全文获取类型
收费全文 | 227篇 |
免费 | 9篇 |
出版年
2021年 | 1篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 3篇 |
2012年 | 6篇 |
2011年 | 4篇 |
2010年 | 5篇 |
2009年 | 4篇 |
2008年 | 6篇 |
2007年 | 14篇 |
2006年 | 14篇 |
2005年 | 8篇 |
2004年 | 11篇 |
2003年 | 8篇 |
2002年 | 9篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 11篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1976年 | 5篇 |
1974年 | 5篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1954年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有236条查询结果,搜索用时 187 毫秒
31.
Arnason E 《Genetics》2004,166(4):1871-1885
An analysis of sequence variation of 250 bp of the mitochondrial cytochrome b gene of 1278 Atlantic cod Gadus morhua ranging from Newfoundland to the Baltic shows four high-frequency (>8%) haplotypes and a number of rare and singleton haplotypes. Variation is primarily synonymous mutations. Natural selection acting directly on these variants is either absent or very weak. Common haplotypes show regular trans-Atlantic clines in frequencies and each of them reaches its highest frequency in a particular country. A shallow multifurcating constellation gene genealogy implies young age and recent turnover of polymorphism. Haplotypes characterizing populations at opposite ends of the geographic distribution in Newfoundland and the Baltic are mutationally closest together. The haplotypes are young and have risen rapidly in frequency. Observed differentiation among countries is due primarily to clinal variation. Hypotheses of historical isolation and polymorphisms balanced by local selection and gene flow are unlikely. Instead the results are explained by demic selection of mitochondria carried by highly fit females winning reproductive sweepstakes. By inference the Atlantic cod, a very high-fecundity vertebrate, is characterized by a high variance of offspring number and strong natural selection that leads to very low effective to actual population sizes. 相似文献
32.
Jing Qin Mao Mohsin Abbas Zaidi John Thor Arnason Illimar Altosaar 《Plant Cell, Tissue and Organ Culture》2006,87(2):121-125
An in vitro regeneration system was developed in cowpea [Vigna unguiculata (L.) Walp.] Blackeye. Among several explants studied, shoot initiation response was observed from shoot apices of 3–5-day-old seedlings. The optimal medium for maximum shoot initiation comprised MS salts, B5 vitamins, 8.88 μM N
6-benzylaminopurine, 1 gl-1 casein hydrolysate, 342 μM L-glutamine, 3% sucrose, 0.3% phytagel, adjusted to pH 5.8. A shift in pH from 5.8 to 7.0 had no effect on shoot initiation and on number of shoots per explant. The highest shoot initiation frequency (77%) was obtained using this preferred medium, reaching a maximum of eight shoots per explant. For shoot elongation, 14 μM gibberellic acid was supplemented in the shoot initiation medium. Presence of indolebutyric acid in the rooting medium had no effect on root induction. The regenerated plants were fertile and developed normally. 相似文献
33.
Quantitative ethnobotany of two east Timorese cultures 总被引:1,自引:0,他引:1
Sean Collins Xisto Martins Andrew Mitchell Awegechew Teshome John Thor Arnason 《Economic botany》2006,60(4):347-361
This is the first time aspects of the ethnobotany of East Timor have been reported. The medicinal plant traditions of two
distinct East Timorese cultures, the Laklei and Idate, were studied and compared using quantitative ethnobotanical methods.
A total of 86 medicinal plant species were identified. The medicinal plant traditions of the Laklei and Idate cultures were
compared using Trotter and Logan’s (1986) quantitative “informant agreement ratio.” On average, informant consensus was greater
in Laklei, suggesting a medicinal plant tradition that is more defined than in Idate, where informants are more likely to
use the same medicinal plants when treating the same usage categories. Furthermore, only 11 of the 86 medicinal plant species
documented were used by both cultures, of which only six had similar mentions. These findings have important implications
for the understanding of ethnobotany as they demonstrate how relatively closely situated cultural groups can have significantly
different traditional knowledge systems. 相似文献
34.
35.
J. T. Arnason G. J. Bourque C. Madhosilngh W. Orr 《Biochemical Systematics and Ecology》1986,14(6):569-574
The acetylenic allelochemical, phenylheptatriyne (PHT), from species of the Asteraceae disrupts membrane function in Fusarium culmorum by both phototoxic and non-phototoxic mechanisms. Treatment of mycelia or macroconidia with 10 ppm PHT leads to an aggregation of lipids visible in Sudan Black stained material. This characteristic stress response increases in conjunction with photosensitizing wavelengths of radiation (near UV). Mild treatment of PHT (10 ppm) and near UV (5 Wm2/50 min) inhibit 14C phenylalanine uptake and respiration and enhance K1 leakage suggesting that the membrane is the primary site of action of PHT. 相似文献
36.
