全文获取类型
收费全文 | 8077篇 |
免费 | 107篇 |
专业分类
公路运输 | 1719篇 |
综合类 | 597篇 |
水路运输 | 2587篇 |
铁路运输 | 770篇 |
综合运输 | 2511篇 |
出版年
2022年 | 114篇 |
2021年 | 58篇 |
2020年 | 49篇 |
2019年 | 86篇 |
2018年 | 202篇 |
2017年 | 116篇 |
2016年 | 148篇 |
2015年 | 90篇 |
2014年 | 246篇 |
2013年 | 1269篇 |
2012年 | 329篇 |
2011年 | 398篇 |
2010年 | 250篇 |
2009年 | 376篇 |
2008年 | 310篇 |
2007年 | 281篇 |
2006年 | 239篇 |
2005年 | 270篇 |
2004年 | 290篇 |
2003年 | 184篇 |
2002年 | 148篇 |
2001年 | 134篇 |
2000年 | 138篇 |
1999年 | 101篇 |
1998年 | 132篇 |
1997年 | 115篇 |
1996年 | 139篇 |
1995年 | 150篇 |
1994年 | 85篇 |
1993年 | 189篇 |
1992年 | 161篇 |
1991年 | 79篇 |
1990年 | 87篇 |
1989年 | 59篇 |
1988年 | 74篇 |
1987年 | 65篇 |
1986年 | 59篇 |
1985年 | 78篇 |
1984年 | 73篇 |
1983年 | 73篇 |
1982年 | 73篇 |
1981年 | 96篇 |
1980年 | 70篇 |
1979年 | 92篇 |
1978年 | 57篇 |
1977年 | 70篇 |
1976年 | 53篇 |
1975年 | 67篇 |
1974年 | 50篇 |
1973年 | 45篇 |
排序方式: 共有8184条查询结果,搜索用时 406 毫秒
911.
The background and the literature in liner fleet scheduling is reviewed and the objectives and assumptions of our approach are explained. We develop a detailed and realistic model for the estimation of the operating costs of liner ships on various routes, and present a linear programming formulation for the liner fleet deployment problem. Independent approaches for fixing both the service frequencies in the different routes and the speeds of the ships, are presented. 相似文献
912.
Rao V. Dukkipati Renguang Dong 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1999,31(2):95-111
Available experimental data of the dynamic force at a rail joint are used to validate the Discrete Support (DS) model of vehicle-track system. The validated DS model is employed to investigate the characteristics of dynamic forces due to a dipped rail joint. The results show that increasing axle load and rail equivalent mass significantly increases the first peak load. The wheel (unsprung) mass, stiffness of bearing rubber pad, and ballast stiffness mainly affect the second peak load. Properly designing a profile near the rail joint may reduce the dynamic load at the joint. The results obtained also indicate that the dynamic load generated at one wheel partially transmits to a neighboring wheel. 相似文献
913.
В.В.НОВИКОВ 《国外铁道车辆》2002,39(3):37-38
针对运用中因轨距减小而导致轮缘磨加剧的问题,设计并试验了统一型减薄轮缘厚度的修理用车轮踏面外形,试验表明,对减少轮缘磨耗,延长车轮使用寿命均有明显效果。 相似文献
914.
The first part of this paper presented the required statistics and stochastic models for reliability analysis of the fatigue fracture of welded plate joints. This present Part 2 suggests a probabilistic damage tolerance supplement to the design S–N curves for welded joints. The goal is to provide the practising engineer with simple tools that predict the reliability against fatigue fracture during service life. The impact of the chosen fatigue design factors (FDF) and the uncertainty in the applied stresses is revealed. The effect of an in-service inspection programme is also predicted. The results are presented as dimensionless matrices and suggested for use in support of decision-making at the design stage, without any advanced fracture mechanics modelling and stochastic simulation. One important advantage of this format is that the probability levels are presented regardless of actual weld class and target service life (TSL). This is obtained by introducing the FDF as a key parameter to the results. This parameter is defined as the ratio of predicted fatigue life over TSL. FDF is always calculated in the S–N approach which is mandatory in fatigue life prediction. Various welded details (classes) will have the same reliability level for the same FDF. This is true at the end of TSL and at earlier stages, i.e. fractions of TSL. The absolute value of TSL is immaterial for a given FDF. In the case of in-service inspection, the inspection interval is also given without dimensions as a fraction of TSL.
Only the influence of future scheduled inspections is treated. Updating based on actual inspection results is not included as the scope of work is inspection planning at the design stage. Results for some frequent cases occurring in practice are readily derived and presented. 相似文献
915.
