全文获取类型
收费全文 | 569篇 |
免费 | 47篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 13篇 |
2020年 | 6篇 |
2019年 | 4篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 20篇 |
2014年 | 19篇 |
2013年 | 24篇 |
2012年 | 28篇 |
2011年 | 36篇 |
2010年 | 19篇 |
2009年 | 17篇 |
2008年 | 35篇 |
2007年 | 22篇 |
2006年 | 28篇 |
2005年 | 22篇 |
2004年 | 18篇 |
2003年 | 20篇 |
2002年 | 13篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 17篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 14篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 15篇 |
1989年 | 7篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1972年 | 5篇 |
1970年 | 3篇 |
1963年 | 2篇 |
排序方式: 共有616条查询结果,搜索用时 78 毫秒
101.
Anthony Makkinje Richard I. Near Giuseppe Infusini Pierre Vanden Borre Alexander Bloom Dongpo Cai Catherine E. Costello Adam Lerner 《Cellular signalling》2009,21(9):1423-1435
NSP protein family members associate with p130Cas, a focal adhesion adapter protein best known as a Src substrate that integrates adhesion-related signaling. Over-expression of AND-34/BCAR3/NSP2 (BCAR3), but not NSP1 or NSP3, induces anti-estrogen resistance in human breast cancer cell lines. BCAR3 over-expression in epithelial MCF-7 cells augments levels of a phosphorylated p130Cas species that migrates more slowly on SDS-PAGE while NSP1 and NSP3 induce modest or no phosphorylation, respectively. Conversely, reduction in BCAR3 expression in mesenchymal MDA-231 cells by inducible shRNA results in loss of such p130Cas phosphorylation. Replacement of NSP3's serine/proline-rich domain with that of AND-34/BCAR3 instills the ability to induce p130Cas phosphorylation. Phospho-amino acid analysis demonstrates that BCAR3 induces p130Cas serine phosphorylation. Mass spectrometry identified phosphorylation at p130Cas serines 139, 437 and 639. p130Cas serine phosphorylation accumulates for several hours after adhesion of MDA-231 cells to fibronectin and is dependent upon BCAR3 expression. BCAR3 knockdown alters p130Cas localization and converts MDA-231 growth to an epithelioid pattern characterized by striking cohesiveness and lack of cellular projections at colony borders. These studies demonstrate that BCAR3 regulates p130Cas serine phosphorylation that is adhesion-dependent, temporally distinct from previously well-characterized rapid Fak and Src kinase-mediated p130Cas tyrosine phosphorylation and that correlates with invasive phenotype. 相似文献
102.
David C. Young Anne Kasmar Garrett Moraski Tan-Yun Cheng Andrew J. Walz Jingdan Hu Yanping Xu Gregory W. Endres Adam Uzieblo Dirk Zajonc Catherine E. Costello Marvin J. Miller D. Branch Moody 《The Journal of biological chemistry》2009,284(37):25087-25096
Mycobacterium tuberculosis survival in cells requires mycobactin siderophores. Recently, the search for lipid antigens presented by the CD1a antigen-presenting protein led to the discovery of a mycobactin-like compound, dideoxymycobactin (DDM). Here we synthesize DDMs using solution phase and solid phase peptide synthesis chemistry. Comparison of synthetic standards to natural mycobacterial mycobactins by nuclear magnetic resonance and mass spectrometry allowed identification of an unexpected α-methyl serine unit in natural DDM. This finding further distinguishes these pre-siderophores as foreign compounds distinct from conventional peptides, and we provide evidence that this chemical variation influences the T cell response. One synthetic DDM recapitulated natural structures and potently stimulated T cells, making it suitable for patient studies of CD1a in infectious disease. DDM analogs differing in the stereochemistry of their butyrate or oxazoline moieties were not recognized by human T cells. Therefore, we conclude that T cells show precise specificity for both arms of the peptide, which are predicted to lie at the CD1a-T cell receptor interface.Pathogens are detected by the host when antigenic molecules directly contact immune receptors during the early stages of infection. The strategy of intracellular infection allows viruses, certain bacteria and protozoa to partially cloak themselves from the immune response by physically encapsulating their antigens within host cells. Intracellular residence also takes advantage of immune tolerance mechanisms that prevent autoimmune destruction of self. T cells play a central role in immunity to intracellular pathogens because they can respond to antigens that are generated inside cells and then transported to the surface of infected cells after binding to antigen-presenting molecules. The antigen-presenting molecules encoded in the major histocompatibility complex are widely known for presenting peptide fragments of proteins (1). More recently, human and mouse members of the CD1 (cluster of differentiation 1) system have been shown to present small amphipathic molecules, including a variety of membrane lipids, glycolipids, and lipopeptides, greatly expanding the molecular structures recognized by the cellular immune system (2, 3).Among human CD1 proteins (CD1a, CD1b, CD1c, CD1d, and CD1e), each CD1 isoform is expressed on a different spectrum of antigen-presenting cells. Human CD1a proteins are distinguished from other CD1 proteins by high expression levels on the surface of intradermal Langerhans cells, which play a role in barrier immune function (4). Human T cell clones have been shown to directly recognize CD1a proteins in the presence of exogenous foreign antigens (5) or in the presence of sulfatide and other self lipids (6, 7), suggesting a role for CD1a in T cell activation. In addition, mycobacteria and other intracellular pathogens have been shown to increase CD1a