全文获取类型
收费全文 | 3839篇 |
免费 | 115篇 |
专业分类
公路运输 | 949篇 |
综合类 | 1306篇 |
水路运输 | 863篇 |
铁路运输 | 728篇 |
综合运输 | 108篇 |
出版年
2024年 | 10篇 |
2023年 | 15篇 |
2022年 | 51篇 |
2021年 | 77篇 |
2020年 | 74篇 |
2019年 | 53篇 |
2018年 | 39篇 |
2017年 | 45篇 |
2016年 | 62篇 |
2015年 | 110篇 |
2014年 | 225篇 |
2013年 | 154篇 |
2012年 | 321篇 |
2011年 | 313篇 |
2010年 | 251篇 |
2009年 | 237篇 |
2008年 | 233篇 |
2007年 | 289篇 |
2006年 | 292篇 |
2005年 | 193篇 |
2004年 | 108篇 |
2003年 | 114篇 |
2002年 | 71篇 |
2001年 | 56篇 |
2000年 | 66篇 |
1999年 | 37篇 |
1998年 | 18篇 |
1997年 | 43篇 |
1996年 | 42篇 |
1995年 | 5篇 |
1994年 | 32篇 |
1993年 | 56篇 |
1992年 | 45篇 |
1991年 | 52篇 |
1990年 | 61篇 |
1989年 | 63篇 |
1988年 | 35篇 |
1987年 | 4篇 |
1984年 | 2篇 |
排序方式: 共有3954条查询结果,搜索用时 218 毫秒
641.
AbstractIn this paper we carry out a thorough review of the current research related to the benefits and costs arising from the implementation of longer and heavier vehicles (LHVs). From this review we concluded that despite the many studies available, little has been said about the sensitivity of the benefits and costs to the ultimate performance of the key variables related to the evolution of the economy, road transport performance, safety, and so on. In order to fill this gap, we have designed a sensitivity approach based on a cost benefit analysis tool to determine which variables demonstrate the greatest influence on the benefits and costs stemming from the implementation of LHVs. In order to test the methodology, we have used it in an analysis of the Spanish trunk network. The results show that the benefits of LHVs for society are significant. Even in the least favorable scenario, the economic benefits are greater than €3500 million over 15 years, and the environment enhanced as well, for CO2 emissions are reduced by 2 Million tonnes. Overall we noted how the results are not very sensitive to the evolution of key variables in determining the final outcome. However, we found that the variables that have the greatest affect on the final benefit, such as traffic growth and social discount rate, depend basically on the performance of the overall economy. Moreover, the private cost for haulers seems to be more important in determining the final benefit than externality costs. 相似文献
642.
SiCp/Al复合材料中增强体SiC含量的测定方法研究 总被引:2,自引:0,他引:2
在利用内耗法和超声衰减法研究SiCp/Al复合材料阻尼性能的基础上,分析SiCp/Al复合材料超声衰减系数中吸收系数与散射系数之间的关系,提出一种用超声法测定SiCp/Al复合材料增强体SiC含量的方法。与传统的测试方法相比,它具有简便、快捷的优点。 相似文献
643.
基于响应面法的双前桥转向机构参数优化 总被引:2,自引:2,他引:0
针对某重型双前桥转向汽车轮胎磨损严重的问题,运用Adams/View建立了该型汽车双前桥转向机构的运动学模型,对其进行了运动学及转向性能仿真分析。针对第二桥车轮实际转角与理想转角之间差异较大的问题,采用灵敏度分析的方法,找出对转角差异影响较大的因子,在Adams/Insight中,使用响应面分析方法,对双前桥转向机构的参数进行了优化。对比优化前后的转角差异可知,实际转角与理想转角之间的差异得到了有效控制,从而降低了轮胎的磨损。 相似文献
644.
韩国军 《武汉船舶职业技术学院学报》2013,(1):104-108
相对传统形式的四、六级考试,网考不但采用了计算机考试,而且考察内容的侧重点也发生了改变,由传统的重读写转变为为重听说。为适应大学英语四六级网考新模式,大学英语教与学也必须做出相应改变。大学英语四六级机考在推行的过程中也应注意多方面的问题,力争让四六级网考在全国早Et推广。 相似文献
645.
646.
Avishai Ceder 《先进运输杂志》2013,47(6):595-618
The idea of designing an integrated smart feeder/shuttle service stemmed from the need to overcome the problem of using an excessive number of cars arriving and parking at a train station within the same time span. This problem results in high parking demand around the train station. Moreover, some potential train riders will, instead, use their cars and hence become a party to increasing the traffic congestion. This work develops a new idea of an integrated and innovative feeder/shuttle system with new operating and routing concepts. The fulfilled objectives are as follows: (i) to construct and examine different operating strategies from both the user and operator perspectives; (ii) to examine different routing models and scenarios; and (iii) to construct a simulation tool for (i) and (ii). Ten different routing strategies are examined, with all the combinations of fixed/flexible routes, fixed/flexible schedules, a unidirectional or bidirectional concept, and shortcut (shortest path) and/or short‐turn (turnaround) concepts. These strategies are investigated by employing a simulation model specifically developed and constructed for this purpose. This simulation model is used in a case study of Castro Valley in California in which the feeder/shuttle service is coordinated with the Bay Area Rapid Transit service, and the 10 routing strategies are compared in regard to four fleet‐size scenarios. One of the interesting results found is that the fixed‐route and flexible‐route concepts are comparable in performance measures when applying a combination of operating strategies. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
647.
648.
以兰渝铁路盖家阴山滑坡为例,进行了滑带土大型直剪试验,讨论了滑带土的c,φ值随含水率变化规律.通过传递系数法进行了滑坡稳定系数对强度参数c,φ值和地下水位变幅的敏感性分析,结果表明:随着含水率的增加,内摩擦角φ基本呈线性减小,黏聚力c呈现先增加而后又逐渐变小的特征;滑带土黏聚力c每降低1 kPa,稳定性系数将减小0.01~0.02;内摩擦角φ每降低1°,稳定性系数将减小0.07~0.09;在降水和地震条件下,当水位变幅系数δ大于0.53时,滑坡体将会发生蠕滑变形,甚至是失稳滑动. 相似文献
649.
针对二维平面设计方法难以对悬挂系统各种工况准确分析校核的问题,介绍了通过建立合理的实体模型,运用Pro/ENGINEER软件骨挂模型中参数化设计的特点对悬挂系统进行协调,并进行动态分析,模拟悬挂系统在各种工况下的运动干涉情况的三维设计方法。此方法可提高设计效率,缩短产品开发周期且便于协同设计。 相似文献
650.