全文获取类型
收费全文 | 22877篇 |
免费 | 2491篇 |
国内免费 | 1899篇 |
专业分类
化学 | 13708篇 |
晶体学 | 371篇 |
力学 | 1494篇 |
综合类 | 139篇 |
数学 | 2815篇 |
物理学 | 8740篇 |
出版年
2024年 | 19篇 |
2023年 | 347篇 |
2022年 | 414篇 |
2021年 | 534篇 |
2020年 | 657篇 |
2019年 | 672篇 |
2018年 | 584篇 |
2017年 | 456篇 |
2016年 | 803篇 |
2015年 | 758篇 |
2014年 | 1023篇 |
2013年 | 1423篇 |
2012年 | 1801篇 |
2011年 | 1920篇 |
2010年 | 1432篇 |
2009年 | 1288篇 |
2008年 | 1423篇 |
2007年 | 1334篇 |
2006年 | 1275篇 |
2005年 | 1067篇 |
2004年 | 854篇 |
2003年 | 743篇 |
2002年 | 724篇 |
2001年 | 869篇 |
2000年 | 652篇 |
1999年 | 525篇 |
1998年 | 446篇 |
1997年 | 376篇 |
1996年 | 396篇 |
1995年 | 332篇 |
1994年 | 305篇 |
1993年 | 242篇 |
1992年 | 224篇 |
1991年 | 221篇 |
1990年 | 171篇 |
1989年 | 161篇 |
1988年 | 115篇 |
1987年 | 77篇 |
1986年 | 63篇 |
1985年 | 84篇 |
1984年 | 78篇 |
1983年 | 43篇 |
1982年 | 51篇 |
1981年 | 43篇 |
1980年 | 38篇 |
1979年 | 22篇 |
1978年 | 28篇 |
1977年 | 22篇 |
1976年 | 20篇 |
1975年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
L. Tong Y. Tian Q. Y. Wang Y. S. Ling 《International Journal of Infrared and Millimeter Waves》2006,27(9):1307-1314
The paper introduces a special system calibration technology in s-parameters measurement of microwave and millimeter wave
devices. The 8-term errors module is built by analyzing the signals flowing in the measurement system. Then the calibration
technology using non-standard kits is designed on the base. Finally, the experiment using the calibration technology is introduced. 相似文献
42.
〈I〉型三角剖分下非张量积连续小波基的构造 总被引:1,自引:0,他引:1
多维非张量积小波是近年小波研究领域中的热点问题之一 ,它们与多维张量积小波相比具有更多的优势 .关于高维张量积、非张量积小波 ,目前已有一些很好的工作 (见文[2 ] [3 ] [4 ] ) ,但关于样条小波 ,还有许多问题有待于研究 .本文针对〈I〉型三角剖分下的二维线性元空间 ,讨论其具有紧支集和对称性的半正交样条小波基 .给定 x1 x2 平面上的〈I〉型三角剖分 (图 1 ( a)所示 ) ,记 j=( j1 ,j2 ) ,| j| =j1 + j2 ,πm= { 0≤ |j|≤ mCj1j2 xj11 xj22 ,Cj1,j2 是任意实数 }为次数不超过 m的代数多项式全体 .引入剖分尺度为 1的线性元空间 V0… 相似文献
43.
44.
F. Chen L. Liu Z. Shen G.Q. Xu T.S.A. Hor 《Applied Physics A: Materials Science & Processing》2002,74(2):317-319
Free-standing and supported hydrogenated amorphous carbon films (a:C–H) were prepared upon pyrolysis of the polymer formed
by ethanolamine (EA) and citric acid (CA), under an ambient atmosphere at 300 °C. EA facilitates the formation of the macroscopic
films, while CA is essential for obtaining the a:C–H microstructure, which comprises a mixture of sp2 and sp3 carbon.
Received: 29 May 2001 / Accepted: 17 August 2001 / Published online: 20 December 2001 相似文献
45.
46.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
47.
双向分束角对称的偏光分束镜设计与性能分析 总被引:4,自引:4,他引:0
为了获得分束角对称的偏光分束棱镜,在双Wollaston棱镜结构的基础上,通过合理设计棱镜左右两端晶体光轴的取向,使棱镜整体呈中心切面对称;在保证对正向入射的光对称分束的同时,对反向入射光同样可以对称分束,达到了双向对称分束的目的;在此基础上给出了晶体光轴的旋转角δ与棱镜结构角S以及与波长的关系;并分析了对633 nm设计的棱镜用于其他波长时分束角的对称性.结果表明:在±300 nm的光谱范围内,分束角的不对称度均小于0.24°. 相似文献
48.
49.
气垫导轨在刚体转动惯量测定实验中的应用 总被引:1,自引:0,他引:1
本文介绍了一种测量刚体转动惯量的新方法。即把气垫导轨和刚体转动仪结合起来来测量刚体的转动惯量,使传统的气垫导轨实验和刚体转动惯量测定实验得以更新,提高了实验测量的精度,拓展了实验内容。 相似文献
50.
Procedures for enhancing the intelligibility of a target talker in the presence of a co-channel competing talker were evaluated in tests involving (i) continuously voiced sentences spoken on a monotone, (ii) continuously voiced sentences with time-varying intonation, and (iii) noncontinuously voiced sentences produced with natural intonation. The procedures were based on the methods of harmonic selection and cepstral filtering [R.J. Stubbs and Q. Summerfield, J. Acoust. Soc. Am. 87, 359-372 (1990)]. Target and competing voices were combined at signal-to-noise ratios (SNRs) between -10 dB and +10 dB. Subjects were a group with normal hearing and a heterogeneous group with mild-moderate cochlear hearing impairments. Processing enhanced the target voice over a range of SNRs for each type of sentence and for most listeners. Enhancement was greatest at negative SNRs. Among the impaired listeners, benefit was generally greater for those with milder losses. These results consolidate and extend previous demonstrations that voice-separation algorithms that exploit the harmonic structure of the voiced portions of speech can enhance intelligibility. However, practical application of such algorithms depends on a solution to the problem of tracking the fundamental-frequency contour of one voice in the presence of a competing voice. 相似文献