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   17224篇
  免费   1210篇
  国内免费   69篇
耳鼻咽喉   134篇
儿科学   464篇
妇产科学   424篇
基础医学   2508篇
口腔科学   501篇
临床医学   1615篇
内科学   4211篇
皮肤病学   335篇
神经病学   1428篇
特种医学   505篇
外国民族医学   4篇
外科学   2225篇
综合类   146篇
一般理论   15篇
预防医学   1525篇
眼科学   311篇
药学   1092篇
中国医学   64篇
肿瘤学   996篇
  2023年   108篇
  2022年   188篇
  2021年   431篇
  2020年   291篇
  2019年   400篇
  2018年   490篇
  2017年   336篇
  2016年   328篇
  2015年   408篇
  2014年   533篇
  2013年   809篇
  2012年   1149篇
  2011年   1251篇
  2010年   679篇
  2009年   577篇
  2008年   1001篇
  2007年   1077篇
  2006年   1065篇
  2005年   966篇
  2004年   917篇
  2003年   867篇
  2002年   854篇
  2001年   334篇
  2000年   363篇
  1999年   351篇
  1998年   176篇
  1997年   146篇
  1996年   136篇
  1995年   134篇
  1994年   105篇
  1993年   104篇
  1992年   189篇
  1991年   196篇
  1990年   166篇
  1989年   118篇
  1988年   111篇
  1987年   91篇
  1986年   108篇
  1985年   104篇
  1984年   86篇
  1983年   63篇
  1982年   81篇
  1981年   41篇
  1980年   36篇
  1979年   46篇
  1978年   48篇
  1977年   40篇
  1975年   39篇
  1973年   44篇
  1970年   33篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
T cells are known to develop a critical role in the pathogenesis of atopic dermatitis (AD) and bronchial asthma. T cells involved in AD express the skin homing receptor CLA, but no lung homing receptor has been identified in bronchial asthma. We compared different cell markers and the cytokine production in T cells from children with AD or bronchial asthma. We studied the involvement of CLA+ and CLA- T-cell subpopulations in these diseases. We studied 20 children with acute AD lesions, 15 with mild persistent asthma, and 15 non-atopic controls. All patients were sensitized to house dust mite (DP) and evaluated during the acute phase. Total and specific IgE were measured by immunoassay and the expression of different cell markers and the cytokine production was analyzed by flow cytometry in peripheral blood mononuclear cells. Total IgE was significantly higher in AD children and IgE to DP in the asthmatic children. There was a significant increase in CD25+ CD4+ cells in asthmatic children and in HLA-DR+ CD4+ and HLA-DR+ CD8+ cells in AD. In the CD4+ subsets, there was an increase in IL-13, IL-5 and TNF-alpha in AD compared to controls, a decrease in IFN-gamma in asthmatic children compared to controls, and an increase in IL-13, IL5, IL2, TNF-alpha, and IFN-gamma in the AD compared to asthmatic children. Changes in cytokine production were mainly detected in CLA+ cells in AD and in CLA- cells in asthma. Differences exist in total and specific IgE, activation markers, and cytokine patterns between AD children and children with asthma, with the former expressing a Th2 pattern whereas in asthmatic children we only detected a decrease in IFN-gamma. Moreover, the subpopulations (CLA+ vs. CLA-) expressing these changes were different, indicating that the underlying mechanisms in the two diseases are not exactly the same.  相似文献   
62.
Stomach rupture can occur as a consequence of the expansion of compressed air during rapid ascent after diving. We present the case of a middle-aged woman who suffered a gastric tear from surfacing too quickly after diving, and discuss the diagnosis and management of such patients by reviewing previously reported similar events. Gastric barotrauma should be suspected in divers who complain of abdominal pain, even in the absence of frank signs of peritoneal irritation. Although pneumoperitoneum is always present in these patients, it can also occur as a consequence of pulmonary barotrauma, making gastroscopy or radiological contrast studies, or both, essential for a definitive diagnosis. Surgical repair represents the treatment of choice for an active full-thickness tear and, if associated with arterial gas embolism or decompression sickness, should ideally be performed in a center where a category I (intensive care-capable) hyperbaric unit is available. Received: March 18, 2002 / Accepted: September 3, 2002 Reprint requests to: L.V. Titu  相似文献   
63.
