Perhaps you should try some spelling variations:
phat nghien » phap nghien, phan nghien, pham nghien
sach phat » sach nha, sach tham, cach pha
nghien de » nghiem de, nghiep ke, nghiem d
bai nghe » thai nghe, nam nghe, cap nghe
so sach » so sanh, bo sach, co sach
tu sach » thu sach, su sach, te sach
dau hoc » dai hoc, du hoc, dan hoc
de hoc » te hoc, du hoc, dien hoc

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( so sach phat nghien de hoc ) or ( tu sach ((bai nghe) or (van nghe)) dau hoc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( so sach phat nghien de hoc ) OR ( tu sach ((bai nghe) OR (van nghe)) dau hoc )).
• Adding a wildcard symbol may retrieve word variants: (( so sach phat nghien de hoc ) or ( tu sach ((bai nghe) or (van nghe)) dau hoc ))*.