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1.
The enzymatic activity of salivary amylase bound to the surface of several species of oral streptococci was determined by the production of acid from starch and by the degradation of maltotetraose to glucose in a coupled, spectrophotometric assay. Most strains able to bind amylase exhibited functional enzyme on their surface and produced acid from the products of amylolytic degradation. These strains were unable to utilise starch in the absence of salivary amylase. Two strains failed to produce acid from starch, despite the presence of functional salivary amylase, because they could not utilise maltose. Strains that could not bind salivary amylase failed to produce acid from starch. In no case was all the bound salivary amylase active, and two strains of Streptococcus mitis which bound amylase did not exhibit any enzyme activity on their cell surface. The ability to bind amylase may confer a survival advantage on oral bacteria which inhabit hosts that consume diets containing starch. 相似文献
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3.
Summary During an ultrastructural study of the eggs of the serpulid wormPomatoceros triqueter L., annulate lamellae were frequently encountered in the cytoplasm. In particular, some observations indicated that they
originate by successive outfoldings of the nuclear envelope. Consequently, annulate lamellae must consist of alternating layers
of nuclear and cytoplasmic material, each layer being separated by part of the nuclear envelope. It was observed that there
was a similarity between nuclear and inter-annulate lamellar material. Moreover tritiated thymidine was shown to be present
in the stacks. It is inferred that this system might well function as an efficient means of transporting nuclear material
into the cytoplasm.
The authors wish to thank Messrs. P. C. Lloyd, P. Henley and D. Williams for technical assistance. 相似文献
4.
Major histocompatibility complex (Mhc) genes influencing transplantation rejections were first described in mice within the H2 complex and secondly in chickens within the B complex. In chickens, Rfp-Y haplotypes have recently been identified which contain class I and class II Mhc-like genes that assort independently of the B complex. Three Rfp-Y haplotypes have been defined in a closed breeding flock of line N chickens. In this study, progeny were obtained from line
N Rfp-Y heterozygous matings to establish the role of Rfp-Y in transplantation immunity. Rfp-Y incompatibility did not induce significant one-way mixed lymphocyte responses. However, Rfp-Y-incompatible skin grafts were rejected more frequently and at a faster rate than Rfp-Y-compatible grafts by two-week-old chicks. The control Mhc B-incompatible grafts were rejected faster than the Rfp-Y-incompatible grafts; the latter were rejected at speeds that resemble rejection of minor histocompatibility antigens. We
conclude that Rfp-Y class I and II Mhc-like genes are linked to the expression of minor histocompatibility antigens in chickens.
Received: 21 June 1996 / Revised: 23 July 1996 相似文献
5.
Approaches to breeding for salinity tolerance - a case study on Porteresia coarctata 总被引:2,自引:0,他引:2
R LATHA C SRINIVAS RAO H M SR SUBRAMANIAM P EGANATHAN M S SWAMINATHAN 《The Annals of applied biology》2004,144(2):177-184
Cereals are the world's major source of food for human nutrition. Among these, rice (Oryza sativa) is the most prominent and represents the staple diet for more than two-fifths (2.4 billion) of the world's population, making it the most important food crop of the developing world (Anon., 2000a). Rice production in vast stretches of coastal areas is hampered due to high soil salinity. This is because rice is a glycophyte and it does not grow well under saline conditions. In order to increase rice production in these areas there is a need to develop rice varieties suited to saline environments. Research has shown that Porteresia coarctata, a highly salt tolerant wild relative of rice growing in estuarine soils, is an important material for transferring salt tolerant characteristics to rice. It is quite possible that Porteresia may be used as a parent for evolving better and truly salt resistant varieties. The inadequate results and the difficulties associated with conventional breeding techniques necessitate the use of the tools of crop biotechnology in unravelling some of the characteristics of Porteresia that have been highlighted in this report. In view of the limited resources available for increasing salinity tolerance to the breeders to wild rice germplasm, Porteresia is undoubtedly one of the key source species for elevating salinity tolerance in cultivated rice. 相似文献
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Rosalind J. Dodd David R. Chadwick Ian M. Harris Adrian Hines Dan Hollis Theodoros Economou Dylan Gwynn‐Jones John Scullion David A. Robinson David L. Jones 《Ecology letters》2021,24(1):60-72
Extreme weather events have become a dominant feature of the narrative surrounding changes in global climate with large impacts on ecosystem stability, functioning and resilience; however, understanding of their risk of co‐occurrence at the regional scale is lacking. Based on the UK Met Office’s long‐term temperature and rainfall records, we present the first evidence demonstrating significant increases in the magnitude, direction of change and spatial co‐localisation of extreme weather events since 1961. Combining this new understanding with land‐use data sets allowed us to assess the likely consequences on future agricultural production and conservation priority areas. All land‐uses are impacted by the increasing risk of at least one extreme event and conservation areas were identified as the hotspots of risk for the co‐occurrence of multiple event types. Our findings provide a basis to regionally guide land‐use optimisation, land management practices and regulatory actions preserving ecosystem services against multiple climate threats. 相似文献
8.
