全文获取类型
收费全文 | 410篇 |
免费 | 51篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 17篇 |
2013年 | 9篇 |
2012年 | 10篇 |
2011年 | 15篇 |
2010年 | 9篇 |
2009年 | 14篇 |
2008年 | 6篇 |
2007年 | 23篇 |
2006年 | 11篇 |
2005年 | 14篇 |
2004年 | 16篇 |
2003年 | 13篇 |
2002年 | 14篇 |
2001年 | 12篇 |
2000年 | 17篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 13篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1973年 | 3篇 |
1946年 | 4篇 |
1936年 | 3篇 |
1925年 | 2篇 |
1922年 | 2篇 |
排序方式: 共有461条查询结果,搜索用时 15 毫秒
171.
The binding of human complement component C4 to antibody-antigen aggregates. 总被引:10,自引:3,他引:7
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The binding of human complement component C4 to antibody-antigen aggregates and the nature of the interaction have been investigated. When antibody-antigen aggregates with optimal C1 bound are incubated with C4, the C4 is rapidly cleaved to C4b, but only a small fraction (1-2%) is bound to the aggregates, the rest remaining in the fluid phase as inactive C4b. It has been found that C4b and th antibody form a very stable complex, due probably to the formation of a covalent bond. On reduction of the C4b-immunoglobulin G (IgG) complex, the beta and gamma chains, but not the alpha' chain, of C4b are released together with all the light chain, but only about half of the heavy chain of IgG. The reduced aggregates contain two main higher-molecular-weight complexes, one shown by the use of radioactive components to contain both IgG and C4b and probably therefore the alpha' chain of C4b and the heavy chain of IgG, and the other only C4b and probably an alpha' chain dimer. The aggregates with bound C1 and C4b show maximal C3 convertase activity, in the presence of excess C2, when the alpha'-H chain component is in relatively highest amounts. When C4 is incubated with C1s in the absence of aggregates, up to 15% of a C4b dimer is formed, which on reduction gives an alpha' chain complex, probably a dimer. The apparent covalent interaction between C4b and IgG and between C4b and other C4b molecules cannot be inhibited by iodoacetamide and hence cannot be catalysed by transglutaminase (factor XIII). The reaction is, however, inhibited by cadaverine and putrescine and 14C-labelled putrescine is incorporated into C4, again by a strong, probably covalent, bond. It is suggested that a reactive group, possibly an acyl group, is generated when C4 is activated by C1 and that this reactive group can react with IgG, with another C4 molecule, or with water. 相似文献
172.
the culture of Jerusalem artichoke (Helianthus tuberosus L.) tuber explants on filter paper discs moistened with liquid medium resulted in rapid and consistent xylem differentiation. The number of tracheary elements increased in discrete steps, the first at 48 h with a second at 56–58 h, following partially synchronous mitoses at 20 and 30 h. Factors favouring xylem cell differentiation were optimum levels of both an auxin and a cytokinin, low medium nitrogen concentrations, small volumes of medium, and high culture temperatures. A cell counting method employing Feulgen-stained nuclei and suitable for quantifyings small numbers of immature tracheary elements is described.Abbreviations 2,4-D
2,4-Dichlorophenoxyacetic acid
- NAA
-naphthalene acetic acid
- BAP
benzylaminopurine
- GA3
gibberellic acid 相似文献
173.
Autoactive alleles of the flax L6 rust resistance gene induce non-race-specific rust resistance associated with the hypersensitive response 总被引:4,自引:0,他引:4
Howles P Lawrence G Finnegan J McFadden H Ayliffe M Dodds P Ellis J 《Molecular plant-microbe interactions : MPMI》2005,18(6):570-582
L6 is a nucleotide binding site-leucine rich repeat (NBS-LRR) gene that confers race-specific resistance in flax (Linum usitatissimum) to strains of flax rust (Melampsora lini) that carry avirulence alleles of the AvrL567 gene but not to rust strains that carry only the virulence allele. Several mutant and recombinant forms of L6 were made that altered either the methionine-histidine-aspartate (MHD) motif conserved in the NBS domain of resistance proteins or exchanged the short domain C-terminal to the LRR region that is highly variable among L allele products. In transgenic flax some of these alleles are autoactive; they cause a gene dosage-dependent dwarf phenotype and constitutive expression of genes that are markers for the plant defense response. Their effects and penetrance ranged from extreme to mild in their degree of plant stunting, survival, and reproduction. Dwarf plants were also resistant to flax rust strains virulent to wild-type L6 plants, and this nonspecific resistance was associated with a hypersensitive response (HR) at the site of rust infection. The strongest autoactive allele, expressed in Arabidopsis from an ethanol-inducible promoter, gave rise to plant death dependent on the enhanced disease susceptibility 1 (EDS1) gene, which indicates that the mutant flax (Linaceae) L6 gene can signal cell death through a defined disease-resistance pathway in a different plant family (Brassicaceae). 相似文献
174.
