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排序方式: 共有197条查询结果,搜索用时 265 毫秒
71.
Sergio A. Carrasco Loes Vandecasteele Marcelo M. Rivadeneira Miriam Fernández Alejandro Pérez-Matus 《Marine Biology Research》2017,13(10):1041-1058
Identifying patterns of spatial and temporal variability in the composition of communities associated with kelp forests is critical to understand the functioning of this productive, yet vulnerable ecosystem. We used a suite of sampling methods (light attraction and airlift devices) to evaluate the variability of larval, post-larval and macrobenthic assemblages associated with kelp forests (Lessonia trabeculata) in Central Chile (30° to 33°S). Pelagic collections identified two assemblages: early-life stages and emerging macrobenthos, with the later contributing three quarters to the total abundance regardless of the source of illumination (permanent or flashing). Field experiments showed that moon phases affected the structure and composition of the samples. Surveys carried out during new moon showed the highest abundances and taxonomic richness of emergent assemblages. However, species composition varied in both assemblages depending on the moon phase. Although the pelagic assemblages collected at sites with contrasting upwelling intensity did not show differences in community structure, differences in composition were evident for early-life stages. The relationship between pelagic and benthic collections indicated that four decapod crustaceans were represented at both larval and early juvenile stages; however, only the high abundances and densities of Paraxanthus barbiger allowed for estimations of benthic-pelagic coupling. For this species, larval abundances and benthic juvenile densities demonstrated contrasting local and regional patterns, suggesting a decoupling between pelagic and benthic environments. These findings highlight the differential variability in smaller components of kelp forests, but also suggest that post-settlement processes may be driving biological interactions through these highly productive and complex environments. 相似文献
72.
Background
Comparative genomic data among organisms allow the reconstruction of their phylogenies and evolutionary time scales. Molecular timings have been recently used to suggest that environmental global change have shaped the evolutionary history of diverse terrestrial organisms. Living xenarthrans (armadillos, anteaters and sloths) constitute an ideal model for studying the influence of past environmental changes on species diversification. Indeed, extant xenarthran species are relicts from an evolutionary radiation enhanced by their isolation in South America during the Tertiary era, a period for which major climate variations and tectonic events are relatively well documented. 相似文献73.
JP Herv s J. Martí -Clú a A. Mu oz-Garcí a MC Santa-Cruz 《Biotechnic & histochemistry》2002,77(1):27-35
We have optimised an indirect immunoperoxidase technique demonstrating bromodeoxyuridine (BrdU) incorporation into dividing cells for cerebellar tissue sections of four-day-old rats injected with this marker. This permits confident identification of granule-cell precursors engaged in DNA synthesis in the external granular layer of the developing cerebellum. Preservation of BrdU immunoreactivity is attained using methanol/acetic acid fixation and different pretreatments before immunostaining, while unlabeled nuclei can be recognized clearly after Feulgen or hematoxylin counterstaining. We established conditions to ensure satisfactory BrdU uptake without affecting cell-cycle progression during the postlabeling time period. The dose of BrdU employed provides saturation S-phase labeling from at least 1 h after BrdU delivery. Various kinetic parameters and phase durations have been determined in experiments involving a single injection or cumulative labeling sequences, and the cycle time was calculated based on two models of generative behavior: steady-state and exponential growth. The working hypothesis of steadystate kinetics can be adopted successfully if the existence of neuroblasts with different proliferation rates is taken into account. 相似文献
74.
Quantification of Expression of Staphylococcus epidermidis Housekeeping Genes with Taqman Quantitative PCR during In Vitro Growth and under Different Conditions 下载免费PDF全文
S. J. Vandecasteele W. E. Peetermans R. Merckx J. Van Eldere 《Journal of bacteriology》2001,183(24):7094-7101
The aims of the present study were (i) to develop and test a sensitive and reproducible method for the study of gene expression in staphylococci and (ii) to study the expression of five housekeeping genes which are involved in nucleic acid metabolism (gmk, guanylate kinase; the dihydrofolate reductase [DHFR] gene), glucose metabolism (tpi, triosephosphate isomerase), and protein metabolism (the 16S rRNA gene; hsp-60, heat-shock protein 60) during in vitro exponential and stationary growth. A modified method for instant mRNA isolation was combined with gene quantification via Taqman real-time quantitative PCR. The detection limit of our method was 10 copies of RNA. The average intersample variability was 16%. A 10-fold increase in the expression of the hsp-60 gene was induced by exposure to a 10 degrees C heat shock (37 to 47 degrees C) for 10 min. During in vitro growth, the expression of all five housekeeping genes showed rapid up-regulation after inoculation of the bacteria in brain heart infusion medum and started to decline during the mid-exponential-growth phase. Maximal gene expression was 110- to 300-fold higher than gene expression during stationary phase. This indicates that housekeeping metabolism is a very dynamic process that is extremely capable of adapting to different growth conditions. Expression of the 16S rRNA gene decreases significantly earlier than that of other housekeeping genes. This confirms earlier findings for Escherichia coli that a decline in bacterial ribosomal content (measured by 16S rRNA gene expression) precedes the decline in protein synthesis (measured by mRNA expression). 相似文献
75.
