全文获取类型
收费全文 | 129篇 |
免费 | 14篇 |
专业分类
143篇 |
出版年
2023年 | 2篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 9篇 |
2014年 | 5篇 |
2013年 | 3篇 |
2012年 | 3篇 |
2011年 | 3篇 |
2010年 | 4篇 |
2009年 | 3篇 |
2008年 | 3篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 8篇 |
2004年 | 6篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 11篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有143条查询结果,搜索用时 15 毫秒
91.
Matthew N Ward Allison M Churcher Kevin J Dick Chris RJ Laver Greg L Owens Megan D Polack Pam R Ward Felix Breden John S Taylor 《BMC evolutionary biology》2008,8(1):210
Background
Comparisons of functionally important changes at the molecular level in model systems have identified key adaptations driving isolation and speciation. In cichlids, for example, long wavelength-sensitive (LWS) opsins appear to play a role in mate choice and male color variation within and among species. To test the hypothesis that the evolution of elaborate coloration in male guppies (Poecilia reticulata) is also associated with opsin gene diversity, we sequenced long wavelength-sensitive (LWS) opsin genes in six species of the family Poeciliidae. 相似文献92.
Ricardo A. Correia Ana C. M. Malhado Lays Lins Norah Costa Gamarra Waltyane A. G. Bonfim Anyelet Valencia-Aguilar Chiara Bragagnolo Paul Jepson Richard J. Ladle 《Biodiversity and Conservation》2016,25(8):1503-1513
Protected areas (PAs) are under increasing pressure to demonstrate their broader value and contribution to society. Scientific research and associated knowledge production comprise one such value, which has received relatively little attention in the academic literature. Here, we use the Amazon region as a case study to quantify scientific knowledge production (as measured by scientific publications in peer-reviewed journals) in PAs and identify the main biophysical, geographical and social characteristics that influence such production. We adopt a multi-model inference approach with an innovative hurdle regression model to independently assess the factors influencing the presence of research and the number of studies in PAs. Our results indicate a highly skewed pattern of scientific production, with many PAs with few or no associated scientific articles. Larger, older and more highly protected PAs in Ecuador and Peru were most likely to have scientific production, while time since first publication was most strongly associated with the number of publications from a PA. These findings provide important insights that could be used to support and strengthen policy aimed at increasing the value of Amazonian protected areas for scientific research. 相似文献
93.
Male dance flies (Diptera: Empididae) are major predators of mating swarms of male nonbiting midges (Diptera: Chironomidae). Studies have indicated that chironomid midges are excellent fliers with extraordinarily high wing muscle power, acceleration and tortuosity for their size. We compared the relative flight performance and morphometrics of male empidsEmpis tesselatta Meigen and their prey, Chironomus plumosus L., in a series of laboratory and field studies. High-speed digital video camera footage revealed that there were no significant differences between predator and prey in terms of straight-line acceleration or maximum flight velocity, although the mean speed of empids was higher. In curved flight, measured as tortuosity, the smaller chironomids held a considerable advantage over their larger predators. Flight muscle ratio (e.g. flight muscle mass/body mass) of chironomids was also greater in chironomids than in empids. In field studies, small male chironomids suffered much lower levels of predation than large males. This result is consistent with the prediction of small midges being less likely to be captured because of superior aerobatics, although we are unable to exclude empirically that empids select large male midges. We discuss the possible mechanisms of prey capture by empids given the greater manoeuvrability of their prey, the coevolutionary dynamics of flight performance and the apparent selective advantage of small size in male chironomids. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. 相似文献
94.
José Gilmar C. Oliveira Júnior Luana P. S. Silva Ana C. M. Malhado Vandick S. Batista Nidia N. Fabré Richard J. Ladle 《PloS one》2016,11(3)
Given limited funds for research and widespread degradation of ecosystems, environmental scientists should geographically target their studies where they will be most effective. However, in academic areas such as conservation and natural resource management there is often a mismatch between the geographic foci of research effort/funding and research needs. The former frequently being focused in the developed world while the latter is greater in the biodiverse countries of the Global South. Here, we adopt a bibliometric approach to test this hypothesis using research on artisanal fisheries. Such fisheries occur throughout the world, but are especially prominent in developing countries where they are important for supporting local livelihoods, food security and poverty alleviation. Moreover, most artisanal fisheries in the Global South are unregulated and unmonitored and are in urgent need of science-based management to ensure future sustainability. Our results indicate that, as predicted, global research networks and centres of knowledge production are predominantly located in developed countries, indicating a global mismatch between research needs and capacity. 相似文献
95.
