全文获取类型
收费全文 | 831篇 |
免费 | 4篇 |
专业分类
公路运输 | 236篇 |
综合类 | 20篇 |
水路运输 | 271篇 |
铁路运输 | 21篇 |
综合运输 | 287篇 |
出版年
2022年 | 16篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 20篇 |
2017年 | 22篇 |
2016年 | 26篇 |
2015年 | 11篇 |
2014年 | 30篇 |
2013年 | 112篇 |
2012年 | 30篇 |
2011年 | 36篇 |
2010年 | 41篇 |
2009年 | 35篇 |
2008年 | 39篇 |
2007年 | 15篇 |
2006年 | 21篇 |
2005年 | 22篇 |
2004年 | 12篇 |
2003年 | 24篇 |
2002年 | 18篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 18篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 16篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 13篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 10篇 |
1972年 | 5篇 |
排序方式: 共有835条查询结果,搜索用时 15 毫秒
561.
A. G. Thompson B. R. Davis 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1988,17(4):179-192
In optimally controlled active suspensions with either full or incomplete state feedback there is tradeoff between system performance and overall stiffness. It is sought to remove this limitation by incorporating integral action which results in a system with infinite stiffness towards static loading, but which is soft with respect to road inputs. The system is also able to eliminate the steady state deflections due to step and (potentially) ramp type inputs at the wheel. Optimality is retained at the cost only of a derivative constraint and the system can be physically realised using output feedback control. 相似文献
562.
G. F. Hayhoe 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1979,8(1):49-72
A model of driver behavior is described which is based on a current theory of neurophysiological processes occurring in the cerebellum. The model learns to control the vehicle through experience, provides discontinuous ramp steer inputs to the vehicle, accepts discontinuous input data, and is applicable to all control situations.
The model is implemented on a simple simulation model of a car and learning is accomplished by the use of an explicit driver model which drives the vehicle along a specified trajectory. 相似文献
The model is implemented on a simple simulation model of a car and learning is accomplished by the use of an explicit driver model which drives the vehicle along a specified trajectory. 相似文献
563.
Hydraulic hybrid powertrains are a critical technology used in buses to improve fuel economy and emission performance. New exploration in configuring a parallel hydraulic hybrid bus (PHHB) is developed in this paper with no changes made to the conventional base bus driveline. An integrated model and simulation of the parallel hydraulic hybrid bus is built based on AMESim, which is used to model the hydraulic powertrain and conventional bus driveline, and interlinked with a Matlab/Simulink/Stateflow model of the control unit. Compared to conventional buses, the fuel economy of the PHHB improved by 28% in real road tests at the SMVIC (National Center of Supervision and Inspection on Motor Products Quality (Shanghai)); the approximate improvement of fuel economy was 30% in simulated runs, which validates our model. Then a Non-linear Programming by Quadratic Lagrangian algorithm (NLPQL), is applied to optimize control strategies for improving fuel economy and emissions. Simulations also demonstrate that fuel economy and emission performance can be significantly improved. However, optimum parameters for maximum fuel economy and minimum emissions are not consistent. Simulation results show tradeoffs between fuel economy and emissions in PHHB, and optimal parameters can be selected by balancing design objectives. 相似文献
564.
Research purposes: Shunt capacitors are the important device of power system in electrified railway. The relay for shunt capacitors is equipped with over-current, harmonic over-current, difference current, differential voltage protections, etc. When HXD locomotive went through some power supply arms on Long-Hai line, mal-operation of differential voltage protection for shunt capacitors occurred frequently. According to load characteristic of AC-DC-AC locomotive and actual situation on site, the fault wave of differential voltage protection in a traction substation is analyzed, the reason of mal-operation is found, and the corresponding solution is got. Research conclusions:(1) The mal-operation reason of differential voltage protection is caused by Fourier transform which is influenced by frequency aliasing. The influence of frequency aliasing results in the amplification of differential voltage value and mal-operation of differential voltage protection. (2) By altering the sampling frequency from 20 points per period to 100 points per period, the influence of frequency aliasing on Fourier transform is eliminated. (3) There have been no longer mal-operations of differential voltage protection, ever since the revised program of protection came into use. (4) In the area of power supply system of electrified railway, this analytical method and solution have important reference value in analysis and application of electrical quantities with higher harmonics. © 2018, Editorial Department of Journal of Railway Engineering Society. All right reserved. 相似文献
565.
