全文获取类型
收费全文 | 412669篇 |
免费 | 2940篇 |
国内免费 | 804篇 |
专业分类
化学 | 199154篇 |
晶体学 | 6100篇 |
力学 | 22309篇 |
综合类 | 17篇 |
数学 | 58028篇 |
物理学 | 130805篇 |
出版年
2020年 | 2954篇 |
2019年 | 3506篇 |
2018年 | 11687篇 |
2017年 | 12234篇 |
2016年 | 10126篇 |
2015年 | 4277篇 |
2014年 | 6391篇 |
2013年 | 14249篇 |
2012年 | 14526篇 |
2011年 | 23308篇 |
2010年 | 15734篇 |
2009年 | 16061篇 |
2008年 | 21070篇 |
2007年 | 23866篇 |
2006年 | 11498篇 |
2005年 | 15324篇 |
2004年 | 11985篇 |
2003年 | 11231篇 |
2002年 | 9686篇 |
2001年 | 9429篇 |
2000年 | 7307篇 |
1999年 | 5448篇 |
1998年 | 4689篇 |
1997年 | 4659篇 |
1996年 | 4440篇 |
1995年 | 3998篇 |
1994年 | 4049篇 |
1993年 | 3803篇 |
1992年 | 4346篇 |
1991年 | 4555篇 |
1990年 | 4296篇 |
1989年 | 4344篇 |
1988年 | 4229篇 |
1987年 | 4175篇 |
1986年 | 3937篇 |
1985年 | 5073篇 |
1984年 | 5286篇 |
1983年 | 4397篇 |
1982年 | 4503篇 |
1981年 | 4354篇 |
1980年 | 4085篇 |
1979年 | 4580篇 |
1978年 | 4757篇 |
1977年 | 4722篇 |
1976年 | 4761篇 |
1975年 | 4483篇 |
1974年 | 4455篇 |
1973年 | 4596篇 |
1972年 | 3298篇 |
1971年 | 2992篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
It is shown that the potential perturbation that shifts a chosen standing wave in space is a block of potential barrier and well for every wave bump between neighbouring knots. The algorithms shifting the range of the primary localization of a chosen bound state in a potential well of finite width are as well applicable to the scattering functions if states of the continuous spectrum are considered as bound states normalized to unity but distributed on an infinite interval with vanishing density. The potential perturbations of the same type on the half-axis concentrate the scattering wave at the origin, thus creating a bound state embedded into the continuous spectrum (zero width resonance). 相似文献
942.
Applying the mass shell condition forq-deformed open and closed strings, new critical space-time dimensions are derived.
Supported by the Algerian Ministry of High Education and Research under contract NoD2501/17/01/93.
Permanent address. 相似文献
943.
New effects are observed wherein the internal structure of the domain walls in a thin magnetic iron garnet film are modified
by the action of focused laser radiation. A single laser pulse with increasing power gives rise to the following: 1) displacement
of vertical Bloch lines in a domain wall; 2) generation of a pair of vertical Bloch lines on initially line-free walls; and,
3) an irreversible change in shape of a domain wall and the domain structure as a whole. The mechanism leading to the generation
and displacement of Bloch lines is connected with the motion of domain walls which is induced by a local change in the distribution
of demagnetizing fields as a result of a heating-induced decrease of the magnetization in the focal spot of the laser radiation.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 398–402 (25 September 1997) 相似文献
944.
The one-loop self-energy correction to the hyperfine splitting of the 1 s and 2 s states of hydrogenlike ions is calculated for both point and finite nuclei. The results of the calculation are combined with
other corrections to find the ground state hyperfine splitting in lithiumlike 209Bi80+ and 165Ho64+.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 1, 19–22 (10 July 1997)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
945.
We provide a detailed investigation of limits of N–soliton solutions of the Toda lattice as N tends to infinity. Our principal results yield new classes of Toda solutions including, in particular, new kinds of soliton–like
(i.e., reflectionless) solutions. As a byproduct we solve an inverse spectral problem for one–dimensional Jacobi operators
and explicitly construct tri–diagonal matrices that yield a purely absolutely continuous spectrum in (-1,1) and give rise
to an eigenvalue spectrum that includes any prescribed countable and bounded subset of .
