全文获取类型
收费全文 | 1588篇 |
免费 | 20篇 |
专业分类
公路运输 | 538篇 |
综合类 | 59篇 |
水路运输 | 518篇 |
铁路运输 | 53篇 |
综合运输 | 440篇 |
出版年
2023年 | 8篇 |
2022年 | 39篇 |
2021年 | 10篇 |
2020年 | 10篇 |
2019年 | 20篇 |
2018年 | 52篇 |
2017年 | 41篇 |
2016年 | 54篇 |
2015年 | 15篇 |
2014年 | 69篇 |
2013年 | 241篇 |
2012年 | 80篇 |
2011年 | 90篇 |
2010年 | 85篇 |
2009年 | 74篇 |
2008年 | 71篇 |
2007年 | 43篇 |
2006年 | 36篇 |
2005年 | 35篇 |
2004年 | 18篇 |
2003年 | 28篇 |
2002年 | 32篇 |
2001年 | 26篇 |
2000年 | 20篇 |
1999年 | 18篇 |
1998年 | 30篇 |
1997年 | 25篇 |
1996年 | 37篇 |
1995年 | 21篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 19篇 |
1991年 | 16篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 21篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 12篇 |
1973年 | 11篇 |
排序方式: 共有1608条查询结果,搜索用时 15 毫秒
151.
The establishment and implementation of a training programme requires a training needs assessment (TNA). Without this approach, more often than not, training programmes have failed to succeed and to make such an assessment the instructional designer, i.e. the person in charge for this work, needs to follow a methodology. Unlike the other industries, the port industry has neglected the use of these methodologies, which is shown by the lack of research work published in academic journals. With a view to fill the existing gap, the paper proposes a five-step TNA methodology to be used in the port industry and applies its first three steps to investigate the port training situation in the new European Union member states. To achieve this objective, the paper is structured in the following way: puts the research work into context; addresses the role of ports; presents a port TNA methodology; explains research methodology; addresses port training issues in the new European-member states; and presents conclusions and further comments. 相似文献
152.
Peter B. Marlow 《Maritime Policy and Management》1991,18(3):201-216
This paper concentrates on the shipping industry and considers the forms of fiscal and financial incentives which are used by different governments to promote or encourage investment in their shipping industry. The analysis reduces the various packages of investment incentives and loan arrangements to a common measurement—the net present value of the package—and uses this to draw international comparisons and rankings. The results are based on different values of rates of return in the shipping industry and under certain assumptions concerning the rate of inflation and the rate of discount. Differences in loan arrangements have also been incorporated. The particular results are valid only for the specified circumstances but the methodology is generally applicable. 相似文献
153.
Hydrographic cruises off northwest Africa: the Canary Current and the Cape Ghir region 总被引:3,自引:0,他引:3
J.L. Pelegrí A. Marrero-Díaz A. Ratsimandresy A. Antoranz J. Cisneros-Aguirre C. Gordo D. Grisolía A. Hernndez-Guerra I. Liz A. Martínez G. Parrilla P. Prez-Rodríguez A. Rodríguez-Santana P. Sangr 《Journal of Marine Systems》2005,54(1-4):39
We present hydrographic data for several sections located along the African coastline and off Cape Ghir, carried out at times of weak surface winds (October 1995 and September 1997). The main sections are near the continental slope, at mean distances between 100 and 150 km from the coastline. North of Cape Ghir (31°N) the geostrophic transport (referenced to 650 m) of North Atlantic Central Water through these sections is 3.7 and 2.0 Sv for 1995 and 1997, respectively. This confirms that a major fraction of the water transport by the Canary Current flows east, into the continental slope off northwest Africa, at latitudes above Cape Ghir. Most of this flow continues south past Cape Ghir, along the coast and probably through the eastern passages of the Canary Archipelago. A significant fraction, however, may escape through surface Ekman transport (0.3–0.5 Sv during the early fall season) and by offshore flow at Cape Ghir (1.1 Sv in September 1997, referenced to 650 m). Despite the weak winds the Cape Ghir filament was clearly visible, characterized by localized coastal upwelling associated to a cyclonic shallow structure and cold (and fresh) waters stretching offshore as a very shallow feature (50–100 m deep). The satellite images show that the surface temperature field is highly variable, in rapid response to the surface winds, always with a core region of relatively cold water and commonly with one or two associated eddies. Our results support the existence of two recirculation cells in the area: a horizontal one that connects the interior eastern boundary currents with the coastal region and a vertical one related to both wind-induced and filament upwelling. The data also show a salinity subsurface maximum at the root of the filament, linked to water inflow from northern latitudes, and a subsurface anticyclonic eddy over the Agadir canyon, likely related to the poleward slope undercurrent. 相似文献
154.
