全文获取类型
收费全文 | 180篇 |
免费 | 7篇 |
出版年
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 2篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 8篇 |
2014年 | 10篇 |
2013年 | 13篇 |
2012年 | 7篇 |
2011年 | 4篇 |
2010年 | 9篇 |
2009年 | 4篇 |
2008年 | 7篇 |
2007年 | 7篇 |
2006年 | 3篇 |
2005年 | 6篇 |
2004年 | 10篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1991年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1968年 | 2篇 |
1943年 | 1篇 |
1942年 | 1篇 |
1930年 | 2篇 |
1929年 | 2篇 |
1928年 | 1篇 |
1927年 | 2篇 |
1925年 | 1篇 |
1924年 | 1篇 |
1922年 | 1篇 |
1921年 | 1篇 |
1920年 | 1篇 |
排序方式: 共有187条查询结果,搜索用时 15 毫秒
121.
K. E. Clinton K. L. Mathers D. Constable C. Gerrard P. J. Wood 《Biological invasions》2018,20(8):2187-2196
Two Ponto-Caspian amphipods, Dikerogammarus villosus and Dikerogammarus haemobaphes, have expanded their geographical ranges from eastern Europe into Great Britain in recent years. This study represents one of the first examining the distribution and habitat preferences of coexisting populations of D. haemobaphes and D. villosus via field and laboratory experiments in the UK. Field surveys of a recently invaded lowland reservoir in the UK are complimented with ex situ laboratory mesocosm experiments examining the substrate preferences of coexisting populations of D. villosus and D. haemobaphes. Results from the field study indicated that D. haemobaphes dominated the macroinvertebrate community within the reservoir and demonstrated a strong affinity for large cobble and artificial substrates. D. villosus occurred at lower abundances but displayed a strong preference for coarse cobble substrates. A third invasive amphipod, Crangonyx pseudogracilis, was largely confined to sand/silt habitats. Laboratory mesocosm experiments clearly supported the field observations of D. villosus and D. haemobaphes with both species demonstrating a preference for cobble substrates. Results from the study highlight the importance of characterising physical habitat when investigating biological invasions and suggest that habitat availability may influence the extent and speed at which range expansion of new amphipod invaders occurs. 相似文献
122.
Alexandra C. Aines John K. Carlson Andre Boustany Alyssa Mathers Nancy E. Kohler 《Environmental Biology of Fishes》2018,101(3):403-415
Tiger sharks, Galeocerdo cuvier, are apex predators that may structure marine communities through predation. Despite a large number of studies in other areas such as the Pacific Ocean, there are no quantitative data on the diet of tiger sharks in the northwest Atlantic Ocean and Gulf of Mexico. Diet was assessed from 169 tiger sharks by life stage, area, and environmental factors. Fifteen prey groups were identified, with teleosts, molluscs, birds, cephalopods, and reptiles being the predominant prey categories. There was an ontogenetic shift in diet, prey size and diversity. Molluscs were the most common prey in smaller sharks, while teleosts and reptiles became more important in the diet of larger sharks. Dietary overlap was significant by area (Gulf of Mexico vs Atlantic Ocean) and among all life stages except for young-of-the-year and adult tiger sharks. Juvenile tiger sharks also demonstrated selective feeding by targeting gastropod feet over ingesting the entire animal. While results were similar to feeding studies conducted on tiger sharks in other ocean basins, an understanding of area-specific trophic interactions is necessary to inform decision support tools for ecosystem-based approaches to management. 相似文献
123.
124.
Sessile invertebrate coelobite communities attached to the walls and roof of cavities in coralgal reefs on the annular rim of the Bermuda platform near North Rock (4 sites) and in the algal cup reef tract on the south shore (3 sites) have been studied by belt photo-transects and direct sampling. Irradiance measurements reveal a light gradient which appears to exert a strong influence on the composition, relative coverage and zonation of the attached biotic communities. Two main communities are recognised from cluster analysis and relative areal coverage data. Near the cavity entrances is a community dominated by crustose coralline algae, with subsidiary ascidians, demosponges, bryozoans and Foraminifera. Species richness is high and there is total biotic coverage of walls and roof. This community grades laterally into an exclusively animal community characterised by encrusting sponges and Foraminifera, with subsidiary bryozoans and unidentified branching organisms. Coverage varies from 100% to 30%, the substrate often exhibiting high micro-relief from the branching growth forms of the Foraminifera. Species richness is high at North Rock sites, less so on the south shore. The distribution of coelobite species is compared with that described from previous studies in Bermuda, Grand Cayman and Madagascar. 相似文献
125.
