你没有正确地遍历代码中所有可能的行和列的组合。我已经重写了你的代码，下面这段代码将从 Dataframe 中提取所需的元素，并将它们附加到结果列表中

import pandas as pd
from itertools import combinations, product

# Replace this line with your own data source
data = [[2, 6], [8, 5]]
dataframe = pd.DataFrame(data)

def get_combinations(dataframe):
    res_list = []
    nrows, ncols = dataframe.shape
    
    for r in range(1, nrows+1):
        for c in range(1, ncols+1):
            row_combinations = list(combinations(range(nrows), r))
            col_combinations = list(combinations(range(ncols), c))
            
            for row_comb, col_comb in product(row_combinations, col_combinations):
                tmp = []
                for i in row_comb:
                    tmp.append([dataframe.iloc[i, j] for j in col_comb])
                if tmp not in res_list:
                    res_list.append(tmp)
    return res_list

result = get_combinations(dataframe)
print(result)