全文获取类型
收费全文 | 427180篇 |
免费 | 19723篇 |
国内免费 | 1137篇 |
专业分类
耳鼻咽喉 | 3920篇 |
儿科学 | 13347篇 |
妇产科学 | 7608篇 |
基础医学 | 49535篇 |
口腔科学 | 6693篇 |
临床医学 | 37728篇 |
内科学 | 84179篇 |
皮肤病学 | 4123篇 |
神经病学 | 40617篇 |
特种医学 | 17287篇 |
外国民族医学 | 13篇 |
外科学 | 67397篇 |
综合类 | 5841篇 |
一般理论 | 324篇 |
预防医学 | 39219篇 |
眼科学 | 9439篇 |
药学 | 26538篇 |
6篇 | |
中国医学 | 986篇 |
肿瘤学 | 33240篇 |
出版年
2023年 | 1370篇 |
2022年 | 2447篇 |
2021年 | 5544篇 |
2020年 | 3321篇 |
2019年 | 5403篇 |
2018年 | 27127篇 |
2017年 | 21257篇 |
2016年 | 23708篇 |
2015年 | 6768篇 |
2014年 | 9453篇 |
2013年 | 12698篇 |
2012年 | 24874篇 |
2011年 | 39345篇 |
2010年 | 28635篇 |
2009年 | 20664篇 |
2008年 | 35522篇 |
2007年 | 38534篇 |
2006年 | 18073篇 |
2005年 | 19583篇 |
2004年 | 19693篇 |
2003年 | 19440篇 |
2002年 | 16675篇 |
2001年 | 2609篇 |
2000年 | 2236篇 |
1999年 | 2681篇 |
1998年 | 3331篇 |
1997年 | 2822篇 |
1996年 | 2341篇 |
1995年 | 2260篇 |
1994年 | 1896篇 |
1993年 | 1678篇 |
1992年 | 1495篇 |
1991年 | 1432篇 |
1990年 | 1317篇 |
1989年 | 1274篇 |
1988年 | 1213篇 |
1987年 | 1195篇 |
1986年 | 1157篇 |
1985年 | 1159篇 |
1984年 | 1398篇 |
1983年 | 1246篇 |
1982年 | 1455篇 |
1981年 | 1377篇 |
1980年 | 1253篇 |
1979年 | 840篇 |
1978年 | 864篇 |
1977年 | 727篇 |
1976年 | 700篇 |
1975年 | 572篇 |
1974年 | 600篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Konrad Matyja Anna Małachowska-Jutsz Anna K. Mazur Kazimierz Grabas 《Ecotoxicology (London, England)》2016,25(5):924-939
Dehydrogenase activity is frequently used to assess the general condition of microorganisms in soil and activated sludge. Many studies have investigated the inhibition of dehydrogenase activity by various compounds, including heavy metal ions. However, the time after which the measurements are carried out is often chosen arbitrarily. Thus, it can be difficult to estimate how the toxic effects of compounds vary during the reaction and when the maximum of the effect would be reached. Hence, the aim of this study was to create simple and useful mathematical model describing changes in dehydrogenase activity during exposure to substances that inactivate enzymes. Our model is based on the Lagergrens pseudo-first-order equation, the rate of chemical reactions, enzyme activity, and inactivation and was created to describe short-term changes in dehydrogenase activity. The main assumption of our model is that toxic substances cause irreversible inactivation of enzyme units. The model is able to predict the maximum direct toxic effect (MDTE) and the time to reach this maximum (TMDTE). In order to validate our model, we present two examples: inactivation of dehydrogenase in microorganisms in soil and activated sludge. The model was applied successfully for cadmium and copper ions. Our results indicate that the predicted MDTE and TMDTE are more appropriate than EC50 and IC50 for toxicity assessments, except for long exposure times. 相似文献
83.
84.
Contraceptive use is an important strategy for the prevention of unwanted pregnancy and avoidance of induced abortion. Of all the contraception methods, emergency contraceptive (EC) offers the last chance to achieve this. However, few studies have documented the use of EC among young people in Ghana. This study explored knowledge and usage of EC as well as the factors associated with it among University of Cape Coast students. Data were obtained on the knowledge and usage of ECs among University of Cape Coast students in 2013. Logistic regression analysis was used to investigate the association between students’ socio-demographic characteristics and EC knowledge and use. More male students (72 %) than females (59 %) were sexually active. Fifty-seven percent of the respondents had ever heard of EC and 36 % had ever used EC. Although males were more likely to be sexually active, females were more likely to have knowledge of EC use compared to males. The study underscores the need to increase awareness regarding EC among University students in order to offer them the opportunity that EC provides if other forms of contraceptives are missed. 相似文献
85.