175.
Cytotoxic T-lymphocyte escape does not always explain the transient control of simian immunodeficiency virus SIVmac239 viremia in adenovirus-boosted and DNA-primed Mamu-A*01-positive rhesus macaques
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
McDermott AB O'Connor DH Fuenger S Piaskowski S Martin S Loffredo J Reynolds M Reed J Furlott J Jacoby T Riek C Dodds E Krebs K Davies ME Schleif WA Casimiro DR Shiver JW Watkins DI 《Journal of virology》2005,79(24):15556-15566
Adenovirus 5 (Ad5) vectors show promise as human immunodeficiency virus vaccine candidates. Indian rhesus macaques vaccinated with Ad5-gag controlled simian-human immunodeficiency virus SHIV89.6P viral replication in the absence of Env immunogens that might elicit humoral immunity. Here we immunized 15 macaques using either a homologous Ad5-gag/Ad5-gag (Ad5/Ad5) or a heterologous DNA-gag/Ad5-gag (DNA/Ad5) prime-boost regimen and challenged them with a high dose of simian immunodeficiency virus SIVmac239. Macaques vaccinated with the DNA/Ad5 regimen experienced a brief viral load nadir of less than 10,000 viral copies per ml blood plasma that was not seen in Mamu-A*01-negative DNA/Ad5 vaccinees, Mamu-A*01-positive Ad5/Ad5 vaccinees, or vaccine-naive controls. Interestingly, most of these animals were not durably protected from disease progression when challenged with SIVmac239. To investigate the reasons underlying this short-lived vaccine effect, we investigated breadth of the T-cell response, immunogenetic background, and viral escape from CD8+ lymphocytes that recognize immunodominant T-cell epitopes. We show that these animals do not mount unusually broad cellular immune response, nor do they express unusual major histocompatibility complex class I alleles. Viral recrudescence occurred in four of the five Mamu-A*01-positive vaccinated macaques. However, only a single animal in this group demonstrated viral escape in the immunodominant Gag181-189 CM9 response. These results suggest that viral "breakthrough" in vaccinated animals and viral escape are not inextricably linked and underscore the need for additional research into the mechanisms of vaccine failure. 相似文献
176.
Nadesalingam J Dodds AW Reid KB Palaniyar N 《Journal of immunology (Baltimore, Md. : 1950)》2005,175(3):1785-1794
Peptidoglycan (PGN) is the major cell wall component (90%, w/w) of Gram-positive bacteria and consists of N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) disaccharide repeating arrays that are cross-linked by short peptides. We hypothesized that PGN is a ligand for pathogen-associated pattern-recognition proteins. Mannose-binding lectin (MBL) and serum amyloid component P are two carbohydrate-binding innate immune proteins present in the blood. In this study we show that human MBL, but not serum amyloid component P, binds significantly to PGN via its C-type lectin domains, and that the interaction can be more effectively competed by GlcNAc than by MurNAc. Surface plasmon resonance analyses show that native MBL binds immobilized PGN with high avidity. Competition experiments also show that both native MBL and MBL(n/CRD), a 48-kDa recombinant trimeric fragment of MBL containing neck and carbohydrate recognition domains, have higher affinity for GlcNAc than for MurNAc. Protein arrays and ELISA show that PGN increases the secretion of TNF-alpha, IL-8, IL-10, MCP-2, and RANTES from PMA-stimulated human monocytic U937 cells. Interestingly, the presence of MBL together with PGN increases the production of IL-8 and RANTES, but reduces that of TNF-alpha. Our results indicate that Gram-positive bacterial is a biologically relevant ligand for MBL, and that the collectin preferentially binds to the GlcNAc moiety of the PGN via its C-type lectin domains. MBL inhibits PGN-induced production of proinflammatory cytokines while enhancing the production of chemokines by macrophages, which suggests that MBL may down-regulate macrophage-mediated inflammation while enhancing phagocyte recruitment. 相似文献
177.
Mutsuro J Tanaka N Kato Y Dodds AW Yano T Nakao M 《Journal of immunology (Baltimore, Md. : 1950)》2005,175(7):4508-4517
Duplication and diversification of several complement components is a striking feature of bony fish complement systems. It gives an interesting insight into an evolutionary strategy for the possible enhancement of the repertoire of innate immunity. The present study is aimed at examining diversity in bony fish C4, a member of the thioester-containing complement components. Two diverged cDNA sequences sharing only approximately 32% identity at the amino acid level were isolated from the common carp and designated C4-1 and C4-2. C4-1 and C4-2 share a number of C4-like structural signatures, such as the thioester site and a disulfide-linked three-chain structure. Interestingly, they differ at the residue corresponding to the thioester-catalytic histidine, as seen in the human C4A and C4B isotypes, suggesting their distinct substrate specificities in the binding reaction of the thioester. Phylogenetic analysis indicates that the divergence of C4-1 and C4-2 predated the separation of the cartilaginous and bony fish lineages. Genomic Southern hybridization suggests the presence of single copy genes each encoding C4-1 and C4-2 in the carp genome. An activation fragment, C4a, was shown to be released from each isotype in carp serum activated via the classical and/or lectin pathways. Synthetic peptides representing a putative C2 binding site on C4-1 and C4-2 inhibited the classical pathway-mediated hemolytic activity of carp serum in a dose-dependent manner. The results suggest that C4-1 and C4-2 represent two major lineages of C4 that are present in carp serum, have distinct binding specificities, and are functional in the classical/lectin pathways of complement activation. 相似文献
178.
