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151.
Virulence of oomycete pathogens from Phragmites australis‐invaded and noninvaded soils to seedlings of wetland plant species
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Soil pathogens affect plant community structure and function through negative plant–soil feedbacks that may contribute to the invasiveness of non‐native plant species. Our understanding of these pathogen‐induced soil feedbacks has relied largely on observations of the collective impact of the soil biota on plant populations, with few observations of accompanying changes in populations of specific soil pathogens and their impacts on invasive and noninvasive species. As a result, the roles of specific soil pathogens in plant invasions remain unknown. In this study, we examine the diversity and virulence of soil oomycete pathogens in freshwater wetland soils invaded by non‐native Phragmites australis (European common reed) to better understand the potential for soil pathogen communities to impact a range of native and non‐native species and influence invasiveness. We isolated oomycetes from four sites over a 2‐year period, collecting nearly 500 isolates belonging to 36 different species. These sites were dominated by species of Pythium, many of which decreased seedling survival of a range of native and invasive plants. Despite any clear host specialization, many of the Pythium species were differentially virulent to the native and non‐native plant species tested. Isolates from invaded and noninvaded soils were equally virulent to given individual plant species, and no apparent differences in susceptibility were observed between the collective groups of native and non‐native plant species. 相似文献
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153.
A. Hermansen M.-L. Herrero E. Gauslaa J. Razzaghian R. Nærstad & S.S. Klemsdal 《The Annals of applied biology》2007,150(2):115-121
Carrot roots with cavity spot lesions from eight different counties in Norway were sampled and Pythium species were isolated on selective medium. Pythium spp. were characterised morphologically and by species-specific PCR. Laboratory experiments with inoculations of carrot roots were performed. A total of 130 isolates out of 230 Pythium -like isolates tested with PCR were identified as pathogenic species of Pythium. These were P. intermedium (29%), P. sulcatum (23%), P. sylvaticum (16%), P. violae (15%) and a possible new Pythium species designated P . ' vipa ' (18%). There were some differences between geographical regions and ages of cavities regarding the frequency of the different species isolated. When rating sunken lesions in the laboratory inoculation experiments, P. ' vipa ' was the most aggressive and P. violae the least aggressive species. P. intermedium and P. ' vipa ' caused more discolouration of the infected carrot tissue than the other species. The importance of the different Pythium spp. as agents of cavity spot in Norway is discussed. 相似文献
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155.
Mitgutsch C Richardson MK Jiménez R Martin JE Kondrashov P de Bakker MA Sánchez-Villagra MR 《Biology letters》2012,8(1):74-77
Talpid moles across all northern continents exhibit a remarkably large, sickle-like radial sesamoid bone anterior to their five digits, always coupled with a smaller tibial sesamoid bone. A possible developmental mechanism behind this phenomenon was revealed using molecular markers during limb development in the Iberian mole (Talpa occidentalis) and a shrew (Cryptotis parva), as shrews represent the closest relatives of moles but do not show these conspicuous elements. The mole's radial sesamoid develops later than true digits, as shown by Sox9, and extends into the digit area, developing in relation to an Msx2-domain at the anterior border of the digital plate. Fgf8 expression, marking the apical ectodermal ridge, is comparable in both species. Developmental peculiarities facilitated the inclusion of the mole's radial sesamoid into the digit series; talpid moles circumvent the almost universal pentadactyly constraint by recruiting wrist sesamoids into their digital region using a novel developmental pathway and timing. 相似文献
156.
Tojo M van West P Hoshino T Kida K Fujii H Hakoda A Kawaguchi Y Mühlhauser HA Van Den Berg AH Küpper FC Herrero ML Klemsdal SS Tronsmo AM Kanda H 《Fungal biology》2012,116(7):756-768
Pythium polare sp. nov. is a new heterothallic oomycete species isolated from fresh water and moss from various locations in both the Arctic and Antarctic. This water mould is able to infect stems and leaves of Sanionia moss (Sanionia uncinata). Pythium polare causes brown discolouration in in vitro inoculation tests at 5 °C after 5 weeks of inoculation. It is characterized by globose sporangia with various lengths of discharge tubes releasing zoospores and aplerotic oospores with usually one to five antheridia. The sexual structures are only produced in a dual culture of antheridial and oogonial isolates. Phylogenetic analysis, based on ITS sequencing, places all isolated strains of P. polare in a unique new clade, hence it is considered a novel species. Pythium canariense and Pythium violae are the most closely related species of P. polare based both on morphology and the phylogenetic analysis. 相似文献
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158.
Nucleotide sequences of the rDNA intergenic spacer (IGS) region in Pythium ultimum were determined in 16 clones obtained from three isolates differing in production of sexual organs. Several sequences with
different lengths were detected in each isolate, showing heterogeneity in the IGS region. In addition, several tandem repeat
regions were detected in all the clones. The sequences, length, and number of each copy largely varied among repeat regions.
Length heterogeneity arose from the complex combination of the number of copy within the repeat regions. Furthermore, the
nucleotide sequence of each copy and the number of repetition varied not only between isolates but also between clones from
an isolate. Based on the sequence similarity and the number of copies in repeat regions, specific patterns different between
homothallic P. ultimum and the Pythium group HS (hyphal swellings) were recognized in a few regions. These results suggest that these two groups have slight genetic
differences in the IGS region, although the differences in most of the repeat regions were not enough to identify each group. 相似文献
159.
Genetic engineering of Streptococcus gordonii for the simultaneous display of two heterologous proteins at the bacterial surface 总被引:4,自引:0,他引:4
Maggi T Spinosa M Ricci S Medaglini D Pozzi G Oggioni MR 《FEMS microbiology letters》2002,210(1):135-141
A new species Pythium canariense (CI-07), isolated from soil samples taken in the San Nicolas region of the Canary islands (Gran Canaria, Spain), is being described here. This species is characterised by its spherical to pyriform, intercalary to catenulate sporangia, smooth-walled terminal oogonia supplied with monoclinous and diclinous antheridia which at times are branched and wrap around the female gametangia. The fungus has an antagonistic effect on Botrytis cinerea, the grey mould fungus. Morphological features are being given here together with the sequence of the complete internal transcribed spacer region of the nuclear ribosomal DNA of the fungus, its comparison with related species, and some aspects of its antagonistic behaviour with B. cinerea. 相似文献
160.