全文获取类型
收费全文 | 2229篇 |
免费 | 75篇 |
专业分类
公路运输 | 564篇 |
综合类 | 493篇 |
水路运输 | 711篇 |
铁路运输 | 294篇 |
综合运输 | 242篇 |
出版年
2023年 | 6篇 |
2022年 | 62篇 |
2021年 | 66篇 |
2020年 | 57篇 |
2019年 | 29篇 |
2018年 | 27篇 |
2017年 | 37篇 |
2016年 | 51篇 |
2015年 | 53篇 |
2014年 | 86篇 |
2013年 | 188篇 |
2012年 | 121篇 |
2011年 | 146篇 |
2010年 | 158篇 |
2009年 | 149篇 |
2008年 | 147篇 |
2007年 | 170篇 |
2006年 | 169篇 |
2005年 | 107篇 |
2004年 | 51篇 |
2003年 | 31篇 |
2002年 | 37篇 |
2001年 | 44篇 |
2000年 | 26篇 |
1999年 | 24篇 |
1998年 | 26篇 |
1997年 | 27篇 |
1996年 | 20篇 |
1995年 | 27篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 13篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 11篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1972年 | 4篇 |
排序方式: 共有2304条查询结果,搜索用时 656 毫秒
811.
J. E. Davies 《Maritime Policy and Management》2013,40(3):249-261
The simulations performed show that demand for quality tankers has to increase by 30% for a two-tier tanker market to emerge. The two-tier freight structure will only last for 3–5 years due to contracting induced by higher freight rates. This means that OPA does not by itself result in higher freight rates for tankers that comply with the requirements. If Western Europe also closes their trades to substandard tankers, a two-tier market emerges and quality tankers obtain a premium. The paper presents a simulation model for international tanker markets. The non-linear complementary equilibrium model solves for a sequence of static equilibria in segmented tanker freight markets, shipbuilding and scrapping markets. Freight markets are segmented according to quality requirements for tankers. The model specifies three tanker classes and one—quality tankers—can operate both market segments. 相似文献
812.
首先建立波浪超定量概率模型,提出超定量抽样分组原则以保证数据独立性,通过检验可知该原则下波浪超定量系列能较好地拟合GP分布;提出根据年平均出现频次、是否服从Possion分布和拟合GP情况综合分析判断,寻找合理阈值的方法;分别用GP分布和相应的复合极值分布分析超定量系列,并比较传统的P-III分布,分析可知,采用GP分布和P-GP(Poisson-GP)复合分布计算超定量系列所得的重现期值基本一致,且P-III曲线所得结果接近。 相似文献
813.
Abstract This paper investigates pedestrians' traffic gap acceptance for mid-block street crossing in urban areas. A field survey was carried out at an uncontrolled mid-block location in Athens, Greece. Pedestrians' decisions and traffic conditions were videotaped in terms of the size of traffic gaps rejected or accepted, waiting times and crossing attempts and vehicle speeds. A lognormal regression model was developed to examine pedestrian gap acceptance. It was found that gap acceptance was better explained by the distance from the incoming vehicle, rather than its speed. Other significant effects included illegal parking, presence of other pedestrians and incoming vehicles’ size. A binary logistic regression model was developed to examine the effect of traffic gaps and other parameters on pedestrians' decisions to cross the street or not. The results reveal that this decision is affected by the distance from the incoming vehicles and the waiting times of pedestrians. 相似文献
814.
Abstract The Internet service attributes desired by shippers were examined as well as a model that seeks to explain the intention of shippers to use Internet services in liner shipping. Using data collected from a survey of a group of shippers in Taiwan, the relationships among the constructs in the model were tested, namely: perceived usefulness, perceived ease of use, security and use intention. The results suggest that shippers perceive tracing to be the most important service attribute of Internet services, followed by checking for customs clearance, vessel schedules and electronic document services. The findings indicate that perceived ease of use is the major factor affecting the intention of shippers to use Internet services, and that perceived ease of use has a strong positive effect on perceived usefulness. The results also indicate that security has a positive effect on a shipper’s perception of ease of use. However, the influence of security on use intention and perceived usefulness was not supported in this study. The theoretical and practical implications of the findings on the intention of shippers to use Internet services in liner shipping are discussed. 相似文献
815.
