全文获取类型
收费全文 | 15238篇 |
免费 | 286篇 |
国内免费 | 77篇 |
专业分类
化学 | 8798篇 |
晶体学 | 107篇 |
力学 | 515篇 |
数学 | 2095篇 |
物理学 | 4086篇 |
出版年
2022年 | 108篇 |
2021年 | 126篇 |
2020年 | 177篇 |
2019年 | 116篇 |
2018年 | 127篇 |
2017年 | 94篇 |
2016年 | 230篇 |
2015年 | 229篇 |
2014年 | 276篇 |
2013年 | 561篇 |
2012年 | 628篇 |
2011年 | 788篇 |
2010年 | 441篇 |
2009年 | 394篇 |
2008年 | 658篇 |
2007年 | 723篇 |
2006年 | 724篇 |
2005年 | 744篇 |
2004年 | 606篇 |
2003年 | 475篇 |
2002年 | 441篇 |
2001年 | 414篇 |
2000年 | 384篇 |
1999年 | 228篇 |
1998年 | 210篇 |
1997年 | 198篇 |
1996年 | 262篇 |
1995年 | 234篇 |
1994年 | 217篇 |
1993年 | 258篇 |
1992年 | 241篇 |
1991年 | 219篇 |
1990年 | 178篇 |
1989年 | 180篇 |
1988年 | 206篇 |
1987年 | 187篇 |
1986年 | 145篇 |
1985年 | 192篇 |
1984年 | 186篇 |
1983年 | 141篇 |
1982年 | 175篇 |
1981年 | 155篇 |
1980年 | 155篇 |
1979年 | 160篇 |
1978年 | 163篇 |
1977年 | 122篇 |
1976年 | 139篇 |
1975年 | 102篇 |
1974年 | 121篇 |
1973年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
22.
A.M. van der Kraan 《Hyperfine Interactions》1998,111(1-4):23-34
In modern society the application of catalysts, and hence, research in the field of catalysis, is becoming more and more important. In the strongly increasing chemical industry most reaction processes are performed with the aid of catalysts. Knowledge about the structure of the active sites present at the surface of catalysts will facilitate the design of new catalysts with better performances. Such knowledge can be obtained by Mössbauer spectroscopy, which is an excellent in-situ characterization technique due to the high penetrating power of the γ-radiation used and the sensitivity of the spectral parameters for the chemical state and local environment of the Mössbauer atoms. 相似文献
23.
Q. Gong R. N tzel P.J. van Veldhoven T.J. Eijkemans J.H. Wolter 《Journal of Crystal Growth》2005,280(3-4):413-418
We report on the shape transition from InAs quantum dashes to quantum dots (QDs) on lattice-matched GaInAsP on InP(3 1 1)A substrates. InAs quantum dashes develop during chemical-beam epitaxy of 3.2 monolayers InAs, which transform into round InAs QDs by introducing a growth interruption without arsenic flux after InAs deposition. The shape transition is solely attributed to surface properties, i.e., increase of the surface energy and symmetry under arsenic deficient conditions. The round QD shape is maintained during subsequent GaInAsP overgrowth because the reversed shape transition from dot to dash is kinetically hindered by the decreased ad-atom diffusion under arsenic flux. 相似文献
24.
Jose Manuel Corcuera Joao Guerra David Nualart Wim Schoutens 《Applied Mathematics and Optimization》2006,53(3):279-309
In this paper we consider the optimal investment problem in a market where the stock price process is modeled by a geometric
Levy process (taking into account jumps).
Except for the geometric Brownian model and the geometric Poissonian model, the
resulting models are incomplete and there are many equivalent martingale measures.
However, the model can be completed by the so-called power-jump assets. By doing this we allow investment in these new assets
and we can try to maximize the expected utility of these portfolios. As particular cases we obtain the optimal portfolios
based in stocks
and bonds, showing that the new assets are superfluous for certain martingale measures
that depend on the utility function we use. 相似文献
25.
Many recent algorithmic approaches involve the construction of a differential equation model for computational purposes, typically
by introducing an artificial time variable. The actual computational model involves a discretization of the now time-dependent differential system, usually
employing forward Euler. The resulting dynamics of such an algorithm is then a discrete dynamics, and it is expected to be
“close enough” to the dynamics of the continuous system (which is typically easier to analyze) provided that small – hence
many – time steps, or iterations, are taken. Indeed, recent papers in inverse problems and image processing routinely report
results requiring thousands of iterations to converge. This makes one wonder if and how the computational modeling process
can be improved to better reflect the actual properties sought.
In this article we elaborate on several problem instances that illustrate the above observations. Algorithms may often lend
themselves to a dual interpretation, in terms of a simply discretized differential equation with artificial time and in terms
of a simple optimization algorithm; such a dual interpretation can be advantageous. We show how a broader computational modeling
approach may possibly lead to algorithms with improved efficiency.
AMS subject classification (2000) 65L05, 65M32, 65N21, 65N22, 65D18 相似文献
26.
27.
David S. Dummit Brett A. Tangedal Paul B. van Wamelen. 《Mathematics of Computation》2004,73(247):1525-1546
Systematic computation of Stark units over nontotally real base fields is carried out for the first time. Since the information provided by Stark's conjecture is significantly less in this situation than the information provided over totally real base fields, new techniques are required. Precomputing Stark units in relative quadratic extensions (where the conjecture is already known to hold) and coupling this information with the Fincke-Pohst algorithm applied to certain quadratic forms leads to a significant reduction in search time for finding Stark units in larger extensions (where the conjecture is still unproven). Stark's conjecture is verified in each case for these Stark units in larger extensions and explicit generating polynomials for abelian extensions over complex cubic base fields, including Hilbert class fields, are obtained from the minimal polynomials of these new Stark units.
28.
29.
We show that reductions of KP hierarchies related to the loop algebra of SLn with homogeneous gradation give solutions of the Darboux-Egoroff system of PDE's. Using explicit dressing matrices of the Riemann-Hilbert problem generalized to include a set of commuting additional symmetries, we construct solutions of the Witten– Dijkgraaf–E. Verlinde–H. Verlinde equations. 相似文献
30.