全文获取类型
收费全文 | 2494篇 |
免费 | 32篇 |
专业分类
公路运输 | 992篇 |
综合类 | 84篇 |
水路运输 | 684篇 |
铁路运输 | 48篇 |
综合运输 | 718篇 |
出版年
2023年 | 10篇 |
2022年 | 29篇 |
2021年 | 19篇 |
2020年 | 16篇 |
2019年 | 21篇 |
2018年 | 116篇 |
2017年 | 122篇 |
2016年 | 182篇 |
2015年 | 34篇 |
2014年 | 101篇 |
2013年 | 311篇 |
2012年 | 138篇 |
2011年 | 193篇 |
2010年 | 177篇 |
2009年 | 131篇 |
2008年 | 157篇 |
2007年 | 84篇 |
2006年 | 52篇 |
2005年 | 50篇 |
2004年 | 43篇 |
2003年 | 29篇 |
2002年 | 28篇 |
2001年 | 31篇 |
2000年 | 38篇 |
1999年 | 33篇 |
1998年 | 24篇 |
1997年 | 26篇 |
1996年 | 31篇 |
1995年 | 34篇 |
1994年 | 16篇 |
1993年 | 26篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 15篇 |
1987年 | 7篇 |
1986年 | 16篇 |
1985年 | 13篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 14篇 |
1978年 | 6篇 |
1976年 | 6篇 |
1975年 | 12篇 |
1974年 | 9篇 |
1973年 | 9篇 |
排序方式: 共有2526条查询结果,搜索用时 218 毫秒
991.
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
992.
Predictive control of a vehicle trajectory using a coupled vector with vehicle velocity and sideslip angle 总被引:2,自引:0,他引:2
In this paper, a predictive algorithm for vehicle trajectory control using the vehicle velocity and sideslip angle is proposed.
Since the driving state of a vehicle generates nonholonomic constraint equations, it is difficult to control the trajectory
with a conventional control algorithm. Furthermore, control vectors such as vehicle velocity and sideslip angle are coupled
together; hence, a separate control for each variable is not suitable. In this study, a coupled control vector that combines
the velocity and sideslip angle is proposed for the predictive control of vehicle trajectory. Since the coupled control vector
is derived from the status of the vehicle’s motion, it is easy to generate a feedback control vector for the predictive controller.
The coupled vector cannot be directly used as input to the vehicle systems; therefore, the vehicle input vector should be
calculated from the control vector using a nonlinear function. Since nonlinear functions are not inserted in the control loop,
they are calculated by the controller. Therefore, this method does not require a linearization process in the control logic,
which enhances the stability and accuracy of the predictive controller. 相似文献
993.
High speed tensile test of steel sheets for the stress-strain curve at the intermediate strain rate 总被引:3,自引:0,他引:3
This paper presents stress-strain curves of steel sheets for an auto-body obtained at intermediate strain rates with a servo-hydraulic
type high speed tensile testing machine. The apparatus has the maximum stroke velocity of 7.8 m/sec to obtain the tensile
material properties at a strain rate of up to 500/sec. A special jig fixture is specially designed for accurate acquisition
of tensile loads with reduction of the load-ringing phenomenon induced by unstable stress wave propagation at high strain
rates. Tensile testing of steel sheets for an auto-body was carried out to obtain stress-strain curves of mild steel and advanced
high strength steels at strain rates ranged from 1/sec to 200/sec. The test results provide interesting information regarding
the stress-strain curves at intermediate strain rates ranged from 1/sec to 200/sec and demonstrate that strain rate hardening
is strongly coupled with strain hardening. 相似文献
994.
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
995.
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
996.
Through the years, traffic engineers and researchers have developed a variety of countermeasures to enhance pedestrian safety.
Pedestrian-vehicle collisions are regarded as the most serious type of accident since they incur high fatality rates. A fundamental
concept in developing effective countermeasures is to analyze pedestrian-vehicle collisions scientifically, which can identify
the causes of accidents and accident severity. The objective of this study was to investigate the pedestrian safety benefit
of the brake assistance system (BAS) and a functional requirement associated with BAS, namely the time needed to safely detect
a pedestrian ahead. An injury severity prediction model for pedestrians was developed to systematically evaluate the BAS in
this study. Ordered multinomial logistic regression analysis was used to establish a statistical model capable of predicting
pedestrian injury severity. In addition to vehicle characteristics, collision speed and pedestrian characteristics were used
as independent predictor variables. The outcomes of this study would be useful in directing the development of safety policies
and technologies associated with pedestrian safety. 相似文献
997.
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
998.
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
999.
东风雪铁龙世嘉是一款很有个性的两厢车,而它的原型车雪铁龙C4在欧洲有着很高的人气,所以世嘉自2008年10月上市以来市场表现还算是不错。由于原型车雪铁龙C4在欧洲的碰撞试验场上表现出色,获得了五星评价,所以地它国产之后在C-NCAP试验场上的表现也寄予了厚望。 相似文献
1000.
为探究出行安全对用户出行选择行为的影响,提出了考虑事故风险成本和旅行时间的多类用户交通分配模型。针对事故发生的随机性特征,定义了路径出行安全可靠性概念,并以此计算用户的事故风险成本预算,体现出行者的安全偏好。基于考虑事故机会和事故风险的基础事故预测模型,针对路段和交叉口的不同特征,分别定义了路段和交叉口的事故风险成本分布。构建的交叉口事故风险成本模型,体现了交叉口不同转向的事故风险成本的差异性。为了求解基于安全可靠性的多类用户交通分配模型,采用路径配流法和相继平均法设计了相应的求解算法,并通过算例分析了模型和算法的有效性。研究结果表明:安全可靠性在用户出行选择中具有重要影响。当在广义出行费用中考虑事故风险成本时,出行者会更多地选择事故风险成本较小的路径;不同风险倾向的用户会有不同的选择特征,保守型出行者倾向于选择路径事故风险成本标准差相对较小的路径,即事故风险成本波动小的路径,而中立型出行者倾向于选择事故风险成本均值相对较低的路径;考虑交叉口的事故风险成本与否会直接影响流量分配结果,即路径交叉口数量和转向的差异性同样会影响出行者的选择。所提出的模型对于客流预测和网络安全评价与管理具有潜在的应用价值。 相似文献