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931.
URANS analysis of a broaching event in irregular quartering seas 总被引:1,自引:0,他引:1
Pablo M. Carrica Kwang-Jun Paik Hamid S. Hosseini Frederick Stern 《Journal of Marine Science and Technology》2008,13(4):395-407
Ship motions in a high sea state can have adverse effects on controllability, cause loss of stability, and ultimately compromise
the survivability of the ship. In a broaching event, the ship losses control, naturally turning broadside to the waves, causing
a dangerous situation and possibly capsizing. Classical approaches to study broaching rely on costly experimental programs
and/or time-domain potential or system-based simulation codes. In this paper the ability of Reynolds averaged Navier–Stokes
(RANS) to simulate a broaching event in irregular waves is demonstrated, and the extensive information available is used to
analyze the broaching process. The demonstration nature of this paper is stressed, as opposed to a validated study. Unsteady
RANS (URANS) provides a model based on first principles to capture phenomena such as coupling between sway, yaw, and roll,
roll damping, effects of complex waves on righting arm, rudders partially out of the water, etc. The computational fluid dynamics
(CFD) method uses a single-phase level-set approach to model the free surface, and dynamic overset grids to resolve large-amplitude
motions. Before evaluating irregular seas two regular wave cases are demonstrated, one causing broaching and one causing stable
surf riding. A sea state 8 is imposed following an irregular Bretschneider spectrum, and an autopilot was implemented to control
heading and speed with two different gains for the heading controller. It is concluded that the autopilot causes the ship
to be in an adverse dynamic condition at the beginning of the broaching process, and thus is partially responsible for the
occurrence of the broaching event. 相似文献
932.
There are many filtering methods that can be used for the initial alignment of an integrated inertial navigation system. This paper discussed the use of GPS, but focused on two kinds of filters for the initial alignment of an integrated strapdown inertial navigation system (SINS). One method is based on the Kalman filter (KF), and the other is based on the robust filter. Simulation results showed that the filter provides a quick transient response and a little more accurate estimate than KF, given substantial process noise or unknown noise statistics. So the robust filter is an effective and useful method for initial alignment of SINS. This research should make the use of SINS more popular, and is also a step for further research. 相似文献
933.
Nie Wu 《船舶与海洋工程学报》2002,1(2):1-5
The appropriate prediction of the hull deflection of a severely damaged warship is an important area in the research of the warship survivability. In this paper, the asymmetrical beam bending theory is applied to set up the damaged model, a comparison of the longitudinal strength, the deflections of damaged hull subjected to both hagging and sagging moments, and shear forces is carried out. The external loads are also calculated according to different damaged positions. Finally, some results and conclusions are obtained. 相似文献
934.
Efficient estimation of extreme non-linear roll motions using the first-order reliability method (FORM) 总被引:1,自引:0,他引:1
Jørgen Juncher Jensen 《Journal of Marine Science and Technology》2007,12(4):191-202
In on-board decision support systems, efficient procedures are needed for real-time estimation of the maximum ship responses
to be expected within the next few hours, given online information on the sea state and user-defined ranges of possible headings
and speeds. For linear responses, standard frequency domain methods can be applied. For non-linear responses, as exhibited
by the roll motion, standard methods such as direct time domain simulations are not feasible due to the required computational
time. However, the statistical distribution of non-linear ship responses can be estimated very accurately using the first-order
reliability method (FORM), which is well known from structural reliability problems. To illustrate the proposed procedure,
the roll motion was modelled by a simplified non-linear procedure taking into account non-linear hydrodynamic damping, time-varying
restoring and wave excitation moments, and the heave acceleration. Resonance excitation, parametric roll, and forced roll
were all included in the model, albeit with some simplifications. The result is the mean out-crossing rate of the roll angle
together with the most probable wave scenarios (critical wave episodes), leading to user-specified specific maximum roll angles.
The procedure is computationally very effective and can thus be applied to real-time determination of ship-specific combinations
of heading and speed to be avoided in the actual sea state. 相似文献
935.
