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   376篇
  免费   5篇
公路运输   21篇
综合类   37篇
水路运输   290篇
铁路运输   16篇
综合运输   17篇
  2023年   4篇
  2022年   1篇
  2021年   3篇
  2020年   6篇
  2019年   3篇
  2018年   7篇
  2017年   9篇
  2016年   8篇
  2015年   8篇
  2014年   17篇
  2013年   28篇
  2012年   8篇
  2011年   13篇
  2010年   13篇
  2009年   29篇
  2008年   38篇
  2007年   52篇
  2006年   24篇
  2005年   18篇
  2004年   10篇
  2003年   12篇
  2002年   13篇
  2001年   8篇
  2000年   14篇
  1999年   9篇
  1998年   11篇
  1997年   10篇
  1996年   4篇
  1994年   1篇
排序方式: 共有381条查询结果,搜索用时 14 毫秒
301.
结合南海TLP前端设计项目,系统分析了影响张力腿平台气隙的因素。针对南海环境条件特点和工程实际,采用二阶非线性方法对张力腿平台的气隙响应进行数值预报,通过水池模型试验对波浪爬升等强非线性现象进行修正,总结出一套适用于中国南海TLP气隙的设计方法,所得结论对工程应用具有借鉴意义。  相似文献   
302.
中国2004年5月底开发春晓油气田后,中日在东海的管辖划界争议升温。日本指责中国侵犯其专属经济区权益。春晓油气田的开发实际涉及的是大陆架的矿物资源,而非专属经济区的生物资源。中日东海争议的焦点是大陆架和专属经济区两种制度,而非日本单方面定的"中间线"。本文以《联合国海洋法公约》为依据,着重分析大陆架和专属经济区的两种制度及其异同;并参照国际上的一些实例,提议中日在东海宜以大陆架和专属经济区两条线来划界,作为过渡措施在两条线之间搞共同开发。文中对日本提出的"中间线"作了法理分析。  相似文献   
303.
以ZPW-2000无绝缘移频轨道电路红光带故障为研究对象,针对其故障的多样性与复杂性,提出一种基于故障树分析(FTA)与改进BP神经网络相结合的轨道电路智能故障诊断方法。根据轨道电路组成与故障关系建立故障树进行FTA定性分析,分析故障成因并提取故障诊断规则,确定诊断模型的输入输出,构建两个BP神经子网以并联方式联接组成诊断模型,采用LM算法和遗传算法对模型参数进行调整。通过仿真分析,表明该方法可行有效,为轨道电路智能故障诊断提供一种新思路。  相似文献   
304.
Parameterisation of clastic sediments including benthic structures   总被引:1,自引:0,他引:1  
The sediment transport processes in the south-western Baltic Sea are predicted by means of a numerical model in the project DYNAS. There are two sediment parameters that influence the results of modelling remarkably: critical shear stress velocity and bottom roughness. This paper presents the way how to parameterise these factors and extrapolate them into the investigation area. The critical shear stress velocity is parameterised basing on grain size data, combining approximations after Hjulström [Hjulström, F., 1935: Studies in the morphological activity of rivers as illustrated by the river Fyris. Geological Institution of University of Uppsala: Bulletin (25): 221–528.], Shields [Shields, A., 1936: Anwendung der Ähnlichkeits-Mechanik und der Turbulenzforschung auf die Geschiebebewegung. Mitteilungen der Preussischen Versuchsanstalt für Wasserbau und Schiffahrt (26): 26 pp.] and Bohling [Bohling, B., 2003: Untersuchungen zur Mobilität natürlicher und anthropogener Sedimente in der Mecklenburger Bucht. unpublished doctoral thesis, Mathematisch-Naturwissenschaftliche Fakultät, Ernst-Moritz-Arndt-Universität Greifswald/Germany, 156 pp.]. The roughness length, in the case of absence of macro zoo-benthos and their structures, is parameterised basing on grain size too employing Soulsby [Soulsby, R.L., 1997: Dynamics of Marine Sands: a Manual for Practical Applications. London, Thomas Telford Publications. 249 pp.], Nielsen [Nielsen, P., 1983: Analytical determination of nearshore wave height variation due to refraction shoaling and friction. Coastal Engineering 7, 233–251.] and Yalin [Yalin, M.S., 1977: Mechanics of Sediment Transport. Pergamon Press, New York. 298 pp.]. No equivalent simple parameterisations for biologically caused bed roughness exist. Here, findings of Friedrichs [Friedrichs, M., 2004: Flow-induced effects of macro zoo-benthic structures on the near-bed sediment transport. Dissertation, Universität Rostock, 80 S.] and estimations by the DYNAS biologists group were combined in order to derive roughness lengths from abundance measurements of four previously selected key species which represent the originators of the dominating benthic structures at the sea floor in the south-western Baltic Sea. Critical shear stress velocity and bed roughness are known at few sample sites only. They were extrapolated into the larger investigation area using a proxy-target concept. The mean near bottom milieu (bathymetry, median grain size, salinity, oxygen) which was derived using results from numerical modelling serves as the proxy. Since the milieu parameters are measured at the sampling sites for which the target parameters have been determined, a combined hierarchical and supervised classification was employed to transfer the local knowledge into the unknown investigation area.  相似文献   
305.
