Perhaps you should try some spelling variations:
hieu van » thien van, lieu va, hieu ve
hai truc » dai truc, hai trac, hang truc
va hanh » van hanh, va thanh, va danh
truc va » thuc va, thuc vat, trung va
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
nang ma » tang ma, sang ma, nang cao
nang xa » nang x, lang xa, mang xa
sac ky » cac ky, sai ky
vi cua » vai cua, di cua
su sac » su sach, su cac, su xac

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

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