全文获取类型
收费全文 | 479篇 |
免费 | 5篇 |
专业分类
公路运输 | 315篇 |
综合类 | 8篇 |
水路运输 | 94篇 |
铁路运输 | 3篇 |
综合运输 | 64篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 7篇 |
2019年 | 2篇 |
2018年 | 41篇 |
2017年 | 29篇 |
2016年 | 36篇 |
2015年 | 10篇 |
2014年 | 35篇 |
2013年 | 49篇 |
2012年 | 41篇 |
2011年 | 50篇 |
2010年 | 41篇 |
2009年 | 44篇 |
2008年 | 46篇 |
2007年 | 9篇 |
2006年 | 6篇 |
2005年 | 6篇 |
2004年 | 2篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有484条查询结果,搜索用时 15 毫秒
471.
As a signatory to the Convention on Biological Diversity, Canada has committed to establishing a network of marine protected areas (MPAs) that effectively conserves at least 10% of coastal and marine areas by 2020. Research shows that the most effective MPAs are large, well enforced, no-take, and designed as part of a network. Canada's Pacific MPAs, designated site-by-site, cover approximately 3% of Canadian Pacific waters. We investigated how these MPAs could effectively contribute to Canada's national network by analyzing the implementation of management intent through the application of fisheries closures and conducting a preliminary assessment of their size and spacing relative to scientific guidelines. Fisheries closures outside of MPAs were similarly assessed. Results showed that 90% of existing MPAs were intended to exclude commercial fishing, yet only 2.5% fully or partially met this goal, therefore management intent was not achieved. Further, existing MPAs were small, 75% less than 10 km2 in size, but were reasonably spaced, from one to 50 km apart. While a suite of fisheries closures may be better suited to effectively contribute to a network than MPAs without fisheries closures, they would require permanent designations and management plans to meet network inclusion criteria. 相似文献
472.
473.
C. Hein S. Hong J. Suh H. Hoffmann N. Kim 《International Journal of Automotive Technology》2008,9(2):211-216
It is essential to develop efficient and cost-effective production methods to achieve or maintain international competitiveness.
An innovative production method, such as rotary blanking, enables manufacturers to both reduce expenses and economize production
time. However, there are not enough numerical analyses for this process. In this paper, numerical simulations of rotary blanking
were performed. After comparing the cutting planes generated by conventional and rotary blanking experimental tests, the cutting
areas of two punch geometries were analyzed. The influence of punch geometry on part quality was then investigated through
simulations. The procedure for die stress analysis was established and stress distributions of the worksheet and the tools
were analyzed. 相似文献
474.
J. Jung J. H. Lee S. Song K. M. Chun 《International Journal of Automotive Technology》2008,9(4):423-428
Understanding the mechanism of carbon oxidation is important for the successful modeling of diesel particulate filter regeneration.
Characteristics of soot oxidation were investigated with carbon black (Printex-U). A flow reactor system that could simulate
the condition of a diesel particulate filter and diesel exhaust gas was designed. Kinetic constants were derived and the reaction
mechanisms were proposed using the experimental results and a simple reaction scheme, which approximated the overall oxidation
process in TPO as well as CTO. From the experiments, the apparent activation energy for carbon oxidation with NO2-O2-H2O was determined to be 40±2 kJ/mol, with the first order of carbon in the range of 10∼90% oxidation and a temperature range
of 250∼500°C. This value was exceedingly lower than the activation energy of NO2-O2 oxidation, which was 60±3 kJ/mol. When NO2 exists with O2 and H2O, the reaction rate increases in proportion to NO2. It increases nonlinearly with O2 or H2O concentration when the other two oxidants are fixed. 相似文献
475.
When soot particles are loaded in a diesel particulate filter, it causes increase in back pressure of the exhaust system.
To minimize this pressure drop due to DPF, the filter needs to be regenerated after a certain amount of soot has been accumulated.
It is crucial to estimate the correct amount of soot that has been accumulated by measuring the differential pressure. It
is also important to understand changes in pressure drop due to flow rate variations of the exhaust gas, since the pressure
drop would be influenced by the exhaust flow rate as well as the amount of soot. Furthermore, the heat transfer characteristics
of the catalyzed diesel particulate filter (CDPF) are another major issue, as the filter is occasionally exposed to high temperature
gas. This study presents the characteristics of pressure drop according to the variation of soot loading and the mass flow
rate in CDPF. In addition, heat transfer characteristics in the filter was investigated when a high temperature gas flows
into the CDPF. Tests were performed in several CDPF samples having varying amounts of catalyst coating. Experimental results
indicate that rig-based experiments are useful in understanding the characteristics of pressure drop in the CDPF. In the cake
filtration region, a pressure drop has a proportional relationship according to soot loading and mass flow rate. It was found
that an increased catalyst coating may lead to enhanced convective heat transfer. 相似文献
476.
