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1.
The development of numerical syntaxonomy during its first 20 yr is reviewed. The use of methods of numerical classification and ordination is the dominating feature of the development. National and local phytosociological data banks were established, large data sets handled and many important vegetation monographs were methodically based on multivariate data analysis. Particularly the development in Italy, the Netherlands, Czechoslovakia, and Sweden contributed to new theoretical elements of numerical syntaxonomy. Ordination became a common tool of searching for reticulate synsystematic relations between community types. The most popular ordination techniques have been Principal Components Analysis and Detrended Correspondence Analysis. Hierarchical agglomerative techniques of clustering still prevail in classification, although the divisive strategy of TWINSPAN has also become an effective tool for phytosociological clustering and table sorting. Extensive program packages, also for personal computers have now become standard equipment for many vegetation scientists. 相似文献
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Molecular analysis of the feline immunodeficiency virus protease: generation of a novel form of the protease by autoproteolysis and construction of cleavage-resistant proteases. 总被引:1,自引:1,他引:0 下载免费PDF全文
G S Laco M C Fitzgerald G M Morris A J Olson S B Kent J H Elder 《Journal of virology》1997,71(7):5505-5511
The feline immunodeficiency virus (FIV) protease is essential for virion maturation and subsequent viral replication in that it cleaves the Gag and Gag/Pol polyproteins at eight sites to release the respective structural proteins and enzymes. During purification of a recombinant FIV protease (PR), we noted that it underwent autoproteolysis (autolysis) to give discrete cleavage products. These additional PR cleavage sites were defined using N-terminal amino acid sequence analysis and mass spectrometry. Protease breakdown products were also found in FIV virions and were of the same apparent molecular weights as the in vitro autolysis products. Four primary PR autolysis sites were blocked via substitution of either the P1 amino acid with a beta-branched amino acid or the P1' amino acid with lysine. Cleavage-resistant PRs which had Km and k(cat) values similar to those of FIV PR were constructed. An autolysis time course determined that blocking all four primary autolysis sites yielded a cleavage-resistant PR which was enzymatically stable. Concomitant with autolysis is the generation of an N-terminally truncated form of the PR (Thr6/PR) which has enhanced stability with respect to that of FIV PR. A structural basis for the Thr6/PR activity is presented, as are the possible roles of autolysis in the viral replication cycle. 相似文献
3.
Kretová M Szemes T Laco J Gronesová P Grones J 《Biochemical and biophysical research communications》2005,328(1):27-31
The DNA sequence of small cryptic plasmid pAG20 in Acetobacter aceti was determined at 3064 bp with 51.6% GC pairs. The plasmid encoded a 186 amino acid protein which is important for plasmid replication in Gram-negative bacteria except Escherichia coli. Two 21 bp large direct repeat sequence 1 and two 13 bp direct repeat sequence 2 were determined in the regulation region upstream from gene encoded Rep protein. Vector pAG24 with kanamycin gene and two deletion derivatives pAG25 and pAG26 without rep gene from plasmid pAG20 were constructed. Plasmid pAG24 was replicated in a broad host range like E. coli, Acetobacter pasteurianus, A. aceti, Comanomonas spp., Serratia marcescens, and Shigella spp. 相似文献
4.
Specificity of a promoter from the rice tungro bacilliform virus for expression in phloem tissues 总被引:5,自引:0,他引:5
5.
