全文获取类型
收费全文 | 852篇 |
免费 | 15篇 |
专业分类
公路运输 | 392篇 |
综合类 | 27篇 |
水路运输 | 221篇 |
铁路运输 | 35篇 |
综合运输 | 192篇 |
出版年
2024年 | 2篇 |
2023年 | 21篇 |
2022年 | 46篇 |
2021年 | 11篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 68篇 |
2017年 | 18篇 |
2016年 | 44篇 |
2015年 | 16篇 |
2014年 | 68篇 |
2013年 | 85篇 |
2012年 | 48篇 |
2011年 | 58篇 |
2010年 | 59篇 |
2009年 | 52篇 |
2008年 | 53篇 |
2007年 | 31篇 |
2006年 | 16篇 |
2005年 | 16篇 |
2004年 | 8篇 |
2003年 | 9篇 |
2002年 | 9篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有867条查询结果,搜索用时 0 毫秒
471.
This paper presents an integrated design procedure for determination of structural arrangement and scantlings for the complete structure of small high-speed craft. The purpose of the procedure is to serve as a tool in the preliminary design stage where it enables generation of weight minimized designs with very limited effort. The design procedure is applied in a material concept study for a high-speed patrol craft. The various concepts include single skin and sandwich composites, aluminum and steel. It is demonstrated that the mass of the aluminum hull structure can be reduced from the original 11.7 tonnes to 9.6 tonnes through application of the presented design procedure. The most weight efficient material concept is a carbon-fiber foam-cored sandwich with a structural mass of 4.8 tonnes, which is about 50% less than the refined aluminum version. Through simple hydromechanic analysis, potential for fuel and CO2 emission reductions of 8% for the refined aluminum version and 27% for the carbon-fiber sandwich version in relation to the original craft are indicated. 相似文献
472.
近年我国煤炭贸易形势变化对航运市场的影响 总被引:1,自引:0,他引:1
为推动我国航运市场发展,分析全球金融危机后的我国煤炭市场情况,以及煤炭贸易形势发生重大变化的主要原因,并展望我国煤炭贸易形势变化对未来航运市场的影响:使全球煤炭平均海运运距增加,成为支撑未来国际煤炭价格的重要因素之一。 相似文献
473.
Quasistatic fractures at high joint angles constitute a chronic quality problem in CV joints. This type of fracture occurs
when a driver unintentionally depresses the brake and accelerator simultaneously under a full-turn retreat condition. In general,
the cage in a ball joint can be broken only at these high joint angles. Here we present a flexible quasistatic simulation
model developed to simulate fracture in a CV joint. The cause and process of the quasistatic fracture were analyzed using
simulations and physical tests. Static fracture simulations and tests at high joint angles showed that, initially, only one
of the six cage posts was damaged. In a simulation of one revolution at constant torque, we found that an imbalance in ball
loads generated an excessive cage load. Moreover, if this high cage load was applied when the cage protruded outward, the
cage post was subjected to severe shear loading. The cage post was damaged in this specific rotational range. Quasistatic
fracture simulations and tests at high joint angles showed that all six cage posts were damaged sequentially. Because entire
cage posts were damaged, the quasistatic fracture torque was approximately half of the static torque. The plastic strain in
each cage post displayed one step-like jump per revolution in the quasistatic simulations. The ball indentation created by
a high ball load was interrupted by the cage-window edges as the ball joint rotated. This hindrance by ball indentation triggered
the final breakage of the cage, although it was not the major cause of cage fractures. 相似文献
474.
J. K. Kim Y. J. Kim W. H. Yang Y. C. Park K.-H. Lee 《International Journal of Automotive Technology》2011,12(3):375-381
This study proposes a structural design method for an outer tie rod installed in a passenger car. The weight of the outer
tie rod is optimized by using the aluminum alloy Al6082M, which is developed as a steel-substitute material, and applying
structural optimization techniques. The high strength aluminum with improved mechanical properties was developed to reduce
the weight of the outer tie rod. The newly developed aluminum alloy Al6082M is applied as the material of the outer tie rod.
The static strength due to inertia force, durability and buckling performances are considered in the structural design of
the outer tie rod. At the proto design stage of a new outer tie rod, it is cost-effective to utilize FE (finite element) analysis
to predict each of these performances. In addition, the current trend in the structural design of automobile parts is to use
optimization techniques to reduce the weights of the parts. First, for an arbitrary base design, the static strength, the
life cycle and the buckling load are calculated to check whether the design satisfies its criteria. Then, the critical performance
is selected so as to include its loading condition only in the optimization process. In this study, the metamodel based optimization
process using kriging is adopted to obtain the minimum weight satisfying the critical design requirement. Then, the feasibility
of the determined optimum shape is investigated against the other performances. Finally, the optimum design of outer tie rod
is modified by considering forging efficiency. The performances of the final design are investigated through simulation and
experiment. 相似文献
475.
M. H. Lee H. M. Lee K. S. Lee S. K. Ha J. I. Bae J. H. Park H. G. Park H. J. Choi H. H. Chun 《International Journal of Automotive Technology》2011,12(5):733-744
In this paper, a hardware-in-the-loop simulation (HILS) system was developed before the development of an electric power steering
(EPS) system in a vehicle. This study was focused on the establishment of the HILS system. Driving conditions are simulated
with the HILS system. The actual steering input parameters are confirmed on the monitor while driving the HILS system. The
steering forces observed in the simulation with the developed HILS system are similar to those in real vehicle tests. The
developed HILS system can be applied in the development of various types of EPS systems. 相似文献
476.
