首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   61篇
  免费   6篇
  国内免费   1篇
地球物理   5篇
海洋学   57篇
综合类   4篇
自然地理   2篇
  2023年   1篇
  2021年   2篇
  2020年   1篇
  2019年   1篇
  2018年   1篇
  2016年   2篇
  2015年   1篇
  2014年   4篇
  2013年   11篇
  2010年   2篇
  2009年   7篇
  2008年   1篇
  2007年   4篇
  2006年   5篇
  2005年   2篇
  2004年   2篇
  2003年   1篇
  2002年   2篇
  2000年   1篇
  1999年   2篇
  1998年   1篇
  1995年   2篇
  1994年   2篇
  1993年   5篇
  1992年   2篇
  1990年   1篇
  1989年   1篇
  1984年   1篇
排序方式: 共有68条查询结果,搜索用时 31 毫秒
1.
The pattern of resource allocation into multiple life‐history traits can vary with the environment; for example, high temperatures generally facilitate growth. Changes in investment in growth due to temperature may alter the allocation to other traits that are in trade‐off with that. Here, we investigated the trade‐off between growth and reproduction and whether the proportion of allocation to these varies with increasing seawater temperature in the lancelet Branchiostoma japonicum. We reared the lancelets of early adult stage under three different temperature treatments (control, + 1°C and + 2°C treatments) for 427 days in the laboratory. Although the total body length at initiation did not differ between treatments, the length was influenced by the interaction between elapsed days and temperature treatments, suggesting that growth rate was temperature‐dependent; the lancelets under higher temperature conditions showed a more rapid growth rate than did those under the control conditions. The frequency of individuals with gonads did not differ between treatments throughout their reproductive season. The monthly growth increments were also not significantly affected by the interaction between the presence/absence of gonads and temperature treatments, although the presence of gonads caused the growth increments to decrease. In addition, the effect of temperature treatments was significant. These results suggest that changes in temperature did not alter the pattern of allocation between growth and reproduction that were in a trade‐off, whereas high temperature would solely result in an increase in resource intake, at least in the early adult stage of this species.  相似文献   
2.
The deep‐sea bivalve Acesta oophaga lives attached to the anterior end of the vestimentiferan tubeworm, Lamellibrachia luymesi, at cold methane seeps. The bivalve is found almost exclusively on female tubeworms, where it consumes the lipid‐rich eggs of L. luymesi that are spawned year round (Biological Bulletin, 209, 2005, 87). It is apparent that A. oophaga benefits directly from this close association, but the consequences for the tubeworm host may be more complicated than just a simple predator–prey interaction. Since A. oophaga completely surrounds the tube opening and plume of the worm, it is likely that its presence would limit oxygen uptake by L. luymesi, thereby inhibiting worm growth and reproduction. We hypothesized that occupied tubeworms would compensate for this by growing larger plumes for oxygen uptake. To explore the effects of bivalve presence/absence on female tubeworms, several morphological features, including body size, plume length, tube diameter, and tube segment length, as well as instantaneous fecundity, were compared. Results suggest that the mere presence of A. oophaga has a significant impact on the morphology of its host worm, as all measures of worm size, except for tube segment length, were significantly greater with clams present. Additionally, instantaneous fecundity was 3.5 times higher in occupied worms, implying that tubeworms are not oxygen‐deprived or energy limited as a result of bivalve presence. Our findings suggest that the association between these two deep‐sea organisms may be a more complex form of symbiosis than the simple predator–prey relationship, as previously thought.  相似文献   
3.
Harvest control measures for Namibia and Angola are defined using reference points for spawning biomass, which requires knowledge of spawning potential and dynamics of fishery stocks. The reproductive biology of two species of horse mackerel, Trachurus capensis and Trachurus trecae, in these waters was investigated for spawning distribution in time and space. Samples were collected during two scientific cruises conducted in February and July/August 2007 off the coast of Namibia and Angola. A total of 396 fish ovaries was examined to determine the spawning dynamics of the two species. The ovaries were histologically analysed and their oocyte distributions mapped. The length (TL)–weight relationships of the two species differed significantly. The observed development of oocyte recruitment and absence of a hiatus in the oocyte distribution indicated that these species are indeterminate spawners. Analyses of the data from the NatMIRC database (2001–2004) indicated annual changes in gonadosomatic index (GSI) for T. capensis at different latitudes, but these changes were small. GSI also fluctuated between years and areas, but there were no clear spatial or temporal trends, with averages ≤4.0% at all stations. The GSI of both species was not indicative of the histologically determined development of gonad maturity. Oocyte maturation for T. capensis indicated that smaller and younger fish spawn first. Batch fecundity (F) for T. trecae was best described by F = 4 986 TL (cm) – 99 645 (r 2 = 0.83). This study provided the first analyses of oocyte development in time and space for the two species in the region.  相似文献   
4.
