Perhaps you should try some spelling variations:
sang mai » sang ma, sang tai, lang mai
mai khoi » mai khoa, tai khoa, cac khoi
hanh mai » hanh ma, hanh mau, hanh may
sach tu » sach thu, cach tu, sach ty
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
va cam » va cham, va cac, va cao
tuc va » thuc va, truc va, duc va
thiet » thieu

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

• Performing a fuzzy search may retrieve terms with similar spellings: su ((sach ky) or (sach tu)) sang mai khoi. hieu va cam ((tuc va) OR (tuc xa)) hanh mai va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ky) OR (sach tu)) sang mai khoi. hieu va cam ((tuc va) OR (tuc xa)) hanh mai va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach ky) or (sach tu)) sang mai khoi. hieu va cam ((tuc va) OR (tuc xa)) hanh mai va thiet".
• Adding a wildcard symbol may retrieve word variants: su ((sach ky) or (sach tu)) sang mai khoi. hieu va cam ((tuc va) OR (tuc xa)) hanh mai va thiet*.