全文获取类型
收费全文 | 265篇 |
免费 | 26篇 |
国内免费 | 23篇 |
专业分类
林业 | 13篇 |
农学 | 1篇 |
基础科学 | 5篇 |
10篇 | |
综合类 | 46篇 |
农作物 | 1篇 |
水产渔业 | 212篇 |
畜牧兽医 | 18篇 |
园艺 | 2篇 |
植物保护 | 6篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 16篇 |
2018年 | 12篇 |
2017年 | 20篇 |
2016年 | 13篇 |
2015年 | 15篇 |
2014年 | 5篇 |
2013年 | 12篇 |
2012年 | 15篇 |
2011年 | 20篇 |
2010年 | 16篇 |
2009年 | 13篇 |
2008年 | 18篇 |
2007年 | 16篇 |
2006年 | 13篇 |
2005年 | 5篇 |
2004年 | 10篇 |
2003年 | 18篇 |
2002年 | 9篇 |
2001年 | 12篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1988年 | 1篇 |
排序方式: 共有314条查询结果,搜索用时 15 毫秒
41.
Otolith chemistry indicates walleye movement and entrainment in a large serial reservoir system 下载免费PDF全文
Understanding fish movement in impounded river systems is important for fisheries management. Otolith chemistry was used to examine walleye Sander vitreus (Mitchill) intra‐ and inter‐reservoir movement in four Missouri River impoundments. Age‐0 individuals were reclassified with 75%–93% accuracy to known natal sites, allowing for reliable evaluation of movement patterns of age‐1 and older fish. Nearly half of walleye occupied the same location annually (i.e. site residency) between 2009 and 2010. In 2011, during the largest flood on record since 1898, downstream movement (49% of age‐1 and older fish) exceeded upstream movement (7%) and site residency (33%) across the study area. After the flood, most walleye moved downstream within reservoirs (45%) or were site residents (37%). Entrainment occurred most frequently during the flood year and was proportionally greatest in downstream reservoirs. Otolith chemistry is useful for understanding walleye movement and entrainment and is a tool for fisheries management with applications such as informing reservoir water releases, harvest regulations and habitat protection and rehabilitation within and outside the Missouri River reservoir system. 相似文献
42.
Alternative life-history tactics of masu salmon Oncorhynchus masou are well documented. Subsequent to the freshwater parr stage (age ≥ 1 + years), an anadromous form migrates to the sea after smolting, while a resident form matures without seaward migration. In addition to this typical migratory dimorphism, anecdotal reports based on field observations have indicated that some underyearling masu salmon use estuarine waters. However, no empirical evidence indicates saltwater utilisation and subsequent survival in the early parr stage. Here, we used otolith microchemistry to examine whether a portion of masu salmon parr in northern Japan enters coastal habitats. The otolith Sr:Ca ratios of most juveniles collected from six rivers had consistently low values, indicating that masu salmon parr inhabiting these rivers stay only in freshwater. In contrast, in individuals from a steep-gradient river the Sr:Ca ratios increased at about a 200-µm distance from the otolith core. These results suggest that some masu salmon parr might use brackish water or sea water temporarily. In addition, three masu salmon parr were found in another steep river where a culvert located only ten metres from the river mouth completely blocked upstream migration for spawning. The Sr:Ca ratios in these fish increased at about >200 µm from the otolith core, indicating the parr had immigrated to the non-natal river from the sea. Such flexible behaviour at an early life stage may contribute to the spatial expansion of masu salmon, and the movement could moreover help to stabilise its population dynamics. 相似文献
43.
44.
An intensive sampling program for yolk-sac herring larvae and microzooplankton was carried out in the main spawning area of Norwegian spring-spawning herring during March to April 1990 (between 62o and 63o30'N) to estimate their hatching period and the abundance of copepod eggs and nauplii. Additional investigations were carried out in the Skagerrak area during January-March and on the Norwegian Shelf in May to study the otolith microstructure of the herring larvae. In May both autumn- and spring-spawned herring larvae were found in the samples from the Norwegian Shelf. They were easily distinguished by differences in otolith microstructure. The pattern in increment widths in the otoliths of the autumn-spawned larvae indicated that these larvae had not been transported through the Skagerrak area, but more likely were carried directly from the northern North Sea across the Norwegian Trench and into the Norwegian Coastal Current system. The calculated hatching of the spring-spawned larvae sampled in May occurred significantly later than the observed hatching over the spawning grounds. The results suggest a mismatch between the abundance of first-feeding herring larvae and their prey organisms, resulting in a higher survival of those herring larvae hatching during the latest part of the spawning period. This coincides with a general increase towards the middle of April in the abundance of prey organisms, from 1 to 4 1_1. There were no differences in otolith microstructure among spring-spawned herring larvae sampled on the shelf in May, indicating that these larvae originated from the same cohort and were well mixed throughout the whole shelf area. 相似文献
45.
46.
