全文获取类型
收费全文 | 1224篇 |
免费 | 16篇 |
专业分类
公路运输 | 556篇 |
综合类 | 45篇 |
水路运输 | 305篇 |
铁路运输 | 25篇 |
综合运输 | 309篇 |
出版年
2023年 | 9篇 |
2022年 | 20篇 |
2021年 | 9篇 |
2020年 | 4篇 |
2019年 | 11篇 |
2018年 | 31篇 |
2017年 | 39篇 |
2016年 | 78篇 |
2015年 | 17篇 |
2014年 | 66篇 |
2013年 | 189篇 |
2012年 | 66篇 |
2011年 | 78篇 |
2010年 | 73篇 |
2009年 | 57篇 |
2008年 | 77篇 |
2007年 | 33篇 |
2006年 | 29篇 |
2005年 | 24篇 |
2004年 | 20篇 |
2003年 | 10篇 |
2002年 | 13篇 |
2001年 | 17篇 |
2000年 | 29篇 |
1999年 | 15篇 |
1998年 | 13篇 |
1997年 | 17篇 |
1996年 | 22篇 |
1995年 | 24篇 |
1994年 | 9篇 |
1993年 | 16篇 |
1992年 | 13篇 |
1991年 | 11篇 |
1990年 | 4篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有1240条查询结果,搜索用时 15 毫秒
241.
营运中的盾构隧道在邻近施工时周围地盘的应力可能因扰动而重新分布,使得盾构隧道暴露在因变形或位移衍生的结构损坏或营运中断等高风险下。为降低相关风险发生的可能性或后果的严重性,高雄计划将高雄车站段地下化工程捷运-R11永久站施工纳入风险管理,通过风险辨识、分析、评估以及以监测、巡检及沟通为基础的风险追踪查核等手段执行风险管理。依本计划执行成果,位于基地两侧营运中的盾构隧道在永久站主体工程开挖施工期间,各项风险均受到妥善的追踪、管控及处置。 相似文献
242.
TBM信息化采集了海量数据,对TBM数据的标准化预处理是进行诸多研究的前提。基于此,提出了一种TBM掘进数据标准化处理方法,依托TBM现场施工掘进大数据,以破岩特征为依据选取基本掘进参数(刀盘转速、推进速度、刀盘推力及刀盘扭矩)分析掘进过程TBM数据特点,提出循环掘进过程空推段、上升段、稳定段及下降段起点的判别方法,对稳定段起点提出了标准差法判别方法、均值判别方法、直方图判别方法,满足实时和非实时的数据划分需求。最后对两个TBM工程的数据进行标准化预处理,实现施工大数据的标准化。结果表明,提出的标准化预处理方法可实现循环掘进过程数据的有效划分。研究成果可推广应用于众多TBM工程的数据标准化处理,有效实现机器学习数据库的建立。 相似文献
243.
Fuel economy comparison of conventional drive trains series and parallel hybrid electric step vans 总被引:1,自引:0,他引:1
S. B. Han Y. H. Chang Y. J. Chung E. Y. Lee B. Suh A. Frank 《International Journal of Automotive Technology》2009,10(2):235-240
A hybrid electric vehicle (HEV) is a vehicle that combines a conventional propulsion system with an on-board rechargeable
energy storage system to achieve better fuel economy than a conventional vehicle HEVs do not have limited ranges like battery
electric vehicles, which use batteries charged by an external source. The different propulsion power systems may have common
subsystems or components. The objective of this study is to compare the fuel economies of a conventional step van, a series
hybrid electric step van (HESV), and a parallel HESV by calculating the fuel consumption using the ADVISOR software by NREL.
We also showed the results of the vehicles in different driving cycles including the Central Business District bus cycles,
the New York City Cycle, and the US EPA City and Highway cycles. 相似文献
244.
Analysis of a regenerative braking system for Hybrid Electric Vehicles using an Electro-Mechanical Brake 总被引:3,自引:0,他引:3
J. K. Ahn K. H. Jung D. H. Kim H. B. Jin H. S. Kim S. H. Hwang 《International Journal of Automotive Technology》2009,10(2):229-234
The regenerative braking system of the Hybrid Electric Vehicle (HEV) is a key technology that can improve fuel efficiency
by 20∼50%, depending on motor size. In the regenerative braking system, the electronically controlled brake subsystem that
directs the braking forces into four wheels independently is indispensable. This technology is currently found in the Electronic
Stability Program (ESP) and in Vehicle Dynamic Control (VDC). As braking technologies progress toward brake-by-wire systems,
the development of Electro-Mechanical Brake (EMB) systems will be very important in the improvement of both fuel consumption
and vehicle safety. This paper investigates the modeling and simulation of EMB systems for HEVs. The HEV powertrain was modeled
to include the internal combustion engine, electric motor, battery and transmission. The performance simulation for the regenerative
braking system of the HEV was performed using MATLAB/Simulink. The control performance of the EMB system was evaluated via
the simulation of the regenerative braking of the HEV during various driving conditions. 相似文献
245.
