首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   323238篇
  免费   37022篇
  国内免费   12540篇
电工技术   17369篇
技术理论   26篇
综合类   20464篇
化学工业   63958篇
金属工艺   16734篇
机械仪表   18870篇
建筑科学   23981篇
矿业工程   9080篇
能源动力   8682篇
轻工业   27682篇
水利工程   5264篇
石油天然气   18677篇
武器工业   2319篇
无线电   37847篇
一般工业技术   43029篇
冶金工业   15442篇
原子能技术   2845篇
自动化技术   40531篇
  2024年   1072篇
  2023年   4507篇
  2022年   8421篇
  2021年   11728篇
  2020年   10126篇
  2019年   10139篇
  2018年   10909篇
  2017年   12268篇
  2016年   11868篇
  2015年   14861篇
  2014年   18162篇
  2013年   21686篇
  2012年   21273篇
  2011年   22588篇
  2010年   20534篇
  2009年   19499篇
  2008年   18783篇
  2007年   17825篇
  2006年   17785篇
  2005年   15186篇
  2004年   10838篇
  2003年   9351篇
  2002年   8707篇
  2001年   7681篇
  2000年   7732篇
  1999年   7724篇
  1998年   6022篇
  1997年   4865篇
  1996年   4593篇
  1995年   3826篇
  1994年   3057篇
  1993年   2127篇
  1992年   1646篇
  1991年   1316篇
  1990年   1006篇
  1989年   800篇
  1988年   595篇
  1987年   365篇
  1986年   301篇
  1985年   212篇
  1984年   147篇
  1983年   109篇
  1982年   129篇
  1981年   102篇
  1980年   90篇
  1979年   46篇
  1978年   28篇
  1977年   23篇
  1976年   40篇
  1975年   16篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
本文根据电子期刊的定义、特点及图书馆期刊工作所需要面对的问题,就高校图书馆网络环境下期刊工作的设施规划、资料收集、信息开发及读者培训等多方面内容进行了简单探讨,并就如何应对网络环境下图书馆期刊工作的变化提出建议。  相似文献   
992.
993.
994.
刘影 《石油商技》2003,21(4):36-38
介绍了摩擦改进剂的类型及作用机理,比较了不同类型的摩擦改进剂。阐述了应用摩擦改进剂减少边界润滑和混合润滑状态下的摩擦损失,从而提高燃料经济性。  相似文献   
995.
Highly transparent and conducting fluorine (F) doped cadmium oxide (CdO) thin films were deposited on glass slides by the sol-gel method. The films were doped by the addition of ammonium fluoride to the precursor solution whose optimum concentration was determined. The films were fired in an open atmosphere at 350 °C and after that, exposed to annealing treatments in different atmospheres (N2, N2/H2 mixture and Ar) at the same temperature. The films were characterized by ultraviolet-visible spectroscopy, X‐ray diffraction and scanning electron microscopy. The resistivity was determined by the four probes method and current-voltage measurements in accordance with the standard Van der Pauw configuration. The CdO:F thin films obtained, showed high polycrystalline quality and high transmission in the visible region (≥ 90%), shifting towards the blue region of the absorption edge as the fluorine concentration in the precursor solution was increased from 0 to 30 at.%. The lowest resistivity values were reached for the samples with F content higher or equal to 5% and annealed in either N2 or a 96/4 N2/H2 gas mixture. Our resistivity value reached in the CdO:F layers was 4.5 × 10− 4 Ω cm (20 Ω/square).  相似文献   
996.
Interfacial-initiated polymerization of styrene (St) was carried out in inversed emulsion with cumene hydroperoxide (CHPO) and ferrous sulfate (FeSO4)/disodium ethylenediaminetetraacetate (NaEDTA)/sodium formaldehyde sulfoxylate (SFS) as the redox initiation system. The water-soluble Fe2+-NaEDTA-SFS acted as the reducing component and the oil-soluble CHPO as the oxidant component of the redox initiation system. Therefore, the primary radicals were produced mainly at the oil/water interface to initiate the polymerization of St. Thus, sub-micrometer hollow polystyrene (PSt) spheres were obtained by one-stage polymerization, which was supported by the techniques of transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM).  相似文献   
997.
This paper presents an application of digital signal processing to data acquired by the radio imaging method (RIM) that was adopted to measure moisture distribution inside the human body. RIM was originally developed for the mining industry; we are applying the method to a biomedical measurement because of its simplicity, economy, and safety. When a two‐dimensional image was constructed from the measured data, the method provided insufficient resolution because the wavelength of the measurement medium, a weak electromagnetic wave in a VHF band, was longer than human tissues. We built and measured a phantom, a model simulating the human body, consisting of two water tanks representing large internal organs. A digital equalizer was applied to the measured values as a weight function, and images were reconstructed that corresponded to the original shape of the two water tanks. As a result, a two‐dimensional image containing two individual peaks corresponding to the original two small water tanks was constructed. The result suggests the method was applicable to biomedical measurement by the assistance of digital signal processing. This technique may be applicable to home‐based medical care and other situations in which safety, simplicity, and economy are important.  相似文献   
998.
催化技术在降低汽油机排放方面的应用   总被引:3,自引:2,他引:1  
本文介绍了当前催化技术在改善和降低汽油机排放方面的应用情况,指出:催化技术是改善汽油机排放的一种有效措施和重要手段。  相似文献   
999.
1000.
Inrecentyears ,rareearthelements (REEs)havebeenwidelyusedinfunctionalmaterials ,cata lystsandotherproductsinindustry ,diagnosisreagentsofmagneticresonanceimaging (MRI)inmedicineandsomefertilizersinagricultureespeciallyinChina .However,asaresultoftheirusage ,moreandmoreREEsaregettingintotheenvironment,andalsointohumanbodyviafoodchain[1,2 ] .Itisnotclearwhetherrareearthelementsareessentialforman ,soitisveryurgenttostudythebiologicaleffectofrareearthelementsinhumanhealthandenvironment .Inthes…  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号