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271.
私人小客车家庭拥有率是出行生成模型的重要输入数据,其准确性直接影响着出行生成模型。鉴于此,在分析国内外私人小客车拥有的基础上,从影响私人小客车家庭拥有率的主要因素入手,利用非线性回归的方法提出私人小客车家庭拥有率预测模型,并通过上海市的实例数据给出模型的验证效果。 相似文献
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为解决混合交通流饱和流率测算的实时性和时变性问题,实时获得混合交通流的饱和流率用以信号配时,本文提出基于自动车牌识别数据(Automatic License Plate Recognition,ALPR)的混合交通流饱和流率实时自动估计方法。首先,分信号周期提取车头时距数据,在当前车和后车车辆类型确定时车头时距满足同一正态分布的假设基础上,构建车头时距的高斯混合模型并应用 EM(Expectation Maximization) 算 法 求 解 ;其 次 ,基 于 赤 池 信 息 准 则 (Akaike Information Criterion,AIC)选取高斯混合模型的最优个数,拟合数据得到高斯混合模型参数;最后,根据车头时距的高斯混合模型推算出混合交通流饱和流率。以杭州城市道路3条路段的ALPR数据为例,分析基于 ALPR 数据获取车头时距的采样误差,对模型进行验证,并与传统的 HCM(Highway Capacity Manual)方法进行对比。结果表明:基于ALPR数据的车头时距采样误差满足精度要求; 与HCM的实测法相比,模型所得的混合饱和交通流率相对误差小,结果准确;该方法与传统的标准车流饱和流率折算法效果相近,并考虑混合交通流时变特性,能自动部署实时计算,鲁棒性良好,有实际应用意义。 相似文献
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Sabyasachee Mishra Snehamay Khasnabis Sunder Lall Dhingra 《Research in Transportation Economics》2013
Traditional economic analysis techniques used in the assessment of Public Private Partnership (PPP) projects are based upon the assumption that future cash flows are fully deterministic in nature and are not designed to account for risks involved in the assessment of future returns. In reality, many of these infrastructure projects are associated with significant risks stemming from the lack of knowledge about future cost and benefit streams. The fundamental premise of the PPP concept is to efficiently allocate risks between the public and the private partner. The return based on deterministic analysis may not depict a true picture of future economic outcomes of a PPP project for the multiple agencies involved. This deficiency underscores the importance of risk-based economic analysis for such projects. In this paper, the authors present the concept of Value-at-Risk (VaR) as a measure of effectiveness (MOE) to assess the risk share for the public and private entity in a PPP project. Bootstrap simulation is used to generate the risk profile savings in vehicle operating cost, and in travel time resulting from demand-responsive traffic. The VaR for Internal Rate of Return (IRR) is determined for public and private entity. The methodology is applied to a case study involving such a joint venture in India, the Mumbai Pune Expressway/National Highway 4 (MPEW/NH4), and fiscal implications from the perspective of the public and the private entities are examined. A comparison between deterministic and risk based economic analysis for MPEW/NH4 is presented. Risk analysis provides insightful results on the economic and financial implications from each participant's viewpoint. 相似文献
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This paper presents a new formula for prediction of the dynamic hardening effect for various marine structural steels, considering dependencies on the strain rates and temperatures. Dynamic tensile tests are carried out for three kinds of marine steels, 2W50, EH36, and DH36, changing the steel layer in the thickness direction, the strain rates, and temperatures. Considering two thickness layers at the middle and surface, five strain rate levels of 0.001/s, 1/s, 10/s, 100/s, and 200/s, three temperature levels of LT (−40 °C), RT, and HT (200 °C), and two repetitions, the total number of tests is 180. Dynamic hardening is clearly seen at LT and RT regardless of the material type, while dynamic strain aging occurs at HT, leads to negative strain rate sensitivity, and thus elevates the quasi-static flow stress above the dynamic flow stress to a certain strain rate. Dynamic hardening factors (DHFs) are derived as a function of the proof strains of 0.05, 0.10, and 0.15 according to each material type and temperature level. A new formula to determine the material constant D of Cowper–Symonds constitutive equation is developed. The correctness of the proposed formula is verified through comparison with test flow stress curves and reference test data in large plastic strain and high strain rate ranges. 相似文献
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中国地形地貌复杂,不同海拔高度的地形地貌,反映了坡体所在地区的地质构造、风速、冻融、降水、气温等自然条件与人类活动强度的较大差别,必然会对斜坡的稳定产生不利影响.利用数据库中所收集的国内721处滑坡样本,对不同海拔高度的山地、丘陵、高原、平原、盆地的滑坡贡献率进行了研究分析.分析结果表明:海拔1000~3500 m的中山地形区及50~200 m的高平原地形区,滑坡的贡献率权重最大;海拔0~50 m的低平原地形区及大于3500 m的高山地形区,滑坡的贡献率权重最小. 相似文献