全文获取类型
收费全文 | 444674篇 |
免费 | 5086篇 |
国内免费 | 1232篇 |
专业分类
化学 | 238277篇 |
晶体学 | 6594篇 |
力学 | 18941篇 |
综合类 | 13篇 |
数学 | 51881篇 |
物理学 | 135286篇 |
出版年
2021年 | 3913篇 |
2020年 | 4309篇 |
2019年 | 4635篇 |
2018年 | 6033篇 |
2017年 | 5943篇 |
2016年 | 9245篇 |
2015年 | 5844篇 |
2014年 | 8829篇 |
2013年 | 20894篇 |
2012年 | 16084篇 |
2011年 | 19811篇 |
2010年 | 13856篇 |
2009年 | 13668篇 |
2008年 | 17932篇 |
2007年 | 17790篇 |
2006年 | 16411篇 |
2005年 | 14699篇 |
2004年 | 13669篇 |
2003年 | 12036篇 |
2002年 | 11856篇 |
2001年 | 13537篇 |
2000年 | 10185篇 |
1999年 | 8028篇 |
1998年 | 6678篇 |
1997年 | 6412篇 |
1996年 | 6190篇 |
1995年 | 5559篇 |
1994年 | 5479篇 |
1993年 | 5291篇 |
1992年 | 5917篇 |
1991年 | 6008篇 |
1990年 | 5744篇 |
1989年 | 5544篇 |
1988年 | 5564篇 |
1987年 | 5456篇 |
1986年 | 5164篇 |
1985年 | 6662篇 |
1984年 | 6782篇 |
1983年 | 5386篇 |
1982年 | 5472篇 |
1981年 | 5441篇 |
1980年 | 5032篇 |
1979年 | 5442篇 |
1978年 | 5568篇 |
1977年 | 5464篇 |
1976年 | 5403篇 |
1975年 | 4984篇 |
1974年 | 4951篇 |
1973年 | 4948篇 |
1972年 | 3506篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
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
132.
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
133.
R. Grac M. Pugnet J.H. Collet B. Lambert C. De Matos H. L'Haridon A. Le Corre J.O. White 《Superlattices and Microstructures》1997,22(4):505-509
We report new results on the diffraction properties of photoinduced gratings in InGaAs/InGaAsP MQW structures. The original feature of this device is that the QWs are enclosed in an asymmetric Fabry–Perot microcavity in order to increase the diffraction efficiency. We observe oscillations in the diffraction efficiency due to resonant effects in the microcavity. The experimental spectra are compared with theory. Diffraction efficiency at 1.55 μm attains a maximum value of 2.7% at a write beam fluence of 260 μ J cm−2, and then decreases at higher fluences. We explain this phenomenon by an absorption saturation at high excitation. 相似文献
134.
The magnetic properties of existing amorphous iron based materials, i.e., Fe--metalloid, Fe--early transition metals and Fe--rare
earth alloys, are briefly discussed for some representative alloys. The spin orientation of amorphous Fe--metalloid alloys
has been determined by the angular dependence of hyperfine interactions. It is shown that in iron--early transition metals
ferromagnetic order is not long-ranged, but determined by magnetic clusters. The magnetic hyperfine field distributions of
Fe-rich iron--early transition metals consist of a high and a low field tail. The magnetic structure has been investigated
for two representative Fe--RE (RE = Er, Ce) amorphous alloys. For the first time, the magnetic coupling phenomenon in amorphous/crystalline
multilayers has been discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
135.
We have calculated inclusive two-jet cross sections in next-to-leading order QCD for low Q 2 ep collisions superimposing direct and resolved contributions. Infrared and collinear singularities in the virtual and real contributions are cancelled with the phase space slicing method. Various inclusive two-jet distributions have been computed. The results are compared with recent data from the ZEUS collaboration at HERA. 相似文献
136.
T. Engel M. Würtz S. Borneis St. Becker I. Klaft A. Kohl T. Kühl F. Laeri D. Marx K. Meier R. Neumann F. Schmitt P. Seelig L. Völker 《Hyperfine Interactions》1997,108(1-3):251-258
Laser spectroscopy at storage rings often suffers from a limited resolution due to Doppler-broadened resonances. Broadening
is caused by the velocity spread of the ions stored in the beam. In the following, the present status of our work on laser
systems specialized on the specific needs of laser spectroscopy at storage rings is reported.
Two pulsed laser systems were developed. One is a dye laser whose spectral bandwidth can be switched by inserting different
Littrow-prisms into the resonator. An increase in bandwidth up to a factor of 45 was achieved. This laser was used for fast
qualitative scans and high resolution measurements. The other laser system is a Nd : YAG laser pumped optical parametric oscillator.
It is a tunable laser system covering the spectral range from 410 to 4000 nm. Furthermore, a continuous wave laser with a
frequency shifted feedback cavity is described. It shows broadband emission with an adjustable bandwidth of up to 4.5 GHz.
This laser can be advantageous for laser cooling of ion beams.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
137.
A. Sánchez-Lavega A. Salazar A. Ocariz L. Pottier E. Gomez L.M. Villar E. Macho 《Applied Physics A: Materials Science & Processing》1997,65(1):15-22
Received: 16 September 1996/Accepted: 6 January 1997 相似文献
138.
139.
140.