86.
87.
88.
Gastroesophageal reflux is the most common benign disorder of the esophagus and laparoscopic Nissen fundoplication has become the standard surgical treatment for its treatment. In our area, where the use of bougie calibration is debatable, postoperative dysphagia is encountered often after this surgery although it is usually not permanent. The aim of this study was to investigate the effect of using a soft silicone tube 39 F in diameter for esophageal calibration during laparoscopic Nissen fundoplication on the incidence of postoperative dysphagia. We divided cases scheduled to undergo laparoscopic Nissen fundoplication between January 2009 and November 2010 into two groups, each consisting 25 patients. Esophageal calibration with a 39 F silicone orogastric tube was used for the first group while there was no operative calibration in the second group. The surgical duration was recorded; the presence and severity of the postoperative dysphagia was calculated by using a dysphagia severity scoring system during the 1-year postoperative follow-up. The dysphagia severity scores were significantly lower in group 1 than group 2 on the postoperative second day and at the end of the first week and first month. We did not find a significant difference at the end of the 6-month and first year. There was also no significant difference regarding surgery duration. The use of a soft orogastric tube 39 F in diameter for esophagus calibration during laparoscopic Nissen fundoplication has significantly decreased the incidence of postoperative transient dysphagia without affecting the duration of surgery. Although dysphagia gradually resolves in the majority of patients, a safe and easy calibration method for its prevention is worth developing, and we believe that the use of our method in larger series could be beneficial. 相似文献
89.
Daniel J. Snyder Thomas R. Kroshus Aakash Keswani Evan B. Garden Karl M. Koenig Kevin J. Bozic David S. Jevsevar Jashvant Poeran Calin S. Moucha 《The Journal of arthroplasty》2019,34(4):613-618
Background
Nursing Home Compare (NHC) ratings, created and maintained by Medicare, are used by both hospitals and consumers to aid in the skilled nursing facility (SNF) selection process. To date, no studies have linked NHC ratings to actual episode-based outcomes. The purpose of this study was to evaluate whether NHC ratings are valid predictors of 90-day complications, readmission, and bundle costs for patients discharged to an SNF after primary total joint arthroplasty (TJA).Methods
All SNF-discharged primary TJA cases in 2017 at a multihospital academic health system were queried. Demographic, psychosocial, and clinical variables were manually extracted from the health record. Medicare NHC ratings were then collected for each SNF. For patients in the Medicare bundle, postacute and total bundle cost was extracted from claims.Results
Four hundred eighty-eight patients were discharged to a total of 105 unique SNFs. In multivariate analysis, overall NHC rating was not predictive of 90-day readmission/major complications, >75th percentile postacute cost, or 90-day bundle cost exceeding the target price. SNF health inspection and quality measure ratings were also not predictive of 90-day readmission/major complications or bundle performance. A higher SNF staffing rating was independently associated with a decreased odds for >75th percentile 90-day postacute spend (odds ratio, 0.58; P = .01) and a 90-day bundle cost exceeding the target price (odds ratio = 0.69; P = .02) but was similarly not predictive of 90-day readmission/complications.Conclusion
Results of our study suggest that Medicare's NHC tool is not a useful predictor of 90-day costs, complications, or readmissions for SNFs within our health system. 相似文献90.
Michelle Linda Ferderbar Thomas E. Doyle Reza Samavi David Koff 《Journal l'Association canadienne des radiologistes》2019,70(2):119-124
Several regulatory bodies have agreed that low-dose radiation used in medical imaging is a weak carcinogen that follows a linear, non-threshold model of cancer risk. While avoiding radiation is the best course of action to mitigate risk, computed tomography (CT) scans are often critical for diagnosis. In addition to the as low as reasonably achievable principle, a more concrete method of dose reduction for common CT imaging exams is the use of a diagnostic reference level (DRL). This paper examines Canada's national DRL values from the recent CT survey and compares it to published provincial DRLs as well as the DRLs in the United Kingdom and the United States of America for the 3 most common CT exams: head, chest, and abdomen/pelvis. Canada compares well on the international scale, but it should consider using more electronic dose monitoring solutions to create a culture of dose optimization. 相似文献