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   34篇
  免费   1篇
理论与方法论   1篇
现状及发展   8篇
研究方法   2篇
综合类   13篇
自然研究   11篇
  2020年   1篇
  2019年   1篇
  2018年   2篇
  2017年   3篇
  2016年   3篇
  2015年   2篇
  2013年   1篇
  2012年   1篇
  2011年   5篇
  2010年   2篇
  2008年   1篇
  2007年   2篇
  2006年   2篇
  2005年   2篇
  2004年   1篇
  2003年   1篇
  2002年   1篇
  1984年   2篇
  1976年   2篇
排序方式: 共有35条查询结果,搜索用时 15 毫秒
11.
I analyse the case of three Japanese-Portuguese interpreters who have given support to technology transfer from a steel company in Japan to one in Brazil for more than thirty years. Their job requires them to be ‘interactional experts’ in steel-making. The Japanese–Portuguese interpreters are immersed in more than the language of steel-making as their job involves a great deal of ‘physical contiguity’ with steel-making practice. Physical contiguity undoubtedly makes the acquisition of interactional expertise easier. This draws attention to the lack of empirical work on the exact way that the physical and the linguistic interact in the acquisition of interactional expertise, or any other kind of expertise.  相似文献   
12.
Ramírez SR  Gravendeel B  Singer RB  Marshall CR  Pierce NE 《Nature》2007,448(7157):1042-1045
Since the time of Darwin, evolutionary biologists have been fascinated by the spectacular adaptations to insect pollination exhibited by orchids. However, despite being the most diverse plant family on Earth, the Orchidaceae lack a definitive fossil record and thus many aspects of their evolutionary history remain obscure. Here we report an exquisitely preserved orchid pollinarium (of Meliorchis caribea gen. et sp. nov.) attached to the mesoscutellum of an extinct stingless bee, Proplebeia dominicana, recovered from Miocene amber in the Dominican Republic, that is 15-20 million years (Myr) old. This discovery constitutes both the first unambiguous fossil of Orchidaceae and an unprecedented direct fossil observation of a plant-pollinator interaction. By applying cladistic methods to a morphological character matrix, we resolve the phylogenetic position of M. caribea within the extant subtribe Goodyerinae (subfamily Orchidoideae). We use the ages of other fossil monocots and M. caribea to calibrate a molecular phylogenetic tree of the Orchidaceae. Our results indicate that the most recent common ancestor of extant orchids lived in the Late Cretaceous (76-84 Myr ago), and also suggest that the dramatic radiation of orchids began shortly after the mass extinctions at the K/T boundary. These results further support the hypothesis of an ancient origin for Orchidaceae.  相似文献   
13.
Primary triple-negative breast cancers (TNBCs), a tumour type defined by lack of oestrogen receptor, progesterone receptor and ERBB2 gene amplification, represent approximately 16% of all breast cancers. Here we show in 104 TNBC cases that at the time of diagnosis these cancers exhibit a wide and continuous spectrum of genomic evolution, with some having only a handful of coding somatic aberrations in a few pathways, whereas others contain hundreds of coding somatic mutations. High-throughput RNA sequencing (RNA-seq) revealed that only approximately 36% of mutations are expressed. Using deep re-sequencing measurements of allelic abundance for 2,414 somatic mutations, we determine for the first time-to our knowledge-in an epithelial tumour subtype, the relative abundance of clonal frequencies among cases representative of the population. We show that TNBCs vary widely in their clonal frequencies at the time of diagnosis, with the basal subtype of TNBC showing more variation than non-basal TNBC. Although p53 (also known as TP53), PIK3CA and PTEN somatic mutations seem to be clonally dominant compared to other genes, in some tumours their clonal frequencies are incompatible with founder status. Mutations in cytoskeletal, cell shape and motility proteins occurred at lower clonal frequencies, suggesting that they occurred later during tumour progression. Taken together, our results show that understanding the biology and therapeutic responses of patients with TNBC will require the determination of individual tumour clonal genotypes.  相似文献   
14.
