| 摘要 |
<p>Abstract The asymmetrical head of a shovel incorporates a vertically oriented edge extending upwardly from the tip of the head to a recessed leading edge. The construction of the head permits it to function both as a pivot and as a lever, as well as facilitating the initial penetration of the head in soil. -, AA1 WA) 31 " Fi e I 36-413</p> |
