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   8566篇
  免费   362篇
  国内免费   63篇
耳鼻咽喉   118篇
儿科学   145篇
妇产科学   37篇
基础医学   1170篇
口腔科学   190篇
临床医学   584篇
内科学   2310篇
皮肤病学   164篇
神经病学   697篇
特种医学   388篇
外科学   1347篇
综合类   22篇
预防医学   261篇
眼科学   124篇
药学   440篇
中国医学   21篇
肿瘤学   973篇
  2023年   54篇
  2022年   82篇
  2021年   143篇
  2020年   69篇
  2019年   99篇
  2018年   132篇
  2017年   117篇
  2016年   123篇
  2015年   183篇
  2014年   241篇
  2013年   325篇
  2012年   442篇
  2011年   473篇
  2010年   266篇
  2009年   243篇
  2008年   405篇
  2007年   487篇
  2006年   508篇
  2005年   476篇
  2004年   509篇
  2003年   491篇
  2002年   544篇
  2001年   182篇
  2000年   165篇
  1999年   208篇
  1998年   148篇
  1997年   116篇
  1996年   108篇
  1995年   106篇
  1994年   94篇
  1993年   86篇
  1992年   131篇
  1991年   119篇
  1990年   106篇
  1989年   82篇
  1988年   99篇
  1987年   107篇
  1986年   66篇
  1985年   89篇
  1984年   58篇
  1983年   47篇
  1982年   42篇
  1981年   45篇
  1979年   29篇
  1978年   31篇
  1977年   32篇
  1976年   28篇
  1975年   31篇
  1974年   27篇
  1971年   26篇
排序方式: 共有8991条查询结果,搜索用时 15 毫秒
91.
CD27 is a T cell activation antigen expressed on a majority of peripheral blood T cells. CD27 is also expressed on a subpopulation of human B cells, and it is reported that CD27+ B cells secrete both IgG and IgM. CD70, a ligand for CD27, is expressed on activated T and B cells, suggesting an interaction between T and B cells via CD27/CD70 ligation. Here, we analyze B cell immunoglobulin synthesis using a CD70 transfectant and present functional data showing that B cells secrete large amounts of IgG and IgM as a result of the CD27/CD70 interaction. A flow cytometric analysis showed that CD27 expression was increased and CD70 was expressed on tonsillar and peripheral blood B cells after activation with Staphylococcus aureus Cowan strain (SAC) plus interleukin (IL-2). In addition, the proliferation of B cells was enhanced mildly by the addition of CD70 transfectant, and its proliferation was blocked by anti-CD70 mAb. More importantly, the CD70 transfectant enhanced IgG and IgM production by purified B cells greatly in the presence of SAC plus IL-2. The enhancement was completely blocked by the addition of either anti-CD70 mAb or anti-CD27 mAb. Strongly suggesting that the interaction of CD27 with its ligand, CD70, on B cells plays an important role in B cell growth and differentiation to produce IgG and IgM.  相似文献   
92.
The proliferative activity and ultrastructural characteristics of proliferating biliary epithelial cells were analysed immunohistocytochemically in 39 biopsied liver specimens from patients with acute viral hepatitis, chronic hepatitis and liver cirrhosis using a monoclonal antibody against DNA polymerase (DNA-PA). In acute viral hepatitis with perivenular confluent necrosis, proliferation of typical bile ducts was found frequently in portal areas. In chronic aggressive hepatitis and cirrhosis, ductular proliferation of both typical and atypical forms was found in enlarged portal and periportal areas and in confluent necrotic areas. The number of proliferating biliary epithelial cells that stained positive for DNA-PA was small. There were very few positively stained cells in atypical bile ducts in confluent necrotic areas of cirrhosis. Atypical bile ducts seen in chronic aggressive hepatitis, cirrhosis and acute hepatitis with confluent necrosis were positively stained for both cytokeratins 8 and 19. In cirrhosis, the number of stained biliary epithelial cells in typical bile ducts was larger than the number of such cells in atypical bile ducts (P< 0.01). By electron microscopy, the cells positively stained for DNA-PA were mostly so-called clear cells with irregular nuclei containing coarse nucleoplasm, and a few small cells with scanty cytoplasm and few organelles.  相似文献   
93.
