全文获取类型
收费全文 | 1631篇 |
免费 | 23篇 |
专业分类
公路运输 | 595篇 |
综合类 | 66篇 |
水路运输 | 488篇 |
铁路运输 | 57篇 |
综合运输 | 448篇 |
出版年
2023年 | 11篇 |
2022年 | 30篇 |
2021年 | 17篇 |
2020年 | 18篇 |
2019年 | 13篇 |
2018年 | 52篇 |
2017年 | 35篇 |
2016年 | 65篇 |
2015年 | 20篇 |
2014年 | 70篇 |
2013年 | 246篇 |
2012年 | 75篇 |
2011年 | 93篇 |
2010年 | 78篇 |
2009年 | 86篇 |
2008年 | 90篇 |
2007年 | 43篇 |
2006年 | 30篇 |
2005年 | 45篇 |
2004年 | 33篇 |
2003年 | 13篇 |
2002年 | 26篇 |
2001年 | 24篇 |
2000年 | 20篇 |
1999年 | 22篇 |
1998年 | 30篇 |
1997年 | 18篇 |
1996年 | 26篇 |
1995年 | 26篇 |
1994年 | 13篇 |
1993年 | 17篇 |
1992年 | 19篇 |
1991年 | 12篇 |
1990年 | 15篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 13篇 |
1981年 | 21篇 |
1980年 | 11篇 |
1979年 | 20篇 |
1977年 | 16篇 |
1976年 | 12篇 |
1975年 | 13篇 |
1974年 | 13篇 |
1973年 | 6篇 |
排序方式: 共有1654条查询结果,搜索用时 31 毫秒
961.
地下结构施工不当会对邻近既有地铁盾构隧道结构产生巨大影响。文章以广州市某地铁线路下穿施工导致既有运营地铁盾构隧道产生较大变形的工程实例为背景,分析了既有隧道结构因地层损失产生不同椭圆度变形情况下管片结构的受力情况。基于工程实测数据,运用三维有限元分析软件,考虑了管片接头处的螺栓孔等细部构造,研究了管片椭圆度与结构应力状态之间的量化关系,并分析了结构的塑性变形情况及其发展趋势。结果表明:随着盾构隧道管片椭圆度的增大,结构最大主应力值与最大剪应力值均增大,且盾构隧道结构最大剪应力与椭圆度呈线性相关关系;盾构隧道结构最大主应力随椭圆度变化更加明显,与椭圆度呈非线性相关关系。 相似文献
962.
中夹岩柱是小净距隧道围岩稳定控制的关键部位,判别中夹岩的安全性是工程设计和施工过程中的重难点。文章通过分析不同围岩级别、埋深情况下中夹岩的破坏模式,建立Ⅳ级围岩条件下水平小净距隧道中夹岩力学分析模型,并确定中夹岩破裂面位置。根据中夹岩上部滑块体形状的不同分为两种情况,通过边坡稳定性原理、极限平衡假设及普氏压力拱理论推导中夹岩上部滑块体的抗滑力、下滑力以及安全系数的计算公式,从而建立起评判中夹岩安全性的安全系数法,并结合数值模拟对其进行验证。将经验证后的安全系数法应用于某实际隧道工程,判断其中夹岩安全性,得出该隧道中夹岩破坏临界厚度为6 m,进而对6 m以下的中夹岩使用锚杆进行加固。 相似文献
963.
S.?Lee Y.?Cho M.?Song H.?Kim J.?Park D.?BaikEmail author 《International Journal of Automotive Technology》2012,13(3):355-363
Particulate matter in diesel engine exhaust, particularly nano-particles, can cause serious human health problems including
diseases such as lung cancer. Because diesel nano-particle issues are of global concern, regulations on particulate matter
emissions specify that not only the weight of particulate matter emitted but also the concentration of nanoparticles must
be controlled. This study aimed to determine the effects on nano-particle and PM emissions from a diesel engine when applying
a urea-SCR system for NOx reduction. We found that PM weight increases by approximately 90% when urea is injected in ND-13 mode over the emission without
urea injection. Additionally, PM weight increases as the NH3/NOx mole ratio is increased at 250 °C. In SEM scans of the collected PM, spherical particles were observed during urea injection,
with sizes of approximately 200 nm to 1 μm. This study was designed to determine the conditions under which nano-particles
and PM are formed in a urea-SCR system and to relate these conditions to particle size and shape via a quantitative analysis
in ND-13 mode. 相似文献
964.
