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 te hoc" » "su sach xet nghiem te hoc", "su sach van nghiem te hoc", "su sach va nghien te hoc", "su sach xa nghiem de hoc", "su sach xa nghiem ve hoc", "su sach xa nghiem tien hoc", "so sach xa nghiem te hoc", "vu sach xa nghiem te hoc", "su sach dao nghiem te hoc", "su sach nha nghiem te hoc", "su sach bai nghiem te 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 te 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 te hoc") OR ("co sach tham nghiem ad hoc")).
• Removing quotes may allow a broader search: (( su sach xa nghiem te hoc ) or ( co sach tham nghiem ad hoc )).
• Adding a wildcard symbol may retrieve word variants: (("su sach xa nghiem te hoc") or ("co sach tham nghiem ad hoc"))*.