全文获取类型
| 收费全文 | 845篇 |
| 免费 | 2篇 |
专业分类
| 公路运输 | 238篇 |
| 综合类 | 21篇 |
| 水路运输 | 275篇 |
| 铁路运输 | 21篇 |
| 综合运输 | 292篇 |
出版年
| 2022年 | 16篇 |
| 2021年 | 4篇 |
| 2020年 | 7篇 |
| 2019年 | 7篇 |
| 2018年 | 21篇 |
| 2017年 | 22篇 |
| 2016年 | 26篇 |
| 2015年 | 11篇 |
| 2014年 | 31篇 |
| 2013年 | 114篇 |
| 2012年 | 30篇 |
| 2011年 | 35篇 |
| 2010年 | 41篇 |
| 2009年 | 35篇 |
| 2008年 | 41篇 |
| 2007年 | 15篇 |
| 2006年 | 21篇 |
| 2005年 | 22篇 |
| 2004年 | 12篇 |
| 2003年 | 24篇 |
| 2002年 | 18篇 |
| 2001年 | 12篇 |
| 2000年 | 12篇 |
| 1999年 | 19篇 |
| 1998年 | 28篇 |
| 1997年 | 20篇 |
| 1996年 | 16篇 |
| 1995年 | 8篇 |
| 1994年 | 4篇 |
| 1993年 | 13篇 |
| 1992年 | 15篇 |
| 1991年 | 12篇 |
| 1990年 | 7篇 |
| 1989年 | 12篇 |
| 1988年 | 7篇 |
| 1987年 | 7篇 |
| 1986年 | 4篇 |
| 1985年 | 12篇 |
| 1984年 | 8篇 |
| 1983年 | 6篇 |
| 1982年 | 8篇 |
| 1981年 | 7篇 |
| 1980年 | 8篇 |
| 1979年 | 6篇 |
| 1978年 | 4篇 |
| 1977年 | 7篇 |
| 1976年 | 5篇 |
| 1975年 | 6篇 |
| 1974年 | 10篇 |
| 1972年 | 5篇 |
排序方式： 共有847条查询结果，搜索用时 15 毫秒
841.
842.
The relationship between the oxygen content in gasoline and the particulate emission (particle number and weight) was investigated. In order to study the influence of the engine configuration on the particulate emission, four vehicles were tested in which the following systems were installed: Vehicle 1 was equipped with direct injection system which uses central mounted outwardly opening injectors. Vehicle 2 and 3 used direct injection with a side mounted multihole injectors and Vehicle 4 had port fuel injection system. Methyl tert-butyl ether (MTBE) was used as the oxygen booster. The oxygen content in the gasoline was varied from 1 to 3 wt%, which corresponds with an MTBE dosage from 3.55% to 16.11%. This study used fuel that contained the same octane number with a 2% oxygen content without oxygen components, and it was used as the reference fuel in order to distinguish the effect of the oxygen content increases and the octane boosts that result from the MTBE. All vehicle tests were performed on a roller type chassis dynamometer using the New European Driving Cycle (NEDC) and Federal Test Procedure-75 (FTP-75) cycle. The experiment results demonstrate that the oxygen content increases in the gasoline reduced the particulate emission in vehicles with direct injection engines. An equivalent phenomenon was observed in a vehicle with a port fuel injection engine, but its absolute particle number was much smaller than that of the gasoline direct injection engine. The amount of reduction of the particle number in the start (cold) phase of the test cycle was significant compared with the later (hot) phase engine operation. However, particulates were emitted even though the engine was fully warmed up, especially when the engine was highly loaded. Other factors such as fuel economy or other exhaust emissions were not significantly affected by the oxygen content. 相似文献
843.
Due to environmental concerns and safety regulations in the automotive industry, the development of strong and lightweight cars has been a hot issue in the last decade. One solution for this purpose would be to use high-strength steel (HSS) and advanced high-strength steel (AHSS). These materials can make the car lighter while maintaining the crash resistance of the vehicle. HSS and AHSS have more resistance force in the die structure compared with conventional steel due to their higher yield and tensile strength and thus, these materials have a greater effect on die deformation during the sheet metal forming process. As a result, die deformation can affect the blank sheet’s drawn pattern, strain, and stress as well as springback. This study presents a sheet metal forming simulation that considers die deformation. The simulation process was compared with conventional simulation methods. Our results indicate that the sheet metal forming simulation with die deformation consideration provides useful information on the die structure as well as formability and springback. 相似文献
844.
