You can search for sample items from these collections by choosing an item from the 'Category' list on the NMSI Collections Online at http://collectionsonline.nmsi.ac.uk/advsearch.php?module=objects 

The data is now downloadable at http://api.sciencemuseum.org.uk/documentation/collections/

Collections at NMSI are listed below:
NMeM - Cinematography
NMeM - New Media
NMeM - Photographic Technology
NMeM - Photographs
NMeM - Printed Materials & Ephemera
NMeM - Television
NRM - Archive Collections
NRM - Display Interactives
NRM - Documents
NRM - Education
NRM - Education Film
NRM - Fixtures & Fittings from Railway Buildings
NRM - Library Collections
NRM - Locomotives and Rolling Stock
NRM - Locomotives and Rolling Stock Components
NRM - Miscellanea & Curiosities
NRM - Moving Images
NRM - National Archive of Railway Oral History
NRM - Passenger Comforts
NRM - Photographic Collections (Railway)
NRM - Pictorial Collection (Railway)

NRM - Postcard Collection
NRM - Railway Furniture
NRM - Railway Heraldry
NRM - Railway Infrastructure
NRM - Railway Maps & Plans
NRM - Railway Models
NRM - Railway Numismatics
NRM - Railway Posters, Notices & Handbills
NRM - Railway Shipping
NRM - Railway Stamps & Covers
NRM - Railway Timepieces
NRM - Railway Uniform & Costume
NRM - Road Vehicles (Railway)
NRM - Signalling & Telecommunications
NRM - Sound Recordings
NRM - Stationary Engines
NRM - Technical File (Object)
NRM - Temporary Exhibitions
NRM - Tickets, Passes & Labels
NRM - Tools of the Trade & Personal Accessories
NRM - Toys & Games
SCM - Acoustics
SCM - Aeronautics
SCM - Agricultural Engineering

SCM - Aircraft Propulsion
SCM - Anaesthesiology
SCM - Anatomy & Pathology
SCM - Antenna
SCM - Archive

SCM - Art
SCM - Astronomy
SCM - Audiology
SCM - Biochemistry
SCM - Biotechnology
SCM - Building Construction
SCM - Cash Registers
SCM - Ceramics
SCM - Children's Gallery
SCM - Chiropody
SCM - Cinematography
SCM - Circulation
SCM - Civil Engineering
SCM - Classical & Medieval Medicine
SCM - Clinical Diagnosis
SCM - Coins, Medals & Tokens
SCM - Computing & Data Processing
SCM - Contemporary Art Collection
SCM - Dentistry
SCM - Docks and Diving
SCM - Domestic Appliances
SCM - Electricity and Magnetism
SCM - Electricity Supply
SCM - Electronic Components
SCM - Environmental Science & Technology
SCM - Ethnography and Folk Medicine
SCM - Experimental Chemistry
SCM - Factory and Mechanical Handling
SCM - Farnborough

SCM - Firefighting
SCM - Firemaking
SCM - Froude
SCM - Gas Industry
SCM - Geophysics
SCM - Glass Technology
SCM - Hand and Machine Tools
SCM - Heat
SCM - Heat Engines (non steam)
SCM - Heating, Cooling and Ventilation
SCM - Hunterian Collection
SCM - Industrial Chemistry
SCM - Industrial Metrology
SCM - Inventions and Discoveries
SCM - James Watt's Garret Workshop
SCM - Kinematics
SCM - King George III
SCM - Laboratory Medicine
SCM - Ledger Items
SCM - Lifting & Mechanical Handling
SCM - Lighting
SCM - Locks & Fastenings
SCM - Making the Modern World
SCM - Marine Engines
SCM - Materia Medica & Pharmacology
SCM - Materials Science Gallery
SCM - Mathematics
SCM - Mechanical Power Transmission
SCM - Medical Ceramic-ware

SCM - Medical Glass-ware
SCM - Medical Handling Collection
SCM - Metallurgy
SCM - Meteorology
SCM - Microbiology
SCM - Microscopes
SCM - Microscopy (Wellcome)
SCM - Mining & Ore Dressing
SCM - MMW Display
SCM - Motive Power
SCM - Navigation
SCM - Nuclear Energy
SCM - Nuclear Physics
SCM - Nursing & Hospital Furnishings
SCM - Nutrition & Food Technology
SCM - Obstetrics, Gynaecology & Contraception
SCM - Oceanography
SCM - Ophthalmology
SCM - Optics
SCM - Oriental Medicine
SCM - Orthopaedics
SCM - Papermaking
SCM - Penn-Gaskell Collection
SCM - Pharmacy-ware
SCM - Photography
SCM - Physics (early centuries)
SCM - Plastics and Modern Materials
SCM - Printed Books
SCM - Printing & Writing

SCM - Production Machinery
SCM - Protective Clothing
SCM - Psychology, Psychiatry & Anthropometry
SCM - Public Health & Hygiene
SCM - Pumping Machinery
SCM - Radar & Radio Location
SCM - Radio Communication
SCM - Radioactive Exhibit Material
SCM - Radiomedicine
SCM - Railways
SCM - Rayleigh
SCM - Road Transport
SCM - Science Teaching
SCM - Sewerage & Sanitation
SCM - Smoking
SCM - Sound Reproduction
SCM - Space Technology
SCM - Surgery
SCM - Surveying
SCM - Telecommunications
SCM - Temporary Exhibitions
SCM - Terrestrial Magnetism
SCM - Textiles Machinery
SCM - Therapeutics
SCM - Time Measurement
SCM - Vacuum Technology
SCM - Veterinary Medicine
SCM - Warships
SCM - Water Supply Metering

SCM - Water Transport
SCM - Weighing & Measuring
SCM - Wellcome (general)
SCM - Wellcome Medals
SCM - Wellcome Wing
SCM - X-rays

Taken from National Museum of Science & Industry Cataloguing Handbook: Data Standards July 2008