Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
hieu van » hieu va, thien van, lieu va
dat van » dao van, dat va, dam van
cac dat » cac dan, cai dat, cac dai
van cac » van hac, van cau, van bac
tang ma » mang may, tang van
sach ky » sach y, sach ty, sach kem
nang ma » sang ma, nang cao, mang may
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: thuat ((sach ky) OR (sac ky)) ((nang ma) or (tang ma)) hoi. hieu van cac dat van hanh vi cua vat~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thuat ((sach ky) OR (sac ky)) ((nang ma) OR (tang ma)) hoi. hieu van cac dat van hanh vi cua vat.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thuat ((sach ky) OR (sac ky)) ((nang ma) or (tang ma)) hoi. hieu van cac dat van hanh vi cua vat".
• Adding a wildcard symbol may retrieve word variants: thuat ((sach ky) OR (sac ky)) ((nang ma) or (tang ma)) hoi. hieu van cac dat van hanh vi cua vat*.