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51.
Extreme differences in rates of molecular evolution of foraminifera revealed by comparison of ribosomal DNA sequences and the fossil record 总被引:8,自引:3,他引:5
Pawlowski J; Bolivar I; Fahrni JF; de Vargas C; Gouy M; Zaninetti L 《Molecular biology and evolution》1997,14(5):498-505
Foraminifera have one of the best known fossil records among the
unicellular eukaryotes. However, the origin and phylogenetic relationships
of the extant foraminiferal lineages are poorly understood. To test the
current paleontological hypotheses on evolution of foraminifera, we
sequenced about 1,000 base pairs from the 3' end of the small subunit rRNA
gene (SSU rDNA) in 22 species representing all major taxonomic groups.
Phylogenies were derived using neighbor- joining, maximum-parsimony, and
maximum-likelihood methods. All analyses confirm the monophyletic origin of
foraminifera. Evolutionary relationships within foraminifera inferred from
rDNA sequences, however, depend on the method of tree building and on the
choice of analyzed sites. In particular, the position of planktonic
foraminifera shows important variations. We have shown that these changes
result from the extremely high rate of rDNA evolution in this group. By
comparing the number of substitutions with the divergence times inferred
from the fossil record, we have estimated that the rate of rDNA evolution
in planktonic foraminifera is 50 to 100 times faster than in some benthic
foraminifera. The use of the maximum-likelihood method and limitation of
analyzed sites to the most conserved parts of the SSU rRNA molecule render
molecular and paleontological data generally congruent.
相似文献
52.
Evidence for a Sex-Linked Haplo-Inviable Locus in the Cut-Singed Region of DROSOPHILA MELANOGASTER 总被引:9,自引:7,他引:2 下载免费PDF全文
Many cytologically normal and rearranged cut mutants have been reported, but no known deficiency involves both ct and its close neighbor, singed. This fact prompted an investigation of the mutational response of the ct–sn interval. Approximately 24,000 F1 female progeny of 7-day-old males given 2000 or 3000r X-ray exposures were examined for the presence of newly induced mutations at the Notch, carmine, ct, and sn loci. One sn, 2 cm-ct, 31 N, and 33 ct mutants were found, indicating that the frequency of recovery of ct mutants is much greater than that of either cm or sn, as high even as N. Among the F1 female progeny were two deficiency mutants that expressed both cm and ct (separated by 21 bands), but none expressed both ct and sn (separated by only 14 bands). Of the 18 cytologically analyzed ct mutants, two proved to be deficiencies; neither extended farther to the right than 7C1. No reported ct deficiency extends with certainty farther to the right than 7C4. This fact, together with the scarcity of sn deficiencies, suggests the presence of a haplo-insufficient locus between ct and sn that prevents recovery of ct-sn deficiencies. The analysis of the deficiency component of Tp snS93, a short transposition which moves most of the ct–sn interval from 7BC to 8D, proved the existence, just to the left of sn, of a haplo-inviable locus that prevents the development of females heterozygous for its deficiency.—A marked similarity between mutants at the N and ct loci was noted. 相似文献
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JF Yuan SJ Zhang O Jafer RA Furlong OE Chausiaux CA Sargent GH Zhang NA Affara 《BMC microbiology》2009,9(1):246
Background
Pseudorabies virus (PRV) is an alphaherpesviruses whose native host is pig. PRV infection mainly causes signs of central nervous system disorder in young pigs, and respiratory system diseases in the adult. 相似文献56.
Background
Most studies examining the commensal human oral microbiome are focused on disease or are limited in methodology. In order to diagnose and treat diseases at an early and reversible stage an in-depth definition of health is indispensible. The aim of this study therefore was to define the healthy oral microbiome using recent advances in sequencing technology (454 pyrosequencing). 相似文献57.
Background
The past several years have seen a flurry of papers seeking to clarify the utility and limits of DNA barcoding, particularly in areas such as species discovery and paralogy due to nuclear pseudogenes. Heteroplasmy, the coexistence of multiple mitochondrial haplotypes in a single organism, has been cited as a potentially serious problem for DNA barcoding but its effect on identification accuracy has not been tested. In addition, few studies of barcoding have tested a large group of closely-related species with a well-established morphological taxonomy. In this study we examine both of these issues, by densely sampling the Hawaiian Hylaeus bee radiation. 相似文献58.
Ponton F Lefevre T Lebarbenchon C Thomas F Loxdale HD Marché L Renault L Perrot-Minnot MJ Biron DG 《Proceedings. Biological sciences / The Royal Society》2006,273(1603):2869-2877
Phylogenetically unrelated parasites often increase the chances of their transmission by inducing similar phenotypic changes in their hosts. However, it is not known whether these convergent strategies rely on the same biochemical precursors. In this paper, we explored such aspects by studying two gammarid species (Gammarus insensibilis and Gammarus pulex; Crustacea: Amphipoda: Gammaridae) serving as intermediate hosts in the life cycle of two distantly related parasites: the trematode, Microphallus papillorobustus and the acanthocephalan, Polymorphus minutus. Both these parasite species are known to manipulate the behaviour of their amphipod hosts, bringing them towards the water surface, where they are preferentially eaten by aquatic birds (definitive hosts). By studying and comparing the brains of infected G. insensibilis and G. pulex with proteomics tools, we have elucidated some of the proximate causes involved in the parasite-induced alterations of host behaviour for each system. Protein identifications suggest that altered physiological compartments in hosts can be similar (e.g. immunoneural connexions) or different (e.g. vision process), and hence specific to the host-parasite association considered. Moreover, proteins required to alter the same physiological compartment can be specific or conversely common in both systems, illustrating in the latter case a molecular convergence in the proximate mechanisms of manipulation. 相似文献
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Recent studies using the mouse showed an inverse correlation between the Caveolin 1 gene expression and lactation, and this was regulated by prolactin. However, current study using mammary explants from pregnant mice showed that while insulin (I), cortisol (F) and prolactin (P) resulted in maximum induction of the β-casein gene, FP and IFP resulted in the downregulation of Caveolin 1. Additionally, IF, FP and IFP resulted in the downregulation of Caveolin 2. Immunohistochemistry confirmed localisation of Caveolin 1 specific to myoepithelial cells and adipocytes. Comparative studies with the tammar wallaby showed Caveolin 1 and 2 had 70–80% homology with the mouse proteins. However, in contrast to the mouse, Caveolin 1 and 2 genes showed a significantly increased level of expression in the mammary gland during lactation. The regulation of tammar Caveolin 1 and 2 gene expression was examined in mammary explants from pregnant tammars, and no significant difference was observed either in the absence or in the presence of IFP. 相似文献