96.
Molecular phylogenetics of Stenodermatini bat genera: congruence of data from nuclear and mitochondrial DNA 总被引:2,自引:1,他引:1
Van den Bussche RA; Baker RJ; Wichman HA; Hamilton MJ 《Molecular biology and evolution》1993,10(5):944-959
Within the tribe Stenodermatini the systematics of the complex of species
allied with the genus Artibeus has generated several alternative
phylogenetic hypotheses. The most recent treatment recognized four genera
(Artibeus, Dermanura, Enchisthenes, and Koopmania) and suggested that the
most recent common ancestor of these four genera would include the common
ancestor of all other currently recognized Stenodermatini genera except
Sturnira. To test this hypothesis, we examined an EcoRI-defined nuclear
satellite DNA repeat and 402 bp of DNA sequence variation from the
mitochondrial cytochrome b gene. Phylogenetic conclusions based on Southern
blot analyses, in situ hybridization, and mitochondrial DNA sequence data
indicate that Enchisthenes is not closely related to Dermanura, Artibeus,
or Koopmania and that Dermanura, Artibeus, and Koopmania shared a common
ancestor after diverging from the remainder of the Stenodermatini. If our
conclusions are correct, then justification for recognizing Dermanura and
Koopmania as generically distinct from Artibeus must be based on the
magnitude of difference that distinguishes each rather than on the
conclusion that to place them as congeneric with Artibeus creates a
paraphyletic taxon.
相似文献
97.
98.
99.
Immunological similarities between specific chloroplast ribosomal proteins from Chlamydomonas reinhardtii and ribosomal proteins from Escherichia coli 总被引:11,自引:0,他引:11
Polyclonal antibodies were elicited against seven of the 33 different
proteins of the large subunit of the chloroplast ribosome from
Chlamydomonas reinhardtii. Three of these proteins are synthesized in the
chloroplast and four are made in the cytoplasm and imported. In western
blots, six of the seven antisera are monospecific for their respective
large subunit ribosomal proteins, and none of these antisera cross-reacted
with any chloroplast small subunit proteins from C. reinhardtii. Antisera
to the three chloroplast-synthesized ribosomal proteins cross-reacted with
specific Escherichia coli large subunit proteins of comparable charge and
molecular weight. Only one of the four antisera to the chloroplast
ribosomal proteins synthesized in the cytoplasm cross-reacted with an E.
coli large subunit protein. None of the antisera cross-reacted with any E.
coli small subunit proteins. On the assumption of a procaryotic,
endosymbiotic origin for the chloroplast, those chloroplast ribosomal
proteins still synthesized within the organelle appear to have retained
more antigenic sites in common with E. coli ribosomal proteins than have
those which are now the products of cytoplasmic protein synthesis. Antisera
to this cytoplasmically synthesized group of chloroplast ribosomal proteins
did not recognize any antigenic sites among C. reinhardtii cytoplasmic
ribosomal proteins, suggesting that the genes for the cytoplasmically
synthesized chloroplast ribosomal proteins either are not derived from the
cytoplasmic ribosomal protein genes or have evolved to a point where no
antigenic similarities remain.
相似文献
100.
Motor circuits in the spinal cord integrate information from various sensory and descending pathways to control appropriate motor behavior. Recent work has revealed that target-derived retrograde signaling mechanisms act to influence sequential assembly of motor circuits through combinatorial action of genetic and experience-driven programs. These parallel activities imprint somatotopic information at the level of the spinal cord in precisely interconnected circuits and equip animals with motor circuits capable of reacting to changing demands throughout life. 相似文献