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   546篇
  免费   47篇
  国内免费   1篇
耳鼻咽喉   4篇
儿科学   11篇
妇产科学   9篇
基础医学   82篇
口腔科学   3篇
临床医学   66篇
内科学   83篇
皮肤病学   15篇
神经病学   75篇
特种医学   17篇
外科学   34篇
预防医学   46篇
眼科学   3篇
药学   84篇
中国医学   2篇
肿瘤学   60篇
  2023年   3篇
  2022年   7篇
  2021年   26篇
  2020年   5篇
  2019年   6篇
  2018年   7篇
  2017年   12篇
  2016年   13篇
  2015年   23篇
  2014年   15篇
  2013年   29篇
  2012年   43篇
  2011年   29篇
  2010年   17篇
  2009年   11篇
  2008年   26篇
  2007年   21篇
  2006年   28篇
  2005年   24篇
  2004年   18篇
  2003年   19篇
  2002年   22篇
  2001年   12篇
  2000年   11篇
  1999年   10篇
  1998年   9篇
  1997年   6篇
  1995年   4篇
  1994年   7篇
  1993年   2篇
  1992年   8篇
  1991年   8篇
  1990年   7篇
  1989年   11篇
  1988年   7篇
  1987年   9篇
  1986年   13篇
  1985年   12篇
  1984年   6篇
  1983年   2篇
  1982年   8篇
  1981年   6篇
  1980年   6篇
  1979年   2篇
  1977年   5篇
  1976年   3篇
  1975年   2篇
  1973年   3篇
  1972年   2篇
  1954年   1篇
排序方式: 共有594条查询结果,搜索用时 31 毫秒
1.

Background  

It has been observed that ras-transformed cell lines in culture have a higher phosphatidylcholine (PC) biosynthesis rate as well as higher PC-degradation rate (increased PC-turnover) than normal cells. In correspondence to these findings, the concentrations of the PC-degradation product lyso-phosphatidylcholine (LPC) in cancer patients were found to be decreased. Our objective was the systematic investigation of the relationship between LPC and inflammatory and nutritional parameters in cancer patients. Therefore, plasma LPC concentrations were assessed in 59 cancer patients and related to nutritional and inflammatory parameters. To determine LPC in blood plasma we developed and validated a HPTLC method.  相似文献   
2.
Abstract: Blast cells derived from peripheral blood of patients with acute myelogenous leukaemia (AML) were cultured in vitro and interleukin 1 receptor antagonist (IL1RA) concentrations determined in culture supernatants. AML blasts derived from patients classified as AML-M4 and AML-M5 subtype showed an increased release of IL1RA. IL1α and IL1β caused a similar increase in AML blast release of IL1RA, and addition of anti-ILl antibodies decreased IL1RA release. IL1RA release from AML blasts was also increased by stem cell factor, tumour necrosis factor α (TNFα), granulocyte-macrophage colony-stimulating factor and macrophage colony-stimulating factor, whereas interleukin 3, interleukin 6, leukaemia inhibitory factor and granulocyte colony- stimulating factor did not significantly alter IL1RA release. When investigating IL1RA serum levels, serum concentrations were decreased in acute leukaemia patients with chemotherapy-induced cytopenia compared with healthy controls. Serum levels of both IL1RA as well as IL1β and soluble TNFα receptors increased when the leucopenic patients developed complicating bacterial infections.  相似文献   
3.
