全文获取类型
收费全文 | 1338篇 |
免费 | 164篇 |
国内免费 | 30篇 |
出版年
2024年 | 7篇 |
2023年 | 17篇 |
2022年 | 14篇 |
2021年 | 38篇 |
2020年 | 63篇 |
2019年 | 58篇 |
2018年 | 50篇 |
2017年 | 68篇 |
2016年 | 47篇 |
2015年 | 67篇 |
2014年 | 69篇 |
2013年 | 90篇 |
2012年 | 52篇 |
2011年 | 61篇 |
2010年 | 51篇 |
2009年 | 91篇 |
2008年 | 87篇 |
2007年 | 66篇 |
2006年 | 78篇 |
2005年 | 59篇 |
2004年 | 64篇 |
2003年 | 40篇 |
2002年 | 48篇 |
2001年 | 39篇 |
2000年 | 26篇 |
1999年 | 30篇 |
1998年 | 24篇 |
1997年 | 23篇 |
1996年 | 14篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有1532条查询结果,搜索用时 15 毫秒
91.
Many animals respond to predation risk by forming groups. Evolutionary explanations for group formation in previously ungrouped, but loosely associated prey have typically evoked the selfish herd hypothesis. However, despite over 600 studies across a diverse array of taxa, the critical assumptions of this hypothesis have remained collectively untested, owing to several confounding problems in real predator–prey systems. To solve this, we manipulated the domains of danger of Cape fur seal (Arctocephalus pusillus pusillus) decoys to provide evidence that a selfish reduction in a seals'' domain of danger results in a proportional reduction in its predation risk from ambush shark attacks. This behaviour confers a survival advantage to individual seals within a group and explains the evolution of selfish herds in a prey species. These findings empirically elevate Hamilton''s selfish herd hypothesis to more than a ‘theoretical curiosity’. 相似文献
92.
Abstract: Astacidean and thalassinidean macrurans (Glyphea sp., ?Eryma sp. and Protaxius sp.) and a new longodromitid crab, Planoprosopon kashimaensis, are recorded from the Upper Jurassic (upper Kimmeridgian to lower Tithonian) of Fukushima Prefecture, northeast Japan. Material was collected from the Tatenosawa Sandstone Member of the Nakanosawa Formation, Somanakamura Group, from which abundant Tethyan‐type marine invertebrates are known. Planoprosopon kashimaensis sp. nov. closely resembles P. heydeni (von Meyer), a common form in the Upper Jurassic of the Tethyan realm in Europe, and represents the oldest record of a brachyuran from the circum‐Pacific region. Similarities to contemporaneous decapod assemblages in southern Germany indicate that closely comparable, parallel decapod faunas in the Tethyan realm, inclusive of brachyurans, had already been established in the western circum‐Pacific region by the Late Jurassic. 相似文献
93.
94.
Abstract Semiocladius Sublette and Wirth, described from adult midges from south-western Pacific Ocean shores, has the Australian Camptocladius crassipennis Skuse as its type. Immature stages previously known only from Semiocladius kuscheli Sublette and Wirth from sub-Antarctic New Zealand were associated tentatively, by co-occurrence. For the first time, the immature stages for the Australian species are associated definitively by rearing. Larvae rear to a pupa identical to a speculatively associated exuviae of Semiocladius from Lord Howe Island. Adults conform to the described S. crassipennis . Larval Semiocladius are distinctive and previous diagnoses are confirmed. In contrast, the putatively associated pupa of S. kuscheli is indistinguishable from that of the marine intertidal Thalassosmittia Strenke and Remmert, whereas the newly associated S. crassipennis pupa is distinct. The pupa of S. kuscheli may have been misassociated. Semiocladius live in the mesohaline of the salinity gradient of the Clyde River estuary, south-east Australia and the genus appears to be a distinctive western Pacific saline/mesohaline taxon. 相似文献
95.
HEATHER M. WILSON PAUL L. FLINT CHRISTINE L. MORAN ABBY N. POWELL 《The Journal of wildlife management》2007,71(2):403-410
ABSTRACT Populations of Pacific common eiders (Somateria mollissima v-nigrum) breeding in Alaska, USA, have declined markedly over the past 40 years. We studied survival of adult female Pacific common eiders using capture—recapture of nesting hens at 3 sites on the Yukon-Kuskokwim Delta (YKD), Alaska from 1994 to 2004. We used data consisting of 268 recapture events from 361 uniquely marked individuals to investigate temporal, geographic, and environmental variation in adult female survival. Our results suggest apparent annual survival of adult eiders from the YKD was high (0.892, SE = 0.022) and spatially and temporally invariant (σ2 = 0.005), a pattern consistent with other long-lived marine birds. Moreover, our results suggest adult survival may be functionally fixed for Pacific common eiders, and at the present, adult survival may be relatively unresponsive to environmental or management perturbations. Our data did not support hypothesized variation in survival relative to mortality factors such as predation on breeding grounds, physiologic costs of reproduction, and wintering conditions. Although changes in adult survival likely have a large potential effect on prospective population growth, our results suggest viable management actions aimed at increasing survival may be extremely limited. 相似文献
96.
