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   8728篇
  免费   1595篇
  国内免费   1086篇
电工技术   588篇
技术理论   2篇
综合类   1185篇
化学工业   200篇
金属工艺   414篇
机械仪表   995篇
建筑科学   649篇
矿业工程   219篇
能源动力   149篇
轻工业   144篇
水利工程   156篇
石油天然气   150篇
武器工业   163篇
无线电   1289篇
一般工业技术   741篇
冶金工业   152篇
原子能技术   36篇
自动化技术   4177篇
  2024年   29篇
  2023年   202篇
  2022年   398篇
  2021年   377篇
  2020年   435篇
  2019年   311篇
  2018年   288篇
  2017年   360篇
  2016年   398篇
  2015年   458篇
  2014年   576篇
  2013年   619篇
  2012年   740篇
  2011年   740篇
  2010年   580篇
  2009年   568篇
  2008年   571篇
  2007年   636篇
  2006年   575篇
  2005年   508篇
  2004年   346篇
  2003年   347篇
  2002年   246篇
  2001年   200篇
  2000年   166篇
  1999年   127篇
  1998年   89篇
  1997年   88篇
  1996年   91篇
  1995年   71篇
  1994年   54篇
  1993年   48篇
  1992年   30篇
  1991年   31篇
  1990年   28篇
  1989年   23篇
  1988年   4篇
  1987年   4篇
  1986年   9篇
  1985年   7篇
  1984年   10篇
  1983年   5篇
  1982年   3篇
  1979年   2篇
  1978年   2篇
  1977年   1篇
  1975年   3篇
  1974年   1篇
  1957年   1篇
  1951年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Analysing a schedule is beneficial to help stakeholders understand the scheduled project. Project schedules, which create time plans based on the critical path method (CPM) or on resource‐constrained project scheduling problem (RCPSP) optimization, are targets herein. The Theory of Constraints (TOC) treats a schedule as a system. Schedule elements are suspected constraints and a goal depends on the schedule creation policy. Resource information is further surveyed herein to identify true constraints. A framework is proposed to integrate identified constraints on a schedule, and the critical resource chain concept is introduced. Three scenarios illustrate the proposed framework under different scheduling considerations. Results explain schedule constraints, and several schedule analysis issues are discussed.  相似文献   
102.
参考美国规范,运用拆除构件法,基于SAP2000通用有限元软件.对一按照我国现行规范设计的RC框架结构进行抗连续性倒塌分析,分析了移除失效柱后,剩余框架柱柱轴力的变化趋势,对比分析了柱失效位置对结构抗连续性倒塌性能的影响,并研究了层高对结构抗连续性倒塌性能的影响.得出在不考虑地震荷栽作用时:角柱失效对结构影响最大;柱失效后,剩余结构的内力重分配只集中在失效跨内,失效点上方柱基本失去支撑作用;层高对结构抗连续性倒塌性能影响较小,建议结构层高取值在3.6m~4.2m之间。  相似文献   
103.
Abstract

The cables in a cable-stayed bridge are critical components supporting the long-span girders and ensuring their functionality. However, cables are prone to fatigue damage and atmospheric corrosion, which directly affect the bridge safety. This study presents a framework for system reliability evaluation of in-service cable-stayed bridges subjected to cable degradation. The effect of cable strength degradation on the system reliability is demonstrated through simulation on a parallel-series system representation. Learning machines are utilised to approximate the non-linear and dynamic response functions of critical components due to cable rupture, and the system reliability is finally evaluated from the event tree established by the β-unzipping method. Both short-span and long-span cable-stayed bridges are selected as prototypes to investigate the influence of cable degradation on the system reliability. On this basis it is revealed that cable degradation can significantly influence the collapse mechanism of a cable-stayed bridge and thereby lead to a significant reduction in the system reliability. This phenomenon is associated with cable spacing, where a spare cable system seems more sensitive to cable gradation. It is demonstrated that the consideration of cable corrosion and correlation is essential for lifetime safety evaluation of in-service cable-stayed bridges.  相似文献   
104.
现阶段,城市产业转型已经成为资源型城市发展的热点与难点问题。本文以安徽省煤炭资源型城市淮北市为例,通过分析其三次产业发展的现状和问题,梳理出了产业转型的总体思路,从而得出了城市产业转型的实施路径。  相似文献   
105.
With the growth in project management as a form of work organisation in many sectors of the economy has come the significant rise in the number of project managers and project team members. This change in work organisation brings issues in forging career paths and determining career support in work situations that are often dynamic, short lived and intense. In the relatively small but substantially robust Australian economy, a unique labour market and the tyranny of distance bring their own difficulties. Innovative and collaborative project structures and increasing prevalence of contract work provide both challenges and opportunities for new career pathways in many industries. A growing percentage of Australia's workforce is employed in project-based or project-oriented organisations, leading to the claim that Australia is a project-based economy. This provided a context for our research into the career paths and the issues of career management for project managers working in a project based economy. Using in-depth interviews with project managers from three industry areas we found generational and gender differences in experiences of work, workplace support and mentoring for career development. For a continued strong performance in this economy, organisations that employ project personnel will need to consider how they will ensure the supply of high quality project professionals into the future.  相似文献   
106.
This paper outlines an historical institutionalist (HI) research agenda for planning history. HI approaches to the understanding of institutions, path dependence, positive feedback effects in public policy, and patterned processes of institutional change offer a robust theoretical framework and a valuable set of conceptual and analytic tools for the analysis of continuity and change in public policy. Yet, to date, there has been no systematic effort to incorporate historical institutionalism into planning history research. The body of the paper proposes planning history relevant definitions of institutions, path dependence, critical junctures, and incremental change processes, outlines recent HI literature applying and extending these concepts, and frames a number of research questions for planning history that these approaches suggest. A concluding section explores the potential application and leverage of HI approaches to the study of planning history and international comparative planning studies and outlines a research agenda.  相似文献   
107.
该文从平面的视角出发,对高层建筑基本平面形式选择、总平面布局对城市风环境带来的影响进行分析.高层建筑的不同基本平面形式,以及总平面布局中朝向、尺度、外部空间等方面的不同设计决策,对城市总体通风的影响有显著差异.根据定性分析,以及PHOENICS流体动力学软件的模拟结果,总结高层建筑设计中需要考虑的平面选型和布局策略,以保证城市风道畅通,提高城市总体通风效率.  相似文献   
108.
王红卫 《建筑施工》2014,36(9):1091-1093
为减少建筑基坑开挖对基坑围护结构变形的影响,提出利用动态规划理论分析大型基坑分区开挖最优路径的方法。结合工程实例,以基坑最大竖向位移和地下连续墙最大水平位移为目标函数,建立了基坑开挖路径分析的动态规划模型,并分析出了现有地质条件下基坑施工的最优开挖路径。其分析方法与结果可供类似工程参考。  相似文献   
109.
立足于滇西典型欠发达中小城市保山市城镇化现状特征,剖析了保山市城镇化竞争优势,探讨了保山新型城镇化的发展路径,提出了保山新型城镇化发展综合策略:引导整合优势资源,强化产业支撑;注重城市整体功能建设,提升城市综合承载力;挖掘城镇特色,明确城镇化发展路径。  相似文献   
110.
结合扬州城建史,对其城河关系与城市功能的发展演变进行了阶段性分析,同时折射出古城扬州的发展轨迹,并对当前滨水区整治的重要措施和成效进行了概述,以供参考借鉴。  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