全文获取类型
收费全文 | 219803篇 |
免费 | 4591篇 |
国内免费 | 2801篇 |
专业分类
化学 | 116957篇 |
晶体学 | 3591篇 |
力学 | 11527篇 |
综合类 | 169篇 |
数学 | 23641篇 |
物理学 | 71310篇 |
出版年
2021年 | 2535篇 |
2020年 | 2744篇 |
2019年 | 3202篇 |
2018年 | 4218篇 |
2017年 | 4165篇 |
2016年 | 5604篇 |
2015年 | 3118篇 |
2014年 | 5252篇 |
2013年 | 9752篇 |
2012年 | 8403篇 |
2011年 | 9668篇 |
2010年 | 7545篇 |
2009年 | 7653篇 |
2008年 | 8797篇 |
2007年 | 8612篇 |
2006年 | 7723篇 |
2005年 | 6773篇 |
2004年 | 6309篇 |
2003年 | 5727篇 |
2002年 | 5712篇 |
2001年 | 6062篇 |
2000年 | 4522篇 |
1999年 | 3573篇 |
1998年 | 3009篇 |
1997年 | 3049篇 |
1996年 | 2877篇 |
1995年 | 2495篇 |
1994年 | 2596篇 |
1993年 | 2424篇 |
1992年 | 2705篇 |
1991年 | 2795篇 |
1990年 | 2684篇 |
1989年 | 2731篇 |
1988年 | 2638篇 |
1987年 | 2616篇 |
1986年 | 2470篇 |
1985年 | 3075篇 |
1984年 | 3131篇 |
1983年 | 2622篇 |
1982年 | 2575篇 |
1981年 | 2545篇 |
1980年 | 2342篇 |
1979年 | 2710篇 |
1978年 | 2671篇 |
1977年 | 2870篇 |
1976年 | 2872篇 |
1975年 | 2664篇 |
1974年 | 2602篇 |
1973年 | 2711篇 |
1972年 | 2085篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
Hydrogenation and dehydrogenation of the Nd16Fe76B8 magnet are studied by X-ray diffraction analysis (XRD) and Mössbauer spectroscopy. The results of the samples treated under different hydrogen gas pressures at different temperatures are discussed. A special hydrogenation-dehydrogenation treatment of the Nd?Fe?B magnet cast can produce excellent isotropic magnet powders and the treated sample has passed a hydrogenation-disproportionation-recombination process. 相似文献
972.
N. Gass 《The Journal of the Operational Research Society》1994,45(2):133-142
A methodology is developed to analyse present and future crisis and conflict potentials of small or large geopolitical regions. A set of criteria is used to describe the present economic, social, political and military conditions of a country and the future criteria trends. A multi-criteria decision analysis model is invoked to compute the crisis and conflict potentials under simultaneous consideration of all other countries in that region. The methodology is demonstrated in the crisis and conflict potentials analysis of the former Soviet republics including bordering countries. 相似文献
973.
974.
A potential of mean torque is derived for a solute at infinite dilution in a uniaxial liquid crystal solvent, which contains terms originating from the dispersion interaction, and the electrostatic interaction between quadrupole moments on both molecules. It is shown that the electrostatic term is non-zero only if the solute-solvent vectors are distributed with lower than spherical symmetry. If this distribution has cylindrical symmetry then both the electrostatic and dispersion terms in the potential of mean torque are shown to depend on order parameters for the orientational distribution of the solute-solvent vectors, as well as on the order parameters of the solvent molecules. 相似文献
975.
Summary Epitaxial films of YBa2Cu3O7−x
were depositedin situ on LaAlO3 substrates using single-target 90° off-axis sputtering. The films were characterized by magnetization measurements (M vs. T, H), applying the field parallel toc-axis. The observed differences in theT
c andJ
c values are attributed to the different oxygen content in the superconducting films.
Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994. 相似文献
976.
An all-fibre optical system for optical interrogation and detection of the vibrations of a silicon microresonator is reported. Metal-coated silicon microresonators are excited by intensity modulated laser light delivered through an optical fibre, while the vibration of the resonators is detected by an optical fibre interferometer. Measurements have shown that an average optical power of 10 μW is sufficient to maintain the flexural vibration of the resonator. When the resonator is used as a pressure sensor, its resonant frequency changes from 62 kHz to 130 kHz as the pressure varies from -0°6 bar to 1 bar (gauge). A silicon resonator with 700 nm aluminium coating functions as a temperature sensor, showing a frequency shift from 262 kHz to 251 kHz when the temperature changes from 25 °C to 80 °C. 相似文献
977.
978.
979.
980.
E. Lippelt P. Birrer F. N. Gygax B. Hitti A. Schenck M. Weber 《Hyperfine Interactions》1991,64(1-4):477-487
The angular dependence of the muon Knight shift,K
μ, and the muon relaxation rate in Bi at 11 K were measured in external magnetic fields up to 1 T. BothK
μ and the second moment,M
2, are field dependent and involveP
4
0(cos θ) andP
4
3(cos θ) terms in the angular dependence. The Knight shift behaviour is discussed in terms of the dipole-dipole interaction
and the de Haas-van Alphen effect, a consistent interpretation was not achieved in either case. The field dependence ofM
2 is in complete contrast to the second moment calculations and points to a field dependent redistribution of the charge distribution
around the interstitial site. 相似文献