Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
o lang » hoa lang, hoi lang
va cam » va cham, va cac, va cao
loc va » luc va
v lang » va lang, _ lang, van lang
vi cua » vai cua, di cua

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 ((v lang) or (o lang)) xa hoi. hieu va cam ((loc va) OR (hoc va)) hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ((v lang) OR (o lang)) xa hoi. hieu va cam ((loc va) OR (hoc va)) hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ((v lang) or (o lang)) xa hoi. hieu va cam ((loc va) OR (hoc va)) hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: doc sach ((v lang) or (o lang)) xa hoi. hieu va cam ((loc va) OR (hoc va)) hanh vi cua tre*.