Perhaps you should try some spelling variations:
cac thoi » cac toi, cac hop, cac tro
thoi dia » hoi dia, thoi gian, thoi diem
tu sach » thu sach, su sach, te sach
qua cac » cua cac
ban cam » ban can, ban ham, bay cam
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
me hoi » le hoi
ban ca » ban cua, ban can, ban cau

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 y nang ((me hoi) or (ma hoa)). hieu qua cac thoi dia ((ban ca) OR (ban cam)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y nang ((me hoi) OR (ma hoa)). hieu qua cac thoi dia ((ban ca) OR (ban cam)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y nang ((me hoi) or (ma hoa)). hieu qua cac thoi dia ((ban ca) OR (ban cam)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach y nang ((me hoi) or (ma hoa)). hieu qua cac thoi dia ((ban ca) OR (ban cam)) cua tre*.