全文获取类型
收费全文 | 65篇 |
免费 | 5篇 |
国内免费 | 2篇 |
出版年
2022年 | 1篇 |
2019年 | 2篇 |
2017年 | 2篇 |
2015年 | 4篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 6篇 |
2011年 | 1篇 |
2010年 | 4篇 |
2009年 | 3篇 |
2008年 | 1篇 |
2006年 | 2篇 |
2005年 | 1篇 |
2004年 | 3篇 |
2002年 | 6篇 |
2000年 | 1篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1934年 | 1篇 |
1929年 | 1篇 |
排序方式: 共有72条查询结果,搜索用时 15 毫秒
51.
Variation in rates of molecular evolution now appears to be widespread. The
demonstration that body size is correlated with rates of molecular
evolution suggests that physiological and ecological factors may be
involved in molecular rate variation, but large-scale comparative studies
are still lacking. Here, we use complete cytochrome b sequences from 85
species of tube-nosed seabirds (order Procellariiformes) and 5 outgroup
species of penguins (order Sphenisciformes) to test for an association
between body mass and rates of molecular evolution within the former avian
order. Cladistic analysis of the 90 sequences estimates a phylogeny largely
consistent with the traditional taxonomy of the Procellariiformes. The
Diomedeidae, Procellariidae, and Pelecanoididae are monophyletic, while the
Hydrobatidae are basal and paraphyletic. However, the two subfamilies
within the Hydrobatidae (Hydrobatinae and Oceanitinae) are monophyletic. A
likelihood ratio test detects significant deviation from clocklike
evolution in our data. Using a sign test for an association between body
mass and branch length in the seabird phylogeny, we find that larger taxa
tend to have shorter terminal branch lengths than smaller taxa. This
observation suggests that rates of mitochondrial DNA evolution are slower
for larger taxa. Rate calibrations based on the fossil record reveal
concordant body size effects. We interpret these results as evidence for a
metabolic rate effect, as the species in this order exhibit large
differences in metabolic rates, which are known to be highly correlated
with body mass in this group. Our results support previous findings of body
size effects and show that this effect can be significant even within a
single avian order. This suggests that even lineage-specific molecular
clocks may not be tenable if calibrations involve taxa with different
metabolic rates.
相似文献
52.
Most of L-asparaginase activity of Tetrahymena pyriformis was found to be present in microsomal membranes from which it has been purified to homogeneity (Tsirka, S.A.E. and Kyriakidis, D.A. Mol. Cell. Biochem. 83: 147–155, 1988). The native enzyme has a relative molecular weight of approximately 200 kDa, while under denaturing conditions the enzyme exhibits. a subunit size of 39 kDa. Aminoacid analysis and an oligopeptide from N-terminal sequence have been determined. Dephosphorylation of L-asparaginase by alkaline phosphatase results in an activation of its catalytic activity. This enzyme also exhibits intrinsic phosphorylation activity with a Km value for ATP of 0.5 mM. Autophosphorylation with -32P ATP of purified L-asparaginase results in the phosphorylation of tyrosine residues as well as in loss of its activity. Mg2+ and Ca2+ added together act synergistically to stimulate the kinase activity by more than 160%. The polyamines putrescine, spermidine and spermine activate the kinase approximately 100%, while neither cAMP or cGMP have any effect. These results indicate that this membrane protein with dual L-asparaginase/kinase activity must play an important role in regulating the intracellular levels of L-asparagine in Tetrahymena pyriformis. 相似文献
53.
54.
Molecular evolution of chloroplast DNA sequences 总被引:13,自引:1,他引:12
Comparative data on the evolution of chloroplast genes are reviewed. The
chloroplast genome has maintained a similar structural organization over
most plant taxa so far examined. Comparisons of nucleotide sequence
divergence among chloroplast genes reveals marked similarity across the
plant kingdom and beyond to the cyanobacteria (blue-green algae). Estimates
of rates of nucleotide substitution indicate a synonymous rate of 1.1 x
10(-9) substitutions per site per year. Noncoding regions also appear to be
constrained in their evolution, although addition/deletion events are
common. There have also been evolutionary changes in the distribution of
introns in chloroplast encoded genes. Relative to mammalian mitochondrial
DNA, the chloroplast genome evolves at a conservative rate.
相似文献
55.
A. Laperche Y. Aigu M. Jubault M. Ollier S. Guichard P. Glory SE. Strelkov A. Gravot MJ. Manzanares-Dauleux 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2017,130(4):669-684
Key message
Nitrogen levels can modulate the effectiveness of clubroot resistance in an isolate- and host-specific manner. While the same QTL were detected under high and low nitrogen, their effects were altered.Abstract
Clubroot, caused by Plasmodiophora brassicae, is one of the most damaging diseases of oilseed rape and is known to be affected by nitrogen fertilization. However, the genetic factors involved in clubroot resistance have not been characterized under nitrogen-limiting conditions. This study aimed to assess the variability of clubroot resistance under different nitrogen levels and to characterize the impact of nitrogen supply on genetic resistance factors. Linkage analyses and a genome-wide association study were conducted to detect QTL for clubroot resistance and evaluate their sensitivity to nitrogen. The clubroot response of a set of 92 diverse oilseed rape accessions and 108 lines derived from a cross between ‘Darmor-bzh’ (resistant) and ‘Yudal’ (susceptible) was studied in the greenhouse under high- and low-nitrogen conditions, following inoculation with the P. brassicae isolates eH and K92-16. Resistance to each isolate was controlled by a major QTL and a few small-effects QTL. While the same QTL were detected under both high and low nitrogen, their effects were altered. Clubroot resistance to isolate eH, but not K92-16, was greater under a low-N supply versus a high-N supply. New sources of resistance were found among the oilseed rape accessions under both low and high-N conditions. The results are discussed relative to the literature and from a crop improvement perspective.56.
