全文获取类型
收费全文 | 41209篇 |
免费 | 4103篇 |
国内免费 | 1847篇 |
专业分类
电工技术 | 2433篇 |
技术理论 | 1篇 |
综合类 | 2619篇 |
化学工业 | 7155篇 |
金属工艺 | 2105篇 |
机械仪表 | 2160篇 |
建筑科学 | 3165篇 |
矿业工程 | 930篇 |
能源动力 | 1278篇 |
轻工业 | 3969篇 |
水利工程 | 724篇 |
石油天然气 | 1807篇 |
武器工业 | 257篇 |
无线电 | 5142篇 |
一般工业技术 | 5020篇 |
冶金工业 | 2032篇 |
原子能技术 | 486篇 |
自动化技术 | 5876篇 |
出版年
2024年 | 228篇 |
2023年 | 800篇 |
2022年 | 1465篇 |
2021年 | 2110篇 |
2020年 | 1558篇 |
2019年 | 1289篇 |
2018年 | 1299篇 |
2017年 | 1568篇 |
2016年 | 1441篇 |
2015年 | 1899篇 |
2014年 | 2374篇 |
2013年 | 2907篇 |
2012年 | 2873篇 |
2011年 | 3124篇 |
2010年 | 2566篇 |
2009年 | 2387篇 |
2008年 | 2292篇 |
2007年 | 2069篇 |
2006年 | 2086篇 |
2005年 | 1689篇 |
2004年 | 1165篇 |
2003年 | 1042篇 |
2002年 | 1037篇 |
2001年 | 802篇 |
2000年 | 687篇 |
1999年 | 721篇 |
1998年 | 639篇 |
1997年 | 531篇 |
1996年 | 501篇 |
1995年 | 399篇 |
1994年 | 325篇 |
1993年 | 230篇 |
1992年 | 196篇 |
1991年 | 142篇 |
1990年 | 117篇 |
1989年 | 103篇 |
1988年 | 104篇 |
1987年 | 68篇 |
1986年 | 56篇 |
1985年 | 33篇 |
1984年 | 36篇 |
1983年 | 27篇 |
1982年 | 31篇 |
1981年 | 20篇 |
1980年 | 21篇 |
1979年 | 25篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 14篇 |
1975年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Numerous power utilities have installed advanced distributed temperature sensing (DTS) systems to measure the temperature of underground cables. This paper presents a general procedure for real-time assessment of underground cable ratings based on DTS. After the identification and location of hot spots on a cable, the cable installation data, load, and DTS-recorded temperature over a period of time are used to estimate soil thermal parameters and assess cable ratings under normal and overloading conditions. In order to accurately estimate soil thermal parameters, a combined technique of the finite-element method and gradient-based optimization is used. The technique was validated in the laboratory and applied to a rating assessment of a 230-kV/500-MVA cable circuit. The assessed continuous and emergency ratings are helpful in improving the operation of this circuit. 相似文献
102.
Yu-Zung Chiou Yan-Kuin Su Shoou-Jinn Chang Yi-Chao Lin Chia-Sheng Chang Chin-Hsiang Chen 《Solid-state electronics》2002,46(12):2227-2229
InGaN/GaN multiquantum well (MQW) p–n junction photodetectors with semi-transparent Ni/Au electrodes were fabricated and characterized. It was found that the fabricated InGaN/GaN MQW p–n junction photodetectors exhibit a 20 V breakdown voltage and a 3.5 V forward 20 mA turn on voltage. It was also found that the photocurrent to dark current contrast ratio is higher than 105 when a 0.4 V reverse bias was applied to the InGaN/GaN MQW p–n junction photodetectors. Furthermore, it was found that the maximum responsivity was 1.28 and 1.76 A/W with a 0.1 and 3 V applied reverse bias, respectively. 相似文献
103.
钼还原过程相变化研究 总被引:5,自引:0,他引:5
采用钼酸铵直接氢还原及钼酸铵先焙解然后再分段氢还原两种不同的还原方法进行了钼粉还原。通过X射线衍射方法分析了两种工艺还原过程中的反应序列及相变化规律,并讨论了不稳定相Mo4O11对于钼粉还原过程的影响。 相似文献
104.
Measurement and modeling of self-heating in SOI nMOSFET's 总被引:4,自引:0,他引:4
Su L.T. Chung J.E. Antoniadis D.A. Goodson K.E. Flik M.I. 《Electron Devices, IEEE Transactions on》1994,41(1):69-75
Self-heating in SOI nMOSFET's is measured and modeled. Temperature rises in excess of 100 K are observed for SOI devices under static operating conditions. The measured temperature rise agrees well with the predictions of an analytical model and is a function of the silicon thickness, buried oxide thickness, and channel-metal contact separation. Under dynamic circuit conditions, the channel temperatures are much lower than predicted from the static power dissipation. This work provides the foundation for the extraction of device modeling parameters for dynamic operation (at constant temperature) from static device characterization data (where temperature varies widely). Self-heating does not greatly reduce the electromigration reliability of SOI circuits, but might influence SOI device design, e.g., requiring a thinner buried oxide layer for particular applications and scaled geometries 相似文献
105.