expression in lesions found in leprosy and tuberculosis patients, implying a possible role for CD1a in the response to infection, especially at mucosal or skin sites (8–10). Analysis of the molecular target recognized by CD1a-restricted T cell clone (CD8-2) allowed the identification of a foreign antigen presented by CD1a as dideoxymycobactin (DDM) (11).2Mycobactin binds iron to promote Mycobacterium tuberculosis survival. DDM was initially isolated (11) from antigenic lipid extracts of M. tuberculosis, a pathogen that kills ∼1.7 million humans annually on a worldwide basis (12). The determination of DDM structure was based on mass spectrometric and NMR studies of limiting amounts of natural material derived from the pathogenic organisms, so that not all elements of its chemical structure could be formally determined. Instead, its assigned structure was facilitated by obvious parallels of dideoxymycobactin with mycobactin, a lipopeptide siderophore (13, 14). Iron is required for reduction-oxidation reactions involving respiration and other basic metabolic pathways in bacterial pathogens (13). Environmental mycobacteria have at least two iron uptake pathways, but mycobactin and the related molecule carboxymycobactin represent the only known dedicated iron uptake pathway for pathogenic species like M. tuberculosis (15, 16). Highlighting the physiological importance of the mycobactin pathway, deletion of mycobactin synthase B limits M. tuberculosis survival in cells (13, 14). Also, mammalian innate immune systems produce siderocalin, a 20-kDa lipocalin that binds both ferric and apo siderophores, preventing their uptake and subsequent iron delivery to microbes (17–20). The small available yields of natural material highlighted the need for a straightforward method to synthesize DDM for studies of its role in mycobacterial iron acquisition and testing T cell responses in human populations, as well as to provide authentic standards to investigate unknown aspects of natural DDM stereochemistry. Here we report two syntheses for production of DDM in solution phase and solid phase. Comparison of synthetic and natural DDMs gives unexpected insight into the stereochemical structures of the methylserine, oxazoline, and butyrate moieties of DDM and provides direct evidence that the T cell response is highly specific for a unique aspect of DDM structure that protrudes from the surface of the CD1a-DDM complexes. 相似文献
103.
Gregory O. Staples Michael J. Bowman Catherine E. Costello Alicia M. Hitchcock James M. Lau Nancy Leymarie Christine Miller Hicham Naimy Xiaofeng Shi Joseph Zaia Professor 《Proteomics》2009,9(3):686-695
A key challenge to investigations into the functional roles of glycosaminoglycans (GAGs) in biological systems is the difficulty in achieving sensitive, stable, and reproducible mass spectrometric analysis. GAGs are linear carbohydrates with domains that vary in the extent of sulfation, acetylation, and uronic acid epimerization. It is of particular importance to determine spatial and temporal variations of GAG domain structures in biological tissues. In order to analyze GAGs from tissue, it is useful to couple MS with an on‐line separation system. The purposes of the separation system are both to remove components that inhibit GAG ionization and to enable the analysis of very complex mixtures. This contribution presents amide–silica hydrophilic interaction chromatography (HILIC) in a chip‐based format for LC/MS of heparin, heparan sulfate (HS) GAGs. The chip interface yields robust performance in the negative ion mode that is essential for GAGs and other acidic glycan classes while the built‐in trapping cartridge reduces background from the biological tissue matrix. The HILIC chromatographic separation is based on a combination of the glycan chain lengths and the numbers of hydrophobic acetate (Ac) groups and acidic sulfate groups. In summary, chip based amide‐HILIC LC/MS is an enabling technology for GAG glycomics profiling. 相似文献
104.
Kristen R. Freeman Monte Y. Pescador Sasha C. Reed Elizabeth K. Costello Michael S. Robeson Steven K. Schmidt 《Environmental microbiology》2009,11(3):674-686
Soil-dominated ecosystems, with little or no plant cover (i.e. deserts, polar regions, high-elevation areas and zones of glacial retreat), are often described as 'barren', despite their potential to host photoautotrophic microbial communities. In high-elevation, subnival zone soil (i.e. elevations higher than the zone of continuous vegetation), the structure and function of these photoautotrophic microbial communities remains essentially unknown. We measured soil CO2 flux at three sites (above 3600 m) and used molecular techniques to determine the composition and distribution of soil photoautotrophs in the Colorado Front Range. Soil CO2 flux data from 2002 and 2007 indicate that light-driven CO2 uptake occurred on most dates. A diverse community of Cyanobacteria , Chloroflexi and eukaryotic algae was present in the top 2 cm of the soil, whereas these clades were nearly absent in deeper soils (2–4 cm). Cyanobacterial communities were composed of lineages most closely related to Microcoleus vaginatus and Phormidium murrayi , eukaryotic photoautotrophs were dominated by green algae, and three novel clades of Chloroflexi were also abundant in the surface soil. During the light hours of the 2007 snow-free measurement period, CO2 uptake was conservatively estimated to be 23.7 g C m−2 season−1 . Our study reveals that photoautotrophic microbial communities play an important role in the biogeochemical cycling of subnival zone soil. 相似文献
105.
