全文获取类型
收费全文 | 1250篇 |
免费 | 29篇 |
国内免费 | 9篇 |
专业分类
化学 | 719篇 |
晶体学 | 4篇 |
力学 | 79篇 |
数学 | 230篇 |
物理学 | 256篇 |
出版年
2023年 | 9篇 |
2022年 | 10篇 |
2021年 | 31篇 |
2020年 | 27篇 |
2019年 | 34篇 |
2018年 | 32篇 |
2017年 | 32篇 |
2016年 | 55篇 |
2015年 | 37篇 |
2014年 | 48篇 |
2013年 | 81篇 |
2012年 | 81篇 |
2011年 | 109篇 |
2010年 | 79篇 |
2009年 | 65篇 |
2008年 | 94篇 |
2007年 | 67篇 |
2006年 | 69篇 |
2005年 | 69篇 |
2004年 | 51篇 |
2003年 | 36篇 |
2002年 | 38篇 |
2001年 | 14篇 |
2000年 | 17篇 |
1999年 | 11篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 11篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 10篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1288条查询结果,搜索用时 15 毫秒
71.
When S is a discrete subsemigroup of a discrete group G suchthat G = S1S, it is possible to extend circle-valuedmultipliers from S to G, to dilate (projective) isometric representationsof S to (projective) unitary representations of G, and to dilate/extendactions of S by injective endomorphisms of a C*-algebra to actionsof G by automorphisms of a larger C*-algebra. These dilationsare unique provided they satisfy a minimality condition. The(twisted) semigroup crossed product corresponding to an actionof S is isomorphic to a full corner in the (twisted) crossedproduct by the dilated action of G. This shows that crossedproducts by semigroup actions are Morita equivalent to crossedproducts by group actions, making powerful tools available tostudy their ideal structure and representation theory. The dilationof the system giving the BostConnes Hecke C*-algebrafrom number theory is constructed explicitly as an application:it is the crossed product C0(Af)Q*+, corresponding to the multiplicativeaction of the positive rationals on the additive group Af offinite adeles. 相似文献
72.
The Einstein–Podolsky–Rosen–Bohm (EPRB) experiment performed with random variable and spatially separated analyzers is a milestone
test in the controversy between Objective Local Theories (OLT) and Quantum Mechanics (QM). Only a few OLT are still possible.
Some of the surviving OLT (specifically, the so called non-ergodic theories) would be undetectable in the averaged statistical
values, but they may leave their trace in the time dynamics. For, while QM predicts random processes, the OLT of this kind
predict the existence of regularities that may be revealed as a low dimensional object in the phase space. We perform a numerical
analysis of the time-resolved data recorded in that experiment to unveil any hypothetical low dimensional dynamics that may
be present. We find no consistent indication of such dynamics except for one data file, the longest of all in the real time.
The possible causes of these dynamics are discussed.
相似文献
73.
Adenilson J. Chiquito Marcia T. Escote Marcelo O. Orlandi Alexandre J.C. Lanfredi Edson R. Leite Elson Longo 《Physica B: Condensed Matter》2007,400(1-2):243-247
This paper reports on the measurements of transport properties of high crystalline quality Sn doped In2O3 nanobelts. The samples presented metallic conduction in a large range of temperatures; however, at low temperatures, the resistivity showed a slight increase and the current–voltage curves showed a tendency to saturate even in the low-voltage range. From these observations, we discuss some arguments on the possibility of low dimensional conducting channels as the main responsible for the conduction at low temperatures. Additionally, we present an alternative technique for production of low resistance ohmic contacts, which can be further used in devices’ construction. 相似文献
74.
75.
Marcelo H. Sousa Geraldo J. da Silva Jrme Depeyrot Francisco A. Tourinho Luiz F. Zara 《Microchemical Journal》2011,97(2):182-187
In this work, inductively coupled plasma emission spectroscopy was utilized to directly determine the chemical composition of magnetic fluids constituted of size-sorted ferrite nanoparticles in aqueous solution. Nickel and cobalt nanoferrites were chemically synthesized following a bottom-up route and dispersed under various pH conditions. Size and structural characteristics of nanograins were investigated by X-ray diffraction using a synchrotron source. Chemical analysis was then carried out by directly introducing diluted magnetic fluid samples (slurries) into the spectrometer. To achieve reliable measurements, sample conditions and apparatus parameters were carefully investigated. Slurry stability must be optimized in order to obtain reproducible and accurate analysis. The instrument must also be calibrated to minimize the difference between the signal produced by slurries and that of aqueous ordinary solutions. Furthermore, slurry sample introduction offers many advantages over conventional sample digestion, including reduced sample pretreatment time, less possibility of contamination and the use of direct calibration with aqueous solutions. 相似文献
76.
77.
78.
79.
Marcelo Samuel Berman 《International Journal of Theoretical Physics》1990,29(6):571-577
We review general relativistic and Brans-Dicke cosmological models of the early universe and for the present phase. Both theories render similar results, in general, as far as Mach's principle is concerned. There is some difference in the stability problem for the inflationary phase, and we point out how to test one theory against the other experimentally. 相似文献
80.
Marcelo Samuel Berman 《International Journal of Theoretical Physics》1990,29(12):1415-1417
A very general flat solution for Brans-Dicke cosmology with a perfect-fluid, Robertson-Walker metric and a perfect gas law of state is examined regarding density perturbations. The model has growing instabilities, but not of exponential character. 相似文献