Perhaps you should try some spelling variations:
sach thu » sach thue, sach thieu, sach tham
thu nang » thi nang, thu hang, thu bang
nang cau » nang cao, hang cau, nang dau
nam thuc » nam thuoc, am thuc, nam thu
thuc dan » thuc hanh, hoc dan, thuc vat
dan hanh » dang hanh, dan khanh, dan thanh
hanh tai » thanh tai, hang tai, han tai
ve triet » va trien, su triet
tu sach » thu sach, su sach, te sach
qua nam » quan nam, cua nam, quang nam
su tien » su kien, su hien, tu tieng

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 thu nang cau hoi. hieu qua nam thuc dan hanh tai ((su tien) or (ve triet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach thu nang cau hoi. hieu qua nam thuc dan hanh tai ((su tien) OR (ve triet)).
• Adding a wildcard symbol may retrieve word variants: tu sach thu nang cau hoi. hieu qua nam thuc dan hanh tai ((su tien) or (ve triet))*.