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   334217篇
  免费   28876篇
  国内免费   21657篇
耳鼻咽喉   3047篇
儿科学   3447篇
妇产科学   4942篇
基础医学   40840篇
口腔科学   5579篇
临床医学   46391篇
内科学   50658篇
皮肤病学   3141篇
神经病学   18997篇
特种医学   12134篇
外国民族医学   213篇
外科学   34217篇
综合类   50347篇
现状与发展   76篇
一般理论   20篇
预防医学   19870篇
眼科学   9771篇
药学   33204篇
  425篇
中国医学   17935篇
肿瘤学   29496篇
  2025年   94篇
  2024年   4375篇
  2023年   6769篇
  2022年   13518篇
  2021年   16710篇
  2020年   13069篇
  2019年   11635篇
  2018年   11499篇
  2017年   10070篇
  2016年   9515篇
  2015年   14436篇
  2014年   17869篇
  2013年   15380篇
  2012年   22897篇
  2011年   25820篇
  2010年   15927篇
  2009年   12269篇
  2008年   17021篇
  2007年   17029篇
  2006年   17063篇
  2005年   16780篇
  2004年   10673篇
  2003年   9760篇
  2002年   8439篇
  2001年   7465篇
  2000年   8273篇
  1999年   9007篇
  1998年   5474篇
  1997年   5498篇
  1996年   4339篇
  1995年   3928篇
  1994年   3217篇
  1993年   2097篇
  1992年   2827篇
  1991年   2415篇
  1990年   2118篇
  1989年   1861篇
  1988年   1563篇
  1987年   1353篇
  1986年   1107篇
  1985年   912篇
  1984年   527篇
  1983年   373篇
  1982年   242篇
  1981年   238篇
  1980年   190篇
  1979年   221篇
  1977年   89篇
  1974年   102篇
  1973年   83篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.

Objectives

We aimed to evaluate the relationship between baseline renal function and changes in telomere length in Han Chinese.

Methods

The telomere restriction fragment (TRF) length of leukocytes in the peripheral blood was measured in healthy volunteers recruited in 2014. The estimated glomerular filtration rate (eGFR) was calculated based on serum creatinine (Scr) and serum cystatin C (CysC)-eGFRcys and eGFRScr-cys through the Cockcroft-Gault formula (eGFRC-G) or the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI / eGFRCKD-EPI) equation. The correlation between telomere length changes over time and renal function was analyzed.

Results

Leukocyte TRF lengths were negatively correlated to age (r = -0.393, p < 0.001) and serum CysC (r = -0.180, p < 0.01), while positively associated with eGFRCKD-EPI, eGFRC-G, eGFRcys, and eGFRScr-cys (r = 0.182, 0.122, 0.290, and 0.254 respectively, p < 0.01). The 3-year change of telomere length was 46 bp/years. When adjusted for age, the associations between telomere length changes and baseline, subsequent TRF lengths, and serum CysC were no longer present. No association was observed between TRF length changes and renal function.

Conclusion

The rate of telomere length changes was affected by age and baseline telomere length. The telomere length changes might be important markers for aging.
  相似文献   
83.
Sewage contains a mixed ecosystem of diverse sets of microorganisms, including human pathogenic viruses. Little is known about how conventional as well as advanced treatments of sewage, such as ozonation, reduce the environmental spread of viruses. Analyses for viruses were therefore conducted for three weeks in influent, after conventional treatment, after additional ozonation, and after passing an open dam system at a full-scale treatment plant in Knivsta, Sweden. Viruses were concentrated by adsorption to a positively charged filter, from which they were eluted and pelleted by ultracentrifugation, with a recovery of about 10%. Ion Torrent sequencing was used to analyze influent, leading to the identification of at least 327 viral species, most of which belonged to 25 families with some having unclear classification. Real-time PCR was used to test for 21 human-related viruses in inlet, conventionally treated, and ozone-treated sewage and outlet waters. The viruses identified in influent and further analyzed were adenovirus, norovirus, sapovirus, parechovirus, hepatitis E virus, astrovirus, pecovirus, picobirnavirus, parvovirus, and gokushovirus. Conventional treatment reduced viral concentrations by one to four log10, with the exception of adenovirus and parvovirus, for which the removal was less efficient. Ozone treatment led to a further reduction by one to two log10, but less for adenovirus. This study showed that the amount of all viruses was reduced by conventional sewage treatment. Further ozonation reduced the amounts of several viruses to undetectable levels, indicating that this is a promising technique for reducing the transmission of many pathogenic human viruses.  相似文献   
84.
Angiolipoma of the tongue: report of a case   总被引:1,自引:0,他引:1  
Angiolipoma is a rare variety of lipoma in the maxillofacial region. Only eight cases have been documented so far. A case in which an angiolipoma occurred within the tongue of a 49-year-old man is described here. The difference from earlier cases occurring in the tongue is noted. Close follow-up has, as yet, revealed no recurrence.  相似文献   
85.
Effect of dental caries on pulp tissue   总被引:1,自引:0,他引:1  
  相似文献   
86.
We investigated the clinical and histopathologic features of 26 cases of mucocele of the glands of Blandin-Nuhn. There was a female predominance, and most patients were younger than 20 years. Fifteen patients first visited a medical doctor and 9 visited a dentist before being referred to our department. The average duration from the time the lesion was first noticed to the patient's visit was 3.6 months. All lesions were located on the ventral surface of the tongue. In 17 patients, mucoceles were seen at the tip of the tongue, whereas 9 lesions occurred more posteriorly. Lesions were situated at the midline in 19 patients and laterally in 7 patients. All lesions presented as an exophytic mass, often with a polypoid appearance. All mucoceles were histopathologically of the extravasation type, suggesting that trauma may represent a frequent initiating factor.  相似文献   
87.
Sporadic cases have been reported of ectopic thymic tissue formed along the path of embryologic descent from the mandibular region to the mediastinum, usually manifesting as an asymptomatic mass. Here is reported the case of an 8-month-old boy with a tender palpable mass in the right upper lateral neck. Preoperative posteroanterior chest radiograph revealed normal structures in the mediastinum superior including the thymus. Magnetic resonance imaging showed a 4-cm x 4-cm soft-tissue mass in the left submandibular region. Surgical resection was performed and histopathologic examination showed that the mass was composed of thymic lymphoid tissue and epithelial cells. Immunohistochemical features included positive expression of LCA, CKpan, EMA, CD20 and CD43 antibodies. The clinical 14-month follow up was negative and the child was growing normally after operation. Ectopic thymus in the submandibular region is uncommon; surgical treatment is the definitive means of pathological diagnosis. Prior to surgery, the presence of a mediastinal thymus should be confirmed to prevent the risk of a total thymectomy.  相似文献   
88.
89.