C. -H. Park H. -J. Shim D. -H. Choi J. -K. Kim S. -M. Lee 《International Journal of Automotive Technology》2012,13(1):61-75
Rubber isolators are mounted between a cooling module and a carrier to isolate the car body from vibration due to the rotation
of the cooling fan. The isolators should be durable against fatigue loads originating from fan rotation and road disturbance.
Thus, the design of rubber isolators is required to maximize both vibration isolation and fatigue life. In this study, the
shapes of the rubber isolators are optimally designed using a process integration and design optimization (PIDO) tool that
integrates the various computer-aided engineering (CAE) tools necessary for vibration and fatigue analyses, automates the
analysis procedure and optimizes the design solution. In this study, we use CAE models correlated to the experimental results.
A regression-based sequential approximate optimizer incorporating Process Integration, Automation and Optimization (PIAnO),
a commercial PIDO tool, is employed to handle numerically noisy responses with respect to the variation in design variables.
Using the analysis and design procedure established in this study, we successfully obtained the optimal shapes of the rubber
isolators in two different cooling modules; these shapes clearly have better vibration isolation capability and fatigue lives
than those of the baseline designs used in industry. 相似文献
965.
Smooth motion control of the adaptive cruise control system by a virtual lead vehicle 总被引:1,自引:0,他引:1
The adaptive cruise control system maintains the appropriate distance to the lead vehicle when the lead vehicle exists and
maintains the desired speed when no lead vehicle is detected. A virtual lead vehicle scheme is introduced to make the switching
between the speed control algorithm and the distance control algorithm unnecessary and simplify the structure of the control
system. The speed and the position of the virtual vehicle can be decided by the control system according to the current situation.
Smoother responses are achieved by the virtual lead vehicle scheme compared to the conventional mode switching scheme. This
method is also shown to provide a good reaction for when a lead vehicle cuts in or out. A linear quadratic controller with
variable weights is suggested to control the virtual lead vehicle. This scheme shows improved performance in terms of passenger
comfort and fuel efficiency of the host vehicle. 相似文献
966.
The controller area network (CAN) protocol is widely used for in-vehicle network (IVN) systems, and many automotive companies
also use the CAN in chassis network systems. However, the increasing number of electronic control units (ECUs) dictated by
the need for more intelligent and fuel-efficient functions requires an IVN system with a greater transmission capacity and
less network delay. Automotive companies have tried several approaches such as segmenting CAN systems and developing time-triggered
protocols. This paper presents a practical method for increasing the transmission capacity and reducing the network delay
in CAN systems using dual communication channels with a traffic-balancing algorithm based on Kalman prediction to forecast
the traffic on each channel and allocate frames to the one that is most appropriate. An experimental testbed using commercial
microcontrollers with two or more CAN protocol controllers was used to demonstrate the feasibility of the Kalman traffic-balancing
algorithm. Experimental results show that the traffic-balancing CAN system with Kalman prediction reduced the transmission
delay of all priority messages compared to that of a simple method, such as a channel-switching CAN, without sacrificing the
performance for high-priority messages. 相似文献
967.
S. Kim K. Park H. J. Song Y. K. Hwang S. J. Moon H. S. Ahn M. Tomizuka 《International Journal of Automotive Technology》2012,13(1):87-95
Developed in this research is a control logic for the ARC (Active Roll Control) system that uses rotary-type hydraulic stabilizer
actuators at the front and rear axles. The hydraulic components of the system were modeled in detail using AMESim, and a driving
logic for the hydraulic circuit was constructed based upon the model. The performance of the driving logic was evaluated on
a test bench, and it demonstrated good pressure tracking capability. The control logic was then designed with the target of
reducing the roll motion of the vehicle during cornering. The control logic consists of two parts: a feedforward controller
that generates anti-roll moments in response to the centrifugal force, and a feedback controller that generates anti-roll
moments in order to make the roll angle to follow its target value. The developed ARC logic was evaluated on a test vehicle
under various driving conditions including a slowly accelerated circular motion and a sinusoidal steering. Through the test,
the ARC system demonstrated successful reduction of the roll motion under all conditions, and any discomfort due to the control
delay was not observed even at a fast steering maneuver. 相似文献
968.
