Perhaps you should try some spelling variations:
nuoc ban » nuoc san, quoc ban, buoc ban
dua tren » dung tren
sach thu » sach thue, sach thieu, sach tham
hanh tai » thanh tai, hang tai, han tai
hieu van » hieu va, thien van, lieu va
ban hanh » ban hang
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
van cac » van hac, van cau, van bac
sach ty » sach y, sach tu, xach tay
cao hoc » co hoc, cho hoc, chat hoc
cua te » cua tu

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu ((sach ty) OR (sach thu)) nang cao hoc. hieu van cac nuoc ban hanh tai ((dua tren) or (cua te))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ty) OR (sach thu)) nang cao hoc. hieu van cac nuoc ban hanh tai ((dua tren) OR (cua te)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ty) OR (sach thu)) nang cao hoc. hieu van cac nuoc ban hanh tai ((dua tren) or (cua te))".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ty) OR (sach thu)) nang cao hoc. hieu van cac nuoc ban hanh tai ((dua tren) or (cua te))*.