全文获取类型
收费全文 | 32785篇 |
免费 | 942篇 |
国内免费 | 249篇 |
专业分类
化学 | 22672篇 |
晶体学 | 223篇 |
力学 | 768篇 |
数学 | 5420篇 |
物理学 | 4893篇 |
出版年
2022年 | 283篇 |
2021年 | 421篇 |
2020年 | 514篇 |
2019年 | 484篇 |
2018年 | 376篇 |
2017年 | 372篇 |
2016年 | 835篇 |
2015年 | 737篇 |
2014年 | 807篇 |
2013年 | 1725篇 |
2012年 | 1866篇 |
2011年 | 2352篇 |
2010年 | 1141篇 |
2009年 | 1004篇 |
2008年 | 2009篇 |
2007年 | 2020篇 |
2006年 | 1996篇 |
2005年 | 1862篇 |
2004年 | 1587篇 |
2003年 | 1382篇 |
2002年 | 1282篇 |
2001年 | 402篇 |
2000年 | 388篇 |
1999年 | 358篇 |
1998年 | 335篇 |
1997年 | 357篇 |
1996年 | 486篇 |
1995年 | 343篇 |
1994年 | 298篇 |
1993年 | 270篇 |
1992年 | 267篇 |
1991年 | 237篇 |
1990年 | 202篇 |
1989年 | 203篇 |
1988年 | 232篇 |
1987年 | 198篇 |
1986年 | 180篇 |
1985年 | 347篇 |
1984年 | 339篇 |
1983年 | 242篇 |
1982年 | 313篇 |
1981年 | 323篇 |
1980年 | 298篇 |
1979年 | 281篇 |
1978年 | 257篇 |
1977年 | 227篇 |
1976年 | 206篇 |
1975年 | 208篇 |
1974年 | 210篇 |
1973年 | 209篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Consider a labeled convex n-gon in the plane and a point x in general position in the interior. We associate with this a collection (x) of 3-element sets, namely those 3-element subsets of the vertices which contain x in their interior. We investigate the problem of characterizing those collections of subsets which can be represented in this matter. We give a complete characterization of this and a related problem.School of Mathematics, University of Minnesota, Minneapolis, MN 55455. This work was supported in part by NSF grant DMS-8700995.Department of Mathematics, University College London, Gower Street, London, WC1E 6BT, England. Work done while Hill Visiting Professor at the University of Minnesota. 相似文献
92.
Current and logarithm-current distributions on a three-dimensional random-bond percolation cubic network were studied at the percolation threshold by computer simulations. Predictions of a hierarchical model that combine fractal structure and randomness agree with our numerical simulations. In the thermodynamic limit the logarithm-current distribution exhibits ann(ln(i))i
1/3 dependence below some characteristic currenti
c. This distribution may scale with lni/lnL, but the data are insufficient to make this a definite conclusion. Due to the small range of lnL considered, a study of the moments does not reveal this behavior and a study of the distribution itself is required. 相似文献
93.
David P. Dobkin Steven J. Friedman Kenneth J. Supowit 《Discrete and Computational Geometry》1990,5(1):399-407
LetS be any set ofN points in the plane and let DT(S) be the graph of the Delaunay triangulation ofS. For all pointsa andb ofS, letd(a, b) be the Euclidean distance froma tob and let DT(a, b) be the length of the shortest path in DT(S) froma tob. We show that there is a constantc (≤((1+√5)/2) π≈5.08) independent ofS andN such that $$\frac{{DT(a,b)}}{{d(a,b)}}< c.$$ 相似文献
94.
David Fryberger 《Foundations of Physics Letters》1990,3(4):379-386
Issues raised by W. A. Rodrigues, Jr. are discussed.1. This is not a new result; see,e.g., Rohrlich.(3)
2. A typographical error in Eq. (77) is corrected here: The productj A in the right-hand parentheses was erroneously transcribed in Ref. (2) as
A.3. I define electromagnetic fieldF = A to be that generated by electric charges and the magnetoelectric fieldG = M to be that generated by magnetic monopoles:F F +5
G.
4. Rodrigues, on the other hand, takes the position that the importance of the Lagrangian formulation should be downgraded if not discarded altogether: ... it is redundant to look for Lagrangians.(1)
5. In fact, he reformulates it using the language of differential forms.6. It is interesting to observe that this bilinear form has the additional virtue of being appropriate for dealing with the monopolecharge parity question, which was pointed out long ago.(14)
7. In fact, even mathematics looks to Nature for its authority.(16) There is evidence that Rodrigues does not understand this concept.(17) 相似文献
95.
Summary We prove the fundamental lemma for spherical functions with respect to the natural (induction) lifting fromPGL(2) toPGL(3) which appears as the unstable counterpart of the stable symmetric-square lifting fromSL(2) toPGL(3) (see [IV] for an introduction to this project, and [VI] for the final results). Thus spherical functions onPGL(2) andPGL(3) which correspond to each other by satisfying an elementary representation theoretic relation are shown to have matching orbital integrals. The proof of this local statement is based on an application of the global trace formula.Partially supported by NSF grants 相似文献
96.
David G. Kirkpatrick 《Discrete and Computational Geometry》1988,3(1):267-280
A planar subdivision is the partition of the plane induced by an embedded planar graph. A representation of such a subdivision isordered if, for each vertexv of the associated graphG, the (say) clockwise sequence of edges in the embedding ofG incident withv appears explicitly.The worst-case complexity of establishing order in a planar subdivision, i.e., converting an unordered representation into an ordered one, is shown to be (n + log (G)), wheren is the size (number of vertices) of the underlying graphG and (G) is (essentially) the number of topologically distinct embeddings ofG in the plane.This work was supported by the National Science and Engineering Research Council of Canada under Grant A3583. A preliminary version of this paper appeared in theProceedings of the Third Annual ACM Symposium on Computational Geometry. 相似文献
97.
Gabriel M. Rebeiz Curtis C. Ling David B. Rutledge 《International Journal of Infrared and Millimeter Waves》1989,10(8):931-936
An accurate monolithic power meter has been developed for millimeter-wave applications. The detector is a large-area Bismuth bolometer, integrated on a fused-Quartz substrate. It simply measures the temperature change caused by the absorption of millimeter-wave radiation. The power meter is simple to fabricate, inexpensive, and can be easily calibrated using a low-frequency network. The measured responsivity for a 50 bolometer, with an area of 1×1cm, at a bias of 1V. and a video modulation of 100Hz, is 1mV/W. The noise spectrum exhibits a 1/f rolloff till 1KHz, and is limited by the Johnson noise for higher frequencies. The NEP of the detector is 3WHz–1/2 at a video modulation of 1KHz. It is possible to decrease the current NEP by fabricating bolometers with higher responsivities. Possible application areas are absolute power calibration and localized power density measurements at millimeter and submillimeter wavelengths. 相似文献
98.
Heptakis(2,6-di-O-methyl)-β-cyclodextrin interacts with 5,15-diphenylporphine to produce a 2:1 complex in dimethyl sulfoxide. This complex possesses a hydrophobic groove that circumscribes the metal binding site of the porphyrin moiety. 相似文献
99.
100.
A new phase selective hydrocarbon soluble polymer support is described. 相似文献