全文获取类型
收费全文 | 448841篇 |
免费 | 1991篇 |
国内免费 | 577篇 |
专业分类
化学 | 198933篇 |
晶体学 | 6453篇 |
力学 | 27461篇 |
综合类 | 9篇 |
数学 | 73867篇 |
物理学 | 144686篇 |
出版年
2020年 | 4162篇 |
2019年 | 5057篇 |
2018年 | 12361篇 |
2017年 | 12757篇 |
2016年 | 11948篇 |
2015年 | 4801篇 |
2014年 | 8491篇 |
2013年 | 15902篇 |
2012年 | 15568篇 |
2011年 | 22759篇 |
2010年 | 16651篇 |
2009年 | 17080篇 |
2008年 | 21021篇 |
2007年 | 23133篇 |
2006年 | 12999篇 |
2005年 | 14269篇 |
2004年 | 12380篇 |
2003年 | 12136篇 |
2002年 | 11318篇 |
2001年 | 10567篇 |
2000年 | 8382篇 |
1999年 | 6225篇 |
1998年 | 5714篇 |
1997年 | 5492篇 |
1996年 | 5177篇 |
1995年 | 4568篇 |
1994年 | 4597篇 |
1993年 | 4587篇 |
1992年 | 4654篇 |
1991年 | 5147篇 |
1990年 | 5070篇 |
1989年 | 5135篇 |
1988年 | 4789篇 |
1987年 | 4863篇 |
1986年 | 4542篇 |
1985年 | 5445篇 |
1984年 | 5659篇 |
1983年 | 4823篇 |
1982年 | 5063篇 |
1981年 | 4725篇 |
1980年 | 4377篇 |
1979年 | 5033篇 |
1978年 | 5221篇 |
1977年 | 5329篇 |
1976年 | 5521篇 |
1975年 | 5110篇 |
1974年 | 4937篇 |
1973年 | 5220篇 |
1972年 | 4342篇 |
1971年 | 3971篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The present paper analyzes the properties of structural phase transitions under the extremal conditions of high pressures. In the context of the theory of density functional (TDF), the pressures of the B1–B2 transitions are calculated for small alkali-halide crystals as functions of the crystal size. The size effect of the B1–B2 transition – an increase in the transition pressure with the decreasing crystal grain radius – has been established for all investigated halides except lithium fluoride for which the dependence is reverse. 相似文献
102.
Nikolaos V. Tsekos Michael Garwood Kmil Ugurbil 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,156(2):187
A new technique is presented for generating myocardial tagging using the signal intensity minima of the transition zones between the bands of 0° and 360° rotations, induced by a tandem of two adiabatic delays alternating with nutations for tailored excitation (DANTE) inversion sequences. With this approach, the underlying matrix corresponds to magnetization that has experienced 0° or 360° rotations. The DANTE sequences were implemented from adiabatic parent pulses for insensitivity of the underlying matrix to B1 inhomogeneity. The performance of the proposed tagging technique is demonstrated theoretically with computer simulations and experimentally on phantom and on the canine heart, using a surface coil for both RF transmission and signal reception. The simulations and the experimental data demonstrated uniform grid contrast and sharp tagging profiles over a twofold variation of the B1 field magnitude. 相似文献
103.
B. Dubrulle F. Hersant 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):379-386
We generalize an analogy between rotating and stratified shear flows. This analogy is summarized in Table 1. We use this analogy
in the unstable case (centrifugally unstable flow vs. convection) to compute the torque in Taylor-Couette configuration, as a function of the Reynolds number. At low Reynolds
numbers, when most of the dissipation comes from the mean flow, we predict that the non-dimensional torque G = T/ν2
L, where L is the cylinder length, scales with Reynolds number R and gap width η, G = 1.46η3/2(1 - η)-7/4
R
3/2. At larger Reynolds number, velocity fluctuations become non-negligible in the dissipation. In these regimes, there is no
exact power law dependence the torque versus Reynolds. Instead, we obtain logarithmic corrections to the classical ultra-hard (exponent 2) regimes: G = 0.50
. These predictions are found to be in excellent agreement with avail-able experimental data. Predictions for scaling of velocity
fluctuations are also provided.
Received 7 June 2001 and Received in final form 7 December 2001 相似文献
104.
105.
106.
107.
108.
Birational equivalence in the symplectic category 总被引:7,自引:0,他引:7
109.
The diffraction of plane surface gravitational waves by the edge of an ice cover lying on the surface of an incompressible fluid of infinitely great depth is considered. The ice cover is simulated by a thin elastic plate. The wave reflection and transmission coefficients are determined when it interacts with the ice cover. A wave field is constructed in the fluid under the conditions that a periodic lumped force and a lumped moment act on the edge of the ice cover. It is shown that as the incident wavelength increases the reflection coefficient tends to zero and the transmission coefficient tends to unity. 相似文献
110.
Results of an experiment on investigating the fluctuations of a sound signal with a frequency of 295 Hz on a stationary 32-km-long acoustic path in a shallow sea are presented. Hydrological conditions on the path were characterized by the presence of a weak thermocline and a frequent occurrence of intense internal wave trains. The space-time characteristics of these internal waves were measured in detail. Experimental evidence of the repetition of the forms of internal solitons in the variations of the amplitude and phase of an acoustic signal was obtained. 相似文献