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   2701篇
  免费   138篇
  国内免费   13篇
耳鼻咽喉   9篇
儿科学   99篇
妇产科学   114篇
基础医学   248篇
口腔科学   234篇
临床医学   248篇
内科学   552篇
皮肤病学   51篇
神经病学   79篇
特种医学   157篇
外国民族医学   78篇
外科学   303篇
综合类   141篇
预防医学   149篇
眼科学   24篇
药学   209篇
  1篇
中国医学   74篇
肿瘤学   82篇
  2021年   30篇
  2015年   47篇
  2014年   52篇
  2013年   67篇
  2012年   91篇
  2011年   102篇
  2010年   71篇
  2009年   67篇
  2008年   92篇
  2007年   69篇
  2006年   85篇
  2005年   70篇
  2004年   44篇
  2003年   47篇
  2002年   48篇
  2001年   56篇
  2000年   55篇
  1999年   48篇
  1998年   52篇
  1997年   62篇
  1996年   50篇
  1995年   46篇
  1994年   62篇
  1993年   39篇
  1992年   43篇
  1991年   41篇
  1990年   44篇
  1989年   57篇
  1988年   49篇
  1987年   49篇
  1986年   56篇
  1985年   43篇
  1984年   28篇
  1983年   27篇
  1982年   28篇
  1981年   30篇
  1980年   29篇
  1977年   26篇
  1976年   32篇
  1974年   31篇
  1973年   29篇
  1972年   38篇
  1971年   36篇
  1970年   25篇
  1959年   35篇
  1958年   58篇
  1957年   87篇
  1956年   45篇
  1955年   75篇
  1954年   67篇
排序方式: 共有2852条查询结果,搜索用时 15 毫秒
51.
52.
BACKGROUND: The clinical diagnosis of stroke subtype is often inaccurate during the first 24 h after stroke onset. Several candidate diagnostic tests might be useful for early determination of subtype, but there is no consensus on what level of accuracy is required to be useful in the selection of patients for subtype-specific studies or therapies. METHODS: A decision analysis was developed to explore the treatment options and estimate the requisite threshold of diagnostic accuracy. Four management strategies were considered: treat all (TA), treat based on new test (TBNT), treat based on clinical diagnosis (TBCD) and treat none (TN). Sensitivity analyses were performed over a wide range of the assumptions in the model. RESULTS: The preferred treatment strategy was dependent on the probability and severity of adverse effects and the positive predictive value (PPV) of the proposed diagnostic test. For a potential therapy with infrequent (7.5%) but severe side effects, TN was preferable, but TBNT dominated if the PPV of the new test was at least 81%. For a therapy with frequent (25%) but mild adverse effects, TBNT was preferable. TA was favored for a therapy with infrequent and mild side effects and TN for a therapy with severe and frequent adverse events. TBCD was never the preferred option unless the PPV of the new test was less accurate than clinical diagnosis alone. CONCLUSIONS: Clinical diagnosis of stroke subtype is insufficient for patient selection, but a new diagnostic test with PPV >/=81% may be useful for early subtype diagnosis and patient selection for stroke subtype-specific clinical trials.  相似文献   
53.
54.
55.
This report describes a rare case of coexistence of benign phyllodes tumor, which measured 9 cm in the right breast, and invasive ductal carcinoma of 6 cm in the left breast, synchronous and independent, in a 66-year-old patient. The patient underwent a bilateral mastectomy due to the size of both lesions. Such situations are rare and usually refer to the occurrence of ductal or lobular carcinoma in situ when associated with malignant phyllodes tumors, and more often in ipsilateral breast or intra-lesional.  相似文献   
56.
Biliary endoscopic drainage using metallic self-expanded stents has become a well-established method for palliative treatment of malignant biliary obstruction. However, its occlusion, mainly by tumor overgrowth, is still the main complication without a standard treatment. We here describe a new method of treatment for biliary metallic stent occlusion, through the echo guided biliary drainage. We present a 68-year-old patient with metastatic pancreatic cancer previously treated for jaundice with ERCP and self-expandable metallic stent insertion. Four weeks later, the patient developed jaundice and symptoms of gastric outlet obstruction. A new ERCP confirmed obstruction of the second portion of the duodenum, due to diffuse tumor growth. EUS was performed, and the previous metal biliary stent was seen occluded at the distal portion in the common bile duct. A EUS-guided choledocododenostomy was performed and then, an overlapping self-expanding metal enteral stent was placed through the malignant obstruction. There were no early complications and the procedure was also clinically effective in relieving jaundice and gastric outlet obstruction symptoms. If ERCP fails in the management of occluded biliary metallic stents, EUS biliary drain can provide effective biliary decompression and should be considered an alternative to other endoscopic techniques.  相似文献   
57.
Endoscopic retrograde cholangiopancreatography(ERCP) is the preferred procedure for biliary and pancreatic drainage.While ERCP is successful in about 95% of cases,a small subset of cases are unsuccessful due to altered anatomy,peri-ampullary pathology,or malignant obstruction.Endoscopic ultrasound-guided drainage is a promising technique for biliary,pancreatic and recently gallbladder decompression,which provides multiple advantages over percutaneous or surgical biliary drainage.Multiple retrospective and some prospective studies have shown endoscopic ultrasoundguided drainage to be safe and effective.Based on the currently reported literature,regardless of the approach,the cumulative success rate is 84%-93% with an overall complication rate of 16%-35%.endoscopic ultrasoundguided drainage seems a viable therapeutic modality for failed conventional drainage when performed by highly skilled advanced endoscopists at tertiary centers with expertise in both echo-endoscopy and therapeutic endoscopy  相似文献   
58.