The alpha-galactosyl-1,4-beta-galactosyl-specific adhesin (P adhesin) was isolated from the fimbria-adhesin complex (FAC) of recombinant Escherichia coli strains expressing the F7(1), F8, or F13 fimbrial antigens. Separation into fimbriae and adhesin was achieved by heating the FAC to 80 degrees C in the presence of Zwittergent 3-16. After removal of the fimbriae by precipitation with lithium chloride, the adhesin was purified by anion-exchange fast protein liquid chromatography in the presence of 4 M urea. The purified adhesins from the three strains had pIs of 4.8 to 5.0 and molecular weights of approximately 35,000. The fimbrillins were smaller, their molecular weights being different with different F antigens. The amino-terminal amino acid sequence of the F7(1)- and F13-derived adhesins were different, that of the F13-derived adhesin being identical to that extrapolated from the DNA sequence of the papG gene (B. Lund, G. Lindberg, B.-I. Marklund, and S. Normark, Proc. Natl. Acad. Sci. USA 84:5898-5902). An antiadhesive monoclonal antibody which reacted with the three P adhesins was prepared. The FAC and the purified adhesins but not the fimbriae from which the adhesins had been removed agglutinated erythrocytes and galactose-galactose-coated latex beads. The adhesion of erythrocytes to the surface-fixed adhesins could be specifically inhibited with alpha-galactosyl-1,4-beta-galactosyl-1,4-glucosyl. The results indicate that the P adhesin(s) of uropathogenic E. coli represents a group of related proteins with conserved receptor recognition domains. The F13-derived P adhesin is the PapG protein postulated by Normark and his colleagues (Lund et al., Proc. Natl. Acad. Sci. USA 84:5898-5902; B. Lund, F. Lindberg, and S. Normark, J. Bacteriol. 170:1887-1894).  相似文献   
4.
S fimbrial adhesins (Sfa), which are able to recognize sialic acid-containing receptors on eukaryotic cells, are produced by Escherichia coli strains causing urinary tract infections or newborn meningitis. We recently described the cloning and molecular characterization of a determinant, termed sfaI, from the chromosome of an E. coli urinary tract infection strain. Here we present data concerning a S fimbria-specific gene cluster, designated sfaII, of an E. coli newborn meningitis strain. Like the SfaI complex, SfaII consists of the major subunit protein SfaA (16 kDa) and the minor subunit proteins SfaG (17 kDa), SfaS (15 kDa), and SfaH (29 kDa). The genes encoding the subunit proteins of SfaII were identified and sequenced. Their protein sequences were calculated from the DNA sequences and compared with those of the SfaI complex subunits. Although the sequences of the two major SfaA subunits differed markedly, the sequences of the minor subunits showed only a few amino acid exchanges (SfaG, SfaH) or were completely identical (SfaS). The introduction of a site-specific mutation into the gene sfaSII and subsequent analysis of an SfaS-negative clone indicated that sfaSII codes for the sialic acid-specific adhesin of the meninigitis isolate. These data were confirmed by the isolation and characterization of the SfaSII protein and the determination of its N-terminal amino acid sequence. The identity between the sialic acid-specific adhesins of SfaI and SfaII revealed that differences between the two Sfa complexes with respect to their capacities to agglutinate erythrocytes must result from sequence alterations of subunit proteins other than SfaS.  相似文献   
5.
We established hybridoma cell lines producing monoclonal antibodies against enterobacterial common antigen (ECA) and a substructure of the outer core of different Escherichia coli lipopolysaccharides (LPSs). Anti-ECA antibodies 865 and 898 reacted with ECA in extracts of heated E. coli and with ECA-bound R1 and R4 core-containing LPS preparations, as well as with a purified sample of ECA from Salmonella montevideo. Antibody 865, but not antibody 898, cross-reacted with K5 capsular polysaccharide, suggesting that 4-linked alpha-N-acetylglucosamine is part of an antigenic determinant shared by both K5 polysaccharide and ECA. Anti-LPS antibody 786 recognized an outer core structure common to E. coli K-12, B, R2, and R4 core type LPS, but not to R1 and R3 core type LPS. Its most probable target is the trisaccharide sequence Hexp(1----2)-alpha-D -Glcp(1----3) alpha-D-Glcp----(Hepp) (where Hex is hexose, p is phosphate, Glc is glucose, and Hep is heptose), the first glucose being the immunodominant moiety. These monoclonal antibodies may be used not only for the detection of ECA, K5, and LPS core structures but also for analysis of the molecular forms resolved on polyacrylamide gels (banding patterns) of both ECA and LPS, independently of one another.  相似文献   
6.
Characterization of pili associated with Escherichia coli O18ac.   总被引:5,自引:15,他引:5       下载免费PDF全文
A strain of Escherichia coli O18ac isolated from the stool sample of a patient with diarrhea was found to agglutinate human erythrocytes. From the results presented it is suggested that this hemagglutination is mediated by pili. Isolated pilus preparations agglutinated human erythrocytes, whereas pilus-negative mutants did not. The serological and chemical analyses indicate that the pili associated with E. coli O18ac are distinct from other types found with E. coli.  相似文献   
7.