New Large Aircraft (NLA) are new aircraft developments larger than any existing aircraft. The NLA's higher seat capacity will significantly impact passenger terminal design and operations. This paper focuses on the issues regarding the departure lounge. Deterministic queuing theory is used to determine the size and seating configuration of the lounge, as well as to decide whether a second level should be built to accommodate the increase in the number of passengers. The paper also discusses the use of the satellite section of a pier‐satellite terminal as a single lounge for the NLA. Spreadsheets are used to implement the analyses. 相似文献
916.
Prediction of fatigue life and estimation of its reliability on the parts of an air suspension system 总被引:1,自引:0,他引:1
K. J. Jun T. W. Park S. H. Lee S. P. Jung J. W. Yoon 《International Journal of Automotive Technology》2008,9(6):741-747
Air suspension systems have been implemented in various commercial vehicles, such as buses and special purpose trucks, because
of the comfortable ride and easy height control. An evaluation of the durability of vehicle parts has been required for service
life and safety starting in the early stages of design. The cyclic load applied to the vehicle can cause fatigue failure of
parts, such as the suspension frame. This paper presents a method to predict the fatigue life of the suspension frame at the
design stage of the air suspension system used in a heavy-duty vehicle. To estimate the fatigue life using the SN method,
the Dynamic Stress Time History (DSTH) is necessary for the part of interest. DSTH can be obtained from the results of the
flexible body dynamic analysis using the Belgian road simulation and the Modal Stress Recovery (MSR) method. Furthermore,
the reliability of the predicted fatigue life can be evaluated by considering the variations in material properties. The probability
and distribution of the expected life cycle can be obtained using experimental design with a minimum number of simulations.
The advantage of using statistical methods to evaluate the life cycle is the ability to predict replacement time and the probability
of failure of mass-produced parts. This paper proposes a rapid and simple method that can be effectively applied to the design
of vehicle parts. 相似文献
917.
The characteristics of auto-ignition and micro-explosion behaviors of one-dimensional arrays of fuel droplets suspended in
a chamber with high surrounding temperature were investigated experimentally with various droplet spacings, numbers of droplet
and surrounding temperatures. The fuels used were pure n-decane and emulsified n-decane with varied water contents ranging
from 10 to 30%. All experiments were performed under atmospheric conditions with high surrounding temperatures. An imaging
technique using a high-speed camera was adopted to measure ignition delay, flame lifetime, and flame spread speed. The camera
was also used to observe micro-explosion behaviors. As the droplet array spacing increased, the ignition delay also increased,
regardless of water content. However, the lifetime of the droplet array decreased as the droplet spacing increased. The micro-explosion
starting time remained unchanged regardless of the number of the droplets or the droplet spacing; however, it tended to be
delayed slightly as the water percentage and droplet spacing increased. 相似文献
918.
Low viscosity engine oil can improve a vehicle’s fuel economy by decreasing the friction between the engine components. Frictional
torque varies with the velocity change due to different viscosity characteristics of SAE grade 5W-20, 5W-30 and 5W-40 engine
oils. The viscosity for each of these grades was measured to outline the effect low viscosity engine oils have on engine friction,
which may lead to improved fuel economy. Engine oil seal frictional torque increases with the shaft rotational speed for all
three engine oil grades. A decrease in engine oil seal frictional torque was confirmed when low viscosity engine oil was used.
Also, the leak-free performance of the engine oil with the seal satisfied the life limit durability test criteria. Thus, low
viscosity engine oil may be used to improve fuel economy by decreasing the frictional loss of the engine oil seal while having
no negative impact on performance due to leak-free functioning. 相似文献
919.
The recursive component mode synthesis method (RCMS) has been implemented for the finite element analysis model of an automobile
structure as an efficient free vibration analysis tool. The RCMS method is intended to obtain a better performance relative
to the block Lanczos method, which is a traditional method in the industry of obtaining eigenvalues, while obtaining the acceptable
accuracy. A numerical example of the automobile finite element model demonstrates the outstanding performance of RCMS compared
to the block Lanczos method. 相似文献
920.
Intelligent transportation systems have been promoted as a means to improve both the efficiency and safety of the road network. The effectiveness of advanced technologies in improving road safety has been an area of research which has thus far yielded mixed results. In order to ensure that advanced technologies deliver on their intended outcomes, more research has to be devoted to understanding road users' perceptions and reactions to these systems. This study examines drivers' perceptions of the use of dynamic message signs and their self‐reported reactions to the messages displayed. In general, drivers support the use of highway electronic boards for traffic incident reports and weather information which have an impact on traffic delays and level of service. They also think that it is a good idea to display road safety messages and to remind drivers to drive safely and be courteous on the roads. Moreover, most drivers reported that they do read and think about the messages displayed and react positively to some of the road safety messages. 相似文献