全文获取类型
收费全文 | 3451篇 |
免费 | 154篇 |
国内免费 | 9篇 |
专业分类
化学 | 2351篇 |
晶体学 | 20篇 |
力学 | 128篇 |
数学 | 572篇 |
物理学 | 543篇 |
出版年
2023年 | 33篇 |
2022年 | 44篇 |
2021年 | 66篇 |
2020年 | 75篇 |
2019年 | 80篇 |
2018年 | 61篇 |
2017年 | 50篇 |
2016年 | 110篇 |
2015年 | 106篇 |
2014年 | 103篇 |
2013年 | 152篇 |
2012年 | 234篇 |
2011年 | 242篇 |
2010年 | 135篇 |
2009年 | 109篇 |
2008年 | 226篇 |
2007年 | 216篇 |
2006年 | 218篇 |
2005年 | 194篇 |
2004年 | 105篇 |
2003年 | 100篇 |
2002年 | 79篇 |
2001年 | 53篇 |
2000年 | 40篇 |
1999年 | 34篇 |
1998年 | 41篇 |
1997年 | 29篇 |
1996年 | 32篇 |
1995年 | 23篇 |
1994年 | 28篇 |
1993年 | 26篇 |
1992年 | 24篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 21篇 |
1988年 | 22篇 |
1987年 | 21篇 |
1986年 | 29篇 |
1985年 | 25篇 |
1984年 | 32篇 |
1983年 | 23篇 |
1982年 | 25篇 |
1981年 | 39篇 |
1980年 | 33篇 |
1978年 | 26篇 |
1977年 | 25篇 |
1976年 | 27篇 |
1975年 | 23篇 |
1974年 | 14篇 |
1972年 | 11篇 |
排序方式: 共有3614条查询结果,搜索用时 15 毫秒
1.
E. Rodriguez E. Jimenez G.J. Jacob A.A.R. Neves C.L. Cesar L.C. Barbosa 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):361
Multilayer PbTe quantum dots (QDs) and SiO2 were grown by pulsed laser deposition (PLD) and Plasma enhanced chemical vapor deposition (PECVD) techniques. The crystalline structure, QD size and size dispersion were observed by high-resolution transmission electron microscopy (HRTEM) measurements. This technique allows one to grow PbTe QDs as small as 1.8 nm diameter and 0.6 nm size dispersion. The whole structure can be used in a Fabry–Perot cavity for an optical device operating at the mid-infrared region. 相似文献
2.
Jacob Schach Møller 《Annales Henri Poincare》2005,6(6):1091-1135
In this paper we analyze the bottom of the energy-momentum spectrum of the translation invariant Nelson model, describing
one electron linearly coupled to a second quantized massive scalar field. Our results are valid for all values of the coupling
constant and include an HVZ theorem, non-degeneracy of ground states, existence of isolated groundstates in dimensions 1 and
2, non-existence of ground states embedded in the bottom of the essential spectrum in dimensions 3 and 4, (i.e., at total
momenta where no isolated groundstate eigenvalue exists), and we study regularity and monotonicity properties of the bottom
of the essential spectrum, as a function of total momentum.
Communicated by Joel Feldman
submitted 04/11/04, accepted 17/02/05 相似文献
3.
Bart M. J. M. Suijkerbuijk Duncan M. Tooke Anthony L. Spek Gerard van Koten Robertus J. M. Klein Gebbink Prof. Dr. 《无机化学与普通化学杂志》2007,633(15):2649-2653
A tin(IV) porphyrin was combined with two axial NCN‐pincer platinum(II) fragments by utilizing the oxophilicity of the apical positions on the tin atom and the acidic nature of the NCN‐pincer platinum derived benzoic acid. The solid‐state structure determined by X‐ray crystallography revealed some close contacts between the pincer complexes and the meso‐p‐tolyl subsitutents of the porphyrin. It was shown by 1H NMR spectroscopy that these close contacts were not present in solution and that this compound can potentially act as a novel building block for supramolecular architectures. 相似文献
4.
Jacob Fox 《Journal of Combinatorial Theory, Series A》2006,113(1):84-100
We prove that Rado's Boundedness Conjecture from Richard Rado's 1933 famous dissertation Studien zur Kombinatorik is true if it is true for homogeneous equations. We then prove the first nontrivial case of Rado's Boundedness Conjecture: if a1,a2, and a3 are integers, and if for every 24-coloring of the positive integers (or even the nonzero rational numbers) there is a monochromatic solution to the equation a1x1+a2x2+a3x3=0, then for every finite coloring of the positive integers there is a monochromatic solution to a1x1+a2x2+a3x3=0. 相似文献
5.
The periodic precipitation pattern formation in gelatinous media is interpreted as a moving boundary problem. The time law,
spacing law and width law are revisited on the basis of the new scenario. The explicit dependence of the geometric structure
on the initial concentrations of the reactants is derived. Matalon—Packter law, which relates the spacing coefficient with
the initial concentrations is reformulated removing many ambiguities and impractical parameters. Experimental results are
discussed to establish the significance of moving boundary concept in the diffusion controlled pattern forming systems 相似文献
6.
Bart De Bruyn 《Journal of Algebraic Combinatorics》2006,24(1):23-29
Brouwer and Wilbrink [3] showed the nonexistence of regular near octagons whose parameters s, t2, t3 and t satisfy s ≥ 2, t2 ≥ 2 and t3 ≠ t2(t2+1). Later an arithmetical error was discovered in the proof. Because of this error, the existence problem was still open
for the near octagons corresponding with certain values of s, t2 and t3. In the present paper, we will also show the nonexistence of these remaining regular near octagons.
MSC2000 05B25, 05E30, 51E12
Postdoctoral Fellow of the Research Foundation - Flanders 相似文献
7.
Valuations of dense near polygons were introduced in 16 . In the present paper, we classify all valuations of the near hexagons ??1 and ??2, which are related to the respective Witt designs S(5,6,12) and S(5,8,24). Using these classifications, we prove that if a dense near polygon S contains a hex H isomorphic to ??1 or ??2, then H is classical in S. We will use this result to determine all dense near octagons that contain a hex isomorphic to ??1 or ??2. As a by‐product, we obtain a purely geometrical proof for the nonexistence of regular near 2d‐gons, d ≥ 4, whose parameters s, t, ti (0 ≤ i ≤ d) satisfy (s, t2, t3) = (2, 1, 11) or (2, 2, 14). The nonexistence of these regular near polygons can also be shown with the aid of eigenvalue techniques. © 2005 Wiley Periodicals, Inc. J Combin Designs 14: 214–228, 2006 相似文献
8.
9.
Two bases of states are presented for modules of the graded parafermionic conformal field theory associated to the coset
. The first one is formulated in terms of the two fundamental (i.e., lowest-dimensional) parafermionic modes. In that basis, one can identify the completely reducible representations, i.e., those whose modules contain an infinite number of singular vectors; the explicit form of these vectors is also given. The second basis is a quasiparticle basis, determined in terms of a modified version of the
exclusion principle. A novel feature of this model is that none of its bases are fully ordered and this reflects a hidden structural
exclusion principle. 相似文献
10.
We consider the semilinear Cauchy problem for a class of pseudo-differential operators generating sub-Markovian semigroups.
Solutions of such problems with negative definite nonlinearity play an important role in constructing branching measure-valued
processes. We establish local existence and uniqueness of solutions in the context of the Dirichlet space associated to the
problem. Comparison and global properties of solutions are also studied.
Accepted 29 August 2001. Online publication 17 December 2001. 相似文献