全文获取类型
| 收费全文 | 3711篇 |
| 免费 | 4篇 |
专业分类
| 公路运输 | 855篇 |
| 综合类 | 712篇 |
| 水路运输 | 1216篇 |
| 铁路运输 | 54篇 |
| 综合运输 | 878篇 |
出版年
| 2023年 | 11篇 |
| 2022年 | 36篇 |
| 2021年 | 17篇 |
| 2020年 | 15篇 |
| 2019年 | 17篇 |
| 2018年 | 389篇 |
| 2017年 | 328篇 |
| 2016年 | 316篇 |
| 2015年 | 17篇 |
| 2014年 | 80篇 |
| 2013年 | 294篇 |
| 2012年 | 151篇 |
| 2011年 | 298篇 |
| 2010年 | 300篇 |
| 2009年 | 133篇 |
| 2008年 | 269篇 |
| 2007年 | 164篇 |
| 2006年 | 37篇 |
| 2005年 | 86篇 |
| 2004年 | 70篇 |
| 2003年 | 82篇 |
| 2002年 | 38篇 |
| 2001年 | 24篇 |
| 2000年 | 35篇 |
| 1999年 | 20篇 |
| 1998年 | 29篇 |
| 1997年 | 35篇 |
| 1996年 | 32篇 |
| 1995年 | 45篇 |
| 1994年 | 20篇 |
| 1993年 | 20篇 |
| 1992年 | 14篇 |
| 1991年 | 11篇 |
| 1990年 | 14篇 |
| 1989年 | 12篇 |
| 1988年 | 15篇 |
| 1987年 | 14篇 |
| 1986年 | 11篇 |
| 1985年 | 19篇 |
| 1984年 | 17篇 |
| 1983年 | 14篇 |
| 1982年 | 22篇 |
| 1981年 | 27篇 |
| 1980年 | 18篇 |
| 1979年 | 33篇 |
| 1978年 | 12篇 |
| 1977年 | 18篇 |
| 1976年 | 8篇 |
| 1975年 | 10篇 |
| 1974年 | 8篇 |
排序方式： 共有3715条查询结果，搜索用时 0 毫秒
201.
David J. M. Sampson David Cebon 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2003,40(4):229-270
Summary Strategies are investigated for controlling active anti-roll systems in single unit heavy road vehicles, so as to maximise roll stability. The achievable roll stability improvements that can be obtained by applying active anti-roll torques to truck suspensions are discussed. Active roll control strategies are developed, based on linear quadratic controllers. It is shown that an effective controller can be designed using the LQG approach, combined with the loop transfer recovery method to ensure adequate stability margins. A roll controller is designed for a torsionally flexible single unit vehicle, and the vehicle response to steady-state and transient cornering manoeuvres is simulated. It is concluded that roll stability can be improved by between 26% and 46% depending on the manoeuvre. Handling stability is also improved significantly. 相似文献
202.
T. A. Wenzel K. J. Burnham M. V. Blundell R. A. Williams 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2006,44(2):153-171
The article demonstrates the implementation of a model-based vehicle estimator, which can be used for combined estimation of vehicle states and parameters. The estimator is realised using the dual extended Kalman filter (DEKF) technique, which makes use of two Kalman filters running in parallel, thus 'splitting' the state and parameter estimation problems. Note that the two problems cannot be entirely separated due to their inherent interdependencies. This technique provides several advantages, such as the possibility to switch off the parameter estimator, once a sufficiently good set of estimates has been obtained. The estimator is based on a four-wheel vehicle model with four degrees of freedom, which accommodates the dominant modes only, and is designed to make use of several interchangeable tyre models. The paper demonstrates the appropriateness of the DEKF. Results to date indicate that this is an effective approach, which is considered to be of potential benefit to the automotive industry. 相似文献
203.
204.
Undesired lateral force inevitably exists in a MacPherson suspension system, which is liable to damper rod’s side wear and promotes the damper’s inner friction decreasing the ride performance from the suspension system. Substituting a new side load spring with curved centerline for the conventional coil spring has been proven able to solve these problems and Multi-body Dynamics combining with Finite Elements Analysis may be an efficient method in optimizing its design. Therefore, taking a passenger car as example, a detailed multi-body dynamics model for the suspension system is built to simulate forces exerted on the damper and the minimization of its lateral component is selected as the design target for the spring. When the structure optimization of the side load spring is performed using FEA software ANSYS, its vertical and lateral elastic characteristics, supported by test data, are analyzed. After importing FEA results back to the suspension system, the dynamics simulation can be performed to validate the optimization result. 相似文献
205.
