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To improve the quality of our products, we asked for suggestions______ had used the products. [ ]
1年前
铁心插入通电螺线管,铁心被______,产生了______,于是通电螺线管周围既有______产生的磁场,又有______产生的磁场,使磁场大大增强.
1年前
图示外伸梁承受集中载荷Fp作用,尺寸如图所示。已知Fp= 20kN,许用应力[σ] = 160 MPa,试选择工字钢的号码。
1年前
若bn=2(1-n)an(n≥2),求证:b22+b32+…+bn2<1.
1年前
Which of the following sentences doesn't have a liaison(连读)?
1年前