全文获取类型
收费全文 | 76725篇 |
免费 | 7955篇 |
国内免费 | 5120篇 |
专业分类
电工技术 | 6274篇 |
技术理论 | 4篇 |
综合类 | 6735篇 |
化学工业 | 10572篇 |
金属工艺 | 4779篇 |
机械仪表 | 4971篇 |
建筑科学 | 5870篇 |
矿业工程 | 2318篇 |
能源动力 | 1994篇 |
轻工业 | 8989篇 |
水利工程 | 1962篇 |
石油天然气 | 3273篇 |
武器工业 | 1020篇 |
无线电 | 8582篇 |
一般工业技术 | 7398篇 |
冶金工业 | 3113篇 |
原子能技术 | 944篇 |
自动化技术 | 11002篇 |
出版年
2024年 | 420篇 |
2023年 | 1269篇 |
2022年 | 2682篇 |
2021年 | 3405篇 |
2020年 | 2627篇 |
2019年 | 1937篇 |
2018年 | 2222篇 |
2017年 | 2530篇 |
2016年 | 2296篇 |
2015年 | 3483篇 |
2014年 | 4225篇 |
2013年 | 5061篇 |
2012年 | 6067篇 |
2011年 | 6508篇 |
2010年 | 5998篇 |
2009年 | 5650篇 |
2008年 | 5867篇 |
2007年 | 5492篇 |
2006年 | 4756篇 |
2005年 | 3850篇 |
2004年 | 2747篇 |
2003年 | 2196篇 |
2002年 | 2138篇 |
2001年 | 1835篇 |
2000年 | 1304篇 |
1999年 | 826篇 |
1998年 | 512篇 |
1997年 | 428篇 |
1996年 | 320篇 |
1995年 | 272篇 |
1994年 | 190篇 |
1993年 | 156篇 |
1992年 | 94篇 |
1991年 | 111篇 |
1990年 | 83篇 |
1989年 | 45篇 |
1988年 | 36篇 |
1987年 | 28篇 |
1986年 | 27篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 12篇 |
1980年 | 23篇 |
1979年 | 8篇 |
1976年 | 6篇 |
1973年 | 3篇 |
1959年 | 13篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
To realize joint optimization of spatial diversity and equalization combining in the intersymbol interference (ISI) channel, an iterative equalization combining algorithm is proposed. The proposed algorithm uses the coefficients of Turbo equalization to calculate the combination weights without estimating the signal to noise ratio in each diversity branch. The equalized symbols from different diversity branches are combined, and the extrinsic information output from the decoder is fed back to the equalizers, so as to exchange soft information between the equalizers and the decoder. The performance of the proposed algorithm is analyzed using the extrinsic information transfer (EXIT) chart and verified by simulations. Results show that our approach fully exploits time domain information from the multipath channel and spatial domain information from multi receiving antennas, which efficiently improve the performance of the receiver in the severe ISI channel. 相似文献
4.
Private information retrieval(PIR) is an important privacy protection issue of secure multi-party computation, but the PIR protocols based on classical cryptography are vulnerable because of new technologies,such as quantum computing and cloud computing. The quantum private queries(QPQ) protocols available, however, has a high complexity and is inefficient in the face of large database. This paper, based on the QKD technology which is mature now, proposes a novel QPQ protocol utilizing the key dilution and auxiliary parameter. Only N quits are required to be sent in the quantum channel to generate the raw key, then the straight k bits in the raw key are added bitwise to dilute the raw key, and a final key is consequently obtained to encrypt the database. By flexible adjusting of auxiliary parameters θ and k, privacy is secured and the query success ratio is improved. Feasibility and performance analyses indicate that the protocol has a high success ratio in first-trial query and is easy to implement, and that the communication complexity of O(N) is achieved. 相似文献
5.
6.
稠油微生物开采技术现状及进展 总被引:2,自引:0,他引:2
综述了用微生物方法开采稠油的技术现状与进展,论题如下。①概述。②基本方法:异源微生物采油,包括微生物吞吐和微生物驱;本源微生物采油压大港孔店油田的实例。③主要机理,包括产表面活性剂,降解稠油中重质组分及其他。④技术研究,包括机理性、可行性及经济效益研究,列举了国内外6个实例。⑤现场应用,包括国外1个、国内6个实例。⑥该技术的优势及问题。参22。 相似文献
7.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献
8.
W. Shieh R. Hui X. Yi 《Photonics Technology Letters, IEEE》2006,18(10):1122-1124
We perform a systematic measurement of the degree-of-polarization (DOP) and eye-closure penalty for optical signals with orthogonal polarizations. We find that the symmetry of DOP is maintained for the orthogonal polarizations under both first and higher order polarization-mode dispersion (PMD), whereas the symmetry of eye-closure penalty is broken under second-order PMD. An orthogonal polarization pair can have large disparity of eye-closure penalty despite an identical DOP. We also demonstrate a novel approach to estimate the maximum eye-closure penalty asymmetry with three orthogonal polarizations on the Poincare/spl acute/ sphere. 相似文献
9.
The current Internet and wireless networks are harsh environments for transporting high-bandwidth multimedia data. We examine the technical issues involved, and describe an end-to-end solution to support a Web-based learn-on-demand system that operates in a wireless campus environment. 相似文献
10.
介绍如何利用AutoCAD开发适合电气专业使用的CAD系统,通过编制电气CAD的功能菜单,构造电气元件库,增强CAD的专业性能。编制电气CAD可以有效地统一本单位电气制图标准,方便电气工程师使用CAD进行专业设计。 相似文献