全文获取类型
收费全文 | 1995篇 |
免费 | 42篇 |
国内免费 | 12篇 |
学科分类
数理化 | 2049篇 |
出版年
2022年 | 17篇 |
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 | 38篇 |
1995年 | 27篇 |
1994年 | 14篇 |
1993年 | 29篇 |
1992年 | 25篇 |
1991年 | 20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 | 22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 |
排序方式: 共有2049条查询结果,搜索用时 15 毫秒
1.
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
2.
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
3.
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
4.
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
5.
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
6.
A E Abdel-Megied P Hansen E B Pedersen C M Nielsen 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1991,45(10):1060-1063
The 3'-iodonucleoside 4 and the 3'-O-methylsulfonylthymidine 9 have been synthesized by condensation of silylated uracils 2 with methyl 5-O-tert-butyldiphensilyl-2,3-dideoxy-3-iodo-D-threo-pentofuran oside (3) and methyl 5-O-tert-butyldiphenylsilyl-2-deoxy-3-methylsulfonyl-D-erythro- pentofuranoside (8), respectively. The nucleoside 4 and 9 produced the corresponding 2',3'-didehydro-2',3'-dideoxynucleosides 5 in an elimination reaction on treatment with sodium methoxide. The compounds 5b showed no antiviral activity against HIV-1. 相似文献
7.
Trace pollutants analysis in soil by a time-resolved laser-induced breakdown spectroscopy technique 总被引:5,自引:0,他引:5
A. Ciucci V. Palleschi S. Rastelli R. Barbini F. Colao R. Fantoni A. Palucci S. Ribezzo H. J. L. van der Steen 《Applied physics. B, Lasers and optics》1996,63(2):185-190
The results of a joint experiment of IFAM-Pisa and ENEA-Frascati for the detection of traces of pollutants in soil by a time-resolved laser-induced spectroscopy technique are reported. Using samples of soil with known pollutants' concentration [Geochemical Exploration Reference (GXR) silicate from US Geological Survey], we were able to estimate the sensitivity of this Laser-Induced Breakdown Spectroscopy (LIBS) technique to be of the order of some parts per million for a vast class of metallic pollutants, including extremely dangerous soil pollutants such as copper, lead and chromium.ENEA guest with HC&M fellowship 相似文献
8.
Steen Mørup 《Hyperfine Interactions》1994,90(1):171-185
Interactions between magnetic nanoparticles can lead to superferromagnetic ordering, i.e. ordering of their magnetic moments at low temperatures. The use of a simple mean field theory, describing the temperature dependence of the order parameter is discussed. This model is found to give excellent fits to experimental results. In systems of particles with pure dipole interactions, the degree of ordering depends critically on the geometrical configuration of the particles. The application of superferromagnetic nanostructures for magnetic refrigeration is also discussed. 相似文献
9.
10.