Baumhueter  S; Dybdal  N; Kyle  C; Lasky  LA 《Blood》1994,84(8):2554-2565
Extravasation of leukocytes into organized lymphoid tissues and into sites of inflammation is critical to immune surveillance. Leukocyte migration to peripheral lymph nodes (PLN), mesenteric lymph nodes (MLN) and Peyer's patches (PP) depends on L-selectin, which recognizes carbohydrate-bearing, sialomucin-like endothelial cell surface glycoproteins. Two of these ligands have been identified at the molecular level. One is the potentially soluble mucin, GlyCAM 1, which is almost exclusively produced by high endothelial venules (HEV) of PLN and MLN. The second HEV ligand for L-selectin is the membrane-bound sialomucin CD34. Historically, this molecule has been successfully used to purify human pluripotent bone marrow stem cells, and limited data suggest that human CD34 is present on the vascular endothelium of several organs. Here we describe a comprehensive analysis of the vascular expression of CD34 in murine tissues using a highly specific antimurine CD34 polyclonal antibody. CD34 was detected on vessels in all organs examined and was expressed during pancreatic and skin inflammatory episodes. A subset of HEV-like vessels in the inflamed pancreas of nonobese diabetic (NOD) mice are positive for both CD34 and GlyCAM 1, and bind to an L-selectin/immunoglobulin G (IgG) chimeric probe. Finally, we found that CD34 is present on vessels of deafferentiated PLN, despite the fact that these vessels are no longer able to interact with L-selectin or support lymphocyte binding in vitro or trafficking in vivo. Our data suggest that the regulation of posttranslational carbohydrate modifications of CD34 is critical in determining its capability to act as an L-selectin ligand. Based on its ubiquitous expression, we propose that an appropriately glycosylated form of vascular CD34 may act as a ligand for L-selectin-mediated leukocyte trafficking to both lymphoid and nonlymphoid sites.  相似文献   
59.
Limited red blood cell (RBC) regeneration often prevents collection of sufficient blood from autologous donors. We studied the effects of subcutaneous recombinant erythropoietin (rEPO) in subjects making frequent blood donations. Six healthy iron-replete male subjects took rEPO (200 U/kg) subcutaneously daily, and donated blood (450 mL) twice a week for 3 weeks. During a control study, these subjects also attempted twice-weekly blood donations without rEPO. Four other males given rEPO, including one with idiopathic hemochromatosis, waited until day 8 to begin blood donations. All healthy subjects took oral ferrous sulfate. Subcutaneous rEPO given with blood donations resulted in a marked reticulocytosis (mean peak value 568 +/- 159 x 10(9)/L v 235 +/- 77 x 10(9)/L, control study; P < .05), and enhanced RBC production at 28 days (1,208 +/- 227 mL v 719 +/- 161 mL, P < .05). rEPO in advance of blood donations was slightly less effective in normal subjects (941 +/- 139 mL, P < .05); however, the subject with hemochromatosis produced substantially more RBCs (1,764 mL) than any normal subject. rEPO-treated normal subjects (but not the rEPO-treated patient with hemochromatosis or untreated controls) produced iron-deficient RBCs with elevated zinc protoporphyrin levels and low hemoglobin content. These cells appeared within 1 week of rEPO administration and before laboratory confirmation of depleted iron stores. Thus, subcutaneous rEPO is an effective stimulant of erythropoiesis in nonanemic blood donors. However, in addition to eventual depletion of iron stores, early functional iron deficiency affects response to the drug.  相似文献   
60.
Simon  SI; Rochon  YP; Lynam  EB; Smith  CW; Anderson  DC; Sklar  LA 《Blood》1993,82(4):1097-1106
We have recently found that antibodies to L-selectin, the homing receptor on neutrophils, are as effective as those to beta 2-integrin at blocking formyl peptide-stimulated aggregation. Therefore, we investigated the requirements for expression of L-selectin and beta 2- integrin on adjacent cells during aggregation. Fluorescence flow cytometry allowed characterization of aggregates on the basis of size and color, as well as antibody binding to these two adhesive molecules. Formyl peptide-stimulated aggregate formation was measured for individual populations fluorescently labeled red (LDS-751) or green (CD44-FITC), and interpopulation red-green cell conjugates. Blocking either the beta 2-integrin or L-selectin adhesive epitope with monoclonal antibody on individual cell populations resulted in an approximately 50% reduction in two-color aggregation as compared with that in unblocked samples. Shedding the L-selectin on a cell population by preincubation with complexes of lipopolysaccharide and its plasma membrane binding protein also decreased aggregation to a control population by approximately 50%. We examined the aggregation of neutrophils from patients genetically deficient in beta 2-integrin and clinically leukocyte adhesion deficient (LAD). LAD adhesion to normal neutrophils was dependent on the expression of L-selectin on LAD cells and beta 2-integrin on normal cells. Thus, the minimum requirement for adhesion between two mixed populations of neutrophils was that one population expressed the beta 2-integrin and the other expressed the L- selectin adhesive epitope.  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