Werner Rothengatter 《Transportation Research Part B: Methodological》1979,13(1):49-63
The paper describes some possibilities for modifying the optimal network algorithm developed by Boyce, Farhi and Weischedel in a way that makes it applicable to some practical problems of network planning. The modifications, which have been tested with respect to their effect on the efficiency of the algorithm, include the introduction of asymmetrical demand structures, the integration of an existing network, the lexico-minimization of a dynamic objective function, and the consideration of constraints related to interdependencies between candidate links. Two small network problems and one medium-sized problem (61 nodes, 104 links, 16 candidates) have been computed; the results support the hypothesis that the algorithm may be applied to produce approximate solutions to problems of practical dimensions within a reasonable range of time. 相似文献
936.
LIUZhuo-fu SANGEn-fang 《船舶与海洋工程学报》2003,2(1):49-52
A new gray-spatial histogram is proposed, which incorporates spatial information with gray compositions without sacrificing the robustness of traditional gray histograms. The purpose is to consider the representation role of gray compositions and spatial information simultaneously. Each entry in the gray-spatial histogram is the gray frequency and corresponding position information of images. In the experiments of sonar image recognition, the results show that the gray-spatial histogram is effective in practical use. 相似文献
937.
938.
Stated choice experiments have proven to be a powerful tool in eliciting preferences across a broad range of choice settings.
This paper outlines the elements of a group-based experiment designed for interdependent urban freight stakeholders, along
with the procedure to administer the questionnaire sequentially. The focus is on the design of a computer-assisted personal
survey instrument and the value in disseminating the details of a new approach to design and collect stated choice data for
interacting agents. The paper also discusses how to specify a reference alternative, and then how to recruit appropriate real-market
or representative decision-making group members to participate in a subsequent phase of the survey, which incorporates the
reference alternative and contextual information from an initial phase. The empirical strategy, set out in some detail, provides
a new framework within which to understand more fully the role that specific attributes, such as variable user charges, influencing
freight distribution chains might play, and who in the supply chain is affected by specific attributes in terms of willingness
to pay for the gains in distribution efficiency.
相似文献
Andrew CollinsEmail: |
939.
Galit Cohen-Blankshtain 《Transportation》2008,35(3):411-424
Transportation analysis emphasizes the necessity to internalize the transport externalities of car usage through taxation.
Yet taxation decisions are often made with non-transport goals in mind. In such cases, transport policies are made ‘by the
way.’ This paper examines such a case: Israel’s taxation policy on company cars. It shows that current taxation policies result
in increasing numbers of company cars and growing numbers of transport users who are not sensitive to the marginal cost of
car use and make excessive use of the car. As a result, a significant portion of Travel Demand Management (TDM) measures cannot
affect this group. The Israeli case of company car tax reform demonstrates the problematic effect of a policy that does not
take its overall consequences on other policy fields into account and thereby impairs efforts to reduce the negative impacts
of the transport system. Also, it demonstrates the importance of institutional aspects of transport policymaking.
Cohen-Blankshtain is a lecturer at the department of Geography and School of Public Policy at the Hebrew University. Her research interests include urban policy, transport and ICT policy and participation process in public policy. 相似文献
Galit Cohen-BlankshtainEmail: |
Cohen-Blankshtain is a lecturer at the department of Geography and School of Public Policy at the Hebrew University. Her research interests include urban policy, transport and ICT policy and participation process in public policy. 相似文献
940.
Using the supercavitation phenomenon is necessary to reach high velocities underwater. Supercavitation can be achieved in two ways: natural and artificial. In this article, the simulation of flows around a torpedo was studied naturally and artificially. The validity of simulation using theoretical and practical data in the natural and artificial phases was evaluated. Results showed that the simulations were consistent with the laboratory results. The results in different injection coefficient rates, injection angles, and cavitation numbers were studied. The obtained results showed the importance of cavitation number, injection rate coefficient, and injection angle in cavity shape. At the final level, determining the performance conditions using the Design of Experiment (DOE) method was emphasized, and the performance of cavitation number, injection rate coefficient, and injection angle in drag and lift coefficient was studied. The increase in injection angle in the low injection rate coefficient resulted in a diminished drag coefficient and that in the high injection rate coefficient resulted in an enhanced drag coefficient. 相似文献