Each site has its own electronic address - URL. Access to some is restricted, e.g. Current Contents or Web of Science (available via the Chemistry@Library). For these subscription-only sites, the URL need not be given.
Numeric superscript: ...ATSDR10... OR
Numeric: ...ATSDR (10)... OR
Author-date: ...(ATSDR, 2004)...
Bibliography - order of citation
10 U.S. Department of Health and Human Services. Agency for Toxic Substances and Disease Registry. http://www.atsdr.cdc.gov/ (accessed Sept 2004).
If numeric system used - reference number: 10
Author (if any): U.S. Department of Health and Human Services.
Title of site: Agency for Toxic Substances and Disease Registry homepage.