Perhaps you should try some spelling variations:
sach ty » sach y, sach tu, sach thu
su sach » so sach, vu sach
ty nang » ky nang, ty xang, ty hang
hieu ve » hieu va, hieu van
ve cac » va cac, vien cac
bao va » bao ve, tao va, ban va
bac va » ban va, bac ha, tac va
x hoi » xa hoi, o hoi, x ho
vi va » vai va, vu va, bi va

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 ty nang x hoi. hieu ve cac ((bac va) OR (bao va)) tinh ((vi va) or (vi van)) thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ty nang x hoi. hieu ve cac ((bac va) OR (bao va)) tinh ((vi va) OR (vi van)) thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ty nang x hoi. hieu ve cac ((bac va) OR (bao va)) tinh ((vi va) or (vi van)) thiet".
• Adding a wildcard symbol may retrieve word variants: su sach ty nang x hoi. hieu ve cac ((bac va) OR (bao va)) tinh ((vi va) or (vi van)) thiet*.