全文获取类型
收费全文 | 19528篇 |
免费 | 6030篇 |
国内免费 | 8776篇 |
专业分类
化学 | 11669篇 |
晶体学 | 733篇 |
力学 | 3965篇 |
综合类 | 735篇 |
数学 | 4876篇 |
物理学 | 12356篇 |
出版年
2024年 | 196篇 |
2023年 | 627篇 |
2022年 | 799篇 |
2021年 | 809篇 |
2020年 | 679篇 |
2019年 | 629篇 |
2018年 | 531篇 |
2017年 | 702篇 |
2016年 | 751篇 |
2015年 | 812篇 |
2014年 | 1747篇 |
2013年 | 1394篇 |
2012年 | 1443篇 |
2011年 | 1530篇 |
2010年 | 1486篇 |
2009年 | 1609篇 |
2008年 | 1715篇 |
2007年 | 1366篇 |
2006年 | 1445篇 |
2005年 | 1618篇 |
2004年 | 1382篇 |
2003年 | 1605篇 |
2002年 | 1250篇 |
2001年 | 1261篇 |
2000年 | 986篇 |
1999年 | 719篇 |
1998年 | 665篇 |
1997年 | 573篇 |
1996年 | 568篇 |
1995年 | 587篇 |
1994年 | 569篇 |
1993年 | 408篇 |
1992年 | 417篇 |
1991年 | 401篇 |
1990年 | 434篇 |
1989年 | 346篇 |
1988年 | 86篇 |
1987年 | 67篇 |
1986年 | 45篇 |
1985年 | 28篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
32.
33.
34.
35.
提出了一种新的高功率宽带放大器,它由速调管和自由电子脉塞组成,用永久周期磁铁聚焦。研究了这种器件的电子束聚焦、群聚和辐射。在速调管提供一阶调制系数为30%,波导管的半径1.51cm,摇摆器的磁场振幅0.16T,周期7.92cm,电子束的电压490kV,电流50A和半径0.368cm的条件下,预估这种器件的辐射波频率为11.4GHz,输出辐射功率为18MW,输出辐射带宽为44%。 相似文献
36.
LiAlO2 single crvstals doped with Ti at concentration 0.2at.% are grown by the Czochralskl technique with dimensions φ42×55mm. Ti ions in the crystal are quadrivalence proven by comparing the absorption and fluorescence spectra of pure LiAlO2 and Ti: LiAlO2. After air and Li-rich atmosphere annealing, the absorption peaks in the range of 600-800nm disappear. We conclude that 682 and 756nm absorption peaks are attributed to the VLi and Vo absorptions, respectively: The peaks at 716nm and 798nm may stem from the VLi^+ and absorptions. The colour-centre model can be applied to explain the experimental phenomena. Ti^4+-doping produces more lithium vacancies in the LiAlO2 crystal. The intensities of [LiO4] and the associated bonds remain unchanged, which improves the anti-hydrolyzation and thermal stability of LiAlO2 crystals. 相似文献
37.
在微拢QCD框架内,利用重子结构的夸克模型,计算了r→pp^-ΛcΛ^-c,∑c∑^-c,ΞcΞ^-c,Ξcc Ξcc-,ΩcccΩ^-ccc。衰变的分支比,讨论了在T衰变中寻找Ωccc粲重子的可能性. 相似文献
38.
Viscosities and liquid structure of alloys Cu75Al25, Cu87Sn13 and Al-12.5%Si and pure metals Cu and Sn are investigated by using torsional oscillation viscometry and high temperature x-ray diffractometry. The viscosities of pure metals and eutectic alloy melts along with the short-range order structure are found to follow the Arrhenius law in a wide range of temperature above the liquidus. The breakpoints in Arrhenius plots emerge when the structures of alloy melts are transformed from the medium-range order structure to the short-range order structure. It has been found that the change of the viscosity of the metallic alloys is a characteristic of microstructure transformation in the related melts. 相似文献
39.
胡迪鹤 《数学物理学报(B辑英文版)》2005,25(1):23-29
This paper is a continuation of [8]. In Section 1, three kinds of communication are introdnced for two states and the relations among them are investigated. In Section 2, two kinds of period of a state are introdnced and it is obtained that the period is a “class property” ,i.e. two states x and y belong to same class implies the period of x is equal to the period of y. 相似文献
40.
Nanoporous Structure in Low-Dielectric Films with Positronium Annihilation Lifetime Spectroscopy 下载免费PDF全文
We investigate nano-porous structures in thin low-dielectric films, i.e. the pore sizes, distributions, and interconnectivity, by using depth profiled positronium annihilation lifetime spectroscopy (PALS). It is found that PALS has good sensitivity to probe both interconnected and closed pores in the range from 0.3nm to 3Onto, even in the film buried beneath a diffusion barrier. A series of low dielectric constant films of organosilicon-silsequioxane with different weight percentages of porogen have been comparatively investigated. The PALS technique can be used to distinguish the open porosity from the closed one, to determine the pore size, and to detect the percolation threshold with the increasing porosity that represents the transition from closed pores to interconnected pores.Furthermore, the pore percolation length can be derived. 相似文献