94.
Polymerase chain reaction (PCR)-based diagnosis was carried out in 62 patients (57 probands) with Duchenne or Becker muscular dystrophy (DMD or BMD) and 226 members in 57 families. The PCR studies were also performed for carrier detection in 57 mothers and 58 sisters, and prenatal diagnosis of 4 fetuses at risk of DMD. The PCR with 7 sets of primers, which amplify 7 different exon-sequences of the dystrophin gene, detected gene deletion of at least one exon in 49% of the probands. The PCR with the other 4 primer sets, which amplify 3 intragenic loci, and subsequent endonuclease digestion detected in 84% of the mothers a heterozygous pattern in at least one such locus/segment. Using the same primer sets, carrier detection was successful in 5 sisters of familial DMD cases, while recombination between the ERT87 and the 3 end intragenic loci was observed in 11% of family members studied. Prenatal diagnosis was made in all the 4 fetuses; two males were affected, one male fetus non-affected, and the remaining one female fetus a carrier. Thus, the PCR study and the primers used in the present study are useful and convincing for rapid diagnosis of DMD and/or BMD.  相似文献   
95.
In allogeneic immunity against tumors induced by methylcholanthrene in the W/KA strain rat, serum antibody agglutinated red blood cells of the W/KA strain rat. The allogeneic antiserum was cytotoxic to the lymphocyte, but not to the tumor cells induced by methylcholanthrene.
In vitro and in vivo studies of allogeneic immunization of tumor suggested that immune macrophages or histiocytes play a major role in the rejection of transplanted tumor. Direct adhesion of immune macrophages with target cells is necessary for destruction of allografted tumor.
In antitransplantation immunity of the syngeneic and autochthonous rat, there was no cytotoxic serum antibody demonstrable in so far as routine techniques were employed. However, this may not exclude the existence of specific serum antibody or non-cytotoxic reaction with target cells of specific serum antibody. On the other hand, immune macrophages were always cytotoxic to target tumor cells, thus showing tumor specifity.
Experiment in which diffusion chambers were inserted into syngeneic immune rats suggested the possible participation of a humoral factor which was released from the immune rats immediately after contact with target cells and transform normal macrophages to immunologically active macrophages. The ascites macrophages have the greatest effective cytotoxic action among the three types of cells. In allogeneic tumor immunity, one immune macrophage can damage one target tumor cell showing single hit interaction. ACTA PATH. JAP. 18: 207–225, 1968.  相似文献   
96.
To clarify the essential role of NKT cells in allergy, we investigated the contribution of NKT cells to the pathogenesis of eosinophilic airway inflammation using alpha-galactosylceramide (alpha-GalCer), a selective ligand for NKT cells. Although continuous administration of alpha-GalCer during ovalbumin (OVA) sensitization increased OVA-specific IgE levels and worsened eosinophil inflammation, a single administration of alpha-GalCer at the time of OVA challenge completely prevented eosinophilic infiltration in wild-type mice. This inhibitory effect of alpha-GalCer was associated with a decrease in airway hyperresponsiveness, an increase in IFN-gamma, and decreases in IL-4, IL-5 and IL-13 levels in the bronchoalveolar lavage fluids. Analysis of lung lymphocytes revealed that production of IFN-gamma increased in NK cells, but not in T or NKT cells, following alpha-GalCer administration. Induction of vascular cell adhesion molecule-1 in the lungs of wild-type mice was also significantly attenuated by treatment with alpha-GalCer. These effects of alpha-GalCer were abrogated in J alpha281-/- mice, which lack NKT cells, and in wild-type mice treated with anti-IFN-gamma Ab. Hence, our data indicate that alpha-GalCer suppresses allergen-induced eosinophilic airway inflammation, possibly by inducing a Th1 bias that results in inhibition of eosinophil adhesion to the lung vessels.  相似文献   
97.
