全文获取类型
收费全文 | 2526篇 |
免费 | 70篇 |
国内免费 | 21篇 |
专业分类
化学 | 1699篇 |
晶体学 | 60篇 |
力学 | 39篇 |
数学 | 418篇 |
物理学 | 401篇 |
出版年
2023年 | 24篇 |
2022年 | 26篇 |
2021年 | 42篇 |
2020年 | 46篇 |
2019年 | 54篇 |
2018年 | 25篇 |
2017年 | 17篇 |
2016年 | 46篇 |
2015年 | 57篇 |
2014年 | 48篇 |
2013年 | 128篇 |
2012年 | 135篇 |
2011年 | 156篇 |
2010年 | 78篇 |
2009年 | 57篇 |
2008年 | 136篇 |
2007年 | 117篇 |
2006年 | 134篇 |
2005年 | 144篇 |
2004年 | 100篇 |
2003年 | 91篇 |
2002年 | 100篇 |
2001年 | 42篇 |
2000年 | 25篇 |
1999年 | 32篇 |
1998年 | 26篇 |
1997年 | 35篇 |
1996年 | 42篇 |
1995年 | 44篇 |
1994年 | 45篇 |
1993年 | 39篇 |
1992年 | 41篇 |
1991年 | 24篇 |
1990年 | 28篇 |
1989年 | 26篇 |
1988年 | 25篇 |
1987年 | 24篇 |
1986年 | 17篇 |
1985年 | 23篇 |
1984年 | 31篇 |
1983年 | 19篇 |
1982年 | 28篇 |
1980年 | 27篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 21篇 |
1976年 | 23篇 |
1975年 | 19篇 |
1974年 | 23篇 |
1973年 | 16篇 |
排序方式: 共有2617条查询结果,搜索用时 15 毫秒
21.
A rooted graph is a pair (G,x), where G is a simple undirected graph and x ∈ V(G). If G is rooted at x, its kth rotation number hk (G,x) is the minimum number of edges in a graph F of order |G| + k such that for every v ∈ V(F) we can find a copy of G in F with the root vertex x at v. When k = 0, this definition reduces to that of the rotation number h(G,x), which was introduced in [“On Rotation Numbers for Complete Bipartite Graphs,” University of Victoria, Department of Mathematics Report No. DM-186-IR (1979)] by E.J. Cockayne and P.J. Lorimer and subsequently calculated for complete multipartite graphs. In this paper, we estimate the kth rotation number for complete bipartite graphs G with root x in the larger vertex class, thereby generalizing results of B. Bollobás and E.J. Cockayne [“More Rotation Numbers for Complete Bipartite Graphs,” Journal of Graph Theory, Vol. 6 (1982), pp. 403–411], J. Haviland [“Cliques and Independent Sets,” Ph. D. thesis, University of Cambridge (1989)], and J. Haviland and A. Thomason [“Rotation Numbers for Complete Bipartite Graphs,” Journal of Graph Theory, Vol. 16 (1992), pp. 61–71]. © 1993 John Wiley & Sons, Inc. 相似文献
22.
Tevian Dray Corinne A. Manogue Robin W. Tucker 《General Relativity and Gravitation》1991,23(8):967-971
We consider the (massless) scalar field on 2-dimensional manifolds whose metric changes signature and which admit a spacelike isometry. Choosing the wave equation so that there will be a conserved Klein-Gordon product implicitly determines the junction conditions one needs to impose in order to obtain global solutions. The resulting mix of positive and negative frequencies produced by the presence of Euclidean regions depends only on the total width of the regions, and not on the detailed form of the metric.This essay received honorable mention in the 1991 competition of the Gravity Research Foundation. 相似文献
23.
This paper describes the results of the experimental verification of the idea of wave-like aquatic propulsion of autonomous and man-inhabited vessels first published about 10 years ago by one of the present authors (V.V.K.). The idea is based on employing the unique type of localised flexural elastic waves propagating along edges of wedge-like structures immersed in water (wedge elastic waves). Such wedge-like structures supporting localised elastic waves can be attached like fish fins to a body of a small ship or a submarine and used for their propulsion. The proposed principle of employing localised flexural waves as a source of aquatic propulsion has been biologically inspired by the specific swimming mode used in nature by stingrays. To verify the idea experimentally, the first working prototype of a small catamaran using the above-mentioned wave-like propulsion via the attached rubber keel has been build and tested in Loughborough University. The tests have been carried out in two phases, in a water tank and then in open water. The test results have shown that the catamaran was propelled very efficiently and could achieve the speed of 36 cm/s, i.e., about one vehicle length per second, thus demonstrating that the idea of wave-like propulsion of small man-inhabited craft is viable. The reported proof of the viability of this idea may open new opportunities for marine craft propulsion, which can have far reaching implications. 相似文献
24.
25.
Robin M. Hogarth 《Annals of Operations Research》1989,19(1):29-50
26.
John R. Peterson Tamara J. Winter Hoang D. Do Robin D. Rogers 《Journal of chemical crystallography》1989,19(1):135-145
Structural and conformational information obtained from the crystal structure and solution1H nmr investigations of the title compound are compared. The 4-aryltetralone, C24H24O10, crystallizes as a chloroform solvate in the monoclinic space group, P21/n, witha=12.519(4),b=17.938(6),c=12.534(9)Å,=111.90(5)°, and Dcalc=1.51 g cm–3 forZ=4. The data for this compound were collected at –150°C. Least-squares refinement of 2796 observed [F
o5(F
o)] reflections led to the final agreement index ofR=0.062. A threefold static disorder was observed for one of the carboxyl groups. The second carboxyl group participates in an intramolecular hydrogen bond and is thus ordered. The1H nmr spectrum revealed the title compound to exist as a keto-enol tautomeric mixture in solution. Vicinal hydrogen coupling constant analysis proved reliable in ascertaining B-ring stereochemistry of 2,3-disubstituted-4-aryltetralones. 相似文献
27.
28.
29.
30.
J. G. Pritchard 《Journal of mass spectrometry : JMS》1974,8(1):103-108
The metastable ion spectra of ethylene oxide, acetaldehyde, acetaldehyde-d4, propylene oxide, propionaldehyde and trimethylene oxide are presented. They reveal no reason to suppose that electron-impact-induced isomerisation of oxide to aldehyde structure occurs, although many spectral features are common to various members of this set. The spectra of phenylacetaldehyde and styrene oxide are compared, and the more plausible possibility of partial isomerisation in this case is discussed. 相似文献