ChemGlobe: Thulium: Electronic, thermal, and steric data along with an isotope table.
ChemicalElements.com: Thulium: Basic information, atomic structure, and isotopes.
EnvironmentalChemistry.com: Thulium: Atomic structure, chemical and physical properties, and table of nuclides.
It's Elemental: Thulium: Basic physical and historical information.
LANL: Thulium: Basic information and history.
Lenntech: Thulium: Physical data, chemical properties, health and environmental effects.
Thulium: Data tables and historic information.
Visual Elements: Thulium: Image, uses, physical information, and ionisation energies.
WebElements: Thulium: Extensive information on history, uses, occurrence, compounds, and properties.
Wikipedia: Thulium: Properties of the element, including its history, applications, and characteristics.