全文获取类型
收费全文 | 51771篇 |
免费 | 1660篇 |
国内免费 | 21篇 |
专业分类
化学 | 31219篇 |
晶体学 | 308篇 |
力学 | 862篇 |
综合类 | 1篇 |
数学 | 9905篇 |
物理学 | 11157篇 |
出版年
2023年 | 351篇 |
2022年 | 303篇 |
2021年 | 520篇 |
2020年 | 733篇 |
2019年 | 697篇 |
2018年 | 1051篇 |
2017年 | 964篇 |
2016年 | 1806篇 |
2015年 | 1532篇 |
2014年 | 1524篇 |
2013年 | 3356篇 |
2012年 | 3117篇 |
2011年 | 3026篇 |
2010年 | 2043篇 |
2009年 | 1732篇 |
2008年 | 2626篇 |
2007年 | 2348篇 |
2006年 | 2129篇 |
2005年 | 2109篇 |
2004年 | 1840篇 |
2003年 | 1518篇 |
2002年 | 1334篇 |
2001年 | 1039篇 |
2000年 | 1041篇 |
1999年 | 738篇 |
1998年 | 583篇 |
1997年 | 501篇 |
1996年 | 663篇 |
1995年 | 486篇 |
1994年 | 555篇 |
1993年 | 502篇 |
1992年 | 522篇 |
1991年 | 450篇 |
1990年 | 496篇 |
1989年 | 401篇 |
1988年 | 395篇 |
1987年 | 365篇 |
1986年 | 358篇 |
1985年 | 503篇 |
1984年 | 472篇 |
1983年 | 384篇 |
1982年 | 379篇 |
1981年 | 383篇 |
1980年 | 314篇 |
1979年 | 312篇 |
1978年 | 322篇 |
1977年 | 313篇 |
1976年 | 321篇 |
1974年 | 288篇 |
1973年 | 291篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Jiří Čtyroký 《Optical and Quantum Electronics》2006,38(1-3):45-62
The bi-directional mode expansion propagation algorithm (BEP) is known to be an accurate and efficient method for modelling field distribution in high-index contrast waveguide structures with strong back-reflections like Bragg gratings and photonic crystals. The main difficulty of this method is that for lossy structures, the propagation constants of modes are to be searched in the complex plane. To speed-up this procedure, a two-step algorithm for eigenmode calculation based on the expansion into the modes of an empty metallic waveguide has recently been proposed. Proper truncation rules possessing good convergence of the expansion method for both TE and TM modes have also been recently published. In this contribution, both these approaches are combined in the development of an extremely simple version of the two-dimensional BEP method that makes use of the field expansion into the eigenmodes of a parallel-plate waveguide. The method is strictly reciprocal and appeared to be computationally reliable also for strongly lossy structures. High numerical stability is ensured using the scattering matrix formalism, and an efficient method of calculating Bloch modes for symmetric as well as asymmetric periodic waveguide structures is adopted. A wide range of applicability of the method is demonstrated by a few examples. 相似文献
122.
Márton Kiss 《Acta Mathematica Hungarica》2006,110(3):253-259
Summary New results for the eigenvalue ratios of vibrating strings are presented partially in connection with previous results concerning
Schr?dinger operators. 相似文献
123.
In this note we study uncertainty sequencing situations, i.e., one-machine sequencing situations in which no initial order
is specified. We associate cooperative games with these sequencing situations, study their core, and provide links with the
classic sequencing games introduced by Curiel et al. (Eur J Oper Res 40:344–351, 1989). Moreover, we propose and characterize
two simple cost allocation rules for uncertainty sequencing situations with equal processing times. 相似文献
124.
N. Hegyvári 《Acta Mathematica Hungarica》1989,53(1-2):149-154
125.
In [3] it was shown that a (real) signed measure on a cyclic coarse-grained quantum logic can be extended, as a signed measure,
over the entire power algebra. Later ([9]) this result was re-proved (and further improved on) and, moreover, the non-negative
measures were shown to allow for extensions as non-negative measures. In both cases the proof technique used was the technique
of linear algebra. In this paper we further generalize the results cited by extending group-valued measures on cyclic coarse-grained
quantum logics (or non-negative group-valued measures for lattice-ordered groups). Obviously, the proof technique is entirely
different from that of the preceding papers. In addition, we provide a new combinatorial argument for describing all atoms
of cyclic coarse-grained quantum logics. 相似文献
126.
We study the spectral properties of a large class of compact flat Riemannian manifolds of dimension 4, namely, those whose
corresponding Bieberbach groups have the canonical lattice as translation lattice. By using the explicit expression of the
heat trace of the Laplacian acting on p-forms, we determine all p-isospectral and L-isospectral pairs and we show that in this class of manifolds, isospectrality on functions and isospectrality on p-forms for all values of p are equivalent to each other. The list shows for any p, 1 ≤ p ≤ 3, many p-isospectral pairs that are not isospectral on functions and have different lengths of closed geodesics. We also determine
all length isospectral pairs (i.e. with the same length multiplicities), showing that there are two weak length isospectral
pairs that are not length isospectral, and many pairs, p-isospectral for all p and not length isospectral.
Mathematics Subject Classifications (2000): 58J53, 58C22, 20H15. 相似文献
127.
Summary The gas chromatographic behaviour of crosslinked macroporous 2-hydroxyethyl methacrylate grafted with 2-methyloxazoline was
investigated and the range of applicability of the copolymer was assessed. Retention index values were measured on this copolymer
and compared with those obtained on the terpolymer 2-hydroxyethyl methacrylate-ethylene dimethacrylate-acrylonitrile. Rohrschneider
constants and efficiency data for selected sorbates are given. The use of this type of polymer in the separation of various
types of compounds is documented by various examples. 相似文献
128.
Covering numbers of precompact symmetric convex subsets of Hilbert spaces are investigated. Lower bounds are derived for sets containing orthogonal subsets with norms of their elements converging to zero sufficiently slowly. When these sets are convex hulls of sets with power-type covering numbers, the bounds are tight. The arguments exploit properties of generalized Hadamard matrices. The results are illustrated by examples from machine learning, neurocomputing, and nonlinear approximation. 相似文献
129.
130.