全文获取类型
收费全文 | 368篇 |
免费 | 17篇 |
国内免费 | 3篇 |
专业分类
林业 | 15篇 |
农学 | 14篇 |
基础科学 | 23篇 |
8篇 | |
综合类 | 290篇 |
农作物 | 22篇 |
水产渔业 | 6篇 |
畜牧兽医 | 9篇 |
园艺 | 1篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 7篇 |
2020年 | 16篇 |
2019年 | 16篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 11篇 |
2015年 | 14篇 |
2014年 | 29篇 |
2013年 | 43篇 |
2012年 | 31篇 |
2011年 | 52篇 |
2010年 | 17篇 |
2009年 | 16篇 |
2008年 | 16篇 |
2007年 | 24篇 |
2006年 | 12篇 |
2005年 | 10篇 |
2004年 | 3篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 4篇 |
排序方式: 共有388条查询结果,搜索用时 15 毫秒
51.
52.
53.
54.
Urban green spaces provide critical social and ecological support for cities, but we know little about their diversity and composition in cities of the Global South. This is especially true of lesser known urban spaces such as sacred sites, which are of important cultural and biodiversity significance. We examine tree diversity and composition in sacred sites in Bengaluru, one of India’s fastest growing cities. We recorded 5504 trees from 93 species across 62 temples, churches, and Hindu, Christian and Muslim cemeteries in central areas of Bengaluru. Over half (52%) of the tree species were of native origin, a much higher proportion when compared to other green spaces in the city such as parks. Tree density in sacred sites was much higher than that in parks and informal settlements in Bengaluru. Temples and Hindu cemeteries contained the highest proportion of native species, with large numbers of Ficus benghalensis, a keystone sacred species. Trees in sacred spaces provide an important buffer against urban environmental stress in Indian cities, and serve as refuges for urban wildlife and biodiversity. We need greater information on these lesser known, but culturally significant alternate spaces. They play an important, though ignored role in the environmental sustainability of rapidly growing cities in the Global South. 相似文献
55.
The hydraulic performance of canals designed to deliver water by proportional allocation is highly dependent on the accuracy of construction of water division structures. If construction is inaccurate then inequity of water delivery is built into the system from the onset. A survey of hydraulic performance of Kalpnai distributary in NWFP Pakistan immediately after construction showed that the canal could only deliver 90% of designed discharge due to deficiencies in construction of two siphons, and that the tail end of the canal only received 70% of designed discharge. When operated at 70% of design discharge tail end reaches received 50% of designed discharge. Measurements of outlet structures showed that 57% of structures were built as intended and had not been damaged. All orifice outlets delivered more than 115% of design discharge and on average delivered 40% more than intended. Only 20% of open flumes were within 10% of design width, while 58% were more than 30% wider. As a result of these construction defects many watercourses were able to obtain much higher discharges than intended. The lack of control gates means there is no managerial remedy to redress the existing inequity. The only solution is to reconstruct a high proportion of outlet structures. Potential causes of poor construction are many, including lack of involvement of the agency responsible for subsequent operation, lack of dialogue with water users, and lack of accountability built into the project framework. 相似文献
56.
倪浩 《上海交通大学学报(农业科学版)》1998,(4)
邓小平同志关于加强社会主义精神文明建设的论述,是邓小平理论的重要组成部分。该文紧密联系本院精神文明创建工作的实际,谈了自己学习邓小平同志这方面论述的体会。文章中提出了高等学校应当成为全社会精神文明建设的重要基地和楷模;高等学校的精神文明创建工作应当着重营造有利于“四有”新人健康成长的氛围;高等学校精神文明创建工作还需向更高层次推进和拓展等观点。 相似文献
57.
介绍了Case IH公司A8000系列改进型甘蔗收割机各主要部件的结构特点及技术性能,为我国相关科研单位和生产企业进一步研究和开发甘蔗收割机提供参考。 相似文献
58.
59.
60.