全文获取类型
收费全文 | 154篇 |
免费 | 1篇 |
专业分类
公路运输 | 30篇 |
综合类 | 43篇 |
水路运输 | 37篇 |
铁路运输 | 9篇 |
综合运输 | 36篇 |
出版年
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 12篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 15篇 |
2012年 | 10篇 |
2011年 | 6篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 5篇 |
2007年 | 3篇 |
2006年 | 10篇 |
2005年 | 11篇 |
2004年 | 2篇 |
2003年 | 1篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有155条查询结果,搜索用时 257 毫秒
91.
Konrad Herold Marius Böhmer Rene Savelsberg Alexander Müller Jan Schröter Jan Karthaus Un-Jae Seo Georg Jacbos Kay Hameyer Jakob Andert 《International Journal of Automotive Technology》2018,19(5):869-878
Range extender modules are one option to compensate for short drive ranges of electric vehicles. The close interaction of combustion engine and generator poses new challenges in development. A key requirement for range extender systems is to be light and virtually imperceptible in operation. High-speed electrical machines aim at increasing power density. However, their introduction in a range extender requires a gearbox. The combustion engine torque fluctuations can lead to rattle in the gearbox. The rattle can be overcome by a dual mass flywheel. An interdisciplinary model is developed and used to analyse three different range extender systems: one with a low speed generator without gearbox, one with a high-speed generator, and one with a high-speed generator and a dual mass flywheel. The efficiency was found to be higher for the system with a low speed generator, whereas the power density and the costs are beneficial for the high-speed concept. A dual mass flywheel eliminates the changes of torque direction in the gearbox. It reduces the speed fluctuations of the gearbox and generator by over 90 % compared to the low speed setup. But it increases rolling moment and subsequently chassis excitation compared to a setup with only a gearbox. 相似文献
92.
基于任意欧拉拉格朗日(ALE)方法,忽略流体的粘性,建立水射流冲击刚性平板的数值模型。为了更为精确地捕捉流场中压力波,该文推导了在ALE框架下的间断有限元方法。该方法易于提高数值离散的空间精度,数值稳定性较
好,利于精确模拟高速水射流冲击过程。对于自由液面的变形,采用径向基函数方法确定网格单元的速度。该方法采用边界网格节点的信息去推导出内部网格节点的信息,不需要单元信息。平头水柱射流冲击的数值结果与Autodyn的数值结果吻合较好。在验证方法合理性的基础上,文中对平头及圆头水柱中压力波的分布特性进行了分析。数值结果表明:当冲击在平板表面时,会在产生一个压力波之后向水域内传播,且使得平板受到较大压力的作用。此外,圆头水柱的射流冲击将会产生一个更大的压力峰值。 相似文献
好,利于精确模拟高速水射流冲击过程。对于自由液面的变形,采用径向基函数方法确定网格单元的速度。该方法采用边界网格节点的信息去推导出内部网格节点的信息,不需要单元信息。平头水柱射流冲击的数值结果与Autodyn的数值结果吻合较好。在验证方法合理性的基础上,文中对平头及圆头水柱中压力波的分布特性进行了分析。数值结果表明:当冲击在平板表面时,会在产生一个压力波之后向水域内传播,且使得平板受到较大压力的作用。此外,圆头水柱的射流冲击将会产生一个更大的压力峰值。 相似文献
93.
There is broad and growing consensus regarding the central place of integrated Land Use and Transport (LUT) strategy development
in establishing more efficient and sustainable urban environments. However, empirical evidence shows that such integration
is hard to achieve in daily planning practice, due to many institutional barriers and substantive differences. More specifically,
the tools developed to support LUT strategy development have very low implementation rates in daily planning practice. This
paper introduces the concept of ‘knowledge generation’ as a potentially useful mechanism for closing the gap between support
tools and planning practice. Through two specific Dutch planning cases, we analyze the applicability of this concept in supporting
integrated LUT strategy development. The paper focuses on the developed strategies, how these differ from current practice,
and how knowledge generation supported their development. We argue that socialization produces shared strategies and that
effective socialization needs to be supported by efficient mutual exchange between tacit and explicit knowledge. We conclude
by discussing the implications of this argument for the wider practice of LUT planning integration. 相似文献
94.
Humaninterleukin 18(hIL 18)isanewlyiden tifiedcytokinemainly producedbymonocytesandmacrophages.ThecytokinecaninduceTh1cellstosecreteIFN γ ,IL 2andGM CSF .Itenhancesthecy totoxityofNKandCTLcell,andalsoreducesthelev elofIL 10 .Thus,thereispotentialtherapeuticvalueof… 相似文献
95.
结合纵梁漏孔检测的具体情况对随机Hough变换加以改进和应用,实现对纵梁图像圆的检测,并减少了随机Hough变换中存在的无效积累问题。 相似文献
96.
Today’s vehicles are designed with lighter weight to increase performance and to lower fuel consumption, while at the same
time meeting the demands of safety requirements. Reducing the cross-section of structural elements to achieve weight reduction
can lead to adverse effects on passive safety of the vehicle. In such cases, necessary design modifications must be created
to overcome the adverse effects. For this purpose, front rail columns with crush initiators are used in the front zone of
cars. These shock-absorbing elements act as energy consuming devices that convert impact energy (kinetic energy) into plastic
deformation energy. Simulation of this energy conversion phenomenon is the subject of this paper. The primary objective of
this study is to computationally determine how various crush initiators can reduce the maximum crushing force and how different
types of structural modifications affect the observed folding form. The ribs near the crash area are placed in two rows and
four different configurations on all facing sides of the column in order to decrease reaction forces and absorb more kinetic
energy. These structures are analyzed under axially loaded crushing forces using the explicit nonlinear finite element analysis
solver ANSYS/LS-DYNA. 相似文献
97.
The aim of this paper is to study visual autonomous navigation of unmanned aerial vehicle (UAV) in indoor global positioning system (GPS) denied environment. The UAV platform of the autonomous navigation flight control system is designed and built. The principle of visual localization and mapping algorithm is studied. According to the characteristics of UAV platform, the visual localization is designed and improved. Experimental results demonstrate that the UAV platform can realize the tasks of autonomous localization, navigation and mapping based on visual in unknown environments. 相似文献
98.
99.
Transportation - The combined use of the bicycle and the train in the Netherlands has risen steadily over the past decade. However, little is yet known about the underlying processes driving the... 相似文献
100.
A novel method is presented to improve the recognition rate of warhead in this paper. Firstly, a tool for electromagnetic calculation, like CST Microwave Studio, is used to simulate the frequency response of the electromagnetic scattering. Secondly, the echo and further the range profile are acquired from the frequency response by further processing. Thirdly, a set of discriminative features is extracted from the range profiles of the target. Fourthly, these features are used to construct a dictionary for the sparse representation classifier. Finally, the sample of the target can be classified by solving the sparsest coefficients. Since the reconstruction result is determined by a linear combination of the training samples, this method has a good robustness for the variable features. By formulating the problem within a feature-based sparse representation framework, the presented method combines the discriminative features of each sample during the sparse recovery process rather than in a postprocessing manner. Moreover, based on the feature representation space rather than a single feature or image pixel, the constructed dictionary exhibits both strong expressive and discriminative powers that can enhance the classification performance of the test sample. A series of test results based on the simulated data demonstrates the effectiveness of our method. 相似文献