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   160159篇
  免费   14969篇
  国内免费   6752篇
电工技术   53204篇
技术理论   22篇
综合类   14914篇
化学工业   4997篇
金属工艺   2589篇
机械仪表   6628篇
建筑科学   15830篇
矿业工程   4955篇
能源动力   9698篇
轻工业   2852篇
水利工程   6655篇
石油天然气   2509篇
武器工业   881篇
无线电   18019篇
一般工业技术   6363篇
冶金工业   6547篇
原子能技术   2467篇
自动化技术   22750篇
  2024年   540篇
  2023年   1627篇
  2022年   3188篇
  2021年   3926篇
  2020年   4499篇
  2019年   3464篇
  2018年   3138篇
  2017年   4478篇
  2016年   5042篇
  2015年   5743篇
  2014年   12263篇
  2013年   9808篇
  2012年   12444篇
  2011年   13380篇
  2010年   10005篇
  2009年   10315篇
  2008年   10309篇
  2007年   12261篇
  2006年   10775篇
  2005年   8859篇
  2004年   7422篇
  2003年   6283篇
  2002年   4880篇
  2001年   3906篇
  2000年   3151篇
  1999年   2307篇
  1998年   1551篇
  1997年   1199篇
  1996年   1069篇
  1995年   849篇
  1994年   707篇
  1993年   463篇
  1992年   374篇
  1991年   249篇
  1990年   187篇
  1989年   197篇
  1988年   145篇
  1987年   91篇
  1986年   105篇
  1985年   109篇
  1984年   133篇
  1983年   126篇
  1982年   73篇
  1981年   41篇
  1980年   23篇
  1979年   25篇
  1978年   17篇
  1977年   22篇
  1961年   10篇
  1959年   22篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Digitalization and the trend towards more short‐term and project‐oriented social engagement have had a direct impact on traditional crisis management. This societal change has supported the evolution of new types of volunteers who use low‐threshold potentials to organize and maintain support independently. Traditional institutions like the German Red Cross are challenged to deal with these rapid changes regarding their own organizational culture in relation to the new phenomenon of so‐called unaffiliated volunteers. This paper investigates how unaffiliated volunteers influence and change the organizational culture of German disaster management by analysing and reflecting organizational adaptation processes in the aftermath of the German floods in 2013, the storm events in the west of Germany in 2014 and the refugee relief mission in 2015–2016. Therefore, semi‐structured interviews with experts of the German Red Cross were held to analyse their reactions towards unaffiliated Volunteers during the Floods in 2013 and the refugee relief missions, and further focus group interviews were conducted to validate the extracted results. Findings suggest that among professionals and leading entities in the German Red Cross, a process of rethinking has emerged, recognizing the importance and necessity to open up organizational structures for the collaboration and coordination of unaffiliated volunteers.  相似文献   
62.
针对以前的发电管理系统或只是数据呈现,提供市电及发电相关数据信息,或只是提供出车轨迹,主要实现对出车的管理,不能全面反应发电全过程且不便于对发电事件进行分析的情况,提出可视化发电管理系统的概念。在简要介绍了LBS系统、动力环境监控系统后,讲述了可视化基站发电管理系统的组成以及通过LBS定位管理、短信互动、实时监测数据等进行系统实现。可视化发电管理系统通过可视化的界面帮助发电管理人员进行管理,直观、便捷。  相似文献   
63.
变频开关电源Fuzzy-PID控制器的设计   总被引:1,自引:0,他引:1  
黄晓林 《机床与液压》2005,(12):156-157,145
针对感应式变频开关电源在对金属材料进行热处理过程中,负载的等效参数和谐振频率发生变化,而变频电源的输出频率不能及时调整和跟踪的问题,结合PID和Fuzzy控制技术的优点,设计Fuzzy-PID控制器对变频电源进行控制,在大偏差时用Fuzzy控制,在小偏差时用PID调节。Fuzzy-PID控制器以单片机8098为核心,采用SPWM专用芯片SA4828,实现变频开关电源的电压、电流双闭环控制,使变频电源不仅具有较快的动态响应、更小的超调,并且具有较高的稳态精度和频率跟踪控制特性。  相似文献   
64.
