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   984篇
  免费   12篇
公路运输   281篇
综合类   29篇
水路运输   308篇
铁路运输   23篇
综合运输   355篇
  2023年   13篇
  2022年   22篇
  2021年   5篇
  2019年   13篇
  2018年   31篇
  2017年   26篇
  2016年   40篇
  2015年   14篇
  2014年   41篇
  2013年   155篇
  2012年   38篇
  2011年   43篇
  2010年   50篇
  2009年   63篇
  2008年   57篇
  2007年   41篇
  2006年   31篇
  2005年   17篇
  2004年   17篇
  2003年   14篇
  2002年   15篇
  2001年   10篇
  2000年   9篇
  1999年   16篇
  1998年   7篇
  1997年   14篇
  1996年   14篇
  1995年   17篇
  1994年   5篇
  1993年   9篇
  1992年   10篇
  1991年   11篇
  1990年   6篇
  1989年   4篇
  1988年   7篇
  1986年   4篇
  1985年   10篇
  1984年   3篇
  1983年   7篇
  1982年   4篇
  1981年   9篇
  1980年   6篇
  1979年   8篇
  1978年   9篇
  1977年   10篇
  1976年   13篇
  1975年   10篇
  1974年   5篇
  1973年   3篇
  1972年   4篇
排序方式: 共有996条查询结果,搜索用时 15 毫秒
231.
lIntroductionTheCu26Zn-5Al-0.7Ti(wt%)allOysareshaPeIneInOryalloys.PolytwstallineshaPempalloysareingeneralusedinengineeringaPPlicatons.TheshapempeffectsarecloselyrelatedwiththetextUresforthesing1ecrystalshavetheshmplyanisotrOPicPfOPetw[l-3].ItwasshownthatextUredshaPempal1oyspossessedthebettershaPememOryeffectsthannontextUrdones[4].Cu-basedallOystendeasilytOgrowintolnyegrainsinhotrolling,andarenosultabletocoldrollingbecausethe0PhasehasalowmalleabilityatroomtemperatUre.FortheCuZnAlal…  相似文献   
232.
随着城市和交通路网建设的发展,以及用户对产品认知的提高,用户开始对GPS导航产品的有效性产生了质疑,根源则是现今绝大部分市场上正在使用的导航产品完全依赖于GPS进行定位,由于技术特性的限制,该类导航产品存在很大的缺陷,这些缺陷导致了频繁的误入歧路或者无法给用户有效指导,甚至用户反映用不如不用的结论。  相似文献   
233.
We consider the problem of aligning barge rotations with quay schedules of terminals in the port of Rotterdam. Every time a barge visits the port, it has to make a rotation along, on average, eight terminals to load and unload containers. A central solution, e.g., a trusted party that coordinates the activities of all barges and terminals, is not feasible for several reasons. We propose a multi-agent based approach of the problem, since a multi-agent system can mirror to a large extent the way the business network is currently organized and can provide a solution that is acceptable to each of the parties involved. We examine the value of exchanging different levels of information and evaluate the performance by means of simulation. We compare the results with an off-line scheduling algorithm. The results indicate that, in spite of the limited information available, our distributed approach performs quite well when compared to the central approach. In addition, our experiments indicate that an information exchange based on waiting profiles reduces the average tardiness per barge with almost 80% when compared to the situation with no information exchange. We therefore think that waiting profiles provide a promising protocol to tackle this problem.  相似文献   
234.
目前,针对公路上的“电子眼”,一些车主购买了“反雷达测速器”(俗称电子狗)来对抗,目的是为了避免收到“牛肉干”(罚款单)。但是“电子狗”质量参差不齐,而且价格也不菲,这让车主对“电子狗”又爱又恨。随着国内导航软件技术的进步及导航地图更完整地包含了雷达测速器位置,“电子狗”功能整合在导航系统中已成为现实。导航仪价格的不断下降,  相似文献   
235.