AbstractIn transportation, informal transport refers mainly to the use of paratransit services in the developing world. In this paper we argue that informal travel may include, in addition to mode and users, also other travel pattern elements, such as trip planning, structure, purpose, and destination. Each of these can be placed along an axis ranging from formal manifestations to informal ones, thus creating a ‘formality scale’. Moreover, these elements may be combined in numerous ways, creating a multitude of travel patterns that may be placed all along the formality scale. After providing a definition of formal, semi-formal, and informal travel and characterizing travel patterns according to the formality scale we identify population groups which exemplify semi-formal and informal travel patterns. Next, we analyze the 2009 US National Household Travel Survey, which suggests informal travel may be growing. This leads to a discussion on various factors that might affect travel formality. Most notably, the growing use of information and communication technologies may be shifting travel toward the informal end of the axis. In turn, this might affect trip symmetry, which may result in further effects on the transportation system. 相似文献
816.
利用Creo软件建立了某型动车组头中尾3车编组和不同高度的路堤模型,通过Fluent软件模拟列车在车速分别为300和350 km·h-1,横风风速分别为17.10、20.70、24.40和28.40 m·s-1的环境下运行,将获取的高速列车气动力载荷施加到Simpack建立的动力学模型中,计算其动力学性能参数;深入分析了横风工况下高速列车在不同高度复线路堤背风侧运行时车体的压力分布、气流场结构、气动力与风致安全性,并重点探究了头车在不同运行速度和横风风速下的运行安全性。分析结果表明:在相同车速和横风环境下,随着路堤高度的增加,列车受到的侧向力整体呈增大趋势,尾车在横风作用下受到反向侧向力,头车所受侧向力最大,且升力持续增大,中间车所受升力相对较大,尾车所受阻力最大;横风环境下列车压力峰值点位于头车鼻尖处且向迎风侧偏移,各路堤高度工况下气流场结构基本相同,头车背风侧和底部转向架处有明显的涡流,但尾车处的涡流却在迎风侧,这可能是导致尾车反向侧向力的主因;脱轨系数、轮轴横向力、轮轨垂向力和轮重减载率均随路堤高度和横风风速的增大而增大,轮轨垂向力始终在安全限值内,当横风风速分别为24.40和28.40 m·s-1时,列车运行速度应分别低于350和300 km·h-1,以保证列车行车安全。 相似文献
817.
818.
819.
A method is presented to calculate the resistance of a high-speed displacement ship taking the effect of sinkage and trim and viscosity of fluid into account. A free surface flow field is evaluated by solving Reynolds averaged Navier-Stokes (RANS) equations with volume of fluid (VoF) method. The sinkage and trim are computed by equating the vertical force and pitching moment to the hydrostatic restoring force and moment. The software Fluent, Maxsurf and MATLAB are used to implement this method. With dynamic mesh being used, the position of a ship is updated by the motion of ??ship plus boundary layer?? grid zone. The hull factors are introduced for fast calculating the running attitude of a ship. The method has been applied to the ship model INSEAN2340 for different Froude numbers and is found to be efficient for evaluating the flow field, resistance, sinkage and trim. 相似文献
820.
姚胜华 《湖北汽车工业学院学报》2012,(3):13-15,24
讨论AVL Designer软件在发动机曲轴扭振计算过程中需要注意的3个关键问题:载荷数据、曲轴刚度数据和扭振结果分析。缸压传感器测量获取的载荷数据比Boost软件计算更加精确。曲轴刚度数据由试验、有限元计算或AVL Autoshaft计算获取。扭振结果分析包括临界转速、节点位置等。 相似文献