全文获取类型
收费全文 | 499篇 |
免费 | 6篇 |
专业分类
公路运输 | 195篇 |
综合类 | 49篇 |
水路运输 | 60篇 |
铁路运输 | 44篇 |
综合运输 | 157篇 |
出版年
2024年 | 14篇 |
2023年 | 6篇 |
2022年 | 24篇 |
2021年 | 14篇 |
2020年 | 21篇 |
2019年 | 1篇 |
2018年 | 22篇 |
2017年 | 22篇 |
2016年 | 25篇 |
2015年 | 32篇 |
2014年 | 39篇 |
2013年 | 25篇 |
2012年 | 24篇 |
2011年 | 9篇 |
2010年 | 15篇 |
2009年 | 24篇 |
2008年 | 19篇 |
2007年 | 19篇 |
2006年 | 30篇 |
2005年 | 18篇 |
2004年 | 19篇 |
2003年 | 14篇 |
2002年 | 15篇 |
2001年 | 9篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
排序方式: 共有505条查询结果,搜索用时 0 毫秒
431.
论我国城市公交电动客车的开发 总被引:2,自引:0,他引:2
迈入新世纪,防治城市空气污染的紧迫重任摆在国人面前。据环保部门统计:城市空气污染源的60%以上来自交通运输车辆的废气排放。本文就开发我国零污染的城市公交电动客车作探讨性的论述。 相似文献
432.
Air transportation in Brazil has been recently liberalized and one of the consequences of this process is the concentration of flights in a few hubs. During the years 2006-2007 two fatal accidents created unprecedented chaos in both land and air sides of the system with harmful consequences to tourism in Brazil. The consequences were more airport congestion and many episodes of flight delays and cancellations that lasted for several months. We argue that, among other factors, this state of blackout was a result of the increase in the degree of concentration in few airports, particularly Congonhas (in São Paulo) and Brasília. Using data obtained from a survey with Brazilian experts, a comparison was made with two existing methods (the one used by the US Federal Aviation Administration and the usual Herfindahl-Hirschman method) in order to calculate the number of hubs in Brazil. Due to the huge discrepancy obtained between data from the survey and the other two methods considered, a new mathematical method based on the Herfindahl-Hirschman Index was proposed to identify the number of hubs in a given network. Drawing from the examples of what happened to tourist destinations during and after the air transport crisis in Brazil, the article concludes discussing the need for a more accurate tool to identify and to monitor the concentration of flights at the Brazilian air transportation network and its importance to tourism. 相似文献
433.
陆永红 《舰载武器(含VCD光盘)》2001,(4):39-42
未来防空作战的环境越来越严峻,提高防空能力迫在眉睫,本文指出激光防空武器相对其它防空武器更适合防空反导作战,是精确制导武器的克星,同时介绍了激光防空武器的种类、研制装备情况。 相似文献
434.
环境保护监理是近年来监理工程师的主要工作之一,文章通过对钦州港大榄坪1#、2#散杂货泊位工程施工中存在的环境问题进行分析,提出了防治环境污染的监理措施和方法。 相似文献
435.
This paper is concerned with a problem area of increasing interest, namely the traffic characteristics of specific generators located on non‐residential land use. It concentrates on the problem of modelling traffic generation for goods, service and business movements at the manufacturing establishment. Firstly the contributions of earlier researchers are reviewed in the context of factors which have been considered important. Then a further study conducted by the author in Sheffield and in Manchester, England, is described. This study considers more rigorously than hitherto the questions of similarities in trip rates over different manufacturing activities and geographical areas, and of the choice of explanatory variables. Comparison of regressions is used to formalize indications of similarities in trip rates, and analysis of variance for choosing the most satisfactory explanatory variables. The study provides evidence of similarity in trip rates over seven different manufacturing activities and two geographical areas. It also shows distinctions between different non‐work traffic types in the extent of similarities in trip rates over different manufacturing activities and in explanatory variables for traffic generation relationships. Regarding the latter it is concluded that it is not possible to model accurately such traffic movements on the basis of explanatory variables which are normally available. Instead trip rates should be expressed in simple mathematical terms and should be based on large data populations. The study also makes contributions on peak flow factors for the actual design of facilities of manufacturing establishments. These findings and others are discussed in the context of the work of earlier researchers. Finally conclusions are drawn and guidance offered for future work into this problem. 相似文献
436.
Prateek Sharma Mukesh Khare 《Transportation Research Part D: Transport and Environment》1999,4(6):1105
An Intervention Analysis Model (IAM) (Box and Tiao, 1975) was developed to study the impact of the ‘intervention' brought in by the Government of India (GoI), to control the CO pollution caused by the vehicular exhaust emissions, by the enforcement of the emission standards for the vehicles, on the mean level of the time-series of CO concentration. The study was conducted for an Air Quality Control Region (AQCR) comprising of an urban road intersection in Delhi, India, where almost 100% CO is contributed by vehicular traffic. Application of the model suggests that the ‘intervention' has not been effective in bringing down the desired change; some likely causes of which have also been mentioned. 相似文献
437.
Although the aviation industry is increasingly becoming important for Africa’s economic development and integration, the ability of airlines to access foreign markets remains hindered by restrictive regulatory policies. Attempts have been made to fully liberalize the intra-African air transport market. Except for general assertions about the merits/demerits of liberalization, our empirical understanding of the welfare effects of such polices in Africa remains rudimentary. This study empirically measures the economic effects of air transport liberalization, mainly on two supply side variables: fare and service quality, measured as departure frequency. The empirical models evaluate how air fares and departure frequency respond to measures of openness in air services agreements, while controlling for other determinants. The results show up to 40% increase in departure frequency in routes that experienced some type of liberalization compared to those governed by restrictive bilateral air service agreements. Furthermore, there is a relatively larger increase in departure frequency in routes which experienced partial liberalization compared to fully liberalized ones. This can be explained by the diminishing marginal effect of progressive liberalization on departure frequency. While the effect of liberalization is substantial in improving service quality, there is no evidence of its fare reducing effect. 相似文献
438.
城市客车冬季制动管路经常结冰会导致制动失效,行车有安全隐患,为了解决这个问题,对城市客车制动管路结冰问题进行专项研究。对城市客车的行驶特点、制动系统零部件结构功能和管路安装形式进行了详细介绍,总结出城市客车制动管路结冰的4方面原因。通过理论计算与分析,提出防止制动管路结冰的4项措施,解决了城市客车冬季制动管路结冰这个问题。 相似文献
439.
440.
研究了我国的VMA规定值和计算方法.指出了我国普遍使用的马歇尔设计方法,根据集料公称最大粒径规定的最小VMA值,与美国马歇尔设计方法给定的最小VMA及美国Superpave设计方法规定的最小VMA值,本质上是一致的,但计算方法却不同.采用现行计算VMA的4种方法,计算了25种工地沥青混合料的VMA值.我国的粗集料用毛体积相对密度,细集料用表观相对密度计算VMA的方法和美国的方法所用公式形式一样,但我国计算的VMA比美国方法计算的VMA均偏大.在实际使用时,建议按照细集料含量与细集料平均吸水率的乘积大小,修正我国计算公式,使之接近沥青混合料的真实VMA. 相似文献