全文获取类型
收费全文 | 15737篇 |
免费 | 438篇 |
国内免费 | 95篇 |
专业分类
化学 | 10900篇 |
晶体学 | 107篇 |
力学 | 219篇 |
数学 | 2424篇 |
物理学 | 2620篇 |
出版年
2022年 | 114篇 |
2021年 | 143篇 |
2020年 | 245篇 |
2019年 | 218篇 |
2018年 | 134篇 |
2017年 | 116篇 |
2016年 | 359篇 |
2015年 | 280篇 |
2014年 | 340篇 |
2013年 | 654篇 |
2012年 | 690篇 |
2011年 | 797篇 |
2010年 | 481篇 |
2009年 | 426篇 |
2008年 | 725篇 |
2007年 | 704篇 |
2006年 | 722篇 |
2005年 | 676篇 |
2004年 | 594篇 |
2003年 | 474篇 |
2002年 | 521篇 |
2001年 | 274篇 |
2000年 | 305篇 |
1999年 | 243篇 |
1998年 | 249篇 |
1997年 | 221篇 |
1996年 | 248篇 |
1995年 | 255篇 |
1994年 | 258篇 |
1993年 | 207篇 |
1992年 | 201篇 |
1991年 | 190篇 |
1990年 | 168篇 |
1989年 | 166篇 |
1988年 | 156篇 |
1987年 | 143篇 |
1986年 | 132篇 |
1985年 | 219篇 |
1984年 | 180篇 |
1983年 | 165篇 |
1982年 | 216篇 |
1981年 | 188篇 |
1980年 | 165篇 |
1979年 | 193篇 |
1978年 | 163篇 |
1977年 | 154篇 |
1976年 | 153篇 |
1975年 | 124篇 |
1974年 | 126篇 |
1973年 | 127篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Searching in trees 总被引:1,自引:0,他引:1
Frank Recker 《Discrete Applied Mathematics》2004,140(1-3):169-183
In (Discrete Math. 17 (1977)181) Rivest introduced the search complexity of binary trees and proved that among all binary trees with a fixed search complexity the smallest ones are the so-called Fibonacci trees. This result is extended for q-trees. The structure of the smallest q-trees is again Fibonacci-like but more complicated than in the binary case. In addition an upper bound for the asymptotic growth of these trees is given. 相似文献
12.
Frank C. Spano 《Chemical physics letters》1994,220(6):365-370
A nonperturbative theory for the pump—probe absorption spectrum of Frenkel exciton chains is developed in the early saturation regime. In the J-aggregate configuration, the entire spectrum is blue-shifted in proportion to the pump intensity. The results are in good agreement with experiment. 相似文献
13.
We construct cellular homotopy theories for categories of simplicial presheaves on small Grothendieck sites and discuss applications to the motivic homotopy category of Morel and Voevodsky. 相似文献
14.
Frank H.G.M. Wijnands Charles G. Crookes Paul M. Charles Richard M. Ash Ian F. Lealman Michael J. Robertson Anthony E. Kelly Kevin A. Williams Aeneas B. Massara Richard V. Penty Ian H. White 《Optical and Quantum Electronics》2002,34(10):959-973
An anomalous modulation in the wavelength spectrum has been observed in lasers with spot-size converters. This intensity modulation is shown to be caused by beating between the fundamental lasing mode and radiation modes in the taper. This results in a periodic modulation in the net gain spectrum, which causes wavelength jumps between adjacent net gain maxima, and a drive current dependent spectral width that is expected to affect system performance. The amplitude of this spectral modulation is reduced significantly by either using an angled rear-facet which reflects the beating radiation modes away from the laser axis, or by using a nonlinear, adiabatic taper. 相似文献
15.
16.
Frank Morgan 《Annals of Global Analysis and Geometry》2006,30(1):73-79
In a product M
1 × M
2 of Riemannian manifolds, the least perimeter required to enclose given volume among general regions is at least 1/√ 2 times that among regions of product form, assuming that the isoperimetric profiles of M
1 and M
2 are concave. This result sharpens earlier work of Grigor'yan, generalizes results of Bollobás and Leader and of Barthe, and yields a lower bound on the Cheeger isoperimetric constant of a product. 相似文献
17.
We have characterized multidielectric scaled SONOS nonvolatile memory structures with the quasi-static linear voltage ramp (LVR) technique and dynamic pulse measurements. We have formulated physically-based ERASE/WRITE and retention methods with deep level amphoteric traps which capture and emit carriers to the bands in the silicon nitride film. Amphoteric trap parameters are extracted by the LVR technique. ERASE/WRITE and retention amphoteric trap model simulations agree well with the experimental dynamic pulse measurements. Experimental scaled SONOS structures have been fabricated with tunnel oxide XOT=20 Å, nitride XN=30 Å and blocking oxide XOB=55 Å and demonstrated a static flatband shift of 3.6 V with ±5 V programming voltages. These structures may be used as the nonvolatile memory element in high density VLSI circuits. 相似文献
18.
Kristin Fischer Silvio Prause Stefan Spange Frank Cichos Christian Von Borczyskowski 《Journal of Polymer Science.Polymer Physics》2003,41(11):1210-1218
Solvent‐dependent ultraviolet–visible (UV–vis) absorption and Stokes shifts including strong hydrogen‐bond‐donating (HBD) solvents such as 2,2,2‐trifluoroethanol and 1,1,1,3,3,3‐hexafluoro‐2‐propanol of two coumarine dyes (Co 151 and Co 153) were analyzed with multiple‐square analyses of linear solvation energy relationships and the Kamlet–Taft solvent parameter set to α (HBD capacity), β (hydrogen‐bond‐accepting capacity), and π* (dipolarity/polarizability). The UV–vis absorption and emission spectra of Co 151 and Co 153 were measured when adsorbed on various polysaccharides such as different cellulose batches, carboxymethylcelluloses with different degrees of substitution, and chitine. As a result of this evaluation, Co 153 is recommended as an alternative UV–vis probe for evaluating the dipolarity/polarizability of cellulose and cellulose derivates. Multiple adsorption of Co 153 on Linters cellulose took place indicating a wide‐surface polarity distribution, which makes the determination of a rigid polarity parameter questionable. Thus, fluorescence measurements of adsorbed Co 153 are suitable to detect inhomogenities on a surface but not for the determination of empirical polarity parameters. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1210–1218, 2003 相似文献
19.
Malene Steen Nielsen Flagga Frank Antonsen 《International Journal of Theoretical Physics》2004,43(9):1917-1930
We show that stable causality is related to the vanishing of the top Stiefel–Whitney class of a space-time manifold M, and that if M is a stably causal space-time manifold, then it is the boundary of a five-dimensional space-time. We then propose a scheme for making it both a necessary and sufficient condition. 相似文献
20.