全文获取类型
收费全文 | 6686篇 |
免费 | 215篇 |
国内免费 | 45篇 |
专业分类
化学 | 4194篇 |
晶体学 | 26篇 |
力学 | 275篇 |
数学 | 1406篇 |
物理学 | 1045篇 |
出版年
2023年 | 30篇 |
2022年 | 56篇 |
2021年 | 140篇 |
2020年 | 146篇 |
2019年 | 118篇 |
2018年 | 114篇 |
2017年 | 87篇 |
2016年 | 245篇 |
2015年 | 188篇 |
2014年 | 230篇 |
2013年 | 398篇 |
2012年 | 441篇 |
2011年 | 462篇 |
2010年 | 241篇 |
2009年 | 275篇 |
2008年 | 410篇 |
2007年 | 398篇 |
2006年 | 339篇 |
2005年 | 318篇 |
2004年 | 307篇 |
2003年 | 236篇 |
2002年 | 180篇 |
2001年 | 88篇 |
2000年 | 69篇 |
1999年 | 65篇 |
1998年 | 65篇 |
1997年 | 73篇 |
1996年 | 104篇 |
1995年 | 50篇 |
1994年 | 65篇 |
1993年 | 44篇 |
1992年 | 66篇 |
1991年 | 48篇 |
1990年 | 44篇 |
1989年 | 48篇 |
1988年 | 40篇 |
1987年 | 36篇 |
1986年 | 38篇 |
1985年 | 55篇 |
1984年 | 48篇 |
1983年 | 50篇 |
1982年 | 56篇 |
1981年 | 31篇 |
1980年 | 42篇 |
1979年 | 30篇 |
1978年 | 35篇 |
1977年 | 30篇 |
1976年 | 27篇 |
1974年 | 19篇 |
1973年 | 18篇 |
排序方式: 共有6946条查询结果,搜索用时 296 毫秒
41.
Amihood Amir Alberto Apostolico Moshe Lewenstein 《Journal of Algorithms in Cognition, Informatics and Logic》1997,24(2):325-339
Let a textstringTofnsymbols from some alphabet Σ and an integerm < nbe given. A patternPof lengthmover Σ is sought such thatPminimizes (alternatively, maximizes) the total number of pairwise character mismatches generated whenPis compared with allm-character substrings ofT. Two additional variants of the problem are obtained by adding the constraint thatPbe (respectively, not be) a substring ofT. Efficient sequential algorithms are proposed in this paper for the problem and its variants. 相似文献
42.
Alberto S. Cattaneo 《Communications in Mathematical Physics》1997,189(3):795-828
In the context of the Batalin–Vilkovisky formalism, a new observable for the Abelian BF theory is proposed whose vacuum expectation value is related to the Alexander–Conway polynomial. The three-dimensional case
is analyzed explicitly, and it is proved to be anomaly free. Moreover, at the second order in perturbation theory, a new formula
for the second coefficient of the Alexander–Conway polynomial is obtained. An account on the higher-dimensional generalizations
is also given.
Received: 2 October 1996 / Accepted: 21 March 1997 相似文献
43.
44.
The complexity of searching minimum difference covers, both in Z+ and in Zn, is studied. We prove that these two optimization problems are NP-hard. To obtain this result, we characterize those sets—called extrema—having themselves plus zero as minimum difference cover. Such a combinatorial characterization enables us to show that testing whether sets are not extrema, both in Z+ and in Zn, is NP-complete. However, for these two decision problems we exhibit pseudo-polynomial time algorithms. 相似文献
45.
Pablo Alberca Bjerregaard Alberto Elduque Cndido Martín Gonzlez Francisco Jos Navarro Mrquez 《Journal of Algebra》2002,250(2):397
The well-known Cartan–Jacobson theorem claims that the Lie algebra of derivations of a Cayley algebra is central simple if the characteristic is not 2 or 3. In this paper we have studied these two cases, with the following results: if the characteristic is 2, the theorem is also true, but, if the characteristic is 3, the derivation algebra is not simple. We have also proved that in this last case, there is a unique nonzero proper seven-dimensional ideal, which is a central simple Lie algebra of type A2, and the quotient of the derivation algebra modulo this ideal turns out to be isomorphic, as a Lie algebra, to the ideal itself. The original motivation of this work was a series of computer-aided calculations which proved the simplicity of derivation algebras of Cayley algebras in the case of characteristic not 3. These computations also proved the existence of a unique nonzero proper ideal (which turns out to be seven-dimensional) in the algebra of derivations of split Cayley algebras in characteristic 3. 相似文献
46.
