全文获取类型
收费全文 | 1319篇 |
免费 | 15篇 |
专业分类
公路运输 | 250篇 |
综合类 | 300篇 |
水路运输 | 317篇 |
铁路运输 | 147篇 |
综合运输 | 320篇 |
出版年
2023年 | 11篇 |
2022年 | 38篇 |
2021年 | 24篇 |
2020年 | 14篇 |
2019年 | 16篇 |
2018年 | 41篇 |
2017年 | 25篇 |
2016年 | 42篇 |
2015年 | 25篇 |
2014年 | 33篇 |
2013年 | 135篇 |
2012年 | 78篇 |
2011年 | 109篇 |
2010年 | 79篇 |
2009年 | 97篇 |
2008年 | 74篇 |
2007年 | 82篇 |
2006年 | 84篇 |
2005年 | 68篇 |
2004年 | 17篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 19篇 |
2000年 | 20篇 |
1999年 | 10篇 |
1998年 | 21篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 19篇 |
1994年 | 4篇 |
1993年 | 11篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 5篇 |
1972年 | 2篇 |
排序方式: 共有1334条查询结果,搜索用时 140 毫秒
321.
Dean A. JonesJulie L. Farkas Orr BernsteinChad E. Davis Adam TurkMark A. Turnquist Linda K. NozickBrian Levine Carmen G. RawlsScott D. Ostrowski William Sawaya 《Research in Transportation Economics》2011,32(1):3-14
International containerized freight movement is a vital part of the supply chain for many companies, and a critical element of moving consumer goods to points of retail sale within the U.S. Containerized imports also present a clear security concern (e.g., terrorists attempting to ship “dirty bombs,” chemical, biological or even nuclear weapons, into the U.S. in a shipping container). The goal of the research presented here is to create a modeling tool for analyzing flows of U.S. imports and exports of containerized freight, and the potential changes in those flows under a variety of conditions (e.g., port disruptions, extensive security-related delays, etc.). Our focus is on movements through maritime container ports, and not overland movements between the U.S. and Canada or Mexico.The network model, referred to as the System for Import/Export Routing and Recovery Analysis (SIERRA), represents container movements between the U.S. and 46 other countries that account for the vast majority of U.S. imports and exports. The SIERRA model is a network equilibrium model that predicts flows between foreign countries and North American ports, the total volumes handled (import and export) by each port, the modal volumes (truck and rail) moving domestically into and out of each port, and volumes between each port and a set of transportation analysis zones within the U.S. 相似文献
322.
323.
Joan L. Walker Emily EhlersIpsita Banerjee Elenna R. Dugundji 《Transportation Research Part A: Policy and Practice》2011,45(4):362-374
While psychologists and behavioral economists emphasize the importance of social influences, an outstanding issue is how to capture such influences in behavioral models used to inform urban planning and policy. In this paper we focus on operational models that do not require explicit knowledge of the individual networks of decision makers. We employ a field effect variable to capture social influences, which is calculated as the percent of population in the peer group that has chosen the specific alternative. We define the peer group based on socio-economic status and spatial proximity of residential location. As in behavioral economics and psychology, the concept is that one is influenced by the choices made by one’s peers. However, using such a social influence variable in a behavioral model causes complications because it is likely endogenous; unobserved factors that impact the peer group also influence the decision maker, yielding correlation between the field effect variable and the error. The contribution of this paper is the use of the Berry, Levinsohn, and Pakes (BLP) method to correct the endogeneity in a choice model. The two-stage BLP introduces constants for each peer group to remove the endogeneity from the choice model (where it is difficult to deal with) and insert it into a linear regression model (where endogeneity is relatively easier to deal with). We test the method using a mode choice data set from the Netherlands and readily available software and find there is an upward bias of the field effect parameter when endogeneity is not corrected. The procedure outlined presents a practical and tractable method for incorporating social influences in choice models. 相似文献
324.
