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排序方式: 共有225条查询结果,搜索用时 15 毫秒
11.
Biofilms are a major source of human pathogenic Legionella pneumophila in aquatic systems. In this study, we investigated the capacity of L. pneumophila to colonize floating biofilms and the impact of Acanthamoeba castellanii on the replication of biofilm-associated Legionella. Biofilms were grown in Petri dishes and consisted of Aeromonas hydrophila, Escherichia coli, Flavobacterium breve, and Pseudomonas aeruginosa. Six hours following inoculation, Legionella were detected in floating biofilms in mean concentrations of 1.4 × 104 cells/cm2 (real-time polymerase chain reaction) and 8.3 × 102 CFU/cm2 (culture). Two-way analysis of variance tests and fluorescent in situ hybridization clearly proved that increased biofilm-associated L. pneumophila concentrations were the result of intracellular replication in A. castellanii. Forty-eight hours after the introduction of A. castellanii in the Petri dishes, 90 ± 0.8% of the amoebae (infection rate) were completely filled with highly metabolic active L. pneumophila (mean infection intensity). 相似文献
12.
The synthesis of enantiomerically pure 2-aminocyclobutanecarboxylic acids has been refined to improve both the efficiency
and the simplicity. These improvements provide a shorter and easier access to the racemic cis-cyclobutane β-amino acid core. Derivatization of this material with a chiral non-racemic oxazolidin-2-one allows easy diastereoisomeric
separation and presents the advantage of allowing the non-destructive cleavage of the chiral auxiliary either by hydrolysis
or by ammonolysis, thus providing an efficacious access to N-protected derivatives of all four stereoisomers of Boc-2-aminocyclobutanecarboxylic
acid. 相似文献
13.
Many different cultivation techniques and inoculum products of the plant-beneficial arbuscular mycorrhizal (AM) fungi have
been developed in the last decades. Soil- and substrate-based production techniques as well as substrate-free culture techniques
(hydroponics and aeroponics) and in vitro cultivation methods have all been attempted for the large-scale production of AM
fungi. In this review, we describe the principal in vivo and in vitro production methods that have been developed so far.
We present the parameters that are critical for optimal production, discuss the advantages and disadvantages of the methods,
and highlight their most probable sectors of application. 相似文献
14.
Fenpropimorph and fenhexamid impact phosphorus translocation by arbuscular mycorrhizal fungi 总被引:1,自引:0,他引:1
Fenpropimorph and fenhexamid are sterol biosynthesis inhibitor (SBI) molecules widely used to control diseases in agriculture.
Both molecules, at increasing concentrations, have been shown to impact on the non-target arbuscular mycorrhizal (AM) fungi.
Root colonization, spore production and mycelium architecture, including the branched absorbing structures which are thought
to be involved in phosphorus (P) uptake, were affected. In the present study, we investigated the capacity of Glomus sp. MUCL 43204 to take up, transfer and translocate labelled P to Medicago truncatula in the presence of these SBI molecules. We used a strict in vitro cultivation system associating an autotrophic plant of
M. truncatula with the AM fungus. In addition, the effects of both SBI molecules on the proportion of hyphae with alkaline phosphatases
(ALP), succinate dehydrogenase (SDH) activity and on the expression of the mycorrhiza-specific plant phosphate transporter
MtPT4 gene were examined. We demonstrated that the two SBI molecules impacted the AM fungus. This was particularly evidenced
for fenpropimorph. A decrease in P transport and ALP and SDH activities associated with the extraradical mycelium and MtPT4 expression level was noted. These three factors were closely related to the development of the AM fungus, suggesting a direct
impact not only on the AM fungal growth but also on the physiology and metabolic activities of the AM fungus. These results
further emphasized the interest on the autotrophic in vitro culture system as an alternative to pot experiments to investigate
the mechanisms behind the impact of disease control molecules on the non-target AM fungal symbionts. 相似文献
15.
Ineke?van?Gremberghe Katleen?Van der?Gucht Pieter?Vanormelingen Tsehaye?Asmelash Tadesse?Dejenie Sofie?D’hondt Steven?Declerck Luc?De?Meester Wim?VyvermanEmail author 《Aquatic Ecology》2011,45(2):289-306
The cyanobacterium Microcystis is notorious for forming extensive and potentially toxic blooms in nutrient-rich freshwater bodies worldwide. However, little
is known about the factors underlying the genetic diversity and structure of natural Microcystis populations, despite the fact that this knowledge is essential to understand the build-up of blooms. Microcystis blooms are common and occur year-round in Africa, but are underinvestigated in this continent. We studied the genetic diversity
and structure of Microcystis populations in 30 man-made reservoirs in Tigray (Northern Ethiopia) using Denaturing Gradient Gel Electrophoresis of the
16S–23S rDNA internal transcribed spacer (ITS) region and assessed the importance of local environmental conditions and geographic
position of the reservoirs for the observed patterns. The analyses showed that both regional and local Microcystis ITS diversity in these recently constructed reservoirs was relatively low, with several dense blooms containing only a single
ITS type. Especially one non-toxic ITS type dominated a considerable fraction of Microcystis blooms, but appeared restricted in its geographic distribution. The relationship between Microcystis ITS population structure and abiotic variables (water clarity, pH) and with zooplankton (Daphnia biomass) indicates a (limited) influence of environmental conditions on Microcystis population structure in the reservoirs of Tigray. 相似文献
16.
