Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
hieu van » hieu va, thien van, lieu va
su triet » su viet, su tien, ve triet
nang ma » tang ma, sang ma, nang cao
nang xa » nang x, lang xa, mang xa
sach tu » sach thu, cach tu, sach ty
thuc va » thuc dan, thuc day
dan ki » dan ky, dan ke, dan li
ki su » ky su

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: thu sach tu ((nang xa) or (nang ma)) hoi. hieu van nam ((thuc va) OR (thuc vat)) dan ki su triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach tu ((nang xa) OR (nang ma)) hoi. hieu van nam ((thuc va) OR (thuc vat)) dan ki su triet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach tu ((nang xa) or (nang ma)) hoi. hieu van nam ((thuc va) OR (thuc vat)) dan ki su triet".
• Adding a wildcard symbol may retrieve word variants: thu sach tu ((nang xa) or (nang ma)) hoi. hieu van nam ((thuc va) OR (thuc vat)) dan ki su triet*.