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   8112篇
  免费   114篇
公路运输   1880篇
综合类   595篇
水路运输   2559篇
铁路运输   766篇
综合运输   2426篇
  2023年   43篇
  2022年   112篇
  2021年   61篇
  2019年   85篇
  2018年   196篇
  2017年   123篇
  2016年   191篇
  2015年   94篇
  2014年   243篇
  2013年   1235篇
  2012年   342篇
  2011年   428篇
  2010年   275篇
  2009年   368篇
  2008年   335篇
  2007年   269篇
  2006年   231篇
  2005年   272篇
  2004年   292篇
  2003年   179篇
  2002年   147篇
  2001年   133篇
  2000年   138篇
  1999年   98篇
  1998年   129篇
  1997年   112篇
  1996年   138篇
  1995年   150篇
  1994年   84篇
  1993年   189篇
  1992年   160篇
  1991年   77篇
  1990年   83篇
  1989年   58篇
  1988年   74篇
  1987年   65篇
  1986年   59篇
  1985年   77篇
  1984年   75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   54篇
  1975年   66篇
  1974年   50篇
  1973年   45篇
排序方式: 共有8226条查询结果,搜索用时 31 毫秒
151.
汽车产品的质量总是会受到巨大的关注。质量较差会导致财务成本的增加,这使得制造商把提升质量作为一项商业必要的手段。过去的数年中有无数方法和流程被用来减少浪费和消除缺陷 (比如6-Sigma法和TQM完全质量管理法)。我们并不缺少这样的衡量工具,来衡量因质量问题和返工而产生的负面经济效益。运用这些衡量工具能够理解质量对每辆车或者公司的盈利能力造成的影响,并且帮助公司取得显著的产品质  相似文献   
152.
This study investigates determinants of the vessel, cargo, and other-property damage costs of bulk barge accidents in US inland waterways. Tobit estimation of a three-equation recursive model suggests that, in bulk barge accidents: (1) vessel damage cost is greater for collision, fire/explosion, and material/equipment failure accidents than for groundings; (2) cargo damage cost is greater at night and when the weather is foggy and increases with barge age; and (3) otherproperty damage cost is greater for multi-vessel accidents, but decreases with barge size. A dollar of vessel damage cost increases other-property damage cost by $1.38, while a dollar of cargo damage cost increases this cost by $6.90. An important result for formulating bulk barge accident cost-reduction policies is that a given determinant might have a negative effect on one type of damage cost but a positive effect on another.  相似文献   
153.
Upon the expiry of the concession contract signed between Lebanon and a private company for the Port of Beirut operation (in December 1990), the Government appointed a temporary commission to operate the port under the rules of the expiring concession. The legality of this measure has since always been questioned, while the temporary commission underwent three major personnel changes which clearly prevented any long-term thinking or planning. In 1998, the temporary commission entered into a 20-year joint venture for the establishment of a container terminal. Meanwhile, Lebanon's two main ports were facing major regional competition, while competing against each other to some degree. Thus, the need became urgent to end the temporary status and propose reforms to the entire sector. To that end, the Ministry of Public Works and Transport was commissed by the Government to propose a permanent institutional framework for the port of Beirut while assessing the need for a national maritime sector regulator. This paper presents the recommendations for the institutional reform of the Lebanese maritime transport sector.  相似文献   
154.
During the period 1992–1998, 38 isobaric RAFOS floats were deployed to sample the subsurface flow of the California Undercurrent. The deployments, released over the California continental slope west of San Francisco, have sampled robust year-round poleward subsurface flow associated with the Undercurrent most seasons and the combined inshore current and Undercurrent in winter. Two other types of flow have been seen: a region of weak flow with little net displacement just west of the California Undercurrent, and an active westward propagating eddy field. This eddy field appears to be the primary mechanism for moving floats from the Undercurrent into the ocean interior. The observations and statistics from the RAFOS floats are compared with Lagrangian estimates of particles tracked in a global high resolution ocean simulation in order to evaluate the fidelity of the model along an eastern boundary. The results show that the model reproduces the general character of the flow reasonably well, but underestimates both the mean and eddy energies by a substantial amount.  相似文献   
155.
