首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   42篇
  免费   4篇
  46篇
  2020年   1篇
  2019年   3篇
  2018年   3篇
  2017年   2篇
  2016年   3篇
  2015年   7篇
  2014年   3篇
  2013年   6篇
  2012年   5篇
  2011年   1篇
  2009年   5篇
  2008年   2篇
  2003年   1篇
  2002年   1篇
  2001年   1篇
  1999年   1篇
  1991年   1篇
排序方式: 共有46条查询结果,搜索用时 15 毫秒
1.
The hermaphroditic marine snail species Haminella solitaria was formerly included in the genus Haminoea, but it was recently assigned to the genus Haminella. The copulatory apparatus in H. solitaria was investigated by light and transmission electron microscopy to obtain additional information about this apparatus in cephalaspidean gastropods and to evaluate the taxonomic relevance of its morphofunctional features in the framework of a new phylogenetic tree of the family Haminoeidae. The copulatory apparatus in H. solitaria consisted of the atrium with a muscular wall and papilla, a seminal duct, and a single‐lobed prostate. Epithelial and subepithelial secretory cells were detected in the proximal and middle region of the atrium wall, and a third type of secretory cell occurred in the distal region of the muscular papilla. The seminal duct was lined by ciliated cells and its muscular wall included some vacuolar cells. The prostate in H. solitaria consisted of lateral pouches surrounding a large central lumen that was filled with spermatozoa. A single type of secretory cell intermingled with ciliated cells formed the epithelium of the prostate. A histological comparison between the copulatory apparatus in H. solitaria and Haminoea navicula revealed substantial differences that support the placement of these two species in different genera, as established by recent molecular studies.  相似文献   
2.
3.
The owlet moths (Lepidoptera: Noctuidae) Anicla infecta (Ochsenheimer 1816), Elaphria agrotina (Guenée 1852) and Spodoptera frugiperda (J.E. Smith 1797) occur in the entire American continent. These polyphagous moths have a preference for grasses, and have different biological habits. In this study, the populations of these three species were evaluated monthly with light traps in the Brazilian Savannah, ranging a span of four crop seasons (from July, 2013 to June, 2017). The population data were analyzed and correlated with the meteorological variables: maximum temperature, minimum temperature, relative humidity and precipitation. A total of 4719 individuals were collected in the following percentages: A. infecta (n = 459; 9.73%), E. agrotina (n = 1809; 38.33%) and S. frugiperda (n = 2451; (51.94%). The abundance of all species went down from the first crop season (2013/2014) to the third (2015/2016). In the fourth crop season (2016/2017), the populations of A. infecta and E. agrotina stabilized, but the abundance of S. frugiperda experienced further decrease. The numbers of individuals of three species declined when precipitation was much above (crop season 2014/2015) and below (crop season 2015/2016) than expected by the climatological normal. There were significant, but different degrees of correlation, between the meteorological factors and the ONI index (Oceanic Niño Index - indicator for monitoring El Niño-Southern Oscillation or “ENSO”) with respect to monthly population variations. The results are discussed in accordance with principles of the Integrated Pest Management (IPM) in mind, given the continental distribution and agricultural importance of the three owlet moth species studied.  相似文献   
4.
Schistosomes undergo various morphological and metabolic changes during their development, reflected in a finely tuned regulation of protein and/or gene expression. The mechanisms involved in the control of gene expression during the development of the parasite are not understood. Two actin genes had been previously cloned and observed to be differentially expressed during the maturation of the parasite. The SmAct gene contains four putative cis-regulatory elements (TATA-, CCAAT-, E- and CArG-boxes). Our objective was to investigate in greater detail the expression pattern of two actin genes and verify if the binding of nuclear proteins to the promoter elements of SmAct correlated with the expression profile observed. We detected little variation in the expression of actin genes during the first seven days of schistosomula culture in vitro. However, we observed significantly higher levels of expression in males compared to female adults. CArG and CCAAT elements bound to a greater extent and formed distinct complexes with male in comparison to female nuclear extracts. In contrast, female extracts bound weakly to the E-box probe while no binding was observed with male extracts. Taken together these results describe cis-acting elements that appear to be involved in sexually regulated gene expression in Schistosoma mansoni.  相似文献   
5.
Records of the occurrence of wild relatives of maize in South American lowlands are unprecedented, especially in sympatric coexistence with landraces. This fact is relevant, because regions of occurrence of wild relatives of cultivated plants should be a priority for conservation, even if they do not correspond to the center of origin of the species. The aim of this study was to identify and characterize the wild relatives of maize in the Far West of Santa Catarina, southern Brazil. Therefore, phenotypic characterization was performed for five populations, based on 22 morphological traits deemed as fundamental for classifying the species of the genus Zea, and validated through the characterization of chromosomal knobs of two populations. The occurrence and distribution of teosinte populations were described through semi-structured interviews applied to a sample of 305 farmers. A total of 136 teosinte populations were identified; 75% of them occur spontaneously, 17% are cultivated populations, and 8% occur both ways, for the same farm. Populations that were characterized morphologically had trapezoidal fruits mostly, upright tassel branch (4–18), non-prominent main branch and glabrous glumes, with two protruding outer ribs and 8 inner ribs, on average. Cytogenetic analysis identified 10 pairs of homologous chromosomes (2n = 20) with 26 knobs, located in the terminal region of all chromosomes. The similarity of these results with the information reported in the literature indicates that the five populations of wild relatives of maize in this region of Santa Catarina belong to the botanical species Zea luxurians.  相似文献   
6.
