全文获取类型
收费全文 | 1317篇 |
免费 | 4篇 |
专业分类
公路运输 | 346篇 |
综合类 | 36篇 |
水路运输 | 452篇 |
铁路运输 | 39篇 |
综合运输 | 448篇 |
出版年
2022年 | 5篇 |
2021年 | 10篇 |
2020年 | 12篇 |
2019年 | 8篇 |
2018年 | 27篇 |
2017年 | 26篇 |
2016年 | 43篇 |
2015年 | 16篇 |
2014年 | 26篇 |
2013年 | 215篇 |
2012年 | 63篇 |
2011年 | 66篇 |
2010年 | 54篇 |
2009年 | 55篇 |
2008年 | 63篇 |
2007年 | 47篇 |
2006年 | 27篇 |
2005年 | 29篇 |
2004年 | 24篇 |
2003年 | 26篇 |
2002年 | 20篇 |
2001年 | 28篇 |
2000年 | 18篇 |
1999年 | 22篇 |
1998年 | 41篇 |
1997年 | 18篇 |
1996年 | 22篇 |
1995年 | 22篇 |
1994年 | 16篇 |
1993年 | 18篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 8篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 16篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 17篇 |
1974年 | 10篇 |
1973年 | 9篇 |
排序方式: 共有1321条查询结果,搜索用时 78 毫秒
181.
B. Blanco A. Alonso L. Kari N. Gil-Negrete J. G. Giménez 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2018,56(4):529-552
The finite length nature of rail-pad supports is characterised by a Timoshenko beam element formulation over an elastic foundation, giving rise to the distributed support element. The new element is integrated into a vertical track model, which is solved in frequency and time domain. The developed formulation is obtained by solving the governing equations of a Timoshenko beam for this particular case. The interaction between sleeper and rail via the elastic connection is considered in an analytical, compact and efficient way. The modelling technique results in realistic amplitudes of the ‘pinned–pinned’ vibration mode and, additionally, it leads to a smooth evolution of the contact force temporal response and to reduced amplitudes of the rail vertical oscillation, as compared to the results from concentrated support models. Simulations are performed for both parametric and sinusoidal roughness excitation. The model of support proposed here is compared with a previous finite length model developed by other authors, coming to the conclusion that the proposed model gives accurate results at a reduced computational cost. 相似文献
182.
硬岩隧道掘进机的性能很大程度上取决于其切削刀具的磨损情况。刀具的磨损会降低掘进速度,进而导致掘进时间延长、项目成本增加。通常在隧道项目的规划阶段使用预测模型来进行磨损预测,而常规的磨损试验对磨损系统的考虑还不够准确,并没有考虑到刀具/土体的相互作用、周围介质(水、膨润土)以及掘进过程中的荷载等因素。针对该问题,专门设计了一个水平放置的磨损试验设备。本文介绍了该试验方法,研究并讨论了磨损系统相关因素对磨损率的影响。结果表明,该设备可模拟真实的掘进过程,很好地解决了上述问题,达到了高效、准确预测磨损的效果。 相似文献
183.
On November 30, 2006, USS Boone (FFG 28) lost all steering control in the Mediterranean Sea due to a lost rudder. Within hours of the casualty, numerous US Navy and contractor activities sprung into action to coordinate and complete an emergent voyage repair to return USS Boone to service to support the Global War on Terrorism. The Navy faced a large hurdle to identify and transport a replacement rudder to Rota, Spain, and prepare and carry out an extremely complex repair procedure. Pearl Harbor Naval Shipyard personnel removed the replacement rudder from USS Crommelin (FFG 37) in Pearl Harbor Naval Shipyard and transported the rudder to Rota, Spain. The Navy's Supervisor of Salvage and Diving developed the repair procedure and coordinated the repair operation, which involved over 30 US Navy and contractor divers. The repair team completed the rudder replacement on December 28, 2006 and returned USS Boone to underway operations. 相似文献
184.
185.
Athanasios A. Pallis 《WMU Journal of Maritime Affairs》2007,6(1):3-20
Throughout Europe, a number of maritime interests have re-targeted their lobbying structures and strategies aiming to influence
the development of the maritime related European Union (EU) policies. The paper examines these maritime interests’ mobilisation
in the making of the Common EU Maritime Transport Policy (CMTP). First, it provides a review of the role of these interest
groups and the implications of the observed collective interests’ representation. Then, with the contribution a data-set of
replies to a questionnaire distributed to all the interest groups that are involved in EU maritime affairs, the paper analyses
the variety of interest groups representing the maritime sector in EU affairs. The focus is on the structures (i.e. membership
numbers and types, location, internal structures, budget) and the lobbying practices of the 37 identified EU level maritime
related organisations. The paper also presents an evaluation of the most positive and most negative parameters of the ‘EU
environment’ and the ‘economic environment’ that assist, or undermine, the governability cohesiveness of this collective action.
