全文获取类型
收费全文 | 129664篇 |
免费 | 3722篇 |
国内免费 | 560篇 |
专业分类
电工技术 | 1450篇 |
综合类 | 2370篇 |
化学工业 | 21203篇 |
金属工艺 | 6550篇 |
机械仪表 | 5796篇 |
建筑科学 | 3192篇 |
矿业工程 | 585篇 |
能源动力 | 3173篇 |
轻工业 | 7269篇 |
水利工程 | 1516篇 |
石油天然气 | 428篇 |
武器工业 | 2篇 |
无线电 | 16753篇 |
一般工业技术 | 26588篇 |
冶金工业 | 6355篇 |
原子能技术 | 910篇 |
自动化技术 | 29806篇 |
出版年
2024年 | 50篇 |
2023年 | 570篇 |
2022年 | 870篇 |
2021年 | 1483篇 |
2020年 | 1071篇 |
2019年 | 1179篇 |
2018年 | 15446篇 |
2017年 | 14381篇 |
2016年 | 11360篇 |
2015年 | 1869篇 |
2014年 | 2302篇 |
2013年 | 3183篇 |
2012年 | 6237篇 |
2011年 | 12853篇 |
2010年 | 10693篇 |
2009年 | 8241篇 |
2008年 | 9265篇 |
2007年 | 9662篇 |
2006年 | 2135篇 |
2005年 | 2868篇 |
2004年 | 2641篇 |
2003年 | 2621篇 |
2002年 | 1829篇 |
2001年 | 1226篇 |
2000年 | 1169篇 |
1999年 | 982篇 |
1998年 | 1606篇 |
1997年 | 1017篇 |
1996年 | 846篇 |
1995年 | 565篇 |
1994年 | 472篇 |
1993年 | 414篇 |
1992年 | 301篇 |
1991年 | 296篇 |
1990年 | 258篇 |
1989年 | 241篇 |
1988年 | 212篇 |
1987年 | 168篇 |
1986年 | 119篇 |
1985年 | 115篇 |
1984年 | 92篇 |
1983年 | 63篇 |
1981年 | 39篇 |
1977年 | 38篇 |
1976年 | 61篇 |
1968年 | 47篇 |
1966年 | 45篇 |
1965年 | 46篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
101.
Transmission performance of 10-Gb/s 1550-nm transmitters using semiconductor optical amplifiers as booster amplifiers 总被引:1,自引:0,他引:1
Yonggyoo Kim Hodeok Jang Yonghoon Kim Jeongsuk Lee Donghoon Jang Jichai Jeong 《Lightwave Technology, Journal of》2003,21(2):476-481
We have demonstrated the transmission performance of 10-Gb/s transmitters based on LiNbO/sub 3/ modulator using semiconductor optical amplifiers (SOAs) as booster amplifiers. Utilizing the negative chirp converted in SOAs and self-phase modulation induced by high optical power, we can successfully transmit 10-Gb/s optical signals over 80 km through the standard single-mode fiber with the transmitter using SOAs as booster amplifiers. SOAs can be used for booster amplifiers with a careful adjustment of the operating conditions. In order to further understand an SOA's characteristics as a booster amplifier, we model SOAs and other subsystems to verify the experimental results. Based on the good agreement between the experimental and simulation results, we can find the appropriate parameters of input signals for SOAs, such as extinction ratio, rising/falling time, and chirp parameter to maximize output dynamic range and available maximum output power (P/sub o,max/). 相似文献
102.
The expectation-maximization (EM) algorithm is well established as a computationally efficient method for separable signal parameter estimation. Here, a new geometric derivation and interpretation of the EM algorithm is given that facilitates the understanding of EM convergence properties. Geometric considerations lead to an alternative separable signal parameter estimator based on successive cancellation. The new generalized successive interference cancellation (GSIC) algorithm is then applied to multiuser delay and channel estimation for code-division multiple access (CDMA) radiolocation and communication. The radiolocation application uses a handshaking protocol in which multiple reference nodes transmit acknowledge (ACK) CDMA packets to a master node, which then computes round-trip travel times (RTTs). Simulation results comparing EM and GSIC are presented for the CDMA channel-estimation problem. 相似文献
103.