In this study, a combined system consisting of a heat pump and a PTC heater was developed as a heating unit in electric vehicles. The system consists of a compressor, a condenser, an evaporator, an expansion device and a PTC heater. Experiments were conducted to examine the steady-state performance and dynamic characteristics of this system. The compressor speed, outdoor air inlet temperature, and indoor air inlet temperature were varied, and the performance of the system was experimentally investigated. The heating capacity, compressor power consumption and COP were obtained. Warm-up experiments were performed to investigate the dynamic characteristics of the system with a heat load of 1.5 kW in the indoor chamber. For the heat pump system, the PTC heater and the combined system, the heating performance and efficiency were investigated to determine an optimal control method. The results of this study agree well with the experimental results available in literature. This study provides experimental data of good quality for heating system design and the development of electric vehicles. 相似文献
477.
S. W. Lee Y. S. Cho W. C. Choi J. H. Lee Y. J. Park 《International Journal of Automotive Technology》2012,13(7):1149-1157
This study aims to investigate the combustion characteristics of mixed fuel of liquefied propane gas (LPG) and biodiesel under compression ignition (CI) in an effort to develop highly efficient and environmentally friendly mixed fuelbased CI engines. Although LPG fuel is known to be eco-friendly due to its low CO2 emission, LPG has not yet been widely applied for highly efficient CI engines because of its low cetane number and is usually mixed with other types of CI-friendly fuels. In this study, a number of experiments were prepared with a constant volume chamber (CVC) setup to understand the fundamental combustion characteristics of mixed fuel with LPG and biodiesel in two weight-based ratios and exhaust gas recirculation (EGR) conditions. The results from the current investigations verify the applicability of mixed fuel of LPG and biodiesel in CI engines with a carefully designed combustion control strategy that maximizes the benefits of the mixed fuel. Based on the results of this study, ignition is improved by increasing the cetane value by using higher blending ratios of biodiesel. As the blending ratios of biodiesel increased, CO and HC decreased and CO2 and NOx increases. 相似文献
478.
Ever increasing demand for the petroleum is causing faster than expected oil shortages in the supply and demand balance around
the world and furthermore, many specialists in the field of oil production such as Association for the Study of Peak Oil and
World Energy Outlook are claiming that the petroleum is around the peak of its production (Figure 1). Such shortage made the
greatest impact on the gasoline price hikes at the gas pump and thus, this impact was felt by the consumers severely and became
the greatest motivation for automotive industries to strive to pioneer the researches for the next generation vehicle configurations
ranging from HEV, PHEV, Pure EV to FCHEV (collectively noted as xEV). While the great deal of researches has been carried
over the last few decades, it is still far from mass productions for consumer use except for the HEV mainly due to the high
cost involved with other types of xEV configurations. Therefore, it is critical to design the vehicle to maximize the use
of each component at its highest point regardless of any cost scenarios and it is clear that this optimization can only be
achieved through the accurate energy balance simulation for a specific target vehicle prior to the actual hardware implementation.
In this paper, it is our intention to introduce modified dynamic battery modeling scheme that would provide a more accurate
way of simulating the battery behavior when used in the vehicle energy simulation system. Starting from a typical battery
dynamic model to predict the voltage given an imposed current request, we have introduced a new scheme to establish the relationship
between the voltage and the power (rather than the current) requested by the vehicle simulation system. The proposed scheme
handles the power request from the vehicle simulator considering the dynamic battery characteristics and in turn, contributes
to the better estimation of the current integrated energy usage and battery SOC level in the given battery dynamic system
used in the vehicle energy simulation system. 相似文献
479.
C. H. Zheng Y. I. Park W. S. Lim S. W. Cha 《International Journal of Automotive Technology》2012,13(3):517-522
The fuel economy of a fuel cell hybrid vehicle (FCHV) depends on its power management strategy because the strategy determines
the power split between the power sources. Several types of power management strategies have been developed to improve the
fuel economy of FCHVs. This paper proposes an optimal control scheme based on the Minimum Principle. This optimal control
provides the necessary optimality conditions that minimize the fuel consumption and optimize the power distribution between
the fuel cell system (FCS) and the battery during driving. In this optimal control, the final battery state of charge (SOC)
and the fuel consumption have an approximately proportional relationship. This relationship is expressed by a linear line,
and this line is defined as the optimal line in this research. The optimal lines for different vehicle masses and different
driving cycles are obtained and compared. This research presents a new method of fuel economy evaluation. The fuel economy
of other power management strategies can be evaluated based on the optimal lines. A rule-based power management strategy is
introduced, and its fuel economy is evaluated by the optimal line. 相似文献
480.
One of the most common problems related to ventilated brake discs are crack formations, particularly under high brake loads or from the associated stresses during braking. In this study, three different ventilated brake discs, the crossdrilled disc, the cross-slotted disc, and the cross-slotted with a side groove disc, were manufactured, and their braking force performances were investigated experimentally together with a solid disc. Stress analyses were subsequently performed by the finite element method. Analyses results showed that the maximum stress generations were formed on the ventilated discs in comparison to the solid disc. However, these comparisons indicate that the application of varying force distributions along brake pads reduces the stresses on ventilated discs by 8.8% to 19.1%. 相似文献