全文获取类型
收费全文 | 1322篇 |
免费 | 17篇 |
专业分类
公路运输 | 251篇 |
综合类 | 300篇 |
水路运输 | 321篇 |
铁路运输 | 147篇 |
综合运输 | 320篇 |
出版年
2023年 | 11篇 |
2022年 | 38篇 |
2021年 | 25篇 |
2020年 | 15篇 |
2019年 | 19篇 |
2018年 | 41篇 |
2017年 | 25篇 |
2016年 | 42篇 |
2015年 | 25篇 |
2014年 | 33篇 |
2013年 | 135篇 |
2012年 | 78篇 |
2011年 | 109篇 |
2010年 | 79篇 |
2009年 | 97篇 |
2008年 | 74篇 |
2007年 | 82篇 |
2006年 | 84篇 |
2005年 | 68篇 |
2004年 | 17篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 19篇 |
2000年 | 20篇 |
1999年 | 10篇 |
1998年 | 21篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 19篇 |
1994年 | 4篇 |
1993年 | 11篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 5篇 |
1972年 | 2篇 |
排序方式: 共有1339条查询结果,搜索用时 15 毫秒
481.
Donald L. MARGOLLS 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1982,11(5):267-282
A simple vehicle model is presented incorporating passive, active, and semi-active suspensions. When the desired feedback variables are ideally available, the system response is well understood and excellent sprung mass isolation results. More often than not, the measured variables must be signal processed in some manner prior to their use in some control algorithm. This paper presents the expected response of a simple vehicle with an active and/or semi-active suspension, subject to non-ideal feedback information. 相似文献
482.
Monte Carlo analyses are generally considered the standard for uncertainty analysis. While accurate, these analyses can be expensive computationally. Recently, polynomial chaos has been proposed as an alternative approach to the estimation of uncertainty distributions (Hosder et al. A non-intrusive polynomial chaos method for uncertainty propagation in CFD simulations. In: 44th AIAA aerospace sciences meeting and exhibit, Reno, Nevada, 2006; Wu et al. Uncertainty analysis for parametric roll using non-intrusive polynomial chaos. In: Proceedings of the 12th international ship stability workshop, Washington, DC, USA, 2011). This approach works by representing the function as a series of orthogonal polynomials; the weights for which can be calculated via several methods. Previous studies have demonstrated the usefulness of this technique for comparatively simple systems such as parametric roll modeled by the Mathieu equation with normally distributed parameter values (Wu et al. Uncertainty analysis for parametric roll using non-intrusive polynomial chaos. In: Proceedings of the 12th international ship stability workshop, Washington, DC, USA, 2011). In the present work, a polynomial chaos method is applied to a nonlinear computational ship dynamics model with normally distributed input parameters. Test cases were selected where parametric roll was expected to potentially occur. The resulting probability distributions are compared to the results of a Monte Carlo analysis. In general, these results demonstrate good agreement between Monte Carlo simulation and polynomial chaos in the absence of capsize with significant computation gains found with polynomial chaos. Overall, we conclude that polynomial chaos is an effective tool for reducing simulation time costs when studying parametric roll, and potentially other ship dynamics phenomena, particularly in the absence of capsize-like bifurcations. 相似文献
483.
G. C. Pereira M. M. F. Oliveira L. P. Andrade R. P Espíndola K. G. van Hecke N. F. F. Ebecken 《Journal of Marine Science and Technology》2016,21(4):651-662
Coastal zones are among the most productive areas in the world, offering a wide variety of valuable habitats and ecosystems services. Despite the low population density in the Brazilian coastal zone, their distribution is quite concentrated near some coastal cities and state capitals. This concentration places enormous pressure on coastal resources. Therefore, the main objective of this paper is to present an overview on the current status of SiMoCo (Sistema de Monitoramento Costeiro, or Coastal Monitoring System in English) project as a possible early warning system that can be integrated to the Brazilian Coastal Management Information System. This prototype platform provides a real-time access to the composition, organization and simulation of planktonic communities. First, our results demonstrate such a system detecting a target dinoflagellate; second, we apply structural and functional indexes to compare and characterize the ecological networks from two different coastal areas. Conclusions are made about SiMoCo’s feasibility and its possible contribution to the decision-making process within integrated coastal zone management (ICZM) strategies. 相似文献
484.
