全文获取类型
收费全文 | 201篇 |
免费 | 7篇 |
专业分类
公路运输 | 32篇 |
综合类 | 5篇 |
水路运输 | 65篇 |
铁路运输 | 5篇 |
综合运输 | 101篇 |
出版年
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 13篇 |
2017年 | 9篇 |
2016年 | 10篇 |
2015年 | 9篇 |
2014年 | 2篇 |
2013年 | 47篇 |
2012年 | 13篇 |
2011年 | 11篇 |
2010年 | 12篇 |
2009年 | 13篇 |
2008年 | 9篇 |
2007年 | 6篇 |
2006年 | 5篇 |
2005年 | 4篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 2篇 |
2001年 | 2篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1991年 | 2篇 |
1985年 | 2篇 |
排序方式: 共有208条查询结果,搜索用时 15 毫秒
21.
Seasonal changes in the abundance and biomass of cyanobacteria (Synechococcus and Prochlorococcus) and picoeukaryotes were studied by flow cytometry in the upper layers of the central Cantabrian Sea continental shelf, from April 2002 to April 2006. The study area displayed the typical hydrographic conditions of temperate coastal zones. A marked seasonality of the relative contribution of prokaryotes and eukaryotes was found. While cyanobacteria were generally more abundant for most of the year (up to 2.4 105 cells mL− 1), picoeukaryotes dominated the community (up to 104 cells mL− 1) from February to May. The disappearance of Prochlorococcus from spring through summer is likely related to shifts in the prevailing current regime. The maximum total abundance of picophytoplankton was consistently found in late summer–early autumn. Mean photic-layer picoplanktonic chlorophyll a ranged from 0.06 to 0.53 µg L− 1 with a relatively high mean contribution to total values (33 ± 2% SE), showing maxima around autumn and minima in spring. Biomass (range 0.58–40.16 mg C m− 3) was generally dominated by picoeukaryotes (mean ± SE, 4.28 ± 0.27 mg C m− 3) with an average contribution of cyanobacteria of 30 ± 2%. Different seasonality of pigment and biomass values resulted in a clear temporal pattern of picophytoplanktonic carbon to chlorophyll a ratio, which ranged from 10 (winter) to 140 (summer). This study highlights the important contribution of picoplanktonic chlorophyll a and carbon biomass in this coastal ecosystem. 相似文献
22.
Trip generation of vulnerable populations in three Canadian cities: a spatial ordered probit approach 总被引:1,自引:0,他引:1
Matthew J. Roorda Antonio Páez Catherine Morency Ruben Mercado Steven Farber 《Transportation》2010,37(3):525-548
This paper provides an analysis of trip generation of three vulnerable groups: single-parent families, low income households,
and the elderly. It compares the mobility of these groups to that of the general population in three Canadian urban areas
of Hamilton, Montreal and Toronto, based on data from large-sample metropolitan transport surveys. An ordered probit model
with spatially expanded coefficients is used for the analysis. Spatial expansion shows that there are spatial mobility trends
for elderly populations and low-income populations even after socio-economic attributes are accounted for. Such spatial differences
are not generally found for single parent families. This novel spatial analysis provides clues as to where vulnerable populations
may experience greater degrees of social exclusion. It provides information to help prioritize transportation infrastructure
projects or other social programs to take into account the needs of vulnerable populations with the lowest levels of mobility. 相似文献
23.
Using current meters and systematically repeated vessel mounted ADCP data legs, we describe the role of the semidiurnal and diurnal constituents in the tidal currents and investigate the mesoscale variability of the M2 tidal currents field along three cross-shelf legs over the Galician shelf. We found that the estimated values of the semi-major axes of the main semidiurnal tidal constituents are closely related to those obtained in previous research and that the tidal currents are predominantly semidiurnal. Amplitudes of the M2 and S2 semi-major axes constituents are comparable, and important fortnightly variability should thus be expected in the amplitude of the semidiurnal tidal currents. Vertical profiles of the semi-major axes of the main tidal constituents reveal that, in the absence of stratification, and far from the bottom frictional effects, the tidal currents are mostly barotropic. Over the slope, the tidal ellipses tilt from a north–south orientation toward the northeast–southwest direction and, as we go further into the shelf, their amplitude is increased, a feature that is reasonably explained by the transition from the dynamics of a Poincaré wave offshore to the dynamics of a northward alongshore propagating Kelvin wave over the shelf. The Ría de Vigo exerts a notable influence over the tidal currents, acting as an extension of the shelf and introducing a meridional variation in the orientation of the ellipses from the alongshore direction in the southern straight coast toward the northeast–southwest direction at the latitude of the Rías. Finally, the spatial fitting methods we tried have proved to be successful in VMADCP data detiding in this region. 相似文献
24.
