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351.
Daniel J. Mayor Thomas R. Anderson David W. Pond Xabier Irigoien 《Journal of Marine Systems》2009,78(4):511
The egg production of marine copepods correlates with a range of variables, including the availability of organic carbon (C), nitrogen (N) and the polyunsaturated fatty acids (PUFAs) 20:5(n−3) (EPA) and 22:6(n−3) (DHA). However, an understanding of which substrates limit egg production in the natural environment has yet to be reached. The quantities of C, N, EPA and DHA ingested, derived from parental biomass, and invested in eggs by female Calanus finmarchicus during a 5-day incubation experiment were examined using stoichiometric theory to determine which substrate was limiting. The majority of each substrate was derived from parental biomass, and therefore the existing stoichiometric theory is developed to include this route of supply. The females were essentially devoid of lipid reserves, as evidenced by the lack of the storage fatty acids 20:1(n−9) and 22:1(n−11), and carbon limitation was predicted under most of the scenarios examined. Nitrogen limitation was only apparent when carbon and nitrogen utilisation efficiencies were assumed to be high (0.5) and low (0.4) respectively. PUFAs were assumed to be utilised with high efficiency (0.9), and were never predicted to limit production. This work highlights the need for a more detailed understanding of the maintenance requirements that marine copepods have for C, N, EPA, and DHA and hence the efficiencies with these substrates can be utilised for growth. 相似文献
352.
This paper investigates the role that enhanced service quality introduced into a deregulated market has in improving the experience
of bus travel by a sample of passengers in the Tyne and Wear area of England. A generalised ordered choice (GOC) model that
accounts for preference heterogeneity through random parameters, as well as heteroscedasticity in unobserved variance, and
random parameterisation of thresholds, is implemented to identify sources of influence on the overall experience of bus travel
in the presence and absence of the quality-enhanced treatment of service. The GOC model is contrasted with a standard ordered
logit model, and the marginal effects associated with the preferred GOC model are derived for each influencing attribute,
taking into account the various ways in which each influence contributes to the utility associated with each level of bus
experience. The paper supports a view that the introduction of quality improvements, via a Quality Bus Partnership, does contribute
non-marginally to an increase in a positive bus experience, and signals a way forward through cooperative intervention, to
grow patronage. Knowing which attributes successfully deliver a more positive experience (and those that do not) means that
resources are effectively targeted at the aspect of service provision which will increase patronage and therefore revenues,
satisfying the objectives of both the bus operator and the local authority partner. 相似文献
353.
David A. Hensher John M. Rose Juan de Dios Ortúzar Luis I. Rizzi 《Transportation Research Part A: Policy and Practice》2009,43(7):692-707
In recent years there has been a re-focus on the valuation of a statistical life from the ex post or human capital method to an ex ante willingness to pay (WTP) approach. This is in part a recognition that we may have been undervaluing the cost of fatalities and injuries to society associated with crashes, but also a strong belief in the need to focus on establishing the amount, ex ante, that individuals are willing to pay to reduce the risk of exposure to circumstances that might lead to death or degree of injury on the road network. This study has developed a framework in which to identify the degree of preference heterogeneity in willingness to pay by individuals who are drivers or passengers in cars to avoid being killed or injured. A stated choice experiment approach is developed. The empirical setting is a choice of route for a particular trip that a sample of individuals periodically undertakes in Australia. The particular trip is described in enough detail to provide the respondent with a familiar market environment, providing all the relevant background information required for making a decision. Mixed logit models are estimated to obtain the marginal (dis)utilities associated with each influence on the choice amongst the attribute packages offered in the stated choice scenarios. These estimates are used to obtain the WTP distributions for fatality and injury avoidance, which are then aggregated to obtain estimates of the value of risk reduction (VRR), of which the fatality class is also known as the value of a statistical life (VSL). 相似文献
354.
体验伦敦公共交通系统 总被引:1,自引:0,他引:1
从旅客、业内人士和决策者的不同角度出发,给不太熟悉伦敦但却对其高效的公共交通系统感兴趣的读者,描述了今日伦敦公共交通系统的主要特征和运作方式.伦敦公共交通融合了公共汽车、地铁、轻轨、有轨电车和通勤火车在内的多种交通方式.良好的交通信息、车辆换乘及一票制的使用是该系统的3个主要特征,以此达到旅客的便捷出行.同时指出,伦敦公共交通系统成功在于3个关键因素:一体化的交通政策和规划、由伦敦市长直接领导的统一交通机构(伦敦交通署)负责机制以及充足的资金保障. 相似文献
355.
