Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
van hanh » van thanh, ban hanh, van anh
cua tre » cua te, cua triet, dua tren
hanh di » hanh vi, hanh de, hang di
duc van » duc va, duc tan, duc manh
hieu va » lieu va, hieu qua
cac duc » cac du, cao duc, cac dac
cuu tre » cau tren, cau treo
o lang » hoa lang, hoi lang
v lang » va lang, _ lang, van lang

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach ((v lang) or (o lang)) xa hoi. hieu va cac duc van hanh di ((cua tre) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((v lang) OR (o lang)) xa hoi. hieu va cac duc van hanh di ((cua tre) OR (cuu tre)).
• Adding a wildcard symbol may retrieve word variants: toc sach ((v lang) or (o lang)) xa hoi. hieu va cac duc van hanh di ((cua tre) or (cuu tre))*.