Perhaps you should try some spelling variations:
thu sach » thuat sach, thuoc sach, thu hoach
hieu van » thien van, lieu va, hieu ve
van hanh » van thanh, ban hanh, van anh
hanh de » hanh ve, hanh kem
luc van » luoc van, luu van, duc van
cau luc » cau truc, cau phuc
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
tang xa » trang xa, tang ma, lang xa
ky tang » ky nang, ky dang, kho tang
tu sach » su sach, te sach, tu cach
de cua » le cua, te cua, dieu cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((thu sach) or (tu sach)) ky tang xa hoi. ((hieu van) OR (hieu va)) cau luc van hanh de cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((thu sach) OR (tu sach)) ky tang xa hoi. ((hieu van) OR (hieu va)) cau luc van hanh de cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((thu sach) or (tu sach)) ky tang xa hoi. ((hieu van) OR (hieu va)) cau luc van hanh de cua tre".
• Adding a wildcard symbol may retrieve word variants: ((thu sach) or (tu sach)) ky tang xa hoi. ((hieu van) OR (hieu va)) cau luc van hanh de cua tre*.