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   60173篇
  免费   5412篇
  国内免费   3087篇
电工技术   3949篇
技术理论   4篇
综合类   4332篇
化学工业   9845篇
金属工艺   3401篇
机械仪表   3931篇
建筑科学   4538篇
矿业工程   1324篇
能源动力   1708篇
轻工业   4414篇
水利工程   1198篇
石油天然气   2658篇
武器工业   491篇
无线电   7673篇
一般工业技术   7789篇
冶金工业   2460篇
原子能技术   761篇
自动化技术   8196篇
  2024年   243篇
  2023年   896篇
  2022年   1709篇
  2021年   2396篇
  2020年   1724篇
  2019年   1542篇
  2018年   1641篇
  2017年   1847篇
  2016年   1853篇
  2015年   2499篇
  2014年   2991篇
  2013年   3645篇
  2012年   3910篇
  2011年   4313篇
  2010年   3902篇
  2009年   3555篇
  2008年   3582篇
  2007年   3309篇
  2006年   3293篇
  2005年   2832篇
  2004年   2104篇
  2003年   2000篇
  2002年   2279篇
  2001年   1897篇
  2000年   1528篇
  1999年   1319篇
  1998年   1063篇
  1997年   886篇
  1996年   799篇
  1995年   701篇
  1994年   591篇
  1993年   448篇
  1992年   327篇
  1991年   260篇
  1990年   191篇
  1989年   151篇
  1988年   130篇
  1987年   74篇
  1986年   61篇
  1985年   42篇
  1984年   31篇
  1983年   16篇
  1982年   22篇
  1981年   21篇
  1980年   16篇
  1979年   8篇
  1976年   8篇
  1975年   7篇
  1959年   4篇
  1951年   3篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
11.
广东省大型工程建设中天然放射性核素引起的环境问题   总被引:2,自引:0,他引:2  
孔令丰  金问龙 《辐射防护》2003,23(3):178-183
本文介绍了广东省境内几个大型基本建设工程项目中天然放射性核素引起的环境问题及有关治理对策,并就今后类似建设项目的辐射环境保护工作提出了建议。  相似文献   
12.
Alumina-supported vanadium oxide, VOx/Al2O3, and binary vanadium–antimony oxides, VSbOx/Al2O3, have been tested in the ethylbenzene dehydrogenation with carbon dioxide and characterized by SBET, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction and CO2 pulse methods. VSbOx/Al2O3 exhibited enhanced catalytic activity and especially on-stream stability compared to VOx/Al2O3 catalyst. Incorporation of antimony into VOx/Al2O3 increased dispersion of active VOx species, enhanced redox properties of the systems and formed a new mixed vanadium–antimony oxide phase in the most catalytically efficient V0.43Sb0.57Ox/Al2O3 system.  相似文献   
13.
A tennis novice watching a match for the first time might be surprised that the crowd erupts with cheers when a player wins one point, then barely applauds when he wins the next. The crowd is not necessarily fickle; some points are genuinely more important than others because a tennis match is hierarchically structured. One match consists of several sets. One set consists of several games. One game consists of several points. The match-winning point is the most important one. How can we make that importance visible? Our goal is to let a fan, a player, or a coach examine tennis data visually, extract the interesting parts, and jump from one item to another quickly and easily. The visualization tool should help parse the elements of a match. We developed an interactive system called TennisViewer to visualize the dynamic, tree-structured data representing a tennis match. It provides an interface for users to quickly explore tennis match information. The visualization tool reveals the overall structure of the match as well as the fine details in a single screen. It uses a 2D display of translucent layers, a design that contains elements of Tree-Maps and of the Visual Scheduler system, which was designed to help faculty and students identify mutually available (transparent) time slots when arranging group meetings. TennisViewer provides MagicLens filters to explore specialized views of the information and a time-varying display to animate all or part of a match  相似文献   
14.
金钰 《兵工自动化》1996,(2):39-42,58
文中简要地介绍了一个具有分散采集信号,集中报警的安全报警器的设计,作者利用单片机的优点和功能,成功地设计了复盖地域大,既简单又灵活的报警器。  相似文献   
15.
The humidity response characteristics of La doped BaTiO3 with different sintered densities and room temperature electrical conductivities were investigated using complex impedance measurement. The samples with low density and high resistivity showed the large and nearly linear sensitivity to the change of humidity. The impedance spectra of samples, when exposed to high humidity, can exhibit microstructure-related features, even though they do not give rise to a noticeable characteristic change when exposed to low humidity. The observed impedance patterns were dependent upon the density, and hence the oxidation kinetics of BaTiO3.  相似文献   
16.
The modulation characteristics of first-order backscatter-induced crosstalk noise in a 2-D frequency-division-multiplexed fiber gyro system are analyzed and experimental results presented. The noise can be reduced from 5°/h to 0.2°/h (0.25 NEB) by proper choice of modulation depth and/or frequency  相似文献   
17.
This paper presents a Knowledge-based system (KBS) developed to allow users, who may not be knowledgeable about sensors, to select sensors suitable for their specific needs. The KBS runs on a micro-computer. The selection criteria are user specified and are based on the desired measurement parameters. The system output includes all of the operational and dimensional parameters of the recommended sensor, price, and vendor information.  相似文献   
18.
本文介绍了用标准液体源均匀充入聚氯乙烯制的体模,刻度标准椅全身计数器〔φ8″×4″(NaI)〕的方法和结果。分别就代表6个年龄组的体模,测定了标准椅全身计数器对5种能量(364,637,898,1460和1836keV)γ射线的全能峰效率;给出了全能峰效率与γ射线能量和被测对象体重的关系曲线。  相似文献   
19.
为使北京谱仪端盖族射计数器更好地工作在自猝灭流光SQS模式下,提高其能量分辨以及线性等指标,用Ar,CO2,Lsobutane三元工作气体对探测器的工作性能进行了仔细研究,找出了一适合于主雇地数器的工作气体,此外,还研究了异丁的纯度对探测器性能的影响。  相似文献   
20.
The fabric and faces of threat, and the expediency and efficiency in the communication of threat, are examined with a threat appraisal model. This model is empirically tested on an ongoing communication challenge, the issuance of terror alerts by the United States' Department of Homeland Security (DHS), focusing on how threat is appraised by both the conservative and liberal audiences. Findings showed a shared view by the DHS and conservative audiences on the levels and nature of threats; liberal audiences thought otherwise. Though there appeared to be a consensus between the conservative and liberal audiences on the efficacy of threat communication, more internal consistency within DHS is needed to optimise its effectiveness.  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