This is especially true for the harder materials of construction.

对于较硬的建材更是如此。

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"You can make materials that are harder or softer," says Matyjaszewski. "Every self-healing material is somehow unique and has advantages over the other ones."

Matyjaszewski说，“材料的制作可硬可软，每种自我修复材料都具有一定的独特性和优越性。”

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These materials are also often harder to machine making it more difficult to produce smooth threads.

这些材料通常还难以加工，难以制造出光滑的螺纹。

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Home-building was more labor-intensive then because of cruder tools and equipment, materials were harder to come by and houses were smaller because they didn't include bathrooms or kitchens.

WSJ: Moving Heaven and Earth for a House��WSJ Mansion

In 1994, North Korea agreed to stop making plutonium, in return for which America and its allies would supply the country with fuel oil and build two Western-designed light-water nuclear reactors (since it is a bit harder to produce weapons-grade materials from such reactors than from the ones North Korea had been building).

ECONOMIST: Not a final deal, just a start | The

TVs and monitors are harder to recycle because of the lead and other hazardous materials they contain.

BBC: Computer mountain graphic