Vera Horigue Michael Fabinyi Robert L. Pressey Simon Foale Porfirio M. Aliño 《Coastal management》2016,44(1):71-91
In the Philippines, networks of marine protected areas (MPAs) are more complex than individual MPAs, primarily due to involvement of multiple governance units. Hence, there is a need to understand the influence of governance context of networks on management performance. We addressed this need indirectly by evaluating the participation of network members and the governance capacity of three MPA networks with varying sizes, histories, and compositions of local governments and constituencies. We defined participation as the involvement of local governments and other stakeholders in decision-making processes. We defined governance capacity as the ability to govern interactions of social, economic, and political processes and dynamics in a political unit. We used qualitative, semi-structured key informant interviews and focus group discussions to ascertain whether participation and governance capacity are influenced by network size, institutional arrangements, and social and political contexts. We found that the sizes of the MPA networks did not affect participation and governance capacity. Instead, participation and capacity were influenced by institutional arrangements and the socioeconomic and political contexts of the local governments involved. We found that less complicated network objectives and systems for engagement, more inclusive membership, better communication, incentive systems, and strong leadership enhanced participation and governance capacity. 相似文献
485.
486.
回转型空气弹簧设计、仿真及实验研究 总被引:2,自引:0,他引:2
研究回转型空气弹簧设计计算的方法,采用MTS810试验机以及落锤冲击机对空气弹簧的性能特性进行了实验测试,设计计算及仿真计算结果和实验结果吻合较好.实验结果表明设计计算方法简单、准确,建立的Marc非线性有限元计算模型能够准确地模拟空气弹簧的特点,可用于空气弹簧地工程设计计算.空气弹簧冲击刚度有限元仿真计算及实验测试的方法可用于隔振元件冲击刚度计算与实验测试. 相似文献
487.
石冰 《西安交通大学学报(英文版)》1995,(2)
DIETARYMAGNESIUMDEFICIENCYINCREASESLEVELSANDFUNCTIONOFGiαINTHERATHEARTAFTERMYOCARDIALINFARCTIONShiBing;J.E.Heavner,L.M.Boylan... 相似文献
488.
489.
考虑利用腔QED理论模拟伊辛模型,双原子在腔中演化之后,可以实现特定量子态的稳定存储,调节相互作用时间和外驱动场的频率可以实现最大纠缠态的制备. 相似文献
490.
长期应用糖皮质激素对大鼠股骨头骨组织MMPs/TIMPs系统的影响 总被引:1,自引:0,他引:1
目的观察长期应用糖皮质激素对大鼠股骨头骨组织中基质金属蛋白酶(MMPs)/基质金属蛋白酶组织抑制剂(TIMPs)系统的影响,探讨长期应用糖皮质激素导致股骨头坏死的相关机制。方法健康SD大鼠40只,雌雄各半,随机分为低、中、高剂量激素组和对照组,每组10只。低、中、高剂量组动物分别给予肌肉注射醋酸泼尼松龙7、12.5、25mg/kg体重,每周2次;对照组给予相同体积生理盐水肌注。4周后取左侧股骨头骨组织石蜡包埋,HE染色,鉴定股骨头坏死情况;取右侧股骨头骨组织提取总RNA,采用实时定量聚合酶链反应(RT-PCR)技术检测MMP-2、MMP-9、TIMP-1、TIMP-2mRNA表达水平。结果高、中、低剂量激素组和对照组动物初期股骨头坏死发生率分别为83.33%(5/6)、66.67%(6/9)、30%(3/10)、0(0/10);各激素组与对照组比较,MMP-2、MMP-9mRNA表达增高,与激素用量呈正相关,其中,中、高剂量激素组与对照组比较,差异有统计学意义(P<0.05);TIMP-1、TIMP-2mRNA表达水平降低,且与激素用量呈负相关,差异有统计学意义(P<0.05)。结论长期应用糖皮质激素致股骨头坏死的效应可能与其调控MMPs/TIMPs系统表达有关。 相似文献