全文获取类型
收费全文 | 140篇 |
免费 | 11篇 |
国内免费 | 27篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 10篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 2篇 |
2012年 | 4篇 |
2011年 | 7篇 |
2010年 | 4篇 |
2009年 | 14篇 |
2008年 | 9篇 |
2007年 | 19篇 |
2006年 | 6篇 |
2005年 | 4篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 12篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有178条查询结果,搜索用时 0 毫秒
171.
Lake sturgeon Acipenser fulvescens spawn at the base of Kakabeka Falls, a 39 m waterfall on the Kaministiquia River, a tributary to Lake Superior. Access to this historical spawning site can be restricted or delayed due to hydroelectric flow fluctuations that coincide with the A. fulvescens spawning season. The objectives of this study were to determine (a) the necessary flow conditions that facilitate spawning site access; (b) quantity and duration of flow required for successful spawning and dispersal of larvae; and (c) evaluate recruitment of juvenile A. fulvescens in relation to flow. A. fulvescens spawning migrations were tracked using a stationary telemetry receiver that logged the movements of 166 A. fulvescens fitted with radio-transmitters. Unrestricted access to the spawning site was facilitated when spawning flow was controlled at 23 m3 s−1 in 2004 and 17 m3 s−1 in 2006. Fluctuating (0.5–8.5 m3 s−1) and delayed spawning flows resulted in restricted and delayed access to the spawning site. Flow duration for successful egg incubation, hatch and larval dispersal was determined by sampling larvae using drift nets and quantified using cumulative temperature units (CTU). Over 10 years, 10,083 larvae were captured between 31 May and 20 July with 97% of the drift occurring prior to 30 June. From the date of first spawning to the end of larval dispersal took an average of 38.6 days, and the mean CTU value was 398.6. In general, a minimum flow of approximately 14.5 m3 s−1 from the date of initial spawning to the accumulation of c. 400 CTU ensured successful hatch and larval dispersal. During the timeframe of this study, recruitment was variable. This study described the complex and variable reproductive life history of A. fulvescens and defined spawning flow requirements ecologically, which can be used to develop operational provisions at hydropower facilities to ensure successful reproduction. 相似文献
172.
173.
Comparison of mitochondrial DNA sequences between the European and the Adriatic sturgeon 总被引:2,自引:0,他引:2
Intra- and interspecific diVerences in mitochondrial 12S ribosomal DNA sequences of Acipenser sturio and Acipenser naccarii were investigated. No variable sites were found in the sequences of nine A. sturio or in six A. naccarii . Seven substitutions were detected between A. sturio and A. naccarii . 相似文献
174.
Yoshiharu Honma Tatsuo Ushiki Masaei Takeda Akira Chiba Shunya Oka 《Ichthyological Research》1999,46(2):107-114
Papillomatous growths on the ventral surface of the body and paired fins of the white sturgeon,Acipenser transmontanus Richardson, were described histologically with the aid of light and electron microscopy. Contrary to the usual state of intact
squamous epithelium being equipped with microridges, no such surface structures were apparent in the papillomatous tissue.
The growths appeared to be an aberrant elevations of proliferated dermal tissue, which sustains the hyperplastic Malpighian
layer consisting of the stratum spinosum (prickle cell layer) and sbasale. Many intercellular bridges were found, constructed
from prominent projections, with distinct demosomes and many tonofilaments. The likely causative agent was mechanical irritation
between the small aquarium tank and growing sturgeon, since no viral and/or parasitic inclusion bodies were encountered in
the cells. 相似文献
175.
176.
M. F. Subbotkin T. A. Subbotkina 《Journal of Evolutionary Biochemistry and Physiology》2008,44(4):462-469
Blood proteins of sturgeons of two genera Acipenser and Pseudoscaphirhynchus preserving unidirectional variability in ontogenesis regardless of peculiarities of the fish ecology have heterochronic character. The slowest ontogenetic development lasting for 4–6 years is peculiar to one of antigens of β-globulins. Analysis of the variability of β-globulins in the age range beginning from the 4-month juveniles and including adult spawned individuals indicates different functional significance of their individual components. The βA-globulin absent at early postembryonic stages becomes the second, after albumin, quantitatively predominant antigen in the adult fish blood. The amount of βB-globulin, like antigens of α1and α2-globulins preserving relative ontogenetic stability, can decrease significantly in freshwater sturgeons due to their preparation for spawning. 相似文献
177.
Anatomy and early development of the pectoral girdle,fin, and fin spine of sturgeons (Actinopterygii: Acipenseridae)
下载免费PDF全文
![点击此处可从《Journal of morphology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Acipenseriformes hold an important place in the evolutionary history of bony fishes. Given their phylogenetic position as extant basal Actinopterygii, it is generally held that a thorough understanding of their morphology will greatly contribute to the knowledge of the evolutionary history and the origin of diversity for the major osteichthyan clades. To this end, we examined comparative developmental series from the pectoral girdle in Acipenser fulvescens, A. medirostris, A. transmontanus, and Scaphirhynchus albus to document, describe, and compare ontogenetic and allometric differences in the pectoral girdle. We find, not surprisingly, broad congruence between taxa in the basic pattern of development of the dermal and chondral elements of the pectoral girdle. However, we also find clear differences in the details of structure and development among the species examined in the dermal elements, including the clavicle, cleithrum, supracleithrum, posttemporal, and pectoral‐fin spine. We also find differences in the internal fin elements such as the distal radials as well as in the number of fin rays and their association with the propterygium. Further, there are clear ontogenetic differences during development of the dermal and chondral elements in these species and allometric variation in the pectoral‐fin spine. The characters highlighted provide a suite of elements for further examination in studies of the phylogeny of sturgeons. Determining the distribution of these characters in other sturgeons may aid in further resolution of phylogenetic relationships, and these data highlight the role that ontogenetic and comparative developmental studies provide in systematics. J. Morphol. 276:241–260, 2015. © 2014 Wiley Periodicals, Inc. 相似文献
178.
Lorenzo Zane Tomaso Patarnello Arne Ludwig Francesco Fontana Leonardo Congiu 《Molecular ecology resources》2002,2(4):586-588
We isolated and characterized seven polymorphic microsatellite loci from a partial genomic library of the Adriatic sturgeon (Acipenser naccarii) enriched for GATA repeats. Variability was tested in 20 specimens of this endangered species. Our data support the tetraploid condition for A. naccarii and will be useful for the investigation of the remnant genetic variability of this species as well as for genetic tagging studies. 相似文献