This study provides information on whether and under what conditions maritime interests are able to form comprehensive EU-level
organisations capable of representing their members and their interests in the EU policy making process 相似文献
186.
V. Pracny M. Meywerk A. Lion 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2007,45(1):1-14
The method of numerical multi-body simulation is an often used and well-understood development tool in the automotive industry. In order to reproduce the ride comfort or handling behaviour of vehicles, mathematical models have to be built up. To achieve accurate simulation results, highly detailed component models are required. However, the formulation of appropriate physically-based model equations of complex automotive components (e.g. air springs, shock absorbers, rubber bearings, tyres, etc.) can be very difficult. To handle this, empirical modelling methods have been developed. Simple algebraic equations are used to describe complex system behaviour. This simplification is very effective, although it largely ignores the natural laws of mechanics and thermodynamics but is still capable to predict the component response. This article illustrates how to take advantage of this approach in numerical simulations. We describe the development of a hybrid automotive shock absorber model based on both spline and neural network (NN) approaches. By combining these different approaches, an accurate model is achieved without loss of variability. Non-isothermal laboratory force-displacement measurements of an automotive shock absorber are being used to estimate the parameters of the NN. As shown, the model replicates the measured data with sufficient accuracy, especially the hysteresis. Finally, we present a set of quarter-car simulations with a built-in hybrid NN shock absorber. 相似文献
187.
Static and Dynamic Instabilities of Bogie Railway Vehicles with Linkage Steered Wheelsets 总被引:3,自引:0,他引:3
A.H. Wickens 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1996,26(1):1-16
The root loci of a type of bogie railway vehicle with linkage steered wheelsets are discussed and contrasted with those of conventional configurations. Approximate solutions of the equations of motion are used to derive stability criteria associated with the various modes of static and dynamic instability that are identified. The physical origin of each form of instability is discussed. It is shown that, in addition to the more common forms of dynamic instability arising from the joint action of creep, conicity and inertia, other forms of static and oscillatory instability are the result of structural asymmetry and wheelset articulation. 相似文献
188.
A.Д.KOHЮXOB 《铁道机车车辆工人》2002,(5):22-26
1 货车质量 俄罗斯运用敞车的载重量为68~70 t,车辆自重为22 t,轴重为22.5 t,车辆毛重为90 t,载重量与车辆自重比为3.09~3.18.而美国批量生产的敞车载重量为106~110 t,自重为19~20 t,轴重为32.5 t,车辆毛重130 t,载重量与自重之比为5.5~5.65(表1). 相似文献
189.
R. Pastres C. Solidoro S. Ciavatta A. Petrizzo G. Cossarini 《Journal of Marine Systems》2004,51(1-4):179
The paper aims at investigating the trends of the concentrations of dissolved inorganic nitrogen (DIN) and phosphorous in the Lagoon of Venice, Italy, in the last 35 years. The trend analysis of ammonia nitrogen, nitrate nitrogen and reactive phosphorus (RP) yielded rather different results. The decrease in ammonia nitrogen concentration, in particular, in the basin influenced by severe industrial discharges, is accurately described by a negative exponential model. The nitrate concentration did not show significant interannual trends, while wide seasonal variations have been detected. Reactive phosphorus concentration increased until the end of the 1970s at the stations close to the industrial area as well as in those influenced by river discharges and by sewages of the city of Venice. The sudden decrease that followed was most likely related with environmental policies, namely the improvement of wastewater purification treatments and the regulation of phosphorus use in detergents. 相似文献
190.
Ships of opportunity have been used to investigate ocean–atmosphere CO2 fluxes in the English Channel and Southern Bight of the North Sea. Continuous underway measurements of the fugacity of seawater carbon dioxide (fCO2sw), chlorophyll, temperature and salinity have been performed along 26 transects during the spring and autumn periods. The spatial fCO2sw distribution along the Channel and Southern Bight is modulated by the photosynthetic activity, temperature changes and water mixing between inputs from the North Atlantic Ocean and riverine discharges. The seasonal variability of fCO2sw is assessed and discussed in terms of the biology and temperature effects, these having similar impacts. The variation of fCO2sw shows similar interannual patterns, with lower values in spring. The annual average of air–sea CO2 fluxes places the English Channel as neutral area of CO2 uptake. The spring and autumn data allow differentiating between distal and proximal continental areas. The Southern Bight shows a tendency towards net CO2 uptake on the distal continental shelf, whereas the Scheldt and Thames Plumes show a CO2 source behaviour on the proximal continental shelves. 相似文献