层间水对水下双层结构撞击历程的影响分析 总被引:1,自引:1,他引:0
双层壳体结构是潜艇等大型水下结构的重要结构形式,潜艇结构的水下碰撞是潜艇的主要事故形式,然而,针对双层壳体的潜艇结构水下碰撞问题的研究工作目前却极为有限.文中首先提出潜艇碰撞问题,并对其碰撞特征进行分析,然后针对潜艇水下碰撞环境下,层间水对碰撞历程的影响和双层结构的碰撞特点进行了理论分析,在数值仿真计算的基础上,着重讨论了双层板结构在碰撞过程中,层间水对撞击速度、碰撞力以及双层板吸能特性的影响,分析结果显示,层间水对双层壳板撞击历程的影响主要体现在两方面:一是接触初始阶段,耐压壳板将由于层间水的存在,与非耐压壳板组成抗冲击弹簧体系参与抗冲击作用,吸收冲击能量,这对于双层壳板的防撞性能是有利的;二是非耐压壳板穿透后,层间水的影响主要体现为水对耐压壳板的粘附作用,耐压壳板的抗撞能力显著下降. 相似文献
325.
326.
327.
H.?-Z.?Li L.?LiEmail author L.?He M.?-X.?Kang J.?Song L.?-Y.?Yu C.?Wu 《International Journal of Automotive Technology》2012,13(3):441-450
A Traction Control System (TCS) is used to control the driving force of an engine to prevent excessive slip when a vehicle
starts suddenly or accelerates. The torque control strategy determines the driving performance of the vehicle under various
drive-slip conditions. This paper presents a new torque control method for various drive-slip conditions involving abrupt
changes in the road friction. This method is based on a PID plus fuzzy logic controller for driving torque regulation, which
consists of a PID controller and a fuzzy logic controller. The PID controller is the fundamental component that calculates
the elementary torque for traction control. In addition, the fuzzy logic controller is the compensating component that compensates
for the abrupt change in the road friction. The simulation results and the experimental vehicle tests have validated that
the proposed controller is effective and robust. Compared with conventional PID controllers, the driving performance under
the proposed controller is greatly improved. 相似文献
328.
Y. L. Qi L. C. Dong H. Liu P. V. Puzinauskas K. C. Midkiff 《International Journal of Automotive Technology》2012,13(6):861-872
It is well known that in-cylinder flow is very important factor for the performance of SI engine. An appropriate in-cylinder flow pattern can enhance the turbulence intensity at spark time, therefore increasing the stability of combustion, reducing emission and improving fuel economy. In this paper, the effect of intake port design on in-cylinder flow is studied. It is found a vortex existed at the upper side of intake port of a production SI engine used in the study, during the intake stroke, which will reduce both tumble ratio and volumetric efficiency. A minor modification on intake port is made to eliminate the vortex and increase tumble ratio while keeping volumetric efficiency at the same level. It is demonstrated that the increase in tumble in the new design results in a 20 per cent increase in the fuel vaporization. In this study, both KIVA and STAR-CD are used to simulate the engine cold flow, as well as ICEM CFD and es-ice used as pre-processor respectively due to the complexity of engine geometry. Simulation results from KIVA and STAR-CD are compared and analyzed. 相似文献
329.
S. M. Zhang F. Tian G. F. Ren L. Yang 《International Journal of Automotive Technology》2012,13(5):693-699
The paper presents an innovative method combining artificial neural networks (ANNs) with Fuzzy PID to demonstrate the advantages of this control approach for meeting both NOx emission requirements and NH3 slip targets. An ANN model was utilized to simulate the formation of NOx emissions under various engine operating conditions. Next, an effective closed-loop control strategy with a type of feedback known as fuzzy PID is adopted for on-line, real-time control of 32.5% aqueous urea dosing in the exhaust stream. The new strategy explores the benefits by simulation and testing in the environments of Matlab/Simulink and ESC/ETC, respectively. The notable achievement of considerable NOx reduction and an acceptably small NH3 slip is obtained based on this new, feasible and effective strategy. 相似文献
330.
双层圆柱壳典型基座振动波传递特性优化分析 总被引:1,自引:0,他引:1
采用波动分析法,根据不均质结构中的阻抗特性和波型转换,分析振动噪声在典型双层壳结构中的传递特性。以此为切入点,采用有限元/边界元(FEM/BEM)耦合法分析人为构造的传递损失基座的减振降噪性能。通过对组合板振动波的传递特性的分析可以得出,当定常结构发生突变时,结构阻抗也会随之发生变化,导致结构之间的阻抗失配,从而使得振动波在突变截面处发生反射和透射,降低振动波的传递效率,阻隔振动波能量向下游结构传递。然后,据此理论设计了传递损失基座,并用有限元/边界元耦合法验证了传递损失基座的减振降噪性能。 相似文献