首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   536篇
  免费   38篇
  2024年   1篇
  2023年   2篇
  2022年   1篇
  2021年   7篇
  2020年   14篇
  2019年   7篇
  2018年   16篇
  2017年   16篇
  2016年   14篇
  2015年   20篇
  2014年   16篇
  2013年   43篇
  2012年   16篇
  2011年   23篇
  2010年   14篇
  2009年   27篇
  2008年   48篇
  2007年   33篇
  2006年   28篇
  2005年   25篇
  2004年   33篇
  2003年   13篇
  2002年   29篇
  2001年   18篇
  2000年   16篇
  1999年   7篇
  1998年   11篇
  1997年   8篇
  1996年   11篇
  1995年   6篇
  1994年   3篇
  1993年   7篇
  1992年   4篇
  1991年   2篇
  1990年   4篇
  1989年   5篇
  1988年   5篇
  1987年   5篇
  1986年   1篇
  1985年   4篇
  1984年   1篇
  1982年   3篇
  1981年   1篇
  1980年   1篇
  1977年   1篇
  1976年   2篇
  1974年   1篇
  1973年   1篇
排序方式: 共有574条查询结果,搜索用时 134 毫秒
111.
Transferrin phenotypes of 403 Malagasy were determined by autoradiography after electrophoresis of plasma or serum. Three phenotypes, Tf C, Tf CD, and Tf D, were found. The frequency of TfD was 0.051 in the total sample, 0.041 in tribes of the Madagascar plateau, and 0.075 in tribes of the coastal and lowland regions. Haptoglobin phenotypes of 402 Malagasy were determined. The frequency of Hp1 was 0.41 in the total sample, 0.38 in tribes of the plateau, and 0.49 in coastal-lowland tribes. There is a significant difference in the frequency of Hp1 between the tribes of the plateau and those of the coastal and lowland regions. This confirms earlier observations of significant differences in frequencies of haptoglobins and hemoglobin S. Plasma or serum samples from 405 Malagasy were examined by electrophoresis to determine ceruloplasmin phenotypes. Seven distinct ceruloplasmin bands were observed. These were A, B, Galveston, Bridgeport, New Haven, Tananarive, and X, the last two described for the first time. Ten different phenotypes composed of one or two of the bands were observed. The frequency of the allele for ceruloplasmin B (CpB) was 0.78 in the total sample, 0.73 in tribes of the plateau, and 0.92 in coastal and lowland tribes. There is a significant difference in the frequency of this allele in the two major tribal groups, and this provides additional evidence of genetic differences between the peoples of the plateau and those of the coast and lowland regions of Madagascar.  相似文献   
112.
The coexistence of closely related species is not easily understood on the basis of ecological theories. This study investigates the extent of coexistence of two congeneric species of Microcebus murinus (MUR) and M. ravelobensis (RAV) in northwestern Madagascar. Their presence and local relative population densities were determined by capturing and nocturnal transect counts and compared at 22 study sites in the Ankarafantsika National Park. All sites were characterized with regard to their altitude, access to surface water, and 19 structural vegetation characteristics. RAV and MUR were not equally distributed over this regional scale. RAV occurred in more sites and at higher maximum densities than MUR. The relative population densities of both species were significantly and negatively correlated with each other. Whereas the relative population densities of MUR increased with altitude and were highest in dry habitats far from surface water, the relative population densities of RAV generally decreased with altitude and were highest in low altitude habitats close to surface water. The results of the vegetation characteristics also reflect these general trends. The divergent pattern of local and regional coexistence of these two species is discussed and can be best explained either by the existence of a spatially heterogeneous competitive environment or by independent evolutionary pathways in different historic environments. Am. J. Primatol. 71:928–938, 2009. © 2009 Wiley‐Liss, Inc.  相似文献   
113.
114.
The morphology of the spermatozoon of representative species of the subfamily Nesomyinae (Muroidea: Nesomyidae), a monophyletic group of rodents endemic to Madagascar, was examined by light and electron microscopy to determine the sperm head shape and tail length across the species. Marked interspecific differences were found to occur in both the form of the sperm head and length of the tail. The species that possess a sperm head with an apical hook, which largely contains acrosomal material, generally displayed longer sperm tails, and a species with a spatulate sperm head had the shortest tail. The association between sperm head shape and tail length mirrors that previously found in Eurasian and Australasian murine rodents. Thus, the repeated association between sperm head shape and tail length across these groups of muroid rodents clearly indicates a functional relationship between these two features. A comparison of sperm morphology of the nesomyines to that of related muroid rodents on the mainland of Africa suggests that the possession of an apical hook is the ancestral condition. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.  相似文献   
115.
