全文获取类型
收费全文 | 96785篇 |
免费 | 10084篇 |
国内免费 | 6118篇 |
专业分类
电工技术 | 7822篇 |
技术理论 | 2篇 |
综合类 | 7845篇 |
化学工业 | 13646篇 |
金属工艺 | 5962篇 |
机械仪表 | 7002篇 |
建筑科学 | 7961篇 |
矿业工程 | 2889篇 |
能源动力 | 3094篇 |
轻工业 | 7874篇 |
水利工程 | 2294篇 |
石油天然气 | 4184篇 |
武器工业 | 1046篇 |
无线电 | 11767篇 |
一般工业技术 | 10459篇 |
冶金工业 | 4023篇 |
原子能技术 | 1139篇 |
自动化技术 | 13978篇 |
出版年
2024年 | 469篇 |
2023年 | 1564篇 |
2022年 | 3049篇 |
2021年 | 4077篇 |
2020年 | 3133篇 |
2019年 | 2444篇 |
2018年 | 2888篇 |
2017年 | 3083篇 |
2016年 | 2921篇 |
2015年 | 3994篇 |
2014年 | 5158篇 |
2013年 | 5808篇 |
2012年 | 6859篇 |
2011年 | 7206篇 |
2010年 | 6674篇 |
2009年 | 6552篇 |
2008年 | 6532篇 |
2007年 | 5855篇 |
2006年 | 5678篇 |
2005年 | 4635篇 |
2004年 | 3714篇 |
2003年 | 3551篇 |
2002年 | 4206篇 |
2001年 | 3530篇 |
2000年 | 2273篇 |
1999年 | 1669篇 |
1998年 | 1098篇 |
1997年 | 872篇 |
1996年 | 766篇 |
1995年 | 625篇 |
1994年 | 522篇 |
1993年 | 335篇 |
1992年 | 270篇 |
1991年 | 209篇 |
1990年 | 163篇 |
1989年 | 142篇 |
1988年 | 88篇 |
1987年 | 74篇 |
1986年 | 66篇 |
1985年 | 30篇 |
1984年 | 29篇 |
1983年 | 15篇 |
1982年 | 21篇 |
1981年 | 31篇 |
1980年 | 21篇 |
1979年 | 18篇 |
1978年 | 8篇 |
1976年 | 10篇 |
1959年 | 18篇 |
1951年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
We consider a special growth-curve (SGC) model with a known steering matrix and generalized waveform in the presence of unknown interference and noise. Several estimators of the complex amplitude based on this model are derived, including the methods of approximate maximum likelihood (AML), minimum variance distortionless response (MVDR), and amplitude and phase estimation (APES). We analyze the statistical properties of these estimators and show that in the presence of temporally white but spatially correlated noise and interference, AML is asymptotically statistically efficient for a large snapshot number while MVDR and APES are asymptotically equivalent but not statistically efficient. Via several numerical examples, we also show that when the noise and interference are both spatially and temporally correlated, the APES estimator can achieve better estimation accuracy and exhibit greater robustness than the other methods. 相似文献
102.
Lin-Ping Shen Wei-Ping Huang Shui-Sheng Jian 《Lightwave Technology, Journal of》2003,21(7):1644-1651
A general procedure for design of photonic crystal fibers (PCFs) with desirable dispersion properties is presented. The design model is based on the combination of a rigorous vector mode solver and a scaling transformation for the dispersion properties of the PCFs. In comparison with the conventional design method, the new design procedure is more efficient and can be readily automated for the purpose of design optimization. Several applications of the design procedure, e.g., the design optimization for dispersion shifted fibers, dispersion flattened fibers, and dispersion compensation fibers, are demonstrated and discussed. 相似文献
103.
