relativistic effectsrelativistic massrelativistic quantum theoryrelaxation spectroscopyrelaxation timereleasing agentrelief valverepeating unitreplicating moleculereprecipitationrepresentation theoryrepresentative elementsreproducibilityrepulsion forceresidualresidueresiduumresinresistanceresistantresistivityresolutionresolution powerresolvableresolvable tartaric acidresolving agentresolving powerresonanceresonance energyresonance formresonance hybriderest massrestoring forceresultantretardantretarderretention indexretention of configurationretention timeretention volumeretort cokeretort tarreverse osmosisreversibilityreversibility principlereversiblerhrheniumrheodestructionrheopexy