全文获取类型
收费全文 | 928篇 |
免费 | 92篇 |
国内免费 | 107篇 |
专业分类
林业 | 20篇 |
农学 | 39篇 |
基础科学 | 39篇 |
74篇 | |
综合类 | 295篇 |
农作物 | 12篇 |
水产渔业 | 627篇 |
畜牧兽医 | 16篇 |
植物保护 | 5篇 |
出版年
2024年 | 10篇 |
2023年 | 28篇 |
2022年 | 33篇 |
2021年 | 34篇 |
2020年 | 53篇 |
2019年 | 34篇 |
2018年 | 16篇 |
2017年 | 54篇 |
2016年 | 37篇 |
2015年 | 43篇 |
2014年 | 49篇 |
2013年 | 71篇 |
2012年 | 48篇 |
2011年 | 55篇 |
2010年 | 46篇 |
2009年 | 57篇 |
2008年 | 46篇 |
2007年 | 43篇 |
2006年 | 41篇 |
2005年 | 33篇 |
2004年 | 29篇 |
2003年 | 31篇 |
2002年 | 26篇 |
2001年 | 21篇 |
2000年 | 26篇 |
1999年 | 30篇 |
1998年 | 31篇 |
1997年 | 16篇 |
1996年 | 16篇 |
1995年 | 20篇 |
1994年 | 17篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
排序方式: 共有1127条查询结果,搜索用时 15 毫秒
31.
IntroductionInherent to the practice of intensive aquaculture is the generation of wastes having immediate and verybroad effects on the aquatic environment.There is a growing consensus about the need to reduce waste pro-duction in aquaculture to minimize the negative impacts on the environment.Nitrogen(N) and phosphorus(P) wastes are major concerns for many aquaculture operations.In the past,formulation of diets in intensive aquaculture was often aimed at meeting requirements formaximum growt… 相似文献
32.
33.
通过对漠斑牙鲆淡水池塘网箱养殖试验,掌握了该品种的生活习性,探索出漠斑牙鲆内陆地区淡水养殖模式,总结出养殖过程中应采取的技术措施。25m~2网箱总产漠斑牙鲆102.9 kg,平均单产4.12 kg/m~2,平均规格为306.25 g/尾,成活率达84%。 相似文献
34.
35.
海水池塘养殖模式优化:概念、原理与方法 总被引:5,自引:2,他引:5
随着海洋渔业资源衰退和人类社会对水产品需求的持续增长,海水养殖规模逐年扩大,养殖生产对环境的影响也日益严重[1-6]。现已确认海水鱼虾类养殖是造成海洋沿岸带水域富营养化的重要污染源之一[5-8],这一严峻现实要求今后在发展海水养殖产业时不仅需要宏观上对养殖区域和养 相似文献
36.
利用闲置的鲍鱼养殖池进行豹纹鳃棘鲈工厂化养殖模式的研究。养殖池长宽高为9 m×3 m×2 m,有效水深约1.7 m,设3个进水口,采用下排上溢的排水方式,在距池底高20 cm处建3排6个进气管,管上打孔增氧。在池中放置一长宽高为6.0 m×3.0 m×1.5 m的网箱,将豹纹鳃棘鲈放在网箱中养殖,有效水体深1.2 m。养殖用水处理:海边沙滤井→沉淀池→三级过滤池→紫外线消毒池→活化珊瑚石过滤→养殖池(下排上溢)→上溢养殖废水用于东风螺或双壳贝类养殖,下排养殖废水进入污水沉淀处理池。在2011年7月放养9 000尾全长10 cm的优质豹纹鳃棘鲈苗种,经过约15个月的养殖,共养成每尾平均体重约742 g的商品鱼5 710 kg,养殖成活率达85.5%,单位产量达12.4 kg·m-3。 相似文献
37.
对虾白斑病围栏封闭预防技术 总被引:2,自引:0,他引:2
“对虾白斑病的围栏封闭预防技术”是一项针对沿海低位池塘、以切断传染病源为主旨、以设置防蟹围栏为特色的对虾白斑病综合预防技术。其主要措施为:首先在贮水(兼水处理)池和养殖池周围设置防蟹围栏,将该等池塘封闭起来,使杂蟹不会从陆地侵入池内;然后通过60目滤网进水,并用敌百虫或敌杀死处理上述两种池塘,杀灭以蟹类为主的一切甲壳动物;解毒后,放养经检测不带白斑症病毒的虾苗;采取封闭式养殖,养殖期中只向养殖池加水以补充渗漏和蒸发的水损失;加水时,先将海水在贮水池中用药物处理,杀灭其中的传染该病的媒介生物(主要是桡足类),药物解毒后再注入养殖池。此外,作为辅助措施,在养殖期中从多方面尽量保证虾池中有一个良好的生态环境。该技术已经过预备研究、实验研究和扩大试验等阶段,均证明效果良好。已扩大试验了近33.33hm^2(其中实际养虾池约17.33hm^2),成功率达96%左右。 相似文献
38.
