全文获取类型
收费全文 | 62篇 |
免费 | 8篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 4篇 |
2012年 | 1篇 |
2011年 | 1篇 |
2009年 | 3篇 |
2006年 | 1篇 |
2005年 | 1篇 |
2003年 | 1篇 |
1999年 | 3篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1934年 | 1篇 |
排序方式: 共有70条查询结果,搜索用时 31 毫秒
1.
Jeff A Johnson Heather RL Lerner Pamela C Rasmussen David P Mindell 《BMC evolutionary biology》2006,6(1):65-12
Background
Populations of the Oriental White-backed Vulture (Gyps bengalensis) have declined by over 95% within the past decade. This decline is largely due to incidental consumption of the non-steroidal anti-inflammatory veterinary pharmaceutical diclofenac, commonly used to treat domestic livestock. The conservation status of other Gyps vultures in southern Asia is also of immediate concern, given the lack of knowledge regarding status of their populations and the continuing existence of taxonomic uncertainties. In this study, we assess phylogenetic relationships for all recognized species and the majority of subspecies within the genus Gyps. The continuing veterinary use of diclofenac is an unknown but potential risk to related species with similar feeding habits to Gyps bengalensis. Therefore, an accurate assessment of the phylogenetic relationships among Gyps vultures should aid in their conservation by clarifying taxonomic uncertainties, and enabling inference of their respective relatedness to susceptible G. bengalensis. 相似文献2.
3.
4.
alpha 1-Proteinase inhibitor (alpha 1-PI), a member of the serine
proteinase inhibitor superfamily, has a primary role in controlling
neutrophil elastase activity within the mammalian circulation. Several
studies have indicated that the reactive center region of alpha 1-PI, the
amino acid sequence of which is critical to recognition of and binding to
target proteinases, is highly divergent within and among species. This
appears to be a consequence of accelerated rates of evolution that may have
been driven by positive Darwinian selection. In order to examine this and
other features of alpha 1-PI evolution in more detail, we have isolated and
sequenced cDNAs representing alpha 1- PI mRNAs of the mouse species Mus
saxicola and Mus minutoides and have compared these with a number of other
mammalian alpha 1-PI mRNAs. Relative to other mammalian mRNAs, the extent
of nonsynonymous substitution is generally high throughout the alpha 1-PI
mRNA molecule, indicating greater overall rates of amino acid substitution.
Within and among mouse species, the 5'-half of the mRNA, but not the
3'-half, has been homogenized by concerted evolution. Finally, the reactive
center is under diversifying or positive Darwinian selection in murid
rodents (rats, mice) and guinea pigs yet is under purifying selection in
primates and artiodactyls. The significance of these findings to alpha 1-PI
function and the possible selective forces driving evolution of serpins in
general are discussed.
相似文献
5.
Mitochondrial DNA polymorphisms in subterranean mole-rats of the Spalax ehrenbergi superspecies in Israel, and its peripheral isolates 总被引:1,自引:0,他引:1
Nevo E; Honeycutt RL; Yonekawa H; Nelson K; Hanzawa N 《Molecular biology and evolution》1993,10(3):590-604
Patterns of mitochondrial DNA (mtDNA) variation were examined in 133
mole-rats constituting all four chromosomal species (2n = 52, 2n = 54, 2n =
58, and 2n = 60) of the Spalax ehrenbergi superspecies in Israel, as well
as the peripheral isolates of 2n = 60. In the main range of the complex, a
total of 28 mtDNA haplotypes were found in 64 mole-rats, with most
haplotypes being unique to either a single chromosomal species or
population. mtDNA divergence increased from low to high diploid number in a
north-to-south direction in Israel. Overall levels of mtDNA diversity were
unexpectedly the highest in the 2n = 60, the youngest species of the
complex. The mtDNA haplotypes can be separated into two major groups, 2n =
52-54 and 2n = 58-60, and a phylogenetic analysis for each group revealed
evidence of a few haplotypes not sorted by diploid number. The overall
patterns of mtDNA divergence seen within and among the four chromosomal
species are consistent with the parapatric mode of speciation as suggested
from previous studies of allozyme and DNA hybridization. In a separate data
set the patterns of mtDNA variation were examined across the main
geographic range and across peripheral semi-isolates and isolates of the 2n
= 60 chromosomal species. Fifteen haplotypes were found in 69 mole-rats.
High levels of mtDNA diversity characterized the main range, semi-isolated,
and even some desert isolated populations. The peripheral isolates contain
much mtDNA diversity, including novel haplotypes.
相似文献
6.
Ross L. Goldingay David Rohweder Brendan D. Taylor 《Ecological Management & Restoration》2020,21(2):115-122
Nest boxes have grown in popularity as a habitat management tool in Australia during the last decade. This management use remains contentious because some studies suggest nest boxes are ineffective. There are three recent contentions: (i) nest boxes mostly benefit common species, (ii) exotic species may be dominant users of nest boxes, and (iii) species of conservation concern use nest boxes infrequently. We address these contentions using data from 1865 nest boxes involving eight nest box designs. These nest boxes were installed predominantly <200 m from a road in association with highway duplication and re‐alignment across 16 projects in New South Wales. The Common Brushtail Possum (Trichosurus vulpecula) is the species of most relevance to contention 1. It used 9% of boxes overall including 26% of ‘possum’ designated boxes. The most frequent nest box users were small petaurid gliders (mostly Sugar Gliders, Petaurus breviceps) which used 63% of ‘small glider’ designated boxes. This nest box and another suited to the Sugar Glider comprised 40% of all boxes installed, so it is not surprising that this species might be a common user. Exotic species were uncommon users of the nest boxes enabling contention 2 to be rejected. Active hives of Feral Honeybees (Apis mellifera) occupied just 1% of boxes, and another 1% of boxes were used by introduced rodents and birds. The Squirrel Glider (Petaurus norfolcensis) is the species most relevant to contention 3. It was seen in 80 boxes across 11 projects, representing 7% of the three types most frequently used. These observations are not consistent with the third contention. Nest boxes can provide many important insights about the requirements and interactions of hollow‐dependent fauna. However, they are not intended as an alternative to retaining hollow‐bearing trees. 相似文献
7.
