eg:
torchvision.models.vgg16(pretrained=True)
实际上是调用了torch.utils.model_zoo中的load_url()函数，
load_url()调用了torch.hub中的load_state_dict_from_url(url, model_dir=None, map_location=None, progress=True, check_hash=False)
如果需要修改模型下载的默认路径（.cache/torch）到自定义目录的话，只需修改load_state_dict_from_url()方法中的model_dir即可~~

1. Resnet:
  model_urls = {
      'resnet18': 'https://download.pytorch.org/models/resnet18-5c106cde.pth',
      'resnet34': 'https://download.pytorch.org/models/resnet34-333f7ec4.pth',
      'resnet50': 'https://download.pytorch.org/models/resnet50-19c8e357.pth',
      'resnet101': 'https://download.pytorch.org/models/resnet101-5d3b4d8f.pth',
      'resnet152': 'https://download.pytorch.org/models/resnet152-b121ed2d.pth',
  }

2. inception:
 model_urls = {
      Inception v3 ported from TensorFlow
     'inception_v3_google': 'https://download.pytorch.org/models/inception_v3_google-1a9a5a14.pth',
 }

3. Densenet: 
 model_urls = {
     'densenet121': 'https://download.pytorch.org/models/densenet121-a639ec97.pth',
     'densenet169': 'https://download.pytorch.org/models/densenet169-b2777c0a.pth',
     'densenet201': 'https://download.pytorch.org/models/densenet201-c1103571.pth',
     'densenet161': 'https://download.pytorch.org/models/densenet161-8d451a50.pth',
 }

4. Alexnet:
 model_urls = {
     'alexnet': 'https://download.pytorch.org/models/alexnet-owt-4df8aa71.pth',
}

5. vggnet:
 model_urls = {
     'vgg11': 'https://download.pytorch.org/models/vgg11-bbd30ac9.pth',
     'vgg13': 'https://download.pytorch.org/models/vgg13-c768596a.pth',
     'vgg16': 'https://download.pytorch.org/models/vgg16-397923af.pth',
     'vgg19': 'https://download.pytorch.org/models/vgg19-dcbb9e9d.pth',
     'vgg11_bn': 'https://download.pytorch.org/models/vgg11_bn-6002323d.pth',
     'vgg13_bn': 'https://download.pytorch.org/models/vgg13_bn-abd245e5.pth',
     'vgg16_bn': 'https://download.pytorch.org/models/vgg16_bn-6c64b313.pth',
     'vgg19_bn': 'https://download.pytorch.org/models/vgg19_bn-c79401a0.pth',
 }