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排序方式: 共有121条查询结果,搜索用时 31 毫秒
1.
Cytopathology of pathogenic and nonpathogenic Naegleria species for cultured rat neuroblastoma cells. 总被引:2,自引:0,他引:2
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The cytopathology for rat neuroblastoma cells (B-103) and the pathogenicity for B6C3F1 mice of four species of Naegleria have been compared. Both live amoebae and cell-free extracts of N. australiensis, N. fowleri, N. gruberi, and N. lovaniensis added to 51Cr-labeled B-103 cells caused release of radiolabel. All four species of Naegleria exhibited surface extensions termed food cups. Only N. fowleri and N. australiensis were pathogenic for mice. Electron microscopic observations of cultures of either N. australiensis or N. lovaniensis with B-103 cells established that the cytopathology involved lysis of the B-103 target cells. 相似文献
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Fulford AJ 《Parasitology today (Personal ed.)》1994,10(11):446-448
Geometric means are frequently used to estimate the intensity of parasite infection within a population. In this article, Tony Fulford uses Schistosoma mansoni field data to illustrate that such estimates are biased and, more importantly, that the degree of bias can vary markedly with host age. Similar problems plague the interpretation of prevalence. The cause can be traced back to age-dependent differences in the dispersion of parasites among hosts. 相似文献
3.
AB Zarafi AM Emechebe AD Akpa O Alabi 《Archives Of Phytopathology And Plant Protection》2013,46(4):261-268
Pearl millet downy mildew (DM) incidence, severity and yield losses of two pearl millet varieties (local and improved) due to the disease were determined in the field. Significant differences in the disease incidence and severity were recorded in the plots sown with metalaxyl-treated seeds and those sown with non-treated seeds, indicating the efficacy of the fungicide on the fungus. Yield losses due to non-treatment of seeds with metalaxyl was 40.88 and 45.39% in a local variety and 43.00 and 18.60% in an improved variety in the 2000 and 2001 cropping seasons respectively. Significant differences between plots sown with metalaxyl-treated and those sown with non-treated seeds were obtained for other yield components such as 1000-grains weight, panicle length and weight. 相似文献
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Background
Organisms are capable of developing different phenotypes by altering the genes they express. This phenotypic plasticity provides a means for species to respond effectively to environmental conditions. One of the most dramatic examples of phenotypic plasticity occurs in the highly social hymenopteran insects (ants, social bees, and social wasps), where distinct castes and sexes all arise from the same genes. To elucidate how variation in patterns of gene expression affects phenotypic variation, we conducted a study to simultaneously address the influence of developmental stage, sex, and caste on patterns of gene expression in Vespula wasps. Furthermore, we compared the patterns found in this species to those found in other taxa in order to investigate how variation in gene expression leads to phenotypic evolution. 相似文献7.
Fulford P 《BMJ (Clinical research ed.)》1999,318(7192):1213-1214
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In humans and other mammals, some females are more likely to experience twin pregnancies than others, but the reasons behind such individual variation are poorly understood. One hypothesis invokes variation in the dynamics of the insulin-like growth factor (IGF) system, which also regulates foetal growth. Using data from a rural African population living in a highly seasonal environment, we test a novel prediction generated by this hypothesis, that maternal twinning status predicts offspring birthweight. We found that among singleton offspring who experience a favourable in utero environment (born January-June), births before and after twins are, respectively, associated with a 134.07 g and 226.41 g increase in birthweight compared with those born to non-twinning mothers. These results were not mediated by maternal anthropometry. This is consistent with a role for the IGF system in individual variation in twinning propensity, a possibility with implications for understanding mechanisms of life-history variation in humans and other vertebrates. 相似文献
10.
Jones MB Fulford GR Please CP McElwain DL Collins MJ 《Bulletin of mathematical biology》2008,70(2):323-343
This paper presents an elastohydrodynamic model of the human eyelid wiper. Standard lubrication theory is applied to the fluid
layer between the eyelid wiper and ocular surface. The role of the lubrication film is to reduce the shear stresses by preventing
solid to solid contact between the eyelid wiper and ocular surface. For the lubrication film to be effective, it is required
that the orientation of the eyelid wiper changes between the opening and closing phases of a blink. In order to model this,
the hydrodynamic model is coupled with an elastic mattress model for the soft tissue of the eyelid wiper and ocular surface.
This leads to a one-dimensional non-linear partial differential equation governing the fluid pressure in the lubrication film.
In order to solve the differential equation, a loading condition or constraint equation must be specified. The resulting system
is then solved numerically. The model allows predictions of the tear film flux from under the upper eyelid, as well as normal
and shear stresses acting on the ocular surface. These factors are important in relation to dry eye syndrome, deformation
of the cornea and contact lens design. It is found that the pressure and shear stress under the eyelid act across a length
of approximately 0.1 mm which is consistent with clinical observations. It order to achieve a flow of tears from under the
upper eyelid during a blink, the model requires that the normal force the eyelid applies to the ocular surface during the
closing phase of the blink is significantly higher than during the opening phase of the blink.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献