The diffusive and in situ fluxes of dissolved inorganic carbon (DIC) and total alkalinity (TA) have been measured and an estimation has been made of the water–atmosphere fluxes of CO2 in three estuarine systems of the Cantabrian Sea during the spring of 1998. Each of these systems undergoes a different anthropogenic influence. The diffusive fluxes of dissolved inorganic carbon and total alkalinity obtained present values ranging between 0.54–2.65 and 0.0–2.4 mmol m−2 day−1, respectively. These ranges are in agreement with those of other coastal systems. The in situ fluxes are high and extremely variable (35–284 mmol TA m−2 day−1, 43–554 mmol DIC m−2 day−1 and 22–261 mmol dissolved oxygen (DO) m−2 day−1), because the systems studied are very heterogeneous. The values of the ratio of the in situ fluxes of TA and DIC show on average that the rate of dissolution of CaCO3 is 0.37 times that of organic carbon oxidation. Equally, the interval of variation of the relationship between the benthic fluxes of inorganic carbon and oxygen (FDIC/FDO) is very wide (0.3–13.9), which demonstrates the different contributions made by the processes of aerobic and anaerobic degradation of the organic matter, as well as by the dissolution–precipitation of CaCO3. The water–atmosphere fluxes of CO2 present a clear dependence on the salinity. The brackish water of these systems (salinity<20), where maximum fluxes of 989 mmol m−2 day−1 have been estimated, act as a source of CO2 to the atmosphere. The more saline zones of the estuary (salinity>30) act as a sink of CO2, with fluxes between −5 and −10 mmol m−2 day−1. 相似文献
206.
TANGLi-qiang ZHENGGui CAIYan-hong 《船舶与海洋工程学报》2004,3(2):73-78
A mechanical model of visco-elastic material is established in order to investigate viscous effect in dynamic growing crack-tip field of mode Ⅱ. It is shown that in stable creep growing phase, elastic deformation and viscous deformation are equally dominant in the near-tip field, the stress and strain have the same singularity, namely, (σε) ∝r^-1/(n-1). The asymptotic solutions of separatied variables of stress, stain and displacement in crack-tip field are obtained by asymptotic analysis, and the results of numerical value of stress and strain in crack-tip field are obtained by shooting method. Through numerical calculation, it is shown that the near-tip fields are mainly governed by the creep exponent n and Mach number M. By the asymptotic analysis to the crack-tip field, the fracture criterion of mode Ⅱ dynamic growing crack of visco-elastic materials is put forward from the point of view of strain. 相似文献
207.
The application of prefabricated tunnel technology has been become a new research field both in China and abroad. Based on the running tunnel between Yufuhe station and Wangfuzhuang station of Jinan rail transit line R1, a new prefabricated tunnel construction technology, the PBA method is presented. This paper makes a detailed discussion on section form, supporting scheme and construction process of the PBA method. In this study, 3D a new 3D numerical model for PBA method is presented by finite difference numerical simulation software Flac and the construction processes are modeled. The rule of ground surface settlement, ground deformation and structural stress caused by PBA method is studied in detail. Results show that the structure of PBA method can effectively control the deformation magnitude and scope. Stress concentration appears at the prefabricated connection parts and the reinforcement needs to check. The total assembled structure forms the load-bearing system after the completion of the lateral wall. The built-in depth of the precast pile and pile bottom grouting quality should to be ensured to control the displacement of the precast piles. The results of this study will be a useful reference for similar projects in the future. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved. 相似文献
208.
Modelling the impact of weather conditions on active transportation travel behaviour 总被引：1，自引：0，他引：1
Sheyda Saneinejad Matthew J. RoordaChristopher Kennedy 《Transportation Research Part D: Transport and Environment》2012,17(2):129-137
Three weather sensitive models are used to explore the relationship between weather and home-based work trips within the City of Toronto, focusing on active modes of transportation. The data are restricted to non-captive commuters who have the option of selecting among five basic modes of auto driver, auto passenger, transit, bike and walk. Daily trip rates in various weather conditions are assessed. Overall, the results confirm that impact of weather on active modes of transportation is significant enough to deserve attention at the research, data collection and planning levels. 相似文献
209.
Transportation - The paper studies a general bidirectional public transport line along which demand varies by line section. The length of line sections also varies, and therefore their contribution... 相似文献
210.
We propose a semiparametric approach that can capture the nonlinearity of deterministic components of the utility functions in discrete choice models and demonstrate it by analyzing travel mode choice behaviour for an interregional trip. The proposed smoothing spline-based specification method can be used to make ex ante evaluations regarding the parametric specifications of the deterministic utility functions in discrete choice models. 相似文献