如何加载部分预训练的pytorch模型？

import torch
from torchvision import models

model = models.resnet18(pretrained=True)

for param in model.parameters():
    param.requires_grad = False

num_features = model.fc.in_features
model.fc = torch.nn.Linear(num_features, num_classes)

model.load_state_dict(torch.load('path_to_pretrained_weights.pth'))

model.eval()