全文获取类型
收费全文 | 3923篇 |
免费 | 901篇 |
国内免费 | 570篇 |
专业分类
化学 | 578篇 |
晶体学 | 29篇 |
力学 | 19篇 |
综合类 | 7篇 |
数学 | 32篇 |
物理学 | 2026篇 |
无线电 | 2703篇 |
出版年
2024年 | 13篇 |
2023年 | 56篇 |
2022年 | 79篇 |
2021年 | 126篇 |
2020年 | 82篇 |
2019年 | 90篇 |
2018年 | 122篇 |
2017年 | 171篇 |
2016年 | 176篇 |
2015年 | 230篇 |
2014年 | 292篇 |
2013年 | 278篇 |
2012年 | 326篇 |
2011年 | 321篇 |
2010年 | 260篇 |
2009年 | 208篇 |
2008年 | 300篇 |
2007年 | 287篇 |
2006年 | 300篇 |
2005年 | 248篇 |
2004年 | 205篇 |
2003年 | 176篇 |
2002年 | 168篇 |
2001年 | 146篇 |
2000年 | 122篇 |
1999年 | 88篇 |
1998年 | 79篇 |
1997年 | 70篇 |
1996年 | 87篇 |
1995年 | 42篇 |
1994年 | 58篇 |
1993年 | 34篇 |
1992年 | 28篇 |
1991年 | 27篇 |
1990年 | 17篇 |
1989年 | 16篇 |
1988年 | 17篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有5394条查询结果,搜索用时 0 毫秒
21.
We have proposed a mechanism of nonideality, i.e., the temperature dependence of the ideality factor, in nearly ideal Au/n-Si Schottky barriers. Because of the nature of metal-induced gap states, positively ionized defects close to the interface are considered to cause local lowering of the Schottky barrier height (SBH) due to downward bending of the energy band. These positively charged defects become neutralized in equilibrium with the Fermi level due to the band bending, when they are very close to the interface. However, because the SBH lowering disappears by the neutralization of donor, the energy level of donor with a usual energy level scheme rises above the Fermi level after the neutralization. This contradiction to the equilibrium neutralization is resolved by Si self-interstitial with a large negative-U property, which is generated by the fabrication process. The energy level of the donor estimated from the SBH lowering is in good agreement with that of theoretical calculation of Si self-interstitial. Thus, the defect is concluded to be the Si self-interstitial, which is distributed to more than 10 Å depth from the interface. 相似文献
22.
23.
二极管激光侧泵浦单横模100Hz电光调Q激光器 总被引:3,自引:0,他引:3
介绍了二极管激光侧泵浦单横模100Hz电光调Q激光器的实验结果。泵浦源为一个线阵准连续100W二极管激光器,激光工作介质为NdYAG薄梯形板条,板条与泵浦源间用柱透镜耦合,KD*P电光晶体调Q。在100Hz重复频率下,获得单脉冲能量2.37mJ,脉宽小于7ns,光束质量因子M2=1.1的1.06μm激光,光-光效率为8.5%,斜效率为18.7%。 相似文献
24.
激光二极管自混合干涉和微振动的实验观测 总被引:5,自引:0,他引:5
介绍了利用LabView软件虚拟示波器和信号源,对激光二极管自混合干涉和微振动进行的实验观测.该实验可以作为本科低年级学生的综合设计实验. 相似文献
25.
26.
激光光镊技术是一项在许多科学领域有广阔应用前景的技术。本文详细给出构建一台红外半导体激光光镊的设计思想及实例。由于采用了独特的对大功率多模红外激光选模整形和双透镜陷阱操纵技术等性能价格最优化选择 ,该系统易于构建 ,陷阱操作方便 ,其构建价格仅一般光镊的几十分之一 ,非常适合光镊技术的推广和一般实验室构建 相似文献
27.
Alex M. Green David G. Gevaux Christine Roberts Chris C. Phillips 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):531
In this paper we outline the use of resonant-cavity enhancement for increasing the exterior coupling efficiency of photodetectors and light-emitting diodes (LEDs) in the mid-infrared (MIR) spectral region. This method is potentially very important in the MIR because encapsulation is not presently feasible due to the lack of suitable materials. Among other potential applications, resonant-cavity-enhanced (RCE) photodetectors and LEDs could be particularly suitable for greenhouse gas detection because of their ‘pre-tunable’ spectrally narrowed resonantly enhanced peaks. We also present the optical characterization of an InAs RCE photodetector aimed at the detection of methane gas (λ≈3.3 μm), and an InAs/InAs0.91Sb0.09 resonant-cavity LED (RCLED) aimed at carbon dioxide gas (λ≈4.2 μm). The high peak responsivity of the RCE photodetector was 34.7 A/W at λ=3.14 μm, and the RCLED peaked at λ=3.96 μm. These are among the longest operating wavelengths for III–V RCE photodetectors and RCLEDs reported in the literature. 相似文献
28.
本文自行设计和制作了1.30μmDFB激光器组件的讨论了光隔离和光耦合原理。由于采用的激光器-光隔离器-光纤的一体化结构,大大增加了该组件的可用性。在实验中得到高达55%的耦合效率。 相似文献
29.
High-temperature isothermal capacitance transient spectroscopy (H-ICTS) measurements were conducted to characterize near mid-gap defects, which are the origin of the memory effect in Ni/p-GaN Schottky contacts. A large single peak was detected only under the forward bias conditions. This indicates that the defects were located in the vicinity of the interface. The change of the peak height and position of the ICTS curves under various bias conditions were qualitatively interpreted by the distribution of the defects and the current flow effect. 相似文献
30.