全文获取类型
收费全文 | 48篇 |
免费 | 6篇 |
国内免费 | 4篇 |
专业分类
林业 | 5篇 |
农学 | 3篇 |
9篇 | |
综合类 | 15篇 |
农作物 | 8篇 |
水产渔业 | 5篇 |
畜牧兽医 | 4篇 |
园艺 | 4篇 |
植物保护 | 5篇 |
出版年
2022年 | 3篇 |
2020年 | 1篇 |
2018年 | 4篇 |
2017年 | 1篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 4篇 |
2012年 | 2篇 |
2011年 | 3篇 |
2010年 | 2篇 |
2009年 | 1篇 |
2008年 | 1篇 |
2007年 | 2篇 |
2006年 | 7篇 |
2005年 | 2篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1989年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有58条查询结果,搜索用时 31 毫秒
1.
Divergent, genetically based feeding behaviour of two sympatric Arctic charr, Salvelinus alpinus (L.), morphs 总被引:1,自引:0,他引:1
Abstract – Arctic charr, Salvelinus alpinus (L.), is one of the several northern fishes that show resource polymorphisms in postglacial lakes. Two reproductively isolated morphs of Arctic charr coexist in distinct ecological niches in the subarctic lake Fjellfrøsvatn, North Norway. Offspring of the two morphs (termed littoral charr and profundal charr) were reared separately but under identical conditions. Their feeding behaviour was compared experimentally using different kinds of live prey. The fishes had no experience with natural prey before the experiments. The littoral morph were more effective in eating live plankton ( Daphnia ) and littoral benthos ( Gammarus ), and had a higher attack rate against pleuston (surface prey, Gerris ) compared with the profundal morph. The two morphs behaved in accordance with expectations from their in situ niche utilisation towards the three prey types. This indicates a case of incipient ecological speciation where divergence in resource utilisation in contrasting niches has evolved adaptations in feeding behaviour by natural selection. 相似文献
2.
3.
4.
5.
为了阐明过氧化物酶(POD)同工酶在四棱豆中的分布规律,鉴定不同四棱豆品种间的亲缘关系,选育优势杂交亲本,我们采用聚丙烯酰胺凝胶垂直板电泳技术,研究了同一株四棱豆(K0027)不同节位成熟叶片和16个品种的POD同工酶酶谱特征。结果表明:POD同工酶在同一株四棱豆9个不同节位成熟叶片中的酶带数均为10条,并且各酶带相应的Rf值基本相同;而在16个不同四棱豆品种中酶带数为6~11条,并且各酶带的宽窄、颜色深浅等特征存在明显的差异。结合各酶带的相对迁移率(Rf值)和品种间的联合相似系数(S值)分析可知,(1)POD同工酶在同一株四棱豆不同节位成熟叶片中的表达具有高度的稳定性和相似性;(2)POD同工酶在所选的16个品种间存在明显的差异性,其中K0006和K0035、早熟二号,K0021和K0028品种间的S值在0.2~0.4之间,为最小值,即这两组品种间的亲缘关系最远,为优势杂交亲本组合;(3)同时阐明了POD同工酶在四棱豆中的相关分布规律,为植物分类或品种鉴定提供了科学依据,对杂交育种选材具有重要的实践指导意义。 相似文献
6.
7.
《Plant Production Science》2013,16(4):360-366
We examined biomass dry matter and nutrient uptake of live plant parts, leaf area index, and litter of winged bean (Psophocarpus tetragonolobus) and velvet bean (Mucuna pruriens) 12, 18, 24 and 30 weeks after sowing (WAS). The two plants had similar leaf and stem+petiole biomasses. At 30 WAS winged bean had a significantly lower pod yield than velvet bean. Between 18 and 30 WAS, winged bean produced less litter than velvet bean due to differences in growth stages. The total mulch of live parts and litter of winged bean and velvet bean completely covered the ground by 18 and 12 WAS, respectively. Compared to velvet bean, the leaf and stem+petiole of winged bean had a significantly higher N concentration; significantly higher N uptake at 24 and 30 WAS; significantly lower C/N ratio; and significantly higher P, K and Mg concentrations. In winged bean, P uptake was significantly higher in the leaf at 30 WAS and in the stem+petiole at all harvesting times. The total biomass of the leaf, stem+petiole and litter of winged bean was 317–561 g DM m-2, and their N content was 12.3–17.7 g m-2. The total biomass of live parts and litter of winged bean might be sufficient to suppress weeds and increase soil N. Winged bean is an appropriate legume cover crop and green manure due to its longer growing period and superior ground-covering ability and high N input. 相似文献
8.