Chad Laing Cody Buchanan Eduardo N Taboada Yongxiang Zhang Andrew Kropinski Andre Villegas James E Thomas Victor PJ Gannon 《BMC bioinformatics》2010,11(1):461
Background
The pan-genome of a bacterial species consists of a core and an accessory gene pool. The accessory genome is thought to be an important source of genetic variability in bacterial populations and is gained through lateral gene transfer, allowing subpopulations of bacteria to better adapt to specific niches. Low-cost and high-throughput sequencing platforms have created an exponential increase in genome sequence data and an opportunity to study the pan-genomes of many bacterial species. In this study, we describe a new online pan-genome sequence analysis program, Panseq. 相似文献106.
107.
Tularemia is a severe infectious disease in humans caused by the Gram-negative bacterium Francisella tularensis (Ft). Because of its low infectious dose, high mortality rate, and the threat of its large-scale dissemination in weaponized form, development of vaccines and immunotherapeutics against Ft is essential. Ft lipopolysaccharide (LPS), which contains the linear graded-length saccharide component O-antigen (OAg) attached to a core oligosaccharide, has been reported as a protective antigen. Purification of LPS saccharides of defined length and composition is necessary to reveal the epitopes targeted by protective antibodies. In this study, we purified saccharides from LPS preparations from both the Ft subspecies holarctica live vaccine strain (LVS) and the virulent Ft subspecies tularensis SchuS4 strain using liquid chromatography. We then characterized the fractions using high-resolution mass spectrometry and tandem mass spectrometry. Three types of saccharides were observed in both the LVS and SchuS4 preparations: two consisting of OAg tetrasaccharide repeats attached to one of two core oligosaccharide variants and one consisting of tetrasaccharide repeats only (coreless). The coreless OAg oligosaccharides were shown to contain Qui4NFm (4,6-dideoxy-4-formamido-D-glucose) at the nonreducing end and QuiNAc (2-acetamido-2,6-dideoxy-O-D-glucose) at the reducing end. Purified homogeneous preparations of saccharides of each type will allow mapping of protective epitopes in Ft LPS. 相似文献
108.
There now exists a resurgence of interest in the role of intermediary metabolism in medicine; especially in relation to medical disorders. Coupled with this is the contemporary focus on molecular biology, genetics and proteomics and their integration into studies of regulation and alterations in cellular metabolism in health and disease. This is a marriage that has vast potential for elucidation of the factors and conditions that are involved in cellular metabolic and functional changes, which heretofore could not be addressed by the earlier generations of biochemists who established the major pathways of intermediary metabolism. The achievement of this present potential requires the appropriate application and interpretation of genetic and proteomic studies relating to cell metabolism and cell function. This requires knowledge and understanding of the principles, relationships, and methodology, such as biochemistry and enzymology, which are involved in the elucidation of cellular regulatory enzymes and metabolic pathways. Unfortunately, many and possibly most contemporary molecular biologists are not adequately trained and knowledgeable in these areas of cell metabolism. This has resulted in much too common inappropriate application and misinformation from genetic/proteomic studies of cell metabolism and function. This presentation describes important relationships of cellular intermediary metabolism, and provides examples of the appropriate and inappropriate application of genetics and proteomics. It calls for the inclusion of biochemistry, enzymology, cell metabolism and cell physiology in the graduate and postgraduate training of molecular biology and other biomedical researchers. 相似文献
109.
White Nicholas J Ashley Elizabeth A Recht Judith Delves Michael J Ruecker Andrea Smithuis Frank M Eziefula Alice C Bousema Teun Drakeley Chris Chotivanich Kesinee Imwong Mallika Pukrittayakamee Sasithon Prachumsri Jetsumon Chu Cindy Andolina Chiara Bancone Germana Hien Tran T Mayxay Mayfong Taylor Walter RJ von Seidlein Lorenz Price Ric N Barnes Karen I Djimdé Abdoulaye ter Kuile Feiko Gosling Roly Chen Ingrid Dhorda Mehul J Stepniewska Kasia Guérin Philippe Woodrow Charles J Dondorp Arjen M Day Nicholas PJ Nosten Francois H 《Malaria journal》2014,13(1):1-14