全文获取类型
| 收费全文 | 36篇 |
| 免费 | 5篇 |
| 国内免费 | 10篇 |
专业分类
| 地球物理 | 6篇 |
| 地质学 | 12篇 |
| 海洋学 | 28篇 |
| 综合类 | 2篇 |
| 自然地理 | 3篇 |
出版年
| 2022年 | 2篇 |
| 2019年 | 1篇 |
| 2018年 | 1篇 |
| 2016年 | 3篇 |
| 2015年 | 1篇 |
| 2014年 | 1篇 |
| 2013年 | 5篇 |
| 2012年 | 2篇 |
| 2011年 | 2篇 |
| 2010年 | 2篇 |
| 2009年 | 6篇 |
| 2008年 | 3篇 |
| 2007年 | 1篇 |
| 2005年 | 1篇 |
| 2004年 | 2篇 |
| 2003年 | 1篇 |
| 2002年 | 2篇 |
| 2001年 | 2篇 |
| 2000年 | 1篇 |
| 1999年 | 3篇 |
| 1997年 | 4篇 |
| 1994年 | 2篇 |
| 1992年 | 1篇 |
| 1986年 | 1篇 |
| 1984年 | 1篇 |
排序方式： 共有51条查询结果，搜索用时 31 毫秒
11.
12.
13.
David
Scheel
《Marine Ecology》2002,23(3):185-206
Abstract. Habitat characteristics associated with the giant Pacific octopus, Enteroctopus dofleini (Wülker 1910), were studied in Prince William Sound and Port Graham, Alaska, from beach walk, SCUBA and submersible surveys at depths of 0 to 197 m. Octopus counts on beach walk transects were positively correlated with soft substrates (sand, gravel or broken rubble), the presence of boulders, and dense kelp cover immediately offshore of the transect; and negatively correlated with depth on SCUBA transects. No significant habitat correlations were found with counts on submersible transects. On beach walks, octopus counts were reduced on hard substrates to 38 % of the counts on soft substrates. Counts increased five‐fold in the presence of boulders over counts in their absence, and increased fifteen‐fold adjacent to dense (> 75 %) kelp cover over counts adjacent to sparse (< 25 %) kelp cover. On SCUBA transects, the average density at less than 5 m depth was over five times that below 5 m. No trends in octopus size or sex ratio were detected with depth. Den use was inversely correlated with depth although there was no indication that den availability declined with depth. Octopuses were found at densities from 0 to 2.5 per 1000 m2. These densities were only 1 to 50 % of densities of the same species recorded in British Columbia in the late 1970s and early 1980s. Few data are available to test recruitment, mortality, and habitat selection hypotheses that would account for differences between habitats. However, the presence of the highest octopus densities in intertidal and very shallow subtidal areas indicates the likely importance of near‐shore, shallow‐water habitats, and highlights the vulnerability of octopus populations to changes in these habitats. 相似文献
14.
大亚湾核电站邻近埔渔洲红树林区软体动物生态研究 总被引：1，自引：0，他引：1
本文研究了大亚湾埔渔洲红树林区软体动物种类组成,数量分布和群落结构特点,报道软体动物已鉴定有35种,主要由樱蛤科、帘蛤科和汇螺科组成;按种类性质,大多属于广温广盐广布种。平均生物量为51.15g/㎡,平均栖息密度为58个/㎡,群落可划分高、中、低3个分布带,同时简要地分析了生物群落与环境因子的关系。 相似文献
15.
The Condat tufa is a localised deposit, reaching 8.2m in thickness, composed of freshwater carbonates deposited in a complex series of environments which include marsh, spring and stream facies. Five radiocarbon determinations had previously been obtained from different stratigraphic levels within the tufa and had given a consistent series, ranging from 12320 ± 175 BP to 31050 ± 1500BP. Although the youngest two dates, from near the surface of the tufa, had been rejected as being anomalously young, the older dates were regarded as indicating tufa formation during the last cold stage. Biostratigraphic analyses of the molluscan and ostracod faunas, presented here, demonstrate that the tufa formed under fully temperate conditions throughout. The occurrence of certain snails that are either locally extinct (e.g. Belgrandia marginata) or unknown living in western France (e.g. Daudebardia brevipes), together with the geomorphological setting, suggest that the tufa is of interglacial age. New radiocarbon determinations of the Condat tufa all proved to be >33 Ka BP and support this conclusion. 相似文献
16.
A detailed molluscan succession from a 10 m thick deposit of Holocene tufa at St Germain‐le‐Vasson, Normandy, provides the most complete record from northern France and has shed new light on the historical biogeography of several species of land snail. The succession has been reconstructed from four profiles and a chronology provided by accelerator mass spectrometry radiocarbon dating of charcoal, wood and shell. The onset of tufa formation occurred after 9700±90 yr BP and persisted until 4213±77 yr BP. The tufa appears to have accumulated at a remarkably constant rate (14.4–16.5 cm 100 yr?1), except for the upper levels, where the rate increases fourfold. The succession has been divided into six local molluscan zones. An early assemblage consisting of ecologically tolerant species and those indicative of marshy grassland is replaced by a sequence of shade‐demanding taxa, reflecting the encroachment of woodland. Shaded conditions persist until the end of the sequence but the most hygrophilous elements decline after 5422±60 yr BP (zone 5), a change also reflected in the tufa lithology by the development of silty grey horizons. Notable species recovered from the tufa include Acicula fusca, Vertigo substriata, V. alpestris, V. moulinsiana (all rare or unknown living in northern France). Hygromia limbata, a twentieth century introduction to Britain, was previously thought to be a relatively recent arrival in northern France, but its record at St Germain shows that it has been present in Normandy since 6500 yr BP. Azeca goodalli, another shade‐demanding species, appeared at St Germain much later, just after 4420±65 yr BP. Several other species present in the tufa, such as Pomatias elegans, no longer live on the site, adding to the evidence for a distributional decline in Normandy and elsewhere. Perhaps the most noteworthy record is that of Leiostyla anglica, between about 8500 yr BP and 5000 yr BP, because this constitutes its only Holocene occurrence from mainland Europe. Following this discovery it seems likely that further Holocene sites with L. anglica may be found along the western seaboard of Europe connecting populations in Iberia with those of the British Isles. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
17.