Rose THOROGOOD 《中国鸟类》2013,4(1):39-50
很早人们就已发现一些寄生性繁殖的杜鹃,其外形与Accipiter属的鹰类非常相似。最近的实验表明,大杜鹃(Cuculus canorus)模拟鹰类有助于其接近宿主大苇莺(Acrocephalus scirpaceus)的巢。不过,大苇莺却能够通过公众信息传递来识别大杜鹃的这一计谋。反过来,这也导致了杜鹃外形多态性的进化,以避免宿主对杜鹃的识别。通过比较研究,我们发现在寄生性的杜鹃中,模拟鹰类外形(如虹膜黄色,胸腹部具斑纹,脚黄)的杜鹃种类具有明显的外形多态性(29%的种类),远高于不模拟鹰类外形的杜鹃(仅8%的种类具有多态性)。系统发生分析进一步证实了模拟鹰类外形与杜鹃多态性进化之间的相关性。我们认为,杜鹃对鹰类的动态模拟很可能促进了杜鹃外形多态性的进化,以避免宿主对杜鹃的识别。 相似文献
9.
Tommi Malinen Antti Tuomaala Hannu Lehtonen Kimmo K. Kahilainen 《Ecology of Freshwater Fish》2014,23(3):424-437
Density and biomass estimates of pelagic fish are essential to understand food web interactions and ecosystem functioning. We conducted surveys of six subarctic lakes for assessing both mono‐ and polymorphic whitefish Coregonus lavaretus (L.) populations. Monomorphic whitefish lakes were inhabited by a habitat and diet generalist, large sparsely rakered (LSR) morph, whereas polymorphic whitefish lakes had a littoral benthivorous LSR morph, a pelagic planktivorous densely rakered (DR) morph and in two cases a benthivorous small sparsely rakered (SSR) morph inhabiting the profundal zone. In addition, an introduced specialist zooplanktivore, vendace Coregonus albula (L.), inhabited one of the monomorphic lakes. Hydroacoustics was found to be an appropriate method for estimating coregonid densities and biomasses in large and deep polymorphic lakes occupied by the planktivorous DR morph or vendace, but only during dark nights in autumn. The suitability of hydroacoustic assessment for benthivorous LSR and SSR morphs was low, especially in polymorphic whitefish lakes due to their preference for near‐bottom habitat or shallow areas not sampled with hydroacoustics. The pelagic density of DR morph varied from 330 to 1780 fish·ha?1 and biomass from 1.4 to 13.3 kg·ha?1 in polymorphic whitefish lakes, whereas corresponding estimates for LSR morph were 10–320 fish·ha?1 and 0.5–8.4 kg·ha?1 in monomorphic whitefish lakes. In general, polymorphism tended to increase the density and biomass of whitefish in the pelagic area compared with monomorphic systems. 相似文献
10.
有翅型与无翅型棉蚜发育及繁殖能力比较研究 总被引:1,自引:0,他引:1
在室内采用网罩盆栽苗研究有翅型与无翅型棉蚜若虫及成虫发育历期、繁殖能力、成虫寿命、产仔能力、体重.有翅型与无翅型棉蚜若虫发育历期之间无显著差异.二者成虫寿命、第一次产仔数量、平均每次产仔数差异不显著,而生殖前期、产仔次数、净增殖率与内禀增长率均存在极显著差异(P<0.01).有翅型棉蚜的产仔次数极显著小于无翅型,而有翅型棉蚜生殖前期显著长于无翅型棉蚜.无翅型棉蚜净增殖率显著大于有翅型棉蚜.无翅型棉蚜可能可以将用于翅发育和飞行的能量转而用于繁殖. 相似文献