全文获取类型
收费全文 | 252780篇 |
免费 | 3974篇 |
国内免费 | 1484篇 |
专业分类
化学 | 143412篇 |
晶体学 | 3478篇 |
力学 | 9426篇 |
综合类 | 65篇 |
数学 | 30546篇 |
物理学 | 71311篇 |
出版年
2021年 | 2045篇 |
2020年 | 2261篇 |
2019年 | 2470篇 |
2018年 | 3089篇 |
2017年 | 3096篇 |
2016年 | 4797篇 |
2015年 | 3325篇 |
2014年 | 4504篇 |
2013年 | 10777篇 |
2012年 | 9597篇 |
2011年 | 11485篇 |
2010年 | 7991篇 |
2009年 | 7764篇 |
2008年 | 10665篇 |
2007年 | 10677篇 |
2006年 | 10049篇 |
2005年 | 9211篇 |
2004年 | 8127篇 |
2003年 | 7097篇 |
2002年 | 6848篇 |
2001年 | 7348篇 |
2000年 | 5633篇 |
1999年 | 4138篇 |
1998年 | 3417篇 |
1997年 | 3361篇 |
1996年 | 3431篇 |
1995年 | 2944篇 |
1994年 | 3058篇 |
1993年 | 2901篇 |
1992年 | 3140篇 |
1991年 | 3150篇 |
1990年 | 2957篇 |
1989年 | 2814篇 |
1988年 | 2751篇 |
1987年 | 2699篇 |
1986年 | 2717篇 |
1985年 | 3542篇 |
1984年 | 3622篇 |
1983年 | 2971篇 |
1982年 | 3225篇 |
1981年 | 2992篇 |
1980年 | 2788篇 |
1979年 | 2929篇 |
1978年 | 3125篇 |
1977年 | 3166篇 |
1976年 | 3182篇 |
1975年 | 2898篇 |
1974年 | 2983篇 |
1973年 | 3049篇 |
1972年 | 2371篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
The radiative capture of ultracold neutrons traversing thin and thick homogeneous layers of matter is analyzed. The applicability range of the formulas for the probabilities of reflection, transmission, and capture in thick layers (under certain conditions, they admit a simple interpretation—it is often quoted in the literature—that is based on the effective capture cross section, which is in inverse proportion to the velocity of a neutron in matter) is investigated, along with the conditions under which there arises the effective capture cross section. 相似文献
993.
V. P. Koshelets S. V. Shitov L. V. Filippenko P. N. Dmitriev A. N. Ermakov A. S. Sobolev M. Yu. Torgashin 《Radiophysics and Quantum Electronics》2003,46(8-9):618-630
We overview recent achievements in the field of cryogenic submillimeter-wave receivers based on superconductor–insulator–superconductor (SIS) tunnel junctions. The main attention is paid to the novel superconducting integrated receivers (SIRs) with an on-chip superconducting local oscillator. The single-chip microcircuit of the receiver, which integrates a quantum mixer based on the nonlinearity of a quasi-particle current in the SIS junction, a planar superconducting receiving antenna, and a cryogenic local oscillator, is described. Being dc-powered only by batteries, such a microcircuit operates as a submillimeter-wave superheterodyne receiver without any additional microwave equipment. Such receivers are very attractive for radioastronomical research, space communication systems, and monitoring of the environment from satellites, balloons, and special aircraft. A breadboard of a superconducting spectrometer with a phase-locked flux-flow oscillator (FFO) has been developed and tested. A frequency resolution better than 10 kHz was reached at a frequency of 365 GHz. We describe a balloon-borne 500-650 GHz integrated spectrometer for oblique atmospheric sounding, developed for the international Terahertz Limb Sounder (TELIS) project. The first flight is scheduled for 2005. 相似文献
994.
Ilda Abe Rafael E. de Ges Jos L. Fabris Hypolito J. Kalinowski Mrcia Müller Meire C. Fugihara Rosane Falate Barbara W. Diesel Ricardo C. Kamikawachi Carmen L. Barbosa 《Optics and Lasers in Engineering》2003,39(5-6):537-548
In this work, we report production and modelling of both Bragg gratings and rocking filters in high birefringence fibre optics. Bragg gratings are produced by UV (257.0 nm) external interferometric exposition of a frequency-doubled Ar+ ion laser, whereas for rocking filters formation the visible Ar+ ion laser lines in 488.0 and 514.5 nm are used in an internal method. The spectral characteristics due to the birefringence properties are studied through numerical methods and experimental techniques. The spectral responsivity of the structures under temperature changes and stress application is presented. 相似文献
995.
In this paper, we propose and analyze an SQP-type method for solving linearly constrained convex minimization problems where the objective functions are too complex to be evaluated exactly. Some basic results for global convergence and local superlinear convergence are obtained according to the properties of the approximation sequence. We illustrate the applicability of our approach by proposing a new method for solving two-stage stochastic programs with fixed recourse. 相似文献
996.
997.
Brandau C. Bartsch T. Böhm S. Böhme C. Hoffknecht A. Kieslich S. Knopp H. Schippers S. Shi W. Müller A. Grün N. Scheid W. Steih T. Bosch F. Franzke B. Kozhuharov C. Krämer A. Mokler P. H. Nolden F. Steck M. Stöhlker T. Stachura Z. 《Hyperfine Interactions》2003,146(1-4):41-45
Hyperfine Interactions - An overview of measurements of dielectronic recombination (DR) with the heaviest lithiumlike ions is presented. The experiments have been carried out at the heavy ion... 相似文献
998.
To Professor Guillermo Torres on the occasion of his 70th birthday. 相似文献
999.
1000.
P.A. Postigo A.R. Alija L.J. Martínez M.L. Dotor D. Golmayo J. Snchez-Dehesa C. Seassal P. Viktorovitch M. Galli A. Politi M. Patrini L.C. Andreani 《Photonics and Nanostructures》2007,5(2-3):79-85
Two-dimensional photonic crystal lasers have been fabricated on III–V semiconductor slabs. Tuning of the spontaneous emission in micro and nanocavities has been achieved by accurate control of the slab thickness. Different structures, some of them of new application to photonic crystal lasers, have been fabricated like the Suzuki-phase or the coupled-cavity ring-like resonators. Laser emission has been obtained by pulsed optical pumping. Optical characterization of the lasing modes have been performed showing one or more laser peaks centred around 1.55 μm. Far field characterization of the emission pattern has been realized showing different patterns depending on the geometrical shape of the structures. These kinds of devices may be used as efficient nanolaser sources for optical communications or optical sensors. 相似文献