Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
tay lang » tai lang, tay tang, tay quang
lam duoc » nam duoc, luat duoc, lam thuoc
hieu van » hieu va, thien van, lieu va
van lam » van nam
ty lang » ty xang, ty hang, tu lang
va lang » va nang, hoa lang
va cua » va chua, via cua, ca cua
cua te » cua tu

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach ((ty lang) OR (tay lang)) xa hoi. hieu van lam duoc ((va lang) or (cam nang)) va cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ((ty lang) OR (tay lang)) xa hoi. hieu van lam duoc ((va lang) OR (cam nang)) va cua te*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ((ty lang) OR (tay lang)) xa hoi. hieu van lam duoc ((va lang) or (cam nang)) va cua te*".