Onishi K. Rino Choi Chang Seok Kang Hag-Ju Cho Young Hee Kim Nieh R.E. Jeong Han Krishnan S.A. Akbar M.S. Lee J.C. 《Electron Devices, IEEE Transactions on》2003,50(6):1517-1524
Bias-temperature instabilities (BTI) of HfO/sub 2/ metal oxide semiconductor field effect transistors (MOSFETs) have been systematically studied for the first time. NMOS positive BTI (PBTI) exhibited a more significant V/sub t/ instability than that of PMOS negative BTI (NBTI), and limited the lifetime of HfO/sub 2/ MOSFETs. Although high-temperature forming gas annealing (HT-FGA) improved the interface quality by passivating the interfacial states with hydrogen, BTI behaviors were not strongly affected by the technique. Charge pumping measurements were extensively used to investigate the nature of the BTI degradation, and it was found that V/sub t/ degradation of NMOS PBTI was primarily caused by charge trapping in bulk HfO/sub 2/ rather than interfacial degradation. Deuterium (D/sub 2/) annealing was found to be an excellent technique to improve BTI immunity as well as to enhance the mobility of HfO/sub 2/ MOSFETs. 相似文献
104.
Orthogonal space-time block codes: maximum likelihood detection for unknown channels and unstructured interferences 总被引:3,自引:0,他引:3
Space-time coding (STC) schemes for communication systems employing multiple transmit and receive antennas have been attracting increased attention. The so-called orthogonal space-time block codes (OSTBCs) have been of particular interest due to their good performance and low decoding complexity. In this paper, we take a systematic maximum-likelihood (ML) approach to the decoding of OSTBC for unknown propagation channels and unknown noise and interference conditions. We derive a low-complexity ML decoding algorithm based on cyclic minimization and assisted by a minimum amount of training data. Furthermore, we discuss the design of optimal training sequences and optimal information transfer to an outer decoder. Numerical examples demonstrate the performance of our algorithm. 相似文献
105.
106.
107.
介绍了一个基于Windows操作系统的数据采集软件,该软件用于使用重心法确定的位置信息的位置灵敏探测器,具有方便的人机交互界面,使用专用驱动程序采集数据。 相似文献
108.
本文介绍了宽低温STN-LCD加热装置的设计和制备方法,并对低温加热的实验结果进行了讨论和分析,相应的研究结果表明此法有利于拓宽STN液晶显示器的负温工作范围。 相似文献
109.
Films of electroactive polymers, such as polyaniline (PAN) in its emeraldine base form, and poly(3-alkylthiophene), poly(3-hexylthiophene) (P6TH), poly(3-octylthiophene) (P8TH), and poly(3-dodecylthiophene) (P12TH) can be readily functionalized via thermal or near ultraviolet-light-induced surface graft copolymerization with monomers of polyelectrolyte, polyampholyte and polymeric acids. The monomers used in the present work include dimethyl sulphate quaternized dimethylamino-ethylmethacrylate (DMAEM·C2H6SO4), 3-dimethyl(methacryloyloxyethyl)ammonium propane sulphonate (DMAPS), acrylic acid (AAc) and a sodium salt of styrene sulphonic acid (NaSS). The surface structures and compositions of the electroactive polymer films after functionalization via graft copolymerization were characterized by angle-resolved X-ray photoelectron spectroscopy. Graft copolymerization of poly(3-alkylthiophene) films, but not PAN films, with the hydrophilic monomers readily results in a stratified surface microstructure arising from the migration of the hydrophilic graft chains beneath a thin surface layer which is much richer in the substrate chains. On the other hand, graft copolymerization of PAN films with AAc and NaSS readily gives rise to a self-protonated (and thus conductive) surface structure. 相似文献
110.
北京火车站抗震鉴定与加固技术 总被引:5,自引:3,他引:2
北京火车站抗震加固与改造设计项目组 《工程抗震与加固改造》2003,(1):25-29
北京火车站是首都重要的标志性建筑之一 ,195 9年建成 ,当时按 7度设防考虑 ,存在着许多不符合抗震要求的问题 ,一些设施也明显不能满足现代使用功能要求。北京火车站抗震加固与改造设计项目组 ,运用多种先进的加固手段 ,在保持原建筑外貌不变的前提下 ,实现了抗震能力和改善使用功能的协调 ,取得了大型公共建筑加固改造的新经验 相似文献