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   281篇
  免费   6篇
公路运输   71篇
综合类   20篇
水路运输   82篇
铁路运输   22篇
综合运输   92篇
  2023年   1篇
  2022年   3篇
  2021年   12篇
  2020年   9篇
  2019年   5篇
  2018年   8篇
  2017年   9篇
  2016年   16篇
  2015年   10篇
  2014年   21篇
  2013年   36篇
  2012年   20篇
  2011年   12篇
  2010年   12篇
  2009年   11篇
  2008年   6篇
  2007年   9篇
  2006年   5篇
  2005年   7篇
  2004年   4篇
  2003年   4篇
  2002年   2篇
  2001年   3篇
  2000年   2篇
  1999年   4篇
  1998年   7篇
  1997年   4篇
  1996年   2篇
  1995年   1篇
  1994年   4篇
  1992年   1篇
  1991年   1篇
  1990年   4篇
  1989年   1篇
  1988年   1篇
  1987年   2篇
  1986年   3篇
  1985年   2篇
  1984年   5篇
  1983年   5篇
  1982年   4篇
  1981年   3篇
  1980年   2篇
  1977年   4篇
排序方式: 共有287条查询结果,搜索用时 109 毫秒
81.
The greatest source of human-related mortality for endangered Florida manatees is collisions with watercraft. Regulation of boat speeds is the principal management tool to minimize this threat. Demands on law enforcement limit their ability to monitor boater behavior and managers seek alternative strategies to increase compliance. The purposes of this study were to: (1) explore the effectiveness of an on-site sign to enhance boater compliance in a boating speed zone, and (2) examine the environmental and boating characteristics that influence the probability of compliance. Signs designed to increase compliance were posted halfway through the 18-week study period. The signs were not related to compliance level. Logistic regression models showed that only time of day and boat type were significantly related to compliance. Results suggest that passive methods of persuasion may not be an effective means of influencing boater behavior.  相似文献   
82.
In a car-free city centre car traffic is limited by an area-wide ban to its functionally necessary share. This usually includes delivery and service vehicles and residents' cars. The lock-out of unnecessary car traffic must not be an isolated measure, but part of a pulland-push approach. The most important supporting measure concerns the provision of attractive public transport services. Case studies from Bologna, Lubeck, Aachen, York, and Nuremburg are reported.  相似文献   
83.
船舶右主机控制系统PCP面板显示轴转速故障报警,而机旁和远程控制系统转速显示仪表指示正常.针对这一现象,文章分析了该船控制系统轴转速信号测量和报警电路原理,逐步排查故障原因,最终成功修复.  相似文献   
84.
针对曹妃甸矿石码头三期工程,通过数学模型和物理模型试验,合理确定码头方位和长度。并针对船舶横移量较大的问题,对系缆墩的布置进行优化,减少了风、浪、流组合作用下船舶运动量对装卸作业的影响,且缆绳的受力更加均匀。  相似文献   
85.
This paper seeks to determine the effects of uncertainty in out-of-vehicle times on route choice. Data were collected at two key interchanges in Auckland, New Zealand. Previous work modelled the data using a manual approach to fuzzy logic. This study extends that work by automating the process through defining a black-box function to match the survey data, then employing a genetic algorithm to fine-tune the fuzzy logic model. Results show that automation and the genetic algorithm improve the model’s capability to more accurately predict ridership. The tuning of the membership functions is conducted twice, first using initial fuzzy rules and again after the fuzzy rules have been adjusted to reduce disparity between the output and survey data. The calibrated membership functions provided for operational (transfer waiting and walking time and delay) and physical attributes (safety and seat availability) can be used by practitioners to determine an estimated ridership.  相似文献   
86.
