全文获取类型
收费全文 | 7012篇 |
免费 | 1017篇 |
国内免费 | 1130篇 |
专业分类
化学 | 5870篇 |
晶体学 | 119篇 |
力学 | 295篇 |
综合类 | 91篇 |
数学 | 798篇 |
物理学 | 1986篇 |
出版年
2024年 | 9篇 |
2023年 | 75篇 |
2022年 | 124篇 |
2021年 | 199篇 |
2020年 | 235篇 |
2019年 | 247篇 |
2018年 | 201篇 |
2017年 | 232篇 |
2016年 | 337篇 |
2015年 | 361篇 |
2014年 | 420篇 |
2013年 | 506篇 |
2012年 | 604篇 |
2011年 | 679篇 |
2010年 | 495篇 |
2009年 | 448篇 |
2008年 | 547篇 |
2007年 | 459篇 |
2006年 | 439篇 |
2005年 | 395篇 |
2004年 | 314篇 |
2003年 | 289篇 |
2002年 | 326篇 |
2001年 | 238篇 |
2000年 | 181篇 |
1999年 | 166篇 |
1998年 | 110篇 |
1997年 | 88篇 |
1996年 | 56篇 |
1995年 | 55篇 |
1994年 | 36篇 |
1993年 | 37篇 |
1992年 | 36篇 |
1991年 | 41篇 |
1990年 | 28篇 |
1989年 | 16篇 |
1988年 | 26篇 |
1987年 | 18篇 |
1986年 | 19篇 |
1985年 | 16篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1975年 | 4篇 |
1957年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有9159条查询结果,搜索用时 15 毫秒
31.
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
32.
33.
红外光谱对碱土金属二元羧酸盐结构的研究 总被引:16,自引:2,他引:14
研究了三十种二元羧酸金属盐的红外光谱,讨论了金属离子和二元酸的种类对二元酸盐配位结构的影响。发现Mg盐、Ba盐,Sr盐为螯合配位,Ca盐,Zn盐中同时存在螯合配位和桥式配位,二元酸的种类对羧酸盐配位结构没有影响。对羧酸盐在常温和熔融后的栩位方式和结构上的差异的研究结果表明,Mg盐,Ca盐与Sr盐,Ba盐在熔融后的结构变化不同。 相似文献
34.
We investigate the connection between the entanglement system in Minkowski spacetime and the black hole using the scaling analysis. Here we show that the entanglement system satisfies the Bekenstein entropy bound. Even though the entropies of two systems are the same form, the entanglement energy is different from the black hole energy. Introducing the Casimir energy of the vacuum energy fluctuations rather than the entanglement energy, it shows a feature of the black hole energy. Hence the Casimir energy is more close to the black hole than the entanglement energy. Finally, we find that the entanglement system behaves like the black hole if the gravitational effects are included properly. 相似文献
35.
Pure and Ce4+ doped anatase and rutile TiO2 were prepared by hydrothermal methods and characterized by XRD, TEM, UV-vis diffusion spectroscopy, and XPS measurements. The photocatalytic reactivity of the catalysts was evaluated by the photodegradation of Rhodamine B (RB) under ultraviolet irradiation. The photocatalytic efficiency of the rutile sample doped with an appropriate amount of Ce4+ was enhanced while all Ce4+ doped anatase samples showed a much lower activity than pure anatase. The reasons were discussed 相似文献
36.
37.
38.
39.
正交变换在重积分中某些应用 总被引:2,自引:0,他引:2
姚云飞 《数学的实践与认识》2003,33(9):139-144
正交变换是代数学的基本内容 ,其用途十分广泛 .重积分的计算往往存在技术性的困难 ,若利用“正交变换”的有关理论去解决某些重积分的计算问题是颇有功效的 .本文将以“正交变换”为工具 ,简洁的处理重积分的某些问题 相似文献
40.
Formation of p-type ZnO film on InP substrate by phosphor doping 总被引:3,自引:0,他引:3
Kyu-Hyun Bang Deuk-Kyu Hwang Min-Chul Park Young-Don Ko Ilgu Yun Jae-Min Myoung 《Applied Surface Science》2003,210(3-4):177-182
ZnO thin film was initially deposited on InP substrate by radio frequency (rf) magnetron sputtering and the diffusion process was performed using the closed ampoule technique where Zn3P2 was used as the dopant source. To verify the junction formation of ZnO thin films, the electrical properties were measured, and the effects of Zn3P2 diffusion on ZnO thin films were investigated. It is observed that the electrical property of the film is changed from n-type to p-type by dopant diffusion effect. Based on the results, it is confirmed that ZnO thin films can be a potential candidate for ultraviolet (UV) optical devices. 相似文献