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排序方式: 共有97条查询结果,搜索用时 15 毫秒
71.
Sulphur stable isotopes can distinguish trophic dependence on sediments and plankton in boreal lakes
1. Stable isotopes of carbon are useful for differentiating between freshwater food chains based on planktonic algae or benthic algae, but are reported to be of limited use for identifying food chains based on sedimentary detritus. Because data from marine systems suggest that stable isotopes of sulphur (δ34 S values) have potential in this regard, we tested their utility in freshwater lakes.
2. We found that sulphate in the water column of four boreal lakes was enriched in34 S compared to the sulphur in bulk sediments from these lakes. Furthermore, within a given lake, insects known to feed on sediment (directly or via predation) had δ34 S values similar to those of sediment, whereas planktonic and benthic invertebrates known to feed on suspended particles had δ34 S values similar to those of sulphate in the water column.
3. Using the stable S isotope values of invertebrates that obtain their S from either the sediment or the water column as end members in a two-source mixing model, we show that two fish species obtain their food from both planktonic and sedimentary sources. Furthermore, model results suggest that, as expected, the more benthic-feeding fish species obtains more of its S from the sediment compartment than does the species that feeds in the water-column.
4. Our results suggest that measurements of stable sulphur isotopes provide a means of distinguishing between members of food chains that are based in the water column from those based on sedimentary detritus. As such, they would be a useful complement to stable C isotopes that are used to distinguish between food chains based on planktonic or benthic algae. 相似文献
2. We found that sulphate in the water column of four boreal lakes was enriched in
3. Using the stable S isotope values of invertebrates that obtain their S from either the sediment or the water column as end members in a two-source mixing model, we show that two fish species obtain their food from both planktonic and sedimentary sources. Furthermore, model results suggest that, as expected, the more benthic-feeding fish species obtains more of its S from the sediment compartment than does the species that feeds in the water-column.
4. Our results suggest that measurements of stable sulphur isotopes provide a means of distinguishing between members of food chains that are based in the water column from those based on sedimentary detritus. As such, they would be a useful complement to stable C isotopes that are used to distinguish between food chains based on planktonic or benthic algae. 相似文献
72.
SAMILA SIAVOSHIAN HERV M BLOTTIRE ERIC LE FOLL BERTRAND KAEFFER CHRISTINE CHERBUT JEAN-PAUL GALMICHE 《Cell biology international》1997,21(5):281-287
The aim of this study was to compare the effects of acetate, propionate, butyrate, iso-butyrate, valerate, iso-valerate and caproate on cell growth and on the activities of alkaline phosphatase (AP) and dipeptidyl aminopeptidase IV (DPP IV) by three human colonic adenocarcinoma cell lines. In addition to butyrate, propionate and valerate inhibited cell proliferation of the three cell lines. The other SCFAs did not influence cell proliferation. AP and DPP IV activities were strongly stimulated by butyrate on two of the three cell lines. On HT-29, AP was strongly stimulated, however DPPIV expression remained undetectable. Propionate and valerate exhibited a weaker stimulation, the other SCFAs being ineffective. The effect of SCFAs on cell proliferation and differentiation clearly depends on the number of carbons and on the configuration of the basic structure of the molecule. 相似文献
73.
Quezada-Rivera JJ RE Soria-Guerra FS Pérez-Juárez L Martínez-González SE Valdés- Rodríguez NL Vasco-Méndez JF Morales-Domínguez 《Phyton》2019,88(1):25-35
The use of antimicrobial peptides (AMPs) synthesized
by bacteria (bacteriocins) is an alternative for combating multidrug
resistant bacterial strains and their production by recombinant route
is a viable option for their mass production. The bacteriocin E-760
isolated from the genus Enterococcus sp. has been shown to possess
inhibitory activity against Gram-negative and Gram-positive
bacteria. In this study, the expression of a chimeric protein coding
for E-760 in the nucleus of C. reinhardtii was evaluated, as well as,
its antibacterial activity. The synthetic gene E-760S was inserted
into the genome of C. reinhardtii using Agrobacterium tumefaciens.
A transgenic line was identified in TAP medium with hygromycin
and also by PCR. The increment in the culture medium temperature
of the transgenic strain at 35 °C for 10 minutes, increased the
production level of the recombinant protein from 0.14 (Noninduced
culture, NIC) to 0.36% (Induced culture, IC) of total soluble
proteins (TSP); this was quantified by an ELISA assay. Recombinant
E-760 possesses activity against Staphylococcus aureus in 0.34 U
log, Streptococcus agalactiae in 0.48 U log, Enterococcus faecium in
0.36 U log, Pseudomonas aeruginosa in 2 U log and for Klebsiella
pneumoniae, the activity was 0.07 U log. These results demonstrate
that the nucleus transformation of C. reinhardtii can function as
a stable expression platform for the production of the synthetic
gene E-760 and it can potentially be used as an antibacterial agent. 相似文献
74.
75.