Ching-Chuan Su Jenn-Ming Guan 《Microwave Theory and Techniques》1994,42(10):1998-2006
A numerical procedure using the finite-difference technique, simultaneous iteration based on the power method, and the Chebyshev-polynomial preconditioning is proposed to analyze dielectric-loaded cavities. The merit of this method is that no matrix inversions are invoked and the convergence rate of the power method is greatly accelerated by the preconditioning. The TE, TM, and hybrid modes in axisymmetrical cavities loaded with a rod or ring dielectric resonator are analyzed. For the hybrid modes, an Hr-Hz formulation is proposed. Accurate numerical results are obtained efficiently and no spurious solutions are found by the present method 相似文献
106.
The current-voltage characteristics of the P-N double quantum well resonant interband tunneling (RIT) diodes in InAlAs-InGaAs system have been improved in this letter. The peak-to-valley current ratio (PVCR) is as high as 144 at room temperature. As we know, this is the highest room temperature PVCR ever reported in any tunneling devices. Moreover, the influence of the central barrier thickness varying from 10 Å to 30 Å on the device characteristics is also studied 相似文献
107.
A series of polyurethane microcapsules containing a phase change material (PCM) of n‐octadecane was successfully synthesized by an interfacial polymerization in aqueous styrene‐maleic anhydride (SMA) dispersion with diethylene triamine (DETA) as a chain extender reacting with toluene‐2,4‐diisocyanate (TDI). The average diameter of microPCMs is in the range of 5–10 μm under the stirring speed of 3000–4000 rpm. Optical and SEM morphologies of microPCMs had ensured that the shell was regularly fabricated with the influence of SMA. FTIR results confirmed that the shell material was polyurethane and the SMA chains associated on core material reacted with TDI forming a part of shell material. The shell thickness was decreasing in the range of 0.31–0.55 μm with the molar ratio of DETA/TDI from 0.84 to 1.35 and the weight of core material increasing from 40 to 80% (wt %). By controlling the weight ratio of PCM as 40, 50, 60, 70, and 80% in microPCMs, it was found using DSC that the Tm and Tc of microPCMs were in the range of 29.8–31.0oC and 21.1–22.0°C and an obvious phase change had been achieved nearly the same temperature range of that of PCM. The results from release curves of microPCM samples prepared by 1.4, 1.7, and 2.0 g of SMA indicated the release properties were affected by the amount of the dispersant, which attributed to the emulsion effect and shell polymerization structure. The above results suggest that the shell structure of microPCMs can be controlled and the properties of microPCMs determined by shell will perform proper practical usage. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4996–5006, 2006 相似文献
108.
The major steps of sewerage rehabilitation include inspection of sewerage, assessment of structural conditions, computation of structural condition grades, and determination of rehabilitation methods and materials. Conventionally, sewerage rehabilitation planning relies on experts with professional background that is tedious and time-consuming. This paper proposes an automation model of planning optimal sewerage rehabilitation strategies for the sewer system by integrating image process, clustering technology, optimization, and visualization display. Firstly, image processing techniques, such as wavelet transformation and co-occurrence features extraction, were employed to extract various characteristics of structural failures from CCTV inspection images. Secondly, a classification neural network was established to automatically interpret the structural conditions by comparing the extracted features with the typical failures in a databank. Then, to achieve optimal rehabilitation efficiency, a genetic algorithm was used to determine appropriate rehabilitation methods and substitution materials for the pipe sections with a risk of mal-function and even collapse. Finally, the result from the automation model can be visualized in a geographic information system in which essential information of the sewer system and sewerage rehabilitation plans are graphically displayed. For demonstration, the automation model of optimal sewerage rehabilitation planning was applied to a sewer system in east Taichung, Chinese Taiwan. 相似文献
109.
H.C. Su L.A. Wang 《Photonics Technology Letters, IEEE》2003,15(10):1357-1359
We demonstrate a novel polarized superfluorescent fiber source (SFS) that increases the output power in the desired polarization by a factor of 1.96 over that of an unpolarized SFS at the same pump. This is achieved by inserting a polarizer at the optimal point in the bidirectionally pumped erbium-doped fiber of an unpolarized SFS. Stable pump-power-dependent mean wavelength operation and less sensitivity to the insertion loss, important for fiber-optic gyroscope applications, are obtained in this configuration. 相似文献
110.