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
155.
一种用汽油燃烧系统模拟发动机台架催化剂热老化的方法 总被引:1,自引:0,他引:1
采用通用汽车公司的快速老化程序RAT-A,分别在FOCAS燃烧系统及发动机上对催化剂在老化前和老化后的性能进行对比试验。结果表明,FOCAS燃烧系统能够对催化剂进行和发动机类似的老化。与发动机台架试验相比,FOCAS系统有明显的优点,如严格地控制空燃比使其变化幅度很小、空燃比稳定运行的范围宽、活动部件少及易操作等。 相似文献
156.
The present procedures for processing arriving passengers at the Colombo International Airport cause inordinte waiting times. An alternate plan, which is based on state of the art customs procedures, and which can reduce waiting times significantly while maintaining a high level of enforcement, is proposed. The present and proposed procedures are analyzed and compared with respect to passenger waiting times, using deterministic queueing theory. An optimal inspection rate of passengers by the customs service is proposed taking into account the fraction of inspected passengers, the waiting time of passengers and the cost of customs processing. 相似文献
157.
俄罗斯铁路的微机联锁系统 总被引:2,自引:0,他引:2
C·C·普列斯尼亚克 《中国铁路》2003,(6):65-66
简要回顾俄罗斯铁路联锁系统的发展历史,对继电器成本进行了经济有效性比较,介绍俄罗斯铁路微机联锁系统的组成。 相似文献
158.
The Arabian Sea exhibits a complex pattern of biogeochemical and ecological dynamics, which vary both seasonally and spatially. These dynamics have been studied using a one-dimensional vertical hydrodynamic model coupled to a complex ecosystem model, simulating the annual cycle at three contrasting stations. These stations are characterised by seasonally upwelling, mixed-layer-deepening and a-seasonal oligotrophic conditions, respectively, and coincide with extensively measured stations on the two JGOFS ARABESQUE cruises in 1994. The model reproduces many spatial and temporal trends in production, biomass, physical and chemical properties, both qualitatively and quantitatively and so gives insight into the main mechanisms responsible for the biogeochemical and ecological complexity. Monsoonal systems are typified by classical food web dynamics, whilst intermonsoonal and oligotrophic systems are dominated by the microbial loop. The ecosystem model (ERSEM), developed for temperate regions, is found to be applicable to the Arabian Sea system with little reparameterisation. Differences in in-situ physical forcing are sufficient to recreate contrasting eutrophic and oligotrophic systems, although the lack of lateral terms are probably the greatest source of error in the model. Physics, nutrients, light and grazing are all shown to play a role in controlling production and community structure. Small-celled phytoplanktons are predicted to be dominant and sub-surface chlorophyll maxima are robust centers of production during intermonsoon periods. Analysis of carbon fluxes indicate that physically driven outgassing of CO2 predominates in monsoonal upwelling systems but ecological activity may significantly moderate CO2 outgassing in the Arabian Sea interior. 相似文献
159.
A.G. Thompson B.R. Davis 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1992,21(1):19-37
By the incorporation of frequency-shaping into the linear quadratic methods used in active suspension design it is possible to achieve improvements in both body frequency response and road-holding. The use of a PID filter for this purpose also leads to robustness of the system to disturbance forces. Zero steady-state deflections are achieved for applied body loads by the integral action with excellent attenuation of the transient response. The resulting system consists of a hydraulic actuator in parallel with a body spring of arbitrary stiffness and is optimal with equivalent full state feedback. 相似文献
160.
Vehicles stopping at signalized intersections were examined for the purpose of evaluating the validity of the common assumption of constant and uniform deceleration rates. The data set consisted of the first vehicles to stop upon the onset of the yellow signal interval with measurements of the initial approach speed, deceleration time, and deceleration distance. The deceleration rate may be computed using only two of the three measured values; thus the rate for each vehicle can be determined by three different equations. With nonuniform deceleration profiles, the equations will produce different values; and the degree of nonuniformity can be determined by comparing the differences in the computed deceleration rates. The analysis of the field observations indicated that 69 percent of the vehicles demonstrated deceleration profiles associated with nonuniform deceleration rates. Furthermore, the deceleration profile and the degree of nonuniformity were found to be a function of the initial approach speed. 相似文献