76.
M. Bouchez D. Blanchet J. -P. Vandecasteele 《Applied microbiology and biotechnology》1995,43(5):952-960
The mechanism of phenanthrene transfer to the bacteria during biodegradation by a Pseudomonas strain was investigated using a sensitive respirometric technique (Sapromat equipment) allowing the quasi-continuous acquisition
of data on oxygen consumption. Several systems of phenanthrene supply, crystalline solid and solutions in non-water-miscible
solvents (silicone oil and 2,2,4,4,6,8,8-heptamethylnonane) were studied. In all cases, analysis of the kinetics of oxygen
consumption demonstrated an initial phase of exponential growth with the same specific growth rate. In order to analyze the
second phase of growth and phenanthrene degradation, a study of the kinetics of phenanthrene transfer to the aqueous phase
was conducted by direct experimentation, with the crystal and silicone oil systems, in abiotic conditions. The data allowed
the validation of a model based on phase-transfer laws, describing the variations, with substrate concentrations, of rates
of phenanthrene transfer to the aqueous phase. Analysis of the biodegradation curves then showed that exponential growth ended
in all cases when the rates of phenanthrene consumption reached the maximal transfer rates. Thereafter, the biodegradation
rates closely obeyed, for all systems, the transfer rate values given by the model. These results unambiguously demonstrated
that, in the present case, phenanthrene biodegradation required prior transfer to the aqueous phase. With the silicone oil
system, which allowed high transfer and biodegradation rates, phenanthrene was directed towards higher metabolite production
and lower mineralization, as shown by oxygen consumption and carbon balance determinations.
Received: 30 November 1994/Accepted: 11 January 1995 相似文献
77.
Castagnone-Sereno P; Semblat JP; Leroy F; Abad P 《Molecular biology and evolution》1998,15(9):1115-1122
A highly abundant satellite DNA comprising 20% of the Meloidogyne fallax
(Nematoda, Tylenchida) genome was cloned and sequenced. The satellite
monomer is 173 bp long and has a high A + T content of 72.3%, with frequent
runs of A's and T's. The sequence variability of the monomers is 2.7%,
mainly due to random distribution of single-point mutations. A search for
evidence of internal repeated subunits in the monomer sequence revealed a
6-bp motif (AAATTT) for which five degenerated repeats, differing by just a
single base pair, could be identified. Pairwise comparison of the M. fallax
satellite with those from the sympatric species Meloidogyne chitwoodi and
Meloidogyne hapla revealed a high sequence similarity (68.39%) with one
satellite DNA subfamily in M. chitwoodi, which indicated an unexpected
close relationship between them. Given the high copy number and the extreme
sequence homogeneity among monomeric units, it may be assumed that the
satellite DNA of M. fallax could have evolved through some recent and
extensive amplification burst in the nematode genome. In this case, its
relatively short life would not yet have allowed the accumulation of random
mutations in independent amplified repeats. Considering the morphological
resemblance between the two species and their ability to produce
interspecific fertile hybrids under controlled conditions, these results
indicate that M. fallax may share a common ancestor with M. chitwoodi, from
which it could have diverged recently. All these data suggest that M.
fallax could be the result of a recent speciation process and show that
Meloidogyne satellite DNAs may be of interest to resolve phylogenetic
relationships among closely related species from this genus.
相似文献
78.
D. Michel-Savin R. Marchal J. P. Vandecasteele 《Applied microbiology and biotechnology》1990,32(4):387-392
Summary The parameters that control fermentation performance of butyrate production have been studied with a selected strain ofClostridium tyrobutyricum. Fed-batch supply of glucose increased productivity for butyrate. The ratio of butyrate to total acids was strongly influenced by the growth rate of the bacteria, acetate being produced along with butyrate at higher growth rates. In glucose-limited, fed-batch cultures, initially produced acetate was re-utilized, resulting in exclusive production of butyrate. In cultures with non-limiting glucose feeding, the butyrate concentration reached 42.5 g·1–1 with a selectivity of 0.90, a productivity of 0.82 g·–1 per hour and a yield of 0.36 g·g–1 The effects of the mode of supply of glucose on the production of butyrate and acetate are discussed in relation with the energy requirements for cell growth. 相似文献
79.
80.
Summary Acetone-butanol fermentation of the Jerusalem artichoke has been studied as a case for systematic investigation of the industrial optimization of both strain selection and fermentation operation. Hydrolysis of the inulinic oligofructans of the substrate was found necessary for optimal performance but could be achieved with a selected strain using a moderate amount of inulinase added at the beginning of the fermentation. Apart from ammonia, no nutritional supplementation of the medium was found necessary. The marked influence of pH in the fermentation performance prompted a detailed search for a method of controlling pH during fermentation. With an optimized procedure, solvent production of 23–24 g/l were obtained in 36 h. Detailed fermentation balances are presented. An industrial process for ABE production from Jerusalem artichoke or sugar beet has been defined and tested in the pilot plant. 相似文献