Perhaps you should try some spelling variations:
su sach » so sach, vu sach
hieu ve » hieu va, hieu van
tinh vi » trinh vi, tinh voi, tinh va
y nang » ly nang, v nang, may nang
ve cac » va cac, vien cac
bac va » ban va, bac ha, tac va
bao va » bao ve, tao va, ban va
x hoi » xa hoi, o hoi, x ho
vi va » vi van, vai va, vu 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 ((y nang) or (ky nang)) x hoi. hieu ve cac ((bac va) OR (bao va)) tinh vi va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ((y nang) OR (ky nang)) x hoi. hieu ve cac ((bac va) OR (bao va)) tinh vi va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ((y nang) or (ky nang)) x hoi. hieu ve cac ((bac va) OR (bao va)) tinh vi va thiet".
• Adding a wildcard symbol may retrieve word variants: su sach ((y nang) or (ky nang)) x hoi. hieu ve cac ((bac va) OR (bao va)) tinh vi va thiet*.