tf.contrib.slim.conv2d 源码找了好久才发现：
# Simple alias.
conv2d = convolution2d
conv3d = convolution3d原来 tf.contrib.slim.conv2d 等价于tf.contrib.slim.convolution2d
源码地址：
https://github.com/tensorflow/tensorflow/blob/master/tensorflow/contrib/layers/python/layers/layers.py