The proposal of hunting theH-particle taking advantage of antiproton annihilation at rest on3He is discussed. The obtained K* beam should allow one to obtain a flux ofΞ ? with momentum low enough to optimize the fusion probability (ΞN) to give anH. The experimental apparatus to detectH-events as the only missing mass of the fully reconstructed reaction¯p 3He →KKπ + H is the OBELIX Spectrometer at LEAR. A detailed Monte Carlo simulation of the overall acceptance of OBELIX for the above reaction is performed. The obtained final rate shows the feasibility of the experiment also in a not dedicated detector like OBELIX. 相似文献
47.
P. Lugli C. Erlen A. Pecchia F. Brunetti L. Latessa A. Bolognesi G. Csaba G. Scarpa A. di Carlo 《Applied Physics A: Materials Science & Processing》2007,87(3):593-598
Molecular devices have lately attracted increased attention due to some appealing features such as their low production cost,
flexibility in the substrate choice, possibility of large area deployment, and possibly higher integration capabilities. Starting
from a series of results obtained from our groups, we critically review the state-of-the-art in the field of simulation of
organic and molecular systems, by analyzing and comparing existing approaches, and looking at the open problems and possible
solutions and future developments.
PACS 72.80.Le 相似文献
48.
Carlo Carlini Valentina De Luise Anna Maria Raspolli Galletti Glauco Sbrana 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):200-206
Novel catalytic systems, prepared in situ by the oxidative addition of 8‐hydroxyquinoline ligands to bis(1,5‐cyclooctadiene)nickel(0) and activated by methylaluminoxane, were studied in ethylene polymerization. When 8‐hydroxyquinoline was employed, only oligomeric products were obtained. On the contrary, 5,7‐dinitro‐8‐hydroxyquinoline gave linear polyethylene (PE), but with a modest activity. For the catalyst based on 5‐nitro‐8‐hydroxyquinoline, the productivity was largely dependent on the content of free trimethylaluminum (TMA) present in the commercial aluminoxane. The progressive optimization of the TMA/oligomeric methylaluminoxane ratio increased the productivity, which reached 700 kg of PE/(mol of Ni × h), by an order of magnitude. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 200–206, 2006 相似文献
49.
Alberto Giaconia Giuseppe Filardo Onofrio Scialdone Alessandro Galia 《Journal of polymer science. Part A, Polymer chemistry》2006,44(13):4122-4135
A laboratory‐scale continuous reaction system using a stirred tank reactor was assembled in our laboratory to study the dispersion polymerization of vinyl monomers in supercritical carbon dioxide (scCO2). The apparatus was equipped with a suitable downstream separation section to collect solid particles entrained in the effluent stream from the reactor, whose monomer concentration could be measured online with a gas chromatograph. The dispersion polymerization of methyl methacrylate in scCO2 was selected as a model process to be investigated in the apparatus. The experiments were performed at 65 °C and 25 MPa with 2,2′‐azobisisobutyronitrile as the initiator and a reactive polysiloxane macromonomer as a surfactant to investigate the effect of the mean residence time of the reaction mixture on the monomer conversion, polymerization rate, polymer molecular weight, and particle size distribution. The results were compared with those obtained in batch polymerizations carried out under similar operative conditions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4122–4135, 2006 相似文献
50.
Tight control of flux loci in 2D testing of soft magnetic laminations is realized by a method based on the principle of contraction mapping. It is implemented through digital control of the currents supplying a three-phase yoke magnetizer and the use of circular samples. Faithful realization of the prescribed loci and good measuring accuracy are demonstrated in grain-oriented and non-oriented Fe–Si laminations. 相似文献