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   4921篇
  免费   270篇
  国内免费   105篇
耳鼻咽喉   37篇
儿科学   248篇
妇产科学   102篇
基础医学   603篇
口腔科学   159篇
临床医学   416篇
内科学   746篇
皮肤病学   20篇
神经病学   270篇
特种医学   377篇
外科学   690篇
综合类   463篇
预防医学   477篇
眼科学   177篇
药学   290篇
  3篇
中国医学   91篇
肿瘤学   127篇
  2024年   7篇
  2023年   112篇
  2022年   220篇
  2021年   282篇
  2020年   224篇
  2019年   254篇
  2018年   240篇
  2017年   181篇
  2016年   180篇
  2015年   162篇
  2014年   319篇
  2013年   330篇
  2012年   240篇
  2011年   272篇
  2010年   183篇
  2009年   222篇
  2008年   233篇
  2007年   240篇
  2006年   192篇
  2005年   160篇
  2004年   141篇
  2003年   91篇
  2002年   70篇
  2001年   90篇
  2000年   76篇
  1999年   66篇
  1998年   60篇
  1997年   53篇
  1996年   44篇
  1995年   45篇
  1994年   22篇
  1993年   20篇
  1992年   25篇
  1991年   16篇
  1990年   17篇
  1989年   19篇
  1988年   17篇
  1987年   16篇
  1986年   15篇
  1985年   14篇
  1984年   20篇
  1983年   14篇
  1982年   19篇
  1981年   21篇
  1980年   15篇
  1979年   5篇
  1978年   8篇
  1977年   7篇
  1974年   5篇
  1973年   5篇
排序方式: 共有5296条查询结果,搜索用时 0 毫秒
991.
目的 调查苏州汉族群体中5个X-STR的等位基因和单倍型分布,以及分析这些基因座间的连锁不平衡关系.方法 应用Chelex法提取样本DNA,PCR扩增5个X-STR,应用自动测序仪对PCR产物进行分型.结果 苏州汉族群体中,DXS7423、DXS10147、DXS10146、DXS10134、DXS8377分别观察到5、6、15、21、15个等位基因;男女性样本间,DXS7423、DXS10147、DXS10134的等位基因频率差异无统计学意义,P值分别为0.161、0.756、0.179;DXS10146、DXS8377等位基因频率差异具有统计学意义,P值分别为0.008和0.005.5个X-STR的观察杂合度在0.505~0.845间,DPf值在0.684~0.977间,DPm值在0.487 ~0.902间,MCEtrio值在0.469~0.894间,MCEduo值在0.266~0.860间.男性样本中,观察到111种单倍型,单倍型变异度为0.9916.结论 苏州汉族群体中,5个X-STR中DXS10146、DXS10134、DXS8377多态性较好;5个X- STR构成的单倍型鉴别能力较高.  相似文献   
992.
提出一种基于邻域信息和高斯加权卡方距离的脊椎MR图像椎体的自动分割方法.由于成像过程中存在噪声和各向异性的影响,单个像素的灰度值对噪声敏感,为此采用5像素×5像素窗口,提取每个像素点邻域内的空间-灰度特征,该特征对噪声具有较强的鲁棒性.利用高斯加权的卡方距离度量两个像素的相似性,构造一种全新的相似度矩阵;而单一的尺度参数存在一定局限性,所以引入一种自适应的局部收缩因子,完成脊椎MR图像椎体的自动分割.实验结果表明,新算法克服了传统方法中常见的过分割和欠分割现象,覆盖率均在96%以上;分割的正常和退行性改变椎体光滑且清晰,具有分割结果准确、鲁棒性强的优点.作为一种一般性的分割方法,该算法可以拓展到其他器官的分割中.  相似文献   
993.
Background: A disease outbreak of A (H1N1) PDM09 was reported in Andaman and Nicobar islands in 2009 with an attack rate of 33.5% among settler population and 26.3% among the aboriginal Nicobarese tribe. During the ongoing outbreak of A (H1N1) PDM09 disease in different parts of the world, a subject working in Dubai city of Saudi Arabia, came to Port Blair, following which the pandemic triggered for the first time in these Islands. Materials and Methods: During the period August 2009 to January 2011, 30 confirmed cases of Influenza A (H1N1) PDM09 virus infection was detected. To understand the genetic relationship, the NA gene sequences of the viruses were phylogenetically analysed together along with the virus sequence isolated from other parts of the world. Result: Formation of multiple clusters were observed, with the sequences of Andaman Islands, mainland India, Mexico, Saudi Arabia and few other counties clustering together. The sequence analysis data revealed that there was no specific mutation conferring resistance to oseltamivir among the Andaman A (H1N1) PDM09 virus isolates. The result of phylogenetic analysis have also revealed that the A (H1N1) PDM09 virus might have spread in these remote Islands of India via the subject from Saudi Arabia/Dubai. Conclusion: A (H1N1) PDM09 Influenza outbreak have highlighted the need to strengthen the region-specific pandemic preparedness plans and surveillance strategies.  相似文献   
994.
在腹腔镜模拟训练过程中,研究不同训练模式下被测试者的注视策略,探索腹腔镜训练的新模式。被测试者被随机分为无指导组,视频学习组和专家指导组进行左右移环任务。利用Tobii X1 Light型眼动仪调用模拟训练箱中的摄像头,采集受试者的眼动数据。通过对数据处理分析,计算注视点个数,平均注视时间,注视时间百分比,扫描距离指标。与对照组相比,视频学习和专家指导模式下,任务完成时间降低23%,扫描距离缩短25%,注视点个数减少17%,平均注视时间没有显著差异。视频组和专家指导组之间无明显差异。结果表明不同学习模式下,被测试者的注视行为有明显差异。视频学习和专家指导下效果更好,可以用专家操作时的注视点视频指导初级训练者进行训练。  相似文献   
995.
Abstract

