dark ground method of observation
暗场观察法

• pliotron
• pllane glass
• pllarising microscope in reflected light
• Plochere color system
• Ploessl eyepiece
• plot
• plot diagram
• plotomat
• plotter
• plotting instrument
• plotting objective
• plotting tablet
• plug
• plug gage
• plug-in
• plug-in unit
• plugs
• plug screw gauge
• plumb
• plumbago
• plumb aligner
• plumbico camera tube
• plumbicon
• plumbing mirror
• plumb level