全文获取类型
收费全文 | 2946篇 |
免费 | 21篇 |
专业分类
公路运输 | 959篇 |
综合类 | 105篇 |
水路运输 | 936篇 |
铁路运输 | 89篇 |
综合运输 | 878篇 |
出版年
2023年 | 14篇 |
2022年 | 53篇 |
2021年 | 28篇 |
2020年 | 22篇 |
2019年 | 28篇 |
2018年 | 86篇 |
2017年 | 81篇 |
2016年 | 122篇 |
2015年 | 37篇 |
2014年 | 109篇 |
2013年 | 453篇 |
2012年 | 154篇 |
2011年 | 161篇 |
2010年 | 136篇 |
2009年 | 154篇 |
2008年 | 140篇 |
2007年 | 91篇 |
2006年 | 64篇 |
2005年 | 61篇 |
2004年 | 46篇 |
2003年 | 45篇 |
2002年 | 44篇 |
2001年 | 41篇 |
2000年 | 52篇 |
1999年 | 35篇 |
1998年 | 45篇 |
1997年 | 49篇 |
1996年 | 49篇 |
1995年 | 71篇 |
1994年 | 26篇 |
1993年 | 35篇 |
1992年 | 29篇 |
1991年 | 24篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 20篇 |
1987年 | 21篇 |
1986年 | 16篇 |
1985年 | 25篇 |
1984年 | 25篇 |
1983年 | 18篇 |
1982年 | 25篇 |
1981年 | 32篇 |
1980年 | 28篇 |
1979年 | 40篇 |
1978年 | 21篇 |
1977年 | 21篇 |
1976年 | 11篇 |
1975年 | 18篇 |
1974年 | 15篇 |
排序方式: 共有2967条查询结果,搜索用时 22 毫秒
701.
702.
M.J. Smith 《Transportation Research Part B: Methodological》1981,15(6):443-451
We consider a network with interactions and capacity constraints at each junction. We give conditions on the interactions and constraints which, if satisfied at each separate junction, ensure that any feasible assignment problem has an equilibrium solution. Two illustrative examples are provided; the first arises naturally and does not satisfy our conditions, while the second does satisfy our conditions but is somewhat unnatural. 相似文献
703.
Henk J. Van Zuylen Luis G. Willumsen 《Transportation Research Part B: Methodological》1980,14(3):281-293
For a large number of applications conventional methods for estimating an origin destination matrix become too expensive to use. Two models, based on information minimisation and entropy maximisation principles, have been developed by the authors to estimate an O-D matrix from traffic counts. The models assume knowledge of the paths followed by the vehicles over the network. The models then use the traffic counts to estimate the most likely O-D matrix consistent with the link volumes available and any prior information about the trip matrix. Both models can be used to update and improve a previous O-D matrix. An algorithm to find a solution to the model is then described. The models have been tested with artificial data and performed reasonably well. Further research is being carried out to validate the models with real data. 相似文献
704.
R. M. Stopford 《Maritime Policy and Management》2013,40(4):301-312
At the end of the eighties, fundamental changes took place in Polish shipping. Implementation of the market economy system was at first demonstrated in the introduction of the principles of self-dependence, self-government and self-financing of the shipping companies. Privatization performed a key role in the program of transformation of the centrally planned system into market oriented financially independent shipping organizations. The previous principle of the necessary participation of the home fleet in transporting domestic sea-borne trade has been mostly replaced by cross-trade. Many shipping services have left its basic ports in the country for a West European basis, securing alimentation of home and transit cargoes by feeder–service systems. Joint stock companies in shipping with substantial shares of foreign capital are welcomed, and the previously obligatory system of administrative methods of the state monopoly has been abolished. The principles of shipping policy represented in the past by Poland and also by UNCTAD in the 1960s have lost their impact and must be change and adapted to the new demands of the shipping markets. 相似文献
705.
Vanessa J. Maxwell John Supan Lisa C. Schiavinato Stephanie Showalter Granvil D. Treece 《Coastal management》2013,41(3):241-253
The goal of this study is to apply industrial park concepts to the development of aquaculture parks in public waters. The objectives are to identify the permitting process, relevant agencies, and legislation needed to facilitate development. Gulf of Mexico states are surveyed: private parks exist in Florida, but no public parks have developed yet; plans for parks exist in Mississippi, but lack of funding prevents development; no regulations prohibit parks in Alabama, although none currently exist; Texas regulations hinder development of parks; and an experimental park has been proposed in Louisiana, but regulatory gaps have delayed permit issuance. 相似文献
706.