Background: Investigation of allele and genotype frequencies of microsatellite loci in various populations is an essential pre-requisite in forensic application.

Aim: The present study obtained population genetic data and forensic parameters of 39 autosomal Short Tandem Repeats (STRs) loci from a Chinese Li ethnic group and estimated the genetic relationships between Li and other reference populations.

Subjects and methods: Thirty-nine STR loci, which include D19S433, D5S818, D21S11, D18S51, D6S1043, D3S1358, D13S317, D7S820, D16S539, CSF1PO, Penta D, D2S441, vWA, D8S1179, TPOX, Penta E, TH01, D12S391, D2S1338, FGA, D6S477, D18S535, D19S253, D15S659, D11S2368, D20S470, D1S1656, D22-GATA198B05, D8S1132, D4S2366, D21S1270, D13S325, D9S925, D3S3045, D14S608, D10S1435, D7S3048, D17S1290 and D5S2500, were amplified in two multiplex DNA-STR fluorescence detection systems for 189 unrelated healthy individuals of the Chinese Li ethnic group. The allele frequency distribution and several parameters commonly used in forensic science were statistically analysed.

Results: A total of 378 alleles were observed with corresponding allelic frequencies ranging from 0.0026–0.5899. The power of discrimination and power of exclusion ranged from 0.7569–0.9672 and 0.2513–0.7355, respectively. The power of exclusion (PE) ranged from 0.2580–0.7943 for trio paternity cases and 0.1693–0.5940 for duo paternity cases. The polymorphism information content (PIC) ranged from 0.5001–0.8611. The cumulative match probability across these 39 loci was 2.4242?×?10?38.

Conclusion: The results indicate that 39 STR loci are polymorphic among the Li ethnic group in Hainan Island in the South China Sea. This set of polymorphic STR loci provide highly polymorphic information and forensic efficiency for forensic individual identification and paternity testing, as well as basic population data for population genetics and anthropological research.  相似文献   
996.
Abstract

