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   12208篇
  免费   1171篇
  国内免费   232篇
耳鼻咽喉   84篇
儿科学   224篇
妇产科学   155篇
基础医学   762篇
口腔科学   186篇
临床医学   1557篇
内科学   1455篇
皮肤病学   125篇
神经病学   450篇
特种医学   617篇
外国民族医学   3篇
外科学   908篇
综合类   2340篇
一般理论   2篇
预防医学   1957篇
眼科学   147篇
药学   1255篇
  101篇
中国医学   376篇
肿瘤学   907篇
  2024年   49篇
  2023年   309篇
  2022年   541篇
  2021年   889篇
  2020年   891篇
  2019年   544篇
  2018年   510篇
  2017年   605篇
  2016年   662篇
  2015年   563篇
  2014年   1092篇
  2013年   1083篇
  2012年   806篇
  2011年   725篇
  2010年   510篇
  2009年   453篇
  2008年   423篇
  2007年   449篇
  2006年   346篇
  2005年   317篇
  2004年   230篇
  2003年   203篇
  2002年   169篇
  2001年   146篇
  2000年   121篇
  1999年   98篇
  1998年   104篇
  1997年   85篇
  1996年   86篇
  1995年   70篇
  1994年   76篇
  1993年   69篇
  1992年   52篇
  1991年   40篇
  1990年   39篇
  1989年   38篇
  1988年   29篇
  1987年   24篇
  1986年   30篇
  1985年   30篇
  1984年   20篇
  1983年   12篇
  1982年   21篇
  1981年   12篇
  1980年   8篇
  1979年   8篇
  1978年   9篇
  1976年   4篇
  1974年   2篇
  1973年   4篇
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
81.
研究了长序列心电信号的最佳复杂度。先将原始序列符号化 ,再采用 L empel- Ziv算法来计算复杂度 ,探讨影响复杂度的各种因素 ,然后对三组不同信号即正常心电、心绞痛和心肌梗塞信号进行分析。结果表明 ,采用最佳阈值比用平均值为阈值得到的复杂度更能明显地分辨出正常和异常信号 ,原始序列符号化的阈值以及信号长度直接影响序列复杂度 ,因此 ,在实际信号的复杂度测量上 ,应采用最佳阈值和最佳信号长度。  相似文献   
82.
癫痫的睡眠动态脑电图临床应用价值   总被引:2,自引:0,他引:2  
孔峰 《现代电生理学杂志》2004,11(4):206-207,214
目的:探讨睡眠期动态脑电图(AEEG)在癫痫诊断中的作用。方法:利用 AEEG对836例癫痫患者自然睡眠期脑电波变化进行监测、分析。结果:正常106例 (12.7%),非特异性异常61例(7.3%),痫样波发放669例(80.0%),总异常730例 (87.3%)。痫样波出现于清醒期84例(12.5%),睡眠期408例(61.0%)。睡眠期明显高 于清醒期P<0.01。而睡眠期(NREM Ⅰ-Ⅱ期)占多数473/585例(80.7%)。结论:癫 痫和睡眠密切相关,通过自然和药物诱发睡眠,有助于提高癫痫脑电图阳性率,尤其是自然 睡眠AEEG对癫痫的定位诊断和分类更具有重要意义。对临床诊断困难的非典型发作及各种 不常见类型癫痫的作用更加突出,甚至起着决定性的作用。  相似文献   
83.

Introduction

The usage of formalin-fixed paraffin embedded (FFPE) tissue is characterized by its long shelf-life and simple handling. Therefore it is the most commonly available tissue specimen in routine diagnostics and histological studies. Formaldehyde fixation may result in RNA degradation and cross linking with proteins, while storage conditions also affect RNA integrity. The present study was designed to investigate the influence of these factors on RNA analysis.

Design

FFPE-derived RNA from sections of 23 patients with spontaneous pneumothoraxes was used. Unstained sections of FFPE tissue were stored at various temperatures (?80?°C, ?20?°C, 4?°C, 24?°C) prior to RNA extraction. The potential impact on RNA quality of semi-automatic and manual RNA isolation and three different deparaffinization agents (mineral oil, xylene and d-limonene) were compared.

Results

The storage temperature of FFPE sections affects RNA concentration and fragmentation, with the optimal storage temperature below -20?°C. The RNA extracted with d-limonene shows equivalent quality to the RNA extracted using more toxic standard agents. The manual isolation provides a higher RNA yield compared to the semi-automatic isolation. However, no differences in the amount of longer RNA fragments were observed. Furthermore, the semi-automatic isolation showed an enhanced RNA quality.

