全文获取类型
收费全文 | 1082篇 |
免费 | 16篇 |
国内免费 | 1篇 |
专业分类
化学 | 669篇 |
晶体学 | 8篇 |
力学 | 19篇 |
数学 | 73篇 |
物理学 | 330篇 |
出版年
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 20篇 |
2016年 | 12篇 |
2015年 | 16篇 |
2014年 | 22篇 |
2013年 | 75篇 |
2012年 | 42篇 |
2011年 | 48篇 |
2010年 | 45篇 |
2009年 | 32篇 |
2008年 | 33篇 |
2007年 | 42篇 |
2006年 | 41篇 |
2005年 | 46篇 |
2004年 | 39篇 |
2003年 | 24篇 |
2002年 | 25篇 |
2001年 | 28篇 |
2000年 | 27篇 |
1999年 | 11篇 |
1998年 | 16篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 18篇 |
1994年 | 13篇 |
1993年 | 16篇 |
1992年 | 18篇 |
1991年 | 13篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 14篇 |
1983年 | 16篇 |
1982年 | 18篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1978年 | 9篇 |
1977年 | 15篇 |
1975年 | 12篇 |
1974年 | 9篇 |
1973年 | 18篇 |
1972年 | 13篇 |
1971年 | 8篇 |
1968年 | 12篇 |
1966年 | 8篇 |
排序方式: 共有1099条查询结果,搜索用时 18 毫秒
101.
The polyhedron defined by all the split cuts obtainable directly (i.e. without iterated cut generation) from the LP-relaxation
P of a mixed integer program (MIP) is termed the (elementary, or rank 1) split closure of P. This paper deals with the problem of optimizing over the elementary split closure. This is accomplished by repeatedly solving
the following separation problem: given a fractional point, say x, find a rank-1 split cut violated by x or show that none exists. Following Caprara and Letchford [17], we formulate this separation problem as a nonlinear mixed
integer program that can be treated as a parametric mixed integer linear program (PMILP) with a single parameter in the objective
function and the right hand side. We develop an algorithmic framework to deal with the resulting PMILP by creating and maintaining
a dynamically updated grid of parameter values, and use the corresponding mixed integer programs to generate rank 1 split
cuts. Our approach was implemented in the COIN-OR framework using CPLEX 9.0 as a general purpose MIP solver. We report our
computational results on well-known benchmark instances from MIPLIB 3.0 and several classes of structured integer and mixed
integer problems. Our computational results show that rank-1 split cuts close more than 98% of the duality gap on 15 out of
41 mixed integer instances from MIPLIB 3.0. More than 75% of the duality gap can be closed on an additional 10 instances.
The average gap closed over all 41 instances is 72.78%. In the pure integer case, rank-1 split cuts close more than 75% of
the duality gap on 13 out of 24 instances from MIPLIB 3.0. On average, rank 1 split cuts close about 72% of the duality gap
on these 24 instances. We also report results on several classes of structured problems: capacitated versions of warehouse
location, single-source facility location, p-median, fixed charge network flow, multi-commodity network design with splittable and unsplittable flows, and lot sizing.
The fraction of the integrality gap closed varies for these problem classes between 100 and 67%. We also gathered statistics
on the average coefficient size (absolute value) of the disjunctions generated. They turn out to be surprisingly small.
Research was supported by the National Science Foundation through grant #DMI-0352885 and by the Office of Naval Research through
contract N00014-03-1-0133. 相似文献
102.
103.
R. Nishi I. Houda K. Kitano Y. Sugawara S. Morita 《Applied Physics A: Materials Science & Processing》2001,72(7):S93-S95
Noncontact imaging was successfully performed with the quartz resonator in air by using the FM detection method. A constant frequency shift mode was used. The frequency shift was about -30 mHz, which was induced by the attractive force gradient. A noncontact image of the Si(111) atomic step was obtained with vertical and lateral resolutions of 0.8 Å and 60 Å. 相似文献
104.
105.
106.
