全文获取类型
收费全文 | 1426篇 |
免费 | 22篇 |
专业分类
公路运输 | 568篇 |
综合类 | 45篇 |
水路运输 | 372篇 |
铁路运输 | 48篇 |
综合运输 | 415篇 |
出版年
2023年 | 14篇 |
2022年 | 38篇 |
2021年 | 13篇 |
2020年 | 6篇 |
2019年 | 14篇 |
2018年 | 29篇 |
2017年 | 38篇 |
2016年 | 64篇 |
2015年 | 21篇 |
2014年 | 72篇 |
2013年 | 193篇 |
2012年 | 78篇 |
2011年 | 75篇 |
2010年 | 82篇 |
2009年 | 98篇 |
2008年 | 72篇 |
2007年 | 41篇 |
2006年 | 32篇 |
2005年 | 35篇 |
2004年 | 24篇 |
2003年 | 23篇 |
2002年 | 26篇 |
2001年 | 20篇 |
2000年 | 21篇 |
1999年 | 19篇 |
1998年 | 14篇 |
1997年 | 17篇 |
1996年 | 20篇 |
1995年 | 25篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1975年 | 18篇 |
1974年 | 6篇 |
1973年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有1448条查询结果,搜索用时 676 毫秒
321.
Peter Stokes 《Maritime Policy and Management》1996,23(4):397-405
This papers examines the reasons for the shipping industry's general failure to exploit the enormous capital raising potential offered by the world's major security markets. The basic reason put forward is one of joint ignorance and lack a of communication. On the one hand shipping perceives the market as being unsympathetic to its requierments. On the other hand, the Stock market assess it as a minor activity and this is combined with a presumption of industrial instability. An analysis of recent initial public offering of equaity options in shipping highlights the inadequacy of companies who have ventured that way. In particular it is pointed out that shipping companies who embark on such a course must not forget that equaity is, at one end the same time, the cheapest and the most expensive money which they can raise. There is a further underlying problem for the industry, which is that market capital raising neccessiates the loss of personal control. 相似文献
322.
Knowledge of future traffic flow is an essential input in the planning, implementation and development of a transportation system. It also helps in its operation, management and control. Time series analysis techniques have been extensively adopted for this purpose in the fields of economics, social sciences and in other fields of technology. An attempt has been made in this study to apply the techniques of time series analysis to goods traffic, particularly truck traffic. Four predominant corridors, N.H.3, N.H.4, N.H.8 and Lal Bahadur Shastri Road (L.B. S. Rd.), accounting for majority of truck movement in the Bombay Metropolitan Region (BMR), have been considered for modeling. Raw data was processed initially, to obtain an insight into the structure of time series. Ten candidate models of the Auto-Regressive Moving Average (ARMA) and Auto-Regressive Integrated Moving Average (ARIMA) family are investigated to represent each of the four corridors. Models finally proposed, to represent each of the four corridors have been selected based on Minimum Mean Square Error (MMSE) and Maximum Likelihood Rule (MLR) criteria. Models ARIMA (2, 1, 0), ARMA (1.0), ARMA (1, 1) and ARIMA (1, 1, 0) are proposed for N.H.3, N.H.4, N.H.8 and L.B.S. Rd. respectively, based on significant weekly periodicity. 相似文献
323.
This paper is an attempt to develop a generic simulation‐based approach to assess transit service reliability, taking into account interaction between network performance and passengers' route choice behaviour. Three types of reliability, say, system wide travel time reliability, schedule reliability and direct boarding waiting‐time reliability are defined from perspectives of the community or transit administration, the operator and passengers. A Monte Carlo simulation approach with a stochastic user equilibrium transit assignment model embedded is proposed to quantify these three reliability measures of transit service. A simple transit network with a bus rapid transit (BRT) corridor is analysed as a case study where the impacts of BRT components on transit service reliability are evaluated preliminarily. 相似文献
324.
Spring blooms of bottom ice algae are a common feature of landfast congelation ice in polar regions. Because ice algae are usually associated with a substrate, their population dynamics can be followed with considerable confidence. Although ice algal dynamics are closely related to irradiance, their dynamics and distributions are influenced by other abiotic and biotic factors. Ice algal abundance varies horizontally over all scales examined. Factors such as grazing and nutrient availability may contribute to local and geographic differences. Loss terms for most sea ice assemblages are largely unquantified. Ice algal biomass is most concentrated near the ice-water interface in spring.Environmental factors affecting ice algal abundance and productivity are considered here, emphasizing recent results from several well-studied sites. Biomass accumulation, growth rates and productivity have been documented for spring blooms of bottom interstitial and sub-ice assemblages. On an areal basis biomass accumulation in bottom ice assemblages can be comparable with planktonic systems. At low ambient temperatures and irradiances average specific growth rates (≤ 0.25 d−1) and production rates (≤ 1.0 mg C mg Chl−1 h−1) for ice algae are low. Current methods of measuring productivity are compared. Results are consistently low but variable with little systematic difference among them. At present, apparent differences in productivity between bottom ice assemblages in the Arctic and Antarctic, or among different antarctic assemblages, are so confounded by methodological and other sources of variability that no firm differences can be detected. 相似文献
325.
