全文获取类型
收费全文 | 21347篇 |
免费 | 2838篇 |
国内免费 | 2297篇 |
专业分类
化学 | 12731篇 |
晶体学 | 290篇 |
力学 | 604篇 |
综合类 | 152篇 |
数学 | 1569篇 |
物理学 | 4187篇 |
无线电 | 6949篇 |
出版年
2024年 | 54篇 |
2023年 | 335篇 |
2022年 | 506篇 |
2021年 | 645篇 |
2020年 | 700篇 |
2019年 | 728篇 |
2018年 | 575篇 |
2017年 | 648篇 |
2016年 | 912篇 |
2015年 | 997篇 |
2014年 | 1267篇 |
2013年 | 1527篇 |
2012年 | 1799篇 |
2011年 | 1872篇 |
2010年 | 1465篇 |
2009年 | 1494篇 |
2008年 | 1702篇 |
2007年 | 1457篇 |
2006年 | 1363篇 |
2005年 | 1130篇 |
2004年 | 931篇 |
2003年 | 767篇 |
2002年 | 803篇 |
2001年 | 568篇 |
2000年 | 425篇 |
1999年 | 337篇 |
1998年 | 252篇 |
1997年 | 166篇 |
1996年 | 177篇 |
1995年 | 132篇 |
1994年 | 99篇 |
1993年 | 106篇 |
1992年 | 77篇 |
1991年 | 91篇 |
1990年 | 52篇 |
1989年 | 54篇 |
1988年 | 25篇 |
1987年 | 43篇 |
1986年 | 23篇 |
1985年 | 34篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
111.
112.
Yong-Goo Yoo Seong-Gi Min Ho-Jun Ryu Nam-Seok Park Seong-Cho Yu 《Journal of magnetism and magnetic materials》2006
Exchange biased IrMn/NiFe/IrMn thin films were studied as a function of NiFe thickness. In plane angular dependence of a resonance field distribution which is measured by FMR was analyzed as a combined effect of an unidirectional anisotropy and an uniaxial anisotropy. The unidirectional anisotropic field and the uniaxial anisotropic field were linearly varied with NiFe thickness while the films with a thicker NiFe layer do not follow the linear variation. Resonance field and linewidth variations were also analysed with NiFe thickness. 相似文献
113.
设{u_k}_k≥0为一个线性递归序列.序列{u_k(mod q)}_(k≥0)是周期的,很多人都对其周期有过研究.本文应用二次数域中理想的理论,较完全地刻面了二次线性递归序列模q的周期长度,所获结果加强并推广了Engstrom及Wall的结论. 相似文献
114.
Degradation Behaviors of Metal-Induced Laterally Crystallized n-Type Polycrystalline Silicon Thin-Film Transistors Under DC Bias Stresses 总被引:1,自引:0,他引:1
Min Xue Mingxiang Wang Zhen Zhu Dongli Zhang Man Wong 《Electron Devices, IEEE Transactions on》2007,54(2):225-232
Device degradation behaviors of typical-sized n-type metal-induced laterally crystallized polycrystalline silicon thin-film transistors were investigated in detail under two kinds of dc bias stresses: hot-carrier (HC) stress and self-heating (SH) stress. Under HC stress, device degradation is the consequence of HC induced defect generation locally at the drain side. Under a unified model that postulates, the establishment of a potential barrier at the drain side due to carrier transport near trap states, device degradation behavior such as asymmetric on current recovery and threshold voltage degradation can be understood. Under SH stress, a general degradation in subthreshold characteristic was observed. Device degradation is the consequence of deep state generation along the entire channel. Device degradation behaviors were compared in low Vd-stress and in high Vd-stress condition. Defect generation distribution along the channel appears to be different in two cases. In both cases of SH degradation, asymmetric on current recovery was observed. This observation, when in low Vd-stress condition, is tentatively explained by dehydrogenation (hydrogenation) effect at the drain (source) side during stress 相似文献
115.
针对磷化铟(InP)复合沟道高电子迁移率晶体管(HEMT)的特点,对常规单沟道HEMT的小信号物理模型进行了修正,提出了一种新的用于复合沟道HEMT的小信号物理模型,用商用器件模拟软件ISE(integrated systems engineering)对其进行了仿真验证,对比了实测和仿真的I-V特性及转移特性曲线,重点研究了在InGaAs/InP双层沟道中考虑量子效应后的电场和电流密度随着不同栅电压的变化趋势,研究结果表明,由于在沟道中存在量子效应,在栅下靠源端低电场区域,电流主要分布在InGaAs沟道
关键词:
高电子迁移率晶体管
复合沟道
物理模型
磷化铟 相似文献
116.
117.
Flat-top interleavers with chromatic dispersion compensator based on phase dispersive free space Mach-Zehnder interferometer 总被引:2,自引:0,他引:2
In this paper, novel interleavers using circular cavities (CC) in a Mach-Zehnder interferometer (MZI) has been presented and demonstrated for the first time, in which CCs act as phase dispersive mirrors which exhibit a periodic dependence on the frequency of light. Three implementation schemes have been proposed and investigated. Theoretical analysis shows the spectral characteristics of each scheme in a 50-GHz channel spacing application. Furthermore, the chromatic dispersion (CD) of each output comb can be flattened within passband by appending an additional CC. The result shows that the proposed designs with novel interferometer technique can simultaneously provide flat top passbands, high isolation stopband and low CD value as well. 相似文献
118.
Jooyoung Jeon Youngwoo Kwon Hong-Shick Min 《Microwave and Wireless Components Letters, IEEE》2002,12(9):342-344
A new physics-based noise model of a GaAs PHEMT is developed using the characteristic potential method (CPM). The model calculates the intrinsic noise current sources using CPM. Combined with the extrinsic noise parameters extracted from the measured S-parameters, the model reproduces four noise parameters of the device accurately under low drain bias voltages without using any fitting parameters. The model is verified with a 0.2-/spl mu/m GaAs PHEMT and shows excellent agreement with the measurements for all the noise parameters up to a drain voltage of 1 V Also, the proposed method allows the simulation of the microscopic noise distribution and thus allows one to obtain a physical understanding of noise mechanisms inside the device. 相似文献
119.
120.
Xie Ruixiang Wang Min Duan Changchun Yan Yihua R. A. Sych A. T. Altyntsev 《中国科学A辑(英文版)》2002,45(1):97-105
A complex solar radio moving type IV burst was observed on 23 September 1998 with the broadband (1.0–2.0 GHz and 2.6–3.8 GHz) spectrometers with high temporal and spectral resolutions at National Astronomical Observatories of China (NAOC). Comparing to the high spatial resolution data of Siberian Solar Radio Telescope (SSRT), we find that this burst is a rare type of moving type IV burst which is caused by the expanding arches, and the spatial structure oscillations of the radio sources are related with the time structure pulsations of the radio emission. Furthermore, the burst is associated with the multiple quasi-periodic long-term pulsations, and this suggests the existence of multi-scale magnetic structures in a large expanding coronal arch. We think the moving type IV burst is due to the synchrotron emission of the energetic electrons trapped in the expanding arch, and the multiple quasi-periodic pulsations are due to the second harmonic plasma emission. 相似文献