全文获取类型
| 收费全文 | 96篇 |
| 免费 | 11篇 |
| 国内免费 | 25篇 |
专业分类
| 大气科学 | 1篇 |
| 地球物理 | 15篇 |
| 地质学 | 30篇 |
| 海洋学 | 68篇 |
| 天文学 | 3篇 |
| 综合类 | 10篇 |
| 自然地理 | 5篇 |
出版年
| 2022年 | 4篇 |
| 2021年 | 2篇 |
| 2020年 | 3篇 |
| 2019年 | 1篇 |
| 2018年 | 2篇 |
| 2017年 | 4篇 |
| 2016年 | 2篇 |
| 2015年 | 2篇 |
| 2014年 | 6篇 |
| 2013年 | 15篇 |
| 2012年 | 3篇 |
| 2011年 | 6篇 |
| 2010年 | 3篇 |
| 2009年 | 9篇 |
| 2008年 | 5篇 |
| 2007年 | 7篇 |
| 2006年 | 7篇 |
| 2005年 | 7篇 |
| 2004年 | 1篇 |
| 2003年 | 3篇 |
| 2002年 | 2篇 |
| 2001年 | 6篇 |
| 2000年 | 3篇 |
| 1999年 | 5篇 |
| 1998年 | 4篇 |
| 1997年 | 3篇 |
| 1996年 | 6篇 |
| 1995年 | 1篇 |
| 1994年 | 3篇 |
| 1993年 | 1篇 |
| 1992年 | 3篇 |
| 1991年 | 1篇 |
| 1983年 | 1篇 |
| 1981年 | 1篇 |
排序方式： 共有132条查询结果，搜索用时 140 毫秒
91.
Many estuarine and coastal planktonic copepods depend on the hatching of benthic resting eggs for recruitment of nauplii to the water column population. The distribution and abundance of viable resting eggs of Acartia pacifica in the Xiamen Bay were determined by the presence of nauplii in the laboratory. The number of viable eggs varied temporally and spatially. The maximum number (9.2×104m-2) of viable eggs was in summer. In spring the average abundance of viable eggs was 5.6×104 m-2. The abundances of viable eggs in fall and winter were similar, respectively 2.7×104 and 3.3×104 m-2, which were the lowest in the year. The numbers of viable eggs inside the stations of the Xiamen Bay were higher than those outside the stations. The viable eggs were found at all depths (0～10 cm),although not in every station. The maximin number did not necessarily occur in the uppermost centimeter of the sediments but often occurred several centimeters below the water-sediment interface. The accumulation of viable eggs in the seabed of a subtropical bay constitutes a potential source of recruitment of nauplii into the pelagic population. 相似文献
92.
We consider a scenario where the interior spacetime, described by a heat conducting fluid sphere is matched to a Vaidya metric
in higher dimensions. Interestingly we get a class of solutions, where following heat radiation the boundary surface collapses
without the appearance of an event horizon at any stage and this happens with reasonable properties of matter field. The non-occurrence
of a horizon is due to the fact that the rate of mass loss was exactly counterbalanced by the fall of boundary radius. Evidently
this poses a counter example to the so-called cosmic censorship hypothesis. Two explicit examples of this class of solutions
are also given and it is observed that the rate of collapse is delayed with the introduction of extra dimensions. The work
extends to higher dimensions our previous investigation in 4D. 相似文献
93.
94.
Two closely associated egg types occur at the same locality in the Upper Cretaceous (Maastrichtian) St. Mary River Formation in north central Montana. These specimens represent the first fossil eggs described from this formation. At least fifteen small ovoid eggs or egg portions are scattered through a 25 cm interval of rock. Five significantly larger, round eggs overlie these smaller eggs and are in close proximity to one another on a single bedding plane. The best preserved egg of the smaller size measures 36 mm × 62 mm and exhibits the prismatic, two-layered eggshell structure of a theropod egg. The dispersed distribution and inconsistent angles of these small eggs likely resulted from disturbance by subsequent nesting activity and/or possibly nest predation. At least twelve additional small prismatic eggs also occur at this site. We assign the small eggs as a new oogenus and oospecies, Tetonoolithus nelsoni, within the Prismatoolithidae. The large round eggs measure 130 mm in diameter and the eggshell displays substantial diagenetic alteration. These eggs likely belonged to a hadrosaur due to their similarity in egg size, shape, and eggshell thickness to Maiasaura eggs from the stratigraphically lower Two Medicine Formation. Eggs at different stratigraphic levels at this site indicate that conditions favorable to both dinosaur species persisted for an extended period of time. However, determining whether these dinosaurs occupied the nesting site at the same or different years remains beyond the resolution of the rock record. 相似文献
95.
96.
