全文获取类型
收费全文 | 6425篇 |
免费 | 327篇 |
国内免费 | 20篇 |
专业分类
电工技术 | 77篇 |
综合类 | 10篇 |
化学工业 | 1180篇 |
金属工艺 | 237篇 |
机械仪表 | 320篇 |
建筑科学 | 122篇 |
矿业工程 | 1篇 |
能源动力 | 269篇 |
轻工业 | 514篇 |
水利工程 | 24篇 |
石油天然气 | 12篇 |
无线电 | 1353篇 |
一般工业技术 | 1275篇 |
冶金工业 | 501篇 |
原子能技术 | 87篇 |
自动化技术 | 790篇 |
出版年
2024年 | 6篇 |
2023年 | 70篇 |
2022年 | 104篇 |
2021年 | 161篇 |
2020年 | 94篇 |
2019年 | 130篇 |
2018年 | 172篇 |
2017年 | 154篇 |
2016年 | 200篇 |
2015年 | 162篇 |
2014年 | 243篇 |
2013年 | 457篇 |
2012年 | 384篇 |
2011年 | 484篇 |
2010年 | 328篇 |
2009年 | 380篇 |
2008年 | 328篇 |
2007年 | 281篇 |
2006年 | 231篇 |
2005年 | 239篇 |
2004年 | 170篇 |
2003年 | 183篇 |
2002年 | 168篇 |
2001年 | 130篇 |
2000年 | 130篇 |
1999年 | 115篇 |
1998年 | 244篇 |
1997年 | 134篇 |
1996年 | 133篇 |
1995年 | 118篇 |
1994年 | 80篇 |
1993年 | 88篇 |
1992年 | 58篇 |
1991年 | 54篇 |
1990年 | 46篇 |
1989年 | 43篇 |
1988年 | 31篇 |
1987年 | 31篇 |
1986年 | 23篇 |
1985年 | 21篇 |
1984年 | 23篇 |
1983年 | 19篇 |
1982年 | 22篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 13篇 |
1975年 | 9篇 |
排序方式: 共有6772条查询结果,搜索用时 15 毫秒
1.
Jaehoon Lee Seongha Kim Yonghoon Kim Yunje Oh Seongtaek Hwang Jichai Jeong 《Lightwave Technology, Journal of》2003,21(2):521-527
Optically preamplified receiver performance according to the vestigial sideband (VSB) filtering has been numerically investigated for 40-Gb/s optical signals modulated with nonreturn-to-zero, duobinary nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed RZ, and duobinary carrier-suppressed RZ formats. The VSB filtering enables the spectral widths of NRZ, duobinary NRZ, and RZ signals to be reduced without severe power penalties at the receiver. On the other hand, carrier-suppressed RZ and duobinary carrier-suppressed RZ signals have no large advantages over VSB filtering because of the characteristics of their signals. Our results suggest that RZ signals are the most suitable modulation format for VSB filtering, without considering the filter loss, because of the tolerance of the intersymbol interference and a large spectral width. However, duobinary NRZ signals are the most suitable modulation format for VSB filtering, considering the filter loss, because of their narrow spectral width. 相似文献
2.
Yong Bae Park Keum Cheol Hwang Ikmo Park 《Microwave and Wireless Components Letters, IEEE》2008,18(3):152-154
A tapered coaxial tip in a parallel plate waveguide is investigated. A boundary-value problem of electromagnetic scattering from a tapered coaxial monopole is solved rigorously based on the Fourier transform, eigenfunction expansion, and mode matching. Scattering parameters are represented in a series and computed to understand the behavior of the scattering in terms of the coaxial tip geometry. 相似文献
3.
4.
We propose a new service for digital mobile communication systems. The service enables two or more users to hold a secure conference. Two requirements must be considered: privacy and authentication. Privacy involves ensuring that an eavesdropper cannot intercept the conversations of the parties holding the conference. Authentication involves ensuring that service is not obtained fraudulently in order to avoid usage charges. We present two new conference key distribution schemes for digital mobile communication systems. In these schemes, a group of users can generate a common secret keg over a public channel so that they may hold a secure conference 相似文献
5.
The paper addresses the design of two-level power system stabilizers using an optimal reduced order model whose state variables are torque angles and speeds. The reduced order model retains their physical meaning and is used to design a two-level linear feedback controller that takes into account the realities and constraints of electrical power systems. The two-level control strategy is used, and a global control signal is generated from the output variables to minimize the effect of interactions. The effectiveness of this controller is evaluated and a multimachine system is given as an example to illustrate the advantages of the proposed method. Responses of the system with a two-level scheme and an optimal reduced order scheme are included for comparative analysis. 相似文献
6.
