全文获取类型
收费全文 | 1966篇 |
免费 | 55篇 |
国内免费 | 12篇 |
专业分类
化学 | 1200篇 |
晶体学 | 8篇 |
力学 | 42篇 |
数学 | 259篇 |
物理学 | 524篇 |
出版年
2021年 | 14篇 |
2020年 | 14篇 |
2019年 | 23篇 |
2018年 | 14篇 |
2016年 | 34篇 |
2015年 | 22篇 |
2014年 | 39篇 |
2013年 | 56篇 |
2012年 | 101篇 |
2011年 | 133篇 |
2010年 | 63篇 |
2009年 | 60篇 |
2008年 | 85篇 |
2007年 | 113篇 |
2006年 | 110篇 |
2005年 | 103篇 |
2004年 | 71篇 |
2003年 | 76篇 |
2002年 | 81篇 |
2001年 | 51篇 |
2000年 | 51篇 |
1999年 | 32篇 |
1998年 | 20篇 |
1997年 | 16篇 |
1996年 | 36篇 |
1995年 | 26篇 |
1994年 | 14篇 |
1993年 | 29篇 |
1992年 | 24篇 |
1991年 | 19篇 |
1990年 | 30篇 |
1989年 | 16篇 |
1988年 | 19篇 |
1987年 | 15篇 |
1986年 | 28篇 |
1985年 | 23篇 |
1984年 | 21篇 |
1983年 | 22篇 |
1982年 | 18篇 |
1981年 | 20篇 |
1980年 | 15篇 |
1979年 | 17篇 |
1978年 | 28篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 22篇 |
1974年 | 15篇 |
1973年 | 19篇 |
1969年 | 16篇 |
1904年 | 11篇 |
排序方式: 共有2033条查询结果,搜索用时 15 毫秒
1.
2.
We consider normal ≡ Gaussian seemingly unrelated regressions (SUR) with incomplete data (ID). Imposing a natural minimal set of conditional independence constraints, we find a restricted SUR/ID model whose likelihood function and parameter space factor into the product of the likelihood functions and the parameter spaces of standard complete data multivariate analysis of variance models. Hence, the restricted model has a unimodal likelihood and permits explicit likelihood inference. In the development of our methodology, we review and extend existing results for complete data SUR models and the multivariate ID problem. 相似文献
3.
Lance Nielsen 《Acta Appl Math》2002,74(3):265-292
Stability properties of Feynman's operational calculus are addressed in the setting of exponential functions of noncommuting operators. Applications of some of the stability results are presented. In particular, the time-dependent perturbation theory of nonrelativistic quantum mechanics is presented in the setting of the operational calculus and application of the stability results of this paper to the perturbation theory are discussed. 相似文献
4.
We use the adiabatic hyperspheric expansion and the Faddeev decomposition of the wave function with only s-waves. We derive for a fixed hyperradius an integro-differential equation for the angular eigenvalue and wave function. The
correlations lower the interaction energy for N = 20 by about a factor of 5.
Received October 22, 2001; accepted for publication November 5, 2001 相似文献
5.
6.
Kristian Hougaard Frederik D. Nielsen 《Journal of Optical and Fiber Communications Reports》2004,1(1):63-83
In this paper we will present an overview of the use
of photonic crystal fibers as fiber amplifiers. We
will describe the basic concepts of optical
amplification, and how to do numerical modelling of
such components. We will then identify advantages
and disadvantages of amplifiers based on PCF
technology compared to conventional fibers, and then
go into greater detail on some of these specific
applications, such as low pump power amplifiers, and
high-power double-clad amplifiers and lasers. 相似文献
7.
Steen Ryom-Hansen 《Journal of Algebraic Combinatorics》2006,23(1):5-20
We generalize Soergel's tilting algorithm to singular weights and deduce from this the validity of the Lascoux-Leclerc-Thibon
conjecture on the connection between the canonical basis of the basic submodule of the Fock module and the representation
theory of the Hecke-algebras at root of unity.
Supported in part by Programa Reticulados y Ecuaciones and by FONDECYT grant 1051024. 相似文献
8.
Malene Steen Nielsen Flagga Frank Antonsen 《International Journal of Theoretical Physics》2004,43(9):1917-1930
We show that stable causality is related to the vanishing of the top Stiefel–Whitney class of a space-time manifold M, and that if M is a stably causal space-time manifold, then it is the boundary of a five-dimensional space-time. We then propose a scheme for making it both a necessary and sufficient condition. 相似文献
9.
Morten Nielsen 《Advances in Computational Mathematics》2007,27(2):195-209
Given a dilation matrix A :ℤd→ℤd, and G a complete set of coset representatives of 2π(A
−Tℤd/ℤd), we consider polynomial solutions M to the equation ∑
g∈G
M(ξ+g)=1 with the constraints that M≥0 and M(0)=1. We prove that the full class of such functions can be generated using polynomial convolution kernels. Trigonometric
polynomials of this type play an important role as symbols for interpolatory subdivision schemes. For isotropic dilation matrices,
we use the method introduced to construct symbols for interpolatory subdivision schemes satisfying Strang–Fix conditions of
arbitrary order.
Research partially supported by the Danish Technical Science Foundation, Grant No. 9701481, and by the Danish SNF-PDE network. 相似文献
10.
Örn Helgason Haraldur P. Gunnlaugsson Siguröur Steinthorsson Steen Mørup 《Hyperfine Interactions》1992,70(1-4):981-984
Mössbauer spectroscopy of basalt lava samples, exhibiting reversible thermal magnetization (JS-T) curves with Curie temperatures of about 580°C, has revealed considerable amounts of maghemite (γ-Fe2O3) in many samples. In view of the expected instability, of maghemite at temperatures above 350°C, this reversibility is rather surprising. Here we report Mössbauer studies on heated lava samples, showing high content of maghemite. The samples were kept at 600°C in oxidizing, reducing, and inactive atmospheres, respectively, for different lengths of time, and then analyzed with Mössbauer spectroscopy at room temperature. The Mössbauer spectra showed that maghemite is stable in the oxidizing atmosphere for at least several hours. In the inactive atmosphere a considerable amount of maghemite still exists after two hours heating. In the reducing atmosphere maghemite had transformed to magnetite after only 30 minutes. 相似文献