全文获取类型
收费全文 | 196篇 |
免费 | 0篇 |
专业分类
公路运输 | 61篇 |
综合类 | 30篇 |
水路运输 | 55篇 |
铁路运输 | 19篇 |
综合运输 | 31篇 |
出版年
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 11篇 |
2019年 | 9篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 10篇 |
2013年 | 1篇 |
2012年 | 6篇 |
2011年 | 15篇 |
2010年 | 8篇 |
2009年 | 17篇 |
2008年 | 7篇 |
2007年 | 11篇 |
2006年 | 12篇 |
2005年 | 11篇 |
2004年 | 17篇 |
2003年 | 6篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
排序方式: 共有196条查询结果,搜索用时 31 毫秒
1.
首先分析了当前城域传送网的普遍现状,然后针对宁夏铁通MSTP城域网存在的问题,提出了优化方案和整改建议。 相似文献
2.
3.
发动机冷却水套内三维流动的数值模拟研究 总被引:4,自引:0,他引:4
应用FIRE软件对某一发动机冷却水套进行了三维数值模拟,得到了冷却液流场速率、换热系数分布、压力损失以及流量分布等流场信息。从计算结果中发现,该发动机缸体水套的第2缸、第3缸等区域存在流动死区.水套进、排气侧流量分布相差较大.整体水套压力损失与同类机型相比偏小等不合理的流动现象,是导致其第2缸、第3缸“拉缸”的主要原因。最后提出了相应的解决方案。 相似文献
4.
5.
6.
7.
车用催化转化器流动阻力影响因素的研究 总被引:2,自引:0,他引:2
流动阻力是车用催化转化器的重要性能之一。作者对载体结构参数,入口扩张管和出口收这三个因素进行了试验研究,并对载体通道的流动进行了理论分析,提出了一种计算载体流动阻力的方法。研究结果表明,载体结构参数和扩张管锥角对流动阻力影响显著,而收缩管锥角的影响不明显,在载体结构参数中,减小载体壁厚是降低催化器阻力的有效措施。 相似文献
8.
9.
Effects of countdown timers on queue discharge characteristics of through movement at a signalized intersection 总被引:2,自引:0,他引:2
Thirayoot Limanond Suebpong Chookerd Natcha Roubtonglang 《Transportation Research Part C: Emerging Technologies》2009,17(6):662-671
This study investigates how countdown timers installed at a signalized intersection affect the queue discharge characteristics of through movement during the green phase. Since the countdown timers display the time remaining (in seconds) until the onset of the green phase, drivers waiting in the queue at the intersection are aware of the upcoming phase change, and are likely to respond quicker. Thus, the countdown timers could reduce the start-up lost time, decrease the saturation headway, and increase the saturation flow rate. This study observed vehicle flow at an intersection in Bangkok for 24 h when the countdown timers were operating, and for another 24 h when the countdown timers were switched off. The signal plans and timings remained unchanged in both cases. Standard statistical t-tests were used to compare the difference in traffic characteristics between the “with timer” and “without timer” cases. It was found that the countdown timers had a significant impact on the start-up lost time, reducing it by 1.00–1.92 s per cycle, or a 17–32% time saving. However, the effects on saturation headway were found to be trivial, which implies that the countdown timers do not have much impact on the saturation flow rate of signalized intersections, especially during the off-peak day period and the late night period. The savings in the start-up lost time from the countdown timers was estimated to be equivalent to an 8–24 vehicles/h increase for each through movement lane at the intersection being studied. 相似文献
10.
Sandy sediments in shallow coastal waters of the Baltic Sea are often characterised by large numbers of biogenic structures which are produced by macrozoobenthos species. A series of experiments was devised to quantify how the interaction of such structures with the near-bed flow regime affects the sediment flux. Most experiments were done with simplified replicates of structures generated by typical species commonly found in the Mecklenburg Bight, starting with solitary structures and regularly-spaced arrays in a range of characteristic population densities, followed by a complex benthic macrofauna community, both artificial and alive. A laboratory flume channel, equipped with an acoustic Doppler flow sensor and a topography scanning laser, was used for high-resolution measurements (2 mm horizontal step size and 0.3 mm vertical resolution) of sand erosion (220 µm median grain size, at 20 cm s− 1) and fine particle deposition (8 µm grain size, at 5 cm s− 1). Sediment transport threshold values were measured for each layout. As a rule-of-thumb, both the erosion fluxes and the deposition of suspended matter increased considerably at low population densities (below 2%, expressed as percent of the sediment surface covered, i.e. roughness density RD). Above densities of 4%, erosion almost stopped inside the test arrays, and deposition remained well below the level of unpopulated areas. An attempt to extrapolate these findings to field conditions (using field current velocity data from 2001) showed that the net flux switched from erosion to deposition for densities above 5%. These parameters can now be integrated into a numerical sediment transport model coupling waves, currents, sediment dynamics and biological processes, which is currently under construction at the Baltic Sea Research Institute (IOW), Rostock, Germany. 相似文献