Perhaps you should try some spelling variations:
"co sach tham nghiem ad hoc" » "co sach trac nghiem ad hoc", "co sach thuc nghiem ad hoc", "co sach thi nghiem ad hoc", "co sach nha nghiem ad hoc", "co sach tham nghiem d hoc", "co sach tham nghiem ban hoc", "co sach tham nghiem lam hoc", "bo sach tham nghiem ad hoc", "cuon sach tham nghiem ad hoc", "hoc sach tham nghiem ad hoc"
"su sach xa nghiem de hoc" » "su sach xet nghiem de hoc", "su sach van nghiem de hoc", "su sach va nghien de hoc", "su sach xa nghiem d hoc", "su sach xa nghiem te hoc", "su sach xa nghiem ve hoc", "so sach xa nghiem de hoc", "vu sach xa nghiem de hoc", "su sach dao nghiem de hoc", "su sach nha nghiem de hoc", "su sach bai nghiem de hoc", "su sach xa nghiem du hoc", "su sach xa nghiem dien hoc"

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: (("su sach xa nghiem de hoc") or ("co sach tham nghiem ad hoc"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("su sach xa nghiem de hoc") OR ("co sach tham nghiem ad hoc")).
• Removing quotes may allow a broader search: (( su sach xa nghiem de hoc ) or ( co sach tham nghiem ad hoc )).
• Adding a wildcard symbol may retrieve word variants: (("su sach xa nghiem de hoc") or ("co sach tham nghiem ad hoc"))*.