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351.
Conventional fixed-route bus services are generally preferred to flexible-route services at high demand densities, and vice versa. This paper formulates the problem of integrating conventional and flexible services that connect a main terminal to multiple local regions over multiple time periods. The system’s vehicle size, route spacing (for conventional services), service area (for flexible services), headways and fleet sizes are jointly optimized to minimize the sum of supplier costs and user costs. The route spacing for conventional bus services and service area for flexible bus services are also optimized for each region. The proposed solution method, which uses a genetic algorithm and analytic optimization, finds good solutions quickly. Numerical examples and sensitivity analyses confirm that the single fleet variable-type bus service may outperform either the single fleet conventional bus service or the single fleet flexible bus service when demand densities vary substantially among regions and time periods. 相似文献
352.
Traffic density can be accurately measured by counting the number of vehicles within 1 km; however, it is often calculated between macroscopic traffic parameters using the fundamental equation because of difficulty of observing traffic density directly in the field. Measuring density in this way may be inaccurate and may bias the analysis because the relationship between these traffic parameters can vary across the study sites. The purpose of this study is to find a method for measuring traffic density from aerial photography that is easy and accurate, and for this purpose, we investigated whether the measuring length (i.e., the length of a section of roadway from which observations of traffic are simultaneously collected) can be shorter than 1 km and yet retain the same measured traffic density. We divided an aerial photograph into several 20‐m unit sections, counted the number of vehicles manually, and examined measured traffic density according to central limit theory. According to the results of this study, with the number of 20‐m unit sections for observing traffic density at 15 (the measuring length is 300 m), the measured traffic density was almost the same as the density of a representative section of 1 km. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
353.
Hyung Rim Choi Jae Joong Kim Jae Kee Lee Kang Bae Lee Joong Jo Shin 《Maritime Policy and Management》2018,45(3):388-402
To ensure the successful implementation of China’s Belt and Road (B&R) Initiative, it is essential to enable the real-time monitoring of containers’ locations, prevent theft during cargo delivery, ensure more efficient logistics management and reduce carbon emissions. For this, it is vital to have an economic and effective system to track and control containers across multiple countries. However, this requirement cannot be met by today’s container tracking systems because they are either limited within the borders of each country or expensive to employ internationally. This study thus presents a framework for an IoT-based container tracking system that enables users not only to grasp the international flow of container movement with one check but also to achieve smooth cross-border procedures. To verify the system’s performance, an empirical test was made for an actual container shipped from Korea to Poland. The test results showed that the system could successfully track the location of the container in real time across international borders. Last, this study discusses the policy development and international cooperation that should take place to enable the introduction of this container tracking system. 相似文献
354.
While most aggregate studies of transit ridership are conducted at either the stop or the route level, the present study focused
on factors affecting Metro ridership in the Seoul metropolitan area at the station-to-station level. The station-to-station
analysis made it possible to distinguish the effect of origin factors on Metro ridership from that of destination factors
and to cut down the errors caused by the aggregation of travel impedance-related variables. After adopting two types of direct-demand
patronage forecasting models, the multiplicative model and the Poisson regression model, the former was found to be superior
to the latter because it clearly identified the negative influences of competing modes on Metro ridership. Such results are
rarely found with aggregate level analyses. Moreover, the importance of built environment in explaining Metro demand was confirmed
by separating built environment variables for origin and destination stations and by differentiating ridership by the time
of day. For morning peak hours, the population-related variables of the origin stations played a key role in accounting for
Metro ridership, while employment-related variables prevailed in destination stations. In evening peak hours, both employment-
and population-related variables were significant in accounting for the Metro ridership at the destination station. This showed
that a significant number of people in the Seoul metropolitan area appear to take various non-home-based trips after work,
which is consistent with the results from direct household travel surveys. 相似文献
355.
Justin S. Chang Soo Yon Cho Beom Shin Lee Yonghwan Kim Suk Kang Yun 《Transportation》2012,39(1):33-54
The total economic value for a transportation service consists of use, option, and non-use value. The use benefit is based
on a traveler’s willingness to pay for usual consumption of the service. The optional value, on the other hand, is related
to the possible use of the service for trips not yet anticipated or currently accommodated by other travel modes. The non-use
value, however, is derived from the intrinsic merit of the service, even though a trip-maker never actually or potentially
depends on the mode. A closed-ended contingent valuation method is considered for the quantification of the option and non-use
values. A survey of single- and double-bounded dichotomous choices is conducted with a case study of South Korean bus operations.
A logistic regression model and a survival analysis for the single- and double-bounded approaches, respectively, are applied.
