浅析科技文献检索

简要分析了科技文献的类型和检索途径,同时提供相关网络联接和文献馆藏(特别是船舶和船舶相关类学科文献的馆藏),并介绍有关通过国际互联网实现馆际文献传递、国际联机数据库文献检索和下载等,展现网络时代资源共享的便利和优势.     

进口巴西铁矿石船型经济论证

随着钢铁行业的发展,我国对进口铁矿石依存度逐年增加。干散货船队受市场和成本结构的影响,船舶经济效果变化较大,经济效果将直接影响我国进口铁矿石的船型发展。建立符合目前现状的巴西进口铁矿石单船经济模型,绘制评价指标变化曲线。确定最优船型,进行敏感性分析,为矿石码头制定到港船型规划提供参考。     

移相法在H半桥型励磁电流开关功放中的应用

本文提出采用两路占空比相同但具有一定相位差的PWM控制方法,可以在不影响响应速度的情况下减小电流纹波。分析了H半桥型励磁功放工作原理,给出了0~180°移相的电流纹波统一计算公式。以应用的开关功放为例,进行大量的仿真和实验,结果表明了上述理论分析和纹波计算公式的正确性。该方法简单有效,具有一定的应用价值。     

船舶电力推进的自控式同步电动机驱动控制

本文从同步电机矢量控制原理出发,在MATLAB/Simulink环境下建立了自控式同步电机驱动控制系统,用于船舶电力推进的系统建模与仿真,通过对船舶螺旋桨转速控制的数字仿真,表明设计的控制系统具有转速响应快、稳定性好和指令跟踪能力强等特点,能满足电力推进船舶主动力的要求。     

高速公路圆曲线外侧超车道停车视距分析

该文分析了停车视距计算参数的取值,并计算了高速公路圆曲线外侧超车道在不同设计速度下能够提供的横净距。通过示例分别计算了三种不同参数取值下的停车视距和横净距。     

无锡市中心城区雨水管网改造规划探讨

无锡市中心城区雨水管网改造规划是水网平原地区建成区雨水管网改造的缩影,规划区四面环水,人口、建筑密度大,实施条件复杂。综合分析区块排水的必要性及可行性,通过划分集水分区,调整排水方向,结合地铁施工、控源截污等重点工程建设快速排水通道,提高老城区排水系统标准。     

菲尔兰至尊74

无论黑夜或白昼,随着Squadron 74航行都是一种享受! 我们把近40年来学到的关于建造一流豪华游艇经验中的每一个细节都完美地融合运用进了这款非凡雅致、无与伦比的游艇——Squadron 74的设计生产之中。 从被证明有着良好适航性的船体设计到船上家具的微小细节,我们吸取了制造上万艘Fairline游艇所取得的经验,打造出这款无比奢华、极致完美的游艇。     

An exploration of the competitive relationship between intercity transport systems

A suitable model that enables the analysis of dynamic relationships between transport systems is important for managers to make real-time reaction strategies. This study proposes an autoregressive distributed lag modeling approach that can point a way to interpret the long- and short-term relationships between intercity transport systems. To test the applicability of the approach with regard to evaluating the dynamic competitive relationships between intercity transport systems, an empirical study sample is adopted in evaluating competition between high-speed rail (HSR) and intercity bus services. The results indicate that HSR has a long-run impact on intercity bus transport and the intercity bus transport market is positively affected by its previous operations and negatively influenced by the previous performance of HSR. However, in the short-run, the current period performance of HSR positively affects the intercity bus transport market.     

The Next Step of Devising China's Legal Regime for Deep Seabed Mining—The Environmental Regulation under China's Deep Seabed Mining Law

The due diligence obligation of sponsoring states requires state parties to enact laws and take administrative measures to secure effective regulation of the contractors of deep seabed mining and ensure that the contractors comply with the United Nations Convention on the Law of the Sea (UNCLOS) and regulations issued by International Seabed Authority (ISA). China has invested significantly in the exploration and exploitation of the deep seabed resources in the Area and China enacted its deep seabed mining law (DSM Law) in 2016 to fulfill its due diligence obligation as a sponsoring state. Environmental regulation is an important part of devising the international legal regime of deep seabed mining, and the ISA has been in the process of drafting Environmental Regulations. It is the sponsoring states' obligation to ensure that the contractors comply with the environmental rules issued by the ISA. China's DSM Law has many provisions stating the environmental obligations of its contractors; however, these provisions are phrased in rather general terms. It is necessary for China to take the next step as a sponsoring state and promulgate its domestic environmental regulation under its DSM Law in order to further fulfill its due diligence obligation. A procedure-oriented approach should be adopted for drafting the environmental regulation under China's DSM Law. Ideally, the environmental regulation under China's DSM Law should specify the rights and obligations of the contractors and domestic regulatory agency, delineating the environmental measures that the contractors need to take in different stages of exploring and exploiting deep seabed resources in order to comply with the environmental rules issued by the ISA.     

Microscopic structure and property of double-electrode gas metal arc welding of AZ31B magnesium alloy

This paper focuses on the research on double-electrode gas metal arc welding(DE-GMAW) of AZ31 B magnesium alloy sheet with 2 mm thickness. During the welding process, stable hybrid arc of metal inert gas(MIG) and tungsten inert gas(TIG) is employed as welding heat source. Optical and electron microscopes are used to observe the microstructures of the weld joint. X-ray diffraction(XRD) and energy dispersive spectroscopy(EDS) are employed to identify the components in fusion zone. Microhardness is also tested. When the MIG current is 80 A, the perfect weld joint is obtained, though figures of fish scales are observed in all joints in the research. The fusion zone is formed by dendrites, where β-Mg17(Al, Zn)12is dispersed. The hardness in fusion zone and heat affected zone(HAZ) is lower than that in base metal(BM). The average Vickers hardness of fusion zone and HAZ is about 58 and 56 respectively, while the Vickers hardness of BM is about 63.