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排序方式: 共有682条查询结果,搜索用时 15 毫秒
671.
S. C. Ko K. C. Oh C. K. Seo C. B. Lee 《International Journal of Automotive Technology》2014,15(3):347-352
Several NOx reduction technologies under development in recent years have now been commercialized, including selective catalytic reduction (SCR) with NH3 or hydrocarbons, and Lean NOx Trap. The aim of the present study is to investigate characteristics on NOx adsorption according to the oxygen concentration, de-NOx performance according to lean/rich injection cycle and toxic intermediates at LNT downstram for lean-burn gasoline engine. Under oxygen of 6%, NOx storage capacity was the highest, showed the highest NOx conversion of 98%. The reason for this phenomena is because the excited oxygen atoms at high oxygen concentration increased oxidizing power of NO. Under low temperature of 205°C, LNT catalyst showed the least NOx conversion of 14% because its activity became lower, while the generation rate of toxic HNCO was highest as CO which is generated during the rich condition, reacts with NOx stored on Ba site. 相似文献
672.
Large-Eddy Simulation (LES) was used to perform computations of air entrainment and mixing during diesel spray combustion.
The results of this simulation were compared with those of Reynolds Averaged Navier Stokes (RANS) simulations and an experiment.
The effect of LES on non-vaporizing and vaporizing sprays was evaluated. The validity of the grid size used for the LES analysis
was confirmed by determining the subgrid-scale (SGS) filter threshold on the turbulent energy spectrum plot, which separates
a resolved range from a modeled one. The results showed that more air was entrained into the jet with decreasing ambient gas
temperatures. The mass of the evaporated fuel increased with increasing ambient gas temperatures, as did the mixture fraction
variance, showing a greater spread in the profile at an ambient gas temperature of 920 K than at 820 K. Flame lift-off length
sensitivity was analyzed based on the location of the flame temperature iso-line. The results showed that for the flame temperature
iso-line of 2000oC, the computed lift-off length values in RANS matched the experimental values well, whereas in LES, the
computed lift-off length was slightly underpredicted. The apparent heat release rate (AHRR) computed by the LES approach showed
good agreement with the experiment, and it provided an accurate prediction of the ignition delay; however, the ignition delay
computed by the RANS was underpredicted. Finally, the relationships between the entrained air quantity and mixture fraction
distribution as well as soot formation in the jet were observed. As more air was entrained into the jet, the amount of air-fuel
premixing that occurred prior to the initial combustion zone increased, upstream of the lift-off length, and therefore, the
soot formation downstream of the flame decreased. 相似文献
673.
J. Xu Y. B. Li X. Chen D. Y. Ge B. H. Liu M. Y. Zhu T. H. Park 《International Journal of Automotive Technology》2011,12(5):687-695
During accident, the interlayer of windshield plays an important role in the crash safety of automotive and protection of
pedestrian or passenger. The understanding of its energy absorption capability is of fundamental importance. Conventional
interlayer material of automotive windshield is made by Polyvinyl butyral (PVB). Recently, a new candidate of high-performance
nanoporous energy absorption system (NEAS) has been suggested as a candidate for crashworthiness. For the model problem of
pedestrian head impact with windshield, we compare the energy absorption capabilities of PVB and NEAS interlayers, in terms
of the contact force, acceleration, velocity, head injury criteria, and energy absorption ratio, among which results obtained
from PVB interlayers are validated by literature references. The impact speed is obtained from virtual test field in PC-CRASH,
and the impact simulations are carried out using explicit finite element simulations. Both the accident speed and interlayer
thickness are varied to explore their effects. The explicit relationships established among the energy absorption capabilities,
impact speed, and interlayer material/thickness, are useful for safety evaluation as well as automotive design. It is shown
that the NEAS interlayer may absorb more energy than PVB interlayer and it may be a competitive candidate for windshield interlayer. 相似文献
674.
B. Suh A. Frank Y. J. Chung E. Y. Lee Y. H. Chang S. B. Han 《International Journal of Automotive Technology》2011,12(1):131-139
This research concerns the design of a powertrain system for a plug-in parallel diesel hybrid electric bus equipped with a
continuously variable transmission (CVT) and presents a new design paradigm for the plug-in hybrid electric bus (HEB). The
criteria and method for selecting and sizing powertrain components equipped in the plug-in HEB are presented. The plug-in
HEB is designed to overcome the vulnerable limitations of driving range and performance of a purely electric vehicle (EV),
and it is also designed to improve the fuel economy and exhaust emissions of conventional buses and conventional HEBs. Optimization
of the control strategy for the complicated and interconnected propulsion system in the plug-in parallel HEB is one of the
most significant factors for achieving higher fuel economy and lower exhaust emissions in the hybrid electric vehicle (HEV).
In this research, the proposed control strategy was simulated to prove its validity using the ADVISOR (advanced vehicle simulator)
analysis simulation tool. 相似文献
675.
基于地理信息系统以及热区基本模型,研究了道路热区的鉴别方法。该方法对道路网依据一定优先权进行合并以获取道路基本单元,模拟了交通事故的空间分布,并采用Monte Carlo法定义各道路基本单元交通事故数阈值,通过检验道路基本单元的空间邻近性得到热区,并对上海世博园周边道路热区进行了鉴别。分析结果表明:道路网经合并后,不规则道路基本单元的百分比由41.5%下降到14.8%;世博园周边共有84个仅涉及车辆、33个涉及行人的热区,与实际相符。可见,该方法能有效鉴别道路危险区域。 相似文献
676.
