各位老师，我的是截面数据，想再回归中加入产品固定效应以消除产品差异的影响，该怎么加呢？另外，我想用泊松回归，命令是否一样？产品的变量名字为taxcode。数据如下：
* Example generated by -dataex-. To install: ssc install dataex
clear
input float(numb lndocument lnvalue lnquantity soe fie lngdp lngdpcap lndist mylx)
1 1.0986123  8.278428 2.3025851 1 0 26.33644 10.548587  7.588956 0
1  2.397895 10.605074  7.838737 1 0 28.37142  9.589578  8.664759 0
1  2.397895  12.02146  9.876938 1 0 28.37142  9.589578  8.664759 0
1 1.3862944  9.355566   7.20786 1 0  28.9475  10.74222  8.904267 0
1  1.609438  12.52977  7.380256 1 0 26.96272 11.521077  8.858085 0
1 1.3862944 10.770378  7.943073 1 0  28.9475  10.74222  8.904267 0
1  1.609438 10.194551  6.813445 1 0 26.96272 11.521077  8.858085 0
1 1.3862944 11.960684  9.354267 1 0  28.9475  10.74222  8.904267 0
2  1.609438  13.13928 8.0680895 1 0 26.96272 11.521077  8.858085 0
2  1.609438  13.13928 10.138679 1 0 26.96272 11.521077  8.858085 0
2  1.609438  9.317669  6.228511 1 0  30.4505 10.878839 9.3200245 0
2  1.609438  9.317669  4.465908 1 0  30.4505 10.878839 9.3200245 0
1 1.3862944 12.464406   9.74279 1 0  28.9475  10.74222  8.904267 0
1  1.609438  12.84605  7.804659 1 0 26.96272 11.521077  8.858085 0
1  1.609438  8.062118 4.4998097 1 0  30.4505 10.878839 9.3200245 1
end