《Limnologica》2020
The fitness of animals inhabiting highly unpredictable intermittent ponds depends on the effectiveness of the production of their resting stages. Daphnia living in such an environment produce sexual eggs as well as the males needed to fertilize them. We hypothesize that the strategy of permanent male presence should coexist with the synchronization of the production of males with that of sexual eggs. To test this hypothesis, we collected plankton samples from a model urban pond, two times a week, throughout the growing season. We analyzed in detail a number of environmental factors and the population dynamics of two Daphnia populations. The percentage of ephippial females and males periodically reached c.a. 50 % of the population. Depending on the moment of the growing season, this proportion was primarily influenced by population crowding, the richness of invertebrate predators in the habitat, extreme high temperatures and the occurrence of the autumnal photoperiod. Our results confirm the hypothesis that Daphnia produce simultaneously long-living males and males synchronized with receptive females. Additionally, we have shown that the number of resting eggs deposited by temporally-isolated populations varied significantly; thus the fitness of a particular genotype depends on the season and on the particular timing of its activation. 相似文献
97.
Daniel Doherty-Weason Fernanda Oyarzun Luciano Vera Miguel Bascur Fabián Guzmán Francisco Silva Ángel Urzúa Antonio Brante 《Marine Ecology》2020,41(1):e12574
The level of parental investment for larval nutrition may determine the life cycle in marine invertebrate species laying egg masses or capsules, where the food available for enclosed individuals would determine time and developmental stage of hatching. Most species show a unique type of larval development. However, few species are poecilogonous and combine more than one development type. Poecilogony, although scarcely studied, allows comparing different patterns of parental reproductive investment, without the phylogenetic effect of the species ancestral modes of development (phylogenetic inertia), to help to understand the factors determining life strategy evolution in marine invertebrates. The poecilogonous polychaete worm Boccardia wellingtonensis encapsulates and incubates its offspring, which then hatches as either planktotrophic larvae or benthic juveniles; while Boccardia chilensis shows a non-poecilogonous reproductive type, producing only planktotrophic larvae. In this work, we estimated the bioenergetic and biochemical composition of brooding and non-brooding females of B. wellingtonensis and B. chilensis to compare the costs of reproduction in these two species. Results showed that glucose, protein, lipid, and energy content were significantly higher in non-brooding than in brooding females of B. wellingtonensis; but also contained significantly more glucose, protein, and lipid than females of B. chilensis (in absolute and relative dry weight values). The poecilogonous species showed higher energy content previous to laying offspring. Our results support the idea that the evolution of a certain reproductive and life history traits in marine invertebrates is related to adaptations in the female's reproductive investment. 相似文献
98.
丹江口水库上游梯级开发后产漂流性卵鱼类早期资源及其演变 总被引：1，自引：1，他引：0
2014年对丹江口水库上游四大家鱼等产漂流性卵鱼类进行早期资源的现状调查,结果表明丹江口水库上游现有产漂流性卵鱼类共14种,以银鮈、蛇鮈、花斑副沙鳅、、蒙古鲌等鱼类为主,四大家鱼卵64粒,仅占卵数的1.02%.与1977年、1993年历史调查的产漂流性卵鱼类早期资源数据相比,产卵场数量减少6处,产卵场的规模和位置发生显著变化.丹江口水库上游产漂流性卵鱼类产卵总量下降明显,从1977年的近1745.86亿粒(尾)下降到2014年的455502.76万粒(尾);其中四大家鱼卵苗径流量下降幅度最为显著,从171.27亿粒(尾)下降到4295.22万粒(尾),四大家鱼卵苗径流量占鱼类卵苗总径流量的比例也从9.81%下降到了0.94%以下. 相似文献
99.
Spawning, phases of embryonic development, intracapsular feeding mechanism and development mode of banded murex Hexaplex trunculus (Linnaeus, 1758) were examined using specimens from the Aegean Sea. In addition, the numbers and characteristics of non‐viable nurse eggs during different phases were examined in relation to the development phases of viable embryos. Females spawned between 59 and 162 egg capsules containing 306.76 ± 50.74 eggs. Trochophore larvae first appeared on the 15th day after spawning. Nurse egg consumption began on the 17th day after spawning when the embryos reached the early veliger stage. In the beginning, veligers consumed the nurse eggs by mechanically disintegrating them with velar cilia movement. From the 18th day after spawning, embryos began to consume whole nurse eggs, although mechanical disintegration continued until hatching. Viable embryos consumed the most developed nurse eggs first. The average number of nurse eggs consumed per embryo was 24.67 by the end of the intracapsular period. The average number of hatchlings was 11.95 ± 3.81 per capsule with 1321.48 ± 133.1 μm shell length. According to our observations H. trunculus shows dispersal polymorphism, with most of the hatchlings completing metamorphosis after a short planktonic non‐feeding period (up to 2 days), while others metamorphose prior to hatching. Planktonic hatchlings had both foot and well developed four‐lobed velum and minimum 1 3/4 whorls. Both hatchling types could be seen in the capsule mass from the same female. 相似文献
100.