H. -D. Kang D. -H. Kim S. -W. Chae J. -N. Han D. -S. Kim 《International Journal of Automotive Technology》2009,10(5):583-587
Most of the research on safety belt systems has involved crash simulation that only considered a dynamic human model. However,
belt routing analysis, usually known as comfort level estimation, is also an important factor in safety belt design, considering
that serious injuries of the abdominal region result from the infiltration of a belt into the neck or the chest. Thus, safety
belt evaluations using kinematic human models are also needed. In this paper, a belt fit simulation method is suggested. Using
the proposed process, both comfort and safety analyses can be performed under the same conditions continuously, and thus the
safety belt design parameters, such as the location of anchor points, dummy posture and etc., can be evaluated. In conclusion,
this computer process enables a belt system design to reduce injuries. 相似文献
246.
In this paper, a theoretical approach is suggested for predicting the structural performances and weight reduction rate of
a car body with a box-type section when its material is substituted with a lightweight material for weight saving. For the
material substitution design of a car body for rolling stock, bending, axial, and twisting deformations should be considered
at constant stiffness and strength conditions. To compare the weight reduction effects on different material applications,
some new indices were derived from a structural performance point of view. The derived indices provide good measures to estimate
weight reduction by material substitution design and can be effectively applied to the conceptual design of a car body. 相似文献
247.
In this study, a parallel flow condenser and laminated evaporator for an automotive air-conditioning system were modified
to improve performance. Gas-liquid separation type condensers, in which the condenser and receiver drier are integrated, and
one-tank laminated type evaporators were developed, and their performances were investigated experimentally using HFC-134a.
Heat transfer characteristics in the condenser are examined by means of air temperature, air velocity entering the condenser
and inlet pressure of the refrigerant; heat transfer characteristics in the evaporator are examined by means of air temperature,
relative humidity, flow rate of air, outlet pressure of refrigerant and superheat. Pressure drops for both evaporator and
condenser are also measured, and correlations for pressure drop are derived for the condenser and evaporator, respectively.
Air velocity and mass flow rate of the refrigerant have a significant effect on the overall heat transfer coefficient, and
flow pass is not significantly influenced by the cooling capacity of the condenser. The overall heat transfer coefficient
of the evaporator increases as air flow rate, air temperature and relative humidity increases. 相似文献
248.
K. O. Lee S. K. Hong Y. K. Kang H. J. Yoon S. S. Kang 《International Journal of Automotive Technology》2009,10(6):697-702
A double-quenching (D/Q) process is proposed for heat-treating high carbon-chromium bearing steels to improve the fatigue
properties through refinement of the microstructure. The new heat treatment method has two steps: The first step is a nitrocarburizing
process that results in high surface hardness and lowers the transformation temperature. The second step is the same as in
the conventional quenching process but can be conducted at a considerably lower temperature than in conventional quenching.
The microstructure in the material that is caused by the D/Q heat treatment is much finer than in the conventional Q/T (quenching
and tempering) process. In order to quantify the performance of the proposed heat-treatment process, various mechanical property
tests are carried out. The rolling contact fatigue life of double-quenched bearing steels was eight times higher than in bearing
steels that were treated by conventional Q/T. 相似文献
249.
Dynamics of inorganic nutrient species in the Bohai seawaters 总被引:3,自引:0,他引:3
J. Zhang Z. G. Yu T. Raabe S. M. Liu A. Starke L. Zou H. W. Gao U. Brockmann 《Journal of Marine Systems》2004,44(3-4):189
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
250.
底部薄板附近的水流及泥沙运动特性 总被引:2,自引:0,他引:2
通过水槽实验探讨了在饱和来沙条件下底部薄板附近的水流、泥沙运动特性,包括不同薄板高度、与水流不同夹角的安装方向等情况下,单个底部薄板附近的水流结构、泥沙运动规律、底部薄板的导沙特性及其附近的冲淤现象,以及底部薄板群体的导沙特性。试验结果表明,实验使用的薄板的长度对实验结果影响很大,过短的薄板实验根本观察不到薄板前冲刷沟内的沙波运动,而该沙波运动严重影响薄板的导沙效应。底部薄板附近的水流结构具有强烈的三维特性,流场复杂,对于一定的薄板,水流夹角、沙波的运动是影响薄板的导流导沙促淤的主要因素。 相似文献