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   9514篇
  免费   136篇
公路运输   2160篇
综合类   971篇
水路运输   2867篇
铁路运输   1215篇
综合运输   2437篇
  2023年   48篇
  2022年   131篇
  2021年   97篇
  2020年   71篇
  2019年   96篇
  2018年   210篇
  2017年   125篇
  2016年   173篇
  2015年   126篇
  2014年   300篇
  2013年   1303篇
  2012年   430篇
  2011年   497篇
  2010年   387篇
  2009年   516篇
  2008年   424篇
  2007年   405篇
  2006年   371篇
  2005年   368篇
  2004年   324篇
  2003年   208篇
  2002年   191篇
  2001年   179篇
  2000年   187篇
  1999年   117篇
  1998年   145篇
  1997年   120篇
  1996年   154篇
  1995年   156篇
  1994年   93篇
  1993年   195篇
  1992年   160篇
  1991年   84篇
  1990年   85篇
  1989年   58篇
  1988年   75篇
  1987年   65篇
  1986年   59篇
  1985年   78篇
  1984年   73篇
  1983年   73篇
  1982年   73篇
  1981年   95篇
  1980年   68篇
  1979年   91篇
  1978年   56篇
  1977年   69篇
  1976年   53篇
  1975年   65篇
  1974年   50篇
排序方式: 共有9650条查询结果,搜索用时 125 毫秒
911.
Straddle carriers represent a critical resource in the handling of containers within a container terminal. It is essential that they are deployed in an as efficient manner as possible. The research presented in this paper is motivated by the need to critically evaluate job assignment rules for straddle carriers that operate in a multiple straddle environment. This is achieved by developing a discrete event simulation model using industrial simulation software to model a container terminal located in Melbourne, Australia. The model accounts for variables such as the number of straddle carriers needed, the speed of straddle carriers, the arrival rate of trucks, and the job assignment rule. A principal finding of the study is that increasing the number of straddles in the present set‐up from 6 to 7 has a negligible effect on daily throughput. However, an increase in the number of straddles to 7 is expected to have a profound effect on reducing the average waiting time of trucks within the terminal from over 16 minutes to under 9 minutes, a decrease of 46.5%. However, a further increase in the number of straddles results in no further increase in daily throughput. It was observed that the throughput of the terminal is very sensitive to the speeds at which straddles travel. The management of the terminal has proposed a new heuristic job assignment rule for straddles, because the present rule does not assign the jobs to straddles closest to the truck requesting to load or unload a container. As a result a new heuristic job assignment rule was tested. The simulation results revealed that both the old and new rules performed equally well using performance indicators such as average container flow time, daily throughput, average waiting time of jobs, number of jobs in the queue, and straddle utilisation. Therefore, the new rule will not improve these performance measures if implemented  相似文献   
912.
This article discusses the use of continuous autoregressive models to describe the behavior of traffic indices. From discretely sampled data, second-order differential equation models are constructed to represent dynamic traffic fluctuations as the response of a linear system to a stochastic forcing function. The results are compared to the more common M/G/∞ queueing model approach, and the analysis is demonstrated on time series of aircraft concentration in thirty-one enroute air traffic control sectors.  相似文献   
913.
914.
今天,我将冒着一定的风险来预言一些在下一世纪开始阶段,会出现在航运业内的某些事物的形态.很显然,我会着重谈一些IMO活动范围以内的事.  相似文献   
915.
该文介绍了有关公路桥梁易产生沉降的软土路基点的路基路面的施工技术研究。通过对沉降段结构施工各个环节的有效控制,保证施工质量,大大地降低路桥沉降段路基路面产生不均匀沉降的发生概率,从而避免路桥沉降段产生桥头跳车现象的产生,提高公路的使用性能,保障司机及乘客的生命及财产安全。其成果可供同行借鉴。  相似文献   
916.