Summary Fatty acid anilides, the major xenobiotic found in the cooking oils responsible for the Spanish toxic oil syndrome, are immunogenic for rabbits as ascertained by a skin test reaction, the characterization of specific antibodies against anilides and the immunofluorescent detection of anilide dependent antigens in tissue slices from treated animals.Acknowledgments. This work was supported by a grant from the Fondo de Investigaciones Sanitarias to the C.S.I.C. Programme on Toxic Oil Syndrome. We are indebted to Dr M. Studt and Dr E. Fernández-Alvarez, from the National Center for Organic Chemistry, C.S.I.C., for kindly providing the synthetic fatty acid anilides. We also wish to thank Prof. C. Gitler for helpful discussion.  相似文献   
15.
Comets spend most of their life in a low-temperature environment far from the Sun. They are therefore relatively unprocessed and maintain information about the formation conditions of the planetary system, but the structure and composition of their nuclei are poorly understood. Although in situ and remote measurements have derived the global properties of some cometary nuclei, little is known about their interiors. The Deep Impact mission shot a projectile into comet 9P/Tempel 1 in order to investigate its interior. Here we report the water vapour content (1.5 10(32) water molecules or 4.5 10(6) kg) and the cross-section of the dust (330 km2 assuming an albedo of 0.1) created by the impact. The corresponding dust/ice mass ratio is probably larger than one, suggesting that comets are 'icy dirtballs' rather than 'dirty snowballs' as commonly believed. High dust velocities (between 110 m s(-1) and 300 m s(-1)) imply acceleration in the comet's coma, probably by water molecules sublimated by solar radiation. We did not find evidence of enhanced activity of 9P/Tempel 1 in the days after the impact, suggesting that in general impacts of meteoroids are not the cause of cometary outbursts.  相似文献   
16.
Brazil has the richest anuran biodiversity in the world and many species have not yet been studied for parasites. One hundred and forty frogs belonging to 18 species (Rhinella schneideri, Dendropsophus aff. minutus, Dendropsophus nanus, Hypsiboas albopunctatus, Hypsiboas punctatus, Hypsiboas raniceps, Phyllomedusa tetraploidea, Pseudis platensis, Scinax fuscovarius, Trachycephalus typhonius, Leptodactylus chaquensis, Leptodactylus fuscus, Leptodactylus aff. latrans, Leptodactylus mystacinus, Leptodactylus podicipinus, Physalaemus cuvieri, Physalaemus nattereri and Elachistocleis bicolor) collected in aquatic habitats in forest remnants and surrounding agricultural landscapes in southern Brazil were examined for endoparasites. Twenty-four species of endoparasites were identified among 21 adult and three larval individuals: one species of Monogenea, Polystoma lopezromani; eight species of Digenea, Catadiscus marinholutzi, Catadiscus propinquus, Choledocystus simulans, Gordoderina sp., Neohaematoloechus neivai, Rauschiella lenti, Rauschiella linguatula, Rauschiella repandum; one species of Cestoda, Ophiotaenia sp.; one species of Acanthocephala, Centrorhyncus sp.; 12 species of Nematoda, Aplectana sp., Aplectana travassosi, Cosmocerca podicipinus, Raillietnema sp., Schrankiana formolusa, Falcaustra mascula, Oxyascaris oxyascaris, Ochoterenella digiticauda, Physaloptera sp., Brevimulticecum sp., Rhabdias sp., Parapharyngodon hylidae; and one species of Annelida, Dero (Allodero) lutzi. The endoparasite fauna found is constituted by generalist species. Two new records of occurrence in Brazil and 33 new host records are reported.  相似文献   
17.
