全文获取类型
收费全文 | 700篇 |
免费 | 111篇 |
国内免费 | 33篇 |
专业分类
林业 | 36篇 |
农学 | 51篇 |
基础科学 | 4篇 |
30篇 | |
综合类 | 145篇 |
农作物 | 7篇 |
水产渔业 | 546篇 |
畜牧兽医 | 12篇 |
园艺 | 2篇 |
植物保护 | 11篇 |
出版年
2024年 | 14篇 |
2023年 | 20篇 |
2022年 | 22篇 |
2021年 | 27篇 |
2020年 | 50篇 |
2019年 | 41篇 |
2018年 | 37篇 |
2017年 | 32篇 |
2016年 | 41篇 |
2015年 | 29篇 |
2014年 | 31篇 |
2013年 | 36篇 |
2012年 | 22篇 |
2011年 | 48篇 |
2010年 | 43篇 |
2009年 | 24篇 |
2008年 | 44篇 |
2007年 | 36篇 |
2006年 | 38篇 |
2005年 | 32篇 |
2004年 | 32篇 |
2003年 | 25篇 |
2002年 | 15篇 |
2001年 | 18篇 |
2000年 | 18篇 |
1999年 | 14篇 |
1998年 | 8篇 |
1997年 | 17篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有844条查询结果,搜索用时 343 毫秒
811.
Tae-gi?Oh Kazumi?SakuramotoEmail author Seizo?Hasegawa Naoki?Suzuki 《Fisheries Science》2005,71(4):855-861
ABSTRACT: This paper investigates the relationship between sea-surface temperature (SST) and catch fluctuations in the Pacific stock of walleye pollock Theragra chalcogramma in Japan. Incorporating time lags between years of birth and harvest, the correlation coefficients between the catch and SST in two regions off the east coast of Hokkaido were calculated. The catch in year t had a high negative correlation with the SST during January–April and November–December of the years t- 2 and t- 3 in the spawning area. These results coincided well with the correlation observed in the northern 'Sea of Japan' stock. Both analyses suggested that the long-term catch fluctuations of the two stocks could be explained by the same mechanism, that is, the fluctuations would be explained by the SST in their spawning area during the spawning season using 2–3 or 3–5 years time lags, which corresponded to the dominant age of the catch within these two stocks. 相似文献
812.
813.
Migration of albacore, Thunnus alalunga, in the North Pacific Ocean in relation to large oceanic phenomena 总被引:1,自引:0,他引:1
On the basis of Japanese long-line fishery data during 1970–1988, anticlockwise migration routes of albacore in the North Pacific are newly proposed. The annual migration route for mature albacore is described as a closed ellipse with a centre at 20°N and 170°E, and is wider in El Niño years than non-El Niño years associated with an appearance of a cold-water region in the central and south-western North Pacific. Immature albacore also have an anticlockwise migration route in winter which extends from 25°N to 35°N and from 130°E to 180°E, when the Kuroshio has a relatively straight path. However, the migration does not persist when the Kuroshio takes a large meander path. 相似文献
814.
为解决我国大型加工拖网远洋船队集中北太平洋生产,造成经济效益滑坡的现象,经过连续三年的探捕活动,我国于2003年开始正式在东南太平洋公海捕捞生产智利竹笑鱼,而此区域处于南太平洋常设委员会(CPPS)的管辖范畴。为此简要介绍了智利竹笑鱼渔业状况、CPPS渔业管理趋势。分析了这些趋势对我国发展智利竹笑鱼渔业产生的影响,并提出了一些相应的对策与建议:(1)确保渔船遵守《执行协定》和《框架协议》的规定;(2)加强与智利方面的沟通;(3)健全情报体系,加强船员培训。 相似文献
815.
1994年7月,进行了太平洋牡蛎常温育苗,8月18日将1亿粒蛎苗转入虾池保苗。越冬后,出售3cm左右的商品苗6850万粒,保苗率68.5%,每亩纯益2.2万元,投入产出比1:15.2。 相似文献
816.
利用1958-2010年逐年的12月和1月的NCEP/NCAR格点资料,分别对北半球太平洋和大西洋、欧亚大陆和北美大陆这2组区域的500 hPa高度场进行了奇异值(SVD)分解。结果表明院所选的2组区域太平洋和大西洋、欧亚大陆和北美大陆500 hPa的位势高度场存在协同变化的关系。当太平洋地区位势高度场偏高时,大西洋地区的位势高度场偏低,反之亦然。冬季的1月上述现象最为明显。上述现象在陆地上比海洋上明显,大洋上高纬度比低纬度明显。 相似文献
817.