Mathews V.K. Maddox R.L. Fazan P.C. Rosato J. Hwang H. Lee J. 《Electron Device Letters, IEEE》1992,13(12):648-650
Nitrided gate oxides offer several electrical and reliability advantages over conventional oxides and also provide a good barrier against impurity diffusion. Oxidation in nitrous oxide (N2O) has been very successful in overcoming some of the problems associated with nitridation in ammonia. The authors have observed that the extent of N2O oxidation has a strong detrimental effect on the drain leakage current of MOS transistors in the off state. This phenomenon has been identified to be caused by an increase in the active area junction leakage current 相似文献
7.
Hwang H.-K. Lee L.-S. Chen S.-H. 《Selected Areas in Communications, IEEE Journal on》1989,7(9):1450-1461
Multi-H phase-coded modulation (MHPM) is a bandwidth-efficient modulation scheme which offers substantial coding gain over conventional digital modulation schemes. MHPM with asymmetric modulation indices corresponding to the bipolar data +1 and -1 is considered, and numerical results for the minimum Euclidean distances are provided. It is shown that performance improvements on the error probability over conventional MHPM are gained with essentially the same bandwidth and a very slight modification in implementation. The upper bounds on the error probabilities as functions of observation intervals and received E b/N 0 are also investigated in detail. It is concluded that the concept of asymmetric modulation indices for MHPM is attractive for bandwidth and power-efficient modulation 相似文献
8.
Design of two-level system stabilizers is considered using an optimal reduced-order model whose state variables are torque angles and speeds. The reduced-order model retains their physical meaning and is used to design a two-level linear feedback controller that takes into account the realities and constraints of the electrical power systems. The two-level control strategy is used, and a global control signal is generated from the output variables to minimize the effect of interaction. The effectiveness of this controller is evaluated, and an example, the multimachine system, is given to illustrate the advantages of the proposed method. The responses of the system with the two-level scheme and optimal reduced order scheme are included for comparative analyses 相似文献
9.
Using chloroform/dimethylformamide (CF/DMF) co-solvent, electrospinning of poly[(R)-3-hydroxybutyrate] (PHB) solutions was carried out at ambient temperature. The effects of the applied voltage (V), flow-rate (Q), and solution viscoelastic properties on the Taylor cone, electrified jet, and fiber morphology were investigated. In addition, the electric field developed by the needle-plate electrode configuration was calculated using a finite element analysis to reveal the tip-to-collector (H) effect. Among the processing parameters (V, Q and H), it was found that Q played a key role in determining the jet diameter (dj) and electrospun fiber diameter (df), and scaling laws existed between them, i.e., dj-Q0.61 and df-Q0.33. The diameter reduction ratios of Do/dj (Do is the needle diameter) and dj/df were measured as 50-120 and 5-10, respectively; it suggested that major jet stretching took place in the straight electrified jet region, and further chain orientation could be gained by the subsequent process of jet whipping. By changing PHB concentrations from 5 to 15 wt%, the solution viscosity (ηo) was increased from 100 to 4900 cP, whereas the surface tension and solution conductivity remained unchanged; it provided a good model solution to exclusively reveal the ηo effect on the electrospinning process. Our results showed that the ηo-dependence of dj and df also followed simple scaling laws: dj-ηo0.06, and df-ηo0.39, with a prefactor depending on the processing variables, mainly the flow-rate. Regardless of the PHB concentrations used, the obtained PHB fibers showed a similar crystallinity fraction of ca. 0.63 and possession of major α-crystals together with a small amount of β-crystals with zigzag chain conformation. 相似文献
10.
Bang-Ning Hwang Shih-Chi Chang Hsiao-Cheng Yu Che-Wei Chang 《The International Journal of Advanced Manufacturing Technology》2008,36(7-8):825-832
Taiwan Semiconductor Manufacturing Company (TSMC) is the largest semiconductor foundry in the world. Advanced Semiconductor Engineering Inc. (ASE) is the world’s leader in semiconductor assembly and testing. From 1998 to 2004, the two companies completed electronic integration of 11 key business processes through the Internet. The result is a seamless interface between TSMC, ASE and their joint customers. They can now obtain accurate, timely information on their product status and respond appropriately when needed. While the direct economic benefits are estimated to be around US$ 10 million through productivity increase over a total investment of about US$ 2 million, the indirect benefits of this initiative could be on the order of US $100 million if the joint customers’ benefits are considered. In collaboration with the RosettaNet organization, TSMC and ASE leveraged their pioneering experiences to define three data exchange standards which can then be widely adopted in the semiconductor industry. This case study is a demonstration of how two leading companies in their respective fields can join forces to make a difference in creating value for the entire semiconductor industry, which in turn benefits society at large. With the momentum continuing to build and the sphere of influence continuing to expand, it is anticipated that TSMC, ASE and the entire sector will upgrade their competitiveness in terms of cost, quality, responsiveness and customer orientation. 相似文献