Fourteen native strains of Trichoderma spp. from wildand agricultural pathosystems in the state of Yucatan, Mexico, with growth-promoting ability of Capsicum chinense Jacq. seedlings were evaluated and antagonistic effect of their filtrate against second-stage juveniles (J2) of Meloidogyne incognita. The strains Th05-02 and Th27-08 showed the best significant effects on plant hight variable increments 55.57 and 47.62%, theTh07-04 with 29.48% more root length, theTh02-01 and Th07-04 isolates increased from 48.71 to 84.61% in volume radical and 53.40% of total dry biomass. Statistical analysis (p≤0.001) of Th43 and Th43-13-14 filtrates caused 100% mortality at 24 and 48h. In the test of reversibility to 24 h after replacing the filtrates Th43-13, Th43-14, TH09-06 and TH20-07 by sterile distilled water, the J2 did not recover their viability, so they were considered as the best potential strains of Trichoderma spp. with antagonistic capacity in J2 of M.incognita. 相似文献
57.
In Tetrahymena pyriformis the cytosolic ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) activity is considerably inhibited by the presence of polyamines in the growth medium, while the nuclear ornithine decarboxylase is only slightly affected. Experimental evidence suggests that the presence of putrescine and/or spermidine elicits the appearance of non-competitive inhibitors of ornithine decarboxylase. One of the inhibitors has a molecular weight of 25,000 and properties of antizyme. In addition, two other low molecular weight inhibitors are extracted, one which is a phosphoserine oligopeptide, and the other which is phosphotyrosine. All inhibit non-competitively the homologous and heterologous (Escherichia coli and rat liver) ornithine decarboxylases. Similarly, non-competitive inhibition was obtained when the commercially available phosphoamino acids were tested against the already mentioned ornithine decarboxylases. 相似文献
58.
The ant genus Prenolepis (Hymenoptera: Formicidae) is the nominal member of the recently established Prenolepis genus‐group within the subfamily Formicinae. Our molecular phylogenetic analyses using fragments from five nuclear genes (arginine kinase, carbomoylphosphate synthase, elongation factor 1‐alpha F1, elongation factor 1‐alpha F2, wingless) and one mitochondrial gene (cytochrome oxidase I) indicate that this genus is polyphyletic. Although the majority of Prenolepis species was found to belong to the same monophyletic group (Prenolepis sensu stricto), a smaller subset of Prenolepis species, all found in either Central America or the Greater Antilles, was robustly inferred to comprise a distinct lineage that is sister to the Old World genus Paraparatrechina. Here we describe this newly discovered lineage within the larger Prenolepis genus‐group clade. The genus Zatania, gen.n. is composed of five extant species (Zatania albimaculata, Zatania cisipa, Zatania gibberosa, Zatania gloriosa, sp.n. and Zatania karstica) and one Dominican amber fossil species (Zatania electra?, sp.n. ). These are medium‐sized ants (generally between 2.5 and 3 mm in total length) that are characterized by having long scapes and legs, and elongated mesosomata. A reliance on worker‐based taxonomy has previously prevented the discovery of this new lineage because of worker convergence consisting of various combinations of elongated mesosomata, long scapes and legs, and a constriction immediately behind the pronotum, observed in several distinct lineages within the Prenolepis genus‐group. However, we did find that male morphology complements our molecular results in revealing important diagnostic and potentially phylogenetically informative characters. Our study highlights the value for ant systematics to expand beyond its traditional foundation of worker‐based morphology and embrace character systems from other castes and molecular data. 相似文献
59.
The effects of selective ibotenate lesions of the complete hippocampus (CHip), the hippocampal ventral pole (VP), or the medial prefrontal cortex (mPFC) in male rats were assessed on several measures related to energy regulation (i.e., body weight gain, food intake, body adiposity, metabolic activity, general behavioral activity, conditioned appetitive responding). The testing conditions were designed to minimize the nonspecific debilitating effects of these surgeries on intake and body weight. Rats with CHip and VP lesions exhibited significantly greater weight gain and food intake compared with controls. Furthermore, CHip-lesioned rats, but not rats with VP lesions, showed elevated metabolic activity, general activity in the dark phase of the light-dark cycle, and greater conditioned appetitive behavior, compared with control rats without these brain lesions. In contrast, rats with mPFC lesions were not different from controls on any of these measures. These results indicate that hippocampal damage interferes with energy and body weight regulation, perhaps by disrupting higher-order learning and memory processes that contribute to the control of appetitive and consummatory behavior. 相似文献
60.
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