The estimation result is examined according to the statistical property required and the behavioral validity expected. In
particular, three issues from the output are discussed. First, the results help to show the preferable framework between single-
and double-bounded surveys for addressing an individual’s option and non-use values. Second, the differences in the absolute
values of option and non-use values are compared. Thirdly, the relationship between trip-makers’ willingness to pay and the
level of service of their primary travel modes are investigated. In conclusion, the summary of research and the possibilities
for future studies are given. 相似文献
356.
Hwa-Joong KimYoung-Tae Chang Kwang-Tae KimHyo-Jeong Kim 《Transportation Research Part D: Transport and Environment》2012,17(2):97-103
This paper provides an algorithm to minimize the fixed ordering, purchase, and inventory-carrying costs associated with bunker fuel together with ship time costs; and environmental costs associated with greenhouse gas emissions. It determines the optimum ship speed, bunkering ports, and amounts of bunker fuel for a given ship’s route. To solve the problem, we use an epsilon-optimal algorithm by deriving a property. The algorithm is illustrated by applying it to typical sample data obtained and the effects of bunker prices, carbon taxes, and ship time costs on the ship speed are analyzed. The results indicate that the ship speed and CO2 emissions are highly sensitive to the factors considered. 相似文献
357.
This paper studies the springing response of a flexible floating barge under an oblique wave. A time domain Rankine panel
method was used to represent fluid motion surrounding a flexible seagoing vessel, and a finite element method was used for
structural response. For accurate prediction of the structural response under an oblique wave, special attention was given
to the structural model, such as the effect of warping distortion and bending-torsion coupling. The Vlasov assumption was
followed for a deformable beam element to take into account the effect of warping distortion so that the cross section of
the beam deforms out of its original plane without changing its cross-section contour. The coupled equation for both the fluid
and structural domain was solved by using the implicit iterative method. A fixed point iteration with a relaxation scheme
was employed in this study with the aid of the Aitken δ2 process seeking acceleration of solution convergence. Accuracy of a developed computer program was verified through the comparison
with experimental work done by Remy et al. (Experimental and numerical study of the wave response of a flexible barge, Hydroelasticity in Marine Technology, Wuxi, 2006) resulting in good correspondence between the two results. 相似文献
358.
Computational predictions of ship-speed performance 总被引:1,自引:0,他引:1
Jung-Eun Choi Jung-Hun Kim Hong-Gi Lee Bong-Jun Choi Dong-Hyun Lee 《Journal of Marine Science and Technology》2009,14(3):322-333
This paper examines ship-speed performance based on acomputational method. The computations are carried out under identical
model conditions, i.e., resistance and self-propulsion tests, to predict the speed-power relationship. The self-propulsion
point is obtained from the self-propulsive computational results of two propeller rotative speeds. The speed-power relationship
in full scale is obtained through analyzing the computational results in model scale according to the model-ship performance
analysis method of ITTC’78. The object ship is a VLCC. The limiting streamlines and the distribution of the pressure coefficient
on the hull, the wake characteristics on the propeller plane, and the wave characteristics around a model ship are also investigated.
After completing the computations, a series of model tests are conducted to evaluate the accuracy of the predictions by comparing
the computational results with the experimental results. 相似文献
359.
In this paper, we present a method for estimating the natural frequencies of various engine valve springs such as constant
pitch, two-step variable pitch, three-step variable pitch, and progressive springs. Since a valve spring’s surging amplitude
is magnified when the spring’s natural frequency coincides with the frequency of the cam profile harmonic components, estimating
the natural frequency of the spring is the first step in predicting valve spring surging phenomena. A new method for calculating
the valve spring’s natural frequency is proposed in this paper that considers the end coil effect. This method predicts not
only the natural frequency of a helical spring at a fixed number of active turns, but also the change in the natural frequency
as the spring is compressed. The experimental results demonstrate that nonlinear characteristics of engine valve springs can
be predicted from the given initial pitch curves. 相似文献
360.
B. K. Han M. K. Cho C. Kim C. H. Lim J. J. Kim 《International Journal of Automotive Technology》2009,10(4):469-474
An efficient multibody dynamic model was developed to predict the vibrating transmitted gear forces of loaded and unloaded
pairs of helical gears simultaneously at all speeds. The model can also calculate the bearing forces of a manual transmission
that, in turn, may be converted to rattling noises. The bending of meshing gear teeth and torsional flexibility of transmission
shafts were considered and embodied effectively in the multibody dynamic model by calculating the tooth bending stiffness
and adding a torsion spring on a shaft section between two gears, respectively. The reactive forces on teeth and bearings
were calculated and compared using three different models that were developed for this study — an equivalent model, a rigid-body
model, and a frequency-based model. The equivalent model took only 58% computation time, compared to the frequency-based method,
even though the two showed very similar results. 相似文献