共查询到20条相似文献,搜索用时 15 毫秒
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In supercritical fluid chromatography (SFC) the mobile phase is neither a gas nor a liquid, but is a supercritical fluid. As a result of the unique properties of supercritical fluids, SFC is rapidly becoming a prominent separation technique for the analysis of reactive, thermally labile, and nonvolatile compounds. This article reviews the history, instrumentation, and practice of the technique. Particular emphasis is placed on the different programming methods that allow elution to be selectively controlled in ways that are unique to SFC. 相似文献
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Supercritical fluids (SCFs), compounds heated and pressurized beyond the critical point, have many unusual properties. Homogeneous molecular catalysts, which have far greater control over selectivity than heterogeneous solid catalysts, are now being tested in SCFs, and early results show that high rates, improved selectivity, and elimination of masstransfer problems can be achieved. As industry moves away from toxic or environmentally damaging solvents, supercritical carbon dioxide may be an ideal replacement medium for nonpolar or weakly polar chemical processes. More than simply substitutes for nonpolar solvents, SCFs can radically change the observed chemistry. Supercritical carbon dioxide is also an excellent medium for its own fixation, as demonstrated by studies of its hydrogenation. 相似文献
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Pai RA Humayun R Schulberg MT Sengupta A Sun JN Watkins JJ 《Science (New York, N.Y.)》2004,303(5657):507-510
Well-ordered mesoporous silicate films were prepared by infusion and selective condensation of silicon alkoxides within microphase-separated block copolymer templates dilated with supercritical carbon dioxide. Confinement of metal oxide deposition to specific subdomains of the preorganized template yields high-fidelity, three-dimensional replication of the copolymer morphology, enabling the preparation of structures with multiscale order in a process that closely resembles biomineralization. Ordered mesoporous silicate films were synthesized with dielectric constants as low as 1.8 and excellent mechanical properties. The films survive the chemical-mechanical polishing step required for device manufacturing. 相似文献
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Kerr RA 《Science (New York, N.Y.)》1994,265(5168):31-32
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Kaiser J 《Science (New York, N.Y.)》2011,333(6047):1214-1215
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Dickson D 《Science (New York, N.Y.)》1983,219(4587):933-936
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Marx JL 《Science (New York, N.Y.)》1974,186(4160):247-250
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Enserink M 《Science (New York, N.Y.)》2000,288(5470):1320-1322
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为了提高履带式林木采育机的林地越障能力,在履带式林木采育机的基础上加装越障工作小臂。基于D-H法建立采育机杆系的运动学模型,通过计算获得加装工作小臂条件下林木采育机的理论越障高度。在ADAMS环境下进行动态仿真,对各仿真相关的运动学参数进行分析,并将理论、仿真数据与实测采育机越障高度数据进行比较,验证林木采育机杆系运动学模型的正确性及其越障能力的提升程度。结果表明:在斗杆全收回状态,采育机整机抬升角度为13°,越障高度为693 mm;在斗杆全伸开状态,采育机整机提升角度为6.3°,越障高度为330 mm。加装越障工作小臂的履带式林木采育机能够满足林区越障要求,为实现和满足其上山入林作业,更有效地翻越障碍物提供了理论依据。 相似文献
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采伐机工作臂油缸的设计及其运动分析 总被引:1,自引:1,他引:0
以采伐机工作臂油缸为研究对象,分别对其布置形式、受力情况及其强度校核等方面进行设计计算.借助机械系统动力学分析软件ADAMS,以各油缸为分析对象,选取6种不同位姿下的工作臂,分别进行模拟仿真,分析油缸在不同工况下的运动情况,得出采伐机工作臂的主要作业尺寸及油缸的受力状况.结果表明,当起重量一定且仅主臂油缸进行伸缩运动时,主臂及副臂的姿态影响着采伐机工作臂的工作幅度.因此在工作过程中可以通过调整工作臂的初始工作状态,缩短采伐机工作臂末端需要延长的距离,同时能有效减轻工作臂的负荷,从而提高机械效能. 相似文献
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Anderson C 《Science (New York, N.Y.)》1994,263(5147):627-629