to approximate the true functions even for the traditional β=1,2,4 values. 相似文献
12.
13.
Richard Kotek Kyeong Pang Ben Schmidt Alan Tonelli 《Journal of Polymer Science.Polymer Physics》2004,42(23):4247-4254
Poly(ethylene isophthalate) (PEI) was synthesized for this research with essentially a condensation polymerization of isophthalic acid and ethylene glycol catalyzed by zinc acetate and antimony trioxide. Several samples were obtained, and their characteristics were observed and compared with poly(ethylene terephthalate) (PET). The synthesized PEI samples were chemically identified by 1H NMR. Thermal analysis with differential scanning calorimetry (DSC) yielded results that indicate the samples were primarily amorphous, with a glass‐transition temperature of 55–60 °C. Molecular weights of these PEI samples were also obtained through intrinsic viscosity measurements (Mark–Houwink equation). Molecular weights varied with conditions of the polymerization, and the highest molecular weight achieved was 21,000 g/mol. Finally, the diffusion coefficient, solubility, and permeability of CO2 gas in PEI were measured and found to be substantially lower than in PET, as anticipated from their isomeric chemical structures. This is because in PET the phenyl rings are substituted in the para (1,4) positions, which allows for their facile flipping, effectively permitting gases to pass through. However, the meta‐substituted phenyl rings in PEI do not permit such ring flipping, and thus PEI may be more suitable for barrier applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4247–4254, 2004 相似文献
14.
15.
16.
17.
Il Bong Jung Alan Lambert Jan Stochel 《Proceedings of the American Mathematical Society》2004,132(8):2291-2302
The concept of backward extension for subnormal weighted shifts is generalized to arbitrary subnormal operators. Several differences and similarities in these contexts are explored, with emphasis on the structure of the underlying measures.
18.
19.
Alan L. Andrew 《BIT Numerical Mathematics》2003,43(3):485-503
The asymptotic correction technique of Paine, de Hoog and Anderssen can dramatically improve the accuracy of finite difference or finite element eigenvalues at negligible extra cost if closed form expressions are available for the errors in a simpler related problem. This paper gives closed form expressions for the errors in the eigenvalues of certain Sturm–Liouville problems obtained by various methods, thereby increasing the range of problems for which asymptotic correction can achieve maximum efficiency. It also investigates implementation of the method for more general problems. 相似文献
20.
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