全文获取类型
| 收费全文 | 552篇 |
| 免费 | 61篇 |
| 国内免费 | 12篇 |
专业分类
| 林业 | 2篇 |
| 农学 | 3篇 |
| 基础科学 | 5篇 |
| 5篇 | |
| 综合类 | 40篇 |
| 农作物 | 1篇 |
| 水产渔业 | 558篇 |
| 畜牧兽医 | 6篇 |
| 园艺 | 1篇 |
| 植物保护 | 4篇 |
出版年
| 2025年 | 2篇 |
| 2024年 | 11篇 |
| 2023年 | 14篇 |
| 2022年 | 15篇 |
| 2021年 | 12篇 |
| 2020年 | 30篇 |
| 2019年 | 21篇 |
| 2018年 | 26篇 |
| 2017年 | 18篇 |
| 2016年 | 18篇 |
| 2015年 | 20篇 |
| 2014年 | 14篇 |
| 2013年 | 25篇 |
| 2012年 | 19篇 |
| 2011年 | 25篇 |
| 2010年 | 25篇 |
| 2009年 | 25篇 |
| 2008年 | 29篇 |
| 2007年 | 35篇 |
| 2006年 | 30篇 |
| 2005年 | 28篇 |
| 2004年 | 23篇 |
| 2003年 | 12篇 |
| 2002年 | 16篇 |
| 2001年 | 25篇 |
| 2000年 | 16篇 |
| 1999年 | 11篇 |
| 1998年 | 15篇 |
| 1997年 | 10篇 |
| 1996年 | 9篇 |
| 1995年 | 7篇 |
| 1994年 | 8篇 |
| 1993年 | 7篇 |
| 1992年 | 10篇 |
| 1991年 | 1篇 |
| 1990年 | 4篇 |
| 1989年 | 2篇 |
| 1988年 | 1篇 |
| 1987年 | 1篇 |
| 1986年 | 5篇 |
排序方式： 共有625条查询结果，搜索用时 0 毫秒
591.
Abstract Reliability of underwater snorkel counts of adult Atlantic salmon, Salmo salar L., was analysed in the tributaries of the River Teno, close to the spawning period. In small (width 5–20 m) rivers, the replicated total counts of salmon were reasonably precise (CV = 5.4–8.5%), while in the medium-sized river (width 20–40 m) the precision of the counting method was considerably lower (CV = 15.3%). Low precision in a medium sized river was also observed in an experiment using marked live fish where the observation efficiency varied between 36.4% and 70.0%. In a small river, the detection efficiency of artificial fish silhouettes (test salmon) was almost perfect in pools (98%), but decreased in rapids (84%). Separate counts of males, females, grilse and large salmon were usually more variable than total counts, indicating that divers were more capable of locating a fish than properly identifying its sex and sea-age. The behaviour of adult salmon was favourable to conduct snorkel counts, as fish normally stayed still, or after hesitating, moved upstream (>95%of the cases) when encountering a diver. The high observation efficiency (>90%) and precision, favourable behaviour of salmon and congruence between snorkel counts and catch statistics in small rivers suggest that reliable data on Atlantic salmon spawning stock can be collected by snorkeling provided that the environmental conditions are suitable and the divers are experienced. 相似文献
592.
Kristin G. Loughlin Keith D. Clarke Curtis J. Pennell James H. McCarthy Brent Sellars 《Ecology of Freshwater Fish》2017,26(3):347-359
Landlocked Atlantic salmon (ouananiche, Salmo salar) spawning migration timing varies throughout its range and is influenced by a variety of environmental variables. This study examined the spawning migration time of landlocked Atlantic salmon in a small (4 ha) constructed stream linked to a large reservoir (32,600 ha) in Newfoundland, Canada. Salmon use of the stream was passively monitored using Passive Integrated Transponder (PIT) Tags from 2006 to 2012. Of the salmon tagged throughout the reservoir, 48% entered the stream during the spawning season and remained there for 18–36 days from late September to November before they returned to the reservoir. Most fish entered the stream at dusk (32%). The lunar cycle influenced the timing of migration each year. Mean stream discharge (cubic metres per second) influenced migration timing in some years, and water temperature appeared to have minimal impact on migration timing. Twenty per cent of fish migrated to the stream in multiple years and 51% of these individuals appeared to use the stream on a biennial or alternate year cycle. These results demonstrate that small constructed streams can attract salmon from throughout a large reservoir and can provide valuable habitat in areas where spawning habitat is limited. 相似文献
593.
