Perhaps you should try some spelling variations:
manh hanh » xanh hanh, danh thanh, minh thanh
dua tren » dung tren
sach thu » sach thue, sach thieu, sach tham
duc manh » suc manh, duc anh, duc minh
va pham » van pham, va phat, va phap
hieu va » lieu va, hieu qua
sach ky » sac ky, sach y, sach ty
tang ma » mang may, tang van
cuu tre » cua tre, cau tren, cau treo
ma hoi » mai hoi, xa hoi, ma hoa

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) or (sach thu)) tang ma hoi. hieu va pham duc manh hanh vi ((dua tren) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ky) OR (sach thu)) tang ma hoi. hieu va pham duc manh hanh vi ((dua tren) OR (cuu tre)).
• Adding a wildcard symbol may retrieve word variants: tu ((sach ky) or (sach thu)) tang ma hoi. hieu va pham duc manh hanh vi ((dua tren) or (cuu tre))*.