全文获取类型
收费全文 | 191309篇 |
免费 | 40188篇 |
国内免费 | 36959篇 |
专业分类
化学 | 72633篇 |
晶体学 | 2208篇 |
力学 | 7224篇 |
综合类 | 1307篇 |
数学 | 14312篇 |
物理学 | 67770篇 |
综合类 | 103002篇 |
出版年
2024年 | 790篇 |
2023年 | 1697篇 |
2022年 | 2818篇 |
2021年 | 3166篇 |
2020年 | 3976篇 |
2019年 | 6644篇 |
2018年 | 6527篇 |
2017年 | 7877篇 |
2016年 | 8159篇 |
2015年 | 9183篇 |
2014年 | 10314篇 |
2013年 | 12137篇 |
2012年 | 12882篇 |
2011年 | 14575篇 |
2010年 | 17865篇 |
2009年 | 17902篇 |
2008年 | 11949篇 |
2007年 | 11047篇 |
2006年 | 10114篇 |
2005年 | 9587篇 |
2004年 | 9645篇 |
2003年 | 7366篇 |
2002年 | 7222篇 |
2001年 | 6906篇 |
2000年 | 5772篇 |
1999年 | 4691篇 |
1998年 | 3223篇 |
1997年 | 2914篇 |
1996年 | 3019篇 |
1995年 | 3365篇 |
1994年 | 3478篇 |
1993年 | 3550篇 |
1992年 | 3081篇 |
1991年 | 2742篇 |
1990年 | 2263篇 |
1989年 | 2256篇 |
1988年 | 2313篇 |
1987年 | 1427篇 |
1986年 | 1439篇 |
1985年 | 1020篇 |
1984年 | 1085篇 |
1983年 | 446篇 |
1982年 | 954篇 |
1981年 | 777篇 |
1980年 | 804篇 |
1979年 | 568篇 |
1978年 | 550篇 |
1977年 | 643篇 |
1976年 | 1045篇 |
1972年 | 535篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
The effects of quantum electromagnetic fluctuations upon the motion of a test charged particle are examined in a cylindrical spacetime in which one spatial is compactified. The mean squared fluctuations in the velocity and position of the test particle are calculated. It is found that the random motion of the test particle will be anisotropic. The possible consequences for theories with extra compactified spatial dimensions are discussed. 相似文献
982.
一种新型有机电致微腔结构的双模发射 总被引:4,自引:4,他引:0
采用结构Glass/DBR/ITO/NPB/NPB:Alq/Alq/Al制作了有机微腔电致发光器件。将空穴传输材料与发光材料以一定比例混合作为发光层,为了便于对比,在不改变有机层的膜厚的情况下同时制作了传统的异质结微腔器件,发现两种器件的发光光谱有很大不同,器件的复合效率与传统的异质结器件相比也得到了很大提高,这是因为将两种有机材料混合能消除界面势垒,提高器件的复合效率,从而提高了器件的发光性能,实现了微腔双模发射,且两个模式的半峰全宽分别为8nm和12nm。通过进一步优化器件结构可以实现微腔白光发射。 相似文献
983.
T. G. Kuznetsova K. G. Ione N. F. Salakhutdinov 《Reaction Kinetics and Catalysis Letters》1997,62(2):273-280
The interaction of α-methacrolein with mixedtrans- andcis-alloocimenes on β zeolite has been studied at room temperature in a solvent under various conditions. The scheme of the process
has been specified including the formation of (4+2) and (3+2)-cycloaddition products and strongly adsorbed alloocimene species. 相似文献
984.
WU Jiada WU Changzheng ZHONG Xiaoxia SONG Zhoumo LI Fuming 《Chinese Journal of Lasers》1997,6(2):161-168
l.IntroductionowingtotheirpromisingproPertiesandPOtentialapplications,transitionmetalni-trideshavedrawngreatattentionandthepreparationandinvestigationofthesecom-poundshavebeenasubjectbothofscientificandoftechnologicalinterest.Transitionmetalnitridescombineadvantagesofexce1lenthardness,highmeltingPOint,goodchemi-calstabilityandhigheIectricalconductivity[11,henceoverlaySofthesecompoundshavefoundwideappIicationsinvariousfie1ds.Molybdenumnitrides,inparticular,havealsoemergedasverypromisingcandi… 相似文献
985.
Da-Zhi Li Li Gan Zi-Qiang Yang Zheng Liang Jia-Yin Li 《International Journal of Infrared and Millimeter Waves》1997,18(10):1885-1896
The dispersion characteristic of the plasma-loaded relativistic backward wave oscillator has been analyzed. The theoretical
model has been established and the numerical calculations accord with the experimental results, which provides some useful
suggestions on the designing of slow-wave structure of BWO. 相似文献
986.
987.
988.
Pinning effect of lead lanthanum titanate (PLT) ferroelectric thin films with excess PbO of 20 mol% has been studied for deposition on diffe rent substrates. Silicon, sapphire and quartz were used as substrates on which P t/Ti or LaNiO3 thin films were deposited as bottom electrodes. Electron probe analysis results showed that there was still a certain amount of excess Pb in PLT films after annealing at 550 ℃ for 1 h, and the amount of it was dependent on the substrate used. The distribution of excess Pb in the films was investig ated by Auger electron spectroscopy depth profile. It was shown that the substrates and the bottom electrodes had significant effects on the content and distrib ution of excess Pb in PLT films. The excess Pb and its accumulation at the inter face between the film and bottom electrode may act as pinning centers and have a pinning effect on domains, which can be observed by abnormal P-E hysteresis loops and abnormal C-V curves. The excess Pb content in the films and the accumulation of Pb at the interface were high in PLT films deposited on Pt/Ti/S i, and considerable pinning effect was observed. As LaNiO3 would absorb most part of the excess Pb in PLT films, the content of excess Pb in the films deposited on LaNiO3/Si was very low and the pinning effect was hardly observed. 相似文献
989.
990.
H.-J. Scheibe D. Drescher A. Kolitsch A. Mensch 《Fresenius' Journal of Analytical Chemistry》1995,353(5-8):690-694
Morphology and structure of amorphous carbon films deposited with a pulsed arc source (LASER-ARC) have been studied using microscopical methods (SEM, TEM and AFM), electron diffraction and spectroscopical investigation (EELS). The parameters of the arc source and the deposition conditions (substrate temperature) influence morphology and structure of deposited amorphous carbon films. Especially the incorporation and growth of particles, embedded in the film have been investigated. By particle analysis using an optical microscope a majority of particles that is smaller than 500 nm has been determined. The morphology has been also demonstrated similar by AFM and TEM images. Their number and size of particles is strongly influenced by the deposition temperature. The structure of amorphous film is characterized by the EELS-spectra, but the particle structure was not detectable. 相似文献