生育率趋势学术时序图（学术图表）

def solve():
    import pandas as pd
    import matplotlib.pyplot as plt
    import numpy as np
    
    url = 'https://liangdaima.com/static/data/wooldridge/fertil1.csv'
    df = pd.read_csv(url)
    
    plt.rcParams['font.size'] = 12
    year_stats = df.groupby('year')['kids'].agg(['mean', 'std', 'count']).reset_index()
    year_stats['se'] = year_stats['std'] / np.sqrt(year_stats['count'])
    plt.figure(figsize=(12,6))
    plt.fill_between(year_stats['year'], year_stats['mean'] - 1.96*year_stats['se'], 
                    year_stats['mean'] + 1.96*year_stats['se'], alpha=0.2, color='black')
    plt.plot(year_stats['year'], year_stats['mean'], 'o-', color='black', linewidth=2, markersize=6)
    plt.title('生育率趋势', fontsize=14)
    plt.xlabel('年份', fontsize=12)
    plt.ylabel('平均生育数量', fontsize=12)
    plt.grid(alpha=0.3)
    plt.tight_layout()
    plt.show()
    return "可视化代码执行完成"