Through analyzing the problem of short life of gears in the main gearbox, the design programme for composite hard-surface gears in high-speed level is described.

通过对主减速机齿轮寿命不足问题的分析，提出了在高速级采用组合式硬齿面齿轮的设计方案。

youdao

Teeth have a hard surface layer called enamel.

牙齿有一层叫做釉质的坚硬表层。

《牛津词典》

As he is a hard edged surface against a flat background it should be fairly easy to select him using the Polygonal Lasso Tool.

因为相对于单一的背景，他有一个边缘分明的外观，所以，使用多边形套索工具选取他是十分容易的。

youdao

If you want to dig beneath the hard-scrabble surface of this desert oasis, start with the OriGen Experience.

BBC: Discover life in the Nevada desert

Unfortunately, tragedy can strike with as simple an act as brushing one's elbow across the table, and that's all it took for me to knock my smartphone right onto a hard surface -- facedown in a perfectly horizontal position (the worst imaginable angle).

ENGADGET

He has a well-honed sense of presentation and play--a popular dessert is a "planet" with a raspberry core, grapefruit-cream surface, and hard-sugar atmosphere (his blueberry satellites didn't pan out).

FORBES: Debut