Jorge Alfaro Karol Ulate Maribelle Vargas 《Aquaculture (Amsterdam, Netherlands)》2007,270(1-4):436-442
Transmission electron microscopy was applied to sperm removed from males and females belonging to Litopenaeus vannamei, L. stylirostris and L. occidentalis. It was discovered that a region named filamentous meshwork (FM), located between the nucleus and the hemispherical cap, develops differently in these three closely related species. In L. vannamei, the FM is synthesized in the male reproductive system, but seems to complete its formation after mating. In L. stylirostris, the FM region was not present in spermatophores collected from males or in sperm from the thelycum. In L. occidentalis, the FM region is fully developed in male sperm. It is suggested that completion of the FM is required for acrosome maturation, and the process continues after mating in some species of Litopenaeus. In vitro induction of the acrosome reaction in sperm from males and females of L. occidentalis demonstrated for the first time that reactivity is significantly superior in sperm cells that have been attached to the open thelycum for some hours, as compared to sperm in males (prior to transfer). This finding suggests that matured sperm cells of L. occidentalis become capacitated to react against egg water after mating. 相似文献
39.
Imorou Toko Emile D. Fiogbe Patrick Kestemont 《Aquaculture (Amsterdam, Netherlands)》2007,262(1):65-72
African catfish (Clarias gariepinus) (initial body weight: 34.8 ± 4.8 g) and vundu catfish (Heterobranchus longifilis) (initial body weight: 39.1 ± 8.2 g) fingerlings were stocked at densities of 4, 6 or 8 fish m− 3 in traditional fish ponds (whedos) constructed in the floodplain of the Oueme River (South Benin, West Africa), for 70 days from March to June 2005. Fish were fed twice a day with 34% crude protein feed formulated with locally available ingredients. The effects of stocking density were evaluated in growth responses, gross production and body composition. Water quality variables were similar (p > 0.05) in all compartments. Temperature and pH were at the optimum level for fish. Dissolved oxygen ranged from 0.9 to 1.2 mg l− 1 during the experiment and secchi disc transparency was low (< 14 cm). In both species, growth responses increased with the increasing density, significantly in African catfish stocked at density of 8 fish m− 3 compared to the other densities (4 and 6 fish m− 3) but not significantly in vundu catfish. Production data ranged from 3.1 ± 0.5 to 22.8 ± 4.5 t ha− 1 year− 1 in African catfish and from 6.1 ± 1.2 to 15.1 ± 3.1 t ha− 1 year− 1 in vundu catfish. Production increased with increasing stocking densities but only significantly (p < 0.05) between the density of 8 fish m− 3 and the other densities. In both species, carcass fat increased with increasing density (p < 0.05) while carcass protein and moisture decreased (p > 0.05). These results are important because they indicate that, as far as growth rate and production are concerned, African catfish is more profitable than vundu catfish for culture at high density in whedo. 相似文献
40.
Stimulating effects of pond water on digestive enzyme activity in the Pacific white shrimp, Litopenaeus vannamei (Boone) 总被引:5,自引:0,他引:5
Crude enzyme extracts were obtained from the digestive glands of Pacific white shrimp, Litopenaeus vannamei (Boone), reared in oligotrophic well water and eutrophic shrimp pond water to compare digestive enzyme activity between the two groups. Specific activities of serine protease, collagenase, amylase, cellulase, lipase and acid phosphatase were significantly higher (P < 0.01) in pond water‐reared shrimp (PW shrimp) than in well water reared‐shrimp (WW shrimp). For most enzymes assayed, specific activity was more than two times higher in PW shrimp, and cellulase activity was over six times higher. In contrast, chitinase activity was significantly higher (P < 0.001) in WW shrimp. Higher specific activity of most digestive enzymes in PW shrimp was probably due to natural productivity in the pond water that served as a source of organic substrates, and this increased activity may contribute to the growth‐enhancing effect of shrimp pond water. 相似文献