A time-domain technique for estimating wave-induced ship hull bending moment from ship motion measurements is presented. This technique is developed to improve hull response monitoring systems. Artificial neural networks are used to model the time-domain relationship between the wave-induced vertical bending moment and the coupled heave and pitch motions. The application of the proposed technique is validated using experimental data.  相似文献   
156.
Dynamics of inorganic nutrient species in the Bohai seawaters   总被引:3,自引:0,他引:3  
Within the frame of a Sino-German Joint Research Program, two cruises of “R/V Dong Fang Hong 2” were carried out in September–October 1998 and April–May 1999, respectively, to understand the dynamics of nutrients in the Bohai. Nutrient species (NO3, NO2, NH4+, PO43− and SiO32−) are determined colorimetrically on board for five anchor and 30 grid stations. In situ incubation experiments are performed to determine planktonic nutrient uptake and benthic exchange flux. Nutrient concentrations display short-term variability and seasonal change in the Bohai, with higher levels in shallow coastal waters than in the Central Bohai. The influence of riverine discharge on nutrient levels can be seen from salinity isopleths, nutrient distribution and species ratios. Near-bottom (nb) waters have similar nutrient concentrations as to the surface waters in the Central Bohai, whereas stratification takes place in the Bohai Strait and North Yellow Sea. In situ incubation experiments provide evidence that the uptake ratio (i.e. N, P) by phytoplankton is proportional to the ratios among nutrient species in ambient waters. Based on the data of this study and previously publications, a preliminary estimate of nutrient budgets via riverine input and atmospheric deposition is established. The results indicate that atmospheric deposition gains importance over rivers in delivering nutrients into the Bohai and sustain the new production, following recent decrease in riverine inflow caused by drought periods in North China and damming practices. A historical review of nutrient data indicates that concentrations of nitrogen increase and phosphorus and silica decrease in the Central Bohai over last 40 years. This potentially has an important influence on the health of ecosystem in Bohai (e.g. food web and community structure), though further study is needed to examine the scenario in more detail.  相似文献   
157.
根据现有的地铁整流器柜监控装置的工作原理,提出一种基于C8051F206单片机为核心的地铁整流器监洲系统,该系统通过对整流器交直流侧电压、电流及其他一些状态量的采样,经过微处理器可以实时临测牵引整流器的运行参数,实现对整流器柜的监控.该监控系统具有成本低、可靠性高、抗干扰能力强等优点.  相似文献   
158.
铁路乘客艾滋病知识、态度、行为调查分析   总被引:2,自引:0,他引:2  
目的 调查铁路旅客的艾滋病相关知识、态度和行为情况,为列车开展艾滋病宣传教育提供理论依据。方法 对6趟旅客列车乘客进行抽样问卷调查,调查结果进行统计分析。结果收回有效调查问卷2 083份,艾滋病一般知识正确回答率55.83% ~92.03%,传播途径59.67%~93.52%,临床知识59.00%~77.34%,预防控制68.75%~88.86%,态度行为48.25%~94.33%,政策法规67.64%~84.88%。正确回答率无性别差异(P>0.05);一般知识、传播途径、行为态度存在结婚与否的差异(P<0.05);受教育程度上除一般知识外,其它都有显著性差异(P<0.01)。结论 铁路乘客对艾滋病知识、态度、行为的正确回答率,原则性问题高于具体问题, 71%以上乘客愿意接受健康教育和AIDS教育。针对铁路乘客流动性强的特点,列车上艾滋病宣传教育内容要注重知识具体化。  相似文献   
159.
This paper described the process of generating the optimal parametric hull shape with a fully parametric modeling method for three containerships of different s...  相似文献   
160.
受农历新年影响,春节期间中国出口集装箱运输市场货量明显萎缩,尽管节后逐渐恢复,但各航线恢复情况不一,市场运价走势存在差异。3月16日,上海航运交易所发布的中国出口集装箱综合运价指数为1026.07点,较上月同期基本持平:上海地区出口集装箱运价指数为1025.79点,较上月同期微涨1.5%。  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