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   3619篇
  免费   331篇
公路运输   1144篇
综合类   821篇
水路运输   1438篇
铁路运输   429篇
综合运输   118篇
  2024年   21篇
  2023年   38篇
  2022年   64篇
  2021年   114篇
  2020年   142篇
  2019年   85篇
  2018年   87篇
  2017年   117篇
  2016年   91篇
  2015年   147篇
  2014年   267篇
  2013年   237篇
  2012年   326篇
  2011年   352篇
  2010年   268篇
  2009年   210篇
  2008年   228篇
  2007年   317篇
  2006年   272篇
  2005年   176篇
  2004年   96篇
  2003年   77篇
  2002年   44篇
  2001年   34篇
  2000年   34篇
  1999年   13篇
  1998年   34篇
  1997年   14篇
  1996年   9篇
  1995年   3篇
  1994年   7篇
  1993年   5篇
  1992年   6篇
  1991年   3篇
  1990年   3篇
  1989年   1篇
  1988年   1篇
  1986年   3篇
  1985年   1篇
  1984年   3篇
排序方式: 共有3950条查询结果,搜索用时 31 毫秒
991.
An experimental sediment dumping was carried out in the southern part of the Mecklenburg Bight in June 2001. Foraminiferans and ostracods from superficial sandy sediment were studied in a time series from before dumping until March 2004 in order to assess changes in associations and recolonization patterns of both groups. Additionally, an area sampling covering the dumping site and its surroundings from 15.5 to 20.7 m water depth made it possible to compare associations inside and outside the dumping area as well as the water depth dependent distribution of foraminiferans and ostracods. Salinity values vary within the high alpha-mesohaline and low polyhaline range. The dominating species are Ammotium cassis (Foraminifera) and Sarsicytheridea bradii (Ostracoda). The diversity is low (Fisher alpha index from 0.4 to 3.2 for foraminiferans and 1.0 to 2.5 for ostracods), but higher within the dumping site samples. These higher values are explainable by input of allochthonous tests and valves representing additional species. After the sediment dumping it took two and a half years to re-establish the total foraminiferan association and the total foraminifer/ostracod ratio within the dumping site. Total foraminiferan abundance increases remarkably with water depth (mean 83 tests in 100 ml) driven by higher nutrient availability and more suitable salinity and temperature values within the zone of the oscillating halocline. The distribution of shallow water species such as Cribroelphidium excavatum, Eucythere argus and Hirschmannia viridis, within the transient water layer A. cassis, Nodulina dentaliniformis, S. bradii and Palmoconcha laevata and below Eggerella scabra indicate the depth position of the halocline. Water depth and sediment dumping influence are the main driving factors for the distribution of foraminifer and ostracod associations within the study area. However, a significant sedimentological difference between samples inside and outside the dumping area is not recognizable.  相似文献   
992.
概括云南省水路运输系统及水运人才的现状,从战略的高度对云南省水路运输和水运人才发展作出了具体规划并提出具体措施,指出发展的重点和难点.对提高云南省水运人才的培养和开发能力,改善云南省水运人力资源的总体结构和提升云南省水运人才的总体素质,加速云南地方经济的发展,实现云南省总体战略目标,都具有重要的现实意义和深远的战略意义.  相似文献   
993.
On the basis of previous studies, a series of hazards involving the typical small inland passenger ferries operating in inland Bangladeshi waters have been identified. In particular, stormy weather conditions, overloading, and the risk of crowding to one side have been determined as the typical events that are likely to lead to capsizing in the intact condition. In this article, possible hazard mitigation measures are discussed, both from the regulatory and from the design point of view, for a small inland ferry that is very similar to one that actually capsized in the past. The addressed design options involve ballasting and hull modification by means of additional buoyancy above the waterline. From a regulatory point of view, it is proposed that the present weather criterion in force in Bangladesh be modified by increasing the wind speed to be accounted for and by considering the concurrent effects of wind, rolling, and the crowding of people to one side.  相似文献   
994.
柴油机温度过高主要表现为水温、油温过高两大类。本文就这两类原因进行分析。  相似文献   
995.
为了探讨处治挖方路基过湿土经济适用的方法 ,对其分别进行了换填、石灰处治、塑料网格加筋等室内外试验 ,得出了处治前后过湿土物理力学指标的变化情况 .结果表明 ,采用上述三种处治方法 ,尤其是换填和塑料网格加筋 ,能获得较好的效果 .  相似文献   
996.
铝型树脂混合床制取脱盐水的实验研究   总被引:3,自引:1,他引:2  
研究了铝型阳离子交换树脂与强碱性阴树脂混合床制取脱盐水的工艺方法及其再生过程,通过树脂改性提高再生废液的持续利用价值。从而消除对受纳水体的污染,并且降低系统的投入产出比。  相似文献   
997.
通过大量调查研究和数据分析,阐述了长江流域国际集装箱多式联运以及EDI系统的发展现状,指出目前存在的问题,并提出若干建议。  相似文献   
998.
航行于洲际间的远洋船舶,其压载水系统成为有害水生物入侵的主要途径之一。溶解在水中的氧是水域生命活动不可缺少的物质,但不同水生物对溶解氧的需求不同。实践证明:当溶解氧小于1 mg/L时,在1 h内,水生物将窒息而亡。论述以燃气作为惰性气体,置换远洋船舶压载系统中的空气,使水中的溶解氧小于1 mg/L,让入侵水生物窒息的方法,以保护本地水域生态平衡。结合我国油轮上配置的惰性气体系统(Inert Gases System,简称IGS),提出了方案设想和计算要点,与同行共同探讨。  相似文献   
999.
提出了水位加权系数平均值计算方法,利用水位站与测点的平面位置逐点进行水位改正,能有效提高水深测量的整体精度.新方法有利于计算机编程实现,免去了人工绘制联合潮位曲线,使感潮水域水深测量的整体精度和处理效率明显提高.  相似文献   
1000.
This article concerns thermal radiation hazards associated with unconfined liquefied natural gas (LNG) spills on water. Consequence assessment methods were compared to clarify their model characteristics in large-scale LNG spills from an LNG carrier (LNGC). The consequences of LNG release, pool spread, and pool fire hazards were estimated using the following practical methods: the Federal Energy Regulatory Commission’s (FERC) method, the Sandia National Laboratories’ method, and the Fay method. The sensitivity of consequence analysis results to the breach size of a tank was examined under the assumption that LNG is released from a common type LNGC of 125000 m3 cargo capacity. Consequently, it was found that the FERC method is useful from the practical viewpoint of being applicable to any breach size. Finally, thermal radiation hazards from pool fires involving spills from one of the latest and largest LNGCs (250 000 m3 cargo capacity), which are currently considered for construction, were investigated using the recommended FERC method, and the results are discussed in comparison with those for common type LNGCs. As a result, it was found that the maximum thermal hazard distance is longer by only about 24% compared with the common type LNGC, whereas the spill volume is twice as much.  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