全文获取类型
收费全文 | 811篇 |
免费 | 3篇 |
专业分类
公路运输 | 240篇 |
综合类 | 30篇 |
水路运输 | 281篇 |
铁路运输 | 26篇 |
综合运输 | 237篇 |
出版年
2022年 | 12篇 |
2021年 | 4篇 |
2020年 | 6篇 |
2019年 | 14篇 |
2018年 | 20篇 |
2017年 | 13篇 |
2016年 | 28篇 |
2015年 | 10篇 |
2014年 | 27篇 |
2013年 | 144篇 |
2012年 | 31篇 |
2011年 | 40篇 |
2010年 | 41篇 |
2009年 | 38篇 |
2008年 | 29篇 |
2007年 | 21篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 13篇 |
2003年 | 8篇 |
2002年 | 18篇 |
2001年 | 10篇 |
2000年 | 13篇 |
1999年 | 8篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 17篇 |
1995年 | 11篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 16篇 |
1980年 | 8篇 |
1979年 | 17篇 |
1978年 | 6篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1973年 | 10篇 |
排序方式: 共有814条查询结果,搜索用时 15 毫秒
41.
Steven A. Velinsky Robert A. White 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1980,9(6):359-384
Road roughness and surface texture are known to affect tire rolling resistance; however, little emphasis has been placed on the consequent changes in total vehicle energy dissipation due to road roughness. Thus, tire rolling resistance, in isolation from vehicle contributed losses such as dissipation in the suspension, appears to be a weakness in present evaluation procedures as they relate to fuel economy and pollution level testing: Recent work by Funfsinn and Korst has shown that substantial and measurable increases in energy losses occur for vehicles traveling on rough roads. The present investigation uses vehicle axle accelerations as a means of examining various road surfaces. Correlation with computer simulations has allowed the development of a deterministic road roughness model which permits the prediction of energy dissipation in both the tire and suspension as functions of road roughness, tire pressure, and vehicle speed. Comparison to the experiments of Korst and Funfsinn results in good agreement and shows that total rolling loss increases of up to 20 percent compared to ideal smooth roads are possible. The aerodynamic drag coefficient is also found to increase while driving on rough roads. 相似文献
42.
B. J. Thomas 《Maritime Policy and Management》1981,8(3):179-190
The absence of formal career-development programmes and the apparent low priority given to the development of human resources in the ports of developing countries has led to a severe shortage of suitably qualified and experienced managers. At the centre of this problem lies the formidable barriers to the establishment of a local training capability to meet the diverse and often specialized needs of this industry. This paper examines the nature and scale of the management-training requirements of the ports of developing countries. Further, it briefly describes the background to UNCTAD's role in the field of management training and outlines the objectives of its training strategy for the 1980s. An important component of this strategy is the 'Improving port performance project which is designed to prepare structured learning materials using audio-visual techniques and is proposed as one solution to establishing a local training capability in developing countries. 相似文献
43.
Hans B. Pacejka 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1981,10(4):221-251
During the last decade research has been conducted on the dvnamics of the tvre considered as a vehiclecomponent. Asurvey is given of these developments where tyre mass plays an important role. The underlying theoretical considerations concerning the massless tyre have been discussed as well. Two groups of tyre response have been distinguished: the lateral (out-of-plane) response and the vertical/longitudinal (in-plane) response to motions of the wheel. In both categories tyre compliance, slip and inertia have influence. The dynamic properties of the rolling tyre have been presented in the form of transfer functions and/or differential equations. The frequency of the imposed oscillations is assumed to be below ca. 40 Hz. Non-linear effects and modelling have been briefly touched on. 相似文献
44.
Warren B. Powell 《Transportation Research Part B: Methodological》1983,17(3):221-232
The usual approach to studying bulk service queues is to assume that successive headways are independent. This assumption is frequently violated in systems where vehicles depart according to a fixed schedule, but where deviations from the schedule may occur. A late departure implies there is one long headway followed by a shorter one. This problem is solved exactly using both classical transform techniques and iterative numerical methods. Experiments with the latter approach are presented, and comparisons between the exact results and those obtained by ignoring correlations between headways are performed. The results suggest that upper and lower bounds may be developed using existing results, where the upper bound is accurate in light traffic while the lower bound is accurate in heavy traffic. 相似文献
45.
46.
47.
Giselle P. B. Samonte-Tan Alan T. White Mary Ann Tercero John Diviva Esperanza Tabara Ciemon Caballes 《Coastal management》2013,41(2-3):319-338
This article provides results on the net benefits generated from the natural resources in the Bohol Marine Triangle (BMT) in the Philippines. The BMT spans over 112,000 ha and its coastal ecosystems are rich in biodiversity and provide economic opportunities to the coastal communities. With a 10% discount rate, the accumulated total net benefits for the BMT resources over a 10-year period is US$11.54 million. Tourism and the municipal fisheries are the most important direct use values of the coastal and marine resources of the BMT accounting for 44% and 39% of the total net benefits. Annual revenues attributed to ecosystems were as follows: coral reefs, US$1.26 million; beach/intertidal area, US$1.12 million; marine waters, US$646,501; mangrove, US$239,561; and seagrass, US$105,990. The large market values indicate the dependence of the local community on the BMT coastal and marine resources. In the same way, non-market values show the important life-support functions of coastal and marine ecosystems. The net benefits reflect the magnitude of potential losses due to improper management of coastal and marine resources in the BMT. This valuation highlights the importance of the coastal services to the BMT economy and draws attention to the benefits the local stakeholders derive from BMT coastal resources. Policy measures can now take into account these values to justify a sufficient investment in coastal management efforts to sustain the flow of coastal services in the interest of current and future generations. 相似文献
48.
B. N. Metaxas 《Maritime Policy and Management》2013,40(3):162-177
The purpose of this article is to formulate the problem, to assess its magnitude, and at the same time to suggest the areas that must be investigated before any practical policy recommendations can be made. 相似文献
49.
The potential benefits of general aviation management at a major airport is examined in this paper. The three general aviation management techniques investigated are volume reduction, runway segregation and time restriction. First, a methodology for analyzing these techniques is discussed. The various effects on each user group are quantified for economic comparison between each management technique attempted. A computer simulation model was used to measure the delay effects. Then, these techniques are applied to Denver Stapleton Airport to measure their effects in present and future scenarios. The results show that the best general aviation management technique is volume restriction. The use of peak‐hour pricing mechanism provided better results than random rejection, particularly if only a small degree of diversion is desired. The construction of a new general aviation runway provided equivalent results to the best technique tested. 相似文献
50.
D. B. Sonawane K. Narayan V. S. Rao S. C. Subramanian 《International Journal of Automotive Technology》2011,12(5):697-704
Most commercial vehicles such as buses and trucks use an air brake system, often equipped with an S-cam drum brake, to reduce
their speed and/or to stop. With a drum brake system, the clearance between the brake shoe/pad and the brake drum may increase
because of various reasons such as wearing of the brake shoe and/or brake drum and drum expansion caused by high heat generation
during the braking process. Hence, to ensure proper functioning of the brake system, it is essential that the clearance between
the brake shoe and the brake drum is monitored. In this paper, we present a mathematical model for the mechanical subsystem
of the air brake system that can be used to monitor this clearance. This mathematical model correlates the push rod stroke
transients and the brake chamber pressure transients. A kinematic analysis and a dynamic analysis of the mechanical subsystem
of the air brake system were performed, and the results are corroborated with experimental data. 相似文献