Perhaps you should try some spelling variations:
sach thu » sach thue, sach thieu, sach tham
danh vai » danh sai, doanh van, dang van
cam truc » cau truc, nam truc, lam truoc
hieu van » hieu va, thien van, lieu va
tu sach » thu sach, su sach, te sach
danh va » doanh va, hanh va, anh va
truc va » thuc va, thuc vat, trung va
van cam » van nam, van lam, van cau
nang xa » nang x, lang xa, mang xa
nang ma » tang ma, sang ma, nang cao
cua tre » cua te, cuu tre, cua triet

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 thu ((nang xa) or (nang ma)) hoi. hieu van cam truc va ((danh vai) OR (danh va)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach thu ((nang xa) OR (nang ma)) hoi. hieu van cam truc va ((danh vai) OR (danh va)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach thu ((nang xa) or (nang ma)) hoi. hieu van cam truc va ((danh vai) OR (danh va)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach thu ((nang xa) or (nang ma)) hoi. hieu van cam truc va ((danh vai) OR (danh va)) cua tre*.