Perhaps you should try some spelling variations:
dau tren » dau tien, dat tren, dau tieng
nang doc » nang luc
sach ty » sach y, sach tu, sach thu
tu sach » thu sach, su sach, te sach
nang co » nang cao, nang noi, nang hoc
hieu ve » hieu va, hieu van
ve cam » ve cham, ve cac, va cam
va dan » ca dan, va dap, va dai
va dao » ca dao

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