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   381篇
  免费   10篇
  国内免费   5篇
教育   250篇
科学研究   47篇
体育   50篇
综合类   47篇
信息传播   2篇
  2024年   1篇
  2023年   2篇
  2022年   6篇
  2021年   8篇
  2020年   7篇
  2019年   10篇
  2018年   5篇
  2017年   9篇
  2016年   7篇
  2015年   8篇
  2014年   10篇
  2013年   34篇
  2012年   23篇
  2011年   21篇
  2010年   14篇
  2009年   16篇
  2008年   24篇
  2007年   34篇
  2006年   48篇
  2005年   18篇
  2004年   9篇
  2003年   12篇
  2002年   13篇
  2001年   9篇
  2000年   5篇
  1999年   8篇
  1998年   10篇
  1997年   8篇
  1996年   5篇
  1995年   3篇
  1994年   2篇
  1993年   1篇
  1992年   3篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
排序方式: 共有396条查询结果,搜索用时 0 毫秒
1.
The weighing system designed for large structure object is mainly composed of three parts. The part of hydraulic system is made up of hydraulic cylinders, high pressure hydraulic hoses and electric pumps; the part of computer controlling system comprises pressure sensors, displacement sensors, data acquisitions, RS 485 network and the computer controlling model; the part of loading system is composed of the fulcrum structure and the concrete girder. The measurement principle and composition of the weighing system are discussed in this paper. Credibility and security of the weighing system are fully considered during the design phase. The hydraulic system is controlled by pilot operated check valves in case of the sudden loss of system pressure. The states of all gauges and RS485 network are monitored by computer controlling system functioning in different modules. When the system is running incorrectly, it will be switched to manual mode and give alarm. The finite element method is employed to analyze fulcrum structure so that the system has enough intensity to be lifted. Hence the reliability of the whole system is enhanced.  相似文献   
2.
    
Concreteness fading has been proposed as a general instructional approach to support learning of abstract mathematics and science concepts. Accordingly, organizing external knowledge representations in a three-step concrete-to-idealized sequence should be more beneficial than the reverse, concreteness introduction, sequence. So far, evidence for the benefits of concreteness fading come mainly from studies investigating learning of basic mathematics concepts. Studies on learning natural science concepts are scarce and have not implemented the full three-step-sequence. In an experimental classroom study (N = 70), we compared concreteness fading and concreteness introduction in high school science education about electromagnetic induction using a detailed assessment. Furthermore, we explored whether these sequences differentially affect the use of the different representations during instruction. Both sequences were equally effective and there were no differences in using the representations. We discuss why our results question the proposed advantages of concreteness fading and highlight conceptual differences and learning goals across domains.  相似文献   
3.
In the present paper, a dynamic plastic damage model for concrete has been employed to estimate responses of a reinforced concrete slab subjected to blast loading. The interaction between the blast wave and the concrete slab is considered in 3D simulation. In the first stage, the initial detonation and blast wave propagation is modelled in 2D simulation before the blast wave reaches the concrete slab, then the results obtained from 2D calculation are remapped to a 3D model. The calculated blast load is compared with that obtained from TM5-1300. Numerical results of the concrete slab response are compared with the explosive test carried out- in the Weapons System Division, Defence Science and Technology Organisation, Department of Defence, Australia.  相似文献   
4.
Maintaining leanness and a physically active lifestyle during adulthood reduces systemic inflammation, an underlying factor in multiple chronic diseases. The anti-inflammatory influence of near-daily physical activity in lowering C-reactive protein, total blood leukocytes, interleukin-6, and other inflammatory cytokines may play a key role in lowering risk of cardiovascular disease, certain types of cancer, type 2 diabetes, sarcopenia, and dementia. Moderate exercise training causes favorable perturbations in immunity and a reduction in incidence of upper respiratory tract infection (URTI). During each bout of moderate exercise, an enhanced recirculation of immunoglobulins, neutrophils, and natural killer cells occurs that persists for up to 3-h post-exercise. This exercise-induced surge in immune cells from the innate immune system is transient but improves overall surveillance against pathogens. As moderate exercise continues on a near-daily basis for 12–15 weeks, the number of symptoms days with URTI is decreased 25%–50% compared to randomized sedentary controls. Epidemiologic and animal studies support this inverse relationship between URTI risk and increased physical activity.  相似文献   
5.
The middle of the 1990s saw the creation of a French–German–Swiss history textbook supported by the European Commission. Disseminated to school instructors in the Upper Rhine, it received generally positive reviews, but ended up on the dusty shelves of school libraries. This result was due to several factors, which are analysed in this article. This acknowledgement of failure leads to the argument that European cross-border cooperation is constrained by a key paradox, referred to as ‘low gravity’, i.e. the attraction of small projects toward the local and regional levels, while major projects are pushed up to the national level.  相似文献   
6.
在计算火灾爆炸环境中弹塑性简支薄板变形时,同时考虑了热冲击和均布冲击荷载的作用,建立了薄板的运动方程,研究并分析了弹塑性简支薄板的综合变形,其分析结果表明弹塑性简支薄板受到热冲击和均布冲击荷载作用时,应综合分析这两种不同荷载的作用。  相似文献   
7.
马士华  刘小群 《预测》2005,24(2):64-67,63
研究了零散货物的装载问题。根据待装货物体积、重量与货车客积、载重的相对关系,将货物分为两类。对于不同货物类型的单车装载问题,优先考虑其主要约束目标,而对其他目标则适时调整。对于货物足够多的多车装载问题,关键是按照货物的类型确定不同的装车顺序。对于货车足够多的多车装载问题,则利用上次循环得到的解,对下一次的装车次序进行调整,使解不断趋于优化。  相似文献   
8.
根据火灾温度的变化,考虑火灾高温对结构钢屈服强度和梁塑性弯矩的影响,分析了火灾均布冲击荷载作用下简支钢梁的动力响应,计算了火灾场简支钢梁在均布冲击荷载作用下的残余变形,分析表明冲击荷栽和火灾高温钢梁的变形具有显著的影响。  相似文献   
9.
在涡河亳州境内水质实测资料的基础上,分析区域内的亳州、涡阳、蒙城的四个水质监测断面水污染现状,并将三市县各排污口污染物总排放量采用等标污染负荷法进行评价,分析了涡河水污染特征,确定其主要污染物和主要污染源。在此分析基础上,结合分析区域的社会经济和自然环境条件,对污染原因进行探讨分析,并相应的提出有针对的防治措施和具体要求。  相似文献   
10.
动静载荷耦合作用下岩石破坏过程研究是深部开采等相关岩土工程的应用基础性研究课题.本文对动静载荷耦合作用下岩石破坏过程研究现状进行了分析,并对该领域今后的研究方向进行了探讨.  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