全文获取类型
收费全文 | 5749篇 |
免费 | 112篇 |
专业分类
公路运输 | 1592篇 |
综合类 | 1293篇 |
水路运输 | 1621篇 |
铁路运输 | 1002篇 |
综合运输 | 353篇 |
出版年
2023年 | 39篇 |
2022年 | 115篇 |
2021年 | 137篇 |
2020年 | 119篇 |
2019年 | 53篇 |
2018年 | 102篇 |
2017年 | 73篇 |
2016年 | 104篇 |
2015年 | 112篇 |
2014年 | 190篇 |
2013年 | 347篇 |
2012年 | 362篇 |
2011年 | 448篇 |
2010年 | 423篇 |
2009年 | 442篇 |
2008年 | 414篇 |
2007年 | 585篇 |
2006年 | 542篇 |
2005年 | 360篇 |
2004年 | 115篇 |
2003年 | 90篇 |
2002年 | 68篇 |
2001年 | 90篇 |
2000年 | 103篇 |
1999年 | 67篇 |
1998年 | 41篇 |
1997年 | 33篇 |
1996年 | 34篇 |
1995年 | 48篇 |
1994年 | 28篇 |
1993年 | 31篇 |
1992年 | 17篇 |
1991年 | 22篇 |
1990年 | 24篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有5861条查询结果,搜索用时 0 毫秒
351.
352.
David T. Hartgen 《Transportation》2013,40(6):1133-1157
This study reviews the 50-year history of travel demand forecasting models, concentrating on their accuracy and relevance for public decision-making. Only a few studies of model accuracy have been performed, but they find that the likely inaccuracy in the 20-year forecast of major road projects is ±30 % at minimum, with some estimates as high as ±40–50 % over even shorter time horizons. There is a significant tendency to over-estimate traffic and underestimate costs, particularly for toll roads. Forecasts of transit costs and ridership are even more uncertain and also significantly optimistic. The greatest knowledge gap in US travel demand modeling is the unknown accuracy of US urban road traffic forecasts. Modeling weaknesses leading to these problems (non-behavioral content, inaccuracy of inputs and key assumptions, policy insensitivity, and excessive complexity) are identified. In addition, the institutional and political environments that encourage optimism bias and low risk assessment in forecasts are also reviewed. Major institutional factors, particularly low local funding matches and competitive grants, confound scenario modeling efforts and dampen the hope that technical modeling improvements alone can improve forecasting accuracy. The fundamental problems are not technical but institutional: high non-local funding shares for large projects warp local perceptions of project benefit versus costs, leading to both input errors and political pressure to fund projects. To deal with these issues, the paper outlines two different approaches. The first, termed ‘hubris’, proposes a multi-decade effort to substantially improve model forecasting accuracy over time by monitoring performance and improving data, methods and understanding of travel, but also by deliberately modifying the institutional arrangements that lead to optimism bias. The second, termed ‘humility’, proposes to openly quantify and recognize the inherent uncertainty in travel demand forecasts and deliberately reduce their influence on project decision-making. However to be successful either approach would require monitoring and reporting accuracy, standards for modeling and forecasting, greater model transparency, educational initiatives, coordinated research, strengthened ethics and reduction of non-local funding ratios so that localities have more at stake. 相似文献
353.
介绍了双动薄板冲压机控制系统的改造方案,可编程控制器的硬、软件系统的组成,软件的设计思想.以及系统中压力信号的检测和处理方法。 相似文献
354.
2006年,全路工务工作在完成第六次大面积提速改造工程、确保青藏线开通运营、强化设备安全基础、深化修程修制改革、规范安全管理等方面取得了突出成绩。2007年,全路工务工作要大力提高设备质量,强化设备安全保障能力,确保第六次提速调图工作的顺利实施,管好用好青藏线,探索高速、重载条件下线桥设备的变化规律,提升检修作业的装备水平和科技含量,确保设备质量均衡和长期稳定,提高干部职工技术水平和人员素质,全面完成2007年各项任务,推动铁路又好又快的向前发展,实现和谐铁路的奋斗目标。 相似文献
355.
This paper examines the location choice associated with discretionary activities (in-home vs. out-of-home). These substitution
patterns are important in terms of travel demand as in-home activities do not necessitate travel while out-of-home activities
incur travel. Mixed logit models are estimated using an activity dataset (2003 CHASE data) to analyze the factors associated
with this choice at the individual activity-level. Results suggest that the attributes of an activity significantly contribute
to understanding the likelihood of engaging in out-of-home activities. Activity type interaction terms reveal the varying
influence that socio-demographics, activity attributes and travel have over four different activity types modeled. The results
reveal that the location choice (in-home vs. out-of-home) is sensitive to travel characteristics. As the travel time and cost
increases, an individual is less likely to engage in an activity out-of-home. Compared to passive and social activities, the
location of active activities is more sensitive to changes in travel attributes. 相似文献
356.
357.
358.
359.
该文介绍了至界岭隧道穿越层状围岩段,采用锚喷支护、辅以超前锚杆进行临时支护的方法。按照弱爆破、短进尺、早支护、勤量测的原则施工,获得成功,可供类似施工参考。 相似文献
360.