Perhaps you should try some spelling variations:
"thu sach bai thuat do thi" » "thu sach giai thuat do thi", "thu sach bai thuyet do thi", "thu sach ki thuat do thi", "tu sach bai thuat do thi", "thuat sach bai thuat do thi", "thuoc sach bai thuat do thi", "thu sach dao thuat do thi", "thu cac bai thuat do thi", "thu sach xa thuat do thi"
"toc sach ky thuat co khi" » "hoc sach ky thuat co khi", "doc sach ky thuat co khi", "thuoc sach ky thuat co khi", "toc sac ky thuat co khi", "toc sach y thuat co khi", "toc sach ty thuat co khi", "toc sach ky thuat cbo khi"
"tu cac ky thuat o khi" » "tu cac 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 cac ky thuat o khi") or ("toc sach ky thuat co khi"))) or ("thu sach bai thuat do thi"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("tu cac ky thuat o khi") OR ("toc sach ky thuat co khi"))) OR ("thu sach bai thuat do thi")).
• Removing quotes may allow a broader search: (((( tu cac ky thuat o khi ) or ( toc sach ky thuat co khi ))) or ( thu sach bai thuat do thi )).
• Adding a wildcard symbol may retrieve word variants: (((("tu cac ky thuat o khi") or ("toc sach ky thuat co khi"))) or ("thu sach bai thuat do thi"))*.