Habitat fragmentation is an increasingly serious issue affecting primates in most regions where they are found today. Populations of Lemur catta (ring-tailed lemur) in Madagascar's south-central region are increasingly restricted to small, isolated forest fragments, surrounded by grasslands or small-scale agriculture. Our aim was to evaluate the potential for population viability of L. catta in nine forest fragments of varying sizes (2–46 ha, population range: 6–210 animals) in south-central Madagascar, using a set of comparative, quantitative ecological measures. We used Poisson regression models with a log link function to examine the effects of fragment size, within-fragment food availability, and abundance of matrix resources (food and water sources) on L. catta population sizes and juvenile recruitment. We found a strong association between overall population size and (a) fragment size and (b) abundance of key food resources Melia azedarach and Ficus spp. (per 100 m along transect lines). Juvenile recruitment was also associated with fragment size and abundance of the two above-mentioned food resources. When the largest population, an outlier, was removed from the analysis, again, the model containing fragment size and abundance of M. azedarach and Ficus spp. was the best fitting, but the model that best predicted juvenile recruitment contained only fragment size. While our results are useful for predicting population presence and possible persistence in these fragments, both the potential for male dispersal and the extent of human disturbance within most fragments play crucial roles regarding the likelihood of long-term L. catta survival. While seven of the nine fragments were reasonably protected from human disturbance, only three offered the strong potential for male dispersal, thus the long-term viability of many of these populations is highly uncertain.  相似文献   
116.
117.
118.
2010, Lynx Edicions, Barcelona, Spain

880 pages, 60 colour plates, hardcover

ISBN-13: 978–84-96553–68-2. Price €212  相似文献   
119.
The phylogenetic relationships of the Timaliidae (babblers) and Sylviidae (warblers) have long challenged ornithologists. We focus here on three Malagasy genera currently assigned to the Timaliidae, Mystacornis, Oxylabes, and Neomixis, and on their relationships with other babblers and warblers using the sequences of two mitochondrial genes (cytochrome b and 16S rRNA). Maximum parsimony analyses show that the Malagasy “babblers” are not related to any of the other African and Asian babblers. The genus Mystacornis is neither a babbler nor a warbler. The other Malagasy “babblers” are members of warbler groups (the monophyly of the Sylviidae is not demonstrated). Oxylabes madagascariensis and Hartertula flavoviridis (we recognize Hartertula as a genus for the species flavoviridis, previously Neomixis flavoviridis) constitute, with two presumed sylviine taxa, Thamnornis chloropetoides and Cryptosylvicola randrianasoloi, a warbler radiation endemic to the island of Madagascar. The other Neomixis species (tenella, striatigula, and viridis) belong to another warbler group comprising cisticoline taxa. These results show that the Timaliidae did not disperse to Madagascar. Rather, the island has been colonized, independently, by at least two clades of warblers, probably originating from Africa, where the Sylviidae radiation has been the most extensive.  相似文献   
120.
The newly described molossid bat, Chaerephon atsinanana Goodman et al., 2010, endemic to eastern Madagascar, shows notably high levels of phylogeographic and genetic structure compared with allopatric Chaerephon leucogaster Grandidier, 1869 from western Madagascar. Such highly significant structuring of haplotypes among altitudinally and latitudinally stratified population groups is contrary to the expected panmixia in strong flying bats. The null model of concordance in historical demographic patterns across these two Chaerephon species was not supported. Mismatch and Bayesian skyline analyses indicated ancient stable C. atsinanana populations of constant size during the last two major Pleistocene glacial periods, making retreat into and expansion from glacial refugia an unlikely explanation for such high levels of structure, in accordance with expectations for tropical bats. Analyses were consistent with post‐refugial population expansion in the less diverse and structured C. leucogaster during the end of the last Pleistocene glacial period. We hypothesise that the pronounced genetic structuring in C. atsinanana may result from female philopatry. Furthermore, differing demographic histories of the two species may have been shaped by differing climate or habitat preferences, consistent with evidence from MaxEnt ecological niche modelling, which shows differences in variables influencing the current predicted distributions. Fossil Quaternary pollen deposits further indicate greater stability in past climatic patterns in eastern versus western Madagascar. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 18–40.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号