全文获取类型
收费全文 | 3936篇 |
免费 | 9篇 |
专业分类
公路运输 | 1068篇 |
综合类 | 711篇 |
水路运输 | 1233篇 |
铁路运输 | 51篇 |
综合运输 | 882篇 |
出版年
2023年 | 11篇 |
2022年 | 36篇 |
2021年 | 15篇 |
2020年 | 11篇 |
2019年 | 17篇 |
2018年 | 391篇 |
2017年 | 346篇 |
2016年 | 375篇 |
2015年 | 17篇 |
2014年 | 78篇 |
2013年 | 294篇 |
2012年 | 175篇 |
2011年 | 354篇 |
2010年 | 351篇 |
2009年 | 132篇 |
2008年 | 300篇 |
2007年 | 165篇 |
2006年 | 37篇 |
2005年 | 86篇 |
2004年 | 69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 | 31篇 |
1995年 | 44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3945条查询结果,搜索用时 15 毫秒
51.
Fuzzy-logic applied to yaw moment control for vehicle stability 总被引:6,自引:0,他引:6
B. L. Boada M. J. L. Boada V. Dí az 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2005,43(10):753-770
In this paper, we propose a new yaw moment control based on fuzzy logic to improve vehicle handling and stability. The advantages of fuzzy methods are their simplicity and their good performance in controlling non-linear systems. The developed controller generates the suitable yaw moment which is obtained from the difference of the brake forces between the front wheels so that the vehicle follows the target values of the yaw rate and the sideslip angle. The simulation results show the effectiveness of the proposed control method when the vehicle is subjected to different cornering steering manoeuvres such as change line and J-turn under different driving conditions (dry road and snow-covered). 相似文献
52.
With the development of vehicle gearbox to high-power-density and high-speed, how to predict and optimize the dynamic characteristics of vehicle gearbox becomes increasingly prominent. Aiming at the vehicle gearbox, this paper comprehensively and deeply studies the dynamic characteristics under the multi-boundary conditions. The generation mechanism of the multi-source excitations triggering the gearbox vibration is analyzed firstly. The vibration transfer path of the gearbox is explored. Secondly, the engine excitation, the gear meshing excitation and the bearing support load are numerically calculated. According to the finite element method, a fluid-solid coupling finite element model of the gearbox body is established to predict the gearbox dynamic responses based on the Galerkin method and the Hamiltonian variational principle. Finally, the effects of the excitation condition, oil height and reinforcement forms on the vibration responses of the gearbox body are thoroughly studied by simulation. The analysis indicates that it not only helps to modify and improve the method of forecasting the gearbox dynamic response, and also provides the theoretical and technical guidance for the gearbox design and optimization. 相似文献
53.
The paper aims at the problem of multi-targets threat degree being hard to be evaluated accurately in complex air defense battlefield environments. Combined with multi-sensors information fusion and interval-valued intuitionistic fuzzy sets (IVIFS) theories, the target priority determination is studied. The score and accuracy functions of IVIFS are improved with thinking about the hesitating information in order to increase the rationality. Then, the influence factors of target priority and the nonlinear relationship between the influence factors and target priority are analyzed. Next, the algorithms for calculating the factor weights and sensor weights are given. Based on the theory of IVIFS and technique for order preference by similarity to an ideal solution (TOPSIS), two methods of target priority determination based on the IVIFS and TOPSIS are proposed. At last, an application example verifies the effectiveness and flexibility of the proposed algorithms. 相似文献
54.
H. M. Abdul Aziz Nicholas N. Nagle April M. Morton Michael R. Hilliard Devin A. White Robert N. Stewart 《Transportation》2018,45(5):1207-1229
This study estimates a random parameter (mixed) logit model for active transportation (walk and bicycle) choices for work trips in the New York City (using 2010–2011 Regional Household Travel Survey Data). We explored the effects of traffic safety, walk–bike network facilities, and land use attributes on walk and bicycle mode choice decision in the New York City for home-to-work commute. Applying the flexible econometric structure of random parameter models, we capture the heterogeneity in the decision making process and simulate scenarios considering improvement in walk–bike infrastructure such as sidewalk width and length of bike lane. Our results indicate that increasing sidewalk width, total length of bike lane, and proportion of protected bike lane will increase the likelihood of more people taking active transportation mode This suggests that the local authorities and planning agencies to invest more on building and maintaining the infrastructure for pedestrians. Further, improvement in traffic safety by reducing traffic crashes involving pedestrians and bicyclists, will increase the likelihood of taking active transportation modes. Our results also show positive correlation between number of non-motorized trips by the other family members and the likelihood to choose active transportation mode. The model would be an essential tool to estimate the impact of improving traffic safety and walk–bike infrastructure which will assist in investment decision making. 相似文献
55.