中西太平洋黄鳍金枪鱼随附鱼群区域温度垂直结构的构建与初步分析 总被引:1,自引:0,他引:1
利用梯度依赖相关尺度方法,基于Argo实时观测剖面,以点对点的形式进行中西太平洋黄鳍金枪鱼随附鱼群区域温度垂直结构的构建实验,并在验证该方法有效性的基础上初步分析了捕捞点的温度垂直结构特征。结果表明,与传统方法相比,构建的温度垂直剖面的均方根误差明显减小,在跃层深度处两者相差最大达0.45℃,且构建的温度剖面与实际观测值的温度偏差除跃层处较大(约为±0.5℃)外,其余水层基本接近为零。2017年8月的统计分析结果表明,中西太平洋黄鳍金枪鱼在近表层(5 m)的适宜温度范围为28.5~29.5℃,且随着深度的增加,温度逐渐降低,至300 m处,适宜温度范围约为11.0~12.0℃。各个捕捞点均存在明显的温跃层,对应的平均温跃层上、下界深度和跃层强度分别约为80 m、270 m、0.08℃/m,跃层强度与渔获量近似呈正比关系。这些结论进一步验证了该方法的可靠性,同时表明本文方法可以为构建渔业捕捞点上的次表层信息提供技术支持。 相似文献
818.
The introduction of an alien top predator, the brown treesnake (Boiga irregularis), has resulted in severe losses of native vertebrate populations in Guam. Among these are important pollinators and seed dispersers. This study is a first attempt to document cascading effects on vertebrate-pollinated native plant species in Guam. We investigated flower visitation, seed set and germination in two native plants, the mangrove tree Bruguiera gymnorrhiza and the forest tree Erythrina variegata var. orientalis. Both species are bird-pollinated. Studies were conducted on two Mariana islands, Guam (with high density of snakes) and Saipan (with nearly no snakes). Visitation rates by birds were high on Saipan, but zero on Guam. Insects and lizards visited flowers to a low extent on both islands. Only lizards were potential effective pollinators. Seed set of both species were significantly higher on Saipan compared to Guam, and for B. gymnorrhiza, seedling recruitment was significantly higher on Saipan. Hence, these bird-pollinated species appear highly dependent on bird visitors for reproduction. The eradication of flower-visiting birds by the invasive treesnake thus secondarily results in broken mutualistic interactions, which may, in turn, result in a lower recruitment of native plants. Thus, the treesnake affects not only potential prey species, but its effects cascade through the entire ecosystem on Guam. Conservation actions should be directed towards an improved recruitment (artificial pollination, planting) of the affected plant species. 相似文献
819.
820.
Effects of different feed management treatments on water quality for Pacific white shrimp Litopenaeus vannamei 下载免费PDF全文
Lauren N Jescovitch Carter Ullman Melanie Rhodes Donald Allen Davis 《Aquaculture Research》2018,49(1):526-531
Increasing feeding rates may provide an increase in production, thus nutrients such as nitrogen, phosphorus and organic matter will also increase. These nutrients promote a greater oxygen demand and concentrations of toxic metabolites which can lead to frequent problems with low dissolved oxygen and an abundance of blue‐green algae. Four feed management practices were evaluated among sixteen 0.1 ha ponds culturing Pacific white shrimp (Litopenaeus vannamei). Feeding treatments included hand feeding using the Standard Feeding Protocol (SFP), SFP plus 15% from 8 to 16 weeks, an automatic‐solar timer which fed SFP+15%, and an AQ1 acoustic demand feeder allowing up to 12 kg/day·pond based on shrimps feeding response. Samples were analysed at weeks 0, 4 and 8–16 for the following parameters: chlorophyll a, total ammonia nitrogen, nitrite–nitrogen, nitrate–nitrogen, total nitrogen, total phosphorus, soluble reactive phosphorus, total suspended solids, total suspended volatile solids, turbidity, conductivity, salinity and biological oxygen demand. Samples were collected and shipped overnight to Auburn, Alabama for off‐site analysis. On‐site water quality was also obtained at the farm. The AQ1 acoustic demand feeder produced the most shrimp with a yield of 4,568 kg/ha; however, the AQ1 also had the highest total ammonia nitrogen and nitrite–nitrogen levels late in the growing season. The AQ1 feeder may be a viable, reduced labour and cost alternative for the shrimp commercial industry; however, such technologies must also be matched to the ability of the production system to process nutrients. 相似文献