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