全文获取类型
收费全文 | 333889篇 |
免费 | 6762篇 |
国内免费 | 5028篇 |
专业分类
化学 | 163800篇 |
晶体学 | 4495篇 |
力学 | 18556篇 |
综合类 | 328篇 |
数学 | 49840篇 |
物理学 | 108660篇 |
出版年
2022年 | 2442篇 |
2021年 | 3035篇 |
2020年 | 3339篇 |
2019年 | 3591篇 |
2018年 | 12134篇 |
2017年 | 12653篇 |
2016年 | 9420篇 |
2015年 | 4596篇 |
2014年 | 5820篇 |
2013年 | 11140篇 |
2012年 | 13679篇 |
2011年 | 22569篇 |
2010年 | 14749篇 |
2009年 | 14868篇 |
2008年 | 19635篇 |
2007年 | 22629篇 |
2006年 | 9147篇 |
2005年 | 14074篇 |
2004年 | 10178篇 |
2003年 | 9502篇 |
2002年 | 7863篇 |
2001年 | 6849篇 |
2000年 | 5497篇 |
1999年 | 4119篇 |
1998年 | 3703篇 |
1997年 | 3450篇 |
1996年 | 3374篇 |
1995年 | 3010篇 |
1994年 | 3051篇 |
1993年 | 2838篇 |
1992年 | 3039篇 |
1991年 | 3237篇 |
1990年 | 3019篇 |
1989年 | 2947篇 |
1988年 | 2793篇 |
1987年 | 2687篇 |
1986年 | 2587篇 |
1985年 | 3140篇 |
1984年 | 3273篇 |
1983年 | 2740篇 |
1982年 | 2883篇 |
1981年 | 2699篇 |
1980年 | 2582篇 |
1979年 | 2845篇 |
1978年 | 3030篇 |
1977年 | 2811篇 |
1976年 | 3017篇 |
1975年 | 2794篇 |
1974年 | 2884篇 |
1973年 | 2897篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The steady motions of a vertical rotor balanced by two coupled perfectly rigid bodies (PRBs) are analyzed for stability. The rotor executes plane-parallel motions. The PRBs can rotate together about the rotor axis and about its transverse axes through equal angles but in opposite directions. It is established that when the mass of the PRBs is much less than that of the rotor and the rotor spins with a superresonant speed, only the basic steady motions, which are those of the best-balanced rotor, are asymptotically stable. 相似文献
92.
93.
F. Ameli M. Bonori F. Massa 《The European Physical Journal C - Particles and Fields》2002,25(1):67-75
We describe the measurement of the deep sea optical background in some sites south of Capo Passero, Sicily. A continuous
flux of about 440 photons cm
-2
s
-1
in the wavelength interval 440-550 nm is estimated due to the decays of the 40K contained in the sea water. Bioluminescence light bursts are also observed and an example of time evolution is reported.
All the measurements were accomplished using a deep sea module also described in this article.
Received: 20 April 2002 / Published online: 26 July 2002 相似文献
94.
On mechanical characteristics of nanocrystals 总被引:2,自引:0,他引:2
The dependence of the elastic moduli of a nanocrystal on its size is investigated theoretically with reference to a two-dimensional single-crystal strip. It is shown that the uncertainty (of a fundamental nature) in the size of a nanocrystal causes the determination of many of its mechanical characteristics to be ambiguous. It is found that the Cauchy-Green relations are modified and the elastic-constant tensor ceases to be symmetric; the size and shape of a nanocrystal render its mechanical properties more anisotropic. For a single-crystal strip, the Poisson ratio decreases and the Young modulus increases with decreasing thickness of the strip; in the case of a very thin crystal film (two atomic layers thick), these elastic moduli can differ from their macroscopic values by a factor of two. The size effects which make the continuum elasticity theory inapplicable to nanocrystals are estimated. The size effects that occur when the molecular dynamics method is applied for modeling macroscopic objects are also discussed. 相似文献
95.
A. G. Artukh G. F. Gridnev M. Gruszecki F. Koscielniak A. G. Semchenkov O. V. Semchenkova Yu. M. Sereda J. Szmider Yu. G. Teterev 《Physics of Atomic Nuclei》2002,65(3):393-399
A systematic investigation of the forward-angle inclusive yields of 2≤Z≤11 isotopes produced in collisions of 18O projectile nuclei with a 9Be target in the Fermi energy region (35A MeV) is performed. The measurements were based on the use of the COMBAS double achromatic kinematical separator in the spectrometry mode at the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research, FLNR (JINR, Dubna). The velocity, isotopic, and element distributions are presented. There is no unique mechanism that would explain the total set of results obtained in this experiment. A dominant role of low-energy reaction mechanisms is observed. The intensity of secondary beams of halolike nuclei 11Li, 12Be, and 14Be is determined. 相似文献
96.
97.
An analysis of events in the tunneling junction shows that the interaction of one-electron processes in a many-electron system may be a source of scale-invariant low-frequency fluctuations of conductivity (the interaction consists in that the quantum probability of an electron transition depends on fast random changes in the environment in the course of the transition, including the changes caused by analogous transitions). The theory relates flicker fluctuations in the tunneling conductivity to the discrete character of the spectrum of electron states and explains the nonlinearity of the noise-current characteristic observed in nanocomposites. 相似文献
98.
A method for stabilizing frequency based on using the soliton state of the Bose-Einstein condensate of alkali metal atoms as an atomic source was suggested. The critical total number of lithium condensate particles at which the existence of a quasi-one-dimensional soliton in the condensate was possible and the lifetime of such a soliton were estimated. The attainable accuracy of measuring reference transition frequencies in the suggested standard was shown to be substantially higher than with the known quantum frequency standards. 相似文献
99.
X-ray diffraction patterns of nanocrystalline Fe-Cu-Nb-Si-B (FINEMET) alloys reveal that bcc α-Fe/α-FeSi crystallites with
the average grain size of 20(5) nm are dispersed in amorphous matrix. Enhanced electron—electron interaction (EEI) and quantum
interference (QI) effects as well as electron-magnon (and/or electron-spin fluctuation) scattering turn out to be the main
mechanisms that govern the temperature dependence of resistivity. Of all the inelastic scattering processes, inelastic electron-phonon
scattering is the most effective mechanism to destroy phase coherence of electron wave functions. The diffusion constant,
density of states at the Fermi level and the inelastic scattering time have been estimated, for the first time, for the alloys
in question
Article presented at the International Symposium on Advances in Superconductivity and Magnetism: Materials, Mechanisms and
Devices, ASMM2D-2001, 25–28 September 2001, Mangalore, India. 相似文献
100.