The present study aims at applying structural reliability methods to assess the implicit safety levels of the buckling strength requirements for longitudinal stiffened panels implemented in the IACS Common Structural Rules (CSR) for double hull oil tankers. The buckling strength requirements considered are used in the initial stage of the hull girder scantlings’ design to control the buckling capacity of longitudinal stiffened panels subjected to the compressive loads induced by the hull girder vertical bending. The following buckling collapse failure modes are explicitly considered in the design formulation: uniaxial buckling of the plating between stiffeners, column buckling of stiffeners with attached plating and lateral-torsional buckling or tripping of stiffeners.The paper presents the procedure used to assess the implicit safety levels of the strength requirements for the three buckling collapse failure modes above mentioned, which includes the optimization of the scantlings of the plate panels and longitudinal stiffeners in order to reflect the minimum strength required by the formulation. A first order reliability formulation is adopted, and stochastic models proposed in the literature are used to quantify the uncertainty in the relevant design variables. A sample of five oil tankers representative of the range of application of the IACS-CSR design rules is considered. The effect of corrosion in the implicit safety levels is quantified based on the three corrosion levels of the Net Thickness Approach (NTA) adopted in the design rules. Sensitivity analyses are also performed to quantify the relative contribution or importance of each design random variable to the implicit safety levels. 相似文献
677.
Children are an often overlooked and understudied population group, whose travel needs are responsible for a significant number
of trips made by a household. In addition, children’s travel and activity participation during the post-school period have
direct implication for adults’ activity-travel patterns. A better understanding of children’s after school activity-travel
patterns and the linkages between parents and children’s activity-travel needs is necessary for accurate prediction and forecasting
of activity-based travel demand modeling systems. In this paper, data from the 2002 Child Development Supplement of the Panel
Study of Income Dynamics is used to undertake a comprehensive assessment of the post-school out-of-home activity-location
engagement patterns of children aged 5–17 years. Specifically, this research effort utilizes a multinomial logit model to
analyze children’s post-school location patterns, and employs a multiple discrete–continuous extreme value model to study
the propensity of children to participate in, and allocate time to, multiple activity episode purpose-location types during
the after-school period. The results show that a wide variety of demographic, attitudinal, environmental, and others’ activity-travel
pattern characteristics impact children’s after school activity engagement patterns. 相似文献
678.
Conventional design methods require the lane marking patterns, which are painted on ground showing road users the permissible turning directions on different approach lanes, as exogenous inputs to define the traffic stream grouping for analysis. This predefined grouping of traffic movements may restrict the design of signal timings in the optimisation procedures. More recently, a lane-based design method has been developed to relax the lane markings as binary-type control variables in a mathematical programming approach. The lane marking patterns and the signal timings can then be optimised simultaneously in a unified framework. This paper presents an extension work to further relax the numbers of approach lane in traffic arms as new integer variables which can then be optimised to give optimal lane arrangement in various arms of a junction to manage the given traffic demands more efficiently. All well-defined signal timings variables in the phase-based approach as well as the lane marking and lane flow variables in the lane-based approach together with their governing constraints are all preserved in the new formulation for the reserve capacity optimisation of isolated signal-controlled junctions. 相似文献
679.
[Objectives]Aiming at the current situation in which it is difficult to efficiently evaluate protection probability through traditional lightning rod evaluation methods, an efficient numerical evaluation algorithm is developed on the basis of an electrogeometric model (EGM) and attractive volume to realize the efficient calculation of lightning protection probability at any point in space.[Methods]This method first determines the attractive volume boundary of the lightning rod and protection object according to the interception process of the upward and downward leaders. The collection surface and exposure arc of the lightning stroke distance are then calculated, enabling the attractive risk and interception effect of the lightning rod to be quantified. Finally, the attraction and interception characteristics of the lightning rod are integrated to establish a numerical evaluation model of protection probability. To verify the accuracy of this method, the general rule of lightning rod protection probability is analyzed and the results compared with the existing analysis method.[Result]The evaluation results of this method show good agreement with those of classical leader progression model (LPM) theory.[Conclusions] The method proposed herein has a high degree of quantification and can realize the efficient calculation of lightning protection probability at any point in space, which can provide useful references for lightning protection design work. © 2023 Authors. All rights reserved. 相似文献
680.
[Objectives]It is easy to produce buckling distortion when welding thin plate butt joints, which affects the construction period, cost and performance, but this can be controlled by applying external restraints. [Methods ] First, a butt welding test of a thin plate under external restraints is carried out, and the out-of-plane deformation is measured by the optical surface scanning method. At the same time, finite element (FE) models in a free state and external restraint state are established, and the thermal mechanical phenomena of the two models are subjected to thermal-elastic-plastic FE analysis (TEP FE). The influence of different external restraint distributions on the welding buckling distortion of the joints is then studied, and reasons for controlling welding buckling distortion are analyzed from the perspective of longitudinal plastic strain and longitudinal contraction force.[Results ] The out-of-plane deformation of the corresponding model is in good agreement with the measured results, and milder than the out-of-plane deformation of the model in a free state. When external restraints are applied, the longitudinal plastic strain of the weld and its adjacent metal decreases, and the longitudinal contraction force of the thin plate also decreases.[Conclusions ] The results verify that external restraints can effectively control welding buckling distortion, and the control effects are different depending on the external restraint distribution. © 2023 Chinese Journal of Ship Research. All rights reserved. 相似文献