首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1799篇
  免费   174篇
公路运输   621篇
综合类   547篇
水路运输   464篇
铁路运输   264篇
综合运输   77篇
  2024年   9篇
  2023年   20篇
  2022年   30篇
  2021年   51篇
  2020年   55篇
  2019年   54篇
  2018年   47篇
  2017年   49篇
  2016年   44篇
  2015年   66篇
  2014年   168篇
  2013年   111篇
  2012年   182篇
  2011年   161篇
  2010年   148篇
  2009年   115篇
  2008年   109篇
  2007年   158篇
  2006年   142篇
  2005年   94篇
  2004年   35篇
  2003年   27篇
  2002年   17篇
  2001年   19篇
  2000年   13篇
  1999年   9篇
  1998年   5篇
  1997年   7篇
  1996年   5篇
  1995年   2篇
  1994年   2篇
  1993年   2篇
  1992年   4篇
  1991年   4篇
  1990年   4篇
  1989年   4篇
  1988年   1篇
排序方式: 共有1973条查询结果,搜索用时 15 毫秒
81.
江河中无序的采砂活动对航道条件造成了不同程度的破坏,如何在采砂活动中规范采砂方式、保护航道条件,减小采砂对航道的影响至关重要。以曼厅大沙坝某采区为例,采用平均水深有限元水流运动二维数学模型,对原采砂方案进行优化研究。通过计算和比较,提出采前对原边滩进行加固保护、控制采挖高程以及调整采区平面尺度等优化工程措施。  相似文献   
82.
西沙群岛珊瑚砂运动特性试验研究   总被引:5,自引:1,他引:4  
荀涛  胡鹏  梅弢  高峰 《水道港口》2009,30(4):277-281
珊瑚砂具有颗粒密度较大、孔隙率较高、干密度较小、压缩性较高等物理特性。其形成过程相对短暂,搬运距离有限,珊瑚砂磨圆度较低,颗粒形态差异明显,颗粒之间有效接触面积较小,粘着力较低。这些特性决定了珊瑚砂在动力作用下易于起动搬运的运动特征。文章对西沙群岛珊瑚砂的比重、孔隙率、休止角和渗透性等物理性质以及水流、波浪作用下的起动特性进行了试验测定,试验结果也表明了珊瑚砂起动特性符合目前经验公式计算值。  相似文献   
83.
对铁尾矿砂及尾矿砂加入石灰水泥后的物理力学性能进行了试验研究,并与石灰土进行对比。结果表明:铁尾矿砂掺加石灰、水泥后,其强度随着龄期而增长,具有半刚性材料的特性,用石灰、水泥稳定尾矿砂作为路面基层材料具有很好的路用性能,同时用石灰和水泥稳定的效果更佳。  相似文献   
84.
根据连云港庙岭三期的特殊情况,采用了砂被筑堤法。介绍了连云港庙岭三期突堤砂被堤工程的概况,从砂桩打设、吹填砂被模袋混凝土护坡等几个方面介绍了砂被堤施工的工艺流程。陈述了施工中出现的技术问题和解决方法以及对原施工工艺的改进。这一工艺取得了良好的施工效果。  相似文献   
85.
本文主要介绍哈尔滨至大连铁路客运专线褥垫层施工工艺。  相似文献   
86.
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   
87.
Characteristic flow patterns generated by macrozoobenthic structures   总被引:2,自引:2,他引:0  
A laboratory flume channel, equipped with an acoustic Doppler flow sensor and a bottom scanning laser, was used for detailed, non-intrusive flow measurements (at 2 cm s− 1 and 10 cm s− 1) around solitary biogenic structures, combined with high-resolution mapping of the structure shape and position. The structures were replicates of typical macrozoobenthic species commonly found in the Mecklenburg Bight and with a presumed influence on both, the near-bed current regime and sediment transport dynamics: a worm tube, a snail shell, a mussel, a sand mound, a pit, and a cross-stream track furrow. The flow was considerably altered locally by the different protruding structures (worm tube, snail, mussel and mound). They reduced the horizontal approach velocity by 72% to 79% in the wake zone at about 1–2 cm height, and the flow was deflected around the structures with vertical and lateral velocities of up to 10% and 20% of the free-stream velocity respectively in a region adjacent to the structures. The resulting flow separation (at flow Reynolds number of about 4000 and 20,000 respectively) divided an outer deflection region from an inner region with characteristic vortices and the wake region. All protruding structures showed this general pattern, but also produced individual characteristics. Conversely, the depressions (track and pit) only had a weak influence on the local boundary layer flow, combined with a considerable flow reduction within their cavities (between 29% and 53% of the free-stream velocity). A longitudinal vortex formed, below which a stagnant space was found. The average height affected by the structure-related mass flow rate deficit for the two velocities was 1.6 cm and 1.3 cm respectively (80% of height and 64%) for the protruding structures and 0.6 cm and 0.9 cm (90% and 127% of depth) for the depressions. Marine benthic soft-bottom macrozoobenthos species are expected to benefit from the flow modifications they induce, particularly in terms of food particle capture due to altered particle pathways and residence times, but also for the exchange of gases, solutes and spawn. The present results confirm previous studies on flow interaction effects of various biogenic structures, and they add a deeper level of detail for a better understanding of the fine-scale effects.  相似文献   
88.
89.
A new higher order closure model for the stable boundary layer is presented and compared with Large Eddy Simulation data. The model includes numerical solutions for the mean values, second and third order moments equations. A satisfactory agreement is found between the calculated vertical profiles of the turbulent quantities with those provided by the LES. Furthermore the new model results are compared with profiles obtained with a lower order closure model in order to verify the effective importance of including third order dynamical equations in the model.  相似文献   
90.
苏通大桥大型桩承台桥墩基础的局部冲刷防护试验研究   总被引:1,自引:0,他引:1  
为探讨特大型桩套箱桥墩基础的护底防冲工程问题,通过实验室试验,分别对墩基防冲护底的方案选择、防护工程结构分层和范围确定、防护材料的稳定及成型情况以及护底工程的防冲效果进行了试验研究。并将试验成果应用在苏通长江大桥护底防冲工程的设计、施工中。施工期为期4年的监测结果证明,实施的防护工程及时、有效,确保了桥墩基础的安全。可为相关大桥采取防护措施提供借鉴。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号