In this study, a model for predicting chloride penetration in fly ash concrete under long-term exposure in a marine environment is developed. The empirical model was based on 2-, 3-, 4-, and 5-year investigation of concretes in a marine site. Regression analysis of the data was carried out by applying Fick's second law of diffusion to generate an empirical formula for predicting chloride concentration in concrete. The model uses the water to binder (W/B) ratio, fly ash content, distance from the concrete surface, and exposure time. Model validation revealed that the predicted chloride concentration levels were within a ±25% error margin (R2 = 0.91 ? 0.99) in the samples used to develop the model. The model was also verified using data from previous laboratory and field studies. Most predicted chloride concentration levels were within a ±30% margin of error from field samples. The model also predicted the strong effect of fly ash and W/B ratio on reducing chloride diffusion in concrete. Results clearly indicated that a high volume fly ash replacement (up to 50% by weight of binder) and a low W/B ratio will yield good chloride resistance in concrete under long-term exposure in a marine environment.  相似文献   
236.
Assessment of hub status among Asian ports from a network perspective   总被引:1,自引:0,他引:1  
This paper proposes a novel network-based hub port assessment (NHPA) model through explicit formulations of connectivity and cooperation indices. Such a model is useful for port operators and policy makers to evaluate the relative influences of various quality characteristics from which carriers base their port choices on and identify port partners. Key insights can be obtained for port authorities to improve their port infrastructures and operations to achieve a competitive and sustainable hub port status. Three comprehensive case studies are conducted to assess the current standings and potentials of major Asian ports within networks of major carriers.  相似文献   
237.
Carbon monoxide is a major contributor to air pollution in urban cities, particularly at the roadside. Hourly, monthly and seasonal mean carbon monoxide concentration data are collected from a roadside air monitoring station in Hong Kong over 7-years. The station is a few metres from a major intersection surrounded by tall buildings. In particular, hourly patterns of concentrations on different days of the week are investigated. The data show that hourly carbon monoxide concentrations resemble the traffic pattern of the area and tend to be lower in the summer. Using a seasonal autoregressive integrated moving average models shows that the daily traffic cycle strongly influences concentrations. Further, it is found that urban roadside carbon monoxide monitoring data exhibits a long-memory process, suggesting that a model incorporating long memory and seasonality effects is needed simulate urban roadside air quality.  相似文献   
238.
Road safety is a policy priority due to the high casualties and costs associated with road accidents. Since speed is a major cause of road accidents, in‐vehicle speed limiters or Intelligent Speed Adaptation (ISA), seems a promising solution. ISA implementation, however, is hindered by large uncertainties, for example about the impacts of ISA, the way users might respond to ISA, and the relationship between speed and accidents. Traditional Multi‐Criteria Analysis (MCA) has limitations in handling these uncertainties. We present an MCA approach based on exploratory modeling, which uses computational experiments to explore the multiple outcomes of ISA policies (safety, emissions, throughput, and cost) across a range of future demand scenarios, functional relationships for performance criteria, and user responses to ISA. As an illustration, by testing the impacts of different ISA penetration levels on two driver groups, we show that when compliance with ISA is expected to be low, a policy aimed only at novice drivers outperforms other ISA policies on safety improvement.  相似文献   
239.
Peter 《世界汽车》2007,(1):52-55
Smart近日发布的新一代Fortwo延续独特的城市用微型车概念.新一代的发展更侧重于内涵.提高Fortwo的驾乘舒适性、操控性,主被动安全水平和更环保的排放。新车的外形设计在上一代的基础上渗入了新的设计语言.并试图改变第一代过于女性化的形象.以求新车能得到更多男性买家的认同。  相似文献   
240.
In this paper, motion analysis methods based on the moment features and flicker frequency features for early fire flame from ordinary CCD video camera were proposed, and in order to describe the changing of flame and disturbance of non-flame phenomena further more, the average changing pixel number of the first-order moments of consecutive flames has been defined in the moment analysis as well. The first-order moments of all kinds of flames used in our experiments present irregularly flickering, and their average changing pixel numbers of first-order moments are greater than fire-like disturbances. For the analysis of flicker frequency of flame, which is extracted and calculated in spatial domain, and therefore it is computational simple and fast. The method of extracting flicker frequency from video images is not affected by the catalogues of combustion material and distance. In experiments, we adopted two kinds of flames, i.e. , fixed flame and movable flame. Many comparing and disturbing experiments were done and verified that the methods can be used as criteria for early fire detection.  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