Sebastián Raveau Juan Carlos Muñoz 《Transportation Research Part A: Policy and Practice》2011,45(2):138-147
This article presents a route choice model for public transit networks that incorporates variables related to network topology, complementing those found in traditional models based on service levels (travel time, cost, transfers, etc.) and users’ socioeconomic and demographic characteristics (income level, trip purpose, etc.). The topological variables represent concepts such as the directness of the chosen route and user knowledge of the network. For both of these factors, the necessary data is endogenous to the modelling process and can be quantified without the need for information-gathering beyond what is normally required for building route choice models. Other novel variables in the proposed formulation capture notions of user comfort such as vehicle occupancy rates and certain physical characteristics of network stations. We conclude that these new variables significantly improve the explanatory and predictive ability of existing route choice specifications. 相似文献
25.
Fernando Marín Martínez Isabel García Gutiérrez Alberto Ortiz Oliveira Luis Miguel Arreche Bedia 《运输规划与技术》2013,36(4):261-284
Freight transfer operations are critical in combined transport networks. In this paper a simulation model and modelling approach to the transfer of cargo between trains at rail terminals is presented. The model is used to study the Port-Bou terminal, the main intermodal terminal at the Spanish-French frontier. Four different gantry crane operation modes to interchange containers between trains are evaluated. These operation rules are tested in several scenarios to examine the critical factors of the system and the best operation rule for each situation. Latest generation software is used to develop the model that incorporates modular programming and enhanced graphic systems for output representation. It allows a dynamic display of the simulated system and, likewise, the possibility of developing modules that can be reused in other studies. The research shows how simulation can be a useful planning tool in the rail transportation context. 相似文献
26.
Paula C. Pardo Marcos Vázquez-Rodríguez Fiz F. Pérez Aida F. Rios 《Journal of Marine Systems》2011,84(3-4):67-77
This work estimates new regionalized empirical parameterizations for preformed alkalinity (ATo) and the CO2 air–sea disequilibrium (?Cdis). Both are key terms for the computation of anthropogenic CO2 in the back-calculation methods. Data from the subsurface layer (75–180 m depth range) covering an area from North to South and from 19°E to 67.5°W (Pacific and Indian oceans) were taken from GLODAP (The Global Ocean Data Analysis Project) database. The subsurface layer is proved as a reliable reference for representing the main characteristics of the different water masses of the oceans. Besides, handing data from the two ocean basins altogether makes the new parameterizations of ATo and ?Cdis to be more globally consistent. Nevertheless, each ocean basin, at least in some regions, has different oceanographic characteristics based on its proper dynamical processes and water masses formation. In order to maintain each ocean basin ‘identity’ the whole domain was divided in six different regions (two of them sharing waters from Pacific and Indian oceans) and parameterizations in each region for both terms were obtained. Previously, data were transformed into a grid of 4°lat. × 5°lon. and the results obtained from the parameterizations were visualized and compare with pCO2 climatologies. From the comparisons with previous ?Cdis estimations good results are obtained showing the reliability and robustness of the new regionalized empiric parameterizations. 相似文献
27.
Gábor Orosz 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2016,54(8):1147-1176
Connected vehicle systems (CVS) are considered in this paper where vehicles exchange information using wireless vehicle-to-vehicle (V2V) communication. The concept of connected cruise control (CCC) is established that allows control design at the level of individual vehicles while exploiting V2V connectivity. Due to its high level of modularity the proposed design can be applied to large heterogeneous traffic systems. The dynamics of a simple CVS is analysed in detail while taking into account nonlinearities in the vehicle dynamics as well as in the controller. Time delays that arise due to intermittencies and packet drops in the communication channels are also incorporated. The results are summarised using stability charts which allow one to select control gains to maintain stability and ensure disturbance attenuation when the delay is below a critical value. 相似文献
28.
A probabilistic particle tracking model is used to simulate the oil dispersion after the Prestige wreckage. This oil spill constitutes a suitable benchmark to analyze the capabilities of a probabilistic model, since the time elapsed from wreckage to oil landing (12 days) is much longer than the reliability time associated with forecast winds, usually on the order of 3–4 days. The particle model can be run in two different modes: real time mode (when existing reliable wind fields for the event under scope) and in probabilistic mode (in absence of reliable wind fields but with historical fields corresponding to a similar period). The validity of the particle model is first evaluated in a hindcast way, running the Prestige case with the wind fields corresponding to the period November 19 to November 30, 2002, which were not available at the moment of the wreckage. Calculations show the accuracy of the model to provide the right impact point and timing. The probabilistic model is then used to simulate the same event by means of historical data. The region where the oil landed is shown to be the area with the highest probability to be impacted. 相似文献
29.
Jens C. O. Nielsen Roger Lund n Anders Johansson Tore Vernersson 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2003,40(1):3-54
Summary High-frequency train-track interaction and mechanisms of wheel/rail wear that is non-uniform in magnitude around/along the running surface are surveyed. Causes, consequences and suggested remedies to relieve the problems are discussed for three types of irregular wheel/rail wear: (1) short-pitch rail corrugation on tangent tracks and large radius curves, (2) wheel corrugation as caused by tread braking, and (3) wheel polygonalisation. The state-of-the-art in modelling of dynamic train-track interaction in conjunction with prediction of irregular wear is reviewed. 相似文献
30.