全文获取类型
收费全文 | 4696篇 |
免费 | 351篇 |
国内免费 | 10篇 |
专业分类
耳鼻咽喉 | 39篇 |
儿科学 | 77篇 |
妇产科学 | 124篇 |
基础医学 | 591篇 |
口腔科学 | 32篇 |
临床医学 | 611篇 |
内科学 | 904篇 |
皮肤病学 | 41篇 |
神经病学 | 480篇 |
特种医学 | 166篇 |
外科学 | 668篇 |
综合类 | 120篇 |
一般理论 | 7篇 |
预防医学 | 401篇 |
眼科学 | 109篇 |
药学 | 383篇 |
中国医学 | 9篇 |
肿瘤学 | 295篇 |
出版年
2023年 | 20篇 |
2022年 | 36篇 |
2021年 | 62篇 |
2020年 | 50篇 |
2019年 | 78篇 |
2018年 | 107篇 |
2017年 | 74篇 |
2016年 | 103篇 |
2015年 | 121篇 |
2014年 | 147篇 |
2013年 | 207篇 |
2012年 | 340篇 |
2011年 | 358篇 |
2010年 | 198篇 |
2009年 | 166篇 |
2008年 | 295篇 |
2007年 | 340篇 |
2006年 | 316篇 |
2005年 | 325篇 |
2004年 | 323篇 |
2003年 | 269篇 |
2002年 | 243篇 |
2001年 | 60篇 |
2000年 | 60篇 |
1999年 | 60篇 |
1998年 | 55篇 |
1997年 | 47篇 |
1996年 | 39篇 |
1995年 | 38篇 |
1994年 | 33篇 |
1993年 | 37篇 |
1992年 | 35篇 |
1991年 | 34篇 |
1990年 | 30篇 |
1989年 | 31篇 |
1988年 | 27篇 |
1987年 | 29篇 |
1986年 | 21篇 |
1985年 | 28篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1979年 | 20篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1974年 | 12篇 |
1973年 | 8篇 |
排序方式: 共有5057条查询结果,搜索用时 203 毫秒
81.
Inversion recovery ultrashort echo time imaging of ultrashort T2 tissue components in ovine brain at 3 T: a sequential D2O exchange study
下载免费PDF全文
![点击此处可从《NMR in biomedicine》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Inversion recovery ultrashort echo time (IR‐UTE) imaging holds the potential to directly characterize MR signals from ultrashort T2 tissue components (STCs), such as collagen in cartilage and myelin in brain. The application of IR‐UTE for myelin imaging has been challenging because of the high water content in brain and the possibility that the ultrashort T2* signals are contaminated by water protons, including those associated with myelin sheaths. This study investigated such a possibility in an ovine brain D2O exchange model and explored the potential of IR‐UTE imaging for the quantification of ultrashort T2* signals in both white and gray matter at 3 T. Six specimens were examined before and after sequential immersion in 99.9% D2O. Long T2 MR signals were measured using a clinical proton density‐weighted fast spin echo (PD‐FSE) sequence. IR‐UTE images were first acquired with different inversion times to determine the optimal inversion time to null the long T2 signals (TInull). Then, at this TInull, images with echo times (TEs) of 0.01–4 ms were acquired to measure the T2* values of STCs. The PD‐FSE signal dropped to near zero after 24 h of immersion in D2O. A wide range of TInull values were used at different time points (240–330 ms for white matter and 320–350 ms for gray matter at TR = 1000 ms) because the T1 values of the long T2 tissue components changed significantly. The T2* values of STCs were 200–300 μs in both white and gray matter (comparable with the values obtained from myelin powder and its mixture with D2O or H2O), and showed minimal changes after sequential immersion. The ultrashort T2* signals seen on IR‐UTE images are unlikely to be from water protons as they are exchangeable with deuterons in D2O. The source is more likely to be myelin itself in white matter, and might also be associated with other membranous structures in gray matter. 相似文献
82.
