全文获取类型
收费全文 | 2301篇 |
免费 | 367篇 |
国内免费 | 270篇 |
专业分类
化学 | 1539篇 |
晶体学 | 14篇 |
力学 | 198篇 |
综合类 | 35篇 |
数学 | 356篇 |
物理学 | 796篇 |
出版年
2024年 | 1篇 |
2023年 | 54篇 |
2022年 | 50篇 |
2021年 | 54篇 |
2020年 | 96篇 |
2019年 | 78篇 |
2018年 | 56篇 |
2017年 | 53篇 |
2016年 | 92篇 |
2015年 | 113篇 |
2014年 | 101篇 |
2013年 | 156篇 |
2012年 | 197篇 |
2011年 | 210篇 |
2010年 | 161篇 |
2009年 | 148篇 |
2008年 | 162篇 |
2007年 | 131篇 |
2006年 | 159篇 |
2005年 | 84篇 |
2004年 | 93篇 |
2003年 | 83篇 |
2002年 | 58篇 |
2001年 | 39篇 |
2000年 | 69篇 |
1999年 | 51篇 |
1998年 | 52篇 |
1997年 | 51篇 |
1996年 | 34篇 |
1995年 | 30篇 |
1994年 | 19篇 |
1993年 | 35篇 |
1992年 | 44篇 |
1991年 | 19篇 |
1990年 | 17篇 |
1989年 | 15篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 17篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1959年 | 1篇 |
排序方式: 共有2938条查询结果,搜索用时 15 毫秒
1.
2.
Mingqing Ouyang 《Proceedings of the American Mathematical Society》1997,125(6):1845-1851
In this note we study how the Chern-Simons invariant behaves when two hyperbolic 3-manifolds are glued together along incompressible
thrice-punctured spheres. Such an operation produces many hyperbolic 3-manifolds with different numbers of cusps sharing the same volume and the same Chern-Simons invariant. The results in this note, combined with those of Meyerhoff and Ruberman, give an algorithm for determining the unknown constant in Neumann's simplicial formula for the Chern-Simons invariant of hyperbolic 3-manifolds.
thrice-punctured spheres. Such an operation produces many hyperbolic 3-manifolds with different numbers of cusps sharing the same volume and the same Chern-Simons invariant. The results in this note, combined with those of Meyerhoff and Ruberman, give an algorithm for determining the unknown constant in Neumann's simplicial formula for the Chern-Simons invariant of hyperbolic 3-manifolds.
3.
玻璃陶瓷材料中Tm3+离子红外到蓝色上转换发光 总被引:4,自引:0,他引:4
系统研究了PbF2+GeO2+WO3ⅩⅣTmF3玻璃陶瓷材料中,在近红外光(1.06μm)激发下,Tm3+离子的发光特性.实验中观测到Tm3+离子的两组峰值位置分别在20920cm-1和22173cm-1的蓝色上转换发光,并证实这两组上转换发光分别与吸收三个和四个光子有关,同时建立了上转换发光的模型.为了选择最佳掺杂浓度,详细地测量了Tm3+离子峰值为20920cm-1的蓝色上转换发光强度与TmF3浓度的关系. 相似文献
4.
5.
建立了一个四组分一维混合模型,对电子束注入大气产生大尺度等离子体的过程进行了数值模拟.结果表明了能量为140keV、流强为50mA/cm2的注入电子束,可以产生线度为0.5m,密度为1012cm-3量级的大气环境下等离子体.电子束所伴随的空间电荷效应由于等离子体的产生会很快消失,不影响后续的等离子体产生过程.电子束注入流强主要影响产生等离子体的密度,而电子束能量则同时影响其空间线度和密度.
关键词:
电子束
碰撞
电离 相似文献
6.
Band bending at the Ni/Si(100)-2×1 interface has been monitored by using Si 2p core level photoemission spectra. Two nickel-induced Si 2p components appear in the initial interaction between Ni and Si(100)-2×1, which is confined at the top surface and the first subsurface layers. At Ni coverage less than 0.0375 ML, Ni atoms prefer the adamantane interstitial sites on the first subsurface, but switch to the pedestal sites on Si dimer rows at higher Ni coverage. The change in the preferred occupation sites of Ni atoms on the Si(100)-2×1 surface strongly affects the amount of band bending shift. The shift towards higher binding energy, when Ni atoms occupy the adamantane interstitial sites, is attributed to metal-induced-gap states. While Ni atoms occupy the pedestal sites, the band bending shift is reduced which is attributed to the passivation of surface states. 相似文献
7.
Baochun Guo Xing Ouyang Changgeng Cai Demin Jia 《Journal of Polymer Science.Polymer Physics》2004,42(7):1192-1198
Montmorillonite (MMT) was modified with the acidified cocamidopropyl betaine (CAB) and the resulting organo‐montmorillonite (O‐MMT) was dispersed in an epoxy/methyl tetrahydrophthalic anhydride system to form epoxy nanocomposites. The intercalation and exfoliation behavior of the epoxy nanocomposites were examined by X‐ray diffraction and transmission electron microscopy. The curing behavior and thermal property were investigated by in situ Fourier transform infrared spectroscopy and DSC, respectively. The results showed that MMT could be highly intercalated by acidified CAB, and O‐MMT could be easily dispersed in epoxy resin to form intercalated/exfoliated epoxy nanocomposites. When the O‐MMT loading was lower than 8 phr (relative to 100 phr resin), exfoliated nanocomposites were achieved. The glass‐transition temperatures (Tg's) of the exfoliated nanocomposite were 20 °C higher than that of the neat resin. At higher O‐MMT loading, partial exfoliation was achieved, and those samples possessed moderately higher Tg's as compared with the neat resin. O‐MMT showed an obviously catalytic nature toward the curing of epoxy resin. The curing rate of the epoxy compound increased with O‐MMT loading. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1192–1198, 2004 相似文献
8.
Space time-index plots for probing dynamical nonstationarity 总被引:3,自引:0,他引:3
We propose a simple method to efficiently probe dynamical nonstationarity in observed time series. In a space time-index plot, the density distributions as a function of normalized time-index are V-shaped due to nonstationarity. We show that this method is workable for short data sets and typical examples are illustrated. 相似文献
9.
10.
Abstract We present an alternate definition of the mod Z component of the Atiyah-Patodi-Singer η invariant associated to (not necessary unitary) flat vector bundles, which identifies
explicitly its real and imaginary parts. This is done by combining a deformation of flat connections introduced in a previous
paper with the analytic continuation procedure appearing in the original article of Atiyah, Patodi and Singer.
* Project supported by the Cheung-Kong Scholarship of the Ministry of Education of China and the 973 Project of the Ministry
of Science and Technology of China.
(Dedicated to the memory of Shiing-Shen Chern) 相似文献