Predictive modeling of geographic distribution based on ecological niche has become an important tool in ecology. It uses previous information about distribution of species and environmental variations associated with this distribution, restricting to the models the closest prediction of the ecological niche. The eumastacid grasshoppers are distributed mainly in the Neotropical region, and Temnomastacinae is the subfamily with the largest geographic distribution. Little is known about the biology of Eumastacidae, the only data available reporting the association between some grasshopper species and plants of several families. In the Cerrado only Temnomastax is recorded, which has a wide distribution in the central region of Brazil. The aim of this work was to determine the potential geographic distribution of three species of Temnomastax occurring in the Cerrado biome. We used 446 records of occurrence obtained in specialised literature, inventories, museums and photographs, from the following species: Temnomastax hamus, Temnomastax ricardoi and Temnomastax tigris. The niche modeling was generated with the bioclimatic model DOMAIN through DIVA-GIS. The potential geographic distribution of T. hamus is the largest among all Temnomastax species. Temnomastax ricardoi has its potential distribution in the central-north of Mato Grosso do Sul, in regions surrounding the type locality, while T. tigris. exhibits a restricted potential distribution along the carbonate arc of the Corumbá Formation, which outcrops in the region of Serra da Bodoquena and Corumbá, entering the eastern portion of Bolivia.  相似文献   
18.
Cuticular hydrocarbons (CHs) contain complex mixtures of components that cover the surface of all insects to restrict water loss, and in many species function in chemical communication. The complex mixtures have been used as a chemotaxonomic tool since the 1970s. The majority of CH components can be identified by gas chromatography-mass spectrometry (GC-MS), allowing hydrocarbon profiles to be used as chemotaxonomic characters, which can differentiate insect species, including cryptic species. The present study used GC-MS for the identification of CHs of males and females of three species of calliphorids: Cochliomyia macellaria (Fabricius), Hemilucilia segmentaria (Fabricius) and Lucilia cuprina (Wiedmann), A comparison of the chromatographic profiles from the three species allows them to be readily separated. Hydrocarbons identified from the three species contain 23 to 37 carbons and include n-alkanes, methyl-branched alkanes and alkenes. The most abundant compound for both sexes of C. macellaria was n-heptacosane, while for H. segmentaria it was 2-methyltriacontane; for L. cuprina, however, the most abundant compound was hentriacontene for females and nonacosene for males. The results obtained in this study are important for the establishment of a database to be used in chemotaxonomy of sanitarily and forensically important insects.  相似文献   
19.
Zhao Y  Rodrigo J  Hoveyda AH  Snapper ML 《Nature》2006,443(7107):67-70
Reliable, selective and environmentally friendly chemical transformations are crucial to the development of new therapeutics and the design of novel materials. Chiral catalysts that can be easily prepared and used to obtain organic molecules of high enantiomeric purity are critical to modern chemical synthesis. The development of protecting groups that shield reactive functionalities has also proved indispensable in the preparation of complex biologically active molecules. Here we present a chiral catalyst that promotes the enantioselective protection of a secondary alcohol as one of the most commonly used protected forms of an alcohol: a silyl ether. The catalyst is a small, simple molecule that can be prepared in three steps from commercial materials without the need for rigorously controlled conditions. Enantioselective silylations are performed with commercial silyl chlorides and produce yields of up to 96 per cent at an enantiomeric ratio of up to 98:2. Chiral catalysts for selective formation of commonly used protecting groups such as silyl ethers should significantly enhance the ability of chemical synthesis to deliver, in a more practical and efficient manner, important organic molecules.  相似文献   
20.
Experiments with interactional expertise   总被引:1,自引:0,他引:1  
‘Interactional expertise’ is developed through linguistic interaction without full scale practical immersion in a culture. Interactional expertise is the medium of communication in peer review in science, in review committees, and in interdisciplinary projects. It is also the medium of specialist journalists and of interpretative methods in the social sciences. We describe imitation game experiments designed to make concrete the idea of interactional expertise. The experiments show that the linguistic performance of those well socialized in the language of a specialist group is indistinguishable from those with full blown practical socialization but distinguishable from those who are not well socialized. The imitation game can also be used to indicate whether an individual can enter an esoteric domain and master the interactional expertise, a skill required by interpretative sociologists of science, anthropologists, ethnographers, and the like.  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