Background

The oral health status of rural residents in the People's Republic of China has not been extensively studied and the relationship between poor oral health and esophageal cancer (EC) is unclear. We aim to report the oral health status of adults participating in an EC screening study conducted in a rural high-risk EC area of China and to explore the relationship between oral health and esophageal dysplasia.

Methods

National Health and Nutrition Examination Survey (NHANES) oral health examination procedures and the Modified Gingival Index (MGI) were used in a clinical study designed to examine risk factors for esophageal cancer and to test a new esophageal cytology sampling device. This study was conducted in three rural villages in China with high rates of EC in 2002 and was a collaborative effort involving investigators from the National Institutes of Health and the Cancer Institute of the Chinese Academy of Medical Sciences.

Results

Nearly 17% of the study participants aged 40–67 years old were edentulous. Overall, the mean number of adjusted missing teeth (including third molars and retained dental roots) was 13.8 and 35% had 7 contacts or less. Women were more likely to experience greater tooth loss than men. The average age at the time of first tooth loss for those with no posterior functional contacts was approximately 41 years for men and 36 years for women. The mean DMFT (decayed, missing, and filled teeth) score for the study population was 8.5. Older persons, females, and individuals having lower educational attainment had higher DMFT scores. The prevalence of periodontal disease (defined as at least one site with 3 mm of attachment loss and 4 mm of pocket depth) was 44.7%, and 36.7% of the study participants had at least one site with 6 mm or more of attachment loss. Results from a parsimonious multivariate model indicate that participants with poor oral health wemore likely to have esophageal dysplasia (OR = 1.59; 95% CI 1.06, 2.39).

Conclusion

This report describes the first use of NHANES oral health protocols employed in a clinical study conducted outside of the United States. The extent and severity of poor oral health in this Chinese study group may be an important health problem and contributing factor to the prevalence of EC.  相似文献   
90.
应用牵张成骨术整复腭裂骨质缺损的组织学研究   总被引:1,自引:3,他引:1  
目的 :观察牵张成骨术整复腭裂过程中 ,新骨组织形成与改建活动的特点 ,探讨新骨生成的规律。方法 :家猫 14只为实验对象。其中 12只建立人工腭裂实验模型。实验组 (动物 10只 ) :以 0 .4mm× 2次 /d的速度与频率牵张整复腭裂缺损。于术后固定期 2、4、6、8及 12周 ,观察期结束前 6d ,各对 2只动物肌注四环素标记 ( 30mg/kg)。 6d后取标本 ,切片行荧光显微镜及组织学观察 ,并与实验对照组及空白对照组 (动物各2只 )结果对比。结果 :实验组标本牵张区新骨组织均为膜内成骨 ,由中央向外分为胶原纤维区、新骨形成区及改建成熟区 ;随时间发展 ,新生骨逐渐取代纤维组织并改建成熟。软组织也得到相应伸展。对照组裂隙无自行修复。结论 :应用牵张成骨术矫治腭裂骨质缺损 ,以原位产生新骨 ,增加骨量的方式推移骨运送盘封闭腭裂裂隙。在良好固定条件下 ,新骨形成与改建活跃 ,最终整复腭裂骨质缺损并适应功能需要  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