The extant mammalian groups Monotremata, Marsupialia and Placentalia are, according to the 'Theria' hypothesis, traditionally classified into two subclasses. The subclass Prototheria includes the monotremes and subclass Theria marsupials and placental mammals. Based on some morphological and molecular data, an alternative proposition, the Marsupionta hypothesis, favours a sister group relationship between monotremes and marsupials to the exclusion of placental mammals. Phylogenetic analyses of single genes and even multiple gene alignments have not yet been able to conclusively resolve this basal mammalian divergence. We have examined this problem using one data set composed of expressed sequence tags (EST) and another containing 1 510 509 nucleotide (nt) sites from 1358 inferred cDNA genomic sequences. All analyses of the concatenated sequences unambiguously supported the Theria hypothesis. The Marsupionta hypothesis was rejected with high statistical confidence from both data sets. In spite of the strong support for Theria, a non-negligible number of single genes supported either of the two alternative hypotheses. The divergence between monotremes and therian mammals was estimated to have taken place 168–178 Mya, a dating compatible with the fossil record. Considering the long common evolutionary branch of therians, it is surprising that sequence data from many thousand amino acid sites were needed to conclusively resolve their relationship to monotremes. This finding draws attention to other mammalian divergences that have been taken as unequivocally settled based on much smaller alignments. EST data provide a comprehensive random sample of protein coding sequences and an economic way to produce large amounts of data for phylogenetic analysis of species for which genomic sequences are not yet available. 相似文献
37.
38.
Richard Aucoin Gabriel Guillet Christine Murray Bernard J. R. Philogne J. Thor Arnason 《Archives of insect biochemistry and physiology》1995,29(2):211-226
Plants of the Asteraceae and Hypericaceae possess secondary compounds that induce photooxidation in insect herbivores that consume them. One of the well-established modes of action of these substances is peroxidation of membrane lipids. Some herbivores counteract these defences by avoidance of light and tissues rich in phototoxins or the ability to detoxify these secondary substances. The cytochrome P-450 polysubstrate monooxygenase systems involved, the metabolic products, and a new putative toxin pump have been described. Dietary antioxidants (β-carotene, vitamin E, ascorbate) are additional defences against phototoxicity. They reduce mortality in herbivores exposed to phototoxins and some specialist herbivores have high constitutive levels. Adapted specialist insects also have higher constitutive levels of superoxide dismutase (SOD) and respond to phototoxins in their diet by the induction of catalase (CAT), glutathione reductase (GR), and increased levels of reduced glutathione (GSH). Artificial inhibition of the enzymes SOD and CAT had little effect on phototoxicity but inhibition of GSH synthesis in herbivores enhanced photooxidative effects of administered phototoxins on lipid peroxidation. While insects have many mechanisms to overcome plant photooxidants, the Asteraceae appear to have adopted a strategy of counterattack. We suggest and provide preliminary evidence that a second group of secondary substances, the sesquiterpene lactones, occurring in the Asteraceae can attack key antioxidant defences to synergise phototoxins. © 1995 Wiley-Liss, Inc. 相似文献
39.
The sequence (16,829 nt) of the complete mitochondrial genome of the
greater Indian rhinoceros, Rhinoceros unicornis, was determined. Like other
perissodactyls studied (horse and donkey) the rhinoceros demonstrates
length variation (heteroplasmy) associated with different numbers of
repetitive motifs in the control region. The 16,829-nt variety of the
molecule includes 36 identical control region motifs. The evolution of
individual peptide-coding genes was examined by comparison with a distantly
related perissodactyl, the horse, and the relationships among the orders
Carnivora, Perissodactyla, and Artiodactyla (+ Cetacea) were examined on
the basis of concatenated sequences of 12 mitochondrial peptide-coding
genes. The phylogenetic analyses grouped Carnivora, Perissodactyla, and
Artiodactyla (+ Cetacea) into a superordinal clade and within this clade a
sister group relationship was recognized between Carnivora and
Perissodactyla to the exclusion of Artiodactyla (+ Cetacea) . On the basis
of the molecular difference between the rhinoceros and the horse and by
applying as a reference to Artiodactyl/Cetacean divergence set at 60
million years ago (MYA), the evolutionary divergence between the families
Rhinocerotidae and Equidae was dated to approximately 50 MYA.
相似文献
40.
S. Omar M. Lalonde M. Marcotte M. Cook J. Proulx K. Goel T. Durst B. J. R. Philogne J. T. Arnason 《Agricultural and Forest Entomology》2000,2(4):253-257
1 Thirty extracts of wood and bark of hardwood trees from Eastern North America were examined for insect growth‐reducing activity in a bioassay with European corn borer, Ostrinia nubilalis, and an antifeedant bioassay with the rice weevil, Sitophilus oryzae. 2 Nine of the bark extracts and four of the wood extracts showed significant growth reducing effects at 0.5% in meridic diets, whereas only two bark extracts and one wood extract showed significant antifeedant effect at the same concentration. 3 Slower growing tree species were more biologically active than fast growing ones. Isolation of the bioactive compounds in one of the active species, Prunus serotina, showed that naringenin, its derivative methoxynaringenin, and eriodictyol were responsible for the antifeedant effects. 相似文献