R. Geoffrey Richards Iolo ap Gwynn Kirk J. Bundy Berton A. Rahn 《Cell biology international》1995,19(12):1015-1024
Adhesion of cells to biomaterial surfaces is one of the major factors which mediates their biocompatibility. Quantitative or qualitative cell adhesion measurements would be useful for screening new implant materials. Microjet impingement has been evaluated by scanning electron microscopy, to determine to what extent it measures cell adhesion. The shear forces of the impingement, on the materials tested here, are seen to be greater than the cohesive strength of the cells in the impinged area, causing their rupture. The cell bodies are removed during impingement, leaving the sites of adhesion and other cellular material behind. Thus the method is shown not to provide quantification of cell adhesion forces for the metals and culture plastic tested. It is suggested that with highly adherent biomaterials, the distribution and patterns of these adhesion sites could be used for qualitative comparisons for screening of implant surfaces. 相似文献
9.
Identification, evolution, and essentiality of the mevalonate pathway for isopentenyl diphosphate biosynthesis in gram-positive cocci 下载免费PDF全文
Wilding EI Brown JR Bryant AP Chalker AF Holmes DJ Ingraham KA Iordanescu S So CY Rosenberg M Gwynn MN 《Journal of bacteriology》2000,182(15):4319-4327
The mevalonate pathway and the glyceraldehyde 3-phosphate (GAP)-pyruvate pathway are alternative routes for the biosynthesis of the central isoprenoid precursor, isopentenyl diphosphate. Genomic analysis revealed that the staphylococci, streptococci, and enterococci possess genes predicted to encode all of the enzymes of the mevalonate pathway and not the GAP-pyruvate pathway, unlike Bacillus subtilis and most gram-negative bacteria studied, which possess only components of the latter pathway. Phylogenetic and comparative genome analyses suggest that the genes for mevalonate biosynthesis in gram-positive cocci, which are highly divergent from those of mammals, were horizontally transferred from a primitive eukaryotic cell. Enterococci uniquely encode a bifunctional protein predicted to possess both 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and acetyl-CoA acetyltransferase activities. Genetic disruption experiments have shown that five genes encoding proteins involved in this pathway (HMG-CoA synthase, HMG-CoA reductase, mevalonate kinase, phosphomevalonate kinase, and mevalonate diphosphate decarboxylase) are essential for the in vitro growth of Streptococcus pneumoniae under standard conditions. Allelic replacement of the HMG-CoA synthase gene rendered the organism auxotrophic for mevalonate and severely attenuated in a murine respiratory tract infection model. The mevalonate pathway thus represents a potential antibacterial target in the low-G+C gram-positive cocci. 相似文献
10.
Etienne Karita Matt A Price Shabir Lakhi William Kilembe Anatoli Kamali Eugene Ruzagira Eric Hunter Paul Farmer Susan Allen Gwynn Stevens Paramesh Chetty Sabrina Welsh Annie Yang Jill Gilmour Pat Fast The IAVI Africa HIV Prevention Partnership 《PloS one》2015,10(8)