全文获取类型
收费全文 | 1460篇 |
免费 | 15篇 |
专业分类
公路运输 | 674篇 |
综合类 | 39篇 |
水路运输 | 331篇 |
铁路运输 | 28篇 |
综合运输 | 403篇 |
出版年
2022年 | 11篇 |
2021年 | 9篇 |
2020年 | 10篇 |
2019年 | 6篇 |
2018年 | 65篇 |
2017年 | 75篇 |
2016年 | 156篇 |
2015年 | 12篇 |
2014年 | 46篇 |
2013年 | 137篇 |
2012年 | 95篇 |
2011年 | 164篇 |
2010年 | 150篇 |
2009年 | 68篇 |
2008年 | 119篇 |
2007年 | 53篇 |
2006年 | 21篇 |
2005年 | 28篇 |
2004年 | 22篇 |
2003年 | 12篇 |
2002年 | 16篇 |
2001年 | 17篇 |
2000年 | 6篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 12篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 2篇 |
1972年 | 4篇 |
排序方式: 共有1475条查询结果,搜索用时 625 毫秒
551.
H. S. Wi Y. K. Lee J. I. Park J. H. Lee K. S. Park 《International Journal of Automotive Technology》2009,10(6):771-776
This paper focuses on fuel economy improvement according to the type of power steering system. Usually, a conventional power
steering system is directly driven by the crankshaft of the engine with a belt, known as HPS (hydraulic power steering). However,
there is some inefficiency with this system at high engine speeds. To improve this inefficiency, automobile makers have developed
two power steering systems: EHPS (electro-hydraulic power steering) and MDPS (motor-driven power steering) or EPS (electric
powered steering). However, there has been insufficient study of effects of the type of power steering system on fuel economy.
In this paper, the effect of the type of power steering system on fuel economy is studied experimentally, and calculations
of the effect on vehicle fuel economy are presenting using computer simulation with AVL cruise software. The results demonstrate
that a 1% vehicle fuel economy improvement can be achieved in a vehicle with an electro-hydraulic power steering system compared
to a vehicle with a hydraulic power steering system. In addition, a 1.7% vehicle fuel economy improvement can be achieved
using a full electric power steering system in a FTP-75 driving cycle. These results could be used to choose a power steering
system. 相似文献
552.
C. L. Myung K. H. Choi I. G. Hwang K. H. Lee S. Park 《International Journal of Automotive Technology》2009,10(2):161-166
In SI engines, valve events have a major influence on volumetric efficiency, fuel economy and exhaust emissions. Moreover,
swirl and tumble motions in the intake charge also improve combustion speed and quality by stratifying the mixture as well
as intensifying the mixing rate of air and fuel. This paper investigates the behaviors of an engine and the combustion phenomenon
for various intake valve timings and intake charge motions using CVVT system and port masking schemes. Test condition includes
a part load and a cold idle condition inclusive of a cold start of the engine. Time-resolved HC and NOx emissions were also
measured at an exhaust port to examine their formation mechanisms and behaviors with fast response HC/NOx analyzers. In conclusion,
the fast burning of fuel and improved combustion quality by enhanced charge motions reduced unburned HC emissions, and advancing
the intake valve opening reduced HC as well as NOx. Furthermore, HCs during the cold transient phase and idle conditions decreased
with recalibrated start parameters such as lean air-fuel ratio and spark retardation via the enhancement of intake charge
motions. 相似文献
553.
Empirical approach for predicting the cetane number of biodiesel 总被引:2,自引:0,他引:2
P. K. Bose 《International Journal of Automotive Technology》2009,10(4):421-429
The cetane number is an indicator of ignition quality and thus of fuel quality in the realm of diesel engines. It is conceptually
similar to the octane number used for gasoline. Generally, a compound that has a high octane number tends to have a low cetane
number and vice versa. The cetane number of a diesel fuel is related to the ignition delay time. In our work the first approach
is a statistical one the accuracy of which depends upon the data obtained from various papers and literature sources, as all
equations used were based on this data. During prediction using more than one equation is a good approach, as it provides
the accuracy as well as the relative error. The second approach is also a statistical one, but its value depends upon the
saponification number and iodine value. Therefore the accuracy of this equation may be higher, since we can collect the data
for saponification numbers and iodine values from literature, without needing to calculate them. Using the saponification
number and iodine value we can select an optimal biodiesel as generally a good biodiesel is selected using these three values.
Thus the second approach allows us the freedom to select a biodiesel. 相似文献
554.
S. H. Jun T. K. Kim J. Y. Jang Y. Kidoguchi 《International Journal of Automotive Technology》2009,10(6):663-668
In an earlier study, the current authors showed that an unsteady-state lifted flame generated by an equivalence ratio conversion
system for a given fuel, was similar to a steady-state lifted flame in terms of the change characteristics from a premixed
flame to a critical flame and then to a triple flame with a diffusion flame positioned in the middle according to the concentration
difference. Therefore, this study used an OH-PLIF method to investigate the characteristics of a steady-state lifted flame
and an unsteady-state lifted flame created under conditions identical to the flames in the preceding study. PLIF (Planar laser
induced fluorescence) is practically effective for visualizing the concentration fields within a flame. The resulting OH-radical
measurements showed that an unsteady-state lifted flame created under the specific conditions used in this study showed similar
tendencies in terms of OH-radical distribution, fluorescence intensity, and liftoff height, to a steady-state lifted flame,
thereby confirming that the behavior of an unsteady-state lifted flame can be effectively predicted based on the behavior
of a steady-state lifted flame. 相似文献
555.
