Nuclear Reactor Regulation 
Noise Reduction Rating 
Nobles Rock Railroad 
Net Reproduction Rate 
Non-Repudiation of Receipt 
nasal respiratory resistance 
National Research Register 
Natureair 
Naval Research Reactor 
Naval Research Requirements 
navy research requirements 
Network Restoration Ratio 
neuroretinal rim 
neutral red release 
neutral red retention 
noise of reduction rating 
Noise Reduction Regulations 
nonhomologous random recombination 
Non-Reciprocal Reflectivity 
non-return rate 
non-return rates 
Non-Reversing Relay 
normal radiation region 
Nuclear Reactor Reflector 
nuclear regulatory research 
Noble Rock'n'roll Railroad