Doepper S Kacani L Falkensammer B Dierich MP Stoiber H 《Current molecular medicine》2002,2(8):703-711
Similar to other pathogens, HIV can directly activate the complement pathway even in the absence of antibodies. During and after seroconversion, HIV-specific antibodies enhance the activation of complement and increase deposition of complement fragments on virions dramatically. However, even in the presence of HIV-specific antibodies, no or only poor lysis occurs. HIV has adapted different protection mechanisms to keep complement activation under the threshold necessary to induce virolysis. In addition to its own envelope proteins, the viral envelope contains membrane-anchored host molecules. Among those are complement regulatory proteins that remain functionally active on the surface of HIV and turn down the complement cascade. In addition, serum proteins with complement regulatory activities become secondarily attached onto the virus, thereby enhancing the protection of HIV against complement-mediated damage. Therefore, opsonised virions accumulate in HIV-infected individuals, which subsequently interact with complement receptor (CR) expressing cells. This review is mainly focused on these interactions, which result either in infection of CR-positive cells with high efficiency, or retention of viral particles on their surface via CRs, thereby promoting transmission of virus to other permissive cells. 相似文献
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James L. Tsakalos Michael Renton Mark P. Dobrowolski Erik J. Veneklaas Paul D. Macintyre Sarah J. Broomfield Ladislav Mucina 《Austral ecology》2019,44(5):906-916
The nature of community patterns and environmental drivers in kwongan mediterranean‐type shrubland on nutrient‐poor soils occurring in Western Australia remain poorly examined. We aimed to determine whether (i) classification of the kwongan vegetation of the northern Swan Coastal Plain would be ecologically informative and (ii) which environmental drivers underpin the plant community patterns. The study area was positioned on the northern Swan Coastal Plain, locality of Cooljarloo (30°39′ S, 115°22′ E), situated 170 km north of Perth, Western Australia. Compositional (518 species × 337 relevés) and environmental data set (29 variables × 87 relevés) describing time since last fire, soil chemical and physical properties, and terrain characteristics were analysed using classification and ordination techniques. OptimClass assisted in the selection of a robust data transformation, resemblance function and clustering algorithm to identify the vegetation patterns. Major ecological drivers of the vegetation patterns were detected using distance‐based redundancy analysis (db‐RDA). Classification revealed major groupings of Wet Heath and Banksia Woodland distinguishable by the high prevalence of myrtyoid and proteoid taxa, respectively. On floristic‐sociological grounds, we recognised four Wet Heath and two Banksia Woodland communities. The Wet Heath was constrained to areas of higher litter depth (db‐RDA axis 1: 9%). Soil chemical and physical properties explained the highest proportion (17%) of the compositional variance, while the terrain‐ and fire‐related variables explained 2% and <0.001%, respectively. While fire explained little compositional variance overall, a separate db‐RDA analysis found that it may play an important pattern‐structuring role within Banksia Woodlands. Fine‐scale compositional patterns correspond only to a small extent to environmental data; the substantial unexplained variance may be due to slow‐acting neutral and stochastic processes. 相似文献
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The Cape Fynbos region of South Africa, a global biodiversity hotspot, hosted a diverse large mammal fauna till shortly after
permanent European settlement (1652). How these animals survived in this exceptionally nutrient-poor environment is puzzling
and it is generally believed that they restricted their movements to the more fertile shale areas. We tested the hypothesis
that large herbivores avoid nutrient-poor limestone and sandstone fynbos shrublands in favour of shale-derived renosterveld
vegetation using strontium (Sr) isotope analysis. If this technique could reconstruct the preferred feeding habitats of the
contemporary fauna, it might also be useful for reconstructing the preferred feeding grounds of an extinct fauna. Using the
assumption that small rodents have spatially restricted foraging activities, we determined the 87Sr/86Sr isotope ratios of rodent teeth to establish the isotopic signal characteristic of the different geological substrates in
the area. We then analysed 87Sr/86Sr isotope ratios in the bones of a number of different large herbivores found in De Hoop Nature Reserve using laser ablation
multi-collector inductively coupled plasma mass spectrometry. These values were compared to the bioavailable (rodent) values
on the respective geological substrates. The technique identified differences in feeding substrate selection between different
species and groups of the same species. The results also showed that shale renosterveld shrubland is not the exclusive source
of nutrition for the large herbivores. Strikingly different isotope ratios among individuals in some populations pointed to
significant dispersal events from distant sources. However, we were unable to pinpoint the exact feeding areas using Sr isotope
analysis probably because some animals use a combination of substrates for feeding and because the geology of the study area
is complex with graded isotope signals. We suggest that this technique is a valuable additional tool for exploring large mammal
foraging behaviour on habitats associated with contrasting and less complex geology. 相似文献