杨平 《上海交通大学学报(英文版)》2018,23(4):515-526
The present paper presents a historical review associated with the research works on hull girder strength of ship and ship-shaped structures. Then, a new program is developed to determine the ultimate vertical bending moment of hull girder by applying direct method, stress distribution method, and progressive collapse analysis method. Six ships and ship-shaped structures used in the benchmark study of International Ship and Offshore Structures Congress (ISSC) in 2012 are adopted as examples. The calculation results by applying the developed program are analyzed and compared with the existing results. Finally, the roles of the developed program and its further development are discussed. 相似文献
56.
The present work investigates the compressive axial ultimate strength of fillet-welded steel-plated ship structures subjected to uniaxial compression, in which the residual stresses in the welded plates are calculated by a thermo-elasto-plastic finite element analysis that is used to fit an idealized model of residual stress distribution. The numerical results of ultimate strength based on the simplified model of residual stress show good agreement with those of various methods including the International Association of Classification Societies (IACS) Common Structural Rules (CSR), leading to the conclusion that the simplified model can be effectively used to represent the distribution of residual stresses in steel-plated structures in a wide range of engineering applications. It is concluded that the widths of the tension zones in the welded plates have a quasi-linear behavior with respect to the plate slenderness. The effect of residual stress on the axial strength of the stiffened plate is analyzed and discussed. 相似文献
57.
Project portfolio management (PPM) is the centralized management method, process and technology in multiple projects. When multiple projects in the space industry are implemented, it provides an effective methodology to resolve the problems at the same time such as conflicts among models, decrease in design efficiency, and increase in target deviation. Hence, a PPM dedicated to multiple projects management in space enterprise is presented in this paper. Firstly, an analysis of features and contents in space enterprise portfolio management mode is performed by using PPM based on its specific strategic characteristics. Then, the principle and selection methods of PPM are provided as a reference for the future development of an enterprise. Finally, a multiple-level organization architecture including decision making layers, function management layers and project execution layers is proposed so as to adapt to possible changes in the multiple projects and correspond to the strategic development. As a consequence, a perfect matching mechanism to fit the changes in PPM modes is reached. In addition, the flow chart of PPM is designed and optimized by analyzing the implementation procedure of strategic target and project portfolio life-cycle, which is expected to realize the purpose of improving space enterprise management efficiency, project management capacity, innovation development and economic benefits. 相似文献
58.
Gulsah Akar Kelly J. Clifton Sean T. Doherty 《Transportation Research Part A: Policy and Practice》2012,46(8):1194-1204
This paper analyzes the activity choices of individuals and the links between socio-demographics, daily schedules and activity attributes using a new activity choice framework. Activities are first clustered into groups based on their salient attributes, such as duration, frequency, flexibility, planning times, and number of involved persons, rather than their functional types (work, leisure and household obligations), using a K-means cluster technique. This led to the creation of several new activity groups such as “long, temporally fixed, personally flexible activities”, “short and flexible activities”. These activity groups form the choice set for the mixed logit activity choice modeling structure developed for the leisure activities in the second part of the paper. The model results reveal the significant relationships between socio-demographics, temporal characteristics, and characteristics of the schedules on leisure activity choice. The results demonstrate how changing demographics and other activities in individuals’ schedules may affect the nature of the leisure activities and present the substitution and complimentary effects that these new activity groups have on one another. 相似文献
59.
The effect of interference fits on the fatigue lives of bolted composite joints is investigated by conducting mechanical tests. Static and fatigue tests are carried out on specimens made of carbon-bismaleimide composites joined together as double-lap single-bolt joints. The bolts having interference fits ranging of 0 (neat fit), 0.5%, 0.75% and 1% are performed. The results demonstrate the relationship between fatigue life and different values of interference fits. After the fatigue tests, non-destructive evaluation (NDE) and scanning electron microscope (SEM) are used to observe the damage of the surrender and surface of the hole. The test results show that the interference fitted specimens have improved fatigue life compared to the neat fitted specimen. The NDE and SEM results reveal that the damage degree of interference fitted specimen is weaker than that for the neat fitted one. 相似文献
60.
Transportation - Everyday commuting as a mobility phenomenon is well-investigated and has been the topic of many contributions. Nevertheless, the distinct determinants of the commuting... 相似文献