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41.
Evaluating the impact of public mass transit systems on real-estate values is an important application of the hedonic price model (HPM). Recently, a mathematical transformation of this approach has been proposed to account for the potential omission of latent spatial variables that may overestimate the impact of accessibility to mass transit systems on values. The development of a Difference-in-Differences (DID) estimator, based on the repeat-sales approach, is a move in the right direction. However, such an estimator neglects the possibility that specification of the price equation may follow a spatial autoregressive process with respect to the dependent variable. The objective of this paper is to propose a spatial Difference-in-Differences (SDID) estimator accounting for possible spatial spillover effects. Particular emphasis is placed on the development of a suitable weights matrix accounting for spatial links between observations. Finally, an empirical application of the SDID estimator based on the development of a new commuter rail transit system for the suburban agglomeration of Montréal (Canada) is presented and compared to the usual DID estimator. 相似文献
42.
为有效抑制九江长江大桥三大拱吊杆的涡激振动,曾为其加装了TMD阻尼器.近20 a来其涡激振动得到了控制,但却造成了阻尼器长期大幅振动状态下的疲劳损伤.为避免当损伤积累后将削弱减振效果并危及结构安全,依托该桥三大拱吊杆新型液体-质量双调谐阻尼器(TLMD)研发项目,研究了阻尼器安装质量比与主振系统及阻尼系统动力放大系数的关系,并对阻尼器振动幅值进行了理论分析.研究发现:为保证阻尼器的安全与可靠,应选取合理的阻尼器安装质量比,使得该类阻尼器的动力放大系数不超过30倍.并据此指导了该桥吊杆新增阻尼器实施方案的设计.测试结果表明减振效果良好,且未见阻尼器疲劳损伤现象. 相似文献
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城市轨道交通桥梁纵向制动力传递分析 总被引:3,自引:0,他引:3
以城市轨道交通桥梁为对象,分析制动力作用于轨道面上的传递过程。将轨道、扣件、桥跨结构、支座、墩身及基础划成有限元,建立平衡方程,分析当列车制动时,纵向力的传递与分配。由于无缝线路的联系作用,制动力将分配至较广范围,每一桥墩承受的最大制动荷载只相当于有缝线路制动力的39 6%~56 8%。制动过程中,纵向制动力对钢轨引起的应力不大。当采用扭矩为60N·m的扣件,墩身高度超过10m时,制动过程中局部区段的扣件可能出现滑动现象。 相似文献
45.
In order to investigate the biological impacts of the ocean sequestration of CO2 (carbon dioxide), the dilution processes of CO2 were investigated near injection points in the deep ocean. From a combined fluid-dynamics, chemical, and biological approach,
a two-phase computational fluid dynamics (CFD) method with mass transfer was developed to predict droplet plume flow, the
dissolution of CO2 from droplets into seawater, and the advection–diffusion of dissolved CO2 (DCO2) in the deep ocean. Changes in pH due to the concentration of DCO2 were also calculated. In addition, the isomortality concept of Auerbach et al. was incorporated to predict the lethal damage
to marine organisms caused by DCO2. The simulation results suggested that the biological impacts of CO2 sequestration were insignificant in terms of mortality in both small-scale field experiments and the real-life cases we propose.
Received: October 3, 2001 / Accepted: December 14, 2001 相似文献
46.
针对某出口俄罗斯的拖车因离合器鼓旋转产生的不平衡惯性力引起拖车的剧烈振动的状况,对拖车的离合器鼓进行了动平衡工装设计及校正试验,校正及试验后大大降低了拖车系统的振动,同时也提高了盘类转子动平衡试验及应用的能力。 相似文献
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The Bay of La Paz, a coastal and shallow basin of the Gulf of California (depth<420 m), exchanges mixed-layer waters with the Gulf of California predominantly through Boca Grande (Big Mouth), in the northeastern part of the bay. Equatorial Surface Water (ESW) flows from the gulf to the bay; once there, due to evaporation processes, this water increases its salinity above 35.00, therefore becoming Gulf of California Water (GCW) Mass. During June 1998, the baroclinic circulation in the bay was dominated by a cyclonic gyre. The hydrographic dome, related to this gyre, is depicted until approximately 150-m depth. However, the vertical mixing of water between the mixed-layer and the ones below practically does not occur because of the development of a sharp pycnocline. This fact and the isolation of the bottom of the bay by a bathymetric sill (approximately 250-m depth) at Boca Grande induce low oxygen content, particularly in the bottom-waters (O2<0.1 ml/l). Chlorophyll values are higher and with larger vertical fluctuations within the Bay of La Paz than outside. 相似文献
50.