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191.
重力式挡土墙是山区公路中较为普遍的一种支挡结构形式,在运营中难免出现各种病害。通过介绍新疆山区(6条国省道路)重力式挡土墙常见病害类型,分析了各类病害的成因机制,并对山区重力式挡土墙病害防治经验加以总结,尤其是弯道凹岸防护范围总结和8度及以上地震地区重力式挡土墙防治经验,供同行参考。 相似文献
192.
物流配送中心选址问题是现代物流系统规划的一个重要环节,选址的方法有很多,其中,最普遍的就是我们通常所用的重心法,然而,重心法存在一些为人们所忽略问题,其一,重心法是如何引入的;其二,最后的迭代方案是否最好。本文对重心法的引入、公式的推导做了详尽的阐述,并且对以往的迭代方案做了相应的改进。 相似文献
193.
超细ZnO具有广泛的工业用途,表面修饰可提高其分散性和功能化.试验中采用超重力-离子交换耦合体系,以硝酸锌为原料,强酸性阳离子交换纤维为交换介质,简单、高效的合成超细ZnO粉体;利用离子交换纤维对己酸修饰剂的活化吸附作用,实现ZnO在合成的过程中的同步表面修饰.通过SEM、XRD、IR等表征结果的分析,证明在合成的过程中进行己酸修饰,不但极大的降低产物的粒径、提高产品纯度,还制得花状结构的ZnO. 相似文献
194.
随着沿海港口大型化的发展,码头结构的设计等级也在不断提高,因地制宜地选择合适的码头结构型式是码头建设中研究的关键内容之一。通过对防城港钢铁基地20万吨级(结构兼顾25万吨级)矿石码头结构的选型分析,采用不设消浪孔的大直径圆沉箱方案,该思路可供其它类似工程设计参考。 相似文献
195.
Many problems in transport planning and management tasks require an origindestination (O-D) matrix to represent the travel pattern. However, O-D matrices obtained through a large scale survey such as home or roadside interviews, tend to be costly, labour intensive and time disruptive to trip makers. Therefore, the use of low cost and easily available data is particularly attractive.The need of low-cost methods to estimate current and future O-D matrices is even more valuable in developing countries because of the rapid changes in population, economic activity and land use. Models of transport demand have been used for many years to synthesize O-D matrices in study areas. A typical example of this is the gravity model; its functional form, plus the appropriate values for the parameters involved, is employed to produce acceptable matrices representing trip making behaviour for many trip purposes and time periods.The work reported in this paper has combined the advantages of acceptable travel demand models with the low cost and availability of traffic counts. Three types of demand models have been used: gravity (GR), opportunity (OP) and gravity-opportunity (GO) models. Three estimation methods have been developed to calibrate these models from traffic counts, namely: non-linear-least-squares (NLLS), weighted-non-linear-least-squares (WNLLS) and maximumlikelihood (ML).The 1978 Ripon (urban vehicle movement) survey was used to test these methods. They were found to perform satisfactorily since each calibrated model reproduced the observed O-D matrix fairly closely. The tests were carried out using two assignment techniques, all-or-nothing and the stochastic method due to Burrell, in determining the routes taken through the network.requests for offprints 相似文献
196.
The main purpose of this study is to assess the forecasting capability of the gravity model and to investigate the merit of including K-factors when using the model. Peak hour trip data was obtained for four study year periods 1962, 1971, 1976 and 1981 for the City of Winnipeg. Analysis of the calibration results indicated that the F-factors for the twenty year period were stable within a range of values. In general, however, the K-factors were found to be inconsistent from one prediction period to the next, and when used in forecasting trips they resulted in larger errors than without their use. The validity of using K-factors or the method which has been used to determine them is questionable. It was concluded that while K-factors are very meaningful in theory (as defined), they are not appropriate for use in predicting O-D matrices based on the method by which they are currently estimated (i.e. as a simple ratio). Further study is needed to investigate an alternative method of calibrating the gravity model such as the cell-by-cell regression method. 相似文献
197.
铁路重力式实体桥墩应力分析 总被引:3,自引:2,他引:1
采用 8节点块体元对铁路标准设计中的重力式桥墩 ,特别是双线圆端形桥墩的应力状态进行计算分析。计算结果表明 ,单线桥墩顶帽横向拉应力不大 ,但双线圆端形桥墩顶帽的横向拉应力值较大 ,导致顶帽开裂 ,建议在顶帽内适当增加构造钢筋。 相似文献
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