全文获取类型
收费全文 | 25199篇 |
免费 | 663篇 |
国内免费 | 140篇 |
专业分类
化学 | 17122篇 |
晶体学 | 151篇 |
力学 | 633篇 |
数学 | 4423篇 |
物理学 | 3673篇 |
出版年
2022年 | 147篇 |
2021年 | 268篇 |
2020年 | 312篇 |
2019年 | 328篇 |
2018年 | 239篇 |
2017年 | 198篇 |
2016年 | 492篇 |
2015年 | 456篇 |
2014年 | 499篇 |
2013年 | 1328篇 |
2012年 | 1167篇 |
2011年 | 1463篇 |
2010年 | 750篇 |
2009年 | 718篇 |
2008年 | 1297篇 |
2007年 | 1321篇 |
2006年 | 1294篇 |
2005年 | 1268篇 |
2004年 | 1101篇 |
2003年 | 938篇 |
2002年 | 839篇 |
2001年 | 372篇 |
2000年 | 294篇 |
1999年 | 253篇 |
1998年 | 282篇 |
1997年 | 312篇 |
1996年 | 366篇 |
1995年 | 247篇 |
1994年 | 292篇 |
1993年 | 271篇 |
1992年 | 255篇 |
1991年 | 253篇 |
1990年 | 209篇 |
1989年 | 244篇 |
1988年 | 250篇 |
1987年 | 212篇 |
1986年 | 208篇 |
1985年 | 308篇 |
1984年 | 349篇 |
1983年 | 231篇 |
1982年 | 373篇 |
1981年 | 355篇 |
1980年 | 325篇 |
1979年 | 326篇 |
1978年 | 331篇 |
1977年 | 300篇 |
1976年 | 285篇 |
1975年 | 259篇 |
1974年 | 263篇 |
1973年 | 243篇 |
排序方式: 共有10000条查询结果,搜索用时 640 毫秒
31.
Robert Krauthgamer Nathan Linial Avner Magen 《Discrete and Computational Geometry》2004,31(3):339-356
The extensive study of metric spaces and their embeddings
has so far focused on embeddings that preserve pairwise distances.
A very intriguing concept introduced by Feige
allows us to quantify the extent to which larger
structures are preserved by a given embedding.
We investigate this concept, focusing on several major graph families
such as paths, trees, cubes, and expanders.
We find some similarities to the regular (pairwise) distortion,
as well as some striking differences. 相似文献
32.
33.
Space time-index plots for probing dynamical nonstationarity 总被引:3,自引:0,他引:3
We propose a simple method to efficiently probe dynamical nonstationarity in observed time series. In a space time-index plot, the density distributions as a function of normalized time-index are V-shaped due to nonstationarity. We show that this method is workable for short data sets and typical examples are illustrated. 相似文献
34.
35.
Robert L. Jerrard Halil Mete Soner 《Calculus of Variations and Partial Differential Equations》2002,14(2):151-191
We study the Ginzburg-Landau functional
for , where U is a bounded, open subset of . We show that if a sequence of functions satisfies , then their Jacobians are precompact in the dual of for every . Moreover, any limiting measure is a sum of point masses. We also characterize the -limit of the functionals , in terms of the function space B2V introduced by the authors in [16,17]: we show that I(u) is finite if and only if , and for is equal to the total variation of the Jacobian measure Ju. When the domain U has dimension greater than two, we prove if then the Jacobians are again precompact in for all , and moreover we show that any limiting measure must be integer multiplicity rectifiable. We also show that the total variation
of the Jacobian measure is a lower bound for the limit of the Ginzburg-Landau functional.
Received: 15 December 2000 / Accepted: 23 January 2001 / Published online: 25 June 2001 相似文献
36.
Emily S. Tepe Ellen S. Deutsch MD Quiana Sampson Stephen Lawless James S. Reilly Robert Thayer Sataloff 《Journal of voice》2002,16(2):244-250
The objective of this study was to determine the incidence of vocal problems in young choir singers and to correlate vocal problems with demographic and behavioral information. A questionnaire addressing vocal habits and hygiene was offered to 571 young choir singers, up to 25 years of age, who sing at least weekly; 129 (22.6%) responded. More than one-half of the respondents had experienced vocal difficulty, particularly older adolescents. Detrimental behaviors and circumstances surveyed were not reflective of the incidence of vocal difficulty, except for morning hoarseness, chronic fatigue, insomnia, and female gender after puberty. Voice care professionals should be aware that self-reported voice difficulties are common among young choral singers, especially postpubescent girls, and children with symptoms consistent with reflux (morning hoarseness) and emotional stress (insomnia). Laryngologists should communicate with choral conductors and singing teachers to enhance early identification and treatment of children with voice complaints, and to develop choral educational strategies that help decrease their incidence. 相似文献
37.
Robert W. Baker Geoffrey R. Pocock Melvyn V. Sargent Edi Twiss 《Tetrahedron: Asymmetry》1993,4(12):2423-2426
Introduction of a 2-isopropoxycarbonyl or 2-NN-dimethylcarbamoyl group into homochiral 1-p-tolyl- or 1-t-butyl-sulfinylnaphthalenes, via directed metalation reaction, followed by ligand coupling reaction with 1-naphthylmagnesium bromide, furnished atropisomeric 1,1′-binaphthyls in 82–95% enantiomeric excess (e.e.). 相似文献
38.
39.
40.
The phase behavior of binary blends of poly(ether ether ketone) (PEEK), sulfonated PEEK, and sulfamidated PEEK with aromatic polyimides is reported. PEEK was determined to be immiscible with a poly(amide imide) (TORLON 4000T). Blends of sulfonated and sulfamidated PEEK with this poly(amide imide), however, are reported here to be miscible in all proportions. Blends of sulfonated PEEK and a poly(ether imide) (ULTEM 1000) are also reported to be miscible. Spectroscopic investigations of the intermolecular interactions suggest that formation of electron donoracceptor complexes between the sulfonated/sulfamidated phenylene rings of the PEEKs and the n-phenylene units of the polyimides are responsible for this miscibility. © 1993 John Wiley & Sons, Inc. 相似文献