中文：

国债发行时间是由国家财政部和央行根据宏观经济形势和政策需要共同决定的。通常来说，国债发行时间会根据市场需求和季节变化进行微调，以保障发行的顺利进行。

一般来说，国债发行分为储蓄国债和记账式国债两种。储蓄国债的发行时间通常在3月至11月之间，而记账式国债的发行时间则较为灵活，根据市场情况和政策需要进行调整。

在储蓄国债方面，一般会在3月、4月、5月、6月、7月、8月、9月、10月和11月发行，而记账式国债则根据市场情况和政策需要进行调整。国债发行的品种和期限也会根据市场需求进行调整。

在购买国债方面，投资者可以通过银行、证券公司、基金公司等渠道进行购买。投资者可以根据自己的投资需求和风险承受能力选择不同的投资品种和购买方式。

总的来说，国债发行时间是由国家财政部和央行根据宏观经济形势和政策需要共同决定的，而投资者则可以根据自己的投资需求选择不同的投资品种和购买方式。

英文：

The issuance time of government bonds is jointly decided by the Ministry of Finance and the central bank based on the macroeconomic situation and policy needs. Usually, the issuance time of government bonds will be adjusted slightly based on market demand and seasonal changes to ensure smooth issuance.

Generally speaking, there are two types of government bonds: savings bonds and book-entry bonds. The issuance time of savings bonds is usually between March and November, while the issuance time of book-entry bonds is more flexible, adjusted according to market conditions and policy needs.

For savings bonds, they are usually issued in March, April, May, June, July, August, September, October, and November. Book-entry bonds are adjusted according to market conditions and policy needs. The variety and maturity of government bonds are also adjusted based on market demand.

When purchasing government bonds, investors can purchase through banks, securities companies, fund companies, etc. Investors can choose different investment varieties and purchase methods based on their investment needs and risk tolerance.

Overall, the issuance time of government bonds is jointly decided by the Ministry of Finance and the central bank based on the macroeconomic situation and policy needs, while investors can choose different investment varieties and purchase methods based on their investment needs.