Latest set of self-consistent values of the basic constants of physics and chemistry recommended by CODATA (Committee on Data for Science and Technology)...

International Critical Tables offers data on physical, thermodynamic, mechanical, and other key properties and is a major reference source used by those involved in chemistry, physics, and engineering...

Site covering the essentials of International System of Units (SI)...

Knovel Critical Tables is a reference featuring tables of properties for commonly used chemical compounds in the physical properties tables...

National Institute of Standards and Technology Data site for chemical and physics reference data...

Gateway to data collections on reaction data, thermochemical data, IR spectra, mass spectra, electronic and vibrational spectra, and ion energetics data...

Smithsonian Physical Tables contains 901 tables concentrating on a broad scope of common physical and chemical data, of general interest to physicists, chemists and other scientists...

Thermochemistry of the chemical substances...

Site describes the method of evaluating and expressing uncertainty in used worldwide...