全文获取类型
收费全文 | 3271篇 |
免费 | 23篇 |
专业分类
公路运输 | 1116篇 |
综合类 | 184篇 |
水路运输 | 1001篇 |
铁路运输 | 130篇 |
综合运输 | 863篇 |
出版年
2023年 | 19篇 |
2022年 | 62篇 |
2021年 | 32篇 |
2020年 | 22篇 |
2019年 | 35篇 |
2018年 | 116篇 |
2017年 | 101篇 |
2016年 | 185篇 |
2015年 | 36篇 |
2014年 | 106篇 |
2013年 | 417篇 |
2012年 | 169篇 |
2011年 | 232篇 |
2010年 | 199篇 |
2009年 | 167篇 |
2008年 | 189篇 |
2007年 | 116篇 |
2006年 | 62篇 |
2005年 | 64篇 |
2004年 | 65篇 |
2003年 | 37篇 |
2002年 | 41篇 |
2001年 | 33篇 |
2000年 | 54篇 |
1999年 | 32篇 |
1998年 | 48篇 |
1997年 | 44篇 |
1996年 | 45篇 |
1995年 | 55篇 |
1994年 | 26篇 |
1993年 | 25篇 |
1992年 | 27篇 |
1991年 | 20篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 20篇 |
1987年 | 21篇 |
1986年 | 17篇 |
1985年 | 24篇 |
1984年 | 26篇 |
1983年 | 23篇 |
1982年 | 26篇 |
1981年 | 39篇 |
1980年 | 26篇 |
1979年 | 43篇 |
1978年 | 13篇 |
1977年 | 30篇 |
1976年 | 16篇 |
1975年 | 16篇 |
1974年 | 16篇 |
排序方式: 共有3294条查询结果,搜索用时 31 毫秒
971.
J. Venkatesan G. Nagarajan R. V. Seeniraj R. Murugan 《International Journal of Automotive Technology》2010,11(3):317-322
Mathematical simulation is the process of designing a model of a real system and then conducting experiments with the simulation
to understand the system’s behavior. Mathematical simulation is widely used for investigating and designing compressors, and
with a minimal number of simplifying assumptions, mathematical models can be used in conjunction with modern computing tools
to solve complicated problems. A considerable amount of previous research has focused on the mathematical modeling of reciprocating
air compressors used in automotive braking. The aim of the present work was to experimentally validate the mathematical model
for such compressors. We present a simplified and effective mathematical model for estimating compressor performance, and
this model can easily be executed using personal computers. Parameters such as compressor speed, discharge pressure and clearance
volume were evaluated in terms of their effect on the thermodynamic behavior of compressors. The model can predict cylinder
pressure, cylinder volume, cylinder temperature, valve lift and resultant torque at different crank angles; it can also predict
the free air delivered and the indicated power of the compressor. Therefore, the model has been validated using experimental
results. 相似文献
972.
T. Ciobotaru D. Frunzeti L. Jäntschi 《International Journal of Automotive Technology》2010,11(2):167-172
This paper presents a method for analyzing epicyclic gearboxes by evaluating the speeds, torques and power of the external
elements in epicyclic gear mechanisms, as well as the total ratios of the gear box. The method is based on the equations that
describe each epicyclic gear mechanism and rules that assign appropriate codes to the external elements. The method emphasizes
how power flows are transmitted through the epicyclic gears, as well as power losses. Analysis of an epicyclic gear box is
performed to illustrate the proposed method. 相似文献
973.
Considerations on Rail Corrugation 总被引:4,自引:0,他引:4
974.
Alfred J. Baird 《Maritime Policy and Management》2004,31(4):375-391
Seaports are recognized for their importance in facilitating trade growth and associated economic development. These attributes often give rise to the notion that seaports, or infrastructure elements of seaports, are public goods. Public goods are regarded as goods or services which a market acting in isolation might have difficulty in providing, or at least providing in sufficient quantity and/or at a competitive price. An important element of a public good relates to its non-rival consumption, the implication being that it is impossible to exclude anyone, whether they pay or not. Key questions this paper seeks to address are, what constitutes public goods in seaports, to what extent is it necessary for the public sector to provide these goods, and can such intervention lead to market distortion in respect of competing ports? The paper describes the more common examples of public goods in seaports. This is followed by discussion of public and private sector investment at major north European seaports. The paper considers the potential for market distortion due to public sector expenditure on so-called public goods in seaports, and proposes that a more cohesive policy for major ports, particularly those very large containerports serving a common European hinterland, is necessary in order to deliver a sustainable transport system in the long term. 相似文献
975.