This paper proposes and tests a method of producing macrofauna habitat potential maps based on a weights-of-evidence model (a probabilistic approach) for the Hwangdo tidal flat, Korea. Samples of macrobenthos were collected during field work, and we considered five mollusca species for habitat mapping. A weights-of-evidence model was used to calculate the relative weights of 10 control factors that affect the macrobenthos habitat. The control factors were compiled as a spatial database from remotely sensed data combined with GIS analysis. The relative weight of each factor was integrated as a species potential index (SPI), which produced habitat potential maps. The maps were compared with the surveyed habitat locations, revealing a strong correlation between the potential maps and species locations. The combination of a GIS-based weights-of-evidence model and remote sensing techniques is an effective method in determining areas of macrobenthos habitat potential in a tidal flat setting. 相似文献
18.
Identifying outliers and assessing the accuracy of amino acid racemization measurements for geochronology: I. Age calibration curves 总被引：1，自引：1，他引：0
Numerical ages derived from amino acid racemization (AAR) geochronology are typically based on calibration curves that relate the extent of AAR to the age of independently dated specimens. Here, we compare options for developing calibration curves and quantifying age uncertainties using AAR data from 481 late Holocene shells, and AMS 14C analyses of 36 shells of four molluscan taxa (Ethalia, Natica, Tellina, and Turbo) collected from shallow sediment cores from a back-reef lagoon of the central Great Barrier Reef. The four taxa differed substantially in the quality of their geochronogical results. Explicitly including data from specimens alive at the time of collection improves calibration curves, but weighting numerical ages based on their uncertainty has no effect. Calibration curve statistics do not adequately assess calibration uncertainty. The relation between ages inferred from different amino acids is recommended for identifying aberrant specimens and quantifying the uncertainty of inferred ages. For this study, the AAR ages based on two amino acids (aspartic acid and glutamic acid) exceed 200 yr or 20% of their mean inferred age in 15% of the specimens. Once these were removed, the mean age error (1σ) for individual specimens based on two amino acids analyzed in duplicate subsamples ranged from 53 to 142 yr for Tellina and Turbo, respectively, or about a 30% age error for these relatively young shells. This compares favorably with analytical errors estimated at 50 yr or 5%. The presence of notable outliers undetectable using data from single amino acids emphasizes the importance of analyzing multiple amino acids. 相似文献
19.
Mark Harthun 《Limnologica》1999,29(4):449-464
Due to the return of the beaver an increasing number of brooks become restored to a natural condition. It is characterized by an alternation of flowing and standing sectors. In the summer of 1995, different groups of organisms (Odonata, Mollusca, Trichoptera, Ephemeroptera, Diptera) of two brooks in the Spessart mountains (Hesse, Germany) were studied to compare the composition of invertebrates in beaver homeranges and in the non-influenced sectors above. The new living conditions resulted in the disappearance of some species (Drusus anulatus, Trich., Sericostoma personatum, Trich., Radix peregra, Gastr.). Nevertheless the beaver homeranges accommodate a significant higher number of species of dragon flies and damsel flies, molluscs and caddis flies than the brooks above the homeranges. The heterogeneity of natural river systems make a coexistence of running water and silent water organisms possible. The examinations result in a significant higher group dominance of ephemeras (i.p. Cloeon dipterum) in a beaver pond than in lenitic sectors conditioned by the gradient without beaver influence. Here the dominance of chironomids was much higher. High current sectors with their characteristic organisms are also present in the beaver homeranges. The higher number of insects is the basis of nourishment for predatory insects and fishes. The potential effects of beaver ponds on fishes are discussed. 相似文献
20.
Halkieria is an Early Cambrian fossil genus with proposed phylogenetic affinities ranging from stem group lophotrochozoan to stem-group aculiferan. Skeletal similarities are often cited as evidence in support of a mollusk interpretation for Halkieria and related Cambrian fossils. The skeletal microstructures of the polyplacophoran mollusk （chiton） Ischnochiton hakodadensis, which bears perinotum elements resembling sclerites of halkieriids and other coeloscleritophoran small shelly fossils （SSFs）, were studied to evaluate the interpretations. There are both similarities and differences between chiton skeletal structures and halkieriid sclerites： 1） the head valve of L hakodadensis and the dorsal shell of Halkieria evangelista share a similar pattern of fine concentric growth lines, but halkieriid dorsal shells lack other polyplacophoran valve characteristics, including V-shaped indentation, radiate ribs; 2） the arrangement of I. hakodadensis perinotum elements in three zones is somewhat similar to the arrangement pattern of halkieriid sclerites; 3） the inner perinotum scales of L hakodadensis （-200 μm in diameter） have a base and a blade, remarkably similar in morphology to halkieriid palmate sclerites （-400 μm in diameter）. However, I. hakodadensis perinotum scales are nearly solid whereas halkieriid sclerites are hollow. These observations add a microstructural dimension to the skeletal comparison between mollusks and halkeriids, and may prove to be useful in resolving the phylogenetic affinity of Halkieria and the Halwaxiidae. 相似文献