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571.
水下潜器改进S面控制及控制系统仿真(英文) 总被引:1,自引:0,他引:1
S surface controllers have been proven to provide effective motion control for an autonomous underwater vehicle (AUV). However,
it is difficult to adjust their control parameters manually. Choosing the optimum parameters for the controller of a particular
AUV is a significant challenge. To automate the process, a modified particle swarm optimization (MPSO) algorithm was proposed.
It was based on immune theory, and used a nonlinear regression strategy for inertia weight to optimize AUV control parameters.
A semi-physical simulation system for the AUV was developed as a platform to verify the proposed control method, and its structure
was considered. The simulation results indicated that the semi-physical simulation platform was helpful, the optimization
algorithm has good local and global searching abilities, and the method can be reliably used for an AUV. 相似文献
572.
白令海潮汐能通量和底边界能耗散 总被引:1,自引:0,他引:1
The spatial distribution of the energy flux, bottom boundary layer (BBL) energy dissipation, surface elevation amplitude and
current magnitude of the major semidiurnal tidal constituents in the Bering Sea are examined in detail. These distributions
are obtained from the results of a three-dimensional numerical simulation model (POM). Compared with observation data from
seven stations, the root mean square errors of tidal height are 2.6 cm and 1.2 cm for M2 and N2 respectively, and those of phase-lag are 21.8° and 15.8° respectively. The majority of the tidal energy flux off the deep
basin is along the shelf edge, although some of this flux crosses the shelf edge, especially in the southeast of the shelf
break. The total M2 energy dissipation in the Bering Sea is 30.43 GW, which is about 10 times of that of N2 and S2. The semidiurnal tidal energy enters mainly to the Bering Sea by Samalga Pass, Amukta Pass and Seguam Pass, accounting more
than 60% of the total energy entering the Being Sea from the Pacific. 相似文献
573.
边界任意弹性约束薄板的横向振动(英文) 总被引:1,自引:0,他引:1
This paper presents an analytical study on the influence of edge restraining stiffness on the transverse vibrations of rectangular
plate structure. An improved Fourier series method was employed to analyze the transverse vibration of plate structure with
general elastically restrained boundary conditions. A linear combination of a double Fourier series and eight auxiliary terms
was sought as the admissible function of the flexural displacement of the plate, each term being a combination of a polynomial
function and a single cosine series expansion. The auxiliary terms were introduced to ensure and improve the smoothness of
the original displacement function and its derivatives at the boundaries. Several numerical examples were given to demonstrate
the validity and accuracy of the current solution. The influences of translational and rotational stiffness on the natural
frequencies and mode shapes of plate were analyzed by numerical results. The results show that the translational stiffness
has bigger influence on the natural frequencies than the rotational stiffness. It is generally well known that little change
of the rotational stiffness has little influence on the mode shapes of plate. However, the current work shows that a very
little change of rotational stiffness value may lead to a large change of the mode shapes of a square plate structure. 相似文献
574.
水面无人船的发展与使命(英文) 总被引:5,自引:0,他引:5
575.
Mass transit projects are often a top contender of many cities to meet their increasing demand for travel. Despite the global
trend of privatization, mass transit services, as public goods, remain largely being provided and operated by the public sector.
Hong Kong is one of the few exceptions that all mass transit services are commercially operated. Both rail and bus services
in Hong Kong are reputable for their quality and profitability, often serving as benchmarks for new projects. In this study,
we investigate the factors contributing to this success. In particular, we ascertain the quality of transit service provision
by the private sector over the past two decades. Then, we conduct an in-depth analysis of the account books of leading railway
and bus operators in Hong Kong so as to shed light on their financial viability. Through this study, we hope to present crucial
factors for providing financially viable private transit services. 相似文献
576.
Yung-Hsiang Cheng 《Transportation》2010,37(6):875-896
Although people are often encouraged to use public transportation, the riding experience is not always comfortable. This study
uses service items to measure passenger anxieties by applying a conceptual model based on the railway passenger service chain
perspective. Passenger anxieties associated with train travel are measured using a modern psychometric method, the Rasch model.
This study surveys 412 train passengers. Analytical results indicate that the following service items cause passenger anxiety
during trains travel: crowding, delays, accessibility to a railway station, searching for the right train on a platform, and
transferring trains. Empirical results obtained using the Rasch approach can be used to derive an effective strategy to reduce
train passenger anxiety. This empirical study also demonstrates that anxiety differs based on passenger sex, age, riding frequency,
and trip type. This information will also prove useful for transportation planners and policy-makers when considering the
special travel needs of certain groups to create a user-friendly railway travel environment that promotes public use. 相似文献
577.
This paper seeks to explore the relationship between mode and destination choice in an integrated nested choice model. A fundamental
argument can be made that in certain circumstances, the ordering of choices should be reversed from the usual sequence of
destination choice preceding mode choice. This results in a travel demand model where travelers are more likely to change
destinations than to change transportation modes. For small and medium size urban areas, particularly in the United States,
with less well developed public transit systems that draw few choice riders, this assumption makes much more sense than the
traditional modeling assumptions. The models used in the new travel modeling system developed for Knoxville, Tennessee utilize
this reversed ordering, with generally good results, which required no external tinkering in the logsum parameters. 相似文献
578.
579.
This paper proposes a new activity-based transit assignment model for investigating the scheduling (or timetabling) problem
of transit services in multi-modal transit networks. The proposed model can be used to generate the short-term and long-term
timetables of multimodal transit lines for transit operations and service planning purposes. The interaction between transit
timetables and passenger activity-travel scheduling behaviors is captured by the proposed model, as the activity and travel
choices of transit passengers are considered explicitly in terms of departure time choice, activity/trip chain choices, activity
duration choice, transit line and mode choices. A heuristic solution algorithm which combines the Hooke–Jeeves method and
an iterative supply–demand equilibrium approach is developed to solve the proposed model. Two numerical examples are presented
to illustrate the differences between the activity-based approach and the traditional trip-based method, together with comparison
on the effects of optimal timetables with even and uneven headways. It is shown that the passenger travel scheduling pattern
derived from the activity-based approach is significantly different from that obtained by the trip-based method, and that
a demand-sensitive (with uneven headway) timetable is more efficient than an even-headway timetable. 相似文献
580.
In this paper we review freight forecasting models and current advances and needs with respect to data and model development.
We then present a case study to suggest which models should be developed for the State of California in the US. We suggest
several alternatives including an aggregate commodity flow model, a disaggregate regional logistics model and a hybrid regional
logistics model with a truck touring model. We point out however, that the data requirements for the latter model would be
extensive. In addition, the development of hybrid models, for example progress in the integration of regional logistics models
with urban truck touring models, will introduce new problems such as reconciling the outputs of multiple models for consistency. 相似文献