全文获取类型
收费全文 | 748篇 |
免费 | 3篇 |
专业分类
化学工业 | 5篇 |
机械仪表 | 1篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 9篇 |
一般工业技术 | 4篇 |
冶金工业 | 725篇 |
自动化技术 | 5篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2014年 | 4篇 |
2013年 | 2篇 |
2012年 | 5篇 |
2011年 | 2篇 |
2010年 | 2篇 |
2007年 | 1篇 |
2006年 | 1篇 |
2005年 | 1篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2000年 | 1篇 |
1999年 | 26篇 |
1998年 | 244篇 |
1997年 | 119篇 |
1996年 | 80篇 |
1995年 | 50篇 |
1994年 | 36篇 |
1993年 | 37篇 |
1992年 | 7篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1977年 | 10篇 |
1976年 | 33篇 |
1975年 | 1篇 |
排序方式: 共有751条查询结果,搜索用时 0 毫秒
751.
Large wood (LW) has important physical and ecological functions in streams. Riparian vegetation is extensively removed during urban expansion, and urban streams may experience enhanced fluvial transport of LW due to flashy hydrology. In this study, LW loads were assessed for three reaches on North Buffalo Creek, an urban stream located in Greensboro, North Carolina, United States. These three reaches have similar hydrology but different riparian vegetation densities. We measured the frequencies and sizes of both in-channel LW and riparian vegetation across the three reaches. Our results showed that the recently reforested reach had greater LW volume (22.5 m3/km) compared to the unmanaged forested site (16 m3/km) and the site with low riparian vegetation density (4.78 m3/km). The difference in LW frequency among reaches was statistically significant (). However, the difference in the volume of individual pieces was not significantly different across reaches (, indicating that a similar size of wood is recruited across the three sites. Our findings also showed that there is a positive relationship between riparian vegetation frequency and in-channel LW frequency, which are significantly related as a power function. Spatial lag models (integrating upstream riparian trees) did not show better results compared to a non-lagged model, suggesting that storage and recruitment were predominantly local and that the LW distribution at our reaches is limited by recruitment rather than dominated by fluvial transport. Our findings suggested that a fully forested watershed is not needed to provide some of the benefits of wood to urban streams. 相似文献