Perhaps you should try some spelling variations:
nam thuoc » nam thuc, nam thu, nha thuoc
dau tren » dau tien, dat tren, dau tieng
lang xa » lang ha, dang xay, lang van
sach ty » sach y, sach tu, sach thu
hieu va » lieu va, hieu qua
sach ky » sac ky, sach y, sach kem
va dan » va dao, va dap, va dai
ca dan » cac dan, ca dao
va dau » va dao
va nam » van nam, ha nam, va nay

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 ky) or (sach ty)) lang xa hoi. hieu va nam thuoc ((va dan) OR (ca dan)) va dau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc ((sach ky) OR (sach ty)) lang xa hoi. hieu va nam thuoc ((va dan) OR (ca dan)) va dau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc ((sach ky) or (sach ty)) lang xa hoi. hieu va nam thuoc ((va dan) OR (ca dan)) va dau tren".
• Adding a wildcard symbol may retrieve word variants: doc ((sach ky) or (sach ty)) lang xa hoi. hieu va nam thuoc ((va dan) OR (ca dan)) va dau tren*.