Voets L Dupré de Boulois H Renard L Strullu DG Declerck S 《FEMS microbiology letters》2005,253(1):111-118
An autotrophic culture system was developed for the in vitro mycorrhization of potato plantlets. Roots of micropropagated plantlets were associated to an arbuscular mycorrhizal fungus under in vitro conditions, while shoots developed under open air conditions. Several thousand spores, an extensive extraradical mycelium and an abundant root colonization were obtained. Spores were able to colonize new plantlets under the same conditions. These results support the capacity of the autotrophic culture system to continuously culture arbuscular mycorrhizal fungi and may serve as a powerful tool to investigate various aspects of the symbiosis for which a source-sink relationship and photosynthetic active tissues are necessary. 相似文献
17.
In natural host populations, parasitism is considered to be omnipresent and to play an important role in shaping host life
history and population dynamics. Here, we study parasitism in natural populations of the zooplankton host Daphnia magna investigating their individual and population level effects during a 2-year field study. Our results revealed a rich and
highly prevalent community of parasites, with eight endoparasite species (four microsporidia, one amoeba, two bacteria and
one nematode) and six epibionts (belonging to five different taxa: Chlorophyta, Bacillariophyceae, Ciliata, Fungi and Rotifera).
Several of the endoparasites were associated with a severe overall fecundity reduction of the hosts, while such effects were
not seen for epibionts. In particular, infections by Pasteuria ramosa, White Fat Cell Disease and Flabelliforma magnivora were strongly associated with a reduction in overall D. magna fecundity. Across the sampling period, average population fecundity of D. magna was negatively associated with overall infection intensity and total endoparasite richness. Population density of D. magna was negatively correlated to overall endoparasite prevalence and positively correlated with epibiont richness. Finally, the
reduction in host fecundity caused by different parasite species was negatively correlated to both parasite prevalence and
the length of the time period during which the parasite persisted in the host population. Consistent with epidemiological
models, these results indicate that parasite mediated host damages influence the population dynamics of both hosts and parasites. 相似文献
18.
Dormant propagule banks integrate spatio-temporal heterogeneity in cladoceran communities 总被引:2,自引:0,他引:2
Vandekerkhove J Declerck S Jeppesen E Conde-Porcuna JM Brendonck L De Meester L 《Oecologia》2005,145(1):174-116
The dynamics of populations of short-lived organisms are very patchy, both in space and time. The production of dormant propagules, however, results in an effective increase in generation time. We hypothesize that prolonged dormancy, together with variable regeneration niches, result in integration of temporal variability in community structure. In addition, in aquatic habitats, mechanisms such as sediment focussing can contribute to the integration of spatial variability. We tested the hypothesis that dormant propagule banks integrate spatial and temporal variation in active zooplankton communities. This was done by comparing cladoceran species richness and the community structure of hatchling assemblages retrieved from propagule bank samples collected on a single occasion with assemblages encountered in active community samples covering spatial variation (littoral and pelagic zone), diel (day and night), intra-year (May–October) and inter-year variation (1996–2000). The egg bank community structure differed significantly from the active community structure, but the dissimilarity decreased as spatial and temporal variation was better covered by the active community samples. Furthermore, the identification of all fully grown hatchlings (n=214) yielded an equally high number of species (n=22) to that occurring in all active community samples together (a total of 1,730 individuals were analysed). We conclude that the analysis of dormant propagules may form a cost-efficient alternative tool to the analysis of active community samples for an integrated assessment of cladoceran communities. 相似文献
19.
Shahhoseini M Ziaee AA Pourbabai AA Ghaemi N Declerck N 《Journal of applied microbiology》2005,98(1):24-32
AIMS: Understanding the origin of high thermostability exhibited by the alpha-amylase produced by a natural strain of Bacillus licheniformis. METHODS AND RESULTS: The MSH320 alpha-amylase gene has been cloned from a native strain of B. licheniformis isolated from flour mill wastewaters in Kashan, central Iran, and its nucleotide sequence was determined (GenBank Accession Number AF438149). Whereas previously cloned B. licheniformisalpha-amylase (BLA) genes are nearly identical, the MSH320 gene coding sequence presents only 93% identity with the reference 'wild-type' BLA gene, most of the nucleotide changes leading to silent mutations. Amino acid substitutions occurred at 19 of the 483 residues of the matured protein, distributed all along the protein sequence. Nevertheless, the natural BLA variant presents thermoinactivation kinetics similar to that of the reference BLA. Protein modelling and structural predictions at the substitution sites suggest that half of the mutations may have a significant stabilizing or destabilizing effect on the protein structure. Compensatory mutations thus occurred in the natural variant in order to maintain thermostability to the level of the reference enzyme. CONCLUSIONS: The exceptional high thermostability of BLA, although produced by a nonthermophilic organism, is not fortuitous but subject to a selective pressure still at work in natural environments. SIGNIFICANCE AND IMPACT OF THE STUDY: BLA thermal performances are not naturally maximized and can be substantially improved by protein engineering. 相似文献
20.