The impact of a port on its local economy: the case of Plymouth 总被引:1,自引:0,他引:1
It has been suggested in two potentially influential documents that the development of ports could be an important tool of regional economic growth in areas such as South West England. This proposition is analysed in this article by detailed examination of the case of Plymouth, one of the areas in the region for which port development has been mooted. It is concluded that the Plymouth evidence suggests that it is easy to exaggerate the existing and potential role of ports in the regional development process. Ports are not big employers of labour and are no longer the inter-related industrial complexes that they once were. In most cases, therefore, they serve industry in areas distant from their own. 相似文献
326.
马颖 《变流技术与电力牵引》2005,(1):35-38
只有采用新一代列车才能实现科隆-莱茵/美因新建高速铁路线上科隆至法兰克福两大都市间运行时间缩短1/2的商业目标.而要实现这一商业目标,并且要与环境协调,唯一途径是选择紧靠既有"A3"高速公路的线路.由此提出的列车、轨道、指挥与控制系统工程项目,以及投入运用与审批程序,均对新线的开发与整个系统工程的完成构成了一大挑战. 相似文献
327.
328.
Alfred H. A. Soons 《WMU Journal of Maritime Affairs》2004,3(1):3-16
The combating of the present great variety of criminal activities occurring at sea mainly involves measures to be taken on
land, in particular in ports.However, also actual enforcement at sea will continue to play an essential (complementary) role.
This article surveys the rules of international law governing law enforcement measures at sea. These rules are complex, because
distinctions have to be made between the various jurisdictional zones at sea and between the positions of the flag state,
the coastal state and the port state. Traditionally, ships in the high seas (all sea areas beyond a narrow band of territorial
sea) were under the exclusive jurisdiction of the flag state. In an increasing number of situations, the coastal state now
has law enforcement authority over foreign ships in expanded areas up to 200 nautical miles offshore. But apart from these
situations, flag state jurisdiction still prevails beyond the territorial sea. This makes effective law enforcement difficult.
In practice, many obstacles can be overcome by making more effective use of the authority of the port state, and by concluding
new international agreements providing for specific enforcement systems. 相似文献
329.
提出了抑制变压器冲击电流的新方法.小功率电压源PWM变频器通过匹配的变压器与其他变压器串联.当接通的PWM变频器为阻性时,没有冲击现象发生.单相电路中,电流冲击时充当阻尼电阻的PWM变频器的额定功率为主变压器的14%,而在三相电路中为19%.利用PSCAD/EMTDC技术数字计算机仿真无法确定该方法的有效性和良好的实用性.研制了一台试验样机进行试验,结果证实所提出的方法可以完全避免冲击现象的发生. 相似文献
330.
In the next few years, exciting developments in the field of freight transport are likely to occur. The Channel Tunnel will be perceived as giving railways much greater distance of operation, compared to the current train ferry to/from Great Britain. The further development of swap-body technology will allow easier modal transfer and the creation, in 1992, of a single market in Europe will transform the pattern of trade. All of these are likely to have significant impacts on modal choice, and hence modal split, in freight transport. Reappraisal by many firms of the modes of transport used is likely but will it result in a net transfer of freight from road to rail and, if so, to what extent? To answer such questions, an accurate and reliable method of predicting modal split is required. Research in the past has concentrated on the development of modal split models based on generalised costs. These fail to explain adequately the prevalence of road freight in the UK. From surveys of freight managers within industry, it is clear that models to date rely too heavily on the economic cost factor and too little on behavioural factors (Jeffs 1985). This paper derives from a recent study of freight transport modal choice from the standpoint of the transport decision-maker within the firm. It attempts to shed light on the actual parameters which should be incorporated into a modal split model. Many variables appear to exert an influence on modal choice decision-making process. However, it is possible to categorise them into six main groups, namely: customer-requirements; product-characteristics; company structure/organisation; government interventions; available transport facilities; and perceptions of the decision-maker him/herself. It is the interactions and inter-relationships between these which ultimately determine freight modal split. This study has shown that the relationship between the outcome of the transport decision process and the values of particular determinants of modal split is not straight-forward, due to the complexity and variety of interactions involved. Perhaps one of the main reasons for researchers' failure hitherto to develop a successful modal-split model has been the preoccupation with techniques that rely on the development of common metric (e.g. generalised cost), which has led to the exclusion of some important explanatory variables along quite different dimensions. Another important issue concerns the appropriate level of aggregation. In order not to reduce the explanatory power of the key variables, it is important to work at a disaggregate level, although this does make substantial demands on data. The use of factor analysis enables both the aggregation of information without loss of behavioural reality and the specification of variables in terms of a common metric. In conclusion, freight transport has usually been examined within too narrow a framework. It must be placed firmly within the context of the total industrial process. The demand for freight transport is directly influenced by the level, composition and geographical distribution of production and consumption activities. Freight flows are complex and so it is highly unlikely that a universal mode-choice model can ever be developed. Future research should, therefore, be directed towards developing partial models in response to specific needs of those involved in decision-taking in the freight sector. 相似文献