Saehoon Ju Hyeongdong Kim Hyung-Hoon Kim 《Microwave and Wireless Components Letters, IEEE》2003,13(9):405-407
This letter presents a numerical dispersion relation for the two-dimensional (2-D) finite-difference time-domain method based on the alternating-direction implicit time-marching scheme (2-D ADI-FDTD). The proposed analytical relation for 2-D ADI-FDTD is compared with those relations in the previous works. Through numerical tests, the dispersion equation of this work was shown as correct one for 2-D ADI-FDTD. 相似文献
104.
H.S. Seo Y.G. Choi B.J. Park D.H. Cho K.H. Kim 《Photonics Technology Letters, IEEE》2003,15(9):1198-1200
A flat signal gain over in the entire C- and L-bands by erbium (Er) ions' radiative transition and stimulated Raman scattering in an Er-doped germano-silica fiber can be obtained if proper values of the concentration of Er and background loss in a fiber core are obtained during the fiber fabrication process. The optimized conditions for the flat C- and L-band gain are analyzed as functions of Er concentrations. Even for a low-gain value provided by a germano-silica core fiber with a low Er concentration and an optimum fiber length, a relatively low pump is required to obtain the flat gain band. 相似文献
105.
Bong Keun Kim Wan Kyun Chung 《Industrial Electronics, IEEE Transactions on》2003,50(6):1207-1216
Disturbance-observer (DOB)-based controller design is one of the most popular methods in the field of motion control. In this paper, the generalized disturbance compensation framework, named the robust internal-loop compensator (RIC) is introduced and an advanced design method of a DOB is proposed based on the RIC. The mixed sensitivity optimization problem, which is the main issue of DOB design, is also solved through the parametrization of the DOB in the RIC framework. Differently from conventional methods, the Q-filter is separated from the mixed sensitivity optimization problem and a systematic design law for the DOB is proposed. This guarantees the robustness and optimality of the DOB and enables the design for unstable plants. 相似文献
106.
An antenna array for wideband operation (up to 70%) is presented. The structure has low windloading area and consists of parallel printed circuit boards (PCB) with microstrip dipoles, feed network and metal fences placed between the PCBs. The low profile, low weight antenna array forms the main beam and three difference patterns for sidelobe cancellation. Experimental results are compared with calculations for both microstrip dipole and array 相似文献
107.
Kang-Ngee Chia Hea Joung Kim Lansing S. Mangione-Smith W.H. Villasensor J. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》1998,6(3):364-371
Under the Mojave configurable computing project, we have developed a system for achieving high performance on an automatic target recognition (ATR) application through the use of configurable computing technology. The ATR system studied here involves real-time image acquisition from a synthetic aperture radar (SAR). SAR images exhibit statistical properties which can be used to improve system performance. In this paper, the Mojave configurable computing system uses field programmable gate arrays (FPGA's) to implement highly specialized circuits while retaining the flexibility of programmable components. A controller sequences through a set of specialized circuits in response to real-time events. Computer-aided design (CAD) tools have been developed to support the automatic generation of these specialized circuits. The resulting configurable computing system achieves a significant performance advantage over the existing solution, which is based on application specific integrated circuit (ASIC) technology 相似文献
108.
109.
Zhengmao Ye Campbell J.C. Zhonghui Chen Eui-Tae Kim Madhukar A. 《Quantum Electronics, IEEE Journal of》2002,38(9):1234-1237
An InAs/AlGaAs quantum-dot infrared photodetector based on bound-to-bound intraband transitions in undoped InAs quantum dots is reported. AlGaAs blocking layers were employed to achieve low dark current. The photoresponse peaked at 6.2 /spl mu/m. At 77 K and -0.7 V bias, the responsivity was 14 mA/W and the detectivity, D*, was 10/sup 10/ cm/spl middot/Hz/sup 1/2//W. 相似文献
110.