新型快餐盒生物降解性能试验方法研究 总被引:1,自引:0,他引:1
通过固体培养微生物侵蚀试验、液体培养微生物侵蚀试验、降解过程中纤维素酶活性测定、纤维素酶侵蚀试验和降解过程中 C O2 生成体积分数的测定等试验结果分析,认为固体培养微生物侵蚀试验、纤维素酶侵蚀试验及 C O2 生成量测定试验可用于评价新型快餐盒生物降解性能。 相似文献
566.
瑞士联邦铁路(SBB)现有客运车队的机车车辆类型极多,除了现代大功率机车、摆式列车、低地板车辆和客车外,还包括在这期间作了改进的旧系列机车车辆.今后的采购政策首先是购置新的区间列车. 相似文献
567.
Panos G. Michalopoulos Gregory Stephanopoulos George Stephanopoulos 《Transportation Research Part B: Methodological》1981,15(1):35-51
A real time control policy minimizing total intersection delays subject to queue length constraints at an isolated signalized intersection is developed in this paper. The policy is derived from a new traffic model which describes the simultaneous evolution of queue lengths of two conflicting traffic streams, controlled by a traffic light, in both time and space. The model is based on the examination of shock waves generated upstream of the stop lines by the intermittent service of traffic at the signal. The proposed policy was tested against the existing pre-timed control policy at a high volume intersection and it was found superior, especially when demands increase well above the saturation level. 相似文献
568.
The use of Intelligent Transportation Systems (ITS) in construction work zones to disseminate traffic information has increased significantly in recent years, mainly with the use of Variable Message Signs (VMS). VMS are used based on the assumption that informed drivers will make better travel decisions, thereby reducing congestion. However, the extent of change in driver behavior is difficult to predict prior to ITS deployment. This difficulty leads to the larger problem of justifying investment in ITS. This article proposes an ITS deployment decision support tool using micro‐simulation. The approach determines the required diversion effectiveness of a work zone ITS deployment using VMS. The methodology was tested using the Glenmore Trail/Elbow Drive/5th Street interchange project (GE5) in Calgary, Canada. The results indicate that the proposed approach will assist agencies in justifying ITS investment by exhibiting the potential resultant societal benefits. 相似文献
569.
570.
James G. Mitchell Hidekatsu Yamazaki Laurent Seuront Fabian Wolk Hua Li 《Journal of Marine Systems》2008,69(3-4):247
Marine phytoplankton experience competition, predation, infection and aggregation occurring across distances of micrometres to centimetres. However, the consequences of these interactions influence global processes, such as climate and fisheries productivity. There is a long-standing default assumption that these global processes cannot be traced to plankton distributions and interactions below a few metres because of the homogenising effect of turbulence [Hutchinson, G.E., 1961. The paradox of the plankton. Am. Nat. 95, 137–146.; Siegel, D.A., 1998. Resource competition in a discrete environment: Why are plankton distributions paradoxical? Limnol. Oceanogr. 43, 1133–1146.]. We show that, in active turbulence, phytoplankton patches, on the order of 10 cm, have repeatable asymmetry and regular spacing over distances of centimetres to tens of metres. The regularity and hierarchical nature of the patches in mixed ocean water means that phytoplankton are distributed in a dynamic, but definite seascape topography, where groups of patches coalesce between intermittent turbulent eddies. These patches may link large scale processes and microscale interactions, acting as fundamental components of marine ecosystems that influence grazing efficiency, taxonomic diversity, and the initiation of aggregation and subsequent carbon flux. 相似文献