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   2731篇
  免费   36篇
公路运输   434篇
综合类   902篇
水路运输   867篇
铁路运输   148篇
综合运输   416篇
  2024年   3篇
  2023年   3篇
  2022年   30篇
  2021年   36篇
  2020年   24篇
  2019年   13篇
  2018年   347篇
  2017年   299篇
  2016年   262篇
  2015年   30篇
  2014年   31篇
  2013年   53篇
  2012年   98篇
  2011年   272篇
  2010年   276篇
  2009年   124篇
  2008年   222篇
  2007年   189篇
  2006年   55篇
  2005年   100篇
  2004年   67篇
  2003年   89篇
  2002年   51篇
  2001年   27篇
  2000年   14篇
  1999年   7篇
  1998年   6篇
  1997年   6篇
  1996年   6篇
  1995年   9篇
  1994年   4篇
  1993年   3篇
  1992年   2篇
  1991年   4篇
  1988年   1篇
  1987年   1篇
  1984年   1篇
  1981年   1篇
  1978年   1篇
排序方式: 共有2767条查询结果,搜索用时 375 毫秒
141.
徐宁  陈畅  赵志刚 《机电设备》2010,27(5):52-54
啤酒废水的主要特点之一是BOD/COD高,利于生化处理,N、P含量较少,SS高.徐州某啤酒厂产生的啤酒废水采用UASB-接触氧化工艺处理,取得了较好的效果.出水CODcr75~80mg/L,BOD515~20mg/L,SS65~70mg/L,各项指标都达到了《啤酒工业水污染排放标准》(GB19821-2005)的排放标准.  相似文献   
142.
钢板桩挡土结构加固方法研究   总被引:2,自引:0,他引:2  
李格平  郭畅  骆城  熊洪峰 《水道港口》2010,31(3):215-219
基于天津港某码头钢板桩在恶劣海洋环境下出现的严重锈蚀破损现象,采用ANSYS有限元建立了钢板桩结构与土相互作用的数值计算模型,分析了钢板桩在锈蚀及局部破损状况下的结构安全性。通过对帽板加固法、局部外包法的有限元计算分析,得到了以上2种加固方案下的土体变位和钢板桩受力情况,并结合经济性和施工可行性等指标推荐局部外包法为最优加固方案。  相似文献   
143.
智能高铁是我国高速铁路发展的趋势,BIM技术融合智能化、信息化等手段,可实现铁路项目的全生命周期管理,提高管理水平和工作效率.根据BIM技术特点,基于Autodesk Revit建立铁路线路三维信息平台,为铁路项目信息化管理提供参考.首先,利用PowerCivil并根据线路平、纵断面等资料,生成线路中心线三维线形,为后...  相似文献   
144.
针对地铁换乘站换乘方式适配性评价难题,提出总体技术方案并构建设施平均密度、能力饱和度、平均疏散时间等量化评价指标,以典型十字换乘站——沈阳地铁青年大街站为例,重点分析换乘方式能力适配性问题。通过车站客流仿真及指标计算评价,发现站台能力不足及换乘设施客流冲突等问题突出。因此,从行车组织及车站结构方面提出优化建议,其中压缩行车间隔仅能提升车站运能,但难以解决换乘节点客流冲击问题;而优化车站结构仅能减缓换乘设施压力,若同时实施,则能彻底解决能力不足和冲击性问题。建议大客流换乘站不采用十字节点换乘,应结合工程条件优先考虑T型或L型换乘。  相似文献   
145.
铁路信号安全关键软件的组合测试序列集约简   总被引:2,自引:2,他引:0  
针对现有铁路信号系统安全关键软件t-路组合测试序列生成方法在处理大规模输入时产生冗余测试序列,导致测试执行成本较高的问题,提出了一种基于贪婪-粒子群混合优化算法的t-路组合测试序列集约简方法,用于降低序列集的执行成本. 首先,以执行成本最低为约简目标,建立针对t-路组合测试序列集约简的优化模型;然后,在保证测试序列集逻辑覆盖特性的基础上,采用贪婪-粒子群混合优化算法求解模型,计算约简后的测试序列集;最后,以ZPW-2000轨道电路接收器软件作为研究对象,以其生成的2-路组合测试序列集为例开展约简验证. 结果表明,所提方法在保证2-路组合覆盖和逻辑覆盖的前提下,对单个序列集的执行成本约简幅度最高达到98.33%,对序列集总的执行成本约简幅度达到36.10%,验证了所提方法的可行性和有效性.   相似文献   
146.
