Perhaps you should try some spelling variations:
"sach tran viet nam." » "sach tranh viet nam." (Expand Search), "sach trang viet nam." (Expand Search), "sach tra viet nam." (Expand Search), "sach san viet nam." (Expand Search), "sach gian viet nam." (Expand Search), "sach dan viet nam." (Expand Search)
"sach vien viet nam." » "sach viet viet nam." (Expand Search), "sach dien viet nam." (Expand Search), "sach tien viet nam." (Expand Search), "sach gian viet nam." (Expand Search)
"sach van viet nam." » "tich van viet nam." (Expand Search), "sach san viet nam." (Expand Search), "sach gian viet nam." (Expand Search), "sach dai viet nam." (Expand Search)

Try widening your search to All Fields.

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("sach tran viet nam.") OR ((("sach van viet nam.") OR ("sach vien viet nam."))))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"sach tran viet nam.\") OR (((\"sach van viet nam.\") OR (\"sach vien viet nam.\"))))".
• Removing quotes may allow a broader search: (( sach tran viet nam. ) OR ((( sach van viet nam. ) OR ( sach vien viet nam. )))).
• Adding a wildcard symbol may retrieve word variants: (("sach tran viet nam.") OR ((("sach van viet nam.") OR ("sach vien viet nam."))))*.