2012—2013年3—9月在郁江金陵江段开展了漂流性鱼卵、仔稚鱼补充群体定点调查监测。结果显示共有鱼卵、仔稚鱼21种(类),隶属4目8科。优势种为䱗 (Hemiculter leucisculus) (22.2%)、鰕虎鱼(Gobiidae)(15.0%)、䱻属(Hemibarbus) (14.4%)、银鮈 (Squalidus argentatus) (7.2%)和银鲴(Xenocypris argentea) (5.5%)。每年流经金陵断面的卵苗总量平均为1.29×108尾,以产黏性卵和沉性卵鱼类仔稚鱼为主,产漂流性卵鱼类仔稚鱼占卵苗总量的22.3%,未采集到四大家鱼鱼卵和仔稚鱼。卵苗发生在5—8月,以6月为盛期,月平均卵苗密度达0.041 4 ind·m–3。鱼卵密度、仔稚鱼总密度与径流量之间具有极显著正相关关系(P<0.01,n=270),径流量与䱗、银鮈、䱻属仔稚鱼密度之间也存在显著正相关关系(P<0.05,n=270)。与历史资料对比,郁江鱼类产卵场功能发生了较大的变化,四大家鱼产卵场基本消失,仅赤眼鳟(Squaliobarbus curriculus)、鲮(Cirrhinus molitorella)、银鮈等小型产漂流卵鱼类还能成功补充,但资源量较小。径流量的年际波动是影响郁江中游早期资源补充的重要因素。 相似文献
594.
中华乌塘鳢人工育苗技术研究 总被引：4，自引：0，他引：4
进行了中华乌塘鳢人工育苗试验，采用背鳍基部肌肉注射，多次注射激素促熟催产，控制水温，不断充气等措施，提前１个多月孵出苗，相对延长了养殖期，提高了经济效益，试验证明：培育亲鱼投喂活沙蚕好，雌雄比１：１，孵化水温２６～２８℃，盐度１６～１７注射ＬＲＨ－Ａ剂量１５０μｇ／尾，可提高催产率，受精率和出苗率。 相似文献
595.
为揭示苏通江段刀鲚早期资源的时空分布情况,本实验于2018—2020年每年5～8月对该江段累计进行84 d的早期资源调查。调查期间共采集到刀鲚受精卵646枚,其中2019年采集到328枚,占总数的50.77%;其中在4月没有采集到刀鲚受精卵,5和6月采集到刀鲚受精卵的平均丰度均显著高于其他采集月份,各年采集到刀鲚受精卵峰值分别出现在5月15日(4.96枚/100 m3),6月16日(26.48枚/100 m3),5月24日(26.11枚/100 m3)。Pearson相关性分析显示,各采样断面空间分布存在显著性差异,平均丰度分布江左岸(1.42枚/100 m3)>江右岸(0.87枚/100 m3)>江心(0.69枚/100 m3);苏通江段下游S1(崇明岛绿华镇水域)和S2(海门市新通海沙水域)、中游S5(南通港闸区水域)和上游S8(如皋长青沙典园水域)采集到刀鲚受精卵的平均丰度和频次均显著高于其他采集断面;环境因子分析显示,刀鲚受精卵丰度与温... 相似文献
596.
Michael R Denson Wallace E Jenkins David L Berlinsky & Theodore I J Smith 《Aquaculture Research》2007,38(9):918-925
Mature black sea bass, Centropristis striata L. (200–800 g), were captured in coastal South Carolina during the spawning season and administered hormones for ovulation induction and strip spawning. During both study years, control groups of females were incorporated into the study design and administered sham injections containing physiological saline solution. In 2004, females received a single intramuscular injection of human chorionic gonadotropin (hCG) (330 IU kg−1) (n=8) or two injections of hCG at 24‐h intervals (n=8). In 2005, females received a single injection of hCG (n=10) or an analogue of luteinizing hormone releasing hormone (LHRHa) (n=10). In 2004, all fish administered a single dose of hCG ovulated at least once. Six fish ovulated on two consecutive days and one fish ovulated on 3 days consecutively. In contrast, six of eight fish receiving two doses of hCG ovulated once, five ovulated on 2 days successively and three fish ovulated 3 days in succession. Of the fish that spawned, no differences were found in any reproductive parameters. In 2005, all fish administered hCG or LHRHa ovulated at least once. Three fish administered hCG ovulated twice, four fish ovulated on three consecutive days and one fish 4 days successively. All fish administered LHRHa spawned at least twice, six fish ovulated thrice and three fish ovulated 4 days, successively. A significant difference in fertility was found between hCG (75.6±11.4%) and LHRHa (55.6±27.4%). The results of this study indicate that both hCG and LHRHa are effective for ovulation induction in prespawning black sea bass. 相似文献
597.
《Journal Of Applied Aquaculture》2013,25(4):59-70
ABSTRACT An attempt has been made for multiple spawning of Asian catfish, Clarias batrachus, by sustained hormone administrations through injection and pellet at three different levels of human chorionic gonado-tropin (HCG): 150, 200, and 250 IU. The size of the eggs and biometry of larvae were significantly higher (P< 0.05) in hormone-treated females compared with untreated groups during first as well as second spawning. The administration of all three levels of sustained hormone was also influenced the rate of fertilization and hatching, which were significantly higher (P< 0.05) compared with control group. The total larvae produced by the fish at 200 and 250 IU HCG treatments during both the spawning operations was significantly higher (P< 0.05) than the other groups irrespective of the ways of administration. It was observed that the forms of sustained hormone had no variability on breeding parameters. But the fish can be bred prior to normal season by the use of sustained hormone and those can be again bred during the latter part of the season to augment the seed production. 相似文献
598.