Polarization pattern provides additional information besides spectral signatures. It can be used in many applications, such as navigation, defect detection and object identification. A novel polarization camera composed of four synchronized cameras is proposed, and it can realize real-time polarization measurement. This study particularly concentrates on the geometric calibration of the system. The projection model is analyzed and the multi-camera calibration algorithm is proposed. Firstly, each camera is calibrated separately using planar patterns, and then the geometric calibration algorithms are performed. Due to the geometrical constraint, a global optimization method results in smaller estimation uncertainties. A mean rotation error of 0.025° and a mean translation error of 0.26mm are achieved after geometric calibration. The images are rectified to establish a correspondence among cameras and are combined to acquire the polarization measurement. The polarization pattern of the skylight is measured by the system and the results are consistent with the previous studies.  相似文献   
147.
Legal affair simulation is on the basis of information technology, and can simulate legal scene. College students do legal experiments with virtual reality scene. This helps to train college students. Petri net has not only strict math definition to analyze the dynamic behavior of models, but also intuitive graphic expression. Petri net is used to model for legal process. Reduction rules of Petri net are used to analyze the correctness of the system. At last Java Business Process Management (JBPM) technology is used to realize legal affair simulation models, models are transformed into flow charts. Simulation software deduces processes of legal affair. Many college students have improved their ability with the software, the fact proves that the method is effective.  相似文献   
148.
The magnetic field tuning characteristics of an ultrasonic motor (USM) stator are discussed. The stator consists of two piezoelectric ceramic transducer (PZT) plates and one sandwiched-in Terfenol-D plate. The dimensions of the stator are carefully adjusted to specifically discuss the influence of the magnetic field on the frequency difference between the longitudinal and bending modes of the stator. The frequency difference discussed in this paper is usually small and mainly caused by uneven materials, machining errors and changes in external conditions (temperature, pre-stress or load). The longitudinal and bending modes of the stator are simultaneously excited by an external electric field to generate the elliptic motion trajectories of the driving points. A direct current (DC) magnetic field is applied to decrease the difference between the two mode frequencies of the fabricated stator. In experiments, the dependences of the two mode frequencies and their difference on DC magnetic fields are all investigated. The experimental results indicate that the difference between the longitudinal and bending mode frequencies of the PZT/Terfenol-D/PZT composite stator can be tuned by changing the intensity of the external DC magnetic field.  相似文献   
149.
Traditional control methods of two-wheeled robot are usually model-based and require the robot’s precise mathematic model which is hard to get. A sensorimotor self-learning model named SMM TWR is presented in this paper to handle these problems. The model consists of seven elements: the discrete learning time set, the sensory state set, the motion set, the sensorimotor mapping, the state orientation unit, the learning mechanism and the model’s entropy. The learning mechanism for SMM TWR is designed based on the theory of operant conditioning (OC), and it adjusts the sensorimotor mapping at every learning step. This helps the robot to choose motions. The leaning direction of the mechanism is decided by the state orientation unit. Simulation results show that with the sensorimotor model designed, the robot is endowed the abilities of self-learning and self-organizing, and it can learn the skills to keep itself balance through interacting with the environment.  相似文献   
150.
For the pressure enthalpy of high pressure pneumatics, the computational fluid dynamics (CFD) simulation based on ideal gas assumption fails to obtain the real temperature information. Therefore, we propose a method to compensate the pressure enthalpy of throttling for CFD simulation based on ideal gas assumption. Firstly, the pressure enthalpy is calculated for the pressure range of 0.101 to 30 MPa and the temperature range of 190 to 298 K based on Soave-Redlich-Kwong (S-R-K) equation. Then, a polynomial fitting equation is applied to practical application in the above mentioned range. The basic idea of the compensation method is to convert the pressure enthalpy difference between inlet air and nodes into the compensation temperature. In the above temperature and pressure range, the compensated temperature is close to the real one, and the relative temperature drop error is below 10%. This error is mainly caused by the velocity difference of the orifice between the real and ideal gas models. Finally, this compensation method performs an icing analysis for practical high pressure slide pilot valve.  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