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   8082篇
  免费   415篇
  国内免费   25篇
耳鼻咽喉   77篇
儿科学   153篇
妇产科学   154篇
基础医学   994篇
口腔科学   234篇
临床医学   580篇
内科学   2102篇
皮肤病学   135篇
神经病学   492篇
特种医学   272篇
外科学   1168篇
综合类   39篇
一般理论   2篇
预防医学   274篇
眼科学   164篇
药学   567篇
中国医学   8篇
肿瘤学   1107篇
  2023年   39篇
  2022年   83篇
  2021年   149篇
  2020年   75篇
  2019年   95篇
  2018年   104篇
  2017年   101篇
  2016年   121篇
  2015年   111篇
  2014年   138篇
  2013年   209篇
  2012年   312篇
  2011年   323篇
  2010年   177篇
  2009年   188篇
  2008年   319篇
  2007年   350篇
  2006年   311篇
  2005年   356篇
  2004年   347篇
  2003年   313篇
  2002年   321篇
  2001年   335篇
  2000年   335篇
  1999年   292篇
  1998年   117篇
  1997年   91篇
  1996年   75篇
  1995年   79篇
  1994年   77篇
  1993年   60篇
  1992年   244篇
  1991年   221篇
  1990年   239篇
  1989年   222篇
  1988年   193篇
  1987年   157篇
  1986年   152篇
  1985年   141篇
  1984年   88篇
  1983年   86篇
  1981年   51篇
  1979年   67篇
  1974年   38篇
  1973年   54篇
  1972年   50篇
  1971年   48篇
  1970年   43篇
  1969年   71篇
  1968年   53篇
排序方式: 共有8522条查询结果,搜索用时 15 毫秒
91.
The most frequent nonrandom chromosome rearrangements in B-cell non-Hodgkin lymphoma (NHL) is the t(14;18)(q32;q21) found in follicular lymphomas. The t(14;18) in Hodgkin disease (HD) was rarely observed using cytogenetic techniques. Although Southern blot analysis failed to demonstrate the t(14;18), there have been conflicting reports concerning the occurrence of the translocation using polymerase chain reaction (PCR) methods in HD. In some HD tissues, the translocation might be derived from background lymphocytes rather than Hodgkin and Reed-Sternberg (HRS) cells, because B-cells with t(14;18) are regularly generated in normal individuals. However, the cells bearing the translocation have remained unidentified. We describe a patient with HD who showed t(14;18) in hyperdiploid cells using fluorescence in situ hybridization (FISH) and HRS cells which were strongly positive for BCL2 by immunohistochemistry. These findings suggest that HRS cells may have a t(14;18).  相似文献   
92.
Long-term potentiation (LTP) is thought to be particularly important in the acquisition of hippocampus-associated memory, in part because it develops quickly and persists for indefinite periods. Extracellular proteolysis has been hypothesized to contribute to LTP by modifying adhesive relations of synapses and thus the morphology of excitatory synapses. Here we report that neuropsin (NP), an extracellular serine protease, is critically involved in the formation of both the potentiation effect and hippocampus-dependent forms of memory. NP-knockout mice were significantly impaired in the Morris water maze and Y-mazes and failed to exhibit early phase LTP induced by a single tetanus. Potentiation was also impaired or completely blocked by in vivo application of a specific inhibitor or a neutralizing monoclonal antibody for NP. Intriguingly, recombinant (r-) NP alone, without tetanic stimulation, elicited either long-lasting potentiation or depression, depending on the applied dose. The r-NP-elicited potentiation was occluded by prior induction of LTP, while theta-burst-elicited LTP was occluded by application of r-NP alone, suggesting that the two forms of plasticity have a common signalling pathway. r-NP-elicited potentiation and depression increased phosphorylation at different sites on the GluR1 subunit of the AMPA receptor that had previously been associated with LTP or long-term depression. Thus, we conclude that NP is necessary for establishment of LTP and has a significant role in memory acquisition.  相似文献   
93.
Thymosin alpha 1 was shown to prevent the 5-fluorouracil(5-FU)-induced bone marrow toxicity in BDF1 mice, as determined by the cellularity, haemopoietic stem cells (CFU-s) and granulocyte-macrophage colony forming unit (GM-CFU). Furthermore, thymosin alpha 1 increased the levels of colony stimulating factor (CSF) in sera or in culture media of spleen cells derived from 5-FU-treated mice. The treatment of spleen cells with anti-Thy 1,2 antibody plus complement abolished completely the CSF production. The in vivo treatment of donor mice with anti-Thy 1,2 antibody following 5-FU abolished completely the capability of their bone marrow cells to save lethally irradiated recipients. Thymosin alpha 1 treatment prevented the damage by such combined treatment. The present study indicates that thymosin alpha 1 exerts its protective effect against the 5-FU-induced bone marrow toxicity, at least partially, through its effect on the maturation of immature T cells to functional T cells which produce various kinds of lymphokines including CSF.  相似文献   
94.
95.
