<script language="Javascript">
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eval("sp"+divId+".innerHTML='-'");
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<a href="#" onclick="showLay('Layer1')"><span id="spLayer1">+</span>刀具</a><br>
<div id="Layer1" style="display:none;">
|-<a href="#" onclick="showLay('Layer11')"><span id="spLayer11">+</span>手术刀</a><br>

<div id="Layer11" style="display:none;">
   | |-A型号手术刀<br>
   | |-B<br>
   | |-C<br>
</div>
|<br>
|-<a href="#" onclick="showLay('Layer12')"><span id="spLayer12">+</span>镊子</a><br>
<div id="Layer12" style="display:none;">
   | |-AA<br>
   | |-BB<br>
</div>
   | <a href="#" onclick="showLay('Layer13')"><br>
|-<span id="spLayer13">+</span>钳子</a><br>
<div id="Layer13" style="display:none;">
   | |-CC<br>
    | |-DD<br>
    | <br>
</div>
</div>
<a href="#" onclick="showLay('Layer2')"><span id="spLayer2">+</span>电子仪器</a>
<div id="Layer2" style="display:none;">
|-透视仪<br>
|-验血仪器
</div>