Suction anchors are subjected to inclined, quasi-horizontal or quasi-vertical loadings. The type of the structure and depth of water govern the inclination of the load. Under this load condition, suction anchor experiences a combination of horizontal and vertical translations, and rotation. Therefore the soil's reaction to this load condition can be idealized as horizontal and vertical loadings, together with a moment. The magnitude and combination of the reactions depend on the load inclination, soil property and the point at which the load is applied. The behavior of the suction anchor subjected to the combined V–H-M loading is elaborated in this paper. This is to observe the effects of soil properties on the failure mechanism and ultimate capacity of the foundation. This was achieved by applying the pure horizontal and vertical displacements, and rotation and their combinations to the foundation, on V–H, V-M and H-M spaces and the yield-locus created for each space. The general purpose finite element program DIANA was used for this study. Non-linear analysis was conducted using a simplified elastic-perfectly-plastic model with Von-Mises yield criterion for saturated and consolidated clay.  相似文献   
917.
就地冷再生技术具有施工便捷、污染小、旧料回收利用率高、节约成本等优势,在公路养护中得到了利用.以S49新扬高速为例,从适用条件、混合料设计、路用性能验证以及社会经济效益等方面,对就地冷再生技术进行系统研究,结果表明就地冷再生技术在高速公路养护工程中应用效果理想,可进行推广运用.  相似文献   
918.
The increasing number of electronic control units (ECUs) inside a vehicle implies the need to develop and deploy on board robust, low latency and low complex telecommunication systems. In this respect, power line communications (PLC) is an attractive solution. The benefits provided by the introduction of power line communications in the in-car environment are multiple and they are related to the possibility of exploiting the existing and capillary wiring infrastructure to simplify the design of the in-vehicle data network (IVN) and, more importantly, to save weight and cost of the wiring harness. In this paper, we deal with the analysis of the performance achievable by applying innovative advanced modulation techniques to in-car measured power line channels, i.e., multicarrier (MC) and impulsive ultra wideband (I-UWB) modulation. We show that for low speed command and control applications, I-UWB is suitable since it requires lower power and lower computational efforts w.r.t. MC systems. Furthermore, we study the design of the optimal transmitted pulse to further improve the performance of I-UWB.  相似文献   
919.
Extensive usage of automobiles has certain disadvantages and one of them is its negative effect on environment. Carbon dioxide (CO2), carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOx), sulphur dioxide (SO2) and particulate matter (PM) come out as harmful products during incomplete combustion from internal combustion (IC) engines. As these substances affect human health, regulatory bodies impose increasingly stringent restrictions on the level of emissions coming out from IC engines. This trend suggests the urgent need for the investigation of all aspects relevant to emissions. It is required to modify existing engine technologies and to develop a better after-treatment system to achieve the upcoming emission norms. Diesel engines are generally preferred over gasoline engines due to their undisputed benefit of fuel economy and higher torque output. However, diesel engines produce higher emissions, particularly NOx and PM. Aftertreatment systems are costly and occupy more space, hence, in-cylinder solutions are preferred in reducing emissions. Exhaust gas recirculation (EGR) technology has been utilized previously to reduce NOx. Though it is quite successful for small engines, problem persists with large bore engines and with high rate of EGR. EGR helps in reducing NOx, but increases particulate emissions and fuel consumption. Many in-cylinder solutions such as lower compression ratios, modified injection characteristics, improved air intake system etc. are required along with EGR to accomplish the future emission norms. Modern combustion techniques such as low temperature combustion (LTC), homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI) etc. would be helpful for reducing the exhaust emissions and improving the engine performance. However, controlling of autoignition timing and achieving wider operating range are the major challenges with these techniques. A comprehensive review of diesel engine performance and emission characteristics is given in this paper.  相似文献   
920.
This paper gives a literature review from experimental, epidemiological and naturalistic studies, having tried to measure on the one hand, the impact of mobile phone use on driving and, on the other hand, the risk of accident associated with this practice. The overview of these studies allowed first of all to show that the driving task is altered during the period of mobile phone use, and to quantify the disturbance (experimental studies), then to verify that this disturbance can be at the origin of accidents and quantify this risk (epidemiological studies). The naturalistic studies, consisting in following-up fleet vehicles, give some more explanations and tend to confirm the results. Advantages and limits of each approach are also discussed.  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