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   410篇
  免费   22篇
  国内免费   4篇
耳鼻咽喉   3篇
儿科学   37篇
妇产科学   4篇
基础医学   29篇
口腔科学   10篇
临床医学   26篇
内科学   69篇
皮肤病学   6篇
神经病学   7篇
特种医学   89篇
外科学   32篇
综合类   61篇
预防医学   14篇
眼科学   11篇
药学   16篇
肿瘤学   22篇
  2022年   6篇
  2021年   4篇
  2020年   5篇
  2019年   2篇
  2018年   8篇
  2017年   6篇
  2016年   7篇
  2015年   16篇
  2014年   4篇
  2013年   7篇
  2012年   12篇
  2011年   14篇
  2010年   20篇
  2009年   15篇
  2008年   10篇
  2007年   12篇
  2006年   14篇
  2005年   17篇
  2004年   6篇
  2003年   5篇
  2002年   14篇
  2001年   9篇
  2000年   6篇
  1999年   11篇
  1998年   29篇
  1997年   23篇
  1996年   18篇
  1995年   15篇
  1994年   12篇
  1993年   9篇
  1992年   3篇
  1990年   1篇
  1989年   14篇
  1988年   11篇
  1987年   15篇
  1986年   11篇
  1985年   5篇
  1984年   5篇
  1983年   6篇
  1982年   5篇
  1981年   5篇
  1980年   5篇
  1978年   1篇
  1977年   1篇
  1976年   3篇
  1975年   8篇
  1969年   1篇
排序方式: 共有436条查询结果,搜索用时 12 毫秒
361.
362.
The purpose of this study was to investigate if a secular trend towards an earlier age of menarche still existed in Finland in the 1980s and if social class and regional differences observed previously in the mean age of menarche had disappeared. Questionnaires were mailed to nationwide representative samples of 16- and 18-year-old girls every other year from 1979 to 1989. At the national level, the secular trend towards an earlier menarche was not observed in the 1980s but the trend was significant among girls living in the North-West and rural areas. Clearly observed regional and urban-rural differences in 1979 disappeared in the 1980s. Social class differences persisted: farmers' daughters had a higher mean age of menarche than those of other occupational groups. Adolescents in the 1980s displayed a more even distribution of health than the cohorts born before them. Improved welfare of the Finnish society and reorganization of the primary health care are probable explanations.  相似文献   
363.
We have obtained transgenic mice in which an erythropoietin-SV40 virus T antigen fusion gene is homologously recombined into the native Epo locus. This gene is expressed in a tissue-specific manner closely resembling that of the native Epo gene. Immunohistochemical detection of SV40 T antigen has been used to characterize the hepatic cell populations expressing the transgene. In mice stimulated by anaemia or hypobaric hypoxia, SV40 T antigen was demonstrated in two liver cell populations: a subset of hepatocytes and a nonparenchymal cell type. Immunohistochemical and ultrastructural characterization of these cells by light and electron microscopy showed the nonparenchymal cell type to be the Ito cells, which lie in a persinusoidal position within the space of Disse. We therefore conclude that Ito cells are the nonhepatocytic source of liver Epo production. These cells show many similarities to the Epo-producing fibroblastoid interstitial cells of the kidney.  相似文献   
364.
pS2 is a 60 amino acid secretory polypeptide which belongs to a newly described family of trefoil-shaped growth factors. It is widely distributed throughout the gastrointestinal tract, particularly adjacent to damaged mucosa, and is also expressed by some epithelial tumours such as breast carcinoma. The aim of this study was to examine the expression of pS2 in pancreatic cancer. The presence of pS2 was analysed immunohistochemically using two antibodies, a polyclonal (pNR-2) and a monoclonal (pS2TM) in 42 cases of pancreatic adenocarcinoma and 10 cases of ampullary carcinoma. The findings were compared with chronic pancreatitis and normal pancreas. No immunostaining was seen in normal pancreas, with the exception of one area of ductular proliferation, and although 8/10 cases of chronic pancreatitis expressed pS2, it was focal and confined to the occasional duct. In contrast, a significant proportion of malignant cells in 23/42 (55%) of pancreatic adenocarcinoma and 8/10 (80%) of ampullary tumours expressed immunoreactive pS2. The finding of pS2 expression in more than 50% of pancreatic and ampullary carcinomas in contrast to the findings seen in chronic pancreatitis and normal pancreas suggests that pS2 may play an important role in the growth of these highly malignant tumours.  相似文献   
365.
366.
Porter  CD; Parkar  MH; Collins  MK; Levinsky  RJ; Kinnon  C 《Blood》1996,87(9):3722-3730
The primary immunodeficiencies are attractive candidates for the development of gene therapy approaches based on the transduction of hematopoietic cells. We have constructed a high-titer recombinant retrovirus for expression of gp91-phox, deficiencies of which cause the X-linked form of chronic granulomatous disease (X-CGD). We have used this vector to transduce human bone marrow, using either unfractionated mononuclear cells or purified CD34+ cells as targets and evaluated several infection protocols. Efficient gene transfer to progenitors and long-term culture-initiating cells (LTC-IC) was obtained for each target population. Importantly for potential clinical application, this could be achieved without the use of exogenous cytokines or polybrene. Progenitors representing each of the lineages detectable in vitro were transduced at equal efficiencies. The vector was shown partially to restore gp91-phox deficiency and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity in transduced cells derived from X- CGD patients. These data demonstrate that it is possible to transduce primitive human hematopoietic cells efficiently and reconstitute NADPH oxidase.  相似文献   
367.
