全文获取类型
收费全文 | 13119篇 |
免费 | 435篇 |
国内免费 | 45篇 |
专业分类
化学 | 10453篇 |
晶体学 | 73篇 |
力学 | 210篇 |
数学 | 1676篇 |
物理学 | 1187篇 |
出版年
2023年 | 88篇 |
2022年 | 219篇 |
2021年 | 504篇 |
2020年 | 286篇 |
2019年 | 333篇 |
2018年 | 255篇 |
2017年 | 215篇 |
2016年 | 438篇 |
2015年 | 443篇 |
2014年 | 415篇 |
2013年 | 839篇 |
2012年 | 860篇 |
2011年 | 972篇 |
2010年 | 593篇 |
2009年 | 582篇 |
2008年 | 816篇 |
2007年 | 797篇 |
2006年 | 684篇 |
2005年 | 620篇 |
2004年 | 525篇 |
2003年 | 442篇 |
2002年 | 430篇 |
2001年 | 163篇 |
2000年 | 134篇 |
1999年 | 112篇 |
1998年 | 115篇 |
1997年 | 101篇 |
1996年 | 127篇 |
1995年 | 86篇 |
1994年 | 86篇 |
1993年 | 78篇 |
1992年 | 60篇 |
1991年 | 75篇 |
1990年 | 55篇 |
1989年 | 72篇 |
1988年 | 62篇 |
1987年 | 49篇 |
1986年 | 52篇 |
1985年 | 63篇 |
1984年 | 82篇 |
1983年 | 43篇 |
1982年 | 66篇 |
1981年 | 61篇 |
1980年 | 55篇 |
1979年 | 46篇 |
1978年 | 56篇 |
1977年 | 38篇 |
1976年 | 34篇 |
1975年 | 24篇 |
1963年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Zusammenfassung Die Hydrosole des röntgenamorphen Eisen (III)-hydroxids und seines Polymerysationsprodukts katalysieren in einer Reaktion I. Ordnung mit verschiedener Geschwindigkeit den H2O2-Zerfall, der bei 27° und 37° untersucht wurde. Auch die daraus berechneten Aktivierungsenergien ergaben differente Werte. 相似文献
993.
Maria Cristina Vipera 《Annali dell'Universita di Ferrara》1981,27(1):125-133
Riassunto Si indicano una costruzione e alcune proprietà del morfismo terminale nella categoria degli epimorfismi iniettivi di dato
dominioA, conA anello commutativo unitario ridotto. Si considerano poi certi epimorfismi di dominioA, detti ?S-spezzamenti irriducibili? (S⊂A). GliS-spezzamenti irriducibili a codominio ridotto risultano parametrizzati (a meno di isomorfismi) dai chiusi di una opportuna
topologia su SpecA.
Lavoro eseguito nell’ambito del Gruppo Nazionale Strutture Algebriche e Geometriche e Applicazioni del C.N.R. 相似文献
Summary LetA be any reduced commutative ring with 1. Consider the category of injective ring-epimorphisms with domainA. In the first part of this paper, a construction and some properties of a final morphism in the above category are shown. In the second part, some special epimorphisms with domainA are considered, which are called irreducible ?S-spezzamenti?. A parametrization of the collection of irreducible ?S-spezzamenti? (up to isomorphisms) is given, by the collection of closed sets of a suitable topology on SpecA.
Lavoro eseguito nell’ambito del Gruppo Nazionale Strutture Algebriche e Geometriche e Applicazioni del C.N.R. 相似文献
994.
995.
996.
997.
998.
999.
The purpose of this study was to investigate the reliability of functional magnetic resonance imaging (fMRI) by using either a projection screen or video goggles as stimulus modality. A sequence of visual stimuli were presented to the same subject at different occasions. The sequence was optimized with a genetic algorithm. In five sessions the stimuli were presented using a projection screen viewed through a mirror in the head coil and in five sessions using video goggles. Failure to detect visual activation in the medial left hemisphere was observed in sessions using the projection screen as stimulus modality. Decreased thresholds for P values and cluster size resulted in activation outside the occipital lobe and did not significantly increase activated areas in this region. Results in this study indicate that presentation of fMRI tasks with visual routes is more reliable with direct input through video goggles than with the conventional use of projection screens. Failure to detect crucial visual areas has severe consequences for tumor surgery in the visual cortex. Inferior visual impression might also have negative consequences for cognitive tests with high demand on attention and perception. 相似文献
1000.
Canevali C Mari CM Mattoni M Morazzoni F Nodari L Ruffo R Russo U Scotti R 《The journal of physical chemistry. B》2005,109(15):7195-7202
The mechanism of NO interaction with nanosized Ru(Pd,Pt)-doped SnO(2) was studied by electron paramagnetic resonance, M?ssbauer, and electric resistance measurements. Three steps were proposed for the reaction between the semiconductor oxide and the gaseous component: (i) the formation of bielectronic oxygen vacancies (V(o)) in SnO(2); (ii) their single-ionization (V(o)(*)) with injection of electrons into the SnO(2) conduction band; (iii) the subsequent transfer of electrons from V(o)(*) to [Ru(Pd,Pt)](4+). The last process induces the formation of further oxygen vacancies which reduce the transition metal centers to lower oxidation states; the redox processes is enhanced and the electrical resistance in transition metal-doped SnO(2) is stronger modified with respect to the undoped material. 相似文献