全文获取类型
收费全文 | 32775篇 |
免费 | 3764篇 |
国内免费 | 2940篇 |
专业分类
化学 | 15909篇 |
晶体学 | 276篇 |
力学 | 1330篇 |
综合类 | 187篇 |
数学 | 2297篇 |
物理学 | 8243篇 |
综合类 | 11237篇 |
出版年
2024年 | 82篇 |
2023年 | 516篇 |
2022年 | 778篇 |
2021年 | 965篇 |
2020年 | 975篇 |
2019年 | 904篇 |
2018年 | 796篇 |
2017年 | 827篇 |
2016年 | 1129篇 |
2015年 | 1252篇 |
2014年 | 1485篇 |
2013年 | 1950篇 |
2012年 | 2214篇 |
2011年 | 2368篇 |
2010年 | 1637篇 |
2009年 | 1662篇 |
2008年 | 1915篇 |
2007年 | 1797篇 |
2006年 | 1611篇 |
2005年 | 1321篇 |
2004年 | 1076篇 |
2003年 | 937篇 |
2002年 | 919篇 |
2001年 | 750篇 |
2000年 | 723篇 |
1999年 | 1030篇 |
1998年 | 915篇 |
1997年 | 894篇 |
1996年 | 978篇 |
1995年 | 809篇 |
1994年 | 821篇 |
1993年 | 566篇 |
1992年 | 542篇 |
1991年 | 510篇 |
1990年 | 384篇 |
1989年 | 349篇 |
1988年 | 313篇 |
1987年 | 217篇 |
1986年 | 163篇 |
1985年 | 97篇 |
1984年 | 66篇 |
1983年 | 51篇 |
1982年 | 40篇 |
1981年 | 29篇 |
1980年 | 32篇 |
1979年 | 18篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
J. H. Lu Y. Y. Yang C. C. Chen C. H. Kuan H. T. Chen S. C. Lee 《Infrared Physics & Technology》2003,44(5-6):399-409
Superlattices have been demonstrated previously by our group in the design of the multicolor infrared photodetector. In general, the period number of the superlattice may be up to several dozens. In this paper, we have investigated the performance of the infrared photodetectors especially with 3, 5 and 15 periods. The detector structure contains a thick blocking barrier embedded between two superlattices with different period numbers but with the same well and barrier widths. This double-superlattice structure shows switchable spectral responses between two spectral regions by the voltage polarities. The photoresponse in each spectral region is also tunable by the magnitude of the applied voltage. The voltage-dependent behavior reveals the photoelectron relaxation and transport mechanism in the superlattice miniband. Superlattice with few periods has high electron group velocity, less relaxation effect and less collection efficiency. Therefore the superlattice with few periods may have better responsivity and narrower photoresponse range than the one with many periods. Based on the experimental results of our devices, it is observed that the superlattice with fewer periods has better detectivity, responsivity, wider range of the operational temperature, and more flexible miniband engineering than the conventional multiple quantum well infrared photodetector. 相似文献
112.
A novel Y-branch waveguide with two reflectors is proposed. The normalized transmitted power for the branching angle of 50°is greater than 70%, which is higher than conventional Y-branch with such wide angle. 相似文献
113.
本文针对炼镁还原罐在使用条件下的破坏形式及对该材质的成份设计进行了分析 ,还原罐材质在具有单一奥氏体的基础上 ,进行良好的合金化处理是提高其抗蠕变性和热强性的有效方法 ,对提高材质的使用寿命起到良好的作用。 相似文献
114.
The unified chaotic system contains the Lorenz system and the Chen system as two dual systems at the two extremes of its parameter
spectrum. This paper presents the design of bang bang controller for unified system and multitude of numerical experiments
under various control parameters. Numerical experiments meet the theoretic proof perfectly and convincingly demonstrated the
controller can be effectively used for unified systems with uncertainty of the equilibrium points. The method enriches the
applications of chaotic control.
Foundation item: Supported by the National Natural Science Foundation of China(50209012)
Biography: Deng Xiao-ming (1980-), male, Master candidate, research direction: chaos control. 相似文献
115.
116.
117.
JIN Lu 《数学年刊B辑(英文版)》2004,25(4):483-492
A unicity theorem concerning the total derivative for entire functions of several complex variables is proved. 相似文献
118.
119.
120.
Refractive-diffractive visual system for micro-display of LCOS 总被引:1,自引:0,他引:1
One head-mounted display visual system for computer entertainment and three-dimensional display of virtual-reality was achieved,
which consists of a hybrid refractive-diffractive eyepiece and a relay reflector. It can be used in micro-display of liquid
crystal on silicon (LCOS) diagonal of 18 mm. The whole system has better performance, with 60° field of view, 10 mm exit pupil,
23 mm eye relief, and reduces weight and size. 相似文献