全文获取类型
收费全文 | 285篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 35篇 |
金属工艺 | 36篇 |
机械仪表 | 5篇 |
轻工业 | 1篇 |
石油天然气 | 2篇 |
无线电 | 109篇 |
一般工业技术 | 63篇 |
冶金工业 | 22篇 |
原子能技术 | 3篇 |
自动化技术 | 8篇 |
出版年
2023年 | 3篇 |
2021年 | 3篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 12篇 |
2010年 | 7篇 |
2009年 | 4篇 |
2008年 | 11篇 |
2007年 | 4篇 |
2006年 | 7篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 8篇 |
2002年 | 3篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 11篇 |
1997年 | 3篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 12篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 6篇 |
1971年 | 2篇 |
1970年 | 4篇 |
1969年 | 5篇 |
1968年 | 2篇 |
1966年 | 3篇 |
1962年 | 2篇 |
排序方式: 共有287条查询结果,搜索用时 15 毫秒
101.
An analytical model is proposed which relates the transconductance of submicron GaAs MESFETs to a low field mobility, effective electron saturation velocity and device geometry and doping. The model predicts that the effective saturation velocity determines the performance of the devices at relatively high pinch-off voltages (Vpo > 5 V). At smaller pinch-off voltages (especially for enhancement-mode devices) the low field mobility becomes increasingly important, leading to additional advantages of GaAs devices over Si devices. Another prediction is a higher transconductance in thinner and higher-doped devices. This effect is also more important for devices with low pinch-off voltages. The obtained results may be used to deduce the effective values of the electron drift velocity in GaAs MESFETs as a function of the gate length. 相似文献
102.
The carrier concentration in heterostructure FETs (HFETs) with a p-i-p+ buffer is presented as a function of the gate bias, obtained by self-consistent one-dimensional calculation of 2-D electron density, subband levels, and electrostatic potential. These results quantify certain limitations on the range of geometrical and doping parameters and make it possible to optimize the HFET design and to compare modulation doped FET (MODFET) and doped channel HFET (DCHFET) structures. Monte Carlo simulations demonstrate that this p-i-p+ buffer drastically reduces the short-channel effects 相似文献
103.
Chao P.-C. Shur M.S. Tiberio R.C. Duh K.H.G. Smith P.M. Ballingall J.M. Ho P. Jabra A. 《Electron Devices, IEEE Transactions on》1989,36(3):461-473
Analytical modeling of these very-short-channel HEMTs (high-electron-mobility transistors) using the charge-control model is given. The calculations performed using this model indicate a very high electron velocity in the device channel (3.2±0.2×107 cm/s) and clearly demonstrate the advantages of the planar-doped devices as compared to the conventional uniformly doped HEMTs. Devices with different air-bridged geometries have been fabricated to study the effect of the gate resistance on the sub-0.1-μm HEMT performance. With reduced gate resistance in the air-bridge-drain device, noise figures as low as 0.7 and 1.9 dB were measured at 18 and 60 GHz, respectively. Maximum available gains as high as 13.0 dB at 60 GHz and 9.2 dB at 92 GHz, corresponding to an f max of 270 GHz, have also been measured in the device. Using the planar-doped pseudomorphic structure with a high gate aspect-ratio design, a noise figure of less than 2.0 dB at 94 GHz is projected based on expected further reduction in the parasitic gate and source resistances 相似文献
104.
105.
Both the subthreshold slope and the threshold voltage in inverted-staggered amorphous silicon thin-film transistors (a-Si:H TFTs) are vulnerable to metastable changes in the density of states (DOS) due to Fermi level displacement. In previous work, we have used passivated and unpassivated TFTs to distinguish between the effects of bulk states and interface states at the top passivating nitride interface. Here we report the results of experimental measurements and two-dimensional (2-D) simulations on unpassivated TFTs. Since there are no top interface states, all the observed changes are due solely to the bulk DOS. The subthreshold current activation energies in a-Si:H TFTs are compared for n-channel nonpassivated TFTs before and after bias stress. The experimental results agree well with the 2-D simulations, confirming that the dependence of subthreshold current activation energy on gate bias reveals the distribution of the DOS in energy but cannot resolve the magnitude of features in the DOS. This type of analysis is not accurate for TFTs with a top passivating nitride, since the activation energies in such devices are affected by the interfere states 相似文献
106.
We present a new method of modeling the output conductance dispersion of GaAs MESFET's. High frequency model parameters are extracted and then used to model high frequency output conductance over a wide range of bias conditions. The model is then used to simulate and analyze the effect of output conductance dispersion on the performance of DCFL and SCFL logic gates. Whereas the DCFL performance is not significantly affected by the high frequency effects, the noise margin of SCFL decreases by almost a factor of 30% above 100 kHz, with an associated decrease in the voltage swing and gate delay 相似文献
107.
108.
The effect of collisions on near ballistic electron transport in short GaAs terminal devices at 77°K is analyzed in the frame of the model based on the equations of momentum and energy balance where momentum and energy relaxation times are fit to agree with the results of Monte Carlo calculation for static constant electric fields. Solving the equations by the iteration technique yields the criterion of the ballistic transport for GaAs at low voltages). The computer solution is used to obtain current-voltage characteristics, field, energy, velocity and voltage distributions for GaAs devices at 77°K. The results of the calculation show that the ballistic effects are dominant at 77°K even at relatively high doping levels (such as 1016 cm?3) for short devices (~ 0.2 μm long). These effects lead to a higher electron velocity at low voltages and could be utilized in building high speed GaAs integrated circuits. 相似文献
109.
The successful manufacture of a regulatory approved dry powder inhaler (DPI) product is only achievable by applying robust control systems to all aspects of analytical, engineering, and material based processes. Whilst many aspects of DPI drug product manufacturing can be adequately controlled, it is often the control of materials, that is, drug substance and excipients, which can lead to variation in the quality of the final drug product. This article gives an overview of DPI excipients and highlights the challenges of defining and, importantly, understanding the relationships between quality and functionality for excipient components in DPI formulations. 相似文献
110.
Qingyuan Hu D.O. Alikin P.S. Zelenovskiy A.D. Ushakov D.S. Chezganov Jihong Bian Ye Zhao Ye Tian Yongyong Zhuang Jinglei Li Li Jin Zhuo Xu Vladimir. Ya. Shur Xiaoyong Wei 《Journal of the European Ceramic Society》2019,39(14):4131-4138
Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) single crystals exhibit ultrahigh piezoelectric property and have already been applied in various industrial fields. Here, spatial distribution of coexistent phases and corresponding local piezoelectric responses in a morphotropic phase boundary (MPB) PMN-xPT single crystal are thoroughly investigated by confocal Raman spectroscopy coupled with piezo-response force microscopy (PFM). Different from previous studies on MPB crystals, spatial distribution of coexistent phases is exhibited intuitively in an image obtained by confocal Raman mapping. Via in-situ PFM measurements, domain morphology of each coexistent phase is observed. Moreover, local piezoelectric responses of each coexistent phase are obtained by switching spectroscopy PFM measurements, indicating that Ma and Mc phases behave like PNRs and polar matrix in PMN-xPT crystals Our work clarifies the contribution from different phases to the giant piezoelectric performance, which can deepen the understanding on the ultrahigh piezoelectricity in PMN-xPT crystals and provide the key point for developing novel high piezoelectricity materials. 相似文献