Perhaps you should try some spelling variations:
nham thuc » nhan thuc, nam thuc, nham thu
vanh tai » van tai, hanh tai, anh tai
vanh dai » van dai, lanh dao, van dao
thuc dan » thuc hanh, hoc dan, thuc vat
tu sach » thu sach, su sach, te sach
va nham » va cham, va tham, va nha
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
dong ha » dong hoa, dong va, dong hoc
dang ha » dung ha, lang ha, tang ha
cua tre » cua te, cuu tre, cua triet

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 ((dang ha) OR (dong ha)) hoi. hieu va nham thuc dan ((vanh dai) or (vanh tai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky ((dang ha) OR (dong ha)) hoi. hieu va nham thuc dan ((vanh dai) OR (vanh tai)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky ((dang ha) OR (dong ha)) hoi. hieu va nham thuc dan ((vanh dai) or (vanh tai)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky ((dang ha) OR (dong ha)) hoi. hieu va nham thuc dan ((vanh dai) or (vanh tai)) cua tre*.