全文获取类型
收费全文 | 13974篇 |
免费 | 402篇 |
国内免费 | 48篇 |
专业分类
化学 | 11195篇 |
晶体学 | 75篇 |
力学 | 216篇 |
数学 | 1734篇 |
物理学 | 1204篇 |
出版年
2023年 | 115篇 |
2022年 | 492篇 |
2021年 | 540篇 |
2020年 | 293篇 |
2019年 | 343篇 |
2018年 | 265篇 |
2017年 | 221篇 |
2016年 | 464篇 |
2015年 | 459篇 |
2014年 | 434篇 |
2013年 | 859篇 |
2012年 | 896篇 |
2011年 | 1010篇 |
2010年 | 609篇 |
2009年 | 603篇 |
2008年 | 846篇 |
2007年 | 837篇 |
2006年 | 711篇 |
2005年 | 657篇 |
2004年 | 548篇 |
2003年 | 471篇 |
2002年 | 451篇 |
2001年 | 172篇 |
2000年 | 140篇 |
1999年 | 113篇 |
1998年 | 121篇 |
1997年 | 100篇 |
1996年 | 138篇 |
1995年 | 92篇 |
1994年 | 88篇 |
1993年 | 83篇 |
1992年 | 62篇 |
1991年 | 77篇 |
1990年 | 56篇 |
1989年 | 73篇 |
1988年 | 63篇 |
1987年 | 49篇 |
1986年 | 53篇 |
1985年 | 65篇 |
1984年 | 84篇 |
1983年 | 43篇 |
1982年 | 66篇 |
1981年 | 58篇 |
1980年 | 56篇 |
1979年 | 47篇 |
1978年 | 54篇 |
1977年 | 38篇 |
1976年 | 32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
101.
102.
103.
Anca Petran Teodora Radu Alexandrina Nan Diana Olteanu Adriana Filip Simona Clichici Ioana Baldea Maria Suciu Rodica Turcu 《Journal of nanoparticle research》2017,19(1):10
The paper presents the synthesis, characterization, and in vitro cytotoxicity tests of Fe3O4 magnetic nanoclusters coated with ethylenediaminetetraacetic acid disodium salt (EDTA). Electron microscopy analysis (SEM) evidences that magnetite nanoparticles are closely packed into the clusters stabilized with EDTA with well-defined near spherical shapes and sizes in the range 100–200 nm. From XRD measurements, we determined the mean size of the crystallites inside the magnetic cluster about 36 nm. The saturation magnetization determined for the magnetic clusters stabilized with EDTA has high value, about 81.7 emu/g at 300 K. X-ray photoelectron spectroscopy has been used to determine both the elemental and chemical structure of the magnetic cluster surface. In vitro studies have shown that the magnetic clusters at low doses did not induce toxicity on human umbilical vein endothelial cells or lesions of the cell membrane. In contrast, at high doses, the magnetic clusters increased the lipid peroxidation and reduced the leakage of a cytoplasmic enzyme, lactate dehydrogenase (LDH), in parallel with increasing the antioxidant defense. 相似文献
104.
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
105.
Riassunto In questa nota gli Autori stabiliscono dei principi variazionali che caratterizzano in maniera completa il più generale problema
ai limiti sia della statica sia della dinamica di una miscela isotropa di due solidi elastici lineari. Questi principi sono
del tutto generali poichè non si richiede agli stati o processi ammissibili di soddisfare ad alcuna delle equazioni di campo
e delle condizioni iniziali o al contorno. Tale risultato viene ottenuto esprimendo i problemi considerati in forma operazionale.
Il lavoro è stato eseguito nell’ambito del Gruppo Nazionale per la Fisica Matematica del C.N.R. 相似文献
Summary In this paper the Authors establish variational principles which characterize the most general boundary-value problem for statics and dynamics of an isotropic mixture of two linear elastic solids. These principles are completely general because the admissible states or processes are not required to meet any of the field equations, boundary or initial conditions and they are obtained by expressing the problems in operator form.
Il lavoro è stato eseguito nell’ambito del Gruppo Nazionale per la Fisica Matematica del C.N.R. 相似文献
106.
107.
Maria G. da Fonseca Cassio M. Cardoso Luiza N.H. Arakaki 《Journal of Physics and Chemistry of Solids》2006,67(8):1835-1840
Vermiculite of general formula [Si6.85Al1.15][Mg4.68Al0.51Fe0.63]O20(OH)4Ca0.128Na0.032K0.094 reacted with heteroaromatic amines α-, β-, and γ-picolines from aqueous solution. The products were characterized by elemental analysis, infrared spectroscopy, and X-ray diffraction. The intercalated nanocompounds maintained the crystallinity and changed the original interlayer distance of 1422 pm to 1474, 1456, and 1474 pm, for the sequence of the guest picoline molecules. Natural and intercalated vermiculite can remove copper at the solid/liquid interface; removal 0.40 mmol g−1 was obtained for the original matrix, and 1.10, 0.92, and 1.33 mmol g−1 for the intercalated forms. These values are near the capacity of cation exchange (CEC) of this clay mineral, which can be possibly used as source of copper removal from aqueous solution. 相似文献
108.
Giovanni Bruno Maria M. Giangregorio April S. Brown Soojeong Choi 《Applied Surface Science》2006,253(1):219-223
GaN is grown on Si-face 4H-SiC(0 0 0 1) substrates using remote plasma-assisted methods including metalorganic chemical vapour deposition (RP-MOCVD) and molecular beam epitaxy (MBE). Real time spectroscopic ellipsometry is used for monitoring all the steps of substrate pre-treatments and the heteroepitaxial growth of GaN on SiC. Our characterization emphasis is on understanding the nucleation mechanism and the GaN growth mode, which depend on the SiC surface preparation. 相似文献
109.
A new type of intermittent behavior is described to occur near the boundary of the phase synchronization regime of coupled chaotic oscillators. This mechanism, called ring intermittency, arises for sufficiently high initial mismatches in the frequencies of the two coupled systems. The laws for both the distribution and the mean length of the laminar phases versus the coupling strength are analytically deduced. Very good agreement between the theoretical results and the numerically calculated data is shown. We discuss how this mechanism is expected to take place in other relevant physical circumstances. 相似文献
110.
Maria A. Davidovich E. V. Anda C. A. Büsser G. Chiappe 《Physica B: Condensed Matter》2002,320(1-4):366-369
The T=0 transport properties of a wire interacting with a lateral two-level quantum dot are studied by using an exact numerical calculation. The wire conductance, the spin–spin correlation and the Kondo temperature are obtained as a function of the dot level energy spacing. When the dot has two electrons and spin SD1, the wire current is totally quenched by the S=1 Kondo effect. The Kondo temperature is maximum at the singlet–triplet transition and its dependence upon the dot energy spacing follows a non-universal scaling law. 相似文献