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391.
The goal of this study is to develop a robust methodology for computing zone centrality measures in an urban area. Centrality refers to the relative importance of a zone in terms of network efficiency and utility for both transportation and urban study. Centrality indices that were developed to describe human relationships in the field of structural sociology were adopted. It is important to accommodate the neighborhood effect in dealing with centrality. The neighborhood effect describes the phenomenon whereby the attractiveness of a specific zone is affected by its neighbor zones. Kernel functions were employed to accommodate the neighborhood effect. The optimal bandwidth parameters were derived indirectly within the framework of trip attraction estimation under the assumption that the trip attraction of a zone is influenced by the integrated centrality, which includes the neighborhood effect. The well-known estimation tool of maximum likelihood estimation (MLE) was adopted to find the optimal bandwidth. As a byproduct of accommodating the neighborhood effect in centralities, a considerable advantage of the present study is an enhancement of the performance of trip attraction model. Another meaningful contribution of this study is a solution to the question of an acceptable delineation of the two city centers in Seoul. The boundaries of the two city centers were derived based on both the kernel function and its bandwidth. 相似文献
392.
Valuable mineral resources are widely distributed throughout the seabed. autonomous underwater vehicles (AUVs) are preferable
to remotely-operated vehicles (ROVs) when probing for such mineral resources as the extensive exploration area makes it difficult
to maintain contact with operators. AUVs depend on batteries, so their power consumption should be reduced to extend exploration
time. Power for conventional marine instrument systems is incorporated in their waterproof sealing. External intermittent
control of this power source until termination of exploration is challenging due to limitations imposed by the underwater
environment. Thus, the AUV must have a power control system that can improve performance and maximize use of battery capacity.
The authors developed such a power control system with a three-step algorithm. It automatically detects underwater operational
states and can limit power, effectively decreasing power consumption by about 15%. 相似文献
393.
Yoo-Chul Kim Tae-Wan Kim Sangwoo Pyo Jung-Chun Suh 《Journal of Marine Science and Technology》2009,14(2):161-170
We refine the geometry of a propeller by modifying the blade sections to align them with surface streamlines, obtained by
the panel method. Redefinition of the blade sections aligned with the streamlines is provided together with surface modeling
scheme by which model propellers were built. Numerical simulations and open-water tests on models suggest a possible increase
of 1% in propeller efficiency. 相似文献
394.
Spatial and temporal variability in the pelagic ecosystem of the East Sea (Sea of Japan): A review 总被引:1,自引:0,他引:1
Jae-Young Lee Dong-Jin Kang Il-Nam Kim Taekeun Rho Tongsup Lee Chang-Keun Kang Kyung-Ryul Kim 《Journal of Marine Systems》2009,78(2):288
The East Sea (Sea of Japan) is a unique marginal sea because it exhibits features of oceanic dynamics of much larger ocean basins. This semi-enclosed basin may be considered as a model or microcosm for understanding of how biological processes and distributions in pelagic ecosystem are interacting with physical processes in highly dynamic ocean regions. This overview summarizes the recent progresses concerning spatial and temporal variability of pelagic ecosystem components form an interdisciplinary point of view. Spatial characteristics of physical environments and biogeography in the region are distinguished mainly by the subpolar front. It was also found that long-term changes in biomass and community structure as well as those in the physical and biological environments are associated with climate variability in the region. We conclude by identifying main needs for the information and researches, particularly regular and long-term sampling, and permanent monitoring if possible. 相似文献
395.
Identifying accurate origin-destination (O-D) travel demand is one of the most important and challenging tasks in the transportation planning field. Recently, a wide range of traffic data has been made available. This paper proposes an O-D estimation model using multiple field data. This study takes advantage of emerging technologies – car navigation systems, highway toll collecting systems and link traffic counts – to determine O-D demand. The proposed method is unique since these multiple data are combined to improve the accuracy of O-D estimation for an entire network. We tested our model on a sample network and found great potential for using multiple data as a means of O-D estimation. The errors of a single input data source do not critically affect the model’s overall accuracy, meaning that combining multiple data provides resilience to these errors. It is suggested that the model is a feasible means for more reliable O-D estimation. 相似文献
396.
