全文获取类型
收费全文 | 6045篇 |
免费 | 696篇 |
国内免费 | 743篇 |
专业分类
化学 | 1014篇 |
晶体学 | 35篇 |
力学 | 434篇 |
综合类 | 185篇 |
数学 | 4104篇 |
物理学 | 1712篇 |
出版年
2024年 | 9篇 |
2023年 | 58篇 |
2022年 | 100篇 |
2021年 | 143篇 |
2020年 | 136篇 |
2019年 | 141篇 |
2018年 | 156篇 |
2017年 | 168篇 |
2016年 | 192篇 |
2015年 | 146篇 |
2014年 | 281篇 |
2013年 | 443篇 |
2012年 | 292篇 |
2011年 | 358篇 |
2010年 | 309篇 |
2009年 | 418篇 |
2008年 | 447篇 |
2007年 | 455篇 |
2006年 | 385篇 |
2005年 | 326篇 |
2004年 | 319篇 |
2003年 | 321篇 |
2002年 | 295篇 |
2001年 | 219篇 |
2000年 | 192篇 |
1999年 | 207篇 |
1998年 | 183篇 |
1997年 | 149篇 |
1996年 | 106篇 |
1995年 | 81篇 |
1994年 | 86篇 |
1993年 | 39篇 |
1992年 | 44篇 |
1991年 | 31篇 |
1990年 | 30篇 |
1989年 | 30篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1986年 | 14篇 |
1985年 | 23篇 |
1984年 | 22篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1974年 | 9篇 |
排序方式: 共有7484条查询结果,搜索用时 15 毫秒
11.
James Murdock 《Journal of Differential Equations》2004,205(2):424-465
Hypernormal forms (unique normal forms, simplest normal forms) are investigated both from the standpoint of foundational theory and algorithms suitable for use with computer algebra. The Baider theory of the Campbell-Hausdorff group is refined, by a study of its subgroups, to determine the smallest substages into which the hypernormalization process can be divided. This leads to a linear algebra algorithm to compute the generators needed for each substage with the least amount of work. A concrete interpretation of Jan Sanders’ spectral sequence for hypernormal forms is presented. Examples are given, and a proof is given for a little-known theorem of Belitskii expressing the hypernormal form space (in the inner product style) as the kernel of a higher-order differential operator. 相似文献
12.
We introduce the notion of an invariant of characteristics for a system of first-order partial differential equations. We prove that the existence of invariants is connected with passiveness of some systems. We describe a few methods for construction of new invariants from those already known. We give a scheme for application of the invariants to reduction and integration of systems of partial differential equations. As an application we consider the equation of gas dynamics. 相似文献
13.
Song LI Guo Mao WANG Zhi Song LIU 《数学学报(英文版)》2005,21(6):1475-1486
The purpose of this paper is to investigate the mean size formula of wavelet packets in Lp for 0 〈 p ≤ ∞. We generalize a mean size formula of wavelet packets given in terms of the p-norm joint spectral radius and we also give some asymptotic formulas for the Lp-norm or quasi-norm on the subdivision trees. All results will be given in the general setting, 相似文献
14.
弱拓扑和强可容许拓扑之间的一个关系 总被引:2,自引:0,他引:2
本文对局部凸空间X及其对偶X′,建立了弱拓扑σ(X,X′)和强拓扑β(X,X′)之间的一个新关系,改进了有关(X,X′)--可容许拓扑全体上的不变性结果。 相似文献
15.
曾六川 《高等学校计算数学学报(英文版)》2003,12(1)
The purpose of this paper is to investigate the problem of approximating fixed points of non-Lipschitizian asymptotically pseudocontractive mappings in an arbitrary real Banach space by the modified Ishikawa iterative sequences with errors. 相似文献
16.
Fukuji Higashi Kanako Sugishita 《Journal of polymer science. Part A, Polymer chemistry》2004,42(1):44-51
A two‐stage co‐oligomerization of the oligomers initially formed from an equimolar mixture of isophthalic acid (IPA) and terephthalic acid (TPA) and 2,2‐bis(4‐hydroxyphenyl)propane (BPA, 50 mol %) with bisphenols (BPs, 20 mol %) was carried out using a tosyl chloride/dimethylformamide/pyridine condensing agent. The distributions of the resulting oligomers (nx‐mers), which were quenched with methanol, were determined by a combination of gel permeation chromatography (GPC) and NMR. These distributions (presented by molar percentage) were conveniently calculated with the equation nx (mol %) = nx (% mol by GPC) × n0 (mol % by NMR)/n0 (% mol by GPC), where nx (% mol) = nx (wt % by GPC)/its molecular weight. The results showed the distributions of the preformed IPA/TPA‐BPA oligomers to be in fairly good accord with those obtained directly from GPC and to be supported by the NMR results. The calculation was applied to the co‐oligomers prepared up to a reaction of 0.7, at which there was an increase in the number of higher oligomers indivisible by GPC and the distributions could no longer be determined by molar percentage. The calculated distributions are discussed in relation to the results of copolycondensation. The sequence distributions in the resulting co‐oligomers, which were also examined by NMR, are compared with those in the copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 44–51, 2004 相似文献
17.
18.
Shea-Ming Oon 《Periodica Mathematica Hungarica》2004,49(2):107-118
In this paper we study some pseudo-random properties related to the prime factors of integers. We prove some results concerning the well distribution of the greatest prime factor modulo 4, and give some computational insight on the correlations, which seem to be beyond reach of proof. 相似文献
19.
The main purpose of this paper is to use a mean value theorem of Dirichlet L-functions to study the asymptotic property of a hybrid mean value of a generalized Cochrane sum, and give an interesting mean value formula.2000 Mathematics Subject Classification: Primary—11F20; Secondary—11F99 相似文献
20.
Results of experimental investigations of the volt-brightness characteristics, frequency dependences of brightness, and the
directional radiation pattern of electroluminescent MSDM, MSCM, and MSDCM emitters, where M stands for the first transparent
and second nontransparent electrodes, S is a semiconductor, D is a thin-film dielectric, and C is a silicone-based composite
liquid dielectric with a powdered segnetoelectric filler, developed on conventional “smooth” and rough glass substrates are
presented. It is shown that electroluminescent structures on rough surfaces have a brightness approximately two times higher
than that of similar structures developed on a “smooth” substrate.
Ul’yanovsk State University, 42, L. Tolstoi St., Ul’yanovsk, 432700, Russia. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 64, No. 4, pp. 507–512, July–August, 1997. 相似文献