Ross L. Goldingay Darren G. Quin Orlando Talamo Janice Mentiplay‐Smith 《Ecological Management & Restoration》2020,21(2):131-142
Habitat preferences need to be understood if species are to be adequately managed or conserved. Habitat preferences are presumed to reflect requirements for food, shelter and breeding, as well as interactions with predators and competitors. However, one or more of these requirements may dominate. Tree‐cavity‐dependent wildlife species are one example where shelter or breeding site requirements may dominate. We installed 120 nest boxes across 40 sites to target the vulnerable Brush‐tailed Phascogale (Phascogale tapoatafa) and the non‐threatened Sugar Glider (Petaurus breviceps). The provision of shelter sites where few of quality are available may enable better resolution of habitat preferences. Over three years, we observed the Brush‐tailed Phascogale at 17 sites, whereas the Sugar Glider was observed at 39 sites. We tested four broad hypotheses (H1–H4) relating to habitat that may influence occupancy by these species. There was no influence of hollow (cavity) abundance (H1) on either species suggesting our nest boxes had satisfied their shelter requirements. There was no influence of habitat structure (canopy and tree proximity) (H2) immediately around the nest box trees. We found no influence of distance to the forest edge (H3). Variables at and away from the nest box site that appear to reflect foraging substrates (H4) were influential on the Brush‐tailed Phascogale. Sugar Glider occupancy was only influenced by a single variable at the nest box site. The lack of influence of any other variables is consistent with the very high occupancy observed, suggesting most of the forest habitat is suitable when shelter sites are available. We found no evidence that the Sugar Glider reduced site use by the Brush‐tailed Phascogale. 相似文献
8.
Phylogenetic utility of the nuclear gene arginine decarboxylase: an example from Brassicaceae 总被引:10,自引:2,他引:8
Arginine decarboxylase (ADC) is an important enzyme in the production of
putrescine and polyamines in plants. It is encoded by a single or low-copy
nuclear gene that lacks introns in sequences studied to date. The rate of
Adc amino acid sequence evolution is similar to that of ndhF for the
angiosperm family studied. Highly conserved regions provide several target
sites for PCR priming and sequencing and aid in nucleotide and amino acid
sequence alignment across a range of taxonomic levels, while a variable
region provides an increased number of potentially informative characters
relative to ndhF for the taxa surveyed. The utility of the Adc gene in
plant molecular systematic studies is demonstrated by analysis of its
partial nucleotide sequences obtained from 13 representatives of
Brassicaceae and 3 outgroup taxa, 2 from the mustard oil clade (order
Capparales) and 1 from the related order Malvales. Two copies of the Adc
gene, Adc1 and Adc2, are found in all members of the Brassicaceae studied
to data except the basal genus Aethionema. The resulting Adc gene tree
provides robust phylogenetic data regarding relationships within the
complex mustard family, as well as independent support for proposed tribal
realignments based on other molecular data sets such as those from
chloroplast DNA.
相似文献
9.
Biodiversity and Conservation - Invasive predators, land clearing and altered fire regimes have been implicated in species decline and extinction worldwide. Enhanced knowledge of how these factors... 相似文献
10.
Degree of landscape fragmentation influences genetic isolation among populations of a gliding mammal
Forests and woodlands are under continuing pressure from urban and agricultural development. Tree-dependent mammals that rarely venture to the ground are likely to be highly sensitive to forest fragmentation. The Australian squirrel glider (Petaurus norfolcensis) provides an excellent case study to examine genetic (functional) connectivity among populations. It has an extensive range that occurs in a wide band along the east coast. However, its forest and woodland habitat has become greatly reduced in area and is severely fragmented within the southern inland part of the species' range, where it is recognised as threatened. Within central and northern coastal regions, habitat is much more intact and we thus hypothesise that genetic connectivity will be greater in this region than in the south. To test this we employed microsatellite analysis in a molecular population biology approach. Most sampling locations in the highly modified south showed signatures of genetic isolation. In contrast, a high level of genetic connectivity was inferred among most sampled populations in the more intact habitat of the coastal region, with samples collected 1400 km apart having similar genetic cluster membership. Nonetheless, some coastal populations associated with urbanisation and agriculture are genetically isolated, suggesting the historic pattern observed in the south is emerging on the coast. Our study demonstrates that massive landscape changes following European settlement have had substantial impacts on levels of connectivity among squirrel glider populations, as predicted on the basis of the species' ecology. This suggests that landscape planning and management in the south should be focused on restoring habitat connectivity where feasible, while along the coast, existing habitat connectivity must be maintained and recent losses restored. Molecular population biology approaches provide a ready means for identifying fragmentation effects on a species at multiple scales. Such studies are required to examine the generality of our findings for other tree-dependent species. 相似文献