Enrique Arbeláez-Cortes María Fernanda Castillo-Cárdenas Nelson Toro-Perea Heiber Cárdenas-Henao 《Hydrobiologia》2007,583(1):321-330
Rhizophora mangle, one of the five species of the genus Rhizophora, is found widely distributed along the American and West African coasts. This species is one of the principal constituents
of the mangrove ecosystem in Colombia and is also found within the most important economic activities for the communities
that inhabit the littoral. In order to assess the degree of genetic diversity of R. mangle in five populations of the Colombian Pacific, nuclear microsatellite molecular markers were used. In 92 individuals sampled,
it was found that 100% of the loci were polymorphic
, and no private alleles were detected. The population structure of R. mangle in the Colombian Pacific, was highly significant (P < 0.001); however, the greatest differentiation was detected at the within-population level (94.62%). For the populations
of La Plata, Virudó and Charambirá, the tendency toward panmixia could be the cause of the low differentiation among these
three locations. Within populations, the genetic diversity revealed a deviation from Hardy–Weinberg equilibrium with high
significance in Virudó and Tumaco, where it appears the intense anthropogenic activity has exercised strong pressure on the
red mangrove, resulting in the possible fragmentation of the local landscape and therefore an increase in the rate of endogamy
within these populations. Despite this situation, our study―one of the first developed in genetics of the red mangrove in
Colombia―did not show evidence of recent bottleneck effects or deterioration in its genetic composition, which could be exploited
to propose management and restoration programs for the zones where the forests of this species are degraded.
Handling editor: K. Martens 相似文献
97.
A new epigonid fish, Epigonus cavaticus, is described on the basis of eight specimens (59.2–69.5 in standard length: SL) collected from a cave at depth 20 m, southern
fringing reef of Ngemelis Island, Palau. The species differs from other congeners by having minute teeth on both jaws, no
opercular spine, pyloric caeca 7–8, gill rakers 25–27, total pored lateral line scales 48–50, dorsal fin rays VII-I, 10–11
(mode VII-I, 10), pectoral fin rays 16, vertebrae 10 + 15, body depth 21.4–25.0% SL, pectoral fin length 22.7–24.6% SL, eye
diameter 44.4–47.5% head length: HL, upper jaw length 40.2–42.5% HL. Four paratypes (63.7–66.8 mm SL) of the new species are
female with mature gonads, it is the smallest in size at sexual maturity among the congeners. 相似文献
98.
Three exterilium larvae (18.2 mm notochord length to 113.3 mm standard length) of an ophidiid, Lamprogrammus shcherbachevi, from the western North Pacific are described. The specimens had a highly specialized morph with a remarkably elongate trailing
gut and ventral coracoid process, and many elongate anterior dorsal fin rays, as occur in other exterilium larvae, but were
characterized by unique melanophore patterns (a cluster of melanophores on the back of the stalked pectoral fin base, a row
of clusters midlaterally on the trunk and caudal region, and further clusters on the trailing gut). Although the largest specimen
(113.3 mm standard length, much larger than the previously recorded maximum size of exterilium larvae) retained typical features
of the exterilium stage, the ventral coracoid process was significantly reduced in size compared with that of a smaller specimen
(37.8 mm standard length). Comparison of the largest specimen with an adult suggests that the anterior dorsal fin rays would
disappear during the transformation stage. 相似文献
99.
Phylogeographic structure and deep lineage diversification of the red alga Chondrus ocellatus Holmes in the Northwest Pacific
下载免费PDF全文
![点击此处可从《Molecular ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Zi‐Min Hu Jing‐Jing Li Zhong‐Min Sun Jung‐Hyun Oak Jie Zhang Pablo Fresia W. Stewart Grant De‐Lin Duan 《Molecular ecology》2015,24(19):5020-5033
A major goal of phylogeographic analysis using molecular markers is to understand the ecological and historical variables that influence genetic diversity within a species. Here, we used sequences of the mitochondrial Cox1 gene and nuclear internal transcribed spacer to reconstruct its phylogeography and demographic history of the intertidal red seaweed Chondrus ocellatus over most of its geographical range in the Northwest Pacific. We found three deeply separated lineages A, B and C, which diverged from one another in the early Pliocene–late Miocene (c. 4.5–7.7 Ma). The remarkably deep divergences, both within and between lineages, appear to have resulted from ancient isolations, accelerated by random drift and limited genetic exchange between regions. The disjunct distributions of lineages A and C along the coasts of Japan may reflect divergence during isolation in scattered refugia. The distribution of lineage B, from the South China Sea to the Korean Peninsula, appears to reflect postglacial recolonizations of coastal habitats. These three lineages do not coincide with the three documented morphological formae in C. ocellatus, suggesting that additional cryptic species may exist in this taxon. Our study illustrates the interaction of environmental variability and demographic processes in producing lineage diversification in an intertidal seaweed and highlights the importance of phylogeographic approaches for discovering cryptic marine biodiversity. 相似文献
100.
Risks and advantages of using surface laser photogrammetry on free‐ranging marine organisms: a case study on white sharks Carcharodon carcharias
下载免费PDF全文
![点击此处可从《Journal of fish biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
G. Leurs C. P. O'Connell S. Andreotti M. Rutzen H. Vonk Noordegraaf 《Journal of fish biology》2015,86(6):1713-1728
This study employed a non‐lethal measurement tool, which combined an existing photo‐identification technique with a surface, parallel laser photogrammetry technique, to accurately estimate the size of free‐ranging white sharks Carcharodon carcharias. Findings confirmed the hypothesis that surface laser photogrammetry is more accurate than crew‐based estimations that utilized a shark cage of known size as a reference tool. Furthermore, field implementation also revealed that the photographer's angle of reference and the shark's body curvature could greatly influence technique accuracy, exposing two limitations. The findings showed minor inconsistencies with previous studies that examined pre‐caudal to total length ratios of dead specimens. This study suggests that surface laser photogrammetry can successfully increase length estimation accuracy and illustrates the potential utility of this technique for growth and stock assessments on free‐ranging marine organisms, which will lead to an improvement of the adaptive management of the species. 相似文献