duality
(1)二象性
(2)二重性
(3)对偶性
(4)二元性

• sector arm
• sector gear
• sectorial wave
• sector shaft
• sector shutter
• secular aberration
• secular equation
• sediment
• Seebeck effect
• seed crystal
• seeder
• seedholder
• seeding
• see-in-dark rangefinder
• seeking
• Seeman-Bohlim camera
• Seeman slit
• segmented glass laser
• segmented mirror
• segmented rod
• segmented rod laser
• segment gear
• segment shutter
• segregation
• Seidel aberrations