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921.
Experimental assessment of the ultimate strength of a box girder subjected to severe corrosion 总被引:1,自引:0,他引:1
The objective of this paper is to describe the experimental assessment of the ultimate strength of a severely corroded box girder subjected to a uniform bending moment resulting from four-point loading. Three box girders that could simulate the behaviour of midship sections have been deteriorated in corrosive seawater environment to simulate different levels of corrosion degradation of ageing ship structures. During the deterioration process, various parameters have been controlled and the total weight lost was registered. Corroded plate thicknesses have been measured in 212 points and a statistical analysis has been performed. The resulting corrosion wastage has been fitted by a non-linear time variant degradation model. The experimental results of the ultimate strength test of a severely corroded box girder subjected to a four-point loading have been analysed. The load-displacement and moment-curvature relationship is discussed, different failure modes are identified, and the strain gauges readings are analysed. 相似文献
922.
The inception of porpoising is theoretically predicted for planing vessels. Two different approaches are presented. First,
a linear stability analysis is applied to find the porpoising limits while the hydrodynamic coefficients, i.e. added mass
and damping coefficients, are determined by either a simplified method or a numerical method. Another approach is to seek
the porpoising limits by performing nonlinear time domain simulations. Either the simplified method or the numerical method
is used in the simulations. In the numerical method, a 2D+t theory together with a boundary element method is employed. The
trim angle limits for porpoising are determined by changing the longitudinal position of the centre of gravity (COG) of the
vessel and keeping the forward speed constant. The predicted porpoising limits are compared with Day and Haag’s (Planing boat
porpoising, Thesis, Webb Institute of Naval Architecture, 1952) experimental results. The influences of parameters such as the load coefficient, the vertical position of COG and the radius
of gyration of the ship are investigated by varying those parameters in the linear stability analysis. In the nonlinear time-domain
simulations, by trying different longitudinal position of COG, one can find the critical trim angle when the porpoising commences.
The obtained trim limits agree generally with those predicted by the linear stability analysis. Bounded oscillations for the
unstable cases near the critical trim angle can be seen in the time-domain simulations due to the nonlinear effects. 相似文献
923.
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
924.
The constructive disposition of metallic and plastic layers confers flexible pipes with high and low axial stiffness respectively when tensile and compressive loads are applied. Under certain conditions typically found during deepwater installation or operation, flexible pipes may be subjected to high axial compression, sometimes accompanied by bending. If not properly designed, the structure may not be able to withstand this loading and fails. From practical experience observed offshore and in laboratory tests two principal mechanisms, which will be discussed in this paper, have been identified regarding the configuration of the armor wires. When the pipe fails by compression the armor wires may exhibit localized lateral or radial deflections, consequently permanent damage is observed in the armor wires with a sudden reduction of the structure’s axial stiffness. The pressure armor may also unlock, thus causing potential fluid leakage.In this work a finite element model is developed to estimate the critical instability load and failure modes. An axi-symmetric model is constructed employing a complex combination of beam and spring elements. For each armor layer only one wire needs to be modeled, hence the computational cost is minimized without compromising the phenomenon characterization. A parametric case study is performed for a typical flexible pipe structure, where the friction coefficient between the wire armors and the external pressure are varied, and the critical instability loads and failure modes are obtained and results are discussed. 相似文献
925.
William C. Webster 《船舶与海洋工程学报》2011,10(3):253-258
In this work,Green-Naghdi (GN) equations with general weight functions were derived in a simple way. A wave-absorbing beach was also considered in the general GN equations. A numerical solution for a level higher than 4 was not feasible in the past with the original GN equations. The GN equations for shallow water waves were simplified here, which make the application of high level (higher than 4) equations feasible. The linear dispersion relationships of the first seven levels were presented. The accuracy of dispersion relationships increased as the level increased. Level 7 GN equations are capable of simulating waves out to wave number times depth . Numerical simulation of nonlinear water waves was performed by use of Level 5 and 7 GN equations, which will be presented in the next paper. 相似文献
926.
An experimental program was undertaken to test the feasibility to detect the occurrence of structural damage using a modified mode shape difference technique. The vibration response of a steel beam fixed at one end and hinged at the other was obtained for the intact and damage conditions. Modal analysis was performed to extract the frequencies and mode shapes. The method shows a good potential in detection of occurrence and location of damage. 相似文献
927.
Bundled hybrid offset riser (BHOR) global strength analysis, which is more complex than single line offset riser global strength analysis, was carried out in this paper. At first, the equivalent theory is used to deal with BHOR, and then its global strength in manifold cases was analyzed, along with the use of a three-dimensional nonlinear time domain finite element program. So the max bending stress, max circumferential stress, and max axial stress in the BHOR bundle main section (BMS) were obtained, and the values of these three stresses in each riser were obtained through the "stress distribution method". Finally, the Max Von Mises stress in each riser was given and a check was made whether or not they met the demand. This paper provides a reference for strength analysis of the bundled hybrid offset riser and some other bundled pipelines. 相似文献
928.
929.
930.
Rural seniors are highly dependent on their automobile to meet their trip making needs, yet the effects of aging can make
access to the vehicle difficult or impossible over time. The anticipated growth in the older person population, in concert
with limited travel data available to support rural transportation planning in Canada suggests a disconnect between what rural
older people may require for transportation and the availability of formal alternatives. Many will seek informal alternatives
to driving, such as depending on friends and family, to meet their travel needs, but the degree is not well understood in
the context of their actual vehicle usage and stated ability to adapt. This paper draws from a Global Positioning System (GPS)-based
multi-day travel diary survey of a convenience sample of 60 rural older drivers (29 men, 31 women, average age of 69.6 years)
from New Brunswick, Canada. Participants would rely on “friends and family” for 52% of all trips they undertook as driver
in the survey, “walk or bike” for 14% of trips, and “not take the trip” in 34% of trips if they did not have access to a vehicle.
The formal option of “Transit” was not selected as a viable alternative by any participant for any trip. “Medical trips”,
“Shopping” and “Personal Errands” were the least discretionary of all trip types, yet the most difficult for participants
to find alternate arrangements. This suggests the need to explore different models of service delivery, such as a community-supported,
member-based rural shuttle service with volunteer and paid drivers that build on informal social networks and can provide
service when friends and family are unavailable. 相似文献