全文获取类型
收费全文 | 224篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
林业 | 26篇 |
农学 | 6篇 |
基础科学 | 25篇 |
3篇 | |
综合类 | 153篇 |
农作物 | 9篇 |
水产渔业 | 4篇 |
畜牧兽医 | 3篇 |
园艺 | 3篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2017年 | 6篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 20篇 |
2013年 | 14篇 |
2012年 | 21篇 |
2011年 | 23篇 |
2010年 | 13篇 |
2009年 | 8篇 |
2008年 | 14篇 |
2007年 | 19篇 |
2006年 | 7篇 |
2005年 | 12篇 |
2004年 | 3篇 |
2003年 | 6篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
排序方式: 共有232条查询结果,搜索用时 31 毫秒
1.
2.
乡镇污水处理厂运行管理相关问题探讨 总被引:1,自引:0,他引:1
乡镇污水处理厂作为环保基础设施建设的重点,普遍存在重建设轻运营的问题。笔者结合重庆市实际情况,重点分析了乡镇污水处理厂运行管理中存在的问题,并有针对性地提出了建议,包括提高收集率、完善末端工艺、专业化运营、改变考核体系、优化污泥处置、加强再生利用和远程在线监控等。 相似文献
3.
4.
对滚珠丝杠的温升及热变形的对策进行了探讨,提出解决温升和热变形的方法,为滚珠丝杠的设计、安装、使用和维修提供参考. 相似文献
5.
滚珠丝杠的温升及热变形对策 总被引:1,自引:0,他引:1
对滚珠丝杠的温升及热变形的对策进行了探讨,提出解决温升和热变形的方法,为滚珠丝杠的设计、安装、使用和维修提供参考。 相似文献
6.
A survey was conducted to determine the geometry, operating parameters, and other key features of large circular or octagonal culture tanks used to produce Atlantic salmon smolt and post-smolt at six major Norwegian Atlantic salmon production companies. A total of 55 large tanks were reported at seven land-based hatchery locations, i.e., averaging 7.9 (range of 4–12) large tanks per land-based site. In addition, one 21,000 m3 floating fiberglass tank in sea was reported. Culture volume ranged from 500 to 1300 m3 for each land-based tank. Most tanks were circular, but one site used octagonal tanks. Land-based tank diameters ranged from 14.5 to 20 m diameter, whereas the floating tank was 40 m diameter. Maximum tank depths ranged from 3.5 to 4.5 m at land-based facilities, which produced diameter-to-average-depth ratios of 3.6:1 to 5.5:1 m:m. The floating tank was much deeper at 20 m, with a diameter-to-average-depth ratio of only 2.4:1 m:m. All land-based tanks had floors sloping at 4.0–6.5% toward the tank center and various pipe configurations that penetrated the culture tank water volume at tank center. These pipes and sloping floors were used to reduce labor when removing dead fish and harvesting fish.Maximum flow ranged from 3 to 19 m3/min per land-based tank, with 400 m3/min at the floating tank, but tank flow was adjustable at most facilities. Land-based tanks were flushed at a mean hydraulic retention time (HRT) of 35–170 min. Maximum feed load on each land-based tank ranged from 525 to 850 kg/day, but the floating tank reached 3700 kg/day. Almost half of the large tanks reported in this survey were installed or renovated since 2013, including the three tank systems with the highest flow rate per tank (greater than 17.6 m3/min). These more recent tanks were operated at more rapid tank HRT’s, i.e., from 34.8 to 52.5 min, than the 67–170 min HRT typical of the large tanks built before 2013. In addition, flow per unit of feed load in land-based tanks that began operating before 2010 were lower (19–30 m3 flow/kg feed) than in tanks that began operating later (33–40 m3 flow/kg feed). In comparison, the floating tank operates at a maximum daily tank flow to feed load of 160 m3 flow/kg feed, which is the least intensive of all tanks surveyed. Survey results suggest that the recently built tanks have been designed to operate at a reduced metabolic loading per unit of flow, a tendency that would improve water quality throughout the culture tank, all else equal. This trend is possible due to the ever increasing application of water recirculating systems. 相似文献
7.
以大量原始史料为基础,对中国共产党在特定形势下发起的农业生产互助运动进行了研究,考察了这一时期革命根据地农业生产互助组织的组织特征、运行机制和绩效。 相似文献
8.
伐区作业类型划分与集材作业系统相适应性的研究 总被引:3,自引:0,他引:3
本应用模糊聚类分析方法,选取作业区坡度、单位面积出材量、集材距离以及地表承载能力等作为因子,对吉林林区伐区作业类型进行了区划。又应用层次分析法,对与每类伐区相适应的集材作用系统进行系统分析。 相似文献
9.
应用数理统计方法,结合带岭林业局寒月林场伐木作业,对伐木作业过程中的伐木切削时间和林内行走速度(时间)进行了统计分析.结果表明,伐木切削时间是树种和径级的函数,林内行走速度服从正态分布. 相似文献
10.
(超)轻型飞机防治森林病虫害技术研究 总被引:16,自引:1,他引:15
福建三明市自 1 987年先后引进一种轻型飞机和两种超轻型飞机 ,利用简易临时机场 ,应用GPS卫星定位导航 ,开展超低容量喷洒白僵菌纯孢子液、菌药混合液、氰戊菊酯、甲基硫菌灵等药液 ,防治马尾松毛虫、刚竹毒蛾、毛竹枯梢病、黑荆树害虫等森林病虫害。 1 2年来 ,防治作业 941架次 ,防治面积 2 2 47× 1 0 4 hm2 。总结出一套安全、先进、经济、高效适合轻型飞机防治森林病虫害作业技术规程 ,取得良好的防治效果和社会、生态、经济效益 相似文献