全文获取类型
收费全文 | 350篇 |
免费 | 5篇 |
专业分类
公路运输 | 18篇 |
综合类 | 92篇 |
水路运输 | 188篇 |
铁路运输 | 12篇 |
综合运输 | 45篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 12篇 |
2019年 | 9篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 10篇 |
2015年 | 20篇 |
2014年 | 24篇 |
2013年 | 31篇 |
2012年 | 40篇 |
2011年 | 25篇 |
2010年 | 22篇 |
2009年 | 34篇 |
2008年 | 15篇 |
2007年 | 34篇 |
2006年 | 23篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2001年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
排序方式: 共有355条查询结果,搜索用时 93 毫秒
21.
The East Sea/Sea of Japan is a moderately productive sea that supports a wealth of living marine resources. Of the East Sea subregions, the southwest has the highest productivity. Various authors have proposed coastal upwelling, the Tsushima Current, the Changjiang Dilute Water, eddies, or discharge from the Nagdong River as potential sources of additional nutrients. In this paper, we propose, using satellite data from 1998 to 2006, that the biological productivity of the southwestern region is enhanced mainly by wind-driven upwelling along the Korean coast. Firstly, the climatology of seasonal patterns suggests that the enhanced chlorophyll a along the Korean coast is of local origin. Secondly, coastal upwelling is frequent in all seasons except winter. For example, along the coast of the Ulgi region, enhanced chlorophyll a due to coastal upwelling was observed for 25–92% of the time between Jun and Sep in the period 1998–2006. Thirdly, the advection of upwelled water through various pathways to the deeper basin was observed. Fourthly, there appeared to be a strong correlation between the interannual chlorophyll a variations of the coastal upwelling regions and the Ulleung Basin. The chlorophyll a patterns of both regions were closely related to the wind pattern in the upwelling regions, but not to that in the Ulleung Basin. Finally, changes in advection pathways also appeared to affect the productivity of the Ulleung Basin. Since 2004, there has been a shift in the pathways of upwelled water, and consequent increases in chlorophyll a in the Ulleung Basin were observed. This last observation requires further investigation. 相似文献
22.
A Pacific basin-wide physical–biogeochemical model has been used to investigate the seasonal and interannual variation of physical and biological fields with analyses focusing on the Sea of Japan/East Sea (JES). The physical model is based on the Regional Ocean Model System (ROMS), and the biogeochemical model is based on the Carbon, Si(OH)4, Nitrogen Ecosystem (CoSiNE) model. The coupled ROMS–CoSiNE model is forced with the daily air–sea fluxes derived from the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) reanalysis for the period of 1994 to 2001, and the model results are used to evaluate climate impact on nutrient transport in Mixed Layer Depth (MLD) and phytoplankton spring bloom dynamics in the JES.The model reproduces several key features of sea surface temperature (SST) and surface currents, which are consistent with the previous modeling and observational results in the JES. The calculated volume transports through the three major straits show that the Korea Strait (KS) dominates the inflow to the JES with 2.46 Sv annually, and the Tsugaru Strait (TS) and the Soya Strait (SS) are major outflows with 1.85 Sv and 0.64 Sv, respectively. Domain-averaged phytoplankton biomass in the JES reaches its spring peak 1.8 mmol N m− 3 in May and shows a relatively weak autumn increase in November. Strong summer stratification and intense consumption of nitrate by phytoplankton during the spring result in very low nitrate concentration at the upper layer, which limits phytoplankton growth in the JES during the summer. On the other hand, the higher grazer abundance likely contributes to the strong suppression of phytoplankton biomass after the spring bloom in the JES. The model results show strong interannual variability of SST, nutrients, and phytoplankton biomass with sudden changes in 1998, which correspond to large-scale changes of the Pacific Decadal Oscillation (PDO). Regional comparisons of interannual variations in springtime were made for the southern and northern JES. Variations of nutrients and phytoplankton biomass related to the PDO warm/cold phase changes were detected in both the southern and northern JES, and there were regional differences with respect to the mechanisms and timing. During the warm PDO, the nutrients integrated in the MLD increased in the south and decreased in the north in winter. Conversely, during the cold PDO, the nutrients integrated in the MLD decreased in the south and increased in the north. Wind divergence/convergence likely drives the differences in the southern and northern regions when northerly and northwesterly monsoon dominates in winter in the JES. Subjected to the nutrient change, the growth of phytoplankton biomass appears to be limited neither by nutrient nor by light consistently both in the southern and northern regions. Namely, the JES is at the transition zone of the lower trophic-level ecosystem between light-limited and nutrient-limited zones. 相似文献
23.