Christopher RE McEvoy Paul D van Helden Robin M Warren Nicolaas C Gey van Pittius 《BMC evolutionary biology》2009,9(1):237-21
Background
PPE38 (Rv 2352c) is a member of the large PPE gene family of Mycobacterium tuberculosis and related mycobacteria. The function of PPE proteins is unknown but evidence suggests that many are cell-surface associated and recognised by the host immune system. Previous studies targeting other PPE gene members suggest that some display high levels of polymorphism and it is thought that this might represent a means of providing antigenic variation. We have analysed the genetic variability of the PPE38 genomic region on a cohort of M. tuberculosis clinical isolates representing all of the major phylogenetic lineages, along with the ancestral M. tuberculosis complex (MTBC) member M. canettii, and supplemented this with analysis of publicly available whole genome sequences representing additional M. tuberculosis clinical isolates, other MTBC members and non tuberculous mycobacteria (NTM). Where possible we have extended this analysis to include the adjacent plcABC and PPE39/40 genomic regions. 相似文献76.
PETER J. UNMACK RE P. BENNIN EVELYN M. HABIT PEDRO F. VICTORIANO JERALD B. JOHNSON 《Biological journal of the Linnean Society. Linnean Society of London》2009,97(4):876-892
We examined the role of several earth history events on the phylogeographic distribution of the catfish Trichomycterus areolatus in Chile using the cytochrome b gene. We explored three biogeographic hypotheses: that sea level changes have resulted in the isolation of populations by drainages; that glaciation has impacted genetic diversity; and that ichthyological subprovince boundaries correspond to phylogeographic breaks in our focal species. We found seven well-supported clades within T. areolatus with high levels of genetic divergence. The strongest signal in our data was for an important role of sea level changes structuring populations. Five of the seven clades mapped cleanly to the geographic landscape and breaks corresponded closely to areas of narrowest continental shelf. In addition, few haplotypes were shared between rivers within clades, suggesting that only limited local movement of individuals has occurred. There was no relationship between the levels of genetic diversity and the proportion of individual drainages covered by glaciers during the last glacial maximum. Two phylogeographic breaks within T. areolatus did match the two previously identified faunal boundaries, but we found three additional breaks, which suggests that faunal breaks have only limited utility in explaining phylogeographic patterns. These results imply that the narrow continental shelf coupled with sea level changes had a strong influence on the obligate freshwater fishes in Chile. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 876–892. 相似文献
77.
78.
Conserved sequence motifs, alignment, and secondary structure for the third domain of animal 12S rRNA 总被引:17,自引:3,他引:14
Hickson RE; Simon C; Cooper A; Spicer GS; Sullivan J; Penny D 《Molecular biology and evolution》1996,13(1):150-169
Secondary structure models are an important step for aligning sequences,
understanding probabilities of nucleotide substitutions, and evaluating the
reliability of phylogenetic reconstructions. A set of conserved sequence
motifs is derived from comparative sequence analysis of 184 invertebrate
and vertebrate taxa (including many taxa from the same genera, families,
and orders) with reference to a secondary structure model for domain III of
animal mitochondrial small subunit (12S) ribosomal RNA. A template is
presented to assist with secondary structure drawing. Our model is similar
to previous models but is more specific to mitochondrial DNA, fitting both
invertebrate and vertebrate groups, including taxa with markedly different
nucleotide compositions. The second half of the domain III sequence can be
difficult to align precisely, even when secondary structure information is
considered. This is especially true for comparisons of anciently diverged
taxa, but well-conserved motifs assist in determining biologically
meaningful alignments. Patterns of conservation and variability in both
paired and unpaired regions make differential phylogenetic weighting in
terms of "stems" and "loops" unsatisfactory. We emphasize looking carefully
at the sequence data before and during analyses, and advocate the use of
conserved motifs and other secondary structure information for assessing
sequencing fidelity.
相似文献
79.
Evolutionary dynamics of tandem repeats in the mitochondrial DNA control region of the minnow Cyprinella spiloptera 总被引:3,自引:0,他引:3
Length variation due to tandem repeats is now recognized as a common
feature of animal mitochondrial DNA; however, the evolutionary dynamics of
repeated sequences are not well understood. Using phylogenetic analysis,
predictions of three models of repeat evolution were tested for arrays of
260-bp repeats in the cyprinid fish Cyprinella spiloptera. Variation at
different nucleotide positions in individual repeats supported different
models of repeat evolution. One set of characters included several
nucleotide variants found in all copies from a limited number of
individuals, while the other set included an 8- bp deletion found in a
limited number of copies in all individuals. The deletion and an associated
nucleotide change appear to be the result of a deterministic, rather than
stochastic, mutation process. Parallel origins of repeat arrays in
different mitochondrial lineages, possibly coupled with a homogenization
mechanism, best explain the distribution of nucleotide variation.
相似文献
80.
Ixodes (Pholeoixodes) hexagonus, an efficient vector of Borrelia burgdorferi in the laboratory 总被引:2,自引:0,他引:2
LISE GERN LINA N. TOUTOUNGI CHANG MIN HU RE AESCHLIMANN 《Medical and veterinary entomology》1991,5(4):431-435
Borrelia burgdorferi Johnson et al. was first isolated from the midgut of Ixodes dammini Spielman et al. in the U.S.A. and from the midgut of I.ricinus (L.) in Europe. I.ricinus was considered to be the only tick vector of this borrelia, in Europe, until I.hexagonus Leach, the hedgehog tick, was found to harbour spirochaetes. This paper reports an evaluation of the vector competence of I.hexagonus for the spirochaete B.burgdorferi. Transovarial and trans-stadial survival were demonstrated and the spirochaete was transmitted to laboratory mice via the bites of trans-stadially infected I.hexagonus females. 相似文献