Yosuke Tanaka Atsushi Tawa Taiki Ishihara Etsuro Sawai Misato Nakae Masachika Masujima Taketoshi Kodama 《Fisheries Oceanography》2020,29(1):46-51
Recently, based on the histological studies it is suggested that Pacific bluefin tuna (PBF) spawns in the Kuroshio–Oyashio transition, off the Pacific coast of northeastern Japan, in addition to the previously identified two spawning areas of the northwestern Pacific around the Nansei Islands and the Sea of Japan. Distributional surveys for PBF larvae have not been conducted in the Kuroshio–Oyashio transition, and thus, we conducted PBF larval surveys at twenty stations in this area in early August 2018 to obtain evidence for the spawning of PBF. Twelve PBF larvae (3.9–7.2 mm in body length) were collected at six stations where sea surface temperature ranged from 27.2 to 28.2°C. Otolith microstructure analysis indicated that age of these larvae ranged from 4 to 11 days after hatching and the larvae hatched in late July. Growth of the collected larvae was comparable to those in the other two spawning grounds. Therefore, PBF spawns, hatches, and at least survives to the postflexion stage, 11 days after hatching in the Kuroshio–Oyashio transition. This fact potentially has a large impact on recruitment processes of PBF if they survive to recruitment in this third spawning ground. 相似文献
599.
A paradigm of fisheries science holds that spawning stock biomass (SSB) is directly proportional to total egg production (TEP) of fish stocks. This “SSB–TEP proportionality” paradigm has been a basic premise underlying the spawner–recruitment models for fisheries management and numerous studies on recruitment mechanisms of fish. Studies on maternal effects on reproductive potential of a stock have progressed during the last few decades, leading to doubt concerning the paradigm. Nonetheless, a direct test of the paradigm at multidecadal scales has been difficult because of data limitations in the stock assessment systems worldwide. Here, we tested the paradigm for marine fish based on a novel combination of two independent 38‐year time series: fishery‐dependent stock assessment data and fishery‐independent egg survey data. Through this approach, we show that the SSB–TEP proportionality is distorted by density dependence in total egg production per spawner individual (TEPPS) or spawner unit weight (TEPPSW) at a multidecadal scale. The TEPPS/TEPPSW exponentially declined with biomass and thus was density‐dependent for Japanese sardine, a small pelagic species exhibiting a high level of population fluctuation, in the western North Pacific. By contrast, the TEPPS/TEPPSW was sardine‐density‐dependent for Japanese anchovy, another small pelagic species exhibiting a moderate level of population fluctuation well‐known for being out of phase with sardine. Our analysis revealed intraspecific (sardine) and interspecific (anchovy) density dependence in TEPPS/TEPPSW, which was previously unaccounted for in spawner–recruitment relationships. Such density‐dependent effects at the time of spawning should be considered in fisheries management and studies on recruitment mechanisms. 相似文献
600.
金乌贼新型产卵附着基的实验研究 总被引：5，自引：2，他引：3
2015年6—7月和2016年6—7月在青岛金沙滩水产有限公司室内产卵池中开展了不同材料、不同颜色、不同水深金乌贼(Sepia esculenta)产卵附着基附卵效果对比实验,以及柽柳附卵器对附卵效果的影响实验。实验用产卵附着基为0.33 m×0.33 m×0.33 m的十字形可折叠钢丝框架,上覆黑白2种聚乙烯网衣材料;每个产卵池中金乌贼亲体数量约35只,雌雄比约为1∶1,胴长(139.2±1.1)mm,体重(435.9±8.5)g。同时选用等比例放大的1.0 m×1.0 m×1.0 m钢筋框架与不同颜色网衣制作的十字形可折叠附着基,于2015年6—7月在青岛斋堂岛附近海域(35?36?6?N,119?54?8?E)和杨家洼湾前附近海域(35?36'6?N,119?50'50?E),以及2016年6—7月在青岛薛家岛近海(35?57?24?N,120?16?22?E)和杨家洼湾前附近海域(35?35?45?N,119?50?38?E)开展了海区附卵验证实验。结果表明:室内同一水体环境中柽柳附卵效果最佳,其次是十字形附着基,海参框附卵效果最差;白色十字形附着基的附卵效果显著优于黑色(P0.05);柽柳附卵器对附卵效果有积极影响,加装柽柳附卵器的十字形附着基附卵效果明显提高;产卵池底层摆放的十字形附着基的附卵效果显著优于表层悬挂的十字形附着基(P0.01)。海区附卵验证结果表明:2015年和2016年海区投放的十字形附着基附卵效果良好,最高附卵率分别为82.14%和56.72%;海区投放的黑色和白色十字形附着基的附卵效果差异不显著(P0.05);海底悬挂的十字形附着基的附卵效果显著优于近底层悬挂的十字形附着基(P0.05)。综合分析认为,在金乌贼产卵繁殖季节,选择其重要产卵场和主要增殖放流海区水深15~20 m的缓流区,底层设置十字形可折叠产卵附着基,可有效进行资源增殖与产卵场修复。 相似文献