Cytotoxic function of CD4+ Th1 cells is mediated by Fas (CD95, APO-1) and its ligand (Fas ligand). Recent studies using nontransformed B cells and the Ramos Burkitt's lymphoma (BL) B-cell line cells show that CD40 ligation at the B-cell surface by activated, CD40 ligand (CD40L)- bearing, CD4+ T cells upregulates Fas expression on B cells and primes B cells for Fas-mediated death signals. In this work, we examine whether this CD4+ T-cell-dependent molecular pathway for Fas upregulation and B-cell apoptosis reflects a peculiarity of the Ramos B- cell line or is applicable to other Burkitt's tumors as well. In 5 of the 6 Epstein-Barr virus-negative BL cell lines examined, the cells constitutively express undetectable or low levels of Fas and are resistant to Fas-mediated signals induced by monoclonal anti-Fas antibody. All 6 of the BL cell line B cells upregulate Fas in response to CD40 ligation, and in 4 of the cases they become sensitive to Fas- mediated death signals. In one BL cell line, the cells are constitutively sensitive to Fas-mediated cytolysis and are unaffected by CD40 signals. Next, we applied these immunologic manipulations to cells from a refractory clinical sample and observed that the tumor cells could be induced to express Fas and undergo apoptosis in our system. These results establish CD4+ T cells and the Fas-Fas ligand system as important immune regulators of Burkitt's lymphoma B cells and indicate that the susceptibility of tumor cells to Fas-mediated death signals can be modulated by specific activation events at the cell surface.  相似文献   
368.
Blast cells from 100 cases of acute leukemia were evaluated for the presence of methylthioadenosine phosphorylase (MTAase), an enzyme important in polyamine metabolism. Ten cases (10%) had undetectable levels of MTAase activity. Of the 10, 5 had acute lymphoblastic leukemia (ALL), 3 had acute myeloblastic leukemia (AML) and 2 expressed mixed lineage markers as determined by immunophenotyping. A relatively high frequency (38%) of MTAase deficiency was seen in ALL of T-cell origin. Nonmalignant hematopoietic cells from three patients with MTAase-deficient leukemias had readily detectable enzyme activity. Chromosomal abnormalities were detected in four of the seven MTAase- deficient cases in which karyotypic analysis was performed. No consistent karyotypic defect was apparent, and only one case displayed changes in chromosome 9, the putative location of the MTAase structural gene. The clinical findings among the enzyme-deficient cases were unremarkable except that all patients were male (P less than .01). Only one patient had "lymphomatous" features. We conclude that MTAase deficiency occurs in a wide variety of acute leukemias, that the lack of enzyme activity is specific to the malignant cells, and that an increased incidence occurs in ALL of T-cell origin. Furthermore, no specific gross chromosomal abnormality is associated with the enzyme deficiency. The marked male predominance in patients with MTAase- deficient acute leukemias suggests involvement of the X chromosome in the loss of enzyme activity. The absence of MTAase in some leukemias may be therapeutically exploitable.  相似文献   
369.
不同温度体外循环对血栓栓塞的影响   总被引:1,自引:0,他引:1  
探讨不同温度体外循环中血小板血栓栓塞情况。方法将18只猪均分为3组行体外循环。Ⅰ组,18℃深度温停循环;Ⅱ组,28℃中度低温体外循环;Ⅲ组,37℃常温体外循环。用铟-111标记的自体血小板测定3组心、肺、脑、肝,脾、肾和体外循环设备的血栓栓塞情况。  相似文献   
370.
The effects of bleach reprocessing on the performance of high-flux dialyzers have not been comprehensively characterized. We compared the effects of automated bleach/formaldehyde reprocessing on solute and hydraulic permeability for cellulose triacetate (CT190) and polysulfone (F80B) dialyzers using an in vitro model. Dialyzers were studied after initial blood exposure (R0) and after 1 (R1), 5 (R5), 10 (R10), and 15 (R15) reuse cycles. Ultrafiltration coefficient (K(uf)), serial clearances, and/or sieving coefficients (SCs) of urea, creatinine, vancomycin, inulin, myoglobin, and albumin were determined. Urea, creatinine, and vancomycin clearances and SCs did not significantly differ from R0 to R15 with either dialyzer. Inulin clearances and SC also did not significantly change from R0 to R15 for the CT190. However, these same values for the F80B significantly increased (P < 0.05). The inulin clearance and SC values for the CT190 dialyzer were significantly higher than those for the F80B at all stages except R15. Myoglobin clearances significantly increased over 15 reuses for both dialyzers (P < 0.01). However, CT190 myoglobin clearances were significantly higher at all stages (R0 = 37.7 +/- 9.7; R15 = 52.5 +/- 8.8 mL/min) than the F80B (R0 = negligible; R15 = 41.3 +/- 16.5 mL/min; P < 0.01). Albumin pre- and postdialysis SCs significantly increased for both dialyzers (P < 0.01). K(uf) for R0 and R15 were 52.3 +/- 3.3 and 52.6 +/- 7.6 mL/h/mm Hg for CT190 (P = not significant) and 48.8 +/- 4.4 and 87.3 +/- 7.0 mL/h/mm Hg for F80B (P < 0.0001). We conclude that bleach reprocessing significantly increases larger solute and hydraulic permeability of high-flux cellulosic and polysulfone dialyzers. This effect is more pronounced for the polysulfone membrane. Until 10 reuses or greater, the removal of solutes greater than 1,500 d is significantly compromised with the polysulfone dialyzer used in this study.  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