全文获取类型
收费全文 | 25055篇 |
免费 | 2033篇 |
国内免费 | 1098篇 |
专业分类
化学 | 12427篇 |
晶体学 | 434篇 |
力学 | 1549篇 |
综合类 | 55篇 |
数学 | 2509篇 |
物理学 | 11212篇 |
出版年
2024年 | 33篇 |
2023年 | 279篇 |
2022年 | 485篇 |
2021年 | 519篇 |
2020年 | 479篇 |
2019年 | 473篇 |
2018年 | 554篇 |
2017年 | 458篇 |
2016年 | 786篇 |
2015年 | 631篇 |
2014年 | 886篇 |
2013年 | 1436篇 |
2012年 | 1774篇 |
2011年 | 2015篇 |
2010年 | 1419篇 |
2009年 | 1382篇 |
2008年 | 1511篇 |
2007年 | 1435篇 |
2006年 | 1418篇 |
2005年 | 1132篇 |
2004年 | 962篇 |
2003年 | 739篇 |
2002年 | 678篇 |
2001年 | 1059篇 |
2000年 | 790篇 |
1999年 | 703篇 |
1998年 | 500篇 |
1997年 | 500篇 |
1996年 | 443篇 |
1995年 | 357篇 |
1994年 | 326篇 |
1993年 | 252篇 |
1992年 | 274篇 |
1991年 | 211篇 |
1990年 | 217篇 |
1989年 | 175篇 |
1988年 | 122篇 |
1987年 | 113篇 |
1986年 | 108篇 |
1985年 | 115篇 |
1984年 | 70篇 |
1983年 | 53篇 |
1982年 | 35篇 |
1981年 | 32篇 |
1980年 | 23篇 |
1977年 | 19篇 |
1976年 | 29篇 |
1975年 | 27篇 |
1974年 | 21篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Polycrystalline Sn1−xMnxO2 (0≤x≤0.05) diluted magnetic semiconductors were prepared by solid-state reaction method and their structural and magnetic properties had been investigated systematically. The three Mn-doped samples (x=0.01, 0.03, 0.05) undergo paramagnetic to ferromagnetic phase transitions upon cooling, but their Curie temperatures are far lower than room temperature. The magnetization cannot be attributed to any identified impurity phase. It is also found that the magnetization increases with increasing Mn doping, while the ratio of the Mn ions contributing to ferromagnetic ordering to the total Mn ions decreases. 相似文献
142.
143.
SiC films doped with aluminum (Al) were prepared by the rf-magnetron sputtering technique on p-Si substrates with a composite target of a single crystalline SiC containing several Al pieces on the surface. The as-deposited films were annealed in the temperature range of 400-800 °C under nitrogen ambient. The thin films have been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results show that the introduction of Al into films hinders crystalline formation process. And with the increase of annealing temperature, more Si particles are formed in the films, which strongly affect the optical absorption properties. The photoluminescence (PL) spectra of the samples show two peaks at 370 nm and 412 nm. The intensities of the PL peaks are evidently improved after Al doped. We attribute the origin of the two PL peaks to a kind of Si-related defect centres. The obtained results are expected to have important applications in modern optoelectronic devices. 相似文献
144.
145.
利用扫描隧道显微镜研究石墨表面的大尺度周期性图样.研究结果表明,莫尔图起源于石墨深层的缺陷,实验结果与理论完全吻合,并且第一次在实验上证明了纳米波可以穿透多层石墨而没有明显衰减. 相似文献
146.
147.
针对高功率二极管重复率抽运的V型非稳腔Yb3+∶YAG激光头,提出了利用金刚石窗口冷却和直接水冷相结合的复合冷却设计.在YAG片的抽运面进行直接水冷,同时在激光提取面利用金刚石窗口冷却介质.金刚石优异的导热性能不仅能够有效地冷却激光介质,还能消除横向的温度梯度,解决了高功率激光器冷却和高功率抽运的矛盾.模拟结果表明对掺杂10 at %厚度为1.6 mm的Yb3+∶YAG片在抽运功率密度为20 kW/cm2,重复频率为10 Hz的条件下,要将最高温度控制在可接受的范围内(比如320 K),周围冷却水的对流换热系数约为4000 W/m2K. 相似文献
148.
149.
150.
X.F. Hu 《Applied Surface Science》2006,252(13):4625-4627
The synthetic antiferromagnets (SAF) have been used in spin-valve sensor in data storage industry [1]. We report a new hard/Ru/soft sandwich structure (SHBL) fabricated by pulsed lased deposition to replace current single layer structure for information recording application. SHBL consists of two magnetic layers separated by thin nonmagnetic layers, typically with Ru layers of 0.7-1.2 nm, through which antiferromagnetic coupling is induced. Varying the relative thickness of the magnetic layers, the spacer layers, and the type of magnetic materials can alter magnetic properties of CoCrPt/Ru/CoFe superlattice. The coercivity Hc and grain size of magnetic layer is also dependent on the laser fluence. High laser fluence results in both small grain size and high Hc. The observed phenomena are related to high quenching and deposition rates during PLD at high fluence, resulting in more pronounced phase segregation. 相似文献