全文获取类型
收费全文 | 5003篇 |
免费 | 241篇 |
国内免费 | 33篇 |
专业分类
化学 | 3600篇 |
晶体学 | 17篇 |
力学 | 123篇 |
数学 | 866篇 |
物理学 | 671篇 |
出版年
2023年 | 41篇 |
2022年 | 54篇 |
2021年 | 91篇 |
2020年 | 116篇 |
2019年 | 110篇 |
2018年 | 68篇 |
2017年 | 55篇 |
2016年 | 154篇 |
2015年 | 139篇 |
2014年 | 177篇 |
2013年 | 277篇 |
2012年 | 313篇 |
2011年 | 359篇 |
2010年 | 252篇 |
2009年 | 199篇 |
2008年 | 314篇 |
2007年 | 314篇 |
2006年 | 301篇 |
2005年 | 300篇 |
2004年 | 236篇 |
2003年 | 207篇 |
2002年 | 212篇 |
2001年 | 82篇 |
2000年 | 69篇 |
1999年 | 70篇 |
1998年 | 59篇 |
1997年 | 64篇 |
1996年 | 69篇 |
1995年 | 44篇 |
1994年 | 38篇 |
1993年 | 23篇 |
1992年 | 19篇 |
1991年 | 31篇 |
1990年 | 19篇 |
1989年 | 30篇 |
1988年 | 18篇 |
1986年 | 19篇 |
1985年 | 28篇 |
1984年 | 30篇 |
1983年 | 27篇 |
1982年 | 33篇 |
1981年 | 23篇 |
1980年 | 25篇 |
1979年 | 18篇 |
1978年 | 33篇 |
1977年 | 20篇 |
1976年 | 15篇 |
1975年 | 12篇 |
1974年 | 18篇 |
1973年 | 10篇 |
排序方式: 共有5277条查询结果,搜索用时 15 毫秒
121.
122.
Marc A. Little Jonathan J. Loughrey Amedeo Santoro Malcolm A. Halcrow Michaele J. Hardie 《Tetrahedron letters》2014
The synthesis of four 3,4-di(alkylsulfanyl)benzyl alcohol derivatives is described, in five steps from methyl 3,4-di(hydroxy)benzoate via a Newman–Kwart rearrangement. Incubation of these derivatives in formic acid affords 2,3,7,8,12,13-hexakis(alkylsulfanyl)-10,15-dihydro-5H-tribenzo[a,d,g]cyclononene products, which are hexa-sulfanyl analogues of the well-known supramolecular cavitand host, cyclotriveratrylene (CTV). The yield of this cyclization depends strongly on the alkylsulfanyl substituents present, in the order SMe > SEt ≈ SiPr ? SBn. A crystal structure determination of one of the cyclotrimers shows a mode of self-association that is commonly exhibited by CTV itself. 相似文献
123.
124.
125.
Thomas Courant Valrie Gaëlle Roullin Cyril Cadiou Maït Callewaert Marie Christine Andry Christophe Portefaix Christine Hoeffel Marie Christine deGoltstein Marc Port Sophie Laurent Luce Vander Elst Robert Muller Michaël Molinari Franoise Chuburu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2012,124(36):9253-9256
126.
Marzena Z. Kastyak-Ibrahim Domenico L. Di Curzio Richard Buist Sheryl L. Herrera Benedict C. Albensi Marc R. Del Bigio Melanie Martin 《Magnetic resonance imaging》2013
Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is the most common cause of dementia in aging populations. Although senile plaques and neurofibrillary tangles are well-established hallmarks of AD, changes in cerebral white matter correlate with cognitive decline and may increase the risk of the development of dementia. We used the triple transgenic (3xTg)-AD mouse model of AD, previously used to show that white matter changes precede plaque formation, to test the hypothesis that MRI detectable changes occur in the corpus callosum, external capsule and the fornix. T2-weighted and diffusion tensor magnetic resonance imaging and histological stains were employed to assess white matter in older (11–17 months) 3xTg-AD mice and controls. We found no statistically significant changes in white matter between 3xTg-AD mice and controls, despite well-developed neurofibrillary tangles and beta amyloid immunoreactive plaques. Myelin staining was normal in affected mice. These data suggest that the 3xTg-AD mouse model does not develop MRI detectable white matter changes at the ages we examined. 相似文献
127.
Núria Alegret Marc Mulet-Gas Xavier Aparicio-Anglès Antonio Rodríguez-Fortea Josep M. Poblet 《Comptes Rendus Chimie》2012,15(2-3):152-158
The electronic structure of endohedral metallofullerenes is rationalized by connecting the apparently independent orbital and topological rules that explain the stability of this family of fullerenes. The separation of the 12 pentagons of the fullerene, which is maximized in order to minimize the Coulomb repulsion, is found to be correlated with the orbital energies of the cage that accepts the electron transfer from the internal cluster. An explanation for the absence of non-IPR cages in large-size EMFs is also provided. 相似文献
128.
Eva C. Sonnenschein Marc Stierhof Stephan Goralczyk Floriane M. Vabre Leonie Pellissier Kine Østnes Hanssen Mercedes de la Cruz Caridad Díaz Peter de Witte Daniëlle Copmans Jeanette Hammer Andersen Espen Hansen Venke Kristoffersen José R. Tormo Rainer Ebel Bruce F. Milne Hai Deng Lone Gram Jioji N. Tabudravu 《Tetrahedron》2017,73(18):2633-2637
A new siderophore containing a 4,5-dihydroimidazole moiety was isolated from Pseudoalteromonas piscicida S2040 together with myxochelins A and B, alteramide A and its cycloaddition product, and bromo- and dibromoalterochromides. The structure of pseudochelin A was established by spectroscopic techniques including 2D NMR and MS/MS fragmentation data. In bioassays selected fractions of the crude extract of S2040 inhibited the opportunistic pathogen Pseudomonas aeruginosa. Pseudochelin A displayed siderophore activity in the chrome azurol S assay at concentrations higher than 50 μM, and showed weak activity against the fungus Aspergillus fumigatus, but did not display antibacterial, anti-inflammatory or anticonvulsant activity. 相似文献
129.
Aleksandr I. Chumakov Ilya Sergeev Jean‐Philippe Celse Rudolf Rüffer Marc Lesourd Lin Zhang Manuel Sánchez del Río 《Journal of synchrotron radiation》2014,21(2):315-324
The performance of a cryogenically cooled double‐crystal silicon monochromator was studied under high‐heat‐load conditions with total absorbed powers and power densities ranging from 8 to 780 W and from 8 to 240 W mm?2, respectively. When the temperature of the first crystal is maintained close to the temperature of zero thermal expansion of silicon, the monochromator shows nearly ideal performance with a thermal slope error of 0.6 µrad. By tuning the size of the first slit, the regime of the ideal performance can be maintained over a wide range of heat loads, i.e. from power densities of 110 W mm?2 (at total absorbed power of 510 W) to 240 W mm?2 (at total absorbed power of 240 W). 相似文献
130.