Perhaps you should try some spelling variations:
hoi nhiem » phoi nhiem, chon nhiem, thai nhiem
dat nghe » da nghe, dang nghe, van nghe
day nghe » dang nghe, van nghe, nam nghe
thu sach » tu sach, thuat sach, thuoc sach
sach hoi » sach doi, sach moi, cach thoi
tu manh » tu minh, tu hanh, vu manh
su hoc » du hoc, so hoc, su ho
tu hoc » te hoc
d hoc » du hoc, ad hoc, de hoc

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( tu manh ((dat nghe) or (day nghe)) d hoc ) or ( thu sach hoi nhiem ((su hoc) or (tu hoc)) ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( tu manh ((dat nghe) OR (day nghe)) d hoc ) OR ( thu sach hoi nhiem ((su hoc) OR (tu hoc)) )).
• Adding a wildcard symbol may retrieve word variants: (( tu manh ((dat nghe) or (day nghe)) d hoc ) or ( thu sach hoi nhiem ((su hoc) or (tu hoc)) ))*.