全文获取类型
收费全文 | 5228篇 |
免费 | 875篇 |
国内免费 | 594篇 |
专业分类
化学 | 3639篇 |
晶体学 | 60篇 |
力学 | 319篇 |
综合类 | 35篇 |
数学 | 588篇 |
物理学 | 2056篇 |
出版年
2024年 | 16篇 |
2023年 | 112篇 |
2022年 | 143篇 |
2021年 | 170篇 |
2020年 | 201篇 |
2019年 | 151篇 |
2018年 | 163篇 |
2017年 | 144篇 |
2016年 | 233篇 |
2015年 | 233篇 |
2014年 | 310篇 |
2013年 | 349篇 |
2012年 | 459篇 |
2011年 | 467篇 |
2010年 | 354篇 |
2009年 | 321篇 |
2008年 | 325篇 |
2007年 | 322篇 |
2006年 | 288篇 |
2005年 | 249篇 |
2004年 | 195篇 |
2003年 | 140篇 |
2002年 | 158篇 |
2001年 | 122篇 |
2000年 | 107篇 |
1999年 | 119篇 |
1998年 | 110篇 |
1997年 | 98篇 |
1996年 | 94篇 |
1995年 | 67篇 |
1994年 | 82篇 |
1993年 | 56篇 |
1992年 | 57篇 |
1991年 | 57篇 |
1990年 | 35篇 |
1989年 | 52篇 |
1988年 | 38篇 |
1987年 | 36篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有6697条查询结果,搜索用时 11 毫秒
21.
22.
23.
24.
通过对Eu2-xPbxRu2O7(x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0和1.8)系列样品的结构、电阻和磁化率的观测,结果发现,随着Pb替代浓度x值的增加,样品的电阻率逐渐减小,系统在x=0.8附近发生了金属-绝缘体(M-I)相变;Ru4+的局域磁矩及其自旋玻璃冻结温度TG也随之降低. 在该体系中,Pb2+对Eu3+的部分替代使样品中载流子浓度增加,Pb的6p能带与Ru 4d电子的T2g能带混合,能带得以拓宽,Ru 4d电子的巡游性增强,导致该体系物性的系列变化. 相似文献
25.
使用参数Dioid模块网络法,把含大量摄动参数的在普通极大代数意义下非线性状态空间模型在参数Dioid意义下线性化,在此基础上研究一类过程摄动系统的无阻塞鲁棒性.给出了有限缓冲串行生产系统在没有缓冲器下无阻塞的充要条件和充分条件. 相似文献
26.
27.
Femtosecond laser is a perfect laser source for materials processing when high accuracy and small structure size are required. Due to the ultra short interaction time and the high peak power, the process is generally characterized by the absence of heat diffusion and, consequently molten layers. Various induced structures have been observed in materials after the femtosecond laser irradiation. Here, we report on fabrication of micro-optical devices by the femtosecond laser. 1) formation of optical waveguide with internal loss less than 0.5dB/cm in the wavelength region from 1.2 to 1.6 mm, by translating a silica glass perpendicular to the axis of the focused femtosecond laser beam; 2) nano-scale valence state manipulation of active ions inside transparent materials; 3) space-selective precipitation and control of metal nanoparticles inside transparent materials; The mechanisms and applications of the femtosecond laser induced phenomena were also discussed. 相似文献
28.
The field of photonic crystals has, over the past few years, received dramatically increased attention. Photonic crystals are artificially engineered structures that exhibit a periodic variation in one, two, or three dimensions of the dielectric constant, with a period of the order of the pertinent light wavelength. Such structures in three dimensions should exhibit properties similar to solid-state electronic crystals, such as bandgaps, in other words wavelength regions where light cannot propagate in any direction. By introducing defects into the periodic arrangement, the photonic crystals exhibit properties analogous to those of solid-state crystals. The basic feature of a photonic bandgap was indeed experimentally demonstrated in the beginning of the 1990s, and sparked a large interest in, and in many ways revitalized, photonics research. There are several reasons for this attention. One is that photonic crystals, in their own right, offer a proliferation of challenging research tasks, involving a multitude of disciplines, such as electromagnetic theory, nanofabrication, semi-conductor technology, materials science, biotechnology, to name a few. Another reason is given by the somewhat more down-to-earth expectations that photonics crystals will create unique opportunities for novel devices and applications, and contribute to solving some of the issues that have plagued photonics such as large physical sizes, comparatively low functionality, and high costs. Herein, we will treat some basics of photonic crystal structures and discuss the state-of-the-art in fabrication as well give some examples of devices with unique properties, due to the use of photonic crystals. We will also point out some of the problems that still remain to be solved, and give a view on where photonic crystals currently stand. 相似文献
29.
Au nanoparticles were precipitated inside Au+-doped glass samples after irradiation by femtosecond laser or x-ray. Femtosecond laser and X-ray irradiation result in decreasing of anneal temperature and critical size for the precipitation of Au nanoparticles. 相似文献
30.
CONE-DIRECTED CONTINGENT DERIVATIVES AND GENERALIZED PREINVEX SET-VALUED OPTIMIZATION 总被引:2,自引:0,他引:2
丘京辉 《数学物理学报(B辑英文版)》2007,27(1):211-218
By using cone-directed contingent derivatives, the unified necessary and suffi-cient optimality conditions are given for weakly and strongly minimal elements respectively in generalized preinvex set valued optimization. 相似文献