全文获取类型
收费全文 | 1184篇 |
免费 | 124篇 |
国内免费 | 98篇 |
专业分类
化学 | 780篇 |
晶体学 | 23篇 |
力学 | 58篇 |
综合类 | 4篇 |
数学 | 171篇 |
物理学 | 370篇 |
出版年
2023年 | 17篇 |
2022年 | 22篇 |
2021年 | 34篇 |
2020年 | 28篇 |
2019年 | 34篇 |
2018年 | 36篇 |
2017年 | 30篇 |
2016年 | 39篇 |
2015年 | 48篇 |
2014年 | 70篇 |
2013年 | 92篇 |
2012年 | 92篇 |
2011年 | 100篇 |
2010年 | 66篇 |
2009年 | 44篇 |
2008年 | 57篇 |
2007年 | 61篇 |
2006年 | 63篇 |
2005年 | 45篇 |
2004年 | 50篇 |
2003年 | 29篇 |
2002年 | 26篇 |
2001年 | 25篇 |
2000年 | 25篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 19篇 |
1996年 | 15篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 21篇 |
1979年 | 6篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1969年 | 4篇 |
排序方式: 共有1406条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
A highly efficient and versatile synthetic method for amines was established using nitrobenzenesulfonamides (Ns-amides) as both a protecting and activating group. The alkylation of N-monosubstituted Ns-amides either proceeded conventionally or under Mitsunobu conditions to provide the N,N-disubstituted sulfonamides, and the Ns group was removed easily with soft nucleophiles via Meisenheimer complexes to give the corresponding secondary amines. The major advantage of this protocol is that both alkylation and deprotection proceed under mild conditions. Thus, with this methodology, the total synthesis of linear and/or macrocyclic natural polyamines can be accomplished efficiently. 相似文献
996.
We have investigated the length scale dependence of the transient evolution of surface roughness during homoepitaxial growth on GaAs(100), patterning the surface lithographically with an array of cylindrical pits of systematically varied sizes and spacings. Our atomic force microscopy measurements show that the amplitude of the surface corrugation has nonmonotonic behavior in both the length scale dependence and time evolution. This behavior allows us to rule out a number of existing continuum models of growth. 相似文献
997.
C.X.?Kan W.P.?CaiEmail author G.H.?Fu C.C.?Li L.D.?Zhang 《Applied Physics A: Materials Science & Processing》2004,78(8):1187-1191
This paper describes the preparation, by a novel and simple method, and the thermal stability of gold nanowires within monolithic mesoporous silica, involving soaking monolithic mesoporous silica in HAuCl4 aqueous solution, followed by drying and subsequent step-annealing. It has been shown that reduction of Au3+ within silica pores can occur during the drying process at 80 °C without any special reduction treatment. After initial annealing at 300 °C, Au nanowires are formed within the pores and are stable at temperatures up to 500 °C. Increasing the annealing temperature leads to a wire-to-rod-to-sphere morphological transformation of the Au nanowires. The surface-mediated reducing groups (-OH) on the silica pore are responsible for the low-temperature reduction of Au3+ ions, and the formation of Au nanowires is attributed to the uni-directional diffusion of Au atoms and the confinement of the pore channels. Spheroidization and breaking at some defects in the Au nanowires during annealing at elevated temperature result in the wire-to-rod-to-sphere transformation, accompanied by a blue-shift of the surface plasmon resonance over a very wide region in the optical spectrum. PACS 81.07.-b; 81.40.-z; 81.05.Rm 相似文献
998.
999.
Three limit distributions are obtained for waiting times in the collectors problem with group drawings. Bibliography: 4 titles.__________Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 298, 2003, pp. 126–133. 相似文献
1000.
We have observed a novel modification of a surface state due to a local strain field induced by a nanopattern formation. N adsorption on the Cu(100) surface induces a nanoscale grid pattern, where the clean Cu regions remain periodically. The lattice is contracted on the clean region by adjacent c(2 x 2)N domains, which have a larger lattice constant. On this patterned surface, we have investigated the Tamm-type surface state at M by means of angle-resolved ultraviolet photoelectron spectroscopy. The binding energy of the Tamm state shifts toward the Fermi level continuously with increasing N coverage, i.e., the intensity of the strain field. This behavior due to the strain field is completely different from that caused by electron confinement observed on vicinal surfaces. The Brillouin zone extension corresponding to the lattice contraction was also detected. 相似文献