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   2569040篇
  免费   189376篇
  国内免费   7596篇
耳鼻咽喉   34266篇
儿科学   84952篇
妇产科学   71593篇
基础医学   360767篇
口腔科学   69585篇
临床医学   233310篇
内科学   510948篇
皮肤病学   62422篇
神经病学   211958篇
特种医学   99851篇
外国民族医学   736篇
外科学   385291篇
综合类   50800篇
现状与发展   5篇
一般理论   968篇
预防医学   194552篇
眼科学   56479篇
药学   187739篇
  19篇
中国医学   5361篇
肿瘤学   144410篇
  2019年   20687篇
  2018年   29345篇
  2017年   22706篇
  2016年   26302篇
  2015年   29638篇
  2014年   40614篇
  2013年   60570篇
  2012年   80422篇
  2011年   84680篇
  2010年   51149篇
  2009年   49277篇
  2008年   79144篇
  2007年   83978篇
  2006年   85686篇
  2005年   81833篇
  2004年   78797篇
  2003年   75984篇
  2002年   73182篇
  2001年   128220篇
  2000年   131038篇
  1999年   109835篇
  1998年   29635篇
  1997年   26207篇
  1996年   26439篇
  1995年   27245篇
  1994年   24941篇
  1993年   23288篇
  1992年   85060篇
  1991年   81543篇
  1990年   78737篇
  1989年   76003篇
  1988年   69403篇
  1987年   67953篇
  1986年   63500篇
  1985年   60466篇
  1984年   44884篇
  1983年   37847篇
  1982年   22370篇
  1981年   19905篇
  1979年   38890篇
  1978年   27369篇
  1977年   23164篇
  1976年   21419篇
  1975年   22757篇
  1974年   26737篇
  1973年   25330篇
  1972年   23730篇
  1971年   21933篇
  1970年   20155篇
  1969年   19407篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
105.
The corona virus disease 2019 (COVID-19) pandemic has resulted in most nations deciding upon self-isolation and social distancing policies for their citizens to control the pandemic and reduce hospital admission. This review aimed at evaluating the effect of physical activity on mental well-being during the COVID-19 pandemic. It was concluded that the COVID-19 pandemic may lead to augmented levels of angiotensin-converting enzyme (ACE)-2 that led to cardiovascular and neurological disorders associated with highly inflammatory effects of viral infection affecting the brain tissues leading to damage of the nervous system and resulting in cognition dysfunction, insulin sensitivity reduction, and behavioral impairments. Anxiety and depression may lead to negative effects on various quality of life domains, such as being physically inactive. Regular physical activities may reduce inflammatory responses, improve ACE-2 responses, and improve mental well-being during self-isolation and social distancing policies related to the COVID-19 pandemic. Further studies should be conducted to assess the different intensities of physical activities on cardiovascular function, and mental well-being during the COVID-19 pandemic.  相似文献   
106.
107.
A 21‐year‐old female presented with a 5‐year history of an erythematous papule on her right breast. The biopsy showed a dense, dermal nodular infiltrate, extending focally into the subcutaneous tissue. The infiltrate was composed predominantly of pleomorphic cells with bi‐lobed, multi‐lobed, horseshoe, or ring‐shaped nuclei. There was a smaller subset of monomorphous cells characterized by a round, reniform, or elongated single‐lobed nucleus. Accompanying cells included few foamy histiocytes, lymphocytes, and numerous scattered eosinophils. No necrosis, vascular invasion, or ulceration was present. The pleomorphic and monomorphic granular cells were positive for Giemsa stain as well as for tryptase, CD117, CD68, CD2, and CD30 immunohistochemistry and negative for S100, CD1a, myeloperoxidase, lysozyme, and CD56. Clinical examination was negative for any additional similar lesions and serum tryptase was within normal limits. The bone marrow was not biopsied. In addition, fluorescent in situ hybridization revealed multiple clones with loss of number 5 chromosome and PDGFRA and HRAS mutations. The lesion did not recur or progress after a 6‐year clinical follow‐up. To our full knowledge, we report the first case of pleomorphic mastocytoma with loss of chromosome 5 and PDGFRA and HRAS mutations.  相似文献   
108.
109.
110.
IntroductionOrgan-based tube current modulation (OBTCM) is designed for anterior dose reduction in Computed Tomography (CT). The purpose was to assess dose reduction capability in chest CT using three organ dose modulation systems at different kVp settings. Furthermore, noise, diagnostic image quality and tumour detection was assessed.MethodsA Lungman phantom was scanned with and without OBTCM at 80–135/140 kVp using three CT scanners; Canon Aquillion Prime, GE Revolution CT and Siemens Somatom Flash. Thermo-luminescent dosimeters were attached to the phantom surface and all scans were repeated five times. Image noise was measured in three ROIs at the level of the carina. Three observers visually scored the images using a fivestep scale. A Wilcoxon Signed-Rank test was used for statistical analysis of differences.ResultsUsing the GE revolution CT scanner, dose reductions between 1.10 mSv (12%) and 1.56 mSv (24%) (p < 0.01) were found in the anterior segment and no differences posteriorly and laterally. Total dose reductions between 0.64 (8%) and 0.91 mSv (13%) were found across kVp levels (p < 0.00001). Maximum noise increase with OBTCM was 0.8 HU. With the Canon system, anterior dose reductions of 6–10% and total dose reduction of 0.74–0.76 mSv across kVp levels (p < 0.001) were found with a maximum noise increase of 1.1 HU. For the Siemens system, dose increased by 22–51% anteriorly; except at 100 kVp where no dose difference was found. Noise decreased by 1 to 1.5 HU.ConclusionOrgan based tube current modulation is capable of anterior and total dose reduction with minimal loss of image quality in vendors that do not increase posterior dose.Implications for practiceThis research highlights the importance of being familiar with dose reduction technologies.  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