全文获取类型
收费全文 | 476495篇 |
免费 | 5039篇 |
国内免费 | 1316篇 |
专业分类
化学 | 252246篇 |
晶体学 | 6829篇 |
力学 | 21938篇 |
综合类 | 14篇 |
数学 | 56339篇 |
物理学 | 145484篇 |
出版年
2020年 | 3749篇 |
2019年 | 4156篇 |
2018年 | 5264篇 |
2017年 | 5294篇 |
2016年 | 7843篇 |
2015年 | 4954篇 |
2014年 | 7793篇 |
2013年 | 20359篇 |
2012年 | 15670篇 |
2011年 | 19194篇 |
2010年 | 13300篇 |
2009年 | 13384篇 |
2008年 | 17876篇 |
2007年 | 18057篇 |
2006年 | 17071篇 |
2005年 | 15383篇 |
2004年 | 14146篇 |
2003年 | 12671篇 |
2002年 | 12677篇 |
2001年 | 14333篇 |
2000年 | 10894篇 |
1999年 | 8562篇 |
1998年 | 7213篇 |
1997年 | 6892篇 |
1996年 | 6731篇 |
1995年 | 6194篇 |
1994年 | 5930篇 |
1993年 | 5807篇 |
1992年 | 6289篇 |
1991年 | 6449篇 |
1990年 | 6148篇 |
1989年 | 6022篇 |
1988年 | 6197篇 |
1987年 | 5913篇 |
1986年 | 5655篇 |
1985年 | 7761篇 |
1984年 | 7882篇 |
1983年 | 6536篇 |
1982年 | 6965篇 |
1981年 | 6872篇 |
1980年 | 6448篇 |
1979年 | 6882篇 |
1978年 | 7048篇 |
1977年 | 7121篇 |
1976年 | 7150篇 |
1975年 | 6891篇 |
1974年 | 6698篇 |
1973年 | 6993篇 |
1972年 | 4658篇 |
1971年 | 3800篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The electronic spectrum of an icosahedral quasicrystal with a central-atom decoration of the Amman-Mackay network is investigated
in the tight-binding approximation. The quasicrystal is described as a structural limit of the optimal cubic approximants
with increasing period. The electronic spectra for the first four optimal cubic approximants do not contain the hierarchical
gap structure which is typical for the Cantor set of the spectrum of a one-dimensional quasicrystal. At the same time, as
the order of the approximant increases, the spectrum becomes singular throughout the entire energy scale.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 8, 557–562 (25 April 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
992.
An expression for the probability of thermally activated tunneling ionization in an electric field in the presence of a magnetic
field is obtained. It is shown that the logarithm of the ionization probability is proportional to the squared electric field,
and the coefficient of proportionality decreases with increasing magnetic field.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 10, 763–767 (25 November 1998) 相似文献
993.
994.
Mass distributions of fragments in the low-energy fission of nuclei from 187Ir to 213At have been analysed. This analysis has shown that shell effects in symmetric-mode fragment mass yields from the fission of pre-actinide nuclei could be described if one assumes the existence of two strongly deformed neutron shells in the arising fragments with neutron numbers N1 ≈ 52 and N2 ≈ 68. A new method has been proposed for quantitatively describing the mass distributions of the symmetric fission mode for pre-actinides with A ≈ 180–220. 相似文献
995.
High resolution finite difference schemes for solving the nonlinear model Boltzmann equations are presented for the computations of rarefied gas flows. The discrete ordinate method is first applied to remove the velocity space dependency of the distribution function which renders the model Boltzmann equation in phase space to a set of hyperbolic conservation laws with source terms in physical space. Then a high order essentially nonoscillatory method due to Harten et al. (J. Comput. Phys. 71, 231, 1987) is adapted and extended to solve them. Explicit methods using operator splitting and implicit methods using the lower-upper factorization are described to treat multidimensional problems. The methods are tested for both steady and unsteady rarefied gas flows to illustrate its potential use. The computed results using model Boltzmann equations are found to compare well both with those using the direct simulation Monte Carlo results in the transitional regime flows and those with the continuum Navier-Stokes calculations in near continuum regime flows. 相似文献
996.
997.
998.
P. González D. Fernández J. Pou E. García J. Serra B. León M. Pérez-Amor T. Szörényi 《Applied Physics A: Materials Science & Processing》1993,57(2):181-185
A study of the gas-phase parameters involved in ArF laser induced chemical vapour deposition of silicon-oxide thin films is presented. A complete set of experiments has been performed showing the influence of the concentration of the precursor gases, N2O and SiH4, and their influence on total and partial pressures on film growth and properties. In this paper we demonstrate the ability of this LCVD method to deposit silicon oxide films of different compositions and densities by appropriate control of gas composition and total pressure. Moreover, a material specific calibration plot comprising data obtained using different preparation techniques is presented, allowing determination of the stoichiometry of SiO
x
films by using FTIR spectroscopy independently of the deposition method. For the range of processing conditions examined, the experimental results suggest that chemical processes governing deposition take place mainly in the gas phase. 相似文献
999.
The interactions of Cu(II) in Cu(II)-exchanged K-L gallosilicate with adsorbates containing coordinative nitrogens in ammonia, pyridine, aniline, acetonitrile and hydrazine, and with the adsorbates carbon monoxide, benzene, propanol and dimethyl sulfoxide are investigated by electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies. These results are compared with those in Cu(II)-exchanged K-L aluminosilicate and the differences are discussed. Adsorption of ammonia produces a complex containing four molecules of ammonia based on resolved nitrogen superhyperfine interaction. Upon equilibrium with pyridine, Cu(II) forms a complex containing four molecules of pyridine in CuK-L gallosilicate and a complex containing only three molecules of pyridine in CuK-L aluminosilicate based on resolved nitrogen superhyperfine. Upon adsorption of aniline and acetonitrile, Cu(II) forms complexes containing two molecules of each in CuK-L gallosilicate based on resolved nitrogen superhyperfine. However, no resolved nitrogen superhyperfine between hydrazine and Cu(II) is seen. Adsorption of carbon monoxide, benzene, propanol and dimethyl sulfoxide causes changes in the ESR spectrum of Cu(II), indicating migration of Cu(II) into cation positions in the main channels where adsorbate coordination can occur. Cu(II) forms complexes with one molecule of benzene and two molecules of propanol based on ESEM data in both K-L gallosilicate and K-L aluminosilicate. However, Cu(II) interacts directly with one dimethyl sulfoxide in K-L aluminosilicate but only indirectly at a longer distance with one dimethyl sulfoxide in K-L gallosilicate based on ESEM data. 相似文献
1000.