OBJECTIVE: This study was designed to evaluate the efficacy of magnesium carbonate as a phosphate binder in hemodialysis patients. DESIGN: This study was a prospective, randomized, open-label trial comparing magnesium carbonate/calcium carbonate versus calcium acetate as a sole phosphate binder. SETTING: This study involved outpatient hemodialysis. PARTICIPANTS: We recruited 30 stable hemodialysis patients without a history of frequent diarrhea. INTERVENTION: After receiving informed consent, we randomized patients 2:1 to magnesium carbonate versus calcium acetate. The dose of each binder was titrated to achieve the Kidney Disease Outcomes Quality Initiative (K/DOQI) phosphate target of <5.5 mg/dL. MAIN OUTCOME MEASURE: The efficacy-phase serum phosphorus concentration and the percentage of patients meeting K-DOQI targets for phosphorus, along with the daily elemental calcium intake, were the primary outcome measures. RESULTS: Magnesium carbonate provided equal control of serum phosphorus (70.6% of the magnebind group and 62.5% of the calcium acetate group had their average serum phosphorus within the K-DOQI target during the efficacy phase), while significantly reducing daily elemental calcium ingestion from phosphate binders (908 +/- 24 vs. 1743 +/- 37 mg/day, P < .0001). CONCLUSION: Magnesium carbonate was generally well-tolerated in this selected patient population, and was effective in controlling serum phosphorus while reducing elemental calcium ingestion.  相似文献   
64.
With improvements in the safety of Whipple resection in recent decades, surgeons have continued to explore the role of more extensive lymphadenectomy in hope of improving long-term survival. A systematic literature search of level I evidence addressing the role of the extent of lymphadenectomy was undertaken. Only reports of prospective, randomized controlled trials comparing pancreaticoduodenectomy with standard lymphadenectomy to pancreaticoduodenectomy with extended lymphadenectomy where information regarding survival, morbidity, mortality, the number of resected lymph nodes in each group and detailed operative technique were included. Four prospective, randomized trials comprising some 424 patients and one meta-analysis were identified. In aggregate, these studies confirmed that the number of resected lymph nodes was significantly higher in the pancreaticoduodenectomy with extended lymphadenectomy group. Morbidity and mortality rates were comparable. Postoperative diarrhea in the early months after operation was problematic in patients undergoing extended lymphadenectomy. In none of the studies was a benefit in long-term survival demonstrated. Standard pancreaticoduodenectomy continues to be the operation of choice for adenocarcinoma of the head of the pancreas. Presented at The Society for Surgery of the Alimentary Tract Postgraduate Course “Systematic Reviews of Pancreaticobiliary Disease Customized for the Gastroenterologist and Gastrointestinal Surgeon” on May 20, 2007, Washington, D.C.  相似文献   
65.
66.
67.
68.
The use of stimulus modifications in teaching involves altering the materials of a task in order to simplify its execution. Though their use in teaching stimulus discriminations to people with developmental disabilities has been extensively investigated, less attention has been given to their utilization in teaching response topography. This paper offers some general guidelines about their use for this purpose. In relation to their design, it is suggested that the aim should be to reduce the demands made by task components, to eliminate components, and/or to increase the attentional value of the discriminating features of the response topography. In relation to their application, guidelines are suggested about when they should be employed in conjunction with response prompts; when they should be used, either alone or in conjunction with response prompts, in preference to response prompts alone; whether one or a series of modifications is required; and at what point during teaching should probe trials on the unmodified task be introduced.  相似文献   
69.
The polyanionic compound suramin triggers enterocyte-like differentiation of the human colic adenocarcinoma cell clone HT29-D4. We now demonstrate that suramin interferes with the binding of IGF-I to its receptor at the surface of HT29-D4 cells. Half-maximum inhibition of 125I-IGF-I binding was obtained in the presence of 25 micrograms/ml suramin. Moreover, the drug was able to dissociate 125I-IGF previously bound to its cell surface receptor. Affinity labeling HT29-D4 cells were cultured in the presence of 10 micrograms/ml of alpha-IR3, a monoclonal antibody directed against the binding site of IGF-I, an inhibition of cell proliferation and a stimulation of cell differentiation was observed. After 10 days of treatment with alpha-IR3, HT29-D4 cells formed a regular monolayer of enterocyte-like cells exhibiting an apical brush border and tight junctions delimiting two domains of the plasma membrane (apical and basolateral). Furthermore, we show that IGF-I significantly increased the initial rate of glucose uptake by HT29-D4 cells, while we have previously shown that suramin decreased glucose consumption. From these data we conclude that IGF-I secreted by the cells themselves, stimulates proliferation of HT29-D4 cells via an autocrine mechanism. Blockade of this stimulation by suramin or by a specific monoclonal antibody inhibits cell growth, glucose uptake and triggers the process of enterocytic differentiation.  相似文献   
70.
The effect of the degree of illiteracy (complete or incomplete) on phonological skills, verbal and visual memory and visuospatial skills is examined in 97 normal Brazilian adults who considered themselves illiterate, and 41 Brazilian school children aged 7 to 8 years, either nonreaders or beginning readers. Similar literacy effects were observed in children and in adults. Tasks involving phonological awareness and visual recognition memory of nonsense figures distinguish the best nonreaders and beginning readers. Children performed better than adults at oral repetition of short items and figure recall, and adults better than children at semantic verbal fluency, digit span, and word list recall. A principal component analysis of the correlations between tasks showed that phonological awareness/reading, phonological memory/oral repetition, and semantic verbal memory/fluency tasks, generated different components. The respective role of culturally based preschool activities and literacy on the cognitive functions that are explored in this study is discussed.  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