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   1407篇
  免费   89篇
公路运输   585篇
综合类   379篇
水路运输   204篇
铁路运输   193篇
综合运输   135篇
  2024年   6篇
  2023年   9篇
  2022年   35篇
  2021年   67篇
  2020年   72篇
  2019年   54篇
  2018年   37篇
  2017年   33篇
  2016年   38篇
  2015年   66篇
  2014年   119篇
  2013年   104篇
  2012年   131篇
  2011年   121篇
  2010年   85篇
  2009年   79篇
  2008年   72篇
  2007年   98篇
  2006年   82篇
  2005年   40篇
  2004年   24篇
  2003年   25篇
  2002年   17篇
  2001年   11篇
  2000年   14篇
  1999年   8篇
  1998年   7篇
  1997年   3篇
  1996年   3篇
  1995年   3篇
  1994年   4篇
  1993年   5篇
  1992年   3篇
  1991年   3篇
  1990年   7篇
  1989年   7篇
  1988年   2篇
  1986年   1篇
  1984年   1篇
排序方式: 共有1496条查询结果,搜索用时 78 毫秒
641.
New mobility data sources like mobile phone traces have been shown to reveal individuals’ movements in space and time. However, socioeconomic attributes of travellers are missing in those data. Consequently, it is not possible to partition the population and have an in-depth understanding of the socio-demographic factors influencing travel behaviour. Aiming at filling this gap, we use mobile internet usage behaviour, including one’s preferred type of website and application (app) visited through mobile internet as well as the level of usage frequency, as a distinguishing element between different population segments. We compare the travel behaviour of each segment in terms of the preference for types of trip destinations. The point of interest (POI) data are used to cluster grid cells of a city according to the main function of a grid cell, serving as a reference to determine the type of trip destination. The method is tested for the city of Shanghai, China, by using a special mobile phone dataset that includes not only the spatial-temporal traces but also the mobile internet usage behaviour of the same users. We identify statistically significant relationships between a traveller’s favourite category of mobile internet content and more frequent types of trip destinations that he/she visits. For example, compared to others, people whose favourite type of app/website is in the “tourism” category significantly preferred to visit touristy areas. Moreover, users with different levels of internet usage intensity show different preferences for types of destinations as well. We found that people who used mobile internet more intensively were more likely to visit more commercial areas, and people who used it less preferred to have activities in predominantly residential areas.  相似文献   
642.
Conventional road transport has negative impact on the environment. Stimulating eco-driving through feedback to the driver about his/her energy conservation performance has the potential to reduce CO2 emissions and promote fuel cost savings. Not all drivers respond well to the same type of feedback. Research has shown that different drivers are attracted to different types of information and feedback. The goal of this paper is to explore which different driver segments with specific psychographic characteristics can be distinguished, how these characteristics can be used in the development of an ecodriving support system and whether tailoring eco-driving feedback technology to these different driver segments will lead to increased acceptance and thus effectiveness of the eco feedback technology. The driver segments are based on the value orientation theory and learning orientation theory. Different possibilities for feedback were tested in an exploratory study in a driving simulator. An explorative study was selected since the choice of the display (how and when the information is presented) may have a strong impact on the results. This makes testing of the selected driver segments very difficult. The results of the study nevertheless suggest that adapting the display to a driver segment showed an increase in acceptance in certain cases. The results showed small differences for ratings on acceptation, ease of use, favouritism and a lower general rating between matched (e.g., learning display with learning oriented drivers) and mismatched displays (e.g., learning display with performance oriented drivers). Using a display that gives historical feedback and incorporates learning elements suggested a non-verifiable increase in acceptance for learning oriented drivers. However historical feedback and learning elements may be less effective for performance oriented drivers, who may need comparative feedback and game elements to improve energy conserving driving behaviour.  相似文献   
643.
周政  何忠韬 《铁道车辆》2011,49(5):11-13,47
从机械振动学的角度分析了机车车辆多孔式液气缓冲器的结构模型,并建立了单自由度振动模型,然后运用动力学基本知识建立了运动方程,通过方程的求解明确了多孔式液气缓冲器缓冲过程的运动轨迹以及影响参数,为此类缓冲器的优化设计提供了一定的理论参考。  相似文献   
644.
