Perhaps you should try some spelling variations:
phan thanh » pham thanh, ban thanh, van thanh
loai tren » la tren, thai tren
cau tren » cu tren, dau tren, ca tren
van phan » van phong, van thanh, luan phan
cac duc » cac du, cao duc, cac dac
duc van » duc va, duc tan, duc manh
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
ve cac » va cac, vien cac
o hai » co hai, so hai, o lai
o hoc » co hoc, mo hoc, so hoc

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 ky nang ((o hoc) or (o hai)). hieu ve cac duc van phan thanh ((cau tren) or (loai tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((o hoc) OR (o hai)). hieu ve cac duc van phan thanh ((cau tren) OR (loai tren)).
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((o hoc) or (o hai)). hieu ve cac duc van phan thanh ((cau tren) or (loai tren))*.