Received: 16 October 1995/Accepted: 23 July 1996 相似文献
946.
The diffuse scattering of x rays in a four-layer waveguide-type heterostructure is investigated. The dynamic enhancement of
diffuse scattering is detected experimentally in regions corresponding to the excitation of waveguide modes for both the incident
and scattered waves.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 219–223 (25 August 1997) 相似文献
947.
Luminescence properties of anodic aluminum oxide films with organic luminophores embedded into pores
V. V. Gruzinskii A. V. Kukhto A. M. Mozalev V. F. Surganov 《Journal of Applied Spectroscopy》1997,64(4):497-502
Luminescence properties of porous anodic aluminum oxide films formed in a 0.6 M solution of citric acid and luminescence of
paraterphenyl, perylene, coumarin 7, and rhodamine 6G dyes adsorbed by the films are investigated. The nature of emitting
centers in anodic aluminum oxide is revealed. Intense photoluminescence of all tested dyes embedded into pores of anodic aluminum
oxide has been found. A redshift of fluorescence spectra of dyes adsorbed by the matrix and emergence of an additional longwave
band have been detected. Data obtained can be used in developing new thin-film luminescent coatings for future applications
in optoelectronics and molecular electronics.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No 4, pp. 483–488, July–August, 1997. 相似文献
948.
Results of experimental investigations of the volt-brightness characteristics, frequency dependences of brightness, and the
directional radiation pattern of electroluminescent MSDM, MSCM, and MSDCM emitters, where M stands for the first transparent
and second nontransparent electrodes, S is a semiconductor, D is a thin-film dielectric, and C is a silicone-based composite
liquid dielectric with a powdered segnetoelectric filler, developed on conventional “smooth” and rough glass substrates are
presented. It is shown that electroluminescent structures on rough surfaces have a brightness approximately two times higher
than that of similar structures developed on a “smooth” substrate.
Ul’yanovsk State University, 42, L. Tolstoi St., Ul’yanovsk, 432700, Russia. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 64, No. 4, pp. 507–512, July–August, 1997. 相似文献
949.
N. P. Venediktov M. Yu. Glyavin V. E. Zapevalov A. N. Kuftin A. S. Postnikova M. V. Yulpatova 《Radiophysics and Quantum Electronics》1997,40(4):336-342
A scheme for automated study of current-voltage characteristics of gyroresonance devices is developed. The effective emission
spread at the cathodes of powerful gyrotrons is studied by analysis of current-voltage characteristics. Experimental data
on the effective emission spread parameter for different modes are given. The permissible emission spread at the cathodes
of powerful gyrotrons is estimated, and the dependence of the electron beam parameters on the cathode emission spread is presented.
A complex measurement technique showing the contribution of different physical mechanisms to the cathode emission spread is
proposed.
Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh
Zavedenii, Radiofizika, Vol. 40, No. 4, pp. 506–516, April, 1997. 相似文献
950.
Merck W.F.H. Zatelepin V.N. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1997,25(5):947-953
The aim of this paper is to extend our knowledge about the gas-dynamic processes in arcs during immobility time. For this purpose, the conservation equations in a magnetohydrodynamic approximation were coupled with the thermochemical and Maxwell equations. Special features arc the introduction of dissociation and ionization of nitrogen and oxygen, and the simultaneous calculation of the distributions of current density and magnetic induction in the arc. Numerical calculations were performed with a reduced two-dimensional (2-D) time-dependent model. Results of the calculations were compared with measurements. The development in time of the measured and calculated are voltage and arc chamber pressure show very good agreement. The pumping effect of the double vortex in the arc region was confirmed by optical measurements. It is concluded that the three-layer model is a good representation for the main physical features during the immobility time, and that the presence of highly conducting gas in the downstream region of the arc is essential for its downstream movement 相似文献