Climate change adaptation presents a difficult challenge for coastal towns around the world, forcing local governments to plan for sea level rise in a contentious decision-making space. The concept of “adaptation pathways,” a diagnostic and analytical tool to assist in adaptive planning and decision-making, is gaining traction as a way of framing and informing climate adaptation. It provides decisionmakers a way to acknowledge the inter-temporal complexities and uncertainties associated with the novel dynamics of climate change and a mechanism to manage these challenges in the local context. In 2012, the Australian Government funded an 18-month program to provide decisionmakers in the coastal zone an opportunity to test the utility of the adaptation pathways concept for coastal climate adaptation. Using a selection of completed projects as case studies, we performed a document analysis to better understand the learnings from the projects. The main themes surrounded: (1) the utility of the adaptation pathway framework in developing options, (2) decision-making rationale and criteria, and (3) stakeholder participation in pathway development. A project participant survey was developed to further understand these themes. Our analysis reveals that “adaptation pathways” was generally framed narrowly and conservatively to emphasize extant economic, administrative and legal considerations over community, participatory, or exploratory ones. Although some case study projects were able to reach a point in the pathway discussion to actively involve stakeholders in their decision-making process, many case studies continued to build technical data as a method for defending policies and actions. These results indicate that coastal adaptation can take-up adaptation pathways as a useful concept for decision-making and planning; however, many councils may still require assistance in stakeholder communication processes in order to develop sociallyacceptable plans that take into account the full range of values affecting local coastal environments.  相似文献   
87.
For over thirty years man has studied “outer space” and installed satellites which watch the surface of the Earth. The great depths of the world ocean are, however, practically unknown and there is an urgent need to put abyssal benthic laboratories into “inner space” in order to study basic phenomena of interest to marine science and climatology as well as man's impact on the oceans.In view of the numerous problems related to global change, as a first step emphasis should first be on the role of the oceans and their inherent processes, which are the focus of such international programmes as the World Ocean Circulation Experiment (WOCE) and the Joint Global Ocean Flux Study (JGOFS). Multi-disciplinary registration of key events at selected key sites investigating the variability in time and space are of the utmost importance. The same methods and techniques must be used for the study of human impacts on the deep oceans caused by mining of metalliferous resources and by waste disposal as well as in basic studies. However, the investigation of the inner space of our planet has certain requirements. As long-term and large-scale investigations become more and more important, development of automized systems, largely independent from research vessels will be required. This will demand high capacities of energy for all technical functions as well as high storage capacities for data and samples. As a consequence the needs for two different—although overlapping—functional approaches are defined for future deep-sea deployments.(A) A system for long-term registration of the natural variability and long-term monitoring of human impacts: (B) A system for short-term observations and short-time experimentations. This report summarizes their technological demands. The envisioned interdisciplinary technology should deliver information on physical, biological and geochemical processes and their variabilities in the deep oceans. The prospected systems need to have the ability for real time video observation, data transfer and experimental manipulation, as well as sensing and sampling facilities with large storage capacities for long-term deployments.Prospective costs of the described multipurpose abyssal benthic laboratory will presumably exceed the funds for deep-sea research of a single country. A joint European effort could solve this problem and help to manifest a leading role for European marine science in international deep-sea and global change research.  相似文献   
88.
89.
One of the difficulties of biliary surgery lies inthe treatment of iatrogenic biliary stricture that isexpressed prominently after operation as scar con-tracture and anastomotic stenosis, especiaI1y theanastomotic stenosis at the porta hepatis and thearea above it. ln order to exp1ain the mechansim ofthe formation of iatrogenic biliary stricture, an ani-mal model of trauma--repair of bile duct was madein this experiment and the expression of myofi-broblast (MFB) during the whole process was ob…  相似文献   
90.
The transport sector has been identified as a significant contributor to greenhouse gas emissions. As part of its emissions reduction strategy, the United Kingdom Government is demonstrating support for new vehicle technologies, paying attention, in particular, to electric vehicles.Cluster analysis was applied to Census data in order to identify potential alternative fuel vehicle drivers in the city of Birmingham, United Kingdom. The clustering was undertaken based on characteristics of age, income, car ownership, home ownership, socio-economic status and education. Almost 60% of areas that most closely fitted the profile of an alternative fuel vehicle driver were found to be located across four wards furthest from Birmingham city centre, while the areas with the poorest fit were located towards the centre of Birmingham. The paper demonstrates how Census data can be used in the initial stages of identifying potential early adopters of alternative vehicle drivers. It also shows how such research can provide scope for infrastructure planning and policy development for local and national authorities, while also providing useful marketing information to car manufacturers.  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