全文获取类型
收费全文 | 1462篇 |
免费 | 15篇 |
专业分类
公路运输 | 264篇 |
综合类 | 323篇 |
水路运输 | 383篇 |
铁路运输 | 148篇 |
综合运输 | 359篇 |
出版年
2023年 | 11篇 |
2022年 | 39篇 |
2021年 | 34篇 |
2020年 | 16篇 |
2019年 | 18篇 |
2018年 | 44篇 |
2017年 | 24篇 |
2016年 | 64篇 |
2015年 | 39篇 |
2014年 | 34篇 |
2013年 | 133篇 |
2012年 | 93篇 |
2011年 | 119篇 |
2010年 | 81篇 |
2009年 | 99篇 |
2008年 | 77篇 |
2007年 | 82篇 |
2006年 | 84篇 |
2005年 | 92篇 |
2004年 | 44篇 |
2003年 | 13篇 |
2002年 | 11篇 |
2001年 | 18篇 |
2000年 | 21篇 |
1999年 | 10篇 |
1998年 | 20篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 19篇 |
1994年 | 5篇 |
1993年 | 11篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1973年 | 5篇 |
1972年 | 3篇 |
排序方式: 共有1477条查询结果,搜索用时 11 毫秒
961.
962.
This paper investigates a traffic volume control scheme for a dynamic traffic network model which aims to ensure that traffic volumes on specified links do not exceed preferred levels. The problem is formulated as a dynamic user equilibrium problem with side constraints (DUE-SC) in which the side constraints represent the restrictions on the traffic volumes. Travelers choose their departure times and routes to minimize their generalized travel costs, which include early/late arrival penalties. An infinite-dimensional variational inequality (VI) is formulated to model the DUE-SC. Based on this VI formulation, we establish an existence result for the DUE-SC by showing that the VI admits at least one solution. To analyze the necessary condition for the DUE-SC, we restate the VI as an equivalent optimal control problem. The Lagrange multipliers associated with the side constraints as derived from the optimality condition of the DUE-SC provide the traffic volume control scheme. The control scheme can be interpreted as additional travel delays (either tolls or access delays) imposed upon drivers for using the controlled links. This additional delay term derived from the Lagrange multiplier is compared with its counterpart in a static user equilibrium assignment model. If the side constraint is chosen as the storage capacity of a link, the additional delay can be viewed as the effort needed to prevent the link from spillback. Under this circumstance, it is found that the flow is incompressible when the link traffic volume is equal to its storage capacity. An algorithm based on Euler’s discretization scheme and nonlinear programming is proposed to solve the DUE-SC. Numerical examples are presented to illustrate the mechanism of the proposed traffic volume control scheme. 相似文献
963.
An essential element of demand modeling in the airline industry is the representation of time of day demand—the demand for a given itinerary as a function of its departure or arrival times. It is an important datum that drives successful scheduling and fleet decisions. There are two key components to this problem: the distribution of the time of day demand and how preferred travel time influences itinerary choice. This paper focuses on estimating the time of day distribution. Our objective is to estimate it in a manner that is not confounded with air travel supply; is a function of the characteristics of the traveler, the trip, and the market; and accounts for potential measurement errors in self-reported travel time preferences. We employ a stated preference dataset collected by intercepting people who were booking continental US trips via an internet booking service. Respondents reported preferred travel times as well as choices from a hypothetical set of itineraries. We parameterize the time of day distribution as a mixture of normal distributions (due to the strong peaking nature of travel time preferences) and allow the mixing function to vary by individual characteristics and trip attributes. We estimate the time of day distribution and the itinerary choice model jointly in a manner that accounts for measurement error in the self-reported travel time preferences. We find that the mixture of normal distributions fits the time of day distribution well and is behaviorally intuitive. The strongest covariates of travel time preferences are party size and time zone change. The methodology employed to treat self-reported travel time preferences as potentially having error contributes to the broader transportation time of day demand literature, which either assumes that the desired travel times are known with certainty or that they are unknown. We find that the error in self-reported travel time preferences is statistically significant and impacts the inferred time of day demand distribution. 相似文献
964.
加强对公路建设单位建设项目的效益审计具有重要意义,应从各个环节深入探讨对工程项目进行效益审计的内容和方法。 相似文献
965.
在对磁浮轨道特有的短波测量进行研究的基础上,详细描述磁浮轨道无线短波测量系统的原理、构成和软件硬件设计。该系统拥有成熟的技术思路,在提高可靠性和测量效率的前提下,可同时使用多种形式进行测量,其原理和方法也可供其他测量环境借鉴。 相似文献
966.
伴随着中国城市化进程的加快,城市交通问题日益严重,构建可持续的交通发展模式要求日益紧迫。可持续发展交通规划是全方位的,要考虑多方面因素,而建立合理的交通成本模式是其中很关键的一个环节。鉴于此,介绍当前的交通成本模式,通过分析该种模式的不足之处,提出更完善的交通成本模式,可资借鉴参考。 相似文献
967.
968.
基于三维数字化CAD/CAE应用平台,运用NX 6.0、Pro/E 5.0和Ansys 11.0软件,通过对主减速器、Torsen差速器等总成的参数化建模和虚拟装配、运动仿真,探讨了4WD概念车驱动桥的设计方法。 相似文献
969.
970.
The French-German research project Bahn.Ville, dealing with Rail oriented development and intermodality in German and French urban regions, has consisted in identifying the principles and factors of success of an urban development oriented towards rail, and in testing them in the agglomeration of Saint-Étienne. One of the research-actions focussed on identifying and anticipating the potential impacts in terms of urban development of a new transport system, of the tram-train type, on an existing railway line. The effect of the insertion of new stops on the global journey time is one of the criterion of the evaluation of new stops. A simulation method of the journey times is presented in this paper. The interest and the limits of this approach, regarding the rolling stock choice and the insertion of new stops, are emphasized. 相似文献