崖门出海航道疏浚工程潮流泥沙变化数值模拟   总被引:1,自引:1,他引:0  
崖门出海航道穿越黄茅海,是连接银洲湖和珠海高栏港的重要通道。采用数学模型在对最近的水文数据和地形冲淤资料验证的基础上,对崖门出海航道的进一步浚深方案进行了潮流泥沙运动模拟和航槽回淤计算。计算结果表明:东航道水沙条件相对较优,泥沙回淤主要集中在拦门沙航段,具有进一步提升通航标准的空间,在同等条件下可选择优先开发东航道。  相似文献   
306.
Distribution of drifting seaweeds in eastern East China Sea   总被引:3,自引:0,他引:3  
In offshore waters with relatively low primary production, drifting seaweeds composed of Sargassum species form an identical ecosystem such as an oasis in desert. Commercially important pelagic fishes such as jack mackerel (Trachurus japonicus) and yellow tail (Seriola quinqueradiata) spawn in East China Sea pass their juvenile period accompanying drifting seaweeds. Therefore drifting seaweeds are very important not only in offshore ecosystem but also fishery resources. However the distribution of drifting seaweeds in East China Sea has scarcely known. Then we conducted two research cruises of R/V Hakuho–Maru in May 2002 and in March 2004. During the cruises, drifting seaweeds were visually observed from the bridge and sampled with a towing net. The observation revealed that the drifting seaweeds were distributed along the front between the Kuroshio Current and coastal waters and mainly composed of one seaweed species, Sargassum horneri (Turner) C. Agardh from spring to early summer. There are no reports on geographical distribution of this species in the coasts south of southern Kyushu Island in Japan. Kuroshio Current flows northeastward there. Buoys with GPS attached to drifting seaweeds released off Zhejiang Province, China, in March 2005 to track their transport. Their positions monitored by ORBCOM satellite showed that they were transported to the area in East China Sea, where the drifting seaweeds were observed during the cruises, in 2 months. These facts suggest that S. horneri detached from Chinese coast in March or months earlier than March could be transported to fringe area of continental shelf and waters influenced by Kuroshio Current from March to May. Therefore the Sargassum forests, especially S. horneri, along the Chinese coast play a very important role in the ecosystem of the East China Sea as a source of drifting seaweeds.  相似文献   
307.
随着陆地资源不断枯竭,地球上人类的生存和发展将越来越多地依赖于海洋.特别是世界上人口最多、人均土地资源匮乏的中国,由大陆而海洋的资源开发大转移已势在必行,必须要大力重视和开发海洋资源.通过可持续发展理论分别论述了制海权、海洋资源、海洋开发技术的重要性.  相似文献   
308.
Sovereignty claims over insular features and maritime jurisdiction in the South China Sea have been disputed for decades, and a governance regime to address ocean-related issues is urgently needed. This article first introduces the notion of a regime, and examines details of cooperation mechanisms in the Polar Regions. Lessons that can be applied to the South China Sea include that both soft and hard law regimes work to bring States concerned together to cooperate on the “commons” issues even when military conflicts or sovereignty disputes still exist. Consensus among bordering States would be necessary to make the South China Sea a “zone of peace.” Mechanisms that accommodate the various sovereignty claims and freeze existing and new claims to, as well as to prohibit military activities in, the South China Sea are recommended. Lastly, if a cooperative mechanism were to be established in the future, the Arctic regime would be more applicable to the South China Sea than the Antarctic regime due to their geographic nature. Thus, only States bordering the South China Sea should have voting and decision-making rights in the cooperative mechanism. As always, the political will of all parties is paramount to the success of such an endeavor.  相似文献   
309.
In 2001 China embarked on an ambitious program to improve water quality through creation of the Clean Bohai Sea Program (CBSP). It is the first regional ocean governance program in China. The joint conference of central and local government units directed CBSP under the leadership of the State Environment Protection Administration. To meet the environmental objectives established by the joint conference local governments must pay for the program and operate it, but to date they have not been able to fully fund the effort. Although data indicate a decline of polluted discharges to the Bohai, one tabulation shows that the area of the sea that is polluted has increased each year from 2001 to 2005. Future enhancement of CBSP depends on revising incentives to better link local environmental programs and development, establishing funding mechanisms to equitably spread costs throughout watersheds, and creating comprehensive monitoring programs to better appraise program results.  相似文献   
310.
This article explores existing educational materials available to support integrated coastal management (ICM) in the Philippines and Indonesia. Emphasis is placed on materials gathered from informal education institutions (i.e., nongovernmental organizations, donor-sponsored projects, national initiatives, etc.). Over 100 sets of educational materials were collected and evaluated based upon criteria such as interactive qualities, availability, target audience, geographical focus, etc. Several deficiencies and gaps in the content and coverage of ICM materials were observed. Most significantly, it appears that improved coordination of education programs and dissemination of educational materials is needed. Accessibility and the choice of delivery mechanism (i.e., books, Internet, videos, etc.) also emerged as important considerations when designing educational materials. Surveys conducted with ICM practitioners in the Philippines and Indonesia further illustrate the challenges and opportunities in ICM education. Findings from the assessment of educational materials and surveys facilitated the development of several recommendations for future ICM educational materials, including improved local-level ICM education and focusing on ICM and ICM process sustainability.  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