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1.
JOÃO BATISTA TAVARES DA SILVA ISAAC ROITMAN 《The Journal of eukaryotic microbiology》1990,37(6):521-523
ABSTRACT. Three strains of Phytomonas serpens two from tomatoes, Lycopersicon esculentum one from the insect Phtia picta (Hemiptera, Coreidae), were cultivated in a chemically defined medium developed from a defined medium for cultivating insect flagellates. Besides organic growth factors required by other insect trypanosomatids this flagellate requires, serine and inositol. Glutamine stimulates growth, and, surprisingly, does not require heme. 相似文献
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Enzymatic deconstruction of xylan for biofuel production 总被引:1,自引:0,他引:1
The combustion of fossil-derived fuels has a significant impact on atmospheric carbon dioxide (CO2 ) levels and correspondingly is an important contributor to anthropogenic global climate change. Plants have evolved photosynthetic mechanisms in which solar energy is used to fix CO2 into carbohydrates. Thus, combustion of biofuels, derived from plant biomass, can be considered a potentially carbon neutral process. One of the major limitations for efficient conversion of plant biomass to biofuels is the recalcitrant nature of the plant cell wall, which is composed mostly of lignocellulosic materials (lignin, cellulose, and hemicellulose). The heteropolymer xylan represents the most abundant hemicellulosic polysaccharide and is composed primarily of xylose, arabinose, and glucuronic acid. Microbes have evolved a plethora of enzymatic strategies for hydrolyzing xylan into its constituent sugars for subsequent fermentation to biofuels. Therefore, microorganisms are considered an important source of biocatalysts in the emerging biofuel industry. To produce an optimized enzymatic cocktail for xylan deconstruction, it will be valuable to gain insight at the molecular level of the chemical linkages and the mechanisms by which these enzymes recognize their substrates and catalyze their reactions. Recent advances in genomics, proteomics, and structural biology have revolutionized our understanding of the microbial xylanolytic enzymes. This review focuses on current understanding of the molecular basis for substrate specificity and catalysis by enzymes involved in xylan deconstruction. 相似文献
3.
DANIEL M. GONZÁLEZ‐TOKMAN ISAAC GONZÁLEZ‐SANTOYO HUMBERTO LANZ‐MENDOZA ALEX CÓRDOBA AGUILAR 《Physiological Entomology》2010,35(4):364-372
Adaptive immunity allows vertebrates to gain protection against repeated pathogenic infections. Analogous responses (priming) have been recently uncovered in invertebrates. However, whether such responses are widespread is not known. The present study investigated the presence of immunological priming in males of a species whose phylogenetic position places it in one of the less derived insect orders. It is hypothesized that the efficiency of such a response could be related to animal condition, as assessed by the expression of a sexually selected ornament. Hetaerina americana Fabricius (Odonata: Calopterygidae) males bear a conspicuous ornament (a red wing spot), which is evolutionarily maintained via male territorial competition. Using field‐collected animals, a group of males is challenged with bacteria before exposure to a higher dose of the same or a different bacteria, and survival is compared with that of infected males not previously challenged, as well as control groups. Gram‐positive and Gram‐negative bacteria are used. To explore how long priming may take to work, the second exposure is carried out either after 1 or 5 days. Red spot and body size are entered in the analysis as predictors of survival within and between groups. There is no difference in survival among groups, which suggests no priming effect. Overall, red spot and body size are not consistent in explaining survival. 相似文献
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Wilt of lucerne caused by species of Verticillium 总被引:2,自引:0,他引:2
7.
IVOR ISAAC 《The Annals of applied biology》1953,40(4):630-638
An investigation has been made of the spread of Verticillium disease of tomato and antirrhinum by root contact between diseased and healthy plants, and by the growth of the fungi through the soil. V. alboatrum and V. Dahliae spread rapidly by root contact, while V. tricorpus, V. nigrescens and V. nubilum showed no appreciable spread. Where the tomato and antirrhinum hosts wilted and died the causal organism was invariably isolated from the soil near the roots of the dead plants, but where the inoculated host harboured species without showing disease symptoms, as in the case of V. tricorpus and V. nubilum in antirrhinum, the parasite was never obtained from the soil. Moreover, these species in antirrhinum, and V. nigrescens and V. nubilum in tomato would appear to be mild pathogens since when they were already well established V. alboatrum was later actually found to enter and parasitize the respective hosts and bring about its own typical disease symptoms.
Spread through the soil in the absence of hosts was tested by the insertion into it of infected wheat grains followed by later attempts to isolate the fungi at varying distances from the point of infection. V. alboatrum, V. Dahliae and V. tricorpus showed little or no growth through the soil, whereas V. nigrescens and V. nubilum spread saprophytically to some extent, though never attaining sufficient concentration to cause appreciable infection of later planted tomatoes.
The conclusion is reached that spread of disease caused by species of Verticillium takes place mainly by root contact, with a rapidity relatively proportional to that of the death of the host. This finding, together with the lack of spread from antirrhinum plants infected with the non-lethal V. tricorpus and V. nubilum , suggests that the parasites remain in the vascular tracts until the death of the hosts. 相似文献
Spread through the soil in the absence of hosts was tested by the insertion into it of infected wheat grains followed by later attempts to isolate the fungi at varying distances from the point of infection. V. alboatrum, V. Dahliae and V. tricorpus showed little or no growth through the soil, whereas V. nigrescens and V. nubilum spread saprophytically to some extent, though never attaining sufficient concentration to cause appreciable infection of later planted tomatoes.
The conclusion is reached that spread of disease caused by species of Verticillium takes place mainly by root contact, with a rapidity relatively proportional to that of the death of the host. This finding, together with the lack of spread from antirrhinum plants infected with the non-lethal V. tricorpus and V. nubilum , suggests that the parasites remain in the vascular tracts until the death of the hosts. 相似文献
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9.
JOANNE L. ISAAC 《Mammal Review》2005,35(1):101-115
1. Male-biased sexual size dimorphism (SSD) in mammals has been explained by sexual selection favouring large, competitive males. However, new research has identified other potential factors leading to SSD. The aim of this review is to evaluate current research on the causes of SSD in mammals and to investigate some consequences of SSD, including costs to the larger sex and sexual segregation. 2. While larger males appear to gain reproductive benefits from their size, studies have also identified alternative mating strategies, unexpected variance in mating success and found no clear relationship between degree of polygyny and dimorphism. This implies that sexual selection is unlikely to be the single selective force directing SSD. 3. Latitude seems to influence SSD primarily through variation in overall body size and seasonal food availability, which affect potential for polygyny. Likewise, population density influences resource availability and evidence suggests that food scarcity differentially constrains the growth of the sexes. Diverging growth patterns between the sexes appear to be the primary physiological mechanism leading to SSD. 4. Female-biased dimorphism is most adequately explained by reduced male–male competition resulting in a decrease in male size. Female–female competition for dominance and resources, including mates, may also select for increased female size. 5. Most studies found that sexual segregation arises through asynchrony of activity budgets between the sexes. The larger sex can suffer sex-biased mortality through increased parasite load, selective predation and the difficulty associated with sustaining a larger body size under conditions of resource scarcity. 6. None of the variables considered here appears to contribute a disproportionate amount to SSD in mammals. Several promising avenues of research are currently overlooked and long-term studies, which have previously been biased toward ungulates, should be carried out on a variety of taxa. 相似文献
10.
ISAAC PK 《Stain technology》1958,33(6):261-264