全文获取类型
收费全文 | 423468篇 |
免费 | 3786篇 |
国内免费 | 1461篇 |
专业分类
化学 | 229573篇 |
晶体学 | 6436篇 |
力学 | 17311篇 |
综合类 | 8篇 |
数学 | 48702篇 |
物理学 | 126685篇 |
出版年
2020年 | 3483篇 |
2019年 | 4004篇 |
2018年 | 5252篇 |
2017年 | 5115篇 |
2016年 | 7547篇 |
2015年 | 4635篇 |
2014年 | 7224篇 |
2013年 | 19059篇 |
2012年 | 13957篇 |
2011年 | 17055篇 |
2010年 | 11775篇 |
2009年 | 11519篇 |
2008年 | 15786篇 |
2007年 | 15998篇 |
2006年 | 14749篇 |
2005年 | 13527篇 |
2004年 | 12141篇 |
2003年 | 10945篇 |
2002年 | 10762篇 |
2001年 | 11844篇 |
2000年 | 9183篇 |
1999年 | 7005篇 |
1998年 | 5997篇 |
1997年 | 6032篇 |
1996年 | 5684篇 |
1995年 | 5052篇 |
1994年 | 4956篇 |
1993年 | 5061篇 |
1992年 | 5451篇 |
1991年 | 5538篇 |
1990年 | 5261篇 |
1989年 | 5224篇 |
1988年 | 5224篇 |
1987年 | 5038篇 |
1986年 | 4838篇 |
1985年 | 6481篇 |
1984年 | 6773篇 |
1983年 | 5534篇 |
1982年 | 6059篇 |
1981年 | 5869篇 |
1980年 | 5556篇 |
1979年 | 5821篇 |
1978年 | 6104篇 |
1977年 | 5986篇 |
1976年 | 6175篇 |
1975年 | 5641篇 |
1974年 | 5699篇 |
1973年 | 6156篇 |
1972年 | 3968篇 |
1971年 | 3234篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Periodic sound-pressure time functions with frequency components below 50 Hz were used to measure within their period (a) the temporal course of masking, called a masking-period pattern (MPP), and (b) the temporal course of suppression of delayed evoked otoacoustic emissions, called a suppression-period pattern (SPP). Three different time functions were used: an alternating Gaussian impulse, its first integral, and its second integral. In each case, the course of the SPP is a mirror image of that of the MPP: Small masking corresponds to small suppression, while strong masking coincides with almost total suppression. Since otoacoustic emissions are assumed to have their origin in the inner ear, it can be argued that simultaneous masking, an effect including central processing, is very strongly based on peripheral processes located in the cochlea. Both MPP and SPP are closely related to the second derivative of the sound-pressure time function. 相似文献
102.
103.
J.R. Cooper 《Journal of Molecular Spectroscopy》2006,239(1):51-58
The ν9 fundamental band of ethane occurs in the 12 μm region. It is the strongest band of ethane in a terrestrial window and is commonly used for the identification of ethane in the Jovian planets. The ν9 + ν4 − ν4 band occurs in the same region; neither can be analysed as an isolated band, since both are embedded in the torsional bath of the ground vibrational state. We report here two global fit models including data from both of these bands as well as the ν3 fundamental and the ν4, 2ν4 − ν4, and 3ν4 torsional transitions. The first is restricted to −5 ? KΔK ? 15 in the hot band and gives an excellent fit to the included data. Three resonant interactions are identified in this fit—a Coriolis interaction with two resonant cases between the ν9 torsional stack and that of the ground vibrational state (gs) and a resonant Fermi interaction between the ν3 fundamental and the gs. Hot band lines with KΔK < −5 are influenced by a fourth perturbation, with a crossing at −11 < KΔK < −10, which has been attributed to an interaction with the ν12 fundamental. A second fit, demonstrating a promising treatment of this interaction, is also presented. 相似文献
104.
The effect of hydrogen on the photoluminescence and planar conductivity of GaAs/InGaAs quantum-well heterostructures with an island Pd layer at the anodically oxidized surface was studied. Unlike continuous deposited Pd layers, island layers do not cause the formation of defects in the GaAs surface region and yet the Pd layer maintains high catalytic activity with respect to hydrogen. It is found that the thermal treatment of such a structure in a hydrogen atmosphere causes atomic-hydrogen passivation of the defects in quantum wells. Studies of the characteristics of planar photoresistors with an island Pd layer acting as hydrogen sensors show that their hydrogen detectivity is approximately two orders of magnitude higher than that of diode structures with continuous Pd layers. 相似文献
105.
E. G. Tarakanova 《Journal of Applied Spectroscopy》1991,54(4):357-362
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 4, pp. 581–587, April, 1991. 相似文献
106.
P. E. Cladis 《Journal of statistical physics》1991,62(5-6):899-925
We first discuss nonlinear aspects of phase transition theory applied to a particular liquid crystal phase transition. A simple derivation is given to show how two coupled Goldstone modes (one appearing as gauge fluctuations of the ordered phase) can force a phase transition, against all expectations, to take place discontinuously (theory of Halperin, Lubensky, and Ma)-but the discontinuity may be immeasurably small. Then, we describe a new dynamical test of phase transition order, developed by Cladiset al., that turns out to be more sensitive than x-ray diffraction and adiabatic calorimetry. Quantitative data found by this new method are in excellent agreement with the measurements of adiabatic calorimetry and x-ray diffraction as well as expectations implicit in the predictions of HLM.This is the text of an after-banquet talk given at the CNLS Workshop on the Dynamics of Concentrated Systems. 相似文献
107.
The instability of the plane interface between two uniform, superposed, electrically conducting and counter-streaming fluids through a porous medium is considered in the presence of a horizontal magnetic field. In the absence of surface tension, perturbations transverse to the direction of streaming are found to be unaffected by the presence of streaming if perturbations in the direction of streaming are ignored. For perturbations in all other directions there exists instability for a certain wavenumber range. The instability of this system is postponed by the presence of magnetic field. The magnetic field and surface tension are able to suppress this Kelvin-Helmholtz instability for small wavelength perturbations and the medium porosity reduces the stability range given in terms of a difference between the streaming velocities and the Alfvén velocity.This research forms a part of the research project awarded to the first author (R.C.S.) by the University Grants Commission. 相似文献
108.
E. K. Bashkirov 《Laser Physics》2006,16(8):1218-1226
An exact solution is found for the collective model of two identical two-level atoms that resonantly interact with a two-mode quantum electromagnetic field in an ideal cavity via two-photon nondegenerate transitions. In the case under study, at the initial moment, both field modes are in the coherent state and atoms are in the excited state. The time dependences of the atomic probabilities, the mean number of photons in the modes, and the statistics and squeezing of the photon modes are studied based on the exact solution. 相似文献
109.
110.