Abstract Major air pollutants from maritime shipping operations are sulfur oxides, nitrogen oxides, and particulate matter emissions from combustion of fuel oil during cruise, berth, and start‐up modes. Sulfur oxides emissions are substantial from steamships burning high‐sulfur residual fuel oil, where shipping contributes 66 percent of the total sulfur dioxide emissions from transportation sources, and almost 3 percent of the total for Harris county, Texas. Nitrogen oxides emissions are significant during cruise conditions for both steamships and motor ships, while particulate emissions are substantial during start‐up and tube cleaning. Significant marine air pollutant emission sources are found in busy harbor areas such as the Houston Ship Channel. Offshore terminals for unloading large tankers may result in emissions of 10 to 20 tons of sulfur oxides daily per ship, and 3 to 5 tons of nitrogen oxides daily per ship during pumping operations. Trace‐metal constituents present in the oil may catalyze sulfur dioxide and nitrogen dioxide oxidation to their respective sulfate and nitrate aerosols in the humid Texas Gulf Coast atmospheres to aggravate photochemical air pollution problems once the air masses reach industrial and populated urban areas on land. Onshore sulfur dioxide and particulate‐matter emission controls may be necessary for some large ships in port to minimize potential impact on coastal zone air quality. 相似文献
707.
Using an information-theoretic approach to entropy modelling, expressions for the possible number of microstates are derived from the sets of choices available to households and firms in given location/transport planning situations. In planning applications, the urban space is usually subdivided into discrete zones, and various classes of householders and firms are grouped into separate activities. Nevertheless, the location sites within zones may vary considerably in accessibility, price and quality, and amenity v. cost trade-offs between location and travel many differ markedly between individuals within the same activity group. The inclusion of such variations within a random utility framework is demonstrated to be equivalent to maximizing entropy with the microstates disaggregated to the level where these variations occur. Using constraints based on spatial conditions, observed behaviour and planning policy, entropy maximization is used to determine the most probable macrostate according to each choice set specification. The resulting distributions are compared and their revelance discussed. 相似文献
708.
Photis M. Panayides 《Maritime Policy and Management》2013,40(2):123-140
Ship management has been characterized by strong competition that resulted in structural changes in the industry, with the bigger companies merging or acquiring smaller ones in an effort to remain competitive. Competitiveness, however, may also be attained through the formulation and implementation of competitive business strategies that will improve performance. The aim of this paper has been to empirically examine the competitive strategy-performance relationship in the context of ship management companies. The findings suggest that there is a positive relationship between pursuing competitive strategies and company performance in ship management. Companies that apply competitive strategies are more likely to be high performers. The strongest influences on performance seem to be achieving economies of scale, differentiation (in particular through a wider range of services offered) and market-focus and competitor-analysis. It is suggested that high performers are more likely to pursue a combination of the generic strategies rather than pursuing one of the generic strategies in isolation. 相似文献
709.
Deepati Anil Kumar;Pankaj Biswas;Sujoy Tikader;M. M. Mahapatra;N. R. Mandal 《船舶与海洋工程学报》2013,12(4):493-499
Most of the investigations regarding friction stir welding(FSW)of aluminum alloy plates have been limited to about 5 to 6mm thick plates.In prior work conducted the various aspects concerning the process parameters and the FSW tool geometry were studied utilizing friction stir welding of 12 mm thick commercial grade aluminum alloy.Two different simple-tomanufacture tool geometries were used.The effect of varying welding parameters and dwell time of FSW tool on mechanical properties and weld quality was examined.It was observed that in order to achieve a defect free welding on such thick aluminum alloy plates,tool having trapezoidal pin geometry was suitable.Adequate tensile strength and ductility can be achieved utilizing a combination of high tool rotational speed of about 2000 r/min and low speed of welding around 28 mm/min.At very low and high dwell time the ductility of welded joints are reduced significantly. 相似文献
710.
X. L. Cui H. G. Yang Q. Zhang H. Ouyang M. H. Zhu 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2016,54(3):353-369
In Chinese metro lines, rail corrugation on both tangential and tight curved tracks with Cologne-egg type fasteners is very severe. Based on the viewpoint of friction-induced vibration causing rail corrugation, the rail corrugation on a tangential track with Cologne-egg type fasteners is studied in this paper. A vibration model of an elastic multiple-wheelset-track system with Cologne-egg type fasteners is established. Both the complex eigenvalue analysis and the transient dynamic analysis are performed to study the stability and the dynamic performance of the wheelset-track system. The simulation results show that a low rail support stiffness value is responsible for rail corrugation on the tangential track. When the Cologne-egg fasteners characterised by a lower stiffness value are replaced with the DTVI2 fasteners characterised by a higher stiffness value, rail corrugation disappears. However, rail corrugation on tight curved tracks cannot be suppressed using the same replacement. The above conclusions are consistent with the corrugation occurrences in actual metro tracks. 相似文献