全文获取类型
收费全文 | 8255篇 |
免费 | 104篇 |
专业分类
公路运输 | 1824篇 |
综合类 | 602篇 |
水路运输 | 2621篇 |
铁路运输 | 773篇 |
综合运输 | 2539篇 |
出版年
2022年 | 117篇 |
2021年 | 58篇 |
2020年 | 48篇 |
2019年 | 87篇 |
2018年 | 210篇 |
2017年 | 130篇 |
2016年 | 180篇 |
2015年 | 99篇 |
2014年 | 244篇 |
2013年 | 1273篇 |
2012年 | 335篇 |
2011年 | 420篇 |
2010年 | 267篇 |
2009年 | 390篇 |
2008年 | 336篇 |
2007年 | 282篇 |
2006年 | 233篇 |
2005年 | 275篇 |
2004年 | 294篇 |
2003年 | 181篇 |
2002年 | 157篇 |
2001年 | 133篇 |
2000年 | 142篇 |
1999年 | 100篇 |
1998年 | 132篇 |
1997年 | 113篇 |
1996年 | 140篇 |
1995年 | 150篇 |
1994年 | 87篇 |
1993年 | 193篇 |
1992年 | 163篇 |
1991年 | 78篇 |
1990年 | 83篇 |
1989年 | 58篇 |
1988年 | 74篇 |
1987年 | 67篇 |
1986年 | 60篇 |
1985年 | 79篇 |
1984年 | 73篇 |
1983年 | 75篇 |
1982年 | 74篇 |
1981年 | 95篇 |
1980年 | 69篇 |
1979年 | 92篇 |
1978年 | 58篇 |
1977年 | 69篇 |
1976年 | 53篇 |
1975年 | 69篇 |
1974年 | 50篇 |
1973年 | 47篇 |
排序方式: 共有8359条查询结果,搜索用时 359 毫秒
781.
782.
783.
Two major environmental problems currently affecting the Louisiana coastal zone are a high rate of wetland loss and high levels of surface water pollution. The application of secondarily treated wastewater to wetlands can be a means of dealing with both of these problems. The benefits of wetland wastewater treatment include improved surface water quality, increased accretion rates to balance a high relative water level rise due mainly to subsidence, improved plant productivity and habitat quality, and decreased capital outlays for conventional engineering treatment systems. Wetland treatment systems can, therefore, be designed and operated to restore deteriorating wetlands. Hydrologically altered wetlands, which are common in the Louisiana coastal zone, are appropriate for receiving municipal and some types of industrial effluent. While the U.S. Environmental Protection Agency has determined wetland wastewater treatment is effective in treating municipal effluent, it has discouraged the use of natural wetlands for this purpose. At the same time, funds are being used for the construction of artificial wetlands to treat municipal effluent. In the Louisiana coastal zone, however, wetlands are deteriorating and disappearing due to hydrological alteration and a high rate of relative sea level rise. If no action is taken, these trends will continue. Effluent discharge to existing wetlands should be incorporated into a comprehensive management plan designed to increase sediment and nutrient input into subsiding wetlands in the Louisiana coastal zone, improve water quality, and result in more economical waste‐water treatment. The authors believe that the Louisiana example serves as a model for other coastal areas especially in light of projections of accelerated sea level rise. 相似文献
784.
In the rail industry worldwide, there has been a search for new solutions, including restructuring, corporatization, and outright privatization, but the complexity of the rail industry offers special problems. In the Workshop we looked in detail at the British, Swedish, German, Australian (New South Wales) and New Zealand experiences, as well as considering more general issues such as cost structures, vertical separation and competitive tendering. Whilst it was agreed that some developments, such as greater contracting out, were clearly beneficial, other developments such as the separation of infrastructure from operations remained of uncertain value until the issues of efficient pricing and slot allocation were resolved. 相似文献
785.