The reproductive cycle of the abundant intertidal limpet Cellana ornata (Dillwyn 1817) was examined over 19 months, covering two breeding periods, on a rocky intertidal platform in southern New Zealand. A gonad index was calculated, and histological sections were used to count the numbers of mature and immature eggs present. Fecundity was estimated using counts of eggs before and after spawning. To determine any variation between sites, the gonad index of limpets at a second site dominated by boulders was examined over 6 months during the second breeding period. C. ornata had a single spawning period annually during summer, with greatest gonad sizes in January‐February. There were significant differences in peak gonad indices between two breeding seasons on the platform. Within the second breeding period, both the timing and magnitude of peak gonad development differed between sites, with lower reproductive output at the boulder site. Fecundity increased with increasing size, but individuals are probably capable of reproducing after their first year on the shore. The life history of this species is discussed in comparison to other limpets in New Zealand.  相似文献   
5.
The sea cucumber Holothuria scabra is a widely distributed and economically important species that has been harvested in Kenya for decades. No previous studies have been carried out on the reproduction of this species in Kenya. Standard gonad index methods were used to analyze reproductive patterns of individuals collected monthly in 1998–1999, 2000–2001 and 2006–2007. Morphological characteristics, gonad tubule lengths and fecundity were also measured. Mean monthly gonad indices were significantly correlated between males and females indicating synchronous gonad development between the sexes. Gonad indices showed a biannual pattern that was consistent in all three years with a minor spawning event occurring between August and September and a major spawning event between November and December. The pattern of gonad growth showed significant variability between years and between months. Temporal changes in gonad growth correlated significantly with gonad tubule length and absolute fecundity. Monthly gonad indices also correlated significantly with monthly measurements of air temperature and light suggesting a possible role for both factors in timing gametogenesis and spawning. There was a shift in sex ratio from unity in the 1998–1999 and 2000–2001 samples to significantly more males in the 2006–2007 samples, as well as a significant reduction in mean sizes (body wall weight) and reproductive output (gonad index) which suggests that the reproductive success of this species is potentially negatively affected by fishing.  相似文献   
6.
The sea pen Funiculina quadrangularis (Pallas, 1766) is a species of conservation concern in Scottish coastal waters, due to its restricted geographical distribution and high sensitivity to demersal fishing activities. Reproduction in F. quadrangularis was investigated in a population located in southern Loch Linnhe, west Scotland. This was accomplished through the analysis of trends in oocyte size-frequency distribution and relative fecundity over a 12-month period. Funiculina quadrangularis is dioecious and the study population exhibited a sex ratio of 1:1. Oogenesis in female F. quadrangularis is characterised by the maintenance of a large pool of asynchronously developing oocytes throughout the year, of which a small proportion (<10%) mature with increasing sychronicity and are spawned in midwinter. The reasons for this distinct pattern of oogenesis and winter spawning remain unclear, although the potential influence of environmental cues and the role of endogenous factors in relation to this sea pen's deep-sea habit are discussed. Whilst the duration of oogenesis is prolonged (>12 months), it is proposed that spawning is a brief and synchronous annual event. Relative fecundity is high and is independent of colony size, varying between approximately 500–2000 oocytes per 1 cm rachial midsection. This measure of fecundity exhibited pronounced seasonality and was significantly lower during the post-spawning winter months. Total fecundity in F. quadrangularis is considered to be high; although a small proportion of the total number of oocytes is spawned annually, this is compensated for by large colony size. Funiculina quadrangularis produces large oocytes (>800 μm), indicative of the production of lecithotrophic larvae.  相似文献   
7.
8.
9.
10.
研究了湛江沿海中华乌塘鳢个体生殖力及其与生物学指标的关系。结果表明 :个体绝对生殖力为 840 0~ 3 3 2 70粒 ,个体相对生殖力FL 为 5 67 6~ 1 83 3 2粒 /cm ,Fw为 1 5 5 6~ 482 7粒 /g ;个体绝对生殖力与体长、体重、空壳重、卵巢重呈直线相关 ,与年龄呈二次函数相关 ,与成熟系数和肥满度相关关系不显著 ;个体相对生殖力FL 与各生物学指标正相关 ,Fw除了与卵巢重、肥满度和年龄相关关系不显著外 ,其余均显著相关  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号