We performed a nationwide epidemiologic study of hypersensitivity pneumonitis (HP) in Japan by questionnaire and found that 835 cases of HP were recognized during the 1980s; 74.4% were summer-type HP, 8.1% farmer's lung, 4.3% ventilation pneumonitis, 4.1% bird fancier's lung, 2.3% other types, such as chemical worker's lung, and 6.8% of unknown causative agent. It was found that the CD4/CD8 ratios of bronchoalveolar lavage (BAL) lymphocytes were significantly different with the type of disease. The ratio was 0.6 +/- 0.1 (mean +/- SEM) in summer-type HP (N = 271), 4.4 +/- 0.7 in farmer's lung (N = 22), 1.6 +/- 0.3 in ventilation pneumonitis (N = 19), and 2.0 +/- 0.5 in bird fancier's lung (N = 19). In farmer's lung, the CD4/CD8 ratio in smokers was 6.2 +/- 1.9 (N = 6) in contrast with 3.4 +/- 0.7 for nonsmokers (N = 16) (p less than 0.05). It has been generally considered that the phenotypes of BAL lymphocytes in patients with HP are predominately CD8 cells. Our present results, however, indicate that the phenotypes of BAL lymphocytes vary with the type of HP, probably depending on factors such as causative agent, smoking, or staging of the disease.  相似文献   
96.
The specific immunophenotypic characterization of the hematologic malignant diseases has been obtained most commonly by the immunofluorescent technic. It requires a microscope with illuminator or the expensive flow cytometer that usually precludes morphologic assessment. It was compared with the indirect rosette assay and the immunoperoxidase study, which allowed both immunologic and morphologic assessment. These three technics appeared to be comparable quantitatively, and the latter two technics utilizing cytospin preparations were applied sequentially to the leukemic cells of adult T-cell leukemia with a complex phenotype (OKT4+/OKT8+) and successfully displayed the double markers on each leukemic cell.  相似文献   
97.
A Shimada  N Tamura 《Immunology》1972,22(5):723-731
Two synthetic substrates, TAMe and ATEe, were tested for their abilities to inhibit the formation of SAC14 and SAC142 and found to act as inhibitors in different ways. In addition to inhibition of the formation of SAC142 from SAC14 and C2, TAMe inhibited the formation of SAC14 from SAC1 and C4 and the inactivation of C4 by C1 and EAC1. ATEe inhibited the formation of SAC14, but only slightly inhibited the inactivation of C4 by C1 and EAC1 and further did not interfere with the formation of SAC142. ATEe could be entirely replaced by acetyl-L-tyrosine in these effects on the action of C1 on C4. The possible mechanism of inhibitions by these compounds was discussed.  相似文献   
98.
Acute ulcerative colitis associated with cytomegalic inclusion virus   总被引:2,自引:0,他引:2  
  相似文献   
99.
We report six cases of carcinoma showing sarcomatous change in the urinary tract examined by conventional histochemistry and immunohistochemistry. All of the cases were transitional cell carcinoma with or without focal squamous cell carcinoma. Sarcomatous components resembling spindle cell sarcoma with a marked myxoid stroma or chondrosarcomatous element were also observed in all cases. The sarcomatous elements were closely associated with the areas of squamous cell carcinoma in three cases. Various histochemical staining procedures demonstrated mesenchymal features in the stroma of sarcomatous areas. By immunohistochemical examination, the epithelial components showed positive reactions for keratin, epithelial membrane antigen and, focally, carcinoembryonic antigen. The sarcomatous components revealed a positive immunoreaction for keratin but lacked other epithelial markers in all cases. Chondrosarcomatous elements in two cases were positive for both keratin and S-100 protein. These findings indicate that sarcomatous elements in carcinoma may represent mesenchymal metaplasia with partial or complete loss of epithelial features. However, further study will be necessary in order to determine whether heterogeneous elements, such as chondrosarcomatous areas, are epithelial or truly mesenchymal in origin.  相似文献   
100.
By a direct immunofluorescent technique, glomerular C3d deposition was examined in a total of 50 renal biopsy specimens from patients with lupus nephritis. C3d deposition was then compared with disease activity, glomerular IgG and C3c deposition, and the levels of circulating immune complexes (CIC) measured by a solid-phase anti-C3d assay. There was a good correlation between disease activity and the positivity of glomerular C3d deposits (P less than 0.001), as well as C3c deposits (P less than 0.001). Even in clinically inactive patients, a relatively high percentage (59%) of C3d deposits were positive compared with C3c deposits (17%). Mesangial C3d deposition correlated with clinical disease activity more significantly (P less than 0.005) than capillary wall C3d deposition (P less than 0.025). C3d deposits were detected in all of the 30 cases with positive C3c deposits, and moreover, in 15 of the 20 (75%) cases with negative C3c deposits. Glomerular IgG deposits were almost always associated with C3d deposits, both in mesangial areas and along capillary walls, with statistical significance (P less than 0.005, P less than 0.001, respectively). The serum levels of C3d-fixing immune complexes (IC) were significantly correlated with the positivity and intensity of mesangial C3d deposits. This study demonstrates glomerular deposition of C3d in patients with lupus nephritis and reveals a significant correlation between mesangial C3d deposition and disease activity.  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