· http://mx.iit.edu/

· https://www.library.nd.edu/

· http://www.slovo.bg/showwork.php3?AuID=14&WorkID=5788&Level=3

· https://henke.lbl.gov/optical_constants/

· https://henke.lbl.gov/optical_constants/bilayer.html

· https://www.imenata.com/kalendar-imenni-dni-2012.html

· http://rruff.geo.arizona.edu/AMS/amcsd.php

· https://sonix.bas.bg/