全文获取类型
收费全文 | 355839篇 |
免费 | 6986篇 |
国内免费 | 5045篇 |
专业分类
化学 | 171601篇 |
晶体学 | 5290篇 |
力学 | 20984篇 |
综合类 | 332篇 |
数学 | 54323篇 |
物理学 | 115340篇 |
出版年
2021年 | 3640篇 |
2020年 | 3990篇 |
2019年 | 4643篇 |
2018年 | 12618篇 |
2017年 | 12975篇 |
2016年 | 10754篇 |
2015年 | 4952篇 |
2014年 | 7204篇 |
2013年 | 12689篇 |
2012年 | 14585篇 |
2011年 | 22492篇 |
2010年 | 15485篇 |
2009年 | 15807篇 |
2008年 | 19834篇 |
2007年 | 22461篇 |
2006年 | 9943篇 |
2005年 | 13474篇 |
2004年 | 10504篇 |
2003年 | 10072篇 |
2002年 | 8621篇 |
2001年 | 7736篇 |
2000年 | 6034篇 |
1999年 | 4459篇 |
1998年 | 3976篇 |
1997年 | 3793篇 |
1996年 | 3726篇 |
1995年 | 3190篇 |
1994年 | 3348篇 |
1993年 | 3188篇 |
1992年 | 3415篇 |
1991年 | 3554篇 |
1990年 | 3490篇 |
1989年 | 3458篇 |
1988年 | 3279篇 |
1987年 | 3270篇 |
1986年 | 3114篇 |
1985年 | 3755篇 |
1984年 | 3840篇 |
1983年 | 3253篇 |
1982年 | 3192篇 |
1981年 | 3071篇 |
1980年 | 2871篇 |
1979年 | 3353篇 |
1978年 | 3346篇 |
1977年 | 3424篇 |
1976年 | 3547篇 |
1975年 | 3245篇 |
1974年 | 3207篇 |
1973年 | 3386篇 |
1972年 | 2639篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
941.
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
942.
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
943.
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
944.
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
945.
A. Hoffknecht O. Uwira A. Frank S. Schennach W. Spies M. Wagner S. Schippers A. Müller R. Becker M. Kleinod N. Angert P.H. Mokler 《Hyperfine Interactions》1998,114(1-4):257-261
The origin of the widely observed enhancement of rates for electron-ion recombination at very low energies is still unknown.
We investigated the recombination of Au25+ with free electrons in a merged-beams experiment at the UNILAC accelerator of the GSI in Darmstadt. At E
rel= 0 eV we found an enormous enhancement factor of 365 compared to the theory of radiative recombination. An increase of the
electron density by a factor of 10 had not much influence on the measured rate coefficient.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
946.
947.
We consider the application of asymptotic methods of nonlinear mechanics (the Krylov-Bogolyubov-Mitropol'skii method) and
the method of separation of motions in nonlinear systems for the construction of an approximate solution of a nonlinear equation
that describes a nonstationary wave process.
Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 50, No. 3, pp. 357–371, March, 1998. 相似文献
948.
Yu. A. Mitropol’skii Nguyen Dong Anh Nguyen Dyk Tynh 《Ukrainian Mathematical Journal》1998,50(11):1731-1737
We construct the second approximation for random oscillations described by the Van der Pol equation which are under the action
of a broadband random process.
Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 50, No. 11, pp. 1517–1521, November, 1998. 相似文献
949.
T. N. Mamedov V. N. Duginov A. V. Stoykov I. L. Chaplygin D. Herlach U. Zimmermann V. N. Gorelkin J. Major M. Schefzik 《JETP Letters》1998,68(1):64-70
The residual polarization of negative muons in crystal silicon samples with phosphorus (P: 1.6×1013 cm−3) and antimony (Sb: 2×1018 cm−3) impurities is investigated. The measurements are made in a 1000 G magnetic field oriented in a direction transverse to the
muon spin in the temperature range 4–300 K. The relaxation rate and shift of the precession frequency in the silicon sample
with the phosphorus impurity are measured more accurately than previously. It is found that in antimony-doped silicon the
acceptor center
μ
A1 at temperatures below 30 K can be in both ionized and neutral states. The experimental data are interpreted on the basis
of spin-lattice relaxation of the magnetic moment of an acceptor center, formation of acceptor-donor pairs, and recombination
of charge carriers at the acceptor. Preliminary measurements showed a nonzero residual polarization of negative muons in germanium.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 61–66 (10 July 1998) 相似文献
950.
A dual Ginzburg-Landau model corresponding to SU(3) gluodynamics in the Abelian projection is studied. A string theory describing QCD string dynamics is obtained in this
model. The interaction of static quarks in mesons and baryons is investigated in an approximation to leading order.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 2, 109–114 (25 July 1998) 相似文献