Reduced representation sequencing detects only subtle regional structure in a heavily exploited and rapidly recolonizing marine mammal species
下载免费PDF全文
![点击此处可从《Ecology and evolution》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Nicolas Dussex Helen R. Taylor Willam R. Stovall Kim Rutherford Ken G. Dodds Shannon M. Clarke Neil J. Gemmell 《Ecology and evolution》2018,8(17):8736-8749
Next‐generation reduced representation sequencing (RRS) approaches show great potential for resolving the structure of wild populations. However, the population structure of species that have shown rapid demographic recovery following severe population bottlenecks may still prove difficult to resolve due to high gene flow between subpopulations. Here, we tested the effectiveness of the RRS method Genotyping‐By‐Sequencing (GBS) for describing the population structure of the New Zealand fur seal (NZFS, Arctocephalus forsteri), a species that was heavily exploited by the 19th century commercial sealing industry and has since rapidly recolonized most of its former range from a few isolated colonies. Using 26,026 neutral single nucleotide polymorphisms (SNPs), we assessed genetic variation within and between NZFS colonies. We identified low levels of population differentiation across the species range (<1% of variation explained by regional differences) suggesting a state of near panmixia. Nonetheless, we observed subtle population substructure between West Coast and Southern East Coast colonies and a weak, but significant (p = 0.01), isolation‐by‐distance pattern among the eight colonies studied. Furthermore, our demographic reconstructions supported severe bottlenecks with potential 10‐fold and 250‐fold declines in response to Polynesian and European hunting, respectively. Finally, we were able to assign individuals treated as unknowns to their regions of origin with high confidence (96%) using our SNP data. Our results indicate that while it may be difficult to detect population structure in species that have experienced rapid recovery, next‐generation markers and methods are powerful tools for resolving fine‐scale structure and informing conservation and management efforts. 相似文献
179.
S Avidon SM Marr TA Bellingan KJ Esler OLF Weyl 《African Journal of Aquatic Science》2018,43(3):313-318
We evaluated the impact of non-native rainbow trout Oncorhynchus mykiss on a population of endemic Cedarberg ghost frog Heleophryne depressa in the upper Krom River (Olifants-Doring River Catchment, Cape Fold Ecoregion). We compared H. depressa abundance (using kick-sampling and underwater video analysis) and environmental conditions between sites above and below a waterfall that marks the upper distribution limit of O. mykiss. Heleophryne depressa abundance was significantly greater above the waterfall than that below it, and, because there was no significant difference in measured environmental variables, O. mykiss presence is identified as the most likely explanation for the observed decrease in H. depressa abundance. 相似文献
180.
Influence of Protozoa and Nutrient Availability on Nitrification Rates in Subsurface Sediments 总被引:2,自引:0,他引:2
Abstract
Protozoan abundance, nitrification potential, and related factors in saturated subsurface sediments and the overlying soil
were compared at a nonfertilized grassland and an agricultural cropland site. In a 6-week laboratory experiment, DOC, ammonium,
and protozoan abundance were manipulated in flasks containing groundwater-sediment slurries. Microbial abundance (protozoa,
actively respiring bacteria, and total bacteria) and nutrient concentrations (extractable ammonium and nitrate) were measured.
Results from the soil profile analysis showed that protozoan abundance declined with depth at both sites, but significant
numbers (392 cells g−1dw) were found in groundwater sediments at the cropland site. Nitrification potential declined with depth at the grassland
site and increased with depth at the cropland site. In the laboratory experiment, treatment responses generally were observed
within 3 weeks, but had diminished by 6 weeks. Protozoa reduced bacterial populations through the first 3 weeks, but this
effect was not significant by week 6. In the cropland sediments, increased net nitrate production occurred in the two reduced
protozoa treatments that received ammonium, suggesting that nitrification was occurring and was limited by ammonium. High
protozoan abundance in the cropland sediments increased the nitrate flux response, unless DOC was added; in this case, no
response occurred. No such responses were recorded in the grassland sediments.
Apparently, appreciable nitrification can occur in some groundwater sediments, if sufficient ammonium is present and DOC availability
is low. Furthermore, nitrification can be enhanced when protozoan abundance is elevated. Finally, our results suggest that
surface land use practices can alter subsurface nitrification rates and microbial community structure.
Received: 12 July 1996; Accepted: 2 December 1996 相似文献