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   4104篇
  免费   169篇
  国内免费   13篇
耳鼻咽喉   37篇
儿科学   53篇
妇产科学   90篇
基础医学   554篇
口腔科学   102篇
临床医学   317篇
内科学   1088篇
皮肤病学   66篇
神经病学   277篇
特种医学   131篇
外科学   644篇
综合类   23篇
预防医学   133篇
眼科学   102篇
药学   157篇
中国医学   2篇
肿瘤学   510篇
  2023年   33篇
  2022年   54篇
  2021年   97篇
  2020年   44篇
  2019年   69篇
  2018年   101篇
  2017年   65篇
  2016年   70篇
  2015年   77篇
  2014年   108篇
  2013年   106篇
  2012年   170篇
  2011年   200篇
  2010年   122篇
  2009年   80篇
  2008年   141篇
  2007年   180篇
  2006年   170篇
  2005年   142篇
  2004年   135篇
  2003年   158篇
  2002年   144篇
  2001年   124篇
  2000年   122篇
  1999年   116篇
  1998年   31篇
  1997年   25篇
  1996年   24篇
  1995年   37篇
  1994年   27篇
  1992年   115篇
  1991年   118篇
  1990年   92篇
  1989年   98篇
  1988年   66篇
  1987年   74篇
  1986年   62篇
  1985年   62篇
  1984年   36篇
  1983年   30篇
  1979年   35篇
  1974年   61篇
  1973年   42篇
  1972年   40篇
  1971年   38篇
  1970年   42篇
  1969年   47篇
  1968年   46篇
  1967年   36篇
  1966年   23篇
排序方式: 共有4286条查询结果,搜索用时 15 毫秒
91.
92.
A preverbal toddler who presents with a distended abdomen can pose a difficult clinical problem. The differential diagnosis is extremely broad and consists of etiologies ranging from the benign to the life threatening. In this case report, we present 2 unusual life-threatening cases of abdominal distention in well-appearing toddlers and a review of the clinical evaluation for the emergency practitioner.  相似文献   
93.
High affinity insulin-like growth factor I (IGF-I) receptors are expressed by two human neural derived cell lines, SK-N-SH and SK-N-MC. Specific [125I]IGF-I binding to crude membranes was 23.4% for SK-N-SH and 10.7% for SK-N-MC, with 50% inhibition of binding by unlabeled IGF-I between 0.6-0.7 nM. Scatchard analysis of crude membrane binding was linear, whereas Scatchard analysis after wheat germ agglutinin purification of the receptor became curvilinear. The IGF-I receptor alpha-subunits of SK-N-SH have an apparent Mr of 126K, whereas that for SK-N-MC is 132K. Despite these differences in alpha-subunit structure both cell lines demonstrate IGF-I-induced autophosphorylation of their own beta-subunits as well as specific IGF-I induced tyrosine kinase activity, suggesting normal coupling between the ligand-binding alpha-subunit and the tyrosine kinase-containing beta-subunit. Furthermore, IGF-I stimulated iododeoxyuridine uptake in both SK-N-SH and SK-N-MC in a dose-dependent manner, suggesting that these cells may be used to study the role of IGF-I action on neural tissues.  相似文献   
94.
BACKGROUND AND AIMS: The roles of the virD4 and the cagG genes in the cag pathogenicity island of Helicobacter pylori for gastroduodenal pathogenesis are unclear and their roles in vivo have not been examined. METHODS: Seven week old male Mongolian gerbils were inoculated with the wild type H pylori TN2GF4, its isogenic virD4, or cagG mutants. Animals were sacrificed at 4, 12, and 24 weeks after inoculation. Gastric inflammation and H pylori density were evaluated by histology, inflammatory response (as measured by interleukin (IL)-1beta mRNA levels), proliferative activity (as assessed by 5'-bromo-2'deoxyuridine labelling indices), and host systemic reaction (as measured by anti-H pylori IgG antibody). RESULTS: Degree of gastric inflammation, proliferative activity, and mucosal IL-1beta mRNA levels remained low throughout the first 12 weeks in gerbils infected with the virD4 mutants. Degree of gastric inflammation and proliferative activity increased at 24 weeks with the virD4 mutants reaching levels comparative with those seen at four weeks with the wild-type strains. Mucosal IL-1beta mRNA levels were also increased at 24 weeks with the virD4 mutants and levels at 24 weeks were similar between the wild-type and virD4 mutants. In contrast, gerbils infected with the cagG mutants had reduced ability to colonise gerbils, and no or little gastric inflammation or proliferative activity was observed. CONCLUSIONS: Loss of the virD4 gene temporally retarded but did not abrogate gastric inflammation. Loss of the cagG gene abolished gastric inflammation partially via reduced ability to colonise gerbils. Unknown factors related to the type IV secretion system other than CagA may influence gastric inflammation.  相似文献   
95.
A case of lymphoepithelial cyst in the pancreas was reported. A 64-year-old man without any specific compalints was found to have a cystic lesion in the anterior portion of the pancreas, as revealed by ultrasonography of the abdomen at an annual medical examination in 1988. This was dissected easily from the pancreas. Histologically, it was diagnosed to be a benign lymphoepithelial cyst in the pancreas. Cysts of this type are rare, and their histogenesis is also not well understood.  相似文献   
96.
