全文获取类型
收费全文 | 267418篇 |
免费 | 2363篇 |
国内免费 | 623篇 |
专业分类
化学 | 141992篇 |
晶体学 | 4162篇 |
力学 | 11922篇 |
综合类 | 9篇 |
数学 | 29483篇 |
物理学 | 82836篇 |
出版年
2019年 | 2290篇 |
2018年 | 3115篇 |
2017年 | 3112篇 |
2016年 | 4483篇 |
2015年 | 2657篇 |
2014年 | 4279篇 |
2013年 | 10672篇 |
2012年 | 8067篇 |
2011年 | 9894篇 |
2010年 | 7083篇 |
2009年 | 6875篇 |
2008年 | 9309篇 |
2007年 | 9510篇 |
2006年 | 8879篇 |
2005年 | 8069篇 |
2004年 | 7420篇 |
2003年 | 6732篇 |
2002年 | 6657篇 |
2001年 | 7325篇 |
2000年 | 5659篇 |
1999年 | 4359篇 |
1998年 | 3859篇 |
1997年 | 3845篇 |
1996年 | 3584篇 |
1995年 | 3332篇 |
1994年 | 3490篇 |
1993年 | 3189篇 |
1992年 | 3663篇 |
1991年 | 3666篇 |
1990年 | 3599篇 |
1989年 | 3457篇 |
1988年 | 3568篇 |
1987年 | 3463篇 |
1986年 | 3285篇 |
1985年 | 4360篇 |
1984年 | 4631篇 |
1983年 | 3872篇 |
1982年 | 4005篇 |
1981年 | 3931篇 |
1980年 | 3908篇 |
1979年 | 3876篇 |
1978年 | 4190篇 |
1977年 | 4107篇 |
1976年 | 4173篇 |
1975年 | 3849篇 |
1974年 | 3893篇 |
1973年 | 4050篇 |
1972年 | 2851篇 |
1971年 | 2378篇 |
1970年 | 2177篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
811.
G. Bouwmans B. Ségard P. Glorieux P. A. Khandokhin N. D. Milovsky E. Yu. Shirokov 《Radiophysics and Quantum Electronics》2004,47(10-11):729-742
This paper is devoted to the polarization dynamics of a longitudinally monomode bipolarized Nd:YAG laser: the low-frequency polarization dynamics of a microchip laser is studied experimentally and theoretically. The intensities and the relaxation oscillation spectrum of orthogonally polarized modes versus the direction of pump polarization is observed. A phase-sensitive model of a longitudinally monomode bipolarized solid-state laser with linear polarized diode laser pump is developed to account for the experimental observations. 相似文献
812.
813.
Almost thirty years ago, Penny G. Estabrooks asked “Where and what are the scalar mesons?” (P. Estabrooks, Phys. Rev. D 19, 2678 (1979)). The first part of her question can now be confidently responded (E. van Beveren et al., Z. Phys. C 30, 615 (1986)). However, with respect to the “What” many puzzles remain unanswered. Scalar and axial-vector mesons form part
of a large family of mesons. Consequently, though it is useful to pay them some extra attention, there is no point in discussing
them as isolated phenomena. The particularity of structures in the scattering of --basically-- pions and kaons with zero angular
momentum is the absence of the centrifugal barrier, which allows us to “see” strong interactions at short distances. Experimentally
observed differences and similarities between scalar and axial-vector mesons on the one hand, and other mesons on the other
hand, are very instructive for further studies. Nowadays, there exists an abundance of theoretical approaches towards the
mesonic spectrum, ranging from confinement models of all kinds, i.e., glueballs, and quark-antiquark, multiquark and hybrid configurations, to models in which only mesonic degrees of freedom
are taken into account. Nature seems to come out somewhere in the middle, neither preferring pure bound states, nor effective
meson-meson physics with only coupling constants and possibly form factors. As a matter of fact, apart from a few exceptions,
like pions and kaons, Nature does not allow us to study mesonic bound states of any kind, which is equivalent to saying that
such states do not really exist. Hence, instead of extrapolating from pions and kaons to the remainder of the meson family,
it is more democratic to consider pions and kaons mesonic resonances that happen to come out below the lowest threshold for
strong decay. Nevertheless, confinement is an important ingredient for understanding the many regularities observed in mesonic
spectra. Therefore, excluding quark degrees of freedom is also not the most obvious way of describing mesons in general, and
scalars and axial-vectors in particular. 相似文献
814.
815.
A. F. Semenchev V. G. Gavrilyachenko E. M. Kuznetsova E. N. Sklyarova 《Physics of the Solid State》2006,48(6):1146-1148
The details of the mechanical effects (twinning and microcracking) are clarified at various stages of dynamic fatigue of PbTiO3 crystals using a polarization microscope and selective etching. 相似文献
816.
S. A. Andronati A. A. Krys’ko B. M. Chugunov T. A. Kabanova A. G. Artemenko 《Russian Journal of Organic Chemistry》2006,42(8):1174-1182
A new series of RGDF mimetics, derivatives of 4-(isoindolin-5-yl)amino-4-oxobutanoic acid, was synthesized. The compounds obtained inhibit efficiently the thrombocytes aggregation in experiments in vitro; their biological targets are fibrinogen receptors. The antiaggregatory activity and the affinity correlate with the hydrophobicity of the compounds. 相似文献
817.
We have studied hydrogen adsorption on the Ge(1 1 1) c(2 × 8) surface using scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy (ARPES). We find that atomic hydrogen preferentially adsorbs on rest atom sites. The neighbouring adatoms appear higher in STM images, which clearly indicates a charge transfer from the rest atom states to the adatom states. The surface states near the Fermi-level have been followed by ARPES as function of H exposure. Initially, there is strong emission from the rest atom states but no emission at the Fermi-level which confirms the semiconducting character of the c(2 × 8) surface. With increasing H exposure a structure develops in the close vicinity of the Fermi-level. The energy position clearly indicates a metallic character of the H-adsorbed surface. Since the only change in the STM images is the increased brightness of the adatoms neighbouring a H-terminated rest atom, we identify the emission at the Fermi-level with these adatom states. 相似文献
818.
819.
We investigate the dependence of the relaxation time of the current flowing in a nematic cell submitted to an external dc voltage on the physical properties of the substrate. We show that previously presented analyses of the same problem are not very useful for practical applications. We compare our theoretical predictions with experimental data, and show that the agreement is rather good. The influence of the adsorption-desorption phenomenon on the relaxation time is also discussed. 相似文献
820.
M.W.C. Dharma-wardana A.H. MacDonald G.C. Aers D.J. Lockwood W.T. Moore R.L.S. Devine 《Superlattices and Microstructures》1987,3(6)
Results of Raman scattering experiments on (a) periodic superlattices made up of GaAs/InxGa1−xAs layers with high indium concentrations, (b) GaAs/Ga1−xAlxAs Fibonacci superlattices, are presented. We discuss the observed peak positions and intensities using the continuum theory of acoustic wave propagation in layered media and the photo-elastic coupling model. 相似文献