A key attribute of competitive tendering for the periodic selection of operators of subsidised public transport services is to secure the provision of specified services at efficient cost levels. This has proved particularly effective where services were previously provided by an inefficient monopoly operator. The arguments for the adoption of competitive tendering in preference to negotiation with the incumbent operator may be less clear-cut in other cases.Consideration is given to both theoretical and practical insights into the relative merits of competitive tendering and negotiation approaches in such situations. The limited literature on the topic is reviewed and insights and lessons identified. Influencing issues include prior conditions, the nature of the supplier market, features of contracts, negotiating and competitive tendering strategies and practice, accountability and transparency, and long-term market implications. The evidence suggests that ‘one size does not fit all’, and the choice will depend on specific circumstances.The relative merits of the two approaches for renewal of bus contracts are considered with regard to Adelaide, for contracts which have previously been awarded through competitive tendering. The paper draws out the main factors that could influence the authority’s choice between the options, and discusses the relevance of the findings to other situations. 相似文献
356.
357.
Christopher de Saxe David Cebon 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2019,57(5):752-776
High-capacity vehicles have been shown to be highly effective in reducing emissions associated with road freight transport. However, the reduced manoeuvrability of long vehicles often necessitates the use of active trailer steering. Path-following trailer steering systems are very effective in this regard, but are currently limited to on-highway applications due to the manner in which trailer off-tracking is estimated. In this work, a novel trailer off-tracking measurement concept is introduced which is independent of wheel slip and ground surface conditions, and requires no additional sensor measurements or parameter data from the tractor. The concept utilises a stereo camera pair affixed to the trailer and a visual odometry-based algorithm to calculate off-tracking. The concept was evaluated in detailed simulation and full-scale vehicle tests, demonstrating its feasibility and highlighting some important characteristics. RMS measurement errors of 0.11–0.12?m (3.3–3.6%) were obtained in a challenging visual environment. 相似文献
358.
David Glen 《Maritime Policy and Management》2013,40(5):475-487
This article presents the results of modelling the behaviour of oil spill numbers published by the International Tanker Owners Pollution Federation over the period 1970 to 2005. Poisson count or negative binomial models are estimated to identify the major determinants of oil spill numbers over this period. The results are used to estimate the number of oil spills that would have occurred in the absence of the adoption of double hull technology. Other potential factors, such as changes in the regulatory regimes regarding oil transportation, were found to be insignificant. 相似文献
359.
This article provides a summary of past disasters, and hazard mitigation initiatives in the state of North Carolina, with a focus on the barrier island of Nags Head. The article also highlights the application of GIS technology to assess (i) the built environment and the extent of development and tax base in the "danger" zones (floods, oceanfront hazard zone, incipient inlets); (ii) the status of pre-Flood Insurance Rate Mapping (FlRM) structures on developed parcels; and (iii) vacant land in relation to current zoning. Findings show that 72% of Nags Head was developed, with close to one-third of the developed parcels within the oceanfront hazard zone. A relatively high percentage of structures built prior to Nags Head's regular participation in the Flood Insurance Rate Mapping (FIRM) program also lie within incipient inlets and VE flood zones. These findings were used as part of Nags Head's ongoing hazard mitigation initiatives. 相似文献
360.
AbstractThe stringent ship emission regulations under IMO's (International Maritime Organization) MARPOL Annex VI are a main driver to consider liquefied natural gas (LNG) as a ship fuel. Research into LNG as a marine fuel saw a strong growth in recent years, but no study has analyzed in a systematic way the level of convergence among the findings presented in the wide range of studies. In order to fill this gap, this paper seeks to perform a systematic review to synthesize the findings of 33 published studies on the use of LNG as a ship fuel. The aim is not only to obtain a much broader understanding of the current perspectives and challenges for applying LNG as a bunker for ship propulsion, but also to identify the gaps and weak points in the literature which could suggest future research. Moreover, given the output of the synthesis, the paper presents an extensive decision-making framework for shipowners when deciding on a fuel switch for their fleet from conventional oils to LNG in order to achieve a level of conceptual development beyond that attained in individual studies. In addition, the study also identifies the important role of ports in facilitating and encouraging the large-scale adoption of LNG in the maritime industry. 相似文献