D. Wang Z. C. Liu J. Tian J. W. Liu J. R. Zhang 《International Journal of Automotive Technology》2012,13(7):1023-1032
Particle number measurement is a new approach to determine emission, which may be more accurate at very low emission levels than when using gravimetric measurements. An experimental study was performed to investigate the effect of fuel properties on the performance, combustion process, regulated gaseous emissions and particle number emissions of a diesel engine with an uncatalyzed diesel particulate filter (DPF). The effect of the filter on the particle size distribution was reported. The DPF number-based filtration efficiency in terms of number efficiency and fractional efficiency for petroleum diesel fuel and two alternative fuels, BTL and GTL, were analyzed. For nearly all test modes, the filter had a higher number efficiency for diesel than for BTL and GTL. The DPF fractional efficiency showed it was highly dependent on fuel type and varied widely at each size range. For diesel, the filter fractional efficiency was sufficiently high and behaved as predicted by filtration theory. For BTL and GTL, the fractional performance of the filter decreased when unexpectedly low efficiencies within the nuclei mode were exhibited. This research will be helpful in understanding DPF number-based filtration performance for alternative fuels and will provide information for the development of particulate emission control technology. 相似文献
969.
S. H. Jeong J. E. Lee S. U. Choi J. N. Oh K. H. Lee 《International Journal of Automotive Technology》2012,13(7):1133-1140
Recently, the advanced driver assistance system (ADAS), which helps mitigate car accidents, has been developed using environmental detection sensors, such as long and short range radar, lidar, wide dynamic range cameras, ultrasonic sensors and laser scanners. Among these detection sensors, radars can quickly provide drivers with reliable information about the velocity, distance and direction of a target obstacle, as well as information about the vehicle in changing weather conditions. In the adaptive cruise control system (ACCS), three radar sensors are usually needed because two short range radars are used to detect objects in the adjacent lane and one long range radar is used to detect objects in-path. In this paper, low-cost radar based on a single sensor, which can detect objects in both the adjacent lane and in-path, is proposed for use in the ACCS. Before designing the proposed radar, we analyzed the world-wide radar technology and market trends for ACCS. Based on this analysis, we designed a novel radar sensor for the ACCS using radar components, such as an antenna, transceiver module, transceiver control module and signal processing algorithm. Finally, target detection experiments were conducted. In the experimental results, the proposed single radar can successfully complete the detection required for the ACCS. In the conclusion, the perspective and issues in the future development of the ACCS radar are described. 相似文献
970.
Before 2009, rollover in vehicle accidents had not been significantly studied not only because its rate is lower than other types of accidents but also because it had been easy to meet the rollover regulation, the FMVSS 216 Roof Crush Resistance target. The regulation only requires that the strength-to-weight ratio (SWR) be 1.5, i.e., it was acceptable when the roof could withstand a force of only 1.5 times the vehicle??s weight. In other words, rollover is not considered an important safety factor. However, presently, the situation has completely changed. Rollover is now considered a key safety factor. Recently, the number of rollover incidences has been increasing, reaching as much as the number of front, side and rear accidents. Furthermore, the IIHS has begun to require that the roof must withstand a force of 4.0 times the vehicle??s weight, a more severe restriction than FMVSS. To satisfy this requirement, many manufacturers, universities and institutes are studying the topic. This paper focuses on changing the body structure to minimize injury to the occupant when rollover occurs and help rollover safety performance become excellent. This paper draws on a simple analysis that is based on general factors: changes in the material, the addition of welds and additional reinforcements. The best result will be determined, as described by this paper. 相似文献