全文获取类型
收费全文 | 40465篇 |
免费 | 3117篇 |
国内免费 | 359篇 |
专业分类
耳鼻咽喉 | 437篇 |
儿科学 | 1096篇 |
妇产科学 | 1134篇 |
基础医学 | 5156篇 |
口腔科学 | 678篇 |
临床医学 | 4232篇 |
内科学 | 8540篇 |
皮肤病学 | 919篇 |
神经病学 | 2723篇 |
特种医学 | 1447篇 |
外科学 | 5680篇 |
综合类 | 1248篇 |
一般理论 | 38篇 |
预防医学 | 2334篇 |
眼科学 | 1730篇 |
药学 | 3041篇 |
中国医学 | 335篇 |
肿瘤学 | 3173篇 |
出版年
2023年 | 259篇 |
2022年 | 421篇 |
2021年 | 1025篇 |
2020年 | 666篇 |
2019年 | 844篇 |
2018年 | 1080篇 |
2017年 | 824篇 |
2016年 | 928篇 |
2015年 | 1106篇 |
2014年 | 1467篇 |
2013年 | 1806篇 |
2012年 | 2563篇 |
2011年 | 2740篇 |
2010年 | 1533篇 |
2009年 | 1405篇 |
2008年 | 2183篇 |
2007年 | 2285篇 |
2006年 | 2294篇 |
2005年 | 2198篇 |
2004年 | 1985篇 |
2003年 | 1803篇 |
2002年 | 1690篇 |
2001年 | 1167篇 |
2000年 | 1093篇 |
1999年 | 959篇 |
1998年 | 427篇 |
1997年 | 317篇 |
1996年 | 300篇 |
1995年 | 232篇 |
1994年 | 222篇 |
1993年 | 237篇 |
1992年 | 484篇 |
1991年 | 473篇 |
1990年 | 447篇 |
1989年 | 425篇 |
1988年 | 370篇 |
1987年 | 402篇 |
1986年 | 351篇 |
1985年 | 309篇 |
1984年 | 245篇 |
1983年 | 203篇 |
1982年 | 148篇 |
1981年 | 139篇 |
1980年 | 137篇 |
1979年 | 167篇 |
1978年 | 137篇 |
1977年 | 121篇 |
1976年 | 120篇 |
1975年 | 112篇 |
1972年 | 102篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
31.
We investigated the effects of imaging and display conditions on the detectability of low-contrast objects in digital subtraction angiographic (DSA) images. The test images were produced by superimposition of low-contrast objects on a uniform noisy background obtained with a DSA system. We employed 18-alternative forced-choice (18-AFC) experiments and predictions based on statistical decision theory to study the dependence of the threshold contrasts of the test objects on the object size, incident x-ray exposure, display window width, and display medium. The results indicated that the threshold contrast decreased with increasing object size, and that the detectability of an object of a given size increased with increasing incident x-ray exposure and decreasing width of the display window. We found that the signal-to-noise ratio (SNR) obtained from the perceived statistical decision theory model, which includes the observer's internal noise, can accurately predict the detectability of low-contrast objects in DSA images. The threshold SNR corresponding to 50% correct detection in the 18-AFC experiments had a constant value of 3.8, in agreement with results reported previously for screen-film systems. The theoretical model will be useful for prediction of the performance of a DSA system based on its physical characteristics, and for evaluation of the tradeoff between patient exposure and diagnostic accuracy for a given DSA unit. 相似文献
32.
33.
34.
35.
36.
37.
Eric Y. T. Chan Daniel K. Ng Chung-hong Chan Ka-li Kwok Pok-yu Chow Josephine M. Cheung Suk-yu Leung 《Sleep & breathing》2009,13(1):59-63
Background and objective The purpose of this study is to assess whether Chinese children with high apnea–hypopnea index (AHI) are sleepier by a modified Epworth Sleepiness Scale (ESS).
Materials and methods Records were retrospectively reviewed. We included children who were between 3 and 12 years old, admitted for overnight polysomnogram
because of suspected obstructive sleep apnea syndrome (OSAS). A modified ESS was used to assess excessive daytime sleepiness
(EDS) of the children.
Results One hundred ninety-two Chinese children were included. Children with high AHI, defined as AHI > 5.0, were sleepier than children with AHI less than or equal
to 5. After adjustment by age, gender, and obesity, children with high AHI remained significantly sleepier. Modified ESS was
significantly correlated with AHI (rho = 0.124, 95% CI = 0.004–0.281). Modified ESS score of >8 was the best cutoff point
with the sensitivity and specificity of 0.29 and 0.91, respectively. The odds ratio of children with modified ESS > 10 having
high AHI was 4.231 (95%CI = 1.248 to 14.338) and children with modified ESS > 8 had the highest odds ratio, 4.295(95%CI = 1.66
to 11.1), of having high AHI.
Conclusion
Chinese children with high AHI appear to be sleepier than children with low AHI. Children with suspected OSAS and high modified ESS,
i.e., ESS > 8, had significantly higher odds ratio of having high AHI. Increased sleepiness is a specific but not a sensitive
symptom in snoring children with high AHI. Screening for EDS in snoring children may help us identify those with high AHI
and prioritize the management of those children.
All authors worked and the study was carried out in Kwong Wah Hospital in Hong Kong. There was no conflict of interest and
no specific source of funding for the study. 相似文献
38.
Henry Ho‐Lung Chan 《Clinical & experimental optometry》2005,88(6):410-414
The first‐order kernel analysis in multifocal electroretinogram (mfERG) using low contrast stimulation is suggested as a way to detect the inner retinal responses in animal studies. In this case report, this protocol is applied to human patients with glaucoma to demonstrate the possibility of using mfERG as a tool to detect glaucomatous damage. Two patients with glaucoma were recruited and had mfERG measurements with the 103‐scaled hexagonal stimulus pattern at low (50 per cent) contrast. Their responses were analysed and compared with those from normal subjects with the mfERG measured under the same condition. In the normal subjects, there were obvious oscillatory components on the ascending and descending limbs of the first‐order kernel response to 50 per cent contrast. In the glaucomatous patients, the oscillatory component on the descending limb was obviously diminished. In addition, this component was significantly diminished in the quadrant with a glaucomatous visual field defect. This suggests that the low‐contrast stimulation condition in mERG measurement may provide a good way to detect glaucomatous damage and this may help in clinical diagnosis of glaucoma. 相似文献
39.
Factors influencing family physicians to enter rural practice: Does rural or urban background make a difference? 下载免费PDF全文
40.
Roger S Chan Michael H Duong Aaron V Kaplan 《Catheterization and cardiovascular interventions》2007,70(3):374-378
Percutaneous intervention in saphenous vein grafts (SVG) carries a higher risk of distal embolization than intervention in a native vessel, and use of a distal protection device has been shown to improve the outcomes in SVG interventions. We describe an intervention done in an unexpected 'Y' SVG which required dual distal protection with Filterwires placed in both limbs of the diseased graft and which was performed via a 6 Fr guide catheter. 相似文献