A 522-base-long Y-chromosomal sequence was isolated from a BALB/c genomic
library and was designated "BF046." It is repeated about 200 times in the
male genome, and a difference was detected between the Mus musculus
musculus and the M. m. domesticus type Y chromosomes. BF046- related
sequences were present over the entire length of the Y chromosome as
visualized by in situ hybridization. Southern blot analysis against DNAs
isolated from eight species in the genus Mus showed that BF046-related
sequences were amplified in the Y chromosomes of three closely related
species: M. musculus, M. spicilegus, and M. spretus. To gain insight into
the stability of the BF046 sequence family, we isolated 18 additional
clones from these three mouse species and compared their sequences. The M.
musculus sequences differed from the M. spicilegus and M. spretus sequences
by two indels. The remaining parts of the sequences were very similar, but
both parsimony and distance-based analytical methods divided the sequences
into the same four subgroups, with each species having its own subgroup(s).
Thus, the Y chromosomes of M. musculus, M. spicilegus, and M. spretus can
be distinguished from one another.
相似文献
126.
Valentine RA Jackson KA Christie GR Mathers JC Taylor PM Ford D 《The Journal of biological chemistry》2007,282(19):14389-14393
Zinc is an essential micronutrient, so it is important to elucidate the molecular mechanisms of zinc homeostasis, including the functional properties of zinc transporters. Mammalian zinc transporters are classified in two major families: the SLC30 (ZnT) family and the SLC39 family. The prevailing view is that SLC30 family transporters function to reduce cytosolic zinc concentration, either through efflux across the plasma membrane or through sequestration in intracellular compartments, and that SLC39 family transporters function in the opposite direction to increase cytosolic zinc concentration. We demonstrated that human ZnT5 variant B (ZnT5B (hZTL1)), an isoform expressed at the plasma membrane, operates in both the uptake and the efflux directions when expressed in Xenopus laevis oocytes. We measured increased activity of the zinc-responsive metallothionein 2a (MT2a) promoter when ZnT5b was co-expressed with an MT2a promoter-reporter plasmid construct in human intestinal Caco-2 cells, indicating increased total intracellular zinc concentration. Increased cytoplasmic zinc concentration mediated by ZnT5B, in the absence of effects on intracellular zinc sequestration by the Golgi apparatus or endoplasmic reticulum, was also confirmed by a dramatically enhanced signal from the zinc fluorophore Rhodzin-3 throughout the cytoplasm of Caco-2 cells overexpressing ZnT5B at the plasma membrane when compared with control cells. Our findings demonstrate clearly that, in addition to mediating zinc efflux, ZnT5B at the plasma membrane can function to increase cytoplasmic zinc concentration, thus indicating a need to reevaluate the current paradigm that SLC30 family zinc transporters operate exclusively to decrease cytosolic zinc concentration. 相似文献
127.
128.
A. W. Mathers S. D. Young S. P. McGrath F. J. Zhao N. M. J. Crout E. H. Bailey 《Plant and Soil》2017,412(1-2):61-80
Background and aims
Root hair growth and development are important features of plant response to varying soil conditions and of nutrient and water uptake. Most current methods of characterizing root hairs in the field are unreliable or inefficient. We describe a method to quantify root hair area in digital images, such as those collected in situ by minirhizotron systems.Methods
This method uses ImageJ and R open source software and is partially automated using code presented here. It requires manual tracing of a subset of root hair images (training data set) to which a multivariate logistic regression is fit with each color channel in the image as an independent variable. Thereafter the model is applied to complete sets of selected root hair sections to estimate total root hair area.Results
There was good agreement between the training data sets and the predictions of the regression models in castor (Ricinus communis L.), maize (Zea mays L.), and papaya (Carica papaya L.).Conclusion
This method enables time-efficient and consistent quantification of root hairs using in situ root imaging systems that are already widely in use.129.
130.