全文获取类型
收费全文 | 1625篇 |
免费 | 32篇 |
国内免费 | 3篇 |
专业分类
化学 | 785篇 |
晶体学 | 10篇 |
力学 | 33篇 |
数学 | 154篇 |
物理学 | 678篇 |
出版年
2021年 | 10篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 10篇 |
2017年 | 14篇 |
2016年 | 26篇 |
2015年 | 21篇 |
2014年 | 27篇 |
2013年 | 68篇 |
2012年 | 67篇 |
2011年 | 63篇 |
2010年 | 47篇 |
2009年 | 35篇 |
2008年 | 64篇 |
2007年 | 71篇 |
2006年 | 69篇 |
2005年 | 66篇 |
2004年 | 51篇 |
2003年 | 23篇 |
2002年 | 51篇 |
2001年 | 36篇 |
2000年 | 27篇 |
1999年 | 14篇 |
1998年 | 22篇 |
1997年 | 27篇 |
1996年 | 46篇 |
1995年 | 47篇 |
1994年 | 37篇 |
1993年 | 53篇 |
1992年 | 42篇 |
1991年 | 23篇 |
1990年 | 38篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 20篇 |
1984年 | 17篇 |
1983年 | 18篇 |
1982年 | 20篇 |
1981年 | 23篇 |
1980年 | 18篇 |
1979年 | 25篇 |
1978年 | 21篇 |
1977年 | 19篇 |
1976年 | 16篇 |
1975年 | 20篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1972年 | 10篇 |
排序方式: 共有1660条查询结果,搜索用时 31 毫秒
911.
We show that there is a phase transition in the bounded rational Carfì–Musolino model, and the possibility of a market crash. This model has two types of operators: a real economic subject (Air) and one or more investment banks (Bank). It also has two markets: oil spot market and US dollar futures. Bank agents react to Air and equilibrate much more quickly than Air. Thus Air is an acting external agent due to its longer-term investing, whereas the action of the banks equilibrates before Air makes its next transaction. This model constitutes a potential game, and agents crowd their preferences into one of the markets at a critical temperature when air makes no purchases of oil futures. 相似文献
912.
Gregori G Glenzer SH Fournier KB Campbell KM Dewald EL Jones OS Hammer JH Hansen SB Wallace RJ Landen OL 《Physical review letters》2008,101(4):045003
Spectrally and time-resolved x-ray scattering is used to extract the temperature and charge state evolution in a near solid density carbon foam driven by a supersonic soft x-ray heat wave. The measurements show a rapid heating of the foam material (approximately 200 eV/ns) followed by a similarly fast decline in the electron temperature as the foam cools. The results are compared to an analytic power balance model and to results from radiation-hydrodynamics simulations. Finally, the combination of charge state and temperature extracted from this known density isochorically heated plasma is used to distinguish between dense plasma ionization balance models. 相似文献
913.
Newton MJ Campbell M Gilbert J 《The Journal of the Acoustical Society of America》2008,123(1):EL14-EL20
Mechanical frequency responses of human and artificial lips in brass instrument playing have been measured using a high-speed digital video technique, in an attempt to classify the true nature of the "lip-reed." Four semiprofessional human players were used, and three notes played on a trombone were studied. All measurements revealed a strong mechanical resonance with "outward striking" behavior; the played note always sounded above this frequency. Several measurements also showed a weaker second resonance, above the played frequency, with "inward striking" behavior. The Q values of the dominant resonances in human lips were lower than those typical of artificial lips. 相似文献
914.
The v=1-->0 radiative lifetime of NH(X(3)Sigma(-),v=1,N=0) is determined to be tau_(rad,exp.)=37.0+/-0.5_(stat)+2.0/-0.8_(syst) ms, corresponding to a transition dipole moment of |mu_(10)|=0.0540_(-0.0018)(+0.0009) D. To achieve sufficiently long observation times, NH(X;{3}Sigma;{-},v=1) radicals are magnetically trapped using helium buffer-gas loading. The rate constant for background helium-induced collisional quenching was determined to be k_(v=1)<3.9x10(-15) cm(3) s(-1), which yields the quoted systematic uncertainty on tau_{rad,exp.}. With a new ab initio dipole moment function and a Rydberg-Klein-Rees potential, we calculate a lifetime of 36.99 ms, in agreement with our experimental value. 相似文献
915.
We report and characterize anomalous orbital-energy changes observed during six Earth flybys by the Galileo, NEAR, Cassini, Rosetta, and MESSENGER spacecraft. These anomalous energy changes are consistent with an empirical prediction formula which is proportional to the total orbital energy per unit mass and which involves the incoming and outgoing geocentric latitudes of the asymptotic spacecraft velocity vectors. We use this formula to predict a potentially detectable flyby velocity increase of less than 1 mm/s for a second Rosetta flyby on November 13, 2007. 相似文献
916.
B. Cheal K. Baczynska J. Billowes P. Campbell T. Eronen D. H. Forest T. Kessler I. D. Moore M. Rüffer B. Tordoff G. Tungate J. Äystö 《Hyperfine Interactions》2008,181(1-3):107-110
Optical experiments at the IGISOL isotope separator facility, Jyväskylä, have for many years benefited from the introduction of an ion beam cooler. The device, a gas-filled RF quadrupole, reduces the emittance and longitudinal energy spread of the ion beam. Very recently, use has been made of the axial confinement of slowly travelling ions at the end of the cooler to redistribute the electronic populations through efficient laser excitation. Such a technique has proved beneficial to laser spectroscopic measurements and is a precursor to using the method to polarize the ion beam. 相似文献
917.
The performance of 34-μm-diameter InGaAs/InP charge compensated modified uni-traveling carrier photodiodes (CC MUTCs) is studied
using a commercial device simulator based on a drift-diffusion model. Excellent agreement has been achieved between simulations
and experiments. The origin of the degradation of responsivity at high optical injection level is investigated. Parameters
of the photodiode are further optimized to maximize the saturation current without sacrificing bandwidth and responsivity. 相似文献
918.
G. H. W. Milburn C. Campbell A. J. Shand A. R. Werninck J. Varga K. Belina G. Baksay 《Journal of Thermal Analysis and Calorimetry》1990,36(5):1669-1674
We describe the thermal and optical studies of some diacetylene molecules which were specially designed in an attempt to reduce the temperature at which the mesophase appears. Original studies were on symmetrical molecules and these were extended to include typical liquid crystal molecules with diacetylenes providing a polymeric backbone and unsymmetrically substituted diacetylenes including Schiffs bases with long alkyl chains. 相似文献
919.
Explicit series formulae are given for use in the method of steepest descents, where it is required to find the contribution to an integral of the form ∫evw(z)φ(z)dz from a well-isolated saddle point z0. Here v is a large positive parameter, and w(N)(z0) ≠ 0 while lower-order derivatives at z0 are equal to zero. Examples where the formulae are helpful are presented. 相似文献
920.
New 2-heterospirotetrahydronaphthalenes with 3-, 4- and 5-membered rings have been prepared during the development of routes to tetralone derived spiroaziridines. 相似文献