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探讨了不同应力状态参数对反光镜抛物面质量的影响,并指出消除不良影响的措施。  相似文献   
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Excessive inputs of nitrogen and phosphorus (N and P) degrade surface water quality worldwide. Impoundment of reservoirs alters the N and P balance of a basin. In this study, riverine nutrient loads from the upper Yangtze River basin (YRB) at the Yichang station were estimated using Load Estimator (LOADEST). Long-term load trends and monthly variabilities during three sub-periods based on the construction phases of the Three Gorges Dam (TGD) were analyzed statistically. The dissolved inorganic nitrogen (DIN) loads from the upper YRB for the period from 1990 to 2009 ranged from 30.47?×?104 to 78.14?×?104 t, while the total phosphorus (TP) loads ranged from 2.54?×?104 to 7.85?×?104 t. DIN increased rapidly from 1995 to 2002 mainly as a result of increased fertilizer use. Statistics of fertilizer use in the upper YRB agreed on this point. However, the trend of the TP loads reflected the combined effect of removal by sedimentation in reservoirs and increased anthropogenic inputs. After the TGD impoundment in 2003, decreasing trends in both DIN and TP loads were found. The reduction in DIN was mainly caused by ammonium consumption and transference. From an analysis of monthly loads, it was found that DIN had a high correlation to discharges. For TP loads, an average decrease of 4.91 % in October was found when the TGD impoundment occurred, but an increase of 4.23 % also occurred in July, corresponding to the washout from sediment deposited in the reservoir before July. Results of this study revealed the TGD had affected nutrient loads in the basin, and it had played a role in nutrient reduction after its operation.  相似文献   
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Hu  Fangbing  Wang  Zhongjun  Sheng  Gonghan  Lia  Xia  Chen  Can  Geng  Dehui  Hong  Xinchen  Xu  Nuo  Zhu  Zhipeng  Zhang  Zuofang  Zhu  Liying  Wang  Guangyu 《Environment, Development and Sustainability》2022,24(3):3126-3145
Environment, Development and Sustainability - Communities next to national parks, known as gateway communities, can benefit from national park development. Gateway communities are unique and...  相似文献   
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