全文获取类型
收费全文 | 3591篇 |
免费 | 21篇 |
专业分类
公路运输 | 2082篇 |
综合类 | 425篇 |
水路运输 | 921篇 |
铁路运输 | 138篇 |
综合运输 | 46篇 |
出版年
2024年 | 3篇 |
2023年 | 7篇 |
2022年 | 37篇 |
2021年 | 71篇 |
2020年 | 50篇 |
2019年 | 32篇 |
2018年 | 13篇 |
2017年 | 85篇 |
2016年 | 83篇 |
2015年 | 122篇 |
2014年 | 184篇 |
2013年 | 89篇 |
2012年 | 241篇 |
2011年 | 333篇 |
2010年 | 245篇 |
2009年 | 231篇 |
2008年 | 223篇 |
2007年 | 308篇 |
2006年 | 272篇 |
2005年 | 212篇 |
2004年 | 141篇 |
2003年 | 162篇 |
2002年 | 113篇 |
2001年 | 97篇 |
2000年 | 71篇 |
1999年 | 46篇 |
1998年 | 27篇 |
1997年 | 29篇 |
1996年 | 23篇 |
1995年 | 23篇 |
1994年 | 12篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 9篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有3612条查询结果,搜索用时 31 毫秒
61.
62.
63.
64.
This paper analyses transport energy consumption of conventional and electric vehicles in mountainous roads. A standard round trip in Andorra has been modelled in order to characterise vehicle dynamics in hilly regions. Two conventional diesel vehicles and their electric-equivalent models have been simulated and their performances have been compared. Six scenarios have been simulated to study the effects of factors such as orography, traffic congestion and driving style. The European fuel consumption and emissions test and Artemis urban driving cycles, representative of European driving cycles, have also been included in the comparative analysis. The results show that road grade has a major impact on fuel economy, although it affects consumption in different levels depending on the technology analysed. Electric vehicles are less affected by this factor as opposed to conventional vehicles, increasing the potential energy savings in a hypothetical electrification of the car fleet. However, electric vehicle range in mountainous terrains is lower compared to that estimated by manufacturers, a fact that could adversely affect a massive adoption of electric cars in the short term. 相似文献
65.
随着大型柴油发动机经济性和排放要求的不断提升,以及对发动机稳态、瞬态特性要求的不断提高,传统的涡轮增压系统已无法满足船用发动机全工况性能的要求。为了提高产品竞争力和适配性,针对某8缸直列船用柴油发动机开发了带有定压排气管的相继增压系统,并进行了发动机台架试验研究。结果表明:发动机中、低转速时,相继增压系统使发动机比油耗可以下降5%-10%,排气温度降低30%-45%,烟度下降55%-60%;最大扭矩可以提升15.1%-36.4%;发动机最大扭矩转速工况突加突卸响应性提升约28%-29%;相继增压系统中定压排气管的设计使得发动机高工况性能也有所提升,从而实现发动机全工况性能的提升。 相似文献
66.
分析5 000 PCC"SHANGHAI HIGHWAY"船主机伺服油压低引起主机启动故障的原因、介绍调查与处理过程,在实施了恰当的处理方法后,解决了问题。以期为类似问题的处理与解决提供借鉴和参考。 相似文献
67.
An experimental study to measure the evaporation rates, engine performance and emission characteristics of cotton seed biodiesel (cotton seed oil methyl ester) and its blends in different volumetric proportions with diesel is presented. The thermo-physical properties of all the fuel blends have been measured and presented. Evaporation rates of neat cotton seed biodiesel, neat diesel and their bends have been measured under slow convective environment of air flowing with a constant temperature. Evaporation constants have been determined by using the droplet regression rate data. The neat fuels and fuel blends have been utilized in a test engine with different load conditions to evaluate the performance, combustion and emission characteristics of the fuels. The specific fuel consumption values of the two blends, viz. B25 and B75 are found to be same. At the highest load, B0 records the lowest CO volume followed by B100. From the observed evaporation, performance and emissions characteristics, it is suggested that a blend of B50 and B75 can be optimally used in standard diesel engine settings. 相似文献
68.
Transportation is a major cause for environmental degradation via exhaust emissions. For many transit-oriented metropolitan areas, bus trips often constitute a sizeable mode share. Managing the bus fleet, in particular updating buses to comply with the newer emissions standards, therefore, can have a substantial impact on transportation-induced air quality. This paper presents the approach of remaining life additional benefit–cost (RLABC) analysis for maximising the total net benefit by either early-retiring or retrofitting the current bus fleet within their lifespans. By referring to the net benefits for different bus types estimated by RLABC analysis, the most beneficial management scheme for the current bus fleet can be identified. Optimal bus fleet management (BFM) models based on the RLABC analysis for the operator and the government are developed. Then a government subsidy plan is produced to achieve win–win solutions, which will offer efficient and flexible management schemes. To illustrate the approach, the largest bus company in Hong Kong, which carries more than 23% of the total trips in Hong Kong, is taken as a case study example. Instead of adopting a fixed retirement plan, such as replacing buses at the age of 17 as is currently practised, the proposed method develops an optimal BFM scheme that progressively phases out buses or retrofits them. This study produces promising results to demonstrate the large benefit of this approach for optimal bus fleet management. 相似文献
69.
本文介绍了基于以太网的机舱监测报警系统的组成和功能,并对机舱监测报警系统的硬件、软件进行了设计,为后续的机舱监测系统设计提供参考。 相似文献
70.