全文获取类型
收费全文 | 1483篇 |
免费 | 84篇 |
专业分类
公路运输 | 372篇 |
综合类 | 449篇 |
水路运输 | 428篇 |
铁路运输 | 271篇 |
综合运输 | 47篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 33篇 |
2021年 | 61篇 |
2020年 | 42篇 |
2019年 | 29篇 |
2018年 | 25篇 |
2017年 | 19篇 |
2016年 | 27篇 |
2015年 | 39篇 |
2014年 | 72篇 |
2013年 | 82篇 |
2012年 | 114篇 |
2011年 | 120篇 |
2010年 | 127篇 |
2009年 | 115篇 |
2008年 | 118篇 |
2007年 | 146篇 |
2006年 | 120篇 |
2005年 | 63篇 |
2004年 | 29篇 |
2003年 | 35篇 |
2002年 | 21篇 |
2001年 | 37篇 |
2000年 | 23篇 |
1999年 | 11篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1988年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1567条查询结果,搜索用时 15 毫秒
991.
992.
The kinematic accuracy of space manipulator determines whether the spacecraft performs normally or not. Problems pertaining to structural deformation have received increased attention in recent times. In the space manipulator systems, flexible arms and joints can induce drastic dynamic instabilities. In applications such as the space station, kinematic error due to structural deformation can jointly affect the performance characteristics. And it is crucial for accuracy control of space manipulator to establish a precision index. Here we analyze the dynamics characteristic of flexible space manipulator considering the hysteresis of harmonic reducer based on method of nonconstraint boundary modal. For the sake of describing the output accuracy, we integrate the method of analytic hierarchy process(AHP) to establish a comprehensive evaluation index. A numerical simulation is performed to analyze the nonlinear dynamic characteristics of space manipulator with harmonic reducer. With the analysis of accuracy assessment, the relation among the hysteresis angle, rigidity and output accuracy is revealed. Considering the elastic modulus of flexible space manipulator and the hysteresis angle of harmonic reducer, we conduct an evaluation of output characteristics of flexible space manipulator with the proposed comprehensive evaluation index. The accuracy evaluation of output characteristics based on the proposed comprehensive evaluation index is implemented in the initial stage of space manipulator’s design, which can not only solve the problems existing in the design but also save cost savings for ground tests. The results can be used in designing and optimizing future space manipulators, which may provide valuable references for design and thermal control of the space manipulator. 相似文献
993.
For the realization of green communications in cognitive radio ad hoc networks(CRAHNs), selfadaptive and efficient power allocation for secondary users(SUs) is essential. With the distributed and timevarying network topology, it needs to consider how to optimize the throughput and power consuming, avoid the interference to primary users(PUs) and other SUs, and pay attention to the convergence and fairness of the algorithm. In this study, this problem is modeled as a constraint optimization problem. Each SU would adjust its power and corresponding strategy with the goal of maximizing its throughput. By studying the interactions between SUs in power allocation and strategy selection, we introduce best-response dynamics game theory and prove the existence of Nash equilibrium(NE) point for performance analysis. We further design a fully distributed algorithm to make the SUs formulate their strategy based on their utility functions, the strategy and number of neighbors in local area. Compared with the water-filling(WF) algorithm, the proposed scheme can significantly increase convergent speed and average throughput, and decrease the power consuming of SUs. 相似文献
994.
正At present,big data technologies have been successfully applied in many fields such as medical care,energy,communications,and e-commerce.In the shipping industry,some prophetic companies have tried and achieved some preliminary outcome.It is reported that countries such as Europe,Japan,and South Korea have carried out pre-research,data collection,and exploration of shipping big data 相似文献
995.
996.
捷联系统是惯性导航设备发展的必然趋势.传统双态陀螺罗经模型具有抗干扰能力强、在高纬度区可正常使用、在线测漂等优点,可借鉴到现代捷联罗经设计中.论文介绍了捷联罗经应用传统双态陀螺罗经模型的思路和方法,并给出了模型框图和程序流程图. 相似文献
997.
998.
为提升船闸工程信息模型应用水平,提高信息的利用效率和效益,在《水运工程设计信息模型应用标准》基础上,细化并编制了满足标准要求的船闸工程BIM设计细则,根据应用实践建立了船闸工程BIM设计总体实施流程。以某船闸工程为例,对信息模型的层级组织、模型内容、协同设计、分类编码、模型存储和成果交付等进行了实践,验证了基于标准的实施工作流程的可行性和标准在船闸工程BIM设计的适用性。结果表明,《水运工程设计信息模型应用标准》可以规范船闸工程BIM设计,提升设计成果质量、实现数字化交付和应用,也为船闸工程BIM技术实施和数字孪生建设提供了参考。 相似文献
999.
本文对固定趴杆式起重船在固定吊重下,变化趴杆角度对起重船吃水的影响进行了分析,并结合工程实例进行验证计算,为其他海上吊装作业提供参考及借鉴。 相似文献
1000.
张建国 《现代城市轨道交通》2007,(5):22-25
目前国内外地铁无线通信工程采用漏缆实现电磁场覆盖成为首选方案。地铁工程建设中对漏缆的方案选择、材料选型、配置均需严密的计算和严格的审查,在漏缆采购、漏缆安装、漏缆测试等不同阶段进行严格的质量控制,用以确保漏缆工程质量。 相似文献