全文获取类型
收费全文 | 3934篇 |
免费 | 744篇 |
国内免费 | 599篇 |
专业分类
化学 | 3208篇 |
晶体学 | 56篇 |
力学 | 192篇 |
综合类 | 29篇 |
数学 | 370篇 |
物理学 | 1422篇 |
出版年
2024年 | 6篇 |
2023年 | 80篇 |
2022年 | 104篇 |
2021年 | 139篇 |
2020年 | 196篇 |
2019年 | 190篇 |
2018年 | 173篇 |
2017年 | 160篇 |
2016年 | 221篇 |
2015年 | 233篇 |
2014年 | 221篇 |
2013年 | 332篇 |
2012年 | 357篇 |
2011年 | 384篇 |
2010年 | 247篇 |
2009年 | 249篇 |
2008年 | 302篇 |
2007年 | 232篇 |
2006年 | 234篇 |
2005年 | 188篇 |
2004年 | 154篇 |
2003年 | 141篇 |
2002年 | 124篇 |
2001年 | 100篇 |
2000年 | 85篇 |
1999年 | 79篇 |
1998年 | 49篇 |
1997年 | 33篇 |
1996年 | 43篇 |
1995年 | 30篇 |
1994年 | 37篇 |
1993年 | 22篇 |
1992年 | 27篇 |
1991年 | 20篇 |
1990年 | 25篇 |
1989年 | 12篇 |
1988年 | 14篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有5277条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
Three New Diarylpropanes from Dioscorea composita 总被引:1,自引:0,他引:1
ShunLiYANG XiKuiLIU 《中国化学快报》2005,16(1):57-60
Three new diarylpropanes were isolated from the dried rhizomes of Dioscorea composita Hemsl., and their structures were determined as 1, 3-bis-(2-hydroxy-4-methoxyphenyl) propane (1), 1, 3-bis-(2, 4-dihydroxyphenyl)propane (2), 1-(2′-hydroxy-4′-O-β-D- glucopymnosy-phenyl)-3-(2“, 4“-dihydroxyphenyl)propane (3), by spectroscopic analysis, respectively. 相似文献
45.
In1969,Sweedler[1]giventhedecompositiontheoreyofcoalgebraswhicharecocommu-tative.In1975,Kaplansky[2]showedthatanycoalgebracanbeuniquelydecomposedintoadirectsumofitsindecomposablesubcoalgebras.From1978to1992,Shudo[3]andXu[4]consructuredtheindecomposabledirectsumcomponentsofacoalggebra,viadefineequivalenceralationforthesetofsimplesubcoalgebras.Asweknow,themodolecoalgebraisthennaturalgeneralizationofcoalgebra.AndittakesplayanimportentroleintheDrinfelddouble.Inthispaper,wediscussthedecompositio… 相似文献
46.
47.
AN EFFECTIVE APPROACH FOR TWO-DIMENSIONAL POLARONS IN AN ASYMMETRIC QUANTUM DOT 总被引:1,自引:0,他引:1 下载免费PDF全文
Within the framework of Feynman-Haken path integral theory, we calculate the ground-state energy of two-dimensional polarons in asymmetric quantum dots for arbitrary electron-phonon coupling constants. From a general three-dimensional Hamiltonian, some interesting problems, such as polarons in quasi-one-dimensional quantum wires and quasi-zero-dimensional asymmetric or symmetric quantum dots can be easily discussed only by taking different limit in the whole coupling regime. After the numerical calculation, we find that the relative polaronic correction increases monotonically with the decrease of effective dot size, and it becomes more pronounced with increasing dimension and asymmetry. Moreover, despite the insensitivity of relative polaronic enhancement to the variation of coupling constant at weak coupling, the correction is related to the coupling constant as the latter becomes larger. 相似文献
48.
The conceptual design of a cryogenic system at temperature 2 K for the Peking University Free Electron Laser (PKU-FEL) facility is carried out. In order to minimize the scale of the cryogenic system and the running cost, the superconducting accelerator and the superconducting injector will mainly run at a long-pulsed mode. Optimization of the 2-K cryogenic system is carried out based on the heat load estimation and running parameters. Total cooling power of 52.5 W for the long-pulsed mode is necessary for the PKU cryogenic system. The PKU cryogenic system will be the first 2-K system for accelerators in China and will provide experience for similar facilities. 相似文献
49.
50.