Christian Eckmann Matthew Wasserman Faisal Latif Graeme Roberts Axelle Beriot-Mathiot 《The European journal of health economics》2013,14(5):835-846
Hospital-onset Clostridium difficile infection (CDI) places a significant burden on health care systems throughout Europe, estimated at around €3 billion per annum. This burden is shared between national payers and hospitals that support additional bed days for patients diagnosed with CDI while in hospital or patients re-admitted from a previous hospitalisation. This study was performed to quantify additional hospital stay attributable to CDI in four countries, England, Germany, Spain, and The Netherlands, by analysing nationwide hospital-episode data. We focused upon patients at increased risk of CDI: with chronic obstructive pulmonary disease, heart failure, diabetes, or chronic kidney disease, and aged 50 years or over. Multivariate regression and propensity score matching models were developed to investigate the impact of CDI on additional length of hospital stay, controlling for confounding factors such as underlying disease severity. Patients in England had the longest additional hospital stay attributable to CDI at 16.09 days, followed by Germany at 15.47 days, Spain at 13.56 days, and The Netherlands at 12.58 days, derived using regression analysis. Propensity score matching indicated a higher attributable length of stay of 32.42 days in England, 15.31 days in Spain, and 18.64 days in The Netherlands. Outputs from this study consistently demonstrate that in European countries, for patients whose hospitalisation is complicated by CDI, the infection causes a statistically significant increase in hospital length of stay. This has implications for optimising resource allocation and budget setting at both the national and hospital level to ensure that levels of CDI-complicated hospitalisations are minimised. 相似文献
83.
Additive impact of pre‐liver transplant metabolic factors on survival post‐liver transplant
下载免费PDF全文
![点击此处可从《Journal of gastroenterology and hepatology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
84.
85.
86.
87.
A heparin-like effect was recently described in infants, children, and adults receiving bivalirudin while supported on extracorporeal membrane oxygenation following cardiopulmonary bypass. This is most likely due to endogenous release of glycosaminoglycans from vascular endothelium and mast cells and is associated with longer duration of extracorporeal membrane oxygenation and an increased incidence of sepsis. Further investigation into this effect should include patients without recent cardiopulmonary bypass, exclude the presence of covalent antithrombin-heparin complexes, and employ a variety of different heparinases for thromboelastography. The phenomenon may partially explain the heterogeneity of anticoagulation requirements in patients on extracorporeal life support. 相似文献
88.
A pedunculated aldosterone‐producing adenoma drained by an extra vein causing puzzling results of adrenal vein sampling
下载免费PDF全文
![点击此处可从《Clinical endocrinology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
89.
90.
Sabrine Ghazouani Zoubeir Bjaoui Paul Michael Graeme Spiers Peter Beckett Maher Gtari Kabwe Nkongolo 《Ecotoxicology (London, England)》2020,29(4):417-428
The use of wastewater for irrigation in agroforestry is cost-effective for water management. It is well established that rhizospheric microorganisms such as N2-fixing bacteria are able to modulate rhizobioaugmention and to boost phyoremediation process. To date, no study has been conducted to evaluate biological effects of rhizobioaugmentation in Casuarina glauca trees induced by their symbiont N-fixing actinobacteria of the genus Frankia. The objective of the present study was to evaluate the main effects of rhizobioaugmentation on the biological activity in the C. glauca’s rhizosphere and on C. glauca growth in soils irrigated with industrial wastewater. Two Frankia strains (BMG5.22 and BMG5.23) were used in a single or dual inoculations of C. glauca seedlings irrigated with industrial wastewater. Soil enzymes activity related to carbon, phosphorus, sulfur and nitrogen cycling were measured. Results revealed that the BMG5.22 Frankia strain increases significantly the size (dry weight) of C. glauca shoots and roots while dual inoculation increased significantly the root length. Surprisingly, β-glucosidase (BG), cellobiohydrolase (CBH), β-N-acetylglucosaminidase (NAGase), aryl sulfatase (AS), acid phosphatase (AP), alkaline phosphatase (AlP), glycine aminopeptidase (GAP), leucine aminopeptidase (LAP), and peroxidase (PER) activity in the rhizosphere decreased significantly in soils treated with the two strains of symbionts. This suggests no positive correlations between enzymatic activity and C. glauca growth. 相似文献