A 47-year-old Japanese woman in whom obstructive jaundice had already been diagnosed, was found to have a dome-shaped elevated tumor approximately 3 cm in diameter located in the area very close to the papilla of Vater on endoscopical and radiographical investigations. Histopathologically, the resected tumor was composed mainly of solid nests of atypical argyrophilic cells, and partially of an area of well differentiated tubular adenocarcinoma, showing mutual transition in the mucosal layer. Both immunohistochemical and ultrastructural analyses confirmed the difference in character of tumor cells between these two areas: neuroendocrine cell carcinoma and tubular adenocarcinoma of common type in the intestine. To the best of our knowledge, this is only the third case reported to be a coexisting malignant carcinoid tumor and adenocarcinoma arising in the periampullary region.  相似文献   
97.
Aims/hypothesis Type 2 diabetes is characterised by excessive hepatic glucose production and frequently leads to systemic vascular complications. We therefore analysed the relationship between the gene expression profile in the liver and the pathophysiology of Type 2 diabetes.Methods Liver biopsy samples were obtained from twelve patients with Type 2 diabetes and from nine non-diabetic patients. To assay gene expression globally in the livers of both groups, we made complementary DNA (cDNA) microarrays consisting of 1080 human cDNAs. Relative expression ratios of individual genes were obtained by comparing cyanine 5-labelled cDNA from the patients with cyanine 3-labelled cDNA from reference RNA from the liver of a non-diabetic patient.Results On assessing the similarities of differentially expressed genes, the gene expression profiles of the twelve diabetic patients formed a separate cluster from those of the non-diabetic patients. Of the 1080 genes assayed, 105 (9.7%) were up-regulated and 134 (12%) were down-regulated in the diabetic livers (p<0.005). The genes up-regulated in the diabetic patients included those encoding angiogenic factors such as vascular endothelial growth factor, endothelin and platelet-derived growth factor. They also included TGF superfamily genes such as TGFA and TGFB1 as well as bone morphogenetic proteins. Among the down-regulated genes in the diabetic patients were molecules defending against stress, e.g. flavin-containing monooxygenase and superoxide dismutase.Conclusions/interpretation These findings suggest that livers of patients with Type 2 diabetes have gene expression profiles indicative of an increased risk of systemic vascular complications.Electronic Supplementary Material Supplementary material is available in the online version of this article at Abbreviations aRNA antisense RNA - BMP bone morphogenetic protein - cDNA complementary DNA - Cy cyanine - FMO flavin-containing monooxygenase - NASH non-alcoholic steatohepatitis - PDGF platelet-derived growth factor - SSC standard saline citrate - SOD superoxide dismutase - VCAM vascular cell adhesion molecule - VEGF vascular endothelial growth factor  相似文献   
98.
We report a case, which we believe to be rare, of adenosine-sensitive atrial tachycardia (AT) originating from the mitral valve annulus. The patient, a 73-year-old woman, died of unrelated cause 4 years after radiofrequency (RF) ablation therapy. Histologically, fibrous replacement of atrial musculature by mature collagenous tissue produced by the RF current was observed at the left inferior atrioventricular junction. In serial sections that included the coronary sinus, two distinct nodal structures containing small, pale myocytes within the fibrous tissue matrix were identified around the region of the ablation lesion. Our case appears to be a unique representation of tissue that was associated with the occurrence and maintenance of AT.  相似文献   
99.
Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a key effector molecule expressed by natural killer (NK) cells and has been shown to prevent tumor initiation, growth, and metastasis. Here we demonstrate that TRAIL is the dominant cytotoxic effector molecule expressed by NK cells in fetal mice. On birth and with age, NK cells develop full functional capacity, including the ability to secrete interferon gamma (IFN-gamma) and interleukin 13 (IL-13) and mediate perforin- and Fas ligand-mediated cytotoxicity. However, interestingly, a phenotypically immature TRAIL+ NK cell subpopulation is retained in the liver of adult mice, and its retention is dependent on IFN-gamma but not dependent on host IL-12, IL-18, or endogenous host pathogens. Adoptive transfer of either adult liver or neonatal TRAIL+ NK cells resulted in the appearance of TRAIL- NK cells with a mature phenotype, suggesting that these TRAIL+ NK cells were indeed a precursor. Although inducers of IFN-gamma stimulated TRAIL expression on mature NK cells, our data indicated that constitutive TRAIL expression was a hallmark of immature cytotoxic NK cells. This study is the first to describe the concomitant maturation of NK cell effector function with surface phenotype in vivo and implies an important defense role for NK cell TRAIL in the developing immune system.  相似文献   
100.
Although Helicobacter pylori have been identified in the liver, the role of Helicobacter sp. in human liver diseases remains unclear. This study explored whether H. pylori were internalized and could persist in hepatocytes. The majority of an inoculum of H. pylori (1 x 10(7) colony forming units) adhered to hepatocytes. Using the gentamicin invasion assay we found that approximately 2% were internalized and persisted following passage for more than 2 months. Electron microscopy confirmed the presence of intracellular Helicobacter. The number of adherent or internalized H. pylori was significantly greater with hepatocytes than with gastric epithelial cells (P < 0.05) and was also dependent on cag pathogenicity island (PAI), VacA, OipA, or BabA status. Transmission electron microscopy was used to confirm adherence and invasion of H. pylori into hepatocytes. Internalization of H. pylori was inhibited by antibodies to beta1-integrin receptors, genistein, and cytochalasin D (P < 0.05) consistent with beta1-integrin acting as a surface receptor with additional requirements for tyrosine kinase phosphorylation and actin polymerization. In summary, H. pylori both adhered to and invaded into hepatocytes in vitro, depending on the virulent factors, and persisted within hepatocytes during subcultures. beta1-integrin is likely a receptor involved in internalization of H. pylori into hepatocytes.  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