Perhaps you should try some spelling variations:
va triet » va trien, ve triet, cua triet
phan lap » phan dau
hieu van » hieu va, thien van, lieu va
tu sach » thu sach, su sach, te sach
cac cay » ca cay, cac cam, cac cap
va phan » van phan, va phat, va phap
van cac » van hac, van cau, van bac
ty hang » ly hang, thi hang, thu hang
cay va » chay va, day va, may va
thiet » thieu

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 ((ty hang) or (ty xang)) xa hoi. hieu van cac cay va phan lap ((va triet) OR (va thiet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((ty hang) OR (ty xang)) xa hoi. hieu van cac cay va phan lap ((va triet) OR (va thiet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((ty hang) or (ty xang)) xa hoi. hieu van cac cay va phan lap ((va triet) OR (va thiet))".
• Adding a wildcard symbol may retrieve word variants: tu sach ((ty hang) or (ty xang)) xa hoi. hieu van cac cay va phan lap ((va triet) OR (va thiet))*.