Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
sach ky » sach y, sach ty, sach kem
duc van » duc va, duc tan, duc manh
cac duc » cac du, cao duc, cac dac
hieu ve » hieu va, hieu van
tang ma » mang may, tang van
nang ma » sang ma, nang cao, mang may
ve cac » va cac, vien cac
sac ky » cac ky, sai ky
vi cua » vai cua, di cua

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 ky) or (sac ky)) ((nang ma) OR (tang ma)) hoi. hieu ve cac duc van hanh vi cua vat~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ky) OR (sac ky)) ((nang ma) OR (tang ma)) hoi. hieu ve cac duc van hanh vi cua vat.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ky) or (sac ky)) ((nang ma) OR (tang ma)) hoi. hieu ve cac duc van hanh vi cua vat".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ky) or (sac ky)) ((nang ma) OR (tang ma)) hoi. hieu ve cac duc van hanh vi cua vat*.