全文获取类型
收费全文 | 1671篇 |
免费 | 16篇 |
专业分类
公路运输 | 654篇 |
综合类 | 123篇 |
水路运输 | 426篇 |
铁路运输 | 67篇 |
综合运输 | 417篇 |
出版年
2023年 | 15篇 |
2022年 | 29篇 |
2021年 | 15篇 |
2020年 | 6篇 |
2019年 | 19篇 |
2018年 | 72篇 |
2017年 | 76篇 |
2016年 | 163篇 |
2015年 | 22篇 |
2014年 | 51篇 |
2013年 | 133篇 |
2012年 | 105篇 |
2011年 | 189篇 |
2010年 | 165篇 |
2009年 | 83篇 |
2008年 | 130篇 |
2007年 | 76篇 |
2006年 | 40篇 |
2005年 | 27篇 |
2004年 | 33篇 |
2003年 | 16篇 |
2002年 | 18篇 |
2001年 | 12篇 |
2000年 | 15篇 |
1999年 | 17篇 |
1998年 | 6篇 |
1997年 | 12篇 |
1996年 | 11篇 |
1995年 | 12篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 2篇 |
1972年 | 4篇 |
排序方式: 共有1687条查询结果,搜索用时 156 毫秒
1.
王阳曾庆军戴晓强吴伟 《中国舰船研究》2022,(6):223-235
[目的]为了提高遥控水下航行器(ROV)在复杂水下环境中的姿态控制性能,开展多电机协同推进的ROV姿态控制研究。[方法]首先,针对多电机系统的结构和算法,分别提出一种基于PID速度补偿器的偏差耦合结构和一种新型非奇异终端滑模控制(SMC)算法,并设计一种新颖的基于多电机协同推进的ROV姿态控制方法;然后,建立ROV的运动学和动力学模型,开展推进器组推力建模分析、解耦简化ROV动力学模型研究;最后,设计一种ROV滑模姿态控制器。[结果]仿真结果表明,所提的结构和算法可提高多电机系统的抗干扰性、同步性和快速响应能力,进而提高ROV姿态控制系统的稳定性与鲁棒性。[结论]所提方法可为ROV姿态控制提供一种新的可用方案。 相似文献
2.
[目的]系统地研究初始横倾角对随机横浪下船舶横摇运动响应的影响。[方法]以路径积分法为基础,通过数值求解控制横摇运动微分方程概率属性的Fokker-Planck方程,得到横摇运动响应的概率分布。[结果]结果显示,初始横倾角对船舶横摇运动响应谱的影响有限,但对横摇角概率分布以及横摇运动响应极值分布的影响十分明显,且会造成船舶安全性的显著恶化。[结论]路径积分法可作为研究随机海浪下船舶横摇运动特性的有效数值方法。 相似文献
3.
ABSTRACTThe economic history of the U.S. illustrates how the role of many cities has been changed by being seaports or located on navigable rivers or lakes. Based on the widening of the Panama Canal in 2016, the West Coast ports that include the west coast seaports of California, Oregon, and Washington were expected to become less important, while the freight shares of the East Coast and Gulf ports would increase. By how much it has been not easy to measure or predict so far, but this study attempted to define some of the key parameters in the measurement. As well as several relevant background topics, both the demand- and supply-side versions of the National Interstate Economic Model, have been applied for the measurement of economic impacts. U.S. port authorities and policy makers at the local and national levels who respond and develop plans for coping with the new realities of the Panama Canal are able to understand the extent to which changes in shippers’ and land-mode transporters’ behaviors would undermine the logistics and the costs of their activities. Therefore, this study is important for a diverse spectrum of port development strategies in the U.S. to respond to the Canal expansion. 相似文献
4.
Transportation - Ride-sourcing services are increasingly popular since they were first introduced in the last decade. Particularly in developing countries where public transport systems have... 相似文献
5.
Although counteracting environmental programmes and policies have been strengthened, large oil spills still occur at irregular intervals. The total oil spill costs and their compensations have attracted much interest from various parties, such as local stakeholders, and state and federal governments. This paper addresses five major cost categories whose aggregations are expected to cover the overall direct and indirect costs after the release of an oil spill. Among them, research costs should not be neglected, since they tend to be high if public attention has been drawn to the case. Through an examination of the relationship between the total oil spill costs and their admissible claims, we found that:
- admissible claims do not cover the overall costs of the oil spill, and
- admissible claims cannot be compensated in full in the case of large spills.
6.
在有自由液面的情况下,针对横剖面为圆形的陷落腔模型,在均匀流场条件下,开展水动力实验研究,模拟了大量的工况,测量了腔体壁面的流体脉动压力.本文分析了模型所受的脉动压力随傅汝德数在不同腔体位置的变化趋势,并讨论了晃荡现象对压力分布的影响.实验时发现,傅汝德数小于0.35的工况有明显的晃荡现象发生,而傅汝德数小于0.35的工况的脉动压力系数也明显大于其他工况,且变化剧烈.本文认为,流体剪切层自持振荡与腔内液体深度驻波振荡共振是产生晃荡现象的原因,本文实验中Fr≤0.35的工况对应的流速正是达到以上两种振荡频率耦合所需要的流速.本文对工程应用中的腔体尺度和形式的设计有一定的指导意义. 相似文献
7.
D. W. Shuttlewood D. A. Crolla R. S. Sharp I. L. Crawford 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1993,22(5):383-396
The development of a mathematical model of a limited bandwidth hydro-pneumatic suspension that is incorporated into a vehicle handling model is described. The combined model is used to evaluate a suitable control strategy for eliminating body roll during a cornering manoeuvre. The philosophy behind the roll control strategy has been to use feedback measurements of the body motions which do not compromise the ride control. A study of the influence of the position of the body motion feedback transducer on the effectiveness of the system to reduce the body roll is presented. Non-linear modelling of the suspension components for a 0.8g cornering manoeuvre has revealed performance limitations. Conclusions are drawn as to the effectiveness of the control scheme. 相似文献
8.
介绍了一个多功能智能型航次计划优化系统的设计与实现,得到了一个能在微机网络上运行的有效原型。在设计中引入了人工智能技术,并特别注意了友好的人机界面。 相似文献
9.
C. Julian Parker 《WMU Journal of Maritime Affairs》2003,2(2):99-113
This article is in three parts. The first covers the historical development of qualifying associations. The second covers the particular role of maritime institutions that include The Royal Institution of Naval Architects, The Institute of Marine Engineering Science and Technology and The Nautical Institute. The third and final section considers the future for maritime professional associations in the context of international shipping. 相似文献
10.
企业评价是一种目标导向性活动。面对资源日趋紧张及环境日趋恶化的形势,满足可持续发展和环境治理的要求,对企业的评价应体现其资源的利用效率,因此文章首先提出并论证了构建资源节约导向型的企业评价指标体系的必要性。其次,将企业资源划分为土地、能源、水资源和矿产资源,并从资源占用、资源节约、资源回收利用方面探讨了指标体系的构建方法,给出了基于资源节约的指标体系。最后应用改进后的主成分分析法对该指标体系进行评价,克服以往评价方法客观性不强的缺点。 相似文献