全文获取类型
收费全文 | 37362篇 |
免费 | 1049篇 |
国内免费 | 121篇 |
专业分类
化学 | 24096篇 |
晶体学 | 255篇 |
力学 | 691篇 |
综合类 | 2篇 |
数学 | 6877篇 |
物理学 | 6611篇 |
出版年
2023年 | 221篇 |
2022年 | 381篇 |
2021年 | 546篇 |
2020年 | 584篇 |
2019年 | 570篇 |
2018年 | 1055篇 |
2017年 | 818篇 |
2016年 | 1249篇 |
2015年 | 977篇 |
2014年 | 1030篇 |
2013年 | 2209篇 |
2012年 | 2195篇 |
2011年 | 2293篇 |
2010年 | 1393篇 |
2009年 | 1323篇 |
2008年 | 2047篇 |
2007年 | 2047篇 |
2006年 | 1848篇 |
2005年 | 1773篇 |
2004年 | 1489篇 |
2003年 | 1242篇 |
2002年 | 1090篇 |
2001年 | 755篇 |
2000年 | 741篇 |
1999年 | 530篇 |
1998年 | 400篇 |
1997年 | 388篇 |
1996年 | 496篇 |
1995年 | 354篇 |
1994年 | 402篇 |
1993年 | 339篇 |
1992年 | 317篇 |
1991年 | 290篇 |
1990年 | 295篇 |
1989年 | 259篇 |
1988年 | 239篇 |
1987年 | 233篇 |
1986年 | 224篇 |
1985年 | 295篇 |
1984年 | 319篇 |
1983年 | 215篇 |
1982年 | 228篇 |
1981年 | 255篇 |
1980年 | 232篇 |
1979年 | 170篇 |
1978年 | 180篇 |
1977年 | 178篇 |
1976年 | 163篇 |
1975年 | 152篇 |
1973年 | 133篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Rafael López 《Annals of Global Analysis and Geometry》1997,15(3):201-210
In this paper we study constant mean curvature compact surfaces with two Jordan curves in parallel planes as boundary and we investigate the point at which the surface inherits the symmetries of its boundary. 相似文献
2.
3.
V. Palyok I.A. Szabó D.L. Beke A. Kikineshi 《Applied Physics A: Materials Science & Processing》2002,74(5):683-687
Surface relief formation at holographic recording on amorphous selenium films was demonstrated and investigated. The presence
of this optical phase modulation component is essential for ensuring significant, stable and erasable optical recording in
a-Se films at 290–320 K temperatures, where conventional photodarkening was known as insignificant and unstable. Photocrystallization
can only be observed in super-exposed a-Se films at the given experimental conditions of hologram recording. Erasing behavior
of surface relief gratings under heat treatment was also investigated in order to reveal further details of the mechanism.
Photoinduced structural transformations within the amorphous phase, connected to local ordering under the condition of light-induced
fluidity, are proposed as an explanation for the relief formation and erasing. The observed reversible optical recording process
may be useful for the various optoelectronic applications of photoconductive a-Se layers.
Received: 12 June 2000 / Accepted: 6 June 2001 / Published online: 30 August 2001 相似文献
4.
José E. Valdés 《Operations Research Letters》2006,34(1):49-52
Components C1 and C2 form a series system. Suppose we can allocate the spare R1 in parallel with C1 and the spare R2 in parallel with C2, or otherwise, allocate R1 with C2 and R2 with C1. In this paper, we compare these two options using hazard rate ordering. 相似文献
5.
We present the design and study of waveguide structures based on porous silicon where the light confinement is not due to the usual total reflection effect but to the use of photonic crystals (PCs) as confining walls. These PC are omnidirectional mirrors (OMs), consisting of the periodic repetition of two porous silicon layers with different refractive indices and thicknesses. They reflect the radiation for all angles of incidence within a frequency range called the omnidirectional band gap (OBG). We have followed the PC formalism to investigate the properties of the OM as a multimode waveguide: the number of modes within the band gap, their field spatial distribution and their confinement as a function of the frequency and the core thickness. 相似文献
6.
Gábor Dörnyei Marietta Bárczai-Beke Gábor Blaskó Péter Péchy Csaba Szántay 《Tetrahedron letters》1982,23(28):2913-2916
Regioselective demethylation of 3,4-dihydropapaveraldine (a) at 7 and 3' positions affords a properly substituted diphenolic key intermidiate (d) for the synthesis of reticuline and N-norreticuline. 相似文献
7.
Sauer, Shelah, Vapnik and Chervonenkis proved that if a set system on n vertices contains many sets, then the set system has full trace on a large set. Although the restriction on the size of the
groundset cannot be lifted, Frankl and Pach found a trace structure that is guaranteed to occur in uniform set systems even
if we do not bound the size of the groundset. In this note we shall give three sequences of structures such that every set
system consisting of sufficiently many sets contains at least one of these structures with many sets. 相似文献
8.
G. Tóth 《Journal of Radioanalytical and Nuclear Chemistry》1989,137(4):259-264
The distribution of mono- poly- and unlabelled protein molecules in the radiolabelling mixture was calculated from probability point of view as a function of the radioiodine/protein ratio. 相似文献
9.
In order to study the influence of seeded impurities on ITER like reactor operation the COREDIV code has been extended to include the transport of several sputtered and/or injected impurities. In the COREDIV code the core plasma is treated in the frame of 1D radial transport model whereas in the edge the 2D multifluid code EPIT is used. The EPIT code solves in the slab geometry the MHD equations for densities and velocities for all ions species as well as for electron and ion temperatures. The iteration scheme in the code leads to steady state solution of coupled core and SOL system. The numerical results for Carbon and Nickel plate and seeded impurities Silicon and Neon are presented. 相似文献