Perhaps you should try some spelling variations:
dau tren » dau tien, dat tren, dau tieng
cam truc » cau truc, nam truc, lam truoc
hieu va » lieu va, hieu qua
va hanh » van hanh, va thanh, va danh
nang ma » tang ma, sang ma, nang cao
truc va » thuc va, thuc vat, trung va
hieu ve » hieu van
vi dau » vi dai, va dau, bi dau
tu van » tu va

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu van ky ((mang may) or (nang ma)) hoi. ((hieu ve) or (hieu va)) cam truc va hanh vi dau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu van ky ((mang may) OR (nang ma)) hoi. ((hieu ve) OR (hieu va)) cam truc va hanh vi dau tren.
• Adding a wildcard symbol may retrieve word variants: tu van ky ((mang may) or (nang ma)) hoi. ((hieu ve) or (hieu va)) cam truc va hanh vi dau tren*.