全文获取类型
收费全文 | 217篇 |
免费 | 8篇 |
国内免费 | 8篇 |
专业分类
林业 | 55篇 |
农学 | 8篇 |
基础科学 | 4篇 |
20篇 | |
综合类 | 101篇 |
农作物 | 5篇 |
水产渔业 | 14篇 |
畜牧兽医 | 7篇 |
园艺 | 1篇 |
植物保护 | 18篇 |
出版年
2024年 | 1篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 10篇 |
2015年 | 2篇 |
2014年 | 8篇 |
2013年 | 6篇 |
2012年 | 13篇 |
2011年 | 15篇 |
2010年 | 22篇 |
2009年 | 17篇 |
2008年 | 10篇 |
2007年 | 11篇 |
2006年 | 17篇 |
2005年 | 9篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1986年 | 1篇 |
排序方式: 共有233条查询结果,搜索用时 36 毫秒
1.
2.
3.
Conservation implications of establishment success of the Critically Endangered Twee River redfin ‘Pseudobarbus’ erubescens (Skelton, ) in an artificial impoundment in South Africa 下载免费PDF全文
Martine S. Jordaan Johannes A. van der Walt Zanné Brink Sonja Erasmus Olaf L. F. Weyl 《水产资源保护:海洋与淡水生态系统》2017,27(4):886-889
- This study reports the first known record of breeding of the Critically Endangered Twee River redfin ‘Pseudobarbus’ erubescens in an artificial impoundment. This followed an introduction of 48 individuals into a 10 ha impoundment within the species' native range more than a decade ago.
- Sampling the impoundment using three fyke nets set overnight yielded 2838 P. erubescens, which included both juveniles and adults capable of spawning. Fork length measurements of a subsample of 250 individuals ranged from 29 to 125 mm with length cohorts indicating multiple spawning events.
- This demonstrates that this species can successfully reproduce in lentic environments and suggests that artificial impoundments could be stocked to provide refugia for P. erubescens and other highly threatened small cyprinids while conservation strategies are developed to mitigate against habitat loss resulting from alien fish invasions, increased human use of water, and from climate change in rivers.
4.
Intensification of agriculture has significantly diminished the populations of segetal weeds worldwide in recent decades. Remarkable changes to the entire flora and vegetation of man‐made habitats are being observed in agroecosystems. The present study analyses, for the first time, the threat status of segetal weeds in Tajikistan. A group of 871 weed species were evaluated against IUCN criteria. The assessment of threat status revealed that 214 weed taxa have to be regarded as threatened in Tajikistan, including 18 endemic and four subendemic plants. Five species have been classified as extinct, 27 as critically endangered, 27 as endangered, 39 as vulnerable, 34 as near threatened and 44 as in the ‘least concern’ category. For 38 species, the threat level was not possible, due to lack of data. The most threatened group of taxa is related to rice paddy fields. Numerous losses and disappearances were also observed in cereal communities. Percentages of threatened species in different chorological groups amounted to 58% in the Irano–Turanian, 17% in the Pluriregional, 11% in the Mediterranean, 9.5% in the Cosmopolitan and 4% in the Euro–Siberian species group. Assessment of the threatened status of the rich segetal flora of Tajikistan affords the opportunity to raise awareness of the value of this group of species in the country and may be useful in the conservation management of arable habitats. The results show that even though agriculture in Tajikistan is still based on traditional management and manual work, weed control causes a serious threat to its segetal flora. 相似文献
5.
我国国家级森林公园产业准入负面清单制定与应用 总被引:2,自引:1,他引:1
我国国家级森林公园属于国家生态红线区域。建立国家级森林公园产业准入负面清单制度是对国家级森林公园进行生态红线管控的关键,也是实现国家级森林公园可持续健康发展的基础。文中提出国家级森林公园产业准入负面清单内涵,并从构建主体、实施区域和实施目标3个方面阐述其主要特征;依据相应的法律法规、产业准入政策和指导性文件,在遵循突出因地制宜、强化底线约束、加强监管干预原则指导下,通过研读制度和文件,参考已有的产业负面清单,筛选出我国国家级森林公园内禁止、允许和鼓励3类产业,在此基础上形成国家级森林公园产业准入负面清单;探讨负面清单适用性、管控措施以及如何推动国家级森林公园产业准入负面清单制度的落实。 相似文献
6.
7.
8.
9.
10.
最短路径搜索是路径分析中的热点问题.将双向链表和人口迁移算法的智能进化体制相结合,提出一种新的启发式智能仿生优化算法——双向链表人口迁移算法,并用于求解最短路径问题.仿真实验结果表明:双向链表人口迁移算法求解最短路径搜索问题是可行、有效的. 相似文献