8.
The chromosomally encoded nonfimbrial adhesion I (NFA-I) from Escherichia coli urinary tract isolate 827 (O83:K1:H4) mediates agglutination of human erythrocytes. Subclones were constructed from an NFA-I-expressing recombinant E. coli K-12 clone, derived from a genomic library of E. coli 827. Minicell analysis and nucleotide sequencing revealed that proteins of 30.5, 9, 80, 15, and 19 kDa encoded on a stretch of approximately 6 kb are involved in the expression of NFA-I. NFA-I exhibits a polymeric structure, which disintegrates with elevated temperature into a 19-kDa monomer but with some relatively stable dimers. By using gold-conjugated monoclonal antibodies directed against NFA-I in electron microscopy, the adhesin could be localized on the outer surface of the recombinant E. coli K-12 bacteria. The nucleotide sequence of the nfaA gene encoding the monomeric structural subunit of the adhesin was determined. An open reading frame of 184 amino acids encoding the NfaA precursor, which is processed to the mature protein, was found; it consisted of 156 amino acids with a calculated molecular weight of 16,000. Peptide sequencing of the NFA-I subunit protein confirmed that this open reading frame corresponds to the NfaA coding locus. Furthermore, the nucleotide sequence of the open reading frame termed NfaE, located at the proximal part of the DNA stretch responsible for NFA-I expression, was elaborated. NfaE consists of 247 amino acids, including a presumptive 29-amino-acid signal peptide, leading to a molecular weight of 24,000 for the mature protein. The nfaE sequence shares homology with the 27-kDa CS3 protein, which is involved in the assembly of CS3 fibrillae, and might encode the 30.5-kDa protein, detected in minicells.  相似文献   
9.
Six 8-week-old Sprague-Dawley rats were studied for 9 days divided into three periods of 3 days each: before transferral to metabolism cages, during metabolic cage housing and after return to their home cages. Faeces were collected daily when the animals were housed in their home cages and every 6 h when the animals were housed in metabolic cages during which time urine was also collected every 6 h. The rate of weight gain was slightly reduced during the 3 days in metabolic cages and the animals produced significantly larger amounts of faeces when housed in metabolic cages than when housed in their home cages. The total faecal excretion of corticosterone (nanograms excreted per hour per kilogram body weight) and immunoglobulin A (IgA) (milligrams excreted per hour per kg body weight) quantified by enzyme-linked immunosorbent assays (ELISAs) exhibited a clear diurnal rhythm in the metabolic cage. Urinary excretions of corticosterone and IgA also followed a clear diurnal cycle. The mean daily amounts of corticosterone excreted were not significantly affected by cage change and by housing in metabolic cages. However, the excretion of faecal IgA was significantly reduced during the 3 days after the period in metabolic cages. Taken together the results indicate that metabolic cage housing is mildly stressful for young adult male rats.  相似文献   
10.
Changes in intestinal microbiome and barrier function are critical in the development of alcohol-related liver disease (ALD). Here, we determined the effects of a one-week alcohol withdrawal on parameters of intestinal barrier function in heavy drinkers with ALD in comparison to healthy non-drinkers (controls). In serum samples of 17 controls (m = 10/f = 7) and 37 age-matched ALD patients (m = 26/f = 11) undergoing a one-week alcohol withdrawal, markers of liver health and intestinal barrier function were assessed. Liver damage, e.g., fibrosis and hepatic steatosis, were assessed using FibroScan. Before alcohol withdrawal, markers of liver damage, lipopolysaccharide binding protein (LBP) and overall TLR4/TLR2 ligands in serum were significantly higher in ALD patients than in controls, whereas intestinal fatty acid binding protein (I-FABP) and zonulin protein concentrations in serum were lower. All parameters, with the exception of LBP, were significantly improved after alcohol withdrawal; however, not to the level of controls. Our data suggest that one-week of abstinence improves markers of intestinal barrier function and liver health in ALD patients.  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