| from 06/01/2004 to 02/16/2005 in LexisNexis Academic |
| from 01/01/1997 to 1 year ago in Academic Search Premier |
| from 01/01/2007 to 12/31/2009 in ScienceDirect Physical Sciences College Edition and ScienceDirect Social & Behavioral Sciences College Edition |
| from 01/01/2008 to present in ScienceDirect Physical Sciences College Edition |
| from 04/01/2010 to present in ABI/INFORM Global |
| from 10/12/1999 to present in LexisNexis Academic |
| from 11/11/2002 to present in LexisNexis Academic |
| from 11/11/2002 to present in LexisNexis Academic |