Y. T. Son B. Y. Kim K. J. Park H. Y. Lee H. J. Kim M. W. Suh 《International Journal of Automotive Technology》2009,10(5):635-644
To guarantee the efficiency of maintenance strategies for a complex structure, safety and cost limitations must be considered.
This research introduces RCM-based (Reliability Centered Maintenance) life cycle optimization for reasonable maintenance.
The design variable is the reliability of each part, which consists of a complex structure, while the objective is to minimize
the total cost function in order to maintain the system within the desired system reliability. This research constructs the
cost function that can reflect the current operating condition and maintenance characteristics of individual parts by generating
essential cost factors. To identify the optimal reliability of each component in a system, this paper uses a Neuro-Evolutionary
technique. Additionally, this research analyzes the reliability growth of a system by using the AMSAA (Army Material Systems
Analysis Activity) model to estimate the failure rate of each part. The MTBF (Mean Time Between Failure) and the failure rate
of the whole system, which is responding to the individual parts, are estimated based on the history data by using neural
networks. Finally, this paper presents the optimal life cycle of a complex structure by applying the optimal reliability and
the estimated MTBF to the RAMS (Reliability, Availability, Maintainability, and Safety) algorithm. 相似文献
556.
557.
The motion analysis of fire video images based on moment features and flicker frequency 总被引:2,自引:0,他引:2
In this paper, motion analysis methods based on the moment features and flicker frequency features for early fire flame from ordinary CCD video camera were proposed, and in order to describe the changing of flame and disturbance of non-flame phenomena further more, the average changing pixel number of the first-order moments of consecutive flames has been defined in the moment analysis as well. The first-order moments of all kinds of flames used in our experiments present irregularly flickering, and their average changing pixel numbers of first-order moments are greater than fire-like disturbances. For the analysis of flicker frequency of flame, which is extracted and calculated in spatial domain, and therefore it is computational simple and fast. The method of extracting flicker frequency from video images is not affected by the catalogues of combustion material and distance. In experiments, we adopted two kinds of flames, i.e. , fixed flame and movable flame. Many comparing and disturbing experiments were done and verified that the methods can be used as criteria for early fire detection. 相似文献
558.
[目的]针对无人艇协同围捕过程中逃跑目标具备智能性,现有无人艇策略难以围捕成功的问题,提出一种基于双层切换策略的多无人艇协同围捕算法。[方法]第1层围捕策略采用改进势点法,以无人艇与势点的总直线距离最小为优化目标,采用匈牙利算法为无人艇动态分配势点,并采用人工势场法实现无人艇的协同避碰;第2层围捕策略利用了阿波罗尼奥斯圆的性质,在两艘无人艇前往逃跑目标的目标点进行拦截,剩余无人艇运动方向保持与逃跑目标相同,以不断缩紧包围区域;为应对逃跑目标不同的逃跑方式,第1层围捕策略和第2层围捕策略可互相转化。[结果]仿真实验表明,该算法相较于顺序分配势点算法和极角分配势点算法,围捕时间更少或持平,证明了该算法的有效性和先进性。[结论]该多无人艇协同双层围捕算法,对具备典型智能性的逃跑目标具有围捕效果。 相似文献
559.
This paper proposes an analytical model for investigating transit technology selection problem from a perspective of transit authority. Given a transit technology alternative (e.g., metro, light rail transit, or bus rapid transit), the proposed model aims to maximize the social welfare of the transit system by determining the optimal combination of transit line length, number of stations, station location (or spacing), headway, and fare. In the proposed model, the effects of passenger demand elasticity and capacity constraint are explicitly considered. The properties of the model are examined analytically, and a heuristic solution procedure for determining the model solution is presented. By comparing the optimized social welfare for different transit technology alternatives, the optimal transit technology solution can be obtained together with critical population density. On the basis of a simple population growth rate formula, optimal investment timing of a new transit technology can be estimated. The proposed methodology is illustrated in several Chinese cities. Insightful findings are reported on the interrelation among transit technology selection, population density, transit investment cost, and transit line parameter design as well as the comparison between social welfare maximization and profit maximization regimes. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
560.
X. Ran X. Zhao J. Chen C. Yang C. Yang 《International Journal of Automotive Technology》2016,17(5):817-827
A Traction Control System (TCS) is used to avoid excessive wheel-slip via adjusting active brake pressure and engine torque when vehicle starts fiercely. The split friction and slope of the road are complicated conditions for TCS. Once operated under these conditions, the traction control performance of the vehicle might be deteriorated and the vehicle might lack drive capability or lose lateral stability, if the regulated active brake pressure and engine torque can’t match up promptly and effectively. In order to solve this problem, a novel coordinated algorithm for TCS is brought forward. Firstly, two brake controllers, including a basic controller based on the friction difference between the two drive wheels for compensating this difference and a fuzzy logic controller for assisting the engine torque controller to adjust wheel-slip, are presented for brake control together. And then two engine torque controllers, containing a basic PID controller for wheel-slip control and a fuzzy logic controller for compensating torque needed by the road slope, are built for engine torque control together. Due to the simultaneous and accurate coordination of the two regulated variables the controlled vehicle can start smoothly. The vehicle test and simulation results on various road conditions have testified that the proposed method is effective and robust. 相似文献