Perhaps you should try some spelling variations:
"toc sach hoc tay nguoi" » "toc sach hoc toc nguoi", "toc sach hoc dao nguoi", "hoc sach hoc tay nguoi", "doc sach hoc tay nguoi", "thuoc sach hoc tay nguoi", "toc cach hoc tay nguoi", "toc sach hoi tay nguoi", "toc sach duoc tay nguoi", "toc sach toc tay nguoi", "toc sach hoc may nguoi", "toc sach hoc tai nguoi"
"tim mach hoc lam nguoi" » "tim mach hoc dao nguoi", "tim cach hoc lam nguoi", "tim dich hoc lam nguoi", "tim anh hoc lam nguoi", "tim mach duoc lam nguoi", "time mach hoc lam nguoi"
"toc sach hoc tap nguoi" » "toc sach hoc gap nguoi", "toc sach hoc tac nguoi", "toc sach hoc giap nguoi", "hoc sach hoc tap nguoi", "doc sach hoc tap nguoi", "thuoc sach hoc tap nguoi", "toc cach hoc tap nguoi", "toc sach hoi tap nguoi", "toc sach duoc tap nguoi"

Try widening your search to All Fields.

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("tim mach hoc lam nguoi") or ((("toc sach hoc tay nguoi") OR ("toc sach hoc tap nguoi"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("tim mach hoc lam nguoi") OR ((("toc sach hoc tay nguoi") OR ("toc sach hoc tap nguoi")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"tim mach hoc lam nguoi\") or (((\"toc sach hoc tay nguoi\") OR (\"toc sach hoc tap nguoi\"))))".
• Removing quotes may allow a broader search: (( tim mach hoc lam nguoi ) or ((( toc sach hoc tay nguoi ) OR ( toc sach hoc tap nguoi )))).
• Adding a wildcard symbol may retrieve word variants: (("tim mach hoc lam nguoi") or ((("toc sach hoc tay nguoi") OR ("toc sach hoc tap nguoi"))))*.