Can't find model 'en_core_sci_sm'. It doesn't seem to be a shortcut link, a Python package or a valid path to a data directory

Question

import flair.datasets from flair.datasets 
import NCBI_DISEASE from flair.embeddings 
import WordEmbeddings, FlairEmbeddings,StackedEmbeddings from flair.models 
import SequenceTagger from flair.trainers import ModelTrainer
# 1. get the corpus 
corpus = NCBI_DISEASE() 
print(corpus)

/* Can't find model 'en_core_sci_sm'. It doesn't seem to be a shortcut link, a Python package or a valid path to a data directory. */