全文获取类型
收费全文 | 586523篇 |
免费 | 4600篇 |
国内免费 | 1214篇 |
专业分类
化学 | 270628篇 |
晶体学 | 8803篇 |
力学 | 33221篇 |
综合类 | 10篇 |
数学 | 89899篇 |
物理学 | 189776篇 |
出版年
2021年 | 5071篇 |
2020年 | 5401篇 |
2019年 | 6315篇 |
2018年 | 13239篇 |
2017年 | 13648篇 |
2016年 | 14407篇 |
2015年 | 6796篇 |
2014年 | 11491篇 |
2013年 | 24097篇 |
2012年 | 21383篇 |
2011年 | 29169篇 |
2010年 | 21189篇 |
2009年 | 21572篇 |
2008年 | 26589篇 |
2007年 | 28278篇 |
2006年 | 19055篇 |
2005年 | 19314篇 |
2004年 | 17014篇 |
2003年 | 15930篇 |
2002年 | 15061篇 |
2001年 | 15711篇 |
2000年 | 12159篇 |
1999年 | 9173篇 |
1998年 | 8062篇 |
1997年 | 7731篇 |
1996年 | 7305篇 |
1995年 | 6411篇 |
1994年 | 6378篇 |
1993年 | 6251篇 |
1992年 | 6579篇 |
1991年 | 7114篇 |
1990年 | 6831篇 |
1989年 | 6770篇 |
1988年 | 6401篇 |
1987年 | 6576篇 |
1986年 | 6145篇 |
1985年 | 7473篇 |
1984年 | 7766篇 |
1983年 | 6557篇 |
1982年 | 6719篇 |
1981年 | 6295篇 |
1980年 | 6085篇 |
1979年 | 6723篇 |
1978年 | 6773篇 |
1977年 | 6831篇 |
1976年 | 6879篇 |
1975年 | 6432篇 |
1974年 | 6245篇 |
1973年 | 6455篇 |
1972年 | 5023篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
No analytic solutions of the Schrödinger equation are known for the quartic anharmonic oscillator. We show in this paper that there are closely related modified quartic oscillators with the potential depending on |x| for which analytic solutions for some states exist. These results can be extended to the higher order oscillators 相似文献
992.
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
993.
994.
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
995.
I. Peshko G. Galich M. Lopiychuk A. Khizhnyak V. Nakvasuk 《Optics & Laser Technology》1997,29(4):211-215
A laser system containing four CW Nd:YAG double-rod lasers, transforming optics and a fibre with input-output optics has been designed and investigated. It is shown that reduction of the beam parameter product of the non-Gaussian beams in the image space of the lens has made it possible to collect the emission of four lasers to the same fibre. Independent laser operation has provided the output power control in the range of 10–900 W with a stable light spot size on the input end of the fibre. 相似文献
996.
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
997.
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
998.
Processing-induced residual strains in solid cylinders of Nickel 200 were investigated using phase shifting moiré interferometry. Two different experimental approaches were used to study the strains produced during Tungsten-inert gas spot welding. A comparison of results for a ‘hot/fast’ and a ‘cool/slow’ weld demonstrate the capabilities of the general approach. Both experimental methods revealed distinct differences in the residual displacement and strain fields between the two types of welds. 相似文献
999.
In this article we have studied the nonlinear interaction between ellipticity and dissipation in a set of model equations (1.1) and established the relation between this interaction and chaos. In addition to theoretical investigations, extensive numerical simulations with these equations have been made, and different routes to chaos have been found. The numerical studies have revealed the chaotic nature of the solutions. 相似文献
1000.
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