全文获取类型
收费全文 | 427634篇 |
免费 | 6036篇 |
国内免费 | 1664篇 |
专业分类
化学 | 232903篇 |
晶体学 | 6071篇 |
力学 | 18387篇 |
综合类 | 14篇 |
数学 | 50381篇 |
物理学 | 127578篇 |
出版年
2020年 | 2827篇 |
2019年 | 2809篇 |
2018年 | 2821篇 |
2017年 | 2751篇 |
2016年 | 5589篇 |
2015年 | 4650篇 |
2014年 | 6225篇 |
2013年 | 19434篇 |
2012年 | 14984篇 |
2011年 | 18718篇 |
2010年 | 11652篇 |
2009年 | 11743篇 |
2008年 | 17211篇 |
2007年 | 17527篇 |
2006年 | 16904篇 |
2005年 | 15448篇 |
2004年 | 13889篇 |
2003年 | 12222篇 |
2002年 | 11973篇 |
2001年 | 13656篇 |
2000年 | 10536篇 |
1999年 | 8268篇 |
1998年 | 6589篇 |
1997年 | 6435篇 |
1996年 | 6450篇 |
1995年 | 5889篇 |
1994年 | 5526篇 |
1993年 | 5260篇 |
1992年 | 5900篇 |
1991年 | 5758篇 |
1990年 | 5301篇 |
1989年 | 5164篇 |
1988年 | 5452篇 |
1987年 | 5060篇 |
1986年 | 4891篇 |
1985年 | 7134篇 |
1984年 | 7164篇 |
1983年 | 5836篇 |
1982年 | 6298篇 |
1981年 | 6236篇 |
1980年 | 6026篇 |
1979年 | 6097篇 |
1978年 | 6151篇 |
1977年 | 6099篇 |
1976年 | 6001篇 |
1975年 | 5879篇 |
1974年 | 5678篇 |
1973年 | 5907篇 |
1972年 | 3449篇 |
1971年 | 2466篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
991.
992.
M. Bello-Hernandez G. Lopez-Lagomasino J. Minguez-Ceniceros 《Constructive Approximation》2007,26(3):339-359
We study linear and nonlinear simultaneous Fourier-Pade approximation for Angelesco systems of functions and give the exact
rate of convergence/divergence of the approximants in terms of the solution of associated vector equilibrium potential
problems which differ for the linear and nonlinear cases. 相似文献
993.
We consider queuing systems where customers are not allowed to queue, instead of that they make repeated attempts, or retrials, in order to enter service after some time. We obtain the distribution of the number of retrials produced by a tagged customer, until he finds an available server. 相似文献
994.
Litharge, the red tetragonal form of lead oxide α-PbO and massicot, the yellow orthorhombic form β-PbO, are synthesized from
lead(II) salts in aqueous media at elevated temperatures. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were
used to characterize the size, morphology, and crystallographic structural forms of the products. The role of impurities in
the experimental synthesis of the materials and microstructural variations in the final products are described. The implications
of these observations regarding the synthesis of different conducting lead oxides and other related materials are discussed.
PACS 71.20.Ps; 72.80.Jc; 74.62.Bf; 74.62.Dh; 75.50.Tt 相似文献
995.
In cricket, a rain-affected pitch can make batting more difficult than normal. Several other conditions such as poor light or an initially lively pitch, may also result in difficulties for the batsmen. In this note, we refer to all of them as ‘sticky wickets’. On sticky wickets, lower order batsmen are often sent into ‘hold the fort’ until conditions improve. In this paper, a stochastic dynamic programming model is used to examine the appropriateness of this policy. The model suggests that the tactic is often optimal when the sticky wicket persists until the end of the day's play, but not often when the sticky wicket is transitory. In some circumstances, it is worthwhile, on a normal wicket near the end of the day, to send in a lower order batsman to hold the fort (a night watchman): when the wicket is sticky, this tactic is even more worthwhile. 相似文献
996.
997.
An infinite row of periodically spaced, identical rigid circularcylinders is excited by an acoustic line source which is parallelto the generators of the cylinders. A method for calculatingthe scattered field accurately and efficiently is presented.When the cylinders are sufficiently close together, Rayleigh–Blochsurface waves that propagate energy to infinity along the arrayare excited. An expression is derived which enables the amplitudesof these surface waves to be computed without requiring thesolution to the full scattering problem. 相似文献
998.
E. Chikoidze Y. Dumont H.J. von Bardeleben J. Gleize F. Jomard E. Rzepka G. Berrerar D. Ferrand O. Gorochov 《Applied Physics A: Materials Science & Processing》2007,88(1):167-171
ZnO:Mn thin films are grown by the metal organic chemical vapor deposition technique. Mn (x) varies in the 0<x<0.44 range.
Vegard’s law has been verified for the lattice parameters. Electron paramagnetic resonance (EPR) measurements prove the substitutional
incorporation of Mn2+ on zinc sites. The behavior of the EPR line width regarding temperature is discussed. All ZnO:Mn layers show antiferromagnetic
interaction and a J1/kB=-15 K effective exchange constant. The optical band gap of ZnO:Mn increases with the manganese concentration. Raman spectroscopy
reveals a Mn-related scattering band.
PACS 71.55.Gs; 75.50.Pp; 61.10.Nz; 76.30.Fc; 75.30.Et; 78.40.-q 相似文献
999.
N. Monnanteuil J.M. Colmont 《Journal of Quantitative Spectroscopy & Radiative Transfer》1983,29(2):131-136
Self broadened widths of seven lines of ozone between 75 and 120 GHz have been measured at room temperature. The variation with temperature of the self-broadening parameter for three of these lines has been studied in the range 245–292°K. 相似文献
1000.
We introduce a new technique for imaging oxygen concentrations in fuel/air mixtures that takes advantage of the different
responses of toluene and 3-pentanone to collisional quenching by molecular oxygen. Since laser-induced fluorescence signals
from both tracers upon excitation at 248 nm are spectrally well separated, simultaneous detection is possible. The technique
is first applied to instantaneous imaging in turbulent mixing processes of interacting seeded air and nitrogen flows.
Received: 1 August 2001 / Revised version: 29 October 2001 / Published online: 29 November 2001 相似文献