Aphids cause significant damage to crop plants. Studies regarding predator-prey relationships in fennel (Foeniculum vulgare Mill.) and cotton (Gossypium hirsutum L.) crops are important for understanding essential ecological interactions in the context of intercropping and for establishing pest management programs for aphids. This study evaluated the association among Hyadaphis foeniculi (Passerini) (Hemiptera: Aphididae), Aphis gossypii Glover (Hemiptera: Aphididae) and Cycloneda sanguinea (L.) (Coleoptera: Coccinellidae) in cotton with coloured fibres, fennel and cotton intercropped with fennel. Association analysis was used to investigate whether the presence or absence of prey and predator species can indicate possible interactions between aphids and ladybugs. Significant associations among both apterous and alate H. foeniculi and C. sanguinea were observed in both the fennel and fennel-cotton intercropping systems. The similarity analysis showed that the presence of aphids and ladybugs in the same system is significantly dependent on the type of crop. A substantial amount of evidence indicates that the presence of the ladybug C. sanguinea, is associated with apterous or alate A. gossypii and H. foeniculi in fennel-cotton intercropping system. We recommend that future research vising integrated aphid management taking into account these associations for take decisions.  相似文献   
7.
8.
We investigated the cytokine profile of peripheral mononuclear cells from chronic osteomyelitis (OST) patients following in vitro stimulation with staphylococcal enterotoxin A (SEA). We demonstrate that stimulation with SEA induced prominent lymphocyte proliferation and high levels of tumour necrosis factor (TNF)-α, interleukin (IL)-4 and IL-10 secretion in both OST and non-infected individuals (NI). Even though stimulation with SEA had no impact on IL-6 production in either patient group, the baseline level of IL-6 production by cells from OST patients was always significantly less than that produced by cells from NI. After classifying the osteomyelitic episodes based on the time after the last reactivation event as "early" (1-4 months) or "late" osteomyelitis (5-12 months), we found that increased levels of TNF-α and IL-4 in combination with decreased levels of IL-6 were observed in the early episodes. By contrast, increased levels of IL-10, IL-2 and IL-6 were hallmarks of late episodes. Our data demonstrate that early osteomyelitic episodes are accompanied by an increased frequency of "high producers" of TNF-α and IL-4, whereas late events are characterised by increased frequencies of "high producers" of IL-10, IL-6 and IL-2. These findings demonstrate the distinct cytokine profiles in chronic osteomyelitis, with a distinct regulation of IL-6 production during early and late episodes.  相似文献   
9.
The potential of using a synthetic cardosin-based rennet in cheese manufacturing was recently demonstrated with the development and optimization of production of a recombinant form of cardosin B in Kluyveromyces lactis. With the goal of providing a more detailed characterization of this rennet, we herein evaluate the impact of the plant-specific insert (PSI) on cardosin B secretion in this yeast, and provide a thorough analysis of the specificity requirements as well as the biochemical and structural properties of the isolated recombinant protease. We demonstrate that the PSI domain can be substituted by different linker sequences without substantially affecting protein secretion and milk clotting activity. However, the presence of small portions of the PSI results in dramatic reductions of secretion yields in this heterologous system. Kinetic characterization and specificity profiling results clearly suggest that synthetic cardosin B displays lower catalytic efficiency and is more sequence selective than native cardosin B. Elucidation of the structure of synthetic cardosin B confirms the canonical fold of an aspartic protease with the presence of two high mannose-type, N-linked glycan structures; however, there are some differences in the conformation of the flap region when compared to cardosin A. These subtle variations in catalytic properties and the more stringent substrate specificity of synthetic cardosin B help to explain the observed suitability of this rennet for cheese production.  相似文献   
10.
Multibody simulations of human motion require representative models of the anatomical structures. A model that captures the complexity of the foot is still lacking. In the present work, two detailed 3D multibody foot-ankle models generated based on CT scans using a semi-automatic tool are described. The proposed models consists of five rigid segments (talus, calcaneus, midfoot, forefoot and toes), connected by five joints (ankle, subtalar, midtarsal, tarsometatarsal and metatarsophalangeal), one with 15DOF and the other with 8DOF. The calculated kinematics of both models were evaluated using gait trials and compared against literature, both presenting realistic results. An inverse dynamic analysis was performed for the 8DOF model, again presenting feasible dynamic results.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号