Perhaps you should try some spelling variations:
"nijhoff ebook title 20" » "nijhoff book title 20", "nijhoff book titles 20", "nijhoff ebook title 2", "nijhoff ebook title 10", "nijhoff ebook title 22"
"nijhoff ebook title 25" » "nijhoff book title 25", "nijhoff book titles 25", "nijhoff ebook title 2", "nijhoff ebook title 5", "nijhoff ebook title _"
"nijhoff ebook title 21" » "nijhoff book title 21", "nijhoff book titles 21", "nijhoff ebook title 1", "nijhoff ebook title 2", "nijhoff ebook title _"
"nijhoff ebook title 26" » "nijhoff book title 26", "nijhoff book titles 26", "nijhoff ebook title 2", "nijhoff ebook title _", "nijhoff ebook title a"

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (((((("nijhoff ebook title 20") OR ("nijhoff ebook title 25"))) OR ("nijhoff ebook title 21"))) OR ("nijhoff ebook title 26")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((((\"nijhoff ebook title 20\") OR (\"nijhoff ebook title 25\"))) or (\"nijhoff ebook title 21\"))) or (\"nijhoff ebook title 26\"))".
• Removing quotes may allow a broader search: (((((( nijhoff ebook title 20 ) OR ( nijhoff ebook title 25 ))) or ( nijhoff ebook title 21 ))) or ( nijhoff ebook title 26 )).
• Adding a wildcard symbol may retrieve word variants: (((((("nijhoff ebook title 20") OR ("nijhoff ebook title 25"))) or ("nijhoff ebook title 21"))) or ("nijhoff ebook title 26"))*.