全文获取类型
收费全文 | 17280篇 |
免费 | 2679篇 |
国内免费 | 3128篇 |
专业分类
化学 | 13538篇 |
晶体学 | 247篇 |
力学 | 965篇 |
综合类 | 283篇 |
数学 | 2160篇 |
物理学 | 5894篇 |
出版年
2024年 | 21篇 |
2023年 | 331篇 |
2022年 | 507篇 |
2021年 | 586篇 |
2020年 | 743篇 |
2019年 | 725篇 |
2018年 | 570篇 |
2017年 | 595篇 |
2016年 | 892篇 |
2015年 | 883篇 |
2014年 | 1016篇 |
2013年 | 1353篇 |
2012年 | 1364篇 |
2011年 | 1528篇 |
2010年 | 1199篇 |
2009年 | 1080篇 |
2008年 | 1233篇 |
2007年 | 1123篇 |
2006年 | 1053篇 |
2005年 | 873篇 |
2004年 | 778篇 |
2003年 | 619篇 |
2002年 | 694篇 |
2001年 | 539篇 |
2000年 | 434篇 |
1999年 | 363篇 |
1998年 | 283篇 |
1997年 | 219篇 |
1996年 | 231篇 |
1995年 | 162篇 |
1994年 | 178篇 |
1993年 | 149篇 |
1992年 | 113篇 |
1991年 | 124篇 |
1990年 | 125篇 |
1989年 | 62篇 |
1988年 | 55篇 |
1987年 | 44篇 |
1986年 | 48篇 |
1985年 | 51篇 |
1984年 | 22篇 |
1983年 | 31篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1978年 | 6篇 |
1969年 | 3篇 |
1957年 | 4篇 |
1936年 | 5篇 |
1928年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 718 毫秒
51.
52.
Baowei Qiao Jie Feng Yun Ling Ting’ao Tang Bomy Chen 《Applied Surface Science》2006,252(24):8404-8409
The effects of Si doping on the structural and electrical properties of Ge2Sb2Te5 film are studied in detail. Electrical properties and thermal stability can be improved by doping small amount of Si in the Ge2Sb2Te5 film. The addition of Si in the Ge2Sb2Te5 film results in the increase of both crystallization temperature and phase-transition temperature from face-centered cubic (fcc) phase to hexagonal (hex) phase, however, decreases the melting point slightly. The crystallization activation energy reaches a maximum at 4.1 at.% and then decreases with increasing dopant concentration. The electrical conduction activation energy increases with the dopant concentration, which may be attributed to the increase of strong covalent bonds in the film. The resistivity of Ge2Sb2Te5 film shows a significant increase with Si doping. When doping 11.8 at.% of Si in the film, the resistivity after 460 °C annealing increases from 1 to 11 mΩ cm compared to the undoped Ge2Sb2Te5 film. Current-voltage (I-V) characteristics show Si doping may increase the dynamic resistance, which is helpful to writing current reduction of phase-change random access memory. 相似文献
53.
54.
脉冲中立型时滞抛物方程的振动性 总被引:6,自引:0,他引:6
本文研究了一类脉冲中立型时滞抛物方程解的振动性及强振动性,获得了此类脉冲中立型时滞抛物方程解振动和强振动的代数判据. 相似文献
55.
56.
Xiangtong Qi 《Discrete Applied Mathematics》2007,155(3):416-422
We study a machine scheduling model in which job scheduling and machine maintenance activities have to be considered simultaneously. We develop the worst-case bounds for some heuristic algorithms, including a sharper worst-case bound of the SPT schedule than the results in the literature, and another bound of the EDD schedule. 相似文献
57.
We report the properties of a compact diode-pumped continuous-wave Nd:GdV04 laser with a linear cavity and different Nd-doped laser crystals. In a 0.2at.% Nd-doped Nd:GdVO4 laser, 1.54 W output laser power is achieved at 912nm wavelength with a slope efficiency of 24.8% at an absorbed pump power of 9.4W. With 0.3at.% Nd-doping concentration, we can obtain the either single-wavelength emission at 1064nm or 912nm or the dual-wavelength emission at 1064nm and 912nm by controlling the incident pump power. From an incident pump power of 11.6 W, the 1064nm emission between ^4Fa/2 and ^4I11/2 is suppressed completely by the 912nm emission between ^4Fa/2 and ^4I9/2. We obtain 670 mW output of the 912nm single-wavelength laser emission with a slope efficiency of 5.5% by taking an incident pump power of 18.4 W. Using a Nd:GdV04 laser with 0.4at.% Nd-doping concentration, we obtain either the single-wavelength emission at 1064nm or the dual-wavelength emission at both 1064nm and 912nm by increasing the incident pump power. We observe a strong competition process in the dualavelength laser. 相似文献
58.
59.
On Polynomial Functions over Finite Commutative Rings 总被引:1,自引:0,他引:1
Jian Jun JIANG Guo Hua PENG Qi SUN Qi Fan ZHANG 《数学学报(英文版)》2006,22(4):1047-1050
Let R be an arbitrary finite commutative local ring. In this paper, we obtain a necessary and sufficient condition for a function over R to be a polynomial function. Before this paper, necessary and sufficient conditions for a function to be a polynomial function over some special finite commutative local rings were obtained. 相似文献
60.
Characterization of iron surface modified by 2-mercaptobenzothiazole self-assembled monolayers 总被引:1,自引:0,他引:1
A self-assembled monolayer of 2-mercaptobenzothiazole (MBT) adsorbed on the iron surface was prepared. The films were characterized by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared reflection spectroscopy (FT-IR) and scanning electron microscopy (SEM). Besides, the microcalorimetry method was utilized to study the self-assembled process on iron surface and the adsorption mechanism was discussed from the power-time curve. The results indicated that MBT was able to form a film spontaneously on iron surface and the presence of it could protect iron from corrosion effectively. However, the assembling time and the concentration influence the protection efficiency. Quantum chemical calculations, according to which adsorption mechanism was discussed, could explain the experimental results to some extent. 相似文献