C. Fernández D. F. Llorca M. A. Sotelo I. G. Daza A. M. Hellín S. Álvarez 《International Journal of Automotive Technology》2013,14(1):113-122
This paper describes a real-time vision-based blind spot warning system that has been specially designed for motorcycles detection in both daytime and nighttime conditions. Motorcycles are fast moving and small vehicles that frequently remain unseen to other drivers, mainly in the blind-spot area. In fact, although in recent years the number of fatal accidents has decreased overall, motorcycle accidents have increased by 20%. The risks are primarily linked to the inner characteristics of this mode of travel: motorcycles are fast moving vehicles, light, unstable and fragile. These features make the motorcycle detection problem a difficult but challenging task to be solved from the computer vision point of view. In this paper we present a daytime and nighttime vision-based motorcycle and car detection system in the blind spot area using a single camera installed on the side mirror. On the one hand, daytime vehicle detection is carried out using optical flow features and Support Vector Machine-based (SVM) classification. On the other hand, nighttime vehicle detection is based on head lights detection. The proposed system warns the driver about the presence of vehicles in the blind area, including information about the position and the type of vehicle. Extensive experiments have been carried out in 172 minutes of sequences recorded in real traffic scenarios in both daytime and nighttime conditions, in the context of the Valencia MotoGP Grand Prix 2009. 相似文献
845.
The electric controller is one of the most crucial components in an electric bicycle. The overall performance of the whole system heavily depends on the properties of the controller. The authors use the robust control theory to design a new H∞ robust controller for the closed speed-current dual-loop driving and braking system. The designed controller also incorporates the driving and energy recovery braking circuit. Therefore, it has energy recovery ability, which coverts the kinetic energy wasted in braking into electric energy to recharge the battery. This prolongs the driving distance per battery charge. The simulations and experiments show that the new H∞ robust controller out-performs the traditional PID controller in many respects including stability, error, responding speed and driving distance per battery charge. 相似文献
846.
Michael G.H. Bell Valentina Trozzi Solmaz Haji Hosseinloo Guido Gentile Achille Fonzone 《Transportation Research Part A: Policy and Practice》2012,46(5):790-800
The vehicle navigation problem studied in Bell (2009) is revisited and a time-dependent reverse Hyperstar algorithm is presented. This minimises the expected time of arrival at the destination, and all intermediate nodes, where expectation is based on a pessimistic (or risk-averse) view of unknown link delays. This may also be regarded as a hyperpath version of the Chabini and Lan (2002) algorithm, which itself is a time-dependent A* algorithm. Links are assigned undelayed travel times and maximum delays, both of which are potentially functions of the time of arrival at the respective link. Probabilities for link use are sought that minimise the driver’s maximum exposure to delay on the approach to each node, leading to the determination of a pessimistic expected time of arrival at the destination and all intermediate nodes. Since the context considered is vehicle navigation, the probability of link use measures link attractiveness, so a link with a zero probability of use is unattractive while a link with a probability of use equal to one will have no attractive alternatives. A solution algorithm is presented and proven to solve the problem provided the node potentials are feasible and a FIFO condition applies to undelayed link travel times. The paper concludes with a numerical example. 相似文献
847.
空间分析及基础技术应用是研究集装箱运输的必要手段.大部分交通运输数据集由不同出处、关联性不强的原始数据组成,因而很难得到其空间分布特点.同时,集装箱路径优化和市场可达性在缓解集装箱运输拥堵方面的作用日益凸显.本文基于可用数据库对美国集装箱运输OD分布进行分析.以美国水陆运输理事会的公共货票数据库数据作为内陆铁路线路优化的原始输入.利用类似河流管理的方法优化集装箱运输路径.从进口集装箱的数据集看,从亚洲或者欧洲出发经由北美港口到达美国的集装箱,大部分经由太平洋海岸到达内陆市场.横渡太平洋贸易的进口集装箱枢纽港主要是洛杉矶、长滩和西雅图.横渡大西洋贸易的进口集装箱枢纽港主要是纽约、新泽西州和萨凡纳乔治亚州.太平洋海岸和密西西比河谷地区包括阿尼阿波利斯、芝加哥、堪萨斯城、孟菲斯、达拉斯和休斯顿的流量很高.从美国中西部至东部的集装箱流多经过纽约、新泽西州和诺福克最后到达芝加哥.对于集装箱运输OD分布的分析可以为高成本和多式联运相关分析提供数据基础. 相似文献