首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1279篇
  免费   6篇
公路运输   592篇
综合类   113篇
水路运输   272篇
铁路运输   64篇
综合运输   244篇
  2023年   21篇
  2022年   37篇
  2021年   13篇
  2020年   8篇
  2019年   4篇
  2018年   78篇
  2017年   71篇
  2016年   155篇
  2015年   12篇
  2014年   19篇
  2013年   31篇
  2012年   89篇
  2011年   187篇
  2010年   160篇
  2009年   54篇
  2008年   112篇
  2007年   72篇
  2006年   22篇
  2005年   32篇
  2004年   18篇
  2003年   25篇
  2002年   9篇
  2001年   10篇
  2000年   14篇
  1999年   9篇
  1998年   7篇
  1997年   2篇
  1996年   4篇
  1995年   5篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1989年   1篇
  1983年   1篇
排序方式: 共有1285条查询结果,搜索用时 453 毫秒
401.
The hybridization of the conventional thermal vehicles nowadays constitutes a paramount importance for car manufacturers, facing the challenge of minimizing the consumption of the road transport. Although hybrid power train technologies did not converge towards a single solution, series/parallel power trains with power-split electromechanical transmissions prove to be the most promising hybrid technology. In fact, these power trains show maximum power train overall efficiency and maximum fuel reduction in almost all driving conditions compared to the conventional and other hybrid power trains. This paper addresses the model and design of the electro-mechanical configuration of one of the most effective HEV power trains: case study of the 2nd generation Prius. It presents the simulation work of the overall operation of the Toyota Hybrid System (THS-II) of the Prius, and explores not only its power-split eCVT innovative transmission system but also its overall supervision controller for energy management. The kinematic and dynamic behaviors of the THS-II power train are explained based on the power-split aspect of its transmission through a planetary gear train. Then, the possible regular driving functionalities that result from its eCVT operation and the energy flow within its power train are outlined. A feed-forward dynamic model of the studied power train is next proposed, supervised by a rule-based engineering intuition controller. The energy consumption of the THS-II proposed model has been validated by comparing simulation results to published results on European, American and Japanese regulatory driving cycles.  相似文献   
402.
Behaviour of the Normal Contact Force Under Multiple Wheel/Rail Interaction   总被引:1,自引:0,他引:1  
The wheel/rail contact forces are calculated in the frequency domain using a track model with multiple wheels on the rail. The effects of the wave reflections between the wheels on the contact force are studied. Different pad stiffnesses are used in the calculations to investigate the influence on the contact force. It is shown that the contact force can have up to four main peaks in the frequency region 550-1200?Hz due to the wave reflections between the wheels, so that the wavelengths of short pitch corrugation can be expected to be associated with multiple frequencies. As a conclusion, it is recommended that in a model for predicting short pitch corrugation the effects of multiple wheel/rail interactions need to be included.  相似文献   
403.
通过华蓥山隧道洞身结构有限元分析及衬砌结构设计介绍,阐述了隧道越不良地质(断层、有害气体、涌水、高地应力等)区段的处治。  相似文献   
404.
Atmospheric molar fraction of CO2 (xCO2atm) measurements obtained on board of ships of opportunity are used to parameterize the seasonal cycle of atmospheric xCO2 (xCO2atm) in three regions of the eastern North Atlantic (Galician and French offshore and Bay of Biscay). Three selection criteria are established to eliminate spurious values and identify xCO2atm data representative of atmospheric background values. The filtered data set is fitted to seasonal curve, consisting of an annual trend plus a seasonal cycle. Although the fitted curves are consistent with the seasonal evolution of xCO2atm data series from land meteorological stations, only ship-board measurements can report the presence of winter xCO2atm minimum on Bay of Biscay. Weekly air–sea CO2 flux differences (mmol C·m− 2 day− 1) produced by the several options of xCO2atm usually used (ship-board measurements, data from land meteorological stations and annually averaged values) were calculated in Bay of Biscay throughout 2003. Flux error using fitted seasonal curve relative to on board measurements was minimal, whereas land stations and annual means yielded random (− 0.2 ± 0.3 mmol C·m− 2·day− 1) and systematic (− 0.1 ± 0.4 mmol C·m− 2 day− 1), respectively. The effect of different available sources of sea level pressure, wind speed and transfer velocity were also evaluated. Wind speed and transfer velocity parameters are found as the most critical choice in the estimate of CO2 fluxes reaching a flux uncertainty of 7 mmol C·m− 2·day− 1 during springtime. The atmospheric pressure shows a notable relative effect during summertime although its influence is quantitatively slight on annual scale (0.3 ± 0.2 mmol C·m− 2·day− 1). All results confirms the role of the Bay of Biscay as CO2 sink for the 2003 with an annual mean CO2 flux around − 5 ± 5 mmol C m− 2 day− 1.  相似文献   
405.
Nowadays, bulbous bow forms have become a common design feature in most conventional ship designs. The design of a bulbous bow is usually attempted with the use of certain form parameters that are imposed using the designer's experience or regression values that provide the optimum parameters based on experimental tests or computational fluid dynamics (CFD) calculations. In this article, the geometric modelling of a bulbous bow form that complies with a series of parameters is presented. First, a wire model was constructed with cubic B-spline curves that hold certain form parameters that the designer wants to impose. Second, a B-spline surface that fits these splines was mathematically constructed. A review of the influence of the design parameters used on the bulbous bow properties was made. This method could be used prior to numerical optimization of a bulbous bow because different variations of the design can be easily generated. These variations can be tested numerically using CFD software. A practical application example of the method is shown.  相似文献   
406.
CHARACTERISTICSOFACTIONPOTENTIALANDTHEIRUNDERLYINGOUTWARDCURRENTSINMAMMALIANTASTERECEPTORCELLSChenYushe;X.Sun,M.S.Herness(Ind...  相似文献   
407.
铝合金直流点焊焊接参数对焊点性胡的影响   总被引:3,自引:0,他引:3  
在实验的基础上,就5982铝合金板(1mm+1mm)直流点焊焊接参数对焊点性能的影响进行了分析研究。结果表明,焊接电流在一定范围内与焊点接头的拉剪载荷成正比,通电时间与电极压力都存在一个最佳范围,而加压方式对接头性能影响并不明显。  相似文献   
408.
A model for the numerical simulation of vehicle/track interaction and stick-slip vibration is presented. A finite element model is developed to calculate vertical contact forces. These forces are then coupled through the contact patch into a non-linear time-domain model by which the stick-slip vibration behaviour of a wheel-rail system is analysed. The investigation suggests that stick-slip vibration may occur if a vehicle which has a maligned or an initial 'wind-up' wheeiset meets a vertical irregularity or contaminants on the track.  相似文献   
409.
根据IMO等国际组织及我国法律法规,结合西江后沥至贝水河段通航环境和自然条件,分析历史水上交通事故原因及航道发展前景,提出该河段实施船舶定线制的设想并进行评估。  相似文献   
410.
舰船全寿期各配置视图,既是全寿命优化设计的结果,又是实现舰船预期功能并保证这些功能有效实施的关键技术.为保证配置的唯一性和处理方便,配置是用各主要编码来表达的.本文所提出的各配置之间的算法乃是实现配置自动处理的基础.舰船全寿期配置管理是实现各配置视图生成、相互映射、配置更改及其状态跟踪技术的综合应用,亦是保证舰船质量和有效使用及全寿期信息共享的核心.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号