Perhaps you should try some spelling variations:
"tu sach ky thuat co khi" » "tu sach ky thuat do khi", "thu sach ky thuat co khi", "su sach ky thuat co khi", "tu cach ky thuat co khi", "tu sac ky thuat co khi", "tu sach y thuat co khi", "tu sach ty thuat co khi", "tu sach ky thuat cbo khi"
"tu sach ky thuat o khi" » "thu sach ky thuat o khi", "su sach ky thuat o khi", "tu cach ky thuat o khi", "tu sac ky thuat o khi", "tu sach y thuat o khi", "tu sach ty thuat o khi", "tu sach ky thuat do khi", "tu sach ky thuat bo khi"
"te sach ky thuat o khi" » "te sac ky thuat o khi", "te sach y thuat o khi", "te sach ty thuat o khi", "te sach ky thuat do khi", "toc sach ky thuat o khi", "te sach ky thuat bo khi"

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: (("tu sach ky thuat co khi") or ((("tu sach ky thuat o khi") OR ("te sach ky thuat o khi"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("tu sach ky thuat co khi") OR ((("tu sach ky thuat o khi") OR ("te sach ky thuat o khi")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"tu sach ky thuat co khi\") or (((\"tu sach ky thuat o khi\") OR (\"te sach ky thuat o khi\"))))".
• Removing quotes may allow a broader search: (( tu sach ky thuat co khi ) or ((( tu sach ky thuat o khi ) OR ( te sach ky thuat o khi )))).
• Adding a wildcard symbol may retrieve word variants: (("tu sach ky thuat co khi") or ((("tu sach ky thuat o khi") OR ("te sach ky thuat o khi"))))*.