全文获取类型
收费全文 | 126617篇 |
免费 | 2029篇 |
国内免费 | 390篇 |
专业分类
化学 | 53598篇 |
晶体学 | 1046篇 |
力学 | 7511篇 |
综合类 | 1篇 |
数学 | 40956篇 |
物理学 | 25924篇 |
出版年
2023年 | 364篇 |
2021年 | 556篇 |
2020年 | 744篇 |
2019年 | 693篇 |
2018年 | 11058篇 |
2017年 | 10834篇 |
2016年 | 7684篇 |
2015年 | 2345篇 |
2014年 | 1863篇 |
2013年 | 3717篇 |
2012年 | 6730篇 |
2011年 | 13056篇 |
2010年 | 7352篇 |
2009年 | 7438篇 |
2008年 | 8871篇 |
2007年 | 10782篇 |
2006年 | 2272篇 |
2005年 | 3273篇 |
2004年 | 3261篇 |
2003年 | 3437篇 |
2002年 | 2330篇 |
2001年 | 1278篇 |
2000年 | 1319篇 |
1999年 | 900篇 |
1998年 | 786篇 |
1997年 | 648篇 |
1996年 | 840篇 |
1995年 | 592篇 |
1994年 | 621篇 |
1993年 | 599篇 |
1992年 | 590篇 |
1991年 | 508篇 |
1990年 | 552篇 |
1989年 | 465篇 |
1988年 | 480篇 |
1987年 | 424篇 |
1986年 | 429篇 |
1985年 | 557篇 |
1984年 | 538篇 |
1983年 | 411篇 |
1982年 | 432篇 |
1981年 | 438篇 |
1980年 | 371篇 |
1979年 | 379篇 |
1978年 | 366篇 |
1977年 | 324篇 |
1976年 | 363篇 |
1975年 | 327篇 |
1974年 | 330篇 |
1973年 | 330篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
J D Griffiths Z F Lawson J E Williams 《The Journal of the Operational Research Society》2006,57(12):1413-1424
Advances in recent treatments for HIV/AIDS patients have shown dramatic outcomes in extending the incubation period and AIDS survival time, while also providing significant improvements in the quality of patients' lives. A compartmental model is proposed to analyse the effects of the various treatment regimens which have been introduced. The results produced are in good agreement with routinely collected data relating to levels of HIV/AIDS incidence and prevalence in the UK homosexual population. Some parameter values within the model are obtained from surveys, census results, etc, but others are derived using a maximum likelihood estimation procedure. Finally, the model is used to project levels of incidence and prevalence over the next few years, and to investigate several possible scenarios. 相似文献
992.
J. Balogh D. Kaptás L. F. Kiss T. Kemény L. Bujdosó I. Vincze 《Hyperfine Interactions》2006,169(1-3):1343-1347
Magnetic multilayers of 57Fe with nominal thickness, T
nom, between 0.4 and 1.0 nm separated by 3.0 nm Al spacer layers were prepared by alternate deposition of the constituents in
high vacuum. The samples were investigated at 4.2 K in external magnetic field. A fraction of Fe atoms corresponding to about
0.3 nm equivalent Fe-thickness was found to mix into the Al spacer. The extremely strong magnetic anisotropy observed for
T
nom < 0.8 nm is attributed to Fe layers of approximately two atomic planes thick. The anisotropy decreases considerably after
the building up of the third Fe atomic layer starts at T
nom = 0.8 nm, but full saturation was not achieved even for T
nom = 1 nm and 3 T magnetic field applied perpendicularly to the sample plane. 相似文献
993.
The stoichiometric reactions of trimethylaluminum with 2,6‐(MeOCH2)2C6H3OH (LH) revealed compounds L3Al ( 1 ) and L2AlMe ( 2 ). On the other hand reaction of 1 equiv. of LH with trimethylaluminum did not lead to the formation of complex LAlMe2 ( 3 ), rather 2 together with Me3Al were observed as a result of a disproportionation of 3 . Compounds 1 and 2 were characterized by elemental analysis, 1H and 13C NMR spectroscopy and in the case of 1 by X‐ray diffraction. Derivative 2 underwent transmetalation with Ph3SnOH, giving LSnPh3 ( 4 ) as the result of a migration of ligand L from the aluminum to the tin atom. The identity of 4 was established by elemental analysis, 1H, 13C and 119Sn NMR spectroscopy and 1H, 119Sn HMBC experiments. The system 2 and B(C6F5)3 in a 1:1 molar ratio was shown to be active in the polymerization of propylene oxide and ε‐caprolactone. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
994.
Abull is the (self-complementary) graph with verticesa, b, c, d, e and edgesab, ac, bc, bd, ce; a graphG is calledBerge if neitherG not its complement contains a chordless cycle whose length is odd and at least five. We prove that bull-free Berge graphs are perfect; a part of our argument relies on a new property of minimal imperfect graphs.This work was done while both authors were at the School of Computer Science, McGill University; support by NSERC is gratefully acknowledged. 相似文献
995.
In this article, local optimality in multiobjective combinatorial optimization is used as a baseline for the design and analysis
of two iterative improvement algorithms. Both algorithms search in a neighborhood that is defined on a collection of sets
of feasible solutions and their acceptance criterion is based on outperformance relations. Proofs of the soundness and completeness
of these algorithms are given. 相似文献
996.
We prove the vanishing of the Koszul homology group H
μ(Kos(M)μ), where μ is the minimal number of generators of M. We give a counterexample that the Koszul complex of a module is not always
acyclic and show its relationship with the homology of commutative rings. 相似文献
997.
Anil Kumar Karn 《Positivity》2007,11(2):369-374
An error has been detected (and also corrected) in Theorem 2.8 of the paper entitled “Adjoining an Order Unit to a Matrix
Ordered Space” (Positivity, (2005)9: 207–223; DOI ). Accordingly, some of the results of the paper have been modified. Also, a notion of C*-matricially, Riesz normed spaces has been introduced. 相似文献
998.
This paper presents the results of plasma temperature and pressure calculations in the parallel plate accelerator during the accelerating process. The plasma pressure is calculated by means in Dalton's law. 相似文献
999.
Designing a majorization scheme for the recourse function in two-stage stochastic linear programming
José H. Dulá 《Computational Optimization and Applications》1993,1(4):399-414
We discuss issues pertaining to the domination from above of the second-stage recourse function of a stochastic linear program and we present a scheme to majorize this function using a simpler sublinear function. This majorization is constructed using special geometrical attributes of the recourse function. The result is a proper, simplicial function with a simple characterization which is well-suited for calculations of its expectation as required in the computation of stochastic programs. Experiments indicate that the majorizing function is well-behaved and stable. 相似文献
1000.
Singularity patterns in a chemotaxis model 总被引:3,自引:0,他引:3