Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
cam thuc » am thuc, nam thuc, cam thu
thuc van » thuc vat, thuc dan, thuc va
van hanh » van thanh, ban hanh, van anh
hanh tai » thanh tai, hang tai, han tai
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, mang xa
nang ma » tang ma, sang ma, nang cao
van cam » van nam, van lam, van cau
tai cua » thai cua, tai cuc, tri cua
cua te » cua tu

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach ky ((nang xa) or (nang ma)) hoi. hieu van cam thuc van hanh tai cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky ((nang xa) OR (nang ma)) hoi. hieu van cam thuc van hanh tai cua te.
• Adding a wildcard symbol may retrieve word variants: toc sach ky ((nang xa) or (nang ma)) hoi. hieu van cam thuc van hanh tai cua te*.