Perhaps you should try some spelling variations:
"nijhoff book intitled 2006" » "nijhoff book intituled 2006", "nijhoff book entitled 2006", "nijhoff boston intitled 2006", "nijhoff op intitled 2006"
"nijhoff book untitled 2001" » "nijhoff book entitled 2001", "nijhoff book entituled 2001", "nijhoff book intituled 2001", "nijhoff book untitled 2", "nijhoff boston untitled 2001", "nijhoff op untitled 2001"

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"nijhoff book intitled 2006\") OR (\"nijhoff book untitled 2001\"))".
• Removing quotes may allow a broader search: (( nijhoff book intitled 2006 ) OR ( nijhoff book untitled 2001 )).
• Adding a wildcard symbol may retrieve word variants: (("nijhoff book intitled 2006") OR ("nijhoff book untitled 2001"))*.