全文获取类型
收费全文 | 339410篇 |
免费 | 4433篇 |
国内免费 | 1319篇 |
专业分类
化学 | 186866篇 |
晶体学 | 4614篇 |
力学 | 13666篇 |
综合类 | 7篇 |
数学 | 41272篇 |
物理学 | 98737篇 |
出版年
2021年 | 2048篇 |
2020年 | 2365篇 |
2019年 | 2331篇 |
2018年 | 2282篇 |
2017年 | 2190篇 |
2016年 | 4553篇 |
2015年 | 3808篇 |
2014年 | 5062篇 |
2013年 | 15385篇 |
2012年 | 12133篇 |
2011年 | 15083篇 |
2010年 | 9163篇 |
2009年 | 9047篇 |
2008年 | 13858篇 |
2007年 | 14040篇 |
2006年 | 13656篇 |
2005年 | 12520篇 |
2004年 | 11167篇 |
2003年 | 9845篇 |
2002年 | 9632篇 |
2001年 | 10409篇 |
2000年 | 8023篇 |
1999年 | 6392篇 |
1998年 | 5156篇 |
1997年 | 4997篇 |
1996年 | 5102篇 |
1995年 | 4616篇 |
1994年 | 4345篇 |
1993年 | 4149篇 |
1992年 | 4646篇 |
1991年 | 4476篇 |
1990年 | 4173篇 |
1989年 | 3988篇 |
1988年 | 4289篇 |
1987年 | 3946篇 |
1986年 | 3818篇 |
1985年 | 5589篇 |
1984年 | 5645篇 |
1983年 | 4578篇 |
1982年 | 4993篇 |
1981年 | 5059篇 |
1980年 | 4774篇 |
1979年 | 4892篇 |
1978年 | 4891篇 |
1977年 | 4828篇 |
1976年 | 4770篇 |
1975年 | 4688篇 |
1974年 | 4530篇 |
1973年 | 4701篇 |
1972年 | 2640篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
It is shown that the non-trivial cocycles on simple Lie algebras may be used to introduce antisymmetric multibrackets which
lead to higher-order Lie algebras, the definition of which is given. Their generalised Jacobi identities turn out to be satisfied
by the antisymmetric tensors (or higher-order “structure constants”) which characterise the Lie algebra cocycles. This analysis
allows us to present a classification of the higher-order simple Lie algebras as well as a constructive procedure for them.
Our results are synthesised by the introduction of a single, complete BRST operator associated with each simple algebra.
Received: 3 June 1996 / Accepted: 8 November 1996 相似文献
952.
We give a simple proof that everyk-connected bipartite tournament has a cycle through every set ofk vertices. This was conjectured in [4].This research was done while the first author was visiting Laboratoire de Recherche en Informatique, universite Paris-Sud whose hospitality and financial support is gratefully acknowledged 相似文献
953.
954.
Hyperfine Interactions - Conversion electron Mössbauer spectroscopy measurements have been made on a diamond sample synthesized by chemical vapour deposition. The sample was implanted with 70... 相似文献
955.
A class of long-range predictive adaptive fuzzy relational controllers is presented. The plant behavior is described over an extended time horizon by a fuzzy relational model which is identified based on input-output closed-loop observations of the plant variables. In this class of adaptive controllers the control law attempts to minimize a quadratic cost over an extended control horizon. When used with linear models, this approach has revealed a significant potential for overcoming the limitations of one-step ahead schemes, such as the stabilization of non-minimum phase plants. Here, a uniform framework is adopted for implementing both the fuzzy model and the fuzzy controller, namely distributed fuzzy relational structures gaining from their massive parallel processing features and from the learning capabilities typical of the connectivist approaches. Issues such as maintenance during the adaptation process of the meaning of linguistic terms used at both fuzzy systems interfaces are addressed, namely by introducing a new design methodology for on-line fuzzy systems interface adaptation. The examples presented reinforce the claim of the usefulness of this new approach. 相似文献
956.
M.J. Aslam 《The European Physical Journal C - Particles and Fields》2007,49(3):651-656
The effect of weak annihilation and u-quark penguin contribution on the branching ratio B→K1γ at next-to-leading order of αs are calculated using the LEET approach. It is shown that the value of the LEET form factor remains the same in the range
of the unitarity triangle phase α favored by the standard model. The CP-asymmetry for the above mentioned decay has been calculated,
and its suppression due to the hard-spectator correction has also been incorporated. In addition, the sensitivity of the CP-asymmetry
on the underlying parameters has been discussed. 相似文献
957.
N.N. Smirnov V.F. Nikitin J. Khadem Sh. Alyari-Shourekhdeli 《Proceedings of the Combustion Institute》2007,31(2):2195-2204
Investigations of detonation onset in pulverized fuel–air mixtures were carried out. Combustion and detonation processes in sprays differ greatly from that in homogeneous mixtures, because not only chemical reactions, but physical processes of combustible mixture formation take place within the combustion zone (droplets atomization and evaporation). The polydispersed character of mixture and non-uniformity of droplet spatial distribution strongly affects spray combustion and detonation onset. The present paper contains the results of theoretical and experimental investigations of detonation onset peculiarities in polydispersed non-uniform hydrocarbon–air mixtures. 相似文献
958.
During irradiation of liquid samples of 1-vinylimidazole, 2-vinylnaphthalene, 2-vinylpyridine, 4-vinylpyridine and 1,1-diphenylethene
with positive muons, radicals of the type MuCH2ĊHAr (Ar=the appropriate aromatic group), and the MuCH2ĊPh2 radical were observed by transverse field μSR; the muon hyperfine couplings are considered in the context of the effectiveness
of the aryl groups in delocalising the unpaired electron. 相似文献
959.
C.J. Lu H.M. Shen S.B. Ren Y.N. Wang 《Applied Physics A: Materials Science & Processing》1997,65(4-5):395-401
3 thin films is systematically studied by using X-ray diffraction (XRD). The PbTiO3 thin films with different average grain sizes were prepared on various substrates by a sol-gel process. The films on NaCl
and fused glass are randomly grain-oriented, while those on (111)Pt/Ti/SiO2/Si are highly {100} cubic index grain-oriented . It is found from the XRD patterns of the films on NaCl that with decreasing
average grain size from 230 to 80 nm, the intensities of high h index (h>l) peaks (hkl), such as (100), (110), (200), (201),
(210), (211), etc., decrease rapidly and ultimately disappear, whereas another set of peaks (lkh), including (001), (002),
(102), (112), etc., are still intense. This interesting result suggests that at grain size below a certain critical size an
increasing number of grains no longer show 90°-domains, which is confirmed by TEM observations. Meanwhile, X-ray evidence
of such a grain-size-related absence of 90°-domains is also found for PbTiO3 films on Pt(111) and fused-glass substrates. The volume fractions of single-domain grains (without 90°-domains) in the films
are estimated from their XRD patterns. By combining SEM and TEM investigations, the critical grain size for the formation
of 90°-domains is further determined to be near 200 nm.
Received: 19 December 1996/Accepted: 24 March 1997 相似文献
960.
We derive a q-deformed version of the Lorentz algebra by deforming the algebraSL(2,C). The method is based on linear representations of the algebra on the complex quantum spinor space. We find that the generators usually identified withSL q(2,C) generateSU q (2) only. Four additional generators are added which generate Lorentz boosts. The full algebra of all seven generators and their coproduct is presented. We show that in the limitq→1 the generators are those of the classical Lorentz algebra plus an additionalU(1). Thus we have a deformation ofSL(2,C)×U(1). 相似文献