A. Sánchez-Lamadrid 《Fisheries Management and Ecology》2001,8(3):271-278
This study tested different tags for each size of farm-reared gilthead sea bream, Sparus aurata L. juveniles, used in enhancement programmes. The following tags were tested: dye mark, fingerling tag, opercular tag, anchor tag A (filament diameter of 1.20 mm) and anchor tag B (0.85 mm). Tag/mark retention, wounds produced by the tag, ease of application, ease of detection and cost were examined. Epidermal dye marks had poor retention and detection rates. Of the tags tested, retention was greater for the anchor tag A (80–100%) after 7 months; anchor tag B showed a retention rate of only 20% after 3 months. The fingerling tag had a retention rate of 27.5% after 12 months. The opercular tag had a retention rate of 44% after 20 days but fractured the opercular bone in many cases. Tag incisions and wounds persisted in some fish for the duration of the experiment. 相似文献
47.
The ability to discriminate local stocks of Japanese anchovy Engraulis japonicus was assessed based on data from four elements (K, Na, P, and Sr) using an electron probe micro analyzer (EPMA) and data from
three elements (Ba, Mn, and Sr) using inductively coupled plasma mass spectrometry (ICP-MS) from the otoliths of 40 anchovy
(23.6–47.0 mm body length). Anchovy were caught at three sites (Aki-nada, Hiuchi-nada, and Osaka Bay) in the Seto Inland Sea,
and one site (Kuroshio extension) in the Pacific Ocean in 2002. In order to discriminate different spawning grounds, EPMA
data from the core portion (from core to 30 μm in the core-posterior axis) were used. Results showed that it was difficult
to discriminate between the Seto Inland Sea and the Pacific anchovy by EPMA data. Conversely, it was possible to discriminate
between the Seto Inland Sea and the Pacific anchovy by ICP-MS data from bulk otoliths. Our results showed that Mn contents
of otoliths using ICP-MS discriminate between spawning grounds most, and Ba and Sr discriminate less. The difference in elemental
compositions in anchovy otoliths between the Seto Inland Sea and the Pacific Ocean might be reflected by cumulative experienced
elemental composition of ambient sea water during life history between the Seto Inland Sea and the Pacific anchovy. 相似文献
48.
鱼类耳石研究和应用进展 总被引:6,自引:0,他引:6
鱼类耳石研究是鱼类生长和早期生活史研究的基础。文章阐述了鱼类耳石形态的研究方法及其在鱼类种类识别中的应用、耳石微结构在鱼类年龄鉴定、早期生长研究、产卵期、孵化期和产卵场的推算以及早期生活史中特殊事件的研究等方面的进展,探讨了耳石研究的存在问题并提出了进一步研究的建议。 相似文献
49.
Paul Chittaro Jens Hegg Abby Fuhrman Devin Robichaux Rothboury Doung Brian Beckman Chris Fisher Jeff Vervoort Brian Kennedy 《Ecology of Freshwater Fish》2023,32(1):107-119
Effective species management often requires understanding patterns of movement and habitat use. A common approach in identifying where individuals reside relies upon chemical tracers from the environment that are incorporated into an individual's tissues. For fish, isotopes in their otoliths, specifically the portion of their otolith formed during their larval stage, have been used to identify the natal origin. Complicating this work, however, is the fact that during this life stage, there is a shift in the source of isotopes deposited onto the growing otolith from maternally to environmentally derived. The objective of this study was to identify the portion of the otolith representing this transition to environmentally derived isotopes so as to accurately investigate questions of natal origin for a threatened population of fall Chinook salmon (Oncorhynchus tshawytscha). We exposed developing larvae to four treatments that differed in terms of their water strontium isotope ratio (87Sr/86Sr) and used change-point analysis of otolith 87Sr/86Sr and strontium to calcium ratio (Sr/Ca) to identify the otolith radius corresponding to the transition to environmentally derived isotopes. Our results indicated this transition occurred, on average, at 132 μm (87Sr/86Sr; ±50 μm standard deviation) and 127 μm (Sr/Ca; ±29 μm) from the otolith core, which corresponded to the developmental time between hatching and exogenous feeding. A substantial proportion of our otoliths (i.e., 61%) did not show convergence between otolith and water 87Sr/86Sr by the end of the 113-day experiment, which was likely due to the dietary contribution of marine-based feed. Therefore, we were unable to recommend an otolith radius to target for the purposes of reconstructing natal origin apart from being beyond approximately 130 μm. 相似文献
50.
We applied dendrochronology (tree‐ring) methods to develop multidecadal growth chronologies from the increment widths of yelloweye rockfish (Sebastes ruberrimus) otoliths. Chronologies were developed for the central California coast, a site just north of Vancouver Island, British Columbia, and at Bowie Seamount west of the Queen Charlotte Islands, British Columbia. At each site, synchronous growth patterns were matched among otoliths via the process of cross‐dating, ensuring that the correct calendar year was assigned to all increments. Each time series of growth‐increment measurements was divided by the values predicted by a best‐fit negative exponential function, thereby removing age‐related trends. These detrended time series were averaged into a master chronology for each site, and chronologies were correlated with monthly averages of sea surface temperatures, upwelling, the Northern Oscillation Index, and the Pacific Decadal Oscillation. The two northern growth chronologies positively correlated with indices of warm ocean conditions, especially from the prior summer through the spring of the current year. During the same period, the California chronology positively correlated with indices of cool ocean conditions, indicating an opposing productivity regime for yelloweye rockfish between the California Current and the Gulf of Alaska. Overall, this study demonstrates how tree‐ring techniques can be applied to quickly develop annually resolved chronologies and establish climate–growth relationships across various temporal and spatial scales. 相似文献