全文获取类型
收费全文 | 344862篇 |
免费 | 5360篇 |
国内免费 | 1110篇 |
专业分类
化学 | 188752篇 |
晶体学 | 4600篇 |
力学 | 13697篇 |
综合类 | 7篇 |
数学 | 41902篇 |
物理学 | 102374篇 |
出版年
2020年 | 2440篇 |
2019年 | 2285篇 |
2018年 | 2361篇 |
2017年 | 2278篇 |
2016年 | 4737篇 |
2015年 | 3937篇 |
2014年 | 5229篇 |
2013年 | 15708篇 |
2012年 | 12034篇 |
2011年 | 14904篇 |
2010年 | 9133篇 |
2009年 | 8937篇 |
2008年 | 13808篇 |
2007年 | 13974篇 |
2006年 | 13463篇 |
2005年 | 12307篇 |
2004年 | 10960篇 |
2003年 | 9611篇 |
2002年 | 9449篇 |
2001年 | 10644篇 |
2000年 | 8223篇 |
1999年 | 6485篇 |
1998年 | 5231篇 |
1997年 | 5048篇 |
1996年 | 5216篇 |
1995年 | 4735篇 |
1994年 | 4518篇 |
1993年 | 4418篇 |
1992年 | 4840篇 |
1991年 | 4570篇 |
1990年 | 4321篇 |
1989年 | 4089篇 |
1988年 | 4383篇 |
1987年 | 4050篇 |
1986年 | 3904篇 |
1985年 | 5693篇 |
1984年 | 5760篇 |
1983年 | 4721篇 |
1982年 | 5076篇 |
1981年 | 5151篇 |
1980年 | 4870篇 |
1979年 | 4952篇 |
1978年 | 4986篇 |
1977年 | 4952篇 |
1976年 | 4865篇 |
1975年 | 4752篇 |
1974年 | 4595篇 |
1973年 | 4779篇 |
1972年 | 2676篇 |
1971年 | 1997篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Neodymium-substituted Bi4Ti3O12 (BNdT) thin films were prepared by a chemical solution deposition technique on platinum- coated silicon substrates. All of
the samples were annealed at the relatively low temperature of 600 °C by a rapid thermal annealing process in different atmospheres,
such as O2, air, and nitrogen, and vacuum. Irrespective of different annealing atmospheres, all of the BNdT thin films exhibit good
ferroelectric properties, such as a saturated hysteresis loop, good fatigue endurance, and low leakage current density. A
large remanent polarization (Pr) of ∼48 μC/cm2 with an electric field of 240 kV/cm was observed from the BNdT thin film annealed in O2 atmosphere. The BNdT thin films annealed in nitrogen and vacuum, at reduced oxygen partial pressures, exhibit smaller Pr than that annealed in oxygen. The difference of Pr of the BNdT thin films annealed in different atmospheres may originate from differences in the grain sizes and the number
of oxygen vacancies.
PACS 77.55.+f; 77.80.-e; 77.80.Fm; 81.15.-z 相似文献
192.
J. M. Rubi 《Journal of statistical physics》2006,123(2):497-498
193.
In this paper we study root system generalizations of the quantum Bose-gas on the circle with pair-wise delta-function interactions.
The underlying symmetry structures are shown to be governed by the associated graded algebra of Cherednik's (suitably filtered)
degenerate double affine Hecke algebra, acting by Dunkl-type differential-reflection operators. We use Gutkin's generalization
of the equivalence between the impenetrable Bose-gas and the free Fermi-gas to derive the Bethe ansatz equations and the Bethe
ansatz eigenfunctions. 相似文献
194.
Many operators in Banach spaces occur as the integration operator of a suitable vector measure; their compactness is completely described in [19]. However, many important spaces X in analysis (and integration operators in such spaces) do not fall into this scheme because X is not normable. Characterizing the compactness of integration operators in this setting is the aim of this note. The methods and techniques employed are quite different to the Banach space arguments used in [19]. 相似文献
195.
J. Matkowski 《Aequationes Mathematicae》2002,64(3):297-303
Summary. Iteration semigroups of weighted quasi-arithmetic mean-type mappings are considered. Existence and uniqueness of a mean which is invariant with respect to a continuous semigroup of mean-type mapping is proved. 相似文献
196.
P Vincent A BrioudeC Journet S RabasteS.T Purcell J Le BrusqJ.C Plenet 《Journal of Non》2002,311(2):130-137
We report here the successful inclusion of carbon nanotubes (CNs) into a TiO2 matrix prepared by a sol-gel method. The presence of CNs in the sol-gel matrix and the structure of the film were analyzed principally by transmission electron microscopy. Complementary information about the behavior of embedded carbon nanotubes versus heat treatment and ion irradiation were obtained by X-ray photoelectron spectroscopy. The elaboration of an inorganic matrix containing embedded carbon nanotubes leads to a new nanocomposite. The possible applications of this nanocomposite are discussed. 相似文献
197.
Stefan Nörtemann 《Applied Categorical Structures》2002,10(4):417-429
The Hahn–Banach Theorem for partially ordered totally convex modules [3] and a necessary and sufficient condition for the existence of an extension of a morphism from a submodule C
0 of a partially ordered totally convex module C (with the ordered unit ball of the reals as codomain) to C, are proved. Moreover, the categories of partially ordered positively convex and superconvex modules are introduced and for both categories the Hahn–Banach Theorem is proved. 相似文献
198.
We present a new approach to study the convergence of Newton's method in Banach spaces, which relax the conditions appearing in the usual studies. The approach is based on the bound required for the second derivative of the operator involved. An application to a nonlinear integral equation is presented. 相似文献
199.
Nuclear Magnetic Resonance (NMR) was used to investigate the extrusion behaviour of PTFE pastes in a ram extruder. By means
of 1H-NMR imaging (MRI) it is possible to determine the local proton density and therefore, the local fluid concentration. The
19F-MRI provides the local solid concentration. Thus the local saturation and the local porosity can be calculated with the
information of the local fluid and solid concentration. Furthermore displacement profiles can be derived from NMR images by
means of correlation techniques without any preparation or marking of the pastes.
Received: 8 May 2000 Accepted: 1 May 2001 相似文献
200.
Balázs Szendröi 《Mathematische Zeitschrift》2002,240(2):233-241
This note shows that a certain toric quotient of the quintic Calabi-Yau threefold in provides a counterexample to a recent conjecture of Cox and Katz concerning nef cones of toric hypersurfaces.
Received: 8 February 2001; in final form: 17 September 2001 / Published online: 1 February 2002 相似文献