Conclusion

FFPE sections not directly used for RNA extraction should be stored below -20?°C to increase quality and yield of the RNA. Usage of semi-automatic isolation produces superior results and simplifies routine processes by having less hands-on-time. Replacement of toxic xylene by d-limonene may contribute to improved occupational safety while not influencing analytical results.  相似文献   
84.
目的: 探讨初中生亲社会行为的干预内容及方法.方法: 用自编量表对实验班和控制班的亲社会价值取向和亲社会行为进行前测,以班级管理为途径,通过心理活动课、主题班会等干预形式,借助榜样示范、移情训练、价值澄清、行为训练等具体方法,对实验班学生的亲社会行为进行干预训练,对控制班学生不施加任何专门的干预.三个月后用自编量表对两班进行实验后测.结果: 干预前实验班学生的价值取向在三种类别上的人数分布与控制班学生存在显著差异(P=0.005),表现为利他取向者少于控制班,而难以判断者多于控制班,但干预后两班差异不显著(P>O.05);干预后实验班组内价值取向人数分布亦发生显著变化(P=O.027),表现为利他取向者人数增加,难以判断者人数减少,而控制班前后测差异不显著(P>0.05);干预前实验班学生的亲社会行为总分及调节、利他、习俗、公正和控制维度得分均低于控制班学生(如,总分:28.8±6.5/34.5±6.3,P0.05).结论: 以班级为单位对初中生的亲社会行为进行综合性的教育干预是可行的和有效的.  相似文献   
85.
The predictive value of a comprehensive model with personality characteristics, stressor related cognitions, coping and social support was tested in a sample of 187 nonpregnant women. The emotional response to the unsuccessful treatment was predicted out of vulnerability factors assessed before the start of the treatment. The results indicated the importance of neuroticism as a vulnerability factor in emotional response to a severe stressor. They also underlined the importance of helplessness and marital dissatisfaction as additional risk factors, and acceptance and perceived social support as additional protective factors, in the development of anxiety and depression after a failed fertility treatment. From clinical point of view, these results suggest fertility-related cognitions and social support should receive attention when counselling women undergoing IVF or ICSI treatment.  相似文献   
86.
The prognostic value of early hepatitis C virus (HCV)-RNA load was evaluated among nonresponder patients to previous interferon (IFN) therapy treated with daily IFN and ribavirin. One hundred-six nonresponders (83 men), mean age 44.8 +/- 11 years, were treated with IFN-alpha 2b 3 MU/day for 24 weeks, followed by 3 MU x 3/week for 24 weeks plus ribavirin 1-1.2 g/day for 48 weeks. HCV RNA was quantified by Versant HCV RNA 3.0 assay (Bayer). The predictive values of the baseline and the change in viral load at week 1, 4, and 12 for sustained virological responses were analyzed using receiver operating characteristic (ROC) curves, as well as predictive values of >2 log(10) drop from baseline by weeks 1, 4, and 12 in combination with undetectable HCV RNA for sustained virological response. Thirty-two patients (30.2%) were sustained virological responders. The highest area under the curve was obtained at week 4. The unquantifiable HCV RNA level, in combination with at least a 2 log(10) drop in viral load by week 4 and week 12, had a negative predictive value of 96% and 97%, respectively. Nonresponse can be predicted as early as week 4 or week 12 in nonresponders treated with daily IFN and ribavirin.  相似文献   
87.
Summary In vitro CO2 dissociation curves for oxygenated whole blood were determined in 19 healthy male subjects at rest and during submaximal and maximal bicycle work. Hemoglobin concentration and blood lactate increased with increasing work load and accordingly buffer value of the whole blood increased while bicarbonate and Base Excess (BE) decreased, resulting in a downward shift of the CO2 dissociation curve during exercise. Despite the marked increase in buffer values of the blood, the slopes of the CO2 dissociation curves during exercise were found to be about the same as those obtained at rest. It was inferred that the increasing effect of increased buffer value, on the dissociation slope, was essentially compensated by the decreasing effect of diminished bicarbonate content. The advantages of this relatively constant CO2 dissociation slope for the indirect measurement of cardiac output by the Fick principle are discussed.  相似文献   
88.
Sixty-six percent of the at-risk persons and 74% of the partners in a large survey in Belgium have the intention of making use of predictive testing for Huntington's disease. One third of them, however, have expressed the intention of postponing the final decision for various reasons. The intention to be tested is not at all related to sociodemographic characteristics. A thorough exploration of the reasons for being in favour of or against taking the test reveals that the motivation inspiring this very personal decision is very complex. In the group of at-risk persons, less than half of the variation in the intention to be tested is explained by the role of a series of specific reasons as predictor variables in a regression analysis. The proportion of explained variation is slightly higher in the group of partners. 'To have certainty about my own future' and 'to make arrangements for the future' play a major part in the decision of the total group. 'Making decisions concerning children' and to a larger extent 'informing children about their risk status' are important factors in deciding in favour of the test.  相似文献   
89.
Simultaneous measurements of skin potential (SP) and skin resistance (SR) obtained from 20 male and 20 female adult subjects during 2 sessions held 2 to 9 days apart were used in studying (1) the correlation of change measurements and prestimulus level in the two measures, and (2) the amount of correlation between SP and SR using both simple difference and residual change scores in which the regression of poststimulus values on initial level (prestimulus) has been controlled. Correlations within Ss and correlations among Ss showed large individual variability, correlation differences between males and females, and high correlation between SP and SR change scores. Although the law of initial value (LIV) seemed to have little applicability to the measurement of electrodermal responses, the results underscored the need to control for contamination of change measures by initial level regardless of direction.  相似文献   
90.
目的探讨汉族男女在正常性状表现及基因频率的差异.方法调查湖南境内汉族男女7对正常遗传性状,并用Hardy-Weinberg定律和分离定律计算男女每一性状的基因频率.结果眼睑、拇指末关节的性状在汉族男女之间差异较大,而卷舌、耳垂、前额发际、发式、发旋无明显差异.结论同一民族不同性别在性状表现及基因频率方面存在差异,为中国人群体遗传学研究提供资料.  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