Su-Han Woo Sun-Nam Kim Stephen Pettit Anthony Beresford 《Maritime Policy and Management》2018,45(1):19-33
Global offshoring has increased the need for transport of half-finished goods and components, along with finished goods. The auto-parts industry in Korea has also entered the global market as Korean car manufacturers have started to build overseas factories. Maintaining cost competitiveness by minimising total logistics costs will thus be a critical strategy for the industry. This research compares the total annual costs of four feasible transport routes from Korea to the US using the inventory-theoretic model, which encompasses direct transport costs, in-transit carrying costs, and warehouse inventory costs. We apply this model to real transport data collected from a Korean auto-parts company. A static analysis shows that inventory costs can play a decisive role in altering the cost competitiveness of different routes. In addition, sensitivity and scenario analyses with changes in variables and the market situations reveal that the cost structure of each route plays an important role in determining their relative cost competitiveness in varying market conditions. 相似文献
397.
The adequate provision of charging infrastructure is critical for the effective deployment of electric taxis. This study attempts to locate charging stations for electric taxis reflecting real-world taxi travel patterns identified from taxis equipped with digital tachographs. Data for one week are processed in order to estimate their charge demand. The estimated temporal distribution of charge demand indicates that it varies day-by-day and hour-by-hour. The maximum set covering model is applied for determining the locations of charging stations. The results show that the pre-specified service distance and service coverage rate (defined by the proportion of total demand served) can be critical factors for determining the number and location of charging stations. These factors should be carefully specified by considering the tradeoff between operational efficiency of charging facilities and user convenience. 相似文献
398.
Beom-Seon Jang Hisashi Ito Kyung-Su Kim Yong-Suk Suh Hyun-Tae Jeon Young-Soo Ha 《Journal of Marine Science and Technology》2010,15(2):176-189
Predicting fatigue crack growth after its detection during in-service inspection is necessary to prevent a loss of serviceability,
such as the oil and/or water tightness of critical compartments. This paper focuses on the most typical fatigue cracks that
start at the weld joint between a flat bar stiffener on a transverse web frame and the flange of a longitudinal stiffener
on a bottom plate or inner bottom plate. An experiment is carried out to observe the fatigue crack propagation for two kinds
of flat bars at the abovementioned connection. The experimental results, especially the surface crack growth on the flange
(which dominates during the total fatigue life of the longitudinal stiffener), are compared with crack growth curves predicted
using a few existing formulas. Based on the comparative study, a formula that shows the best agreement with the experiment
results is selected. Weld toe magnification factors for the web stiffener are computed from the crack propagation rates measured
in the experiment, and two equations for the magnification factors versus crack depth are developed for two types of web stiffeners.
The selected existing formula and the proposed equations are applied to two connections at the inner bottom and side longitudinal
bulkhead of an LNG carrier. The equivalent stress approach based on a long-term distribution is employed to avoid the complexity
involved in dealing with the actual stress history. Using this prediction, the remaining service life until an oil or water
leakage occurs at a tank boundary can be estimated when a fatigue crack at the connection is detected. 相似文献
399.
Wu-Joan Kim Jaehoon Yoo Zhengshou Chen Shin Hyung Rhee Hye-Ryoun Chi Haeseong Ahn 《Journal of Marine Science and Technology》2010,15(3):230-241
The results of the design analysis for a sailing yacht’s hull and sails are reported. The results were used to confirm the
design of a 30 ft long sloop, which was planned, designed, and built in Korea for the first time in history. Flows around
a sailing yacht above and under the free surface were analyzed separately using both computational and experimental methods.
For the underwater flow analysis, turbulent flow simulations with and without free surface wave effects were carried out for
the canoe hull with keel/rudder. The computed drag and side forces on the hull model were compared with the measurement data
obtained from the towing tank experiments. In order to assess the sail performance, another set of computations was carried
out for the flow around a sail system composed of main and jib sails with a mast. The present study demonstrates that, for
the design analysis of a sailing yacht, computational fluid dynamics techniques can be utilized with a reasonable level of
confidence. 相似文献
400.
S.-J. Lee M.-S. Jang Y.-G. Kim G.-T. Park 《International Journal of Automotive Technology》2011,12(3):425-432
Occupant classification in a passenger seat is one of the critical components for any advanced airbag system. Many automotive
electronic suppliers and engineers predict that the camera will be the next generation sensor for active and passive safety
systems because it has several advantages compared to other sensors. The present paper describes a stereovision-based occupant
classification system (OCS) and intelligent algorithm with embedded system by which triggering of the airbag deployment can
be controlled. The system consists of a pair of stereo cameras and dual Digital Signal Processor (DSP): the first DSP is for
the stereo matching processing, and the second is for occupant classification. The results show that the reaches 97%, and
the processing time is 960 ms. Such performance indicates that the feasibility of the system as an embedded OCS is high. 相似文献