Victor F. Ushkalov Michael M. Zhechev A. D. McKisic 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2007,45(1):61-76
Three-piece trucks have some drawbacks, particularly unstable operation of the friction wedge damping system. One of the principal features of systems of this kind is the possibility of jamming and wedging. This work is devoted to mathematical and numerical modeling of the plane motion of a freight car with allowance for the mobility of the wedges and then for the compliance of the contacting bodies and to the study of the conditions for the onset of jamming and wedging when the car is in motion. 相似文献
976.
M. Hatzopoulou E.J. Miller 《Transportation Research Part D: Transport and Environment》2010,15(6):315-325
This paper describes the development of an integrated approach for assessing ambient air quality and population exposure as a result of road passenger transportation in large urban areas. A microsimulation activity-based travel demand model for the Greater Toronto Area – the Travel Activity Scheduler for Household Agents – is extended with capabilities for modelling and mapping of traffic emissions and atmospheric dispersion. Hourly link-based emissions and zone-based soak emissions were estimated. In addition, hourly roadway emissions were dispersed at a high spatial resolution and the resulting ambient air concentrations were linked with individual time-activity patterns derived from the model to assess person-level daily exposure. The method results in an explicit representation of the temporal and spatial variation in emissions, ambient air quality, and population exposure. 相似文献
977.
Since Tian Jun proposed the difference expansion embedding technique, based on which, many reversible watermarking techniques
were proposed. However, these methods do not perform well when the payload is high. In this paper, we proposed an expandable
difference threshold controlled scheme for these three methods. Experiments show that our scheme improves the performance
of these three methods for heavy payload. 相似文献
978.
Joseph Sharit Sara J. Czaja Eleftherios Iakovou John Moses 《Maritime Policy and Management》2000,27(1):41-52
An important problem in the US maritime industry is the large number of oil spills that occur as a result of oil transfer operations involving tankbarges. Recently, the US Coast Guard initiated a new programme entitled Prevention Through People that represents a concerted effort towards preventing human errors leading to casualities and oil spills. The purpose of the study reported in this paper was to explore tankbarge oil transfer operations from the standpoint of regulatory, management, and operational perspectives in order to determine the likelihood that this new initiative will indeed result in a better understanding of the causal basis for human error in these operations and, more generally, in the maritime industry. The results of this novel study are discussed and summarized in terms of four broad classes of recommendations. 相似文献
979.
ABSTRACTRidesourcing services such as Uber are nowadays a common feature within available transport options of many cities around the world (E.g. London & San Francisco). There has been much publicity about the potential impacts of ridesourcing services and how (or if) they should be managed or regulated without an objective understanding of who uses these services and why, as well as its current and future implications for public transport (PT).Ridesourcing is part of a broader tech-driven, mobile app-based sharing phenomenon – the ‘sharing economy’ – which has disrupted traditional market models and industries, for example, the transport industry, where new players such as Uber have emerged and have quickly become part of the urban transport landscape. Uber has been at the forefront in disrupting the transport sector since its first launch in 2010 (San Francisco, USA). Since its launch, Uber has generated extensive media coverage and debate among policymakers, transport planners and transport authorities on how these services are affecting traditional transport modes such as buses and taxis. However, without objective empirical data – in terms of impacts on trip making characteristics, PT ridership and congestion – policymakers and transport regulators are yet to fully understand the real impacts ridesourcing services are having on the transport network.This paper is part of broader research that aims to provide insights and empirical-based evidence on how Uber services are used (UberX and Uberpool) in London. A comprehensive survey was undertaken using a detailed questionnaire, issued to UberX and Uberpool users in London to gather detailed data on who uses the Uber services, why they use it and what are the trip purposes, in order to understand Uber user demographics and what effects (if any) Uber services are having on PT usage and trip making characteristics in London. The final findings provide important insights on Uber user demographics, trip purposes, types of trips replaced, impact on car ownership and why travellers use Uber services. 相似文献
980.
川杨河桥主桥为三跨预应力混凝土连续箱梁桥,主桥箱梁采用挂篮悬臂浇筑。该文结合工程实例,介绍挂篮设计、制作和行走的方法,便于今后同类工程借鉴。 相似文献