目前我国路基设计参数取值较低,直接导致路基病害频繁发生。针对此种情况,通过大型有限元软件ANSYS建立了典型道路模型,对不同路基回弹模量(以下简称模量)下的路面结构力学性能进行计算分析;计算结果表明,适当提高目前路基设计指标,可以明显地优化路面结构的受力性能,最大限度降低道路病害发生的风险。  相似文献   
645.
桥梁旋转式伸缩装置的缝宽控制性能   总被引:1,自引:0,他引:1  
针对桥梁的运营过程中某些桥梁的伸缩装置出现的缝宽不均匀、单缝缝宽过大等缺陷给行车安全带来的隐患,结合工程实例,基于力学分析对旋转式伸缩装置的缝宽控制性能进行了研究,讨论了影响缝宽均匀性的主要因素,提出了改善缝宽控制性能的措施。研究结果表明:在伸缩量较大时,旋转式伸缩装置的缝宽可能存在不均匀,且这种不均匀主要集中在靠近伸缩装置两端的单元上;伸缩装置的材料特性、安装工艺和构造参数对缝宽不均匀性都有影响,而构造参数的影响更为显著;布置合理的限位装置可有效改善缝宽的不均匀性。  相似文献   
646.
钒对高铬锰白口铸铁组织和性能的影响   总被引:1,自引:0,他引:1  
探讨了钒以及热处理工艺对高铬锰白口铸铁组织和性能的影响。结果表明:在高铬锰白口铸铁中加入一定数量的钒,能细化晶粒,改善碳化物的形态和分布,提高力学性能。在含钒量为0.25%~0.5%时,热处理温度为1 000℃时,其力学性能最佳。  相似文献   
647.
企业与社会需求是高职专业建设的逻辑起点,而岗位职业标准则是专业建设的理论依据。为了做好机械制造与自动化专业的人才培养,基于机械制造与自动化专业企业人才市场需求调查,得出了该专业对应企业人才需求的岗位分布与工作任务、能力、知识与素质要求,从而提出高职机械制造与自动化专业人才培养目标、人才培养规格与人才培养的新途径。  相似文献   
648.
以连云港港旗台港区25万t级矿石码头机械取制样设施为例,介绍矿石机械取制样的工艺系统.该系统符合国际标准,功能完备,配置优化,布置科学,且充分考虑实际操作需要,体现了人性化的特点.  相似文献   
649.
This work reports the results of a numerical investigation aiming at assessing the structural safety of an actual offshore topside steel structure exposed to accidental localised fire conditions. Particularly, the paper explores the nonlinear thermomechanical and ultimate strength behaviours obtained by means of two fire approaches: sophisticated CFD (Computational Fluid Dynamics) and “LF-ESF” (Localised Fire with Ellipsoidal Solid Flame), previously developed and validated by the authors. CFD-based approaches, which typically solve nearly compressible flow with input energy given by a combustion model, allow accurate evaluation of a fluid-thermo response for the entire duration of the simulated accident. However, the analysis complexity, massive amount of produced data, excessive computational and time-consuming make CFD approaches unsuitable for the current applied design usage. On the other hand, the proposed LF-ESF approach displays quite accurate estimates in comparison to CFD counterparts. Moreover, the LF-ESF can be directly modelled in FE-based commercial software and used to obtain the steel temperature variation and thermomechanical behaviour. The obtained results indicate that the LF-ESF approach combined with FE-based models can provide reliable fire-safety analyses, ensuring that the main safety (load-bearing) functions of the offshore steel structures are not impaired during accidental fire conditions.  相似文献   
650.

R&D in the field of driver support systems is increasingly paid attention to. These systems can contribute significantly to public traffic goals. However, there is much uncertainty about future technology developments, market introduction, and impacts on driver and traffic behaviour. An international Delphi study collecting expert opinions on these issues is partly described here. The Delphi study was organized in three rounds. Opinions of 50 experts from the USA, Japan and Europe were collected. The paper is limited to market introduction, and technological and driver-behavioural barriers. The main conclusion is that future developments are less obvious than often assumed.  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