The relevance of international transport costs on food prices: Endogenous and exogenous effects 总被引:1,自引:0,他引:1
The paper addresses the problem of transport costs and their influence on food prices for South American imports. While transport does not seem to be in the focus of existing analyses, its impact on food prices might be underestimated and even closely linked to the development of commonly mentioned drivers of food prices. Since transport price formation is a function of demand and supply, drivers of food prices are also expected to impact on transport prices. The authors argue that a number of relevant factors that drive transport costs - and in consequence food prices - can be influenced by policy makers. Based on empirical analysis, the authors explain the functioning of the determinants of transport costs in the segment of international shipping, trying to describe their exogenous and endogenous components. These results are discussed in reference to policy development in the region. 相似文献
24.
文中从海事政务中心的发展角度出发,通过分析和研究其产生、存在并发展的法律依据,找出困扰其发展的问题根源,并试图从立法规范、职能定位和运行机制等方面提出推动其健康发展的有效对策。 相似文献
25.
文中总结了上海海事空中巡航一年来的实践,借鉴国内外相关单位的空中巡航的建设和运行情况,提出了海事部门空中巡航发展的一些建议. 相似文献
26.
The crude oil offloading and supply problem (COSP) is a type of operation maritime inventory routing (MIR) problem encountered by petroleum companies. In COSP, the company not only is responsible for the ship scheduling to carry the crude oil from production sites to discharge ports but also must maintain inventory levels at both ports (production and consumption) between safety operational bounds to avoid disruptions in its crude oil production and/or refining processes. We show how to improve significantly the decision-making process in a Brazilian petroleum company using a mixed-integer linear programming (MILP) model to represent COSP. Comparison tests with a current ship-scheduling method adopted in the company indicated that the use of the MILP model increased the transportation efficiency and reduced costs by 20% on average. In addition to the quantitative gains, the use of a MILP model to solve COSP has succeeded when encountering real-life events, such as variation in production or consumption rates, berth unavailability, and changes in the storage capacities at ports. 相似文献
27.
This paper includes discussions on rail in urban areas and railway history. More specifically commonly used terms and definitions for rail services, policy and practice in urban areas are discussed followed by an overview of railway developments around the world. 相似文献
28.
文中分析了当前我国海事司法鉴定工作存在的问题,结合海事审判特点,从建立海事司法鉴定法律体系、完善海事司法鉴定人资格审核制度、建构海事司法鉴定机构、对海事司法鉴定机构实行统一管理、完善鉴定人出庭制度等五个方面提出解决对策,以期对完善我国海事司法鉴定制度有所裨益。 相似文献
29.
Ocean citizenship describes a relationship between our everyday lives and the health of the coastal and marine environment. Through our everyday lives we affect, and are affected by, the marine and coastal environment in numerous ways. As such, individuals have a responsibility to make informed lifestyle choices to minimize this impact. In doing so, the actions of individuals can contribute to the amelioration of large-scale and seemingly insurmountable geographical problems. This article outlines the concept of ocean citizenship within the context of the public understanding of marine environmental issues. The article draws heavily on the experience of the National Maritime Museum as an important contributor to the development of ocean citizenship in the United Kingdom. Specifically, the Planet Ocean initiative will be examined, in which the Museum has adopted a multimodal approach to public engagement through exhibitions, educational resources, and specific research publications. The article concludes by highlighting the importance of geography in the development and sustainability of ocean citizenship. 相似文献
30.
文中对行政备案的定义、分类、目的、作用及主管机关的责任进行了探讨,对海事法规中的行政备案内容进行了归纳,指出了海事管理行政备案工作中存在的问题及疑惑,重点就备案的材料要求、审查原则、办理流程及签注进行了分析,提出了相应建议,以供海事立法及管理参考。 相似文献