Ruminant livestock systems are a significant source of greenhouse gases (GHGs). Thus far, mitigation options for GHG emissions mainly focused on a single gas, and are treated as isolated activities. The present paper proposes a framework for a farm level approach for the full accounting of GHG emissions. The methodology accounts for the relevant direct and indirect emissions of methane, nitrous oxide and carbon dioxide, including carbon sequestration. Furthermore, the potential trade-off with ammonia volatilisation and nitrate leaching are taken into account. A ruminant livestock farm is represented with a conceptual model consisting of five pools: animal, manure, soil, crop and feed. The carbon and nitrogen inputs, throughputs and outputs are described, and the direct emissions are related to the carbon and nitrogen flows. The indirect emissions included in the methodology are mainly carbon dioxide emissions from energy use and nitrous oxide emissions related to imported resources and nitrogen losses. The whole farm approach is illustrated with a case of two dairy farms with contrasting livestock density and grassland management. It is shown that the inclusion of carbon sequestration and all indirect emissions have a major impact on the GHG budget of the farm. For one farm, the effect of four mitigation options on the GHG emissions was quantified. It was concluded that a whole farm approach of full accounting contributes to a better insight in the interactions between the carbon and nitrogen flows and the resulting emissions, within and outside the farm boundaries. Consequently, the methodology can be used to develop efficient and effective mitigation strategies.  相似文献   
65.
The effect of bottom clearance on power draw for anchors is investigated. The results suggest that power input decreases as the bottom clearance ratio b/D increases. A new correlation is proposed in which both bottom and wall clearance effects on power input are considered. The dependence of power input on these effects is additive rather than multiplicative. Thus, the total power consumption is the sum of the power inputs generated by the wall and bottom clearance. Power results from 3D-CFD numerical simulations are also presented. These results confirm fairly well the experimental points.  相似文献   
66.
杜建宏 《煤化工》2002,30(5):36-40
介绍了 6 m大容积焦炉由冷态到转入正常加热温度的烘炉操作过程中 ,按照一定的升温曲线 ,通过对焦炉热工和炉体膨胀的科学管理 ,确保新建焦炉顺利由冷态过渡到生产状态。  相似文献   
67.
Transport phenomena studies on single phase “model” fluids are of limited value in biochemical engineering if they cannot be translated to the heterogeneous systems encountered in real fermentation processes. In this paper we discuss the utility of polymer solutions as models of filamentous fermentation broths for evaluation of: pipeline friction factors and impeller power numbers (turbine and helical ribbon). To a first approximation, polymer solutions can serve as suitable models for the prediction of laminar flow pressure drop in pipelines and turbulent power consumption in stirred tanks. However, results obtained on polymer solutions do not directly apply to filamentous fermentation broths for predictions of laminar flow impeller power consumption and the transition point for turbulent flow in stirred tanks. These discrepancies are believed to result from the existence of a time dependent yield stress in filamentous fermentation broths.  相似文献   
68.
《Information & Management》2014,51(8):1031-1042
Customer relationship management (CRM) has become one of the most influential technologies in the world, and companies are increasingly implementing it to create value. However, despite significant investment in CRM technology infrastructure, empirical research offers inconsistent support for its positive impact on performance. This study develops and tests a research model analyzing the process through which CRM technology infrastructure translates into organizational performance, drawing on the resource-based view (RBV) and the knowledge-based view (KBV) of the firm. Based on an international sample of 125 hotels, the results suggest that organizational commitment and knowledge management fully mediate this process.  相似文献   
69.
针对我国化肥生产企业质检机构的现状 ,结合国家相关政策的要求 ,就如何搞好化肥企业质检机构的管理提出了诸多指导性意见  相似文献   
70.
介绍了如何体现产品质量及如何控制产品质量。  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