Myocardial infarction (MI) is a coronary artery disease acquired due to the lack of blood supply in one or more sections of the myocardium, resulting in necrosis in that region. It has different types based on the region of necrosis. In this paper, a statistical approach for classification of Anteroseptal MI (ASMI) is proposed. The first step of the method involves noise elimination and feature extraction from the Electrocardiogram (ECG) signals, using multi-resolution wavelet analysis and thresholding-based techniques. In the next step a classification scheme is developed using the nearest neighbour classification rule (NN rule). Both temporal and amplitude features relevant for automatic ASMI diagnosis are extracted from four chest leads v1–v4. The distance metric for NN classifier is calculated using both Euclidian distance and Mahalanobis distance. A relative comparison between these two techniques reveals that the later is superior to the former, as evident from the classification accuracy. The proposed method is tested and validated using the PTB diagnostic database. Classification accuracy for Mahalanobis distance and Euclidean distance-based NN rule are 95.14% and 81.83%, respectively.  相似文献   
997.
The authors report a case of a 44‐year‐old male found to have unusual origins of the celiac trunk (CT) and superior mesernteric artrery (SMA) as revealed by routine multidetector computed tomograph (MDCT) angiography. The CT and SMA originate from the thoracic aorta (TA) 21 mm and 9 mm above the aortic hiatus, respectively. The median arcuate ligament (MAL) is located at the level of the L1–L2 intervertebral disc. The course of the CT descends in the thoracic cavity making a 14° acute downward angle in front of the TA; below the level of the MAL, the CT descends, making an angle of 47°. The course of the SMA descends at both the thoracic and abdominal level making an angle of 17°, and having an aortomesenteric distance of 9 mm at the level of the third part of the duodenum. In the present case, the supradiaphragmatic origin of the CT and the SMA was determined by their incomplete caudal descent, associated with a pronounced apparent descent of the diaphragm. A thoracic origin of the CT and SMA and the acute downward aortomesenteric angle (17°) associated with a reduced aortomesenteric distance at the level of the third part of the duodenum (9 mm), although no clinical signs are present, may predispose the patient to develop simultaneously a triple syndrome: the compression of CT by MAL (celiac axis compression syndrome), the compression of SMA by MAL (superior mesenteric artery compression syndrome), and the compression of the duodenum by the SMA (superior mesenteric artery syndrome). Clin. Anat. 26:975–979, 2013. © 2013 Wiley Periodicals, Inc.  相似文献   
998.
Insulin has been shown to influence intestinal structure and absorptive function. The purpose of the present study was to evaluate the effects of parenteral insulin on structural intestinal adaptation, cell proliferation, and apoptosis in a rat model of short bowel syndrome (SBS). Male Sprague-Dawley rats were divided into three experimental groups: sham rats underwent bowel transection and reanastomosis, SBS rats underwent a 75% small bowel resection, and SBS-INS rats underwent a 75% small bowel resection and were treated with insulin given subcutaneously at a dose of 1 U/kg, twice daily, from day 3 through day 14. Parameters of intestinal adaptation, enterocyte proliferation, and enterocyte apoptosis were determined on day 15 following operation. SBS rats demonstrated a significant increase in jejunal and ileal bowel and mucosal weight, villus height and crypt depth, and cell proliferation index compared with the sham group. SBS-INS animals demonstrated higher jejunal and ileal bowel and mucosal weights, jejunal and ileal mucosal DNA and protein, and jejunal and ileal crypt depth compared with SBS animals. SBS-INS rats also had a greater cell proliferation index in both jejunum and ileum and a trend toward a decrease in enterocyte apoptotic index in jejunum and ileum compared with the SBS untreated group. In conclusion, parenteral insulin stimulates structural intestinal adaptation in a rat model of SBS. Increased cell proliferation is the main mechanism responsible for increased cell mass.  相似文献   
999.
According to epidemiological studies, insomnia is associated with an increase in risk of traffic accidents. Recent investigations revealed that patients with insomnia had driving performance impairment under monotonous conditions. However, it is unclear whether other driving abilities may be impacted by insomnia, especially those needing more attentional resources than those involved in monotonous driving. Other findings revealed that impaired performances are more likely to occur with the increase of cognitive demands. However, such tests did not reflect difficulties in situations of everyday life expressed by patients with insomnia, such as driving in an urban environment with traffic and critical situations. Therefore, behaviour in situations encountered in everyday life has to be explored. The aim of the present study was to assess driving performances of patients with insomnia in daily routine tasks such as urban and car‐following tests. For this purpose, 15 patients with insomnia and 16 good sleepers performed an urban test of driving with original risk scenarios and a car‐following test during the middle afternoon. No significant behavioural difference between patients with insomnia and good sleepers has been found in both the urban test and the car‐following test, showing that patients with insomnia have no impairment in behaviour implicated in daily contexts driving tasks of short period of time performed in the late afternoon. Although our results provide a first step towards knowledge of behavioural performance during daily routine driving tasks in patients with insomnia, future studies are needed using on‐the‐road driving tests and/or different population of patients with insomnia before generalisation.  相似文献   
1000.
短肠综合征的康复治疗   总被引:18,自引:0,他引:18  
目的总结27例短肠综合征病人康复治疗的经验,介绍短肠康复治疗的具体方法,探讨改善短肠病人营养状况、促进肠功能代偿的措施。方法短肠康复治疗包括营养支持、应用谷氨酰胺和生长激素促进肠粘膜生长、富含膳食纤维的短肠康复饮食、减轻短肠临床症状以及预防和治疗短肠并发症等措施。1997年1月至2000年7月间共27例短肠患者接受了29次康复治疗,患者平均年龄38.5岁±19.3岁。剩余小肠长度范围15~80cm,平均46.8cm±23.4cm,15例有回盲瓣。从肠切除至接受康复治疗的平均时间为86d±105d。结果治疗后病人的营养状况明显改善,肠道吸收功能有所增强。随访超过2年者8例,4例完全脱离肠外营养,随访时间超过1年者13例,有10例完全脱离肠外营养。结论短肠康复治疗能够有效地改善短肠病人的营养状况、并能促进肠功能代偿,治疗效果与残留小肠长度、治疗开始的时间和病人年龄有关,及早进行康复治疗能够促进肠功能代偿,减少病人对肠外营养的依赖。  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