全文获取类型
收费全文 | 1243篇 |
免费 | 42篇 |
国内免费 | 6篇 |
专业分类
化学 | 735篇 |
晶体学 | 14篇 |
力学 | 44篇 |
数学 | 248篇 |
物理学 | 250篇 |
出版年
2022年 | 7篇 |
2021年 | 13篇 |
2020年 | 13篇 |
2019年 | 13篇 |
2018年 | 16篇 |
2017年 | 15篇 |
2016年 | 24篇 |
2015年 | 32篇 |
2014年 | 42篇 |
2013年 | 65篇 |
2012年 | 62篇 |
2011年 | 74篇 |
2010年 | 44篇 |
2009年 | 51篇 |
2008年 | 47篇 |
2007年 | 70篇 |
2006年 | 68篇 |
2005年 | 52篇 |
2004年 | 62篇 |
2003年 | 48篇 |
2002年 | 52篇 |
2001年 | 32篇 |
2000年 | 23篇 |
1999年 | 17篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 24篇 |
1995年 | 19篇 |
1994年 | 20篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 14篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 30篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1973年 | 3篇 |
1970年 | 3篇 |
排序方式: 共有1291条查询结果,搜索用时 31 毫秒
831.
Jaume Masoliver 《Journal of statistical physics》2002,109(1-2):339-340
832.
833.
S. Fernandez-Valverde E. Ordońez-Regil P. Bosch G. Duplâtre 《Journal of Radioanalytical and Nuclear Chemistry》1998,231(1-2):127b-132
Several attempts have been made to synthesize mixed-valence compound of antimony at low temperature in view of studying the
isotopic exchange in solids. The experimental procedure for the synthesis, at 263 K of Cs4(SbIIICl6)(SbVCl6) has been established. This compound seems very promising for isotopic exchange studies in the solid state. 相似文献
834.
Jaume Gin 《Chaos, solitons, and fractals》2005,26(5):1259-1266
In this work it is shown that the intrinsic phenomenon (the quantization of the energy) that appears in the first and simple systems studied initially by the quantum theory as the harmonic oscillator and the movement of a charged particle under the Coulomb force, can be obtained from the study of dissipative systems. In others words, we show that this phenomenon of the quantization of the energy of a particle which moves as an harmonic oscillator and which loses and wins energy can be obtained via a classical system of equations. The same also applies to the phenomena of the quantization of the energy of a charged particle which moves under the Coulomb force and which loses and wins energy. 相似文献
835.
We present three different ways of getting an actually computable enumeration of Q
+ in the sense of being able to know exactly which rational occupies a given position and vice versa. The first enumeration is based on the Pierce expansion model for representing real numbers. The other two are based on regular continued fractions.The first and third authors were supported by UPF Grant, Support d'Iniciació a la Recerca, # F3087613. 相似文献
836.
J.A. Coarasa David Garcia Jaume Guasch Ricardo A. Jiménez Joan Solà 《The European Physical Journal C - Particles and Fields》1998,2(2):373-392
We analyze the one-loop effects (strong and electroweak) on the unconventional top quark decay mode within the MSSM. The results are presented in the on-shell renormalization scheme with a physically well motivated definition
of . The study of this process at the quantum level is useful to unravel the potential supersymmetric nature of the charged Higgs
emerging from that decay. As compared with the standard mode , the corrections to are large, slowly decoupling and persist at a sizeable level even for all sparticle masses well above the LEP 200 discovery
range. As a matter of fact, the potential size of the SUSY effects, which amount to corrections of several ten percent, could
counterbalance the standard QCD corrections and even make them to appear with the “wrong” sign. Therefore, if the charged
Higgs decay of the top quark is kinematically allowed – a possibility which is not excluded by the existing measurements of
the branching ratio at the Tevatron – it could be an invaluable laboratory to search for “virtual” supersymmetry. While a first significant test
of these effects could possibly be performed at the upgraded Tevatron, a more precise verification would most likely be carried
out in future experiments at the LHC.
Received: 18 April 1997 / Revised version: 18 June 1997 相似文献
837.
838.
Improving the scalability of rule-based evolutionary learning 总被引:2,自引:0,他引:2
Evolutionary learning techniques are comparable in accuracy with other learning methods such as Bayesian Learning, SVM, etc. These techniques often produce more interpretable knowledge than, e.g. SVM; however, efficiency is a significant drawback. This paper presents a new representation motivated by our observations that Bioinformatics and Systems Biology often give rise to very large-scale datasets that are noisy, ambiguous and usually described by a large number of attributes. The crucial observation is that, in the most successful rules obtained for such datasets, only a few key attributes (from the large number of available ones) are expressed in a rule, hence automatically discovering these few key attributes and only keeping track of them contributes to a substantial speed up by avoiding useless match operations with irrelevant attributes. Thus, in effective terms this procedure is performing a fine-grained feature selection at a rule-wise level, as the key attributes may be different for each learned rule. The representation we propose has been tested within the BioHEL machine learning system, and the experiments performed show that not only the representation has competent learning performance, but that it also manages to reduce considerably the system run-time. That is, the proposed representation is up to 2–3 times faster than state-of-the-art evolutionary learning representations designed specifically for efficiency purposes. 相似文献
839.
H. Geissel R. Knöbel Yu. A. Litvinov B. Sun K. Beckert P. Beller F. Bosch D. Boutin C. Brandau L. Chen B. Fabian M. Hausmann C. Kozhuharov J. Kurcewicz S. A. Litvinov M. Mazzocco F. Montes G. Münzenberg A. Musumarra C. Nociforo F. Nolden W. R. Plaß C. Scheidenberger M. Steck H. Weick M. Winkler 《Hyperfine Interactions》2006,173(1-3):49-54
Projectile fragments separated in flight with the FRS have been injected into the storage ring ESR. Operating the ESR in the
isochronous mode has enabled high-resolution mass measurements of short-lived isotopes. Already in our pilot experiments the
Isochronous Mass Spectrometry (IMS) has provided accurate results for a restricted isotope range in the neighborhood of a
selected isotope characterized by the best isochronous condition. In the present experiment this restriction has been overcome
by precise external magnetic rigidity determination (1.5·10–4) at the dispersive midplane of the FRS. In this way the mass resolving power for neutron-rich fission fragments covering
a large mass-over-charge ratio in one spectrum has been improved by up to one order of magnitude and the accuracy by more
than a factor of two. 相似文献
840.
David B. Amabilino Jos‐Luis Serrano Teresa Sierra Jaume Veciana 《Journal of polymer science. Part A, Polymer chemistry》2006,44(10):3161-3174
The preparation of optically active atropoisomeric polymers which present chiral backbones, thanks to induction during their synthesis from stereogenic centers, located far away from the skeleton is possible, thanks principally to semirigid conformations of the promesogenic spacers between them. The result is that chiral “information” can be passed as far as 21 Å from the asymmetric center to the carbon atom that forms the polymeric chain in poly(isocyanide)s. The sense of chiral induction in these conformationally rigid polymers parallels the helical sense of the cholesteric phases, as well as to the helical senses of chiral smectic C phases, induced by the monomers in nematic and smectic C phases, respectively. All these phenomena obey the odd–even rules proposed for chiral sense changes in these liquid crystalline phases. Noncovalent interactions play an important part in the induction process, in which steric arguments can be used to justify the inductions observed. The methodology can be used to prepare macromolecules, which display switching behavior upon thermal or electrochemical stimulus. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3161–3174, 2006 相似文献