全文获取类型
收费全文 | 1921篇 |
免费 | 106篇 |
国内免费 | 4篇 |
专业分类
化学 | 1248篇 |
晶体学 | 22篇 |
力学 | 74篇 |
数学 | 254篇 |
物理学 | 433篇 |
出版年
2023年 | 11篇 |
2022年 | 31篇 |
2021年 | 45篇 |
2020年 | 58篇 |
2019年 | 36篇 |
2018年 | 37篇 |
2017年 | 41篇 |
2016年 | 77篇 |
2015年 | 86篇 |
2014年 | 88篇 |
2013年 | 112篇 |
2012年 | 164篇 |
2011年 | 208篇 |
2010年 | 115篇 |
2009年 | 68篇 |
2008年 | 154篇 |
2007年 | 129篇 |
2006年 | 119篇 |
2005年 | 95篇 |
2004年 | 75篇 |
2003年 | 44篇 |
2002年 | 27篇 |
2001年 | 14篇 |
2000年 | 16篇 |
1999年 | 13篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 16篇 |
1995年 | 6篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1972年 | 4篇 |
1969年 | 2篇 |
1968年 | 4篇 |
1952年 | 2篇 |
排序方式: 共有2031条查询结果,搜索用时 31 毫秒
111.
Julien Legault Abderrazak Mejdi Noureddine Atalla 《Journal of sound and vibration》2011,330(24):5928-5948
This paper investigates the effects of finite dimensions on the vibro-acoustic response of orthogonally stiffened panels. Three types of excitations are considered: acoustical excitation, point force excitation and random excitation by a turbulent boundary layer. In each case, a spatially windowed periodic model is compared with a Rayleigh-Ritz model where the modes of the un-stiffened panel are used as the basis functions. The latter model accounts for the reflected wave field generated at the boundaries by assuming that the panel is simply supported. On the contrary, the windowed periodic model only accounts for finiteness on sound radiation (the assumption of an infinite periodic structure is used to calculate the panel response). Numerical studies show that when the bending wavelength becomes comparable or smaller than the stiffener spacing, the periodic model is able to reproduce the results obtained with the Rayleigh-Ritz model. To complement the study, the developed models are compared with numerical simulations (finite element method) and with experimental results. 相似文献
112.
113.
Viciu L Caruntu G Royant N Koenig J Zhou WL Kodenkandath TA Wiley JB 《Inorganic chemistry》2002,41(13):3385-3388
A new series of transition-metal oxyhalides (MCl)LaNb(2)O(7) (M = Cr, Mn, Fe, Co) have been prepared by a simple topochemical route. Layered perovskite hosts (ALaNb(2)O(7), A = Li, Na, K or Rb) were reacted with the corresponding anhydrous metal halides under mild reaction conditions (<400 degrees C). The compounds were examined by X-ray powder diffraction; the series appears to be isostructural with (CuCl)LaNb(2)O(7), and the layer spacings, with the exception of M = Co, follow the trend expected from transition-metal cationic radii. Thermal analysis with differential scanning calorimetry (DSC) shows the materials to be metastable where all four compounds decompose exothermically above 690 degrees C. 相似文献
114.
The high resolution two-photon spectroscopy of hydrogen is often limited by the second-order Doppler effect. To determine this effect, we apply a magnetic field perpendicular to the atomic beam. This field induces a quadratic motional Stark shift proportional, as the second-order Doppler effect, to v(2) (v atomic velocity). For some magnetic field, these two effects are opposite and the total shift due to the atomic velocity is reduced. We present the first observation of this effect for the 1S-3S transition in hydrogen. 相似文献
115.
This paper presents a study on the wave surfaces of anisotropic solids. In addition to the classical and real rays, which are defined by the normal to the slowness surfaces, it is obtained complex rays, which are associated to specific inhomogeneous plane waves. Referring to the complex Christoffel's equation and to the Fermat's principle, an intrinsic equation can be associated to these complex rays. Limiting the study to principal planes and plotting the associated complex wave surfaces, it can be shown that four energetic rays always exist in any directions for both quasi-isotropic and anisotropic media (even beyond the cusp). Consequently, it is always possible to define four closed wave surfaces (real or not). 相似文献
116.
117.
The modified CNDO method previously reported has been used to calculate the electronic spectra of five-membered rings containing sulphur. 相似文献
118.
119.
Folegot T de Rosny J Prada C Fink M 《The Journal of the Acoustical Society of America》2005,117(6):3757-3765
Time reversal arrays are becoming common tools whether for detection or tomography. These applications require the measurement of the response from the array to one or several receivers. The most natural way to record the impulse responses for several sources is to generate pulses successively from each emitting point and record simultaneously the signals from the receivers. However, this method is very time consuming or inefficient in terms of signal-to-noise ratio. To overcome this limitation quasi-orthogonal pseudonoise signals like Kasami sequences can be used. For guided wave propagation, a very high degree of orthogonality between the signal is necessary to allow an accurate measure of the whole multipath structure of the transfer function. Hence, in this work, we propose a new family of pseudo-orthogonal signals that is adapted to the environment and more specifically, to highly dispersive media. These adaptive instant records signals are used experimentally to detect targets using the time reversal operator decomposition method. The accuracy of the 15 x 15 transfer functions acquired simultaneously, and therefore the detection capability, are demonstrated in an experimental ultrasonic waveguide as a small-scale model of shallow water propagation including bottom absorption and reverberation. 相似文献
120.
We describe a spontaneous symmetry-breaking phenomenon between the intensities of the ordinary and extraordinary components of the fundamental field in intracavity type II harmonic generation. It is based on a triply resonant cavity containing a type II chi(2) crystal pumped at fundamental frequency omega0. The pump beam generates a second-harmonic mode at frequency 2omega0 that acts as a pump for frequency-degenerate type II parametric downconversion. Under operating conditions symmetric with respect to the ordinary and extraordinary components of the fundamental wave, we show a breaking of the symmetry of the intensities of these two waves. 相似文献