Yoshida T Nishi I Ideta S Fujimori A Kubota M Ono K Kasahara S Shibauchi T Terashima T Matsuda Y Ikeda H Arita R 《Physical review letters》2011,106(11):117001
We have studied the three-dimensional shapes of the Fermi surfaces (FSs) of BaFe(2)(As(1-x)P(x))(2) (x=0.38), where superconductivity is induced by isovalent P substitution and by angle-resolved photoemission spectroscopy. Moderately strong electron mass enhancement has been identified for both the electron and hole FSs. Among two observed hole FSs, the nearly two-dimensional one shows good nesting with the outer two-dimensional electron FS, but its orbital character is different from the outer electron FS. The three-dimensional hole FS shows poor nesting with the electron FSs. The present results suggest that the three dimensionality and the difference in the orbital character weaken FS nesting while partial nesting among the outer electron FSs of d(xy) character and/or that within the three-dimensional hole FS becomes dominant, which may lead to the nodal superconductivity. 相似文献
107.
R.K. Bhan Raghvendra Sahai Saxena N.K. Saini L. Sareen R. Pal R.K. Sharma 《Infrared Physics & Technology》2011,54(5):379-381
Hg1−xCdxTe Metal–Insulator–Semiconductor (MIS) capacitors were studied both experimentally and theoretically to investigate the capacitance contributions due to band-to-band (btb) tunnelling and generation–recombination (gr) of carriers to inversion layer capacitance. A good fit to the data has been obtained by including the btb contributions rather than gr contributions. 相似文献
108.
Sheetal Saxena Alexander Summa Dominik Elsässer Michael Rüger Karl Mannheim 《The European Physical Journal C - Particles and Fields》2011,71(11):1815
As the largest mass concentrations in the local Universe, nearby clusters of galaxies and their central galaxies are prime
targets in searching for indirect signatures of dark matter annihilation (DMA). We seek to constrain the dark matter annihilation
emission component from multi-frequency observations of the central galaxy of the Virgo cluster. The annihilation emission
component is modeled by the prompt and inverse-Compton gamma rays from the hadronization of annihilation products from generic
weakly interacting dark matter particles. This component is fitted to the excess of the observed data above the spectral energy
distribution (SED) of the jet in M87, described with a best-fit synchrotron-self-Compton (SSC) spectrum. While this result
is not sufficiently significant to claim a detection, we emphasize that a dark matter “double hump signature” can be used
to unambiguously discriminate the dark matter emission component from the variable jet-related emission of M87 in future,
more extended observation campaigns. 相似文献
109.
Silicon nanoclusters formation in pulsed laser deposited (PLD) silicon suboxide (SiOX) films by thermal annealing is reported. The SiOX films are prepared by ablation of silicon target at different oxygen partial pressures. The different deposition conditions are employed to study the effect of oxygen concentration on the size of the nanoclusters. Post deposition thermal annealing of the films leads to the phase separation in silicon suboxide films. Fourier transform infrared spectroscopy, micro-Raman spectroscopy and UV-vis absorption spectroscopy studies were carried out to characterize the formation of silicon nanoclusters in SiOX films. 相似文献
110.
Cryopreservation of shoot tips and cotyledons of the north american ginseng (Panax quinquefolius l.)
North American ginseng (NAG) (Panax quinqueolius L.) is a medicinal plant in high demand due to its health benefits. Cryopreservation is a good alternative for long-term conservation of NAG germplasm. Pretreatments of shoot tips (0.8-1 mm) and cotyledons (1-2 mm) on sucrose and abscisic acid (ABA) enriched medium were tested to determine the effects on regrowth following cryopreservation in liquid nitrogen. The maximum regrowth (60 percent) following PVS2 vitrification occurred with shoot tips after three weeks of cold acclimation and pretreatment on sucrose (0.3 M) or a combination of ABA (0.1 M) and sucrose in the third week. Cotyledon recovery was best with the combination pretreatment. Shoot tips showed normal development and cotyledons produced embryogenic callus after the cryopreservation process. This is the first report on cryopreservation of shoot tips and cotyledons of Panax species. This cryopreservation protocol provides a safe long-term storage method for important NAG selections and makes it possible to use cryopreservation for improving the security of NAG germplasm. 相似文献