Perhaps you should try some spelling variations:
thanh vai » thanh hai, thanh van, thanh tai
va trien » va truyen, va thiet, va tuyen
va thanh » gia thanh, ban thanh, va tinh
cap nuoc » dat nuoc
hieu van » hieu va, thien van, lieu va
sach tu » sach thu, cach tu, sach ty
tu sach » thu sach, su sach, te sach
tu lang » cu lang, tu lanh, xu lang
hieu ve » hieu va
vai va » mai va, dai va, hai va
o hoc » co hoc, mo hoc, so hoc
o hoi » co hoi, o hai, o hoa

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 tu lang ((o hoi) OR (o hoc)). ((hieu ve) or (hieu van)) cap nuoc va thanh vai va trien~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach tu lang ((o hoi) OR (o hoc)). ((hieu ve) OR (hieu van)) cap nuoc va thanh vai va trien.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach tu lang ((o hoi) OR (o hoc)). ((hieu ve) or (hieu van)) cap nuoc va thanh vai va trien".
• Adding a wildcard symbol may retrieve word variants: tu sach tu lang ((o hoi) OR (o hoc)). ((hieu ve) or (hieu van)) cap nuoc va thanh vai va trien*.