To analyze the mechanisms of increased nonspecific immunity in pregnant women, the effect of various hormones on the phagocytic activity was estimated by a luminol-dependent chemiluminescence (CL) response during phagocytosing opsonized zymosan. The CL response of whole blood supplemented with exogenous human chorionic gonadotropin (hCG) increased significantly in all the male and female subjects and pregnant women. An approximate two- to fourfold increase was observed in comparison with the unsupplemented control in each subject at concentrations ranging from 1 to 1,000 IU/ml after 48 h of incubation (P less than 0.05). Progesterone slightly stimulated the CL response in female subjects only, but had no effect on male and pregnant women. Estradiol (E2) did not stimulate the CL response in any subject. The expression of Fc and C3b receptors on the surface of polymorphonuclear leucocytes (PMNL) in pregnant women was also investigated by measuring the immunofluorescence stained with monoclonal antibody to Fc and C3b receptors, respectively. The relative numbers of Fc receptors increased significantly in the third trimester compared to those of female control (P less than 0.05). Those of C3b receptor also increased in the second and third trimester (P less than 0.005). These results suggested that the nonspecific immunity represented by phagocytic activity in pregnant women increased with both oxidative metabolic responsiveness and the expression of membrane receptors. Besides, the increased phagocytic activity of the maternal host is probably due to the stimulatory effect of both endogenous and exogenous hCG on their peripheral blood phagocytes.  相似文献   
98.
Summary Ventilatory response lines to carbon dioxide at rest were determined by the rebreathing method in 10 untrained subjects, 17 sprint swimmers, and 11 long-distance swimmers. It was found that the mean slope of the ventilatory response line of the swimmer was lower than that of the untrained group, and the mean slope of the long distance swimmer was lower as compared with the sprint swimmer, though these differences were statistically not significant. The differences in the hypercapnic drive between untrained subjects and swimmers obtained here is discussed in connection with their maximum oxygen uptake.  相似文献   
99.
Isolation of antigenic peptides from the MHC-groove has contributed to the understanding of T cell responses. However, these MHC-associated peptides have been isolated from various murine and human cell lines. The specific antigen responsible for the pathogenesis of inflammatory bowel disease is unknown. We examined antigenic peptides bound to the class II major histocompatibility complex (MHC) groove in human intestine by ion-trap tandem mass spectrometry equipped with online reverse-phase high performance liquid chromatography. We detected 55 parent proteins from 4 controls, 9 patients with ulcerative colitis, and 9 patients with Crohn's disease. The calculated molecular masses (m/z) of these peptides ranged from 874.4 to 2727.4, representing 10-26 amino acid residues. Fifty-one of these 55 parent proteins were exogenous proteins. Escherichia coli-, Saccharomyces cerevisiae-, and Caenorhabditis elegans-derived peptides were found frequently in patients with inflammatory bowel disease. The present results suggest that in vivo antigen processing by antigen-presenting cells and T lymphocytes in human intestine participate with exogenous antigen presentation. Increased immune responses against E. coli, S. cerevisiae and C. elegans found in patients with inflammatory bowel may participate as dysregulated immune responses to enteric flora in the pathogenesis of inflammatory bowel disease.  相似文献   
100.
The expression of -GlcNAcβ1–6Man-(β1–6) branched oligosaccharides In carcinoma cells has been considered to influence their metastatic potentials. In the present paper, the lectin histochemistry of oral squamous cell carcinomas obtained in biopsy from 34 patients with Phaseolus vulgaris leukoagglutinin (L-PHA), which potentially binds to N-glycosidic carbohydrates with β1–6 linked lactosamin antennae, was studied in order to analyze the relationship between their staining patterns and metastases. The L-PHA-binding oligosaccharides of the carcinomas were expressed on the cell surface in the following patterns: (i) all cells were positive for the staining ('positive'); (ii) some cells were positive but the rest of the carcinoma cells were negative ('weakly positive'); and (iii) all were negative ('negative'). Statistical analysis revealed that the incidence of the metastasis to regional lymph nodes in the 'positive' cases was significantly higher than that in the 'negative' cases. Moreover, the number of the CD14 positive cells including macrophages in the Stroma adjacent to the cardnomas in the 'positive' cases was less than that in the 'negative' or 'weakly positive' cases. The expression of L-PHA-binding oligosaccharides in oral squamous cell carcinoma may be responsible for their metastatic potential to regional lymph nodes, possibly Including their ability to escape macrophage recognition.  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