The public transport system of Karlsruhe, in particular its innovative services on jointly used heavy rail lines, has received substantial attention throughout the past 20 years. The discussion of the system and of its development has been rather limited in the past, mostly highlighting technical aspects. This paper provides an overview of the development, including the urban development, of the region and of the funding system. The ridership and financial development of the operator is documented in detail. Three case studies focus on the integration of the system development in the general political process of the region and demonstrate the limitations of the operator under its current ownership structures. 相似文献
786.
Frank J. Cesario 《运输规划与技术》2013,36(1):57-62
There are many shortcomings commonly associated with the conventional urban transportation modeling process. This paper focuses on one of the more important problems — the inconsistency between trip generation and distribution components — and suggests a possible way of alleviating it. The suggested approach involves sorting out the independent effects on tripmaking of origin, destination and travel cost characteristics, and introducing accessibility measures explicitly into the modeling process. The resulting modeling framework can be used to obtain consistent estimates of trip generation and distribution quantities which are responsive to changes in the transportation and spatial systems. 相似文献
787.
W. E. Scobie 《Maritime Policy and Management》2013,40(2):73-74
This paper describes a model which may be used in the evaluation of the relative effectiveness of policies used in the areas of ship chartering and the switching of combined carriers between the dry-cargo market and the tanker market. The policies for chartering and market switiching are expressed in the form of ‘desired proportions’ of the fleet operating in a particular charter-mode or a particular market. Graphical illustration of this form of expression of policies can be easily understood, so that alternative policies can be designed with relative case. The effectiveness of a particular from of policy under various freight market conditions can be determined from the model, the use of which is illustrated by its application to the deployment of the fleet of an hypothetical shipping company. It is assumed that the feedback connection between the company's actions and the market-place is negligible. 相似文献
788.
Traffic movement conflict points at intersections are the points at which traffic movements intersect (including crossing, merging, and diverging). Numbers and distribution of different types of conflict points are used to evaluate intersection access management designs and safety performance. Traditionally, the determination of the numbers of conflict points for different traffic movements is based on manual methods, which causes the difficulty for computerized procedures to evaluate safety performance of different access management designs. Sometimes, a programmable calculation procedure may provide more effective solutions as compared with manual methods. This paper presents a programmable calculation procedure for the determination of the numbers of conflict points, which could be used as a basis for a computerized procedure. Concepts of virtual movement lanes and intersection quadrants are introduced to specify types of intersections, traffic lane configurations, and traffic movement regulations. Calculation models, based on such concepts, for traffic movement conflict points at signalized and unsignalized intersections can be obtained. In support of the procedure, case studies are presented in the paper. The procedure presented in the paper can be programmed into a computer program for the purpose of a computerized evaluation of intersection safety and design performance of different access management or control approaches. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
789.
S. R. C. Wanhill 《Maritime Policy and Management》2013,40(1):48-55
The correct number of berths that a port should provide is solved by a model which minimizes the total port usage cost in terms of the costs of berth provision and the costs accruing to ships from time spent in the port. This model is then applied to Mina Zayed in the Arabian Gulf as an aid to future planning, and from different sets of cargo forecasts an optimal stategy is derived using a game-theoretic approach. 相似文献
790.
Remoteness and accessibility in the vulnerability analysis of regional road networks 总被引:2,自引:0,他引:2
Michael A.P. Taylor 《Transportation Research Part A: Policy and Practice》2012,46(5):761-771
This paper considers the development of a method for network vulnerability analysis which considers the socio-economic impacts of network degradation and seeks to determine the most critical locations in the network. The method compares the levels of remoteness (or its inverse, accessibility) of localities within the study region, on the basis of the impacts of degradation of the road network on a recognised accessibility/remoteness index that can be applied to each and every location within the region. It thus extends the earlier work on accessibility-based vulnerability analysis which was limited to assessment of impacts on selected nodes in a network. The new method allows study of impacts on both specified locations (which do not have to be represented as network nodes) and the region as a whole. The accessibility/remoteness index is defined so that an accessibility surface can be calculated for the region, and the volume under this surface provides an overall measure of accessibility. Changes in the volume under different network states thus reflect the overall impacts. The method is applied to a rural region in south east Australia. 相似文献