In the following paper, a numerical study of the atomization, vaporization and wall impingement processes of hollow-cone fuel
spray from high-pressure swirl injectors under various ambient temperature conditions was carried out. Also, the availability
of applied models and the effect of ambient temperature on spray characteristics is discussed. The Linearized Instability
Sheet Atomization (LISA) model combined with the Aerodynamically Progressed Taylor Analogy Breakup (APTAB) model, the improved
Abramzon model and the Gosman model are used to calculate the atomization, vaporization and wall impingement processes of
hollow-cone fuel spray, respectively. Spray models are implemented with the modified KIVA code. The calculation results of
the spray characteristics under two ambient temperatures, including spray tip penetration, spray structure and radial distance
after spray-wall impingement are compared to the experimental results obtained by the Laser Induced Exciplex Fluorescence
(LIEF) technique. The droplet size distribution, ambient gas velocity field, vapor phase distribution and fuel film mass generated
by spray-wall impingement, measurements which are generally difficult to obtain by experimental methods, are also calculated
and discussed. Quantitative discussions on the effect of the ambient temperature on the spray development process are conducted.
It is shown that the applied models are applicable even in the high ambient temperature condition. 相似文献
477.
S. -H. Kim E. -J. Han S. -W. Kang S. -S. Cho 《International Journal of Automotive Technology》2008,9(2):233-247
This paper investigates the brake corner system to reduce brake torque variation in the brake judder problem. A numerical
model for determining brake torque variation was constructed using the multi-body dynamics model. Using this model, the brake
torque variation for a given disc thickness variation was obtained in the time domain. The multi-body dynamics model was verified
by a dynamometer test via the comparison of brake torque variation and load distribution patterns of the pad. To reduce the
simulation time and cost required to determine factors that influence the reduction in brake torque variation, a simple mathematical
model was constructed and used to determine both the brake torque variation and influential factors. The multi-body dynamics
model and dynamometer test were modified on the basis of the results of the simple mathematical model and deformed shape of
the multi-body dynamics model. These influential factors were verified to reduce the brake torque variation. 相似文献
478.
Seung Hyun Kim 《运输规划与技术》2016,39(6):574-585
The delivery service provided by large-scale retailers continues to grow as online sales occupy an increasingly large share of the market. This study aims to tease out efficient vehicle scheduling times as well as optimal delivery routes by applying meta-heuristic algorithms. Monthly data on existing routes were obtained from a branch of Korea’s leading large-scale online retailer. The first task was to examine the status of existing routes by comparing delivery routes created using Dijkstra’s algorithm with existing delivery routes and their vehicle scheduling. The second task was to identify optimal delivery routes through a comparative analysis of the genetic algorithm and Tabu search algorithm, known for its superior applicability amongst other meta-heuristic algorithms. These findings demonstrate that the optimal vehicle routing problem not only has the potential to reduce distribution costs for operators and expedite delivery for consumers, but also the added social benefit of reduced carbon emissions. 相似文献
479.
J.-H. Yoo J.-S. Jang J. K. Kwon H.-C. Kim D.-W. Song S.-Y. Jung 《International Journal of Automotive Technology》2016,17(2):347-352
With the emergence of LED lighting, IT convergence technology using the visible spectrum of LEDs, such as Visible Light Communication (VLC), has been highlighted. Among the many VLC applications, vehicular VLCs based on LED headlamps and transportation lighting infrastructure, such as street lamps, traffic lights, etc., are considered good alternatives for Intelligent Transportation Systems (ITS) or Active Safety applications. This paper introduces a demonstration system of vehicle-to-vehicle (V2V) VLC based on LED headlamps. By applying an inverse 4-PPM modulation scheme satisfying a 75 % dimming level under the light distribution regulation of LED headlamp, the proposed system showed its capability for V2V VLC with a 10 kbps data rate for more than 30 m under day time conditions. By measuring the BER performance according to distance, outdoor V2V VLC was possible for more than 30 m even in the day time. 相似文献
480.
Taeksu Jung Yunhwa Hong Sungsu Park Cheongmin Kim Younghoon Hong Chongdu Cho 《International Journal of Automotive Technology》2018,19(2):281-289
Automotive brake noise has become a stubborn problem as automotive cars achieve higher driving torques, since that the increased torque induces the generation of severe noise dissipation during brake operation. Moreover, the global brake tuning market for achieving higher performance of the vehicle has expanded recently. The need to control the noise grows more in this connection. The tuning brake kits have employed cross-drilled and slotted machining pattern on the surface of the rotor. These designs have advantages to improve air ventilation, temperature control, and surface cleaning of brake pad. However, the effects of modal frequency by patterned rotor surfaces are rarely discussed, even if it is highly related with brake squeal phenomenon. Therefore, this study deals with the relationship between patterned surfaces and brake squeal through the numerical methods. The commercial software of a finite element analysis is employed for calculation by varying geometric design factors of each rotor pattern. As a result, the cross-drilled machining patterns are concluded to be an influential factor for in-plane mode frequency while the slotted patterns have more leverage for out-of-plane mode frequency. 相似文献