全文获取类型
收费全文 | 2415篇 |
免费 | 155篇 |
国内免费 | 8篇 |
专业分类
耳鼻咽喉 | 33篇 |
儿科学 | 54篇 |
妇产科学 | 57篇 |
基础医学 | 333篇 |
口腔科学 | 47篇 |
临床医学 | 215篇 |
内科学 | 550篇 |
皮肤病学 | 74篇 |
神经病学 | 329篇 |
特种医学 | 51篇 |
外科学 | 387篇 |
综合类 | 11篇 |
预防医学 | 149篇 |
眼科学 | 26篇 |
药学 | 105篇 |
中国医学 | 9篇 |
肿瘤学 | 148篇 |
出版年
2023年 | 15篇 |
2022年 | 41篇 |
2021年 | 64篇 |
2020年 | 41篇 |
2019年 | 66篇 |
2018年 | 70篇 |
2017年 | 52篇 |
2016年 | 62篇 |
2015年 | 74篇 |
2014年 | 83篇 |
2013年 | 122篇 |
2012年 | 176篇 |
2011年 | 140篇 |
2010年 | 92篇 |
2009年 | 75篇 |
2008年 | 113篇 |
2007年 | 123篇 |
2006年 | 125篇 |
2005年 | 110篇 |
2004年 | 129篇 |
2003年 | 104篇 |
2002年 | 88篇 |
2001年 | 57篇 |
2000年 | 61篇 |
1999年 | 44篇 |
1998年 | 18篇 |
1997年 | 21篇 |
1996年 | 17篇 |
1995年 | 4篇 |
1994年 | 17篇 |
1993年 | 6篇 |
1992年 | 43篇 |
1991年 | 33篇 |
1990年 | 29篇 |
1989年 | 33篇 |
1988年 | 39篇 |
1987年 | 36篇 |
1986年 | 17篇 |
1985年 | 22篇 |
1984年 | 15篇 |
1983年 | 18篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1969年 | 4篇 |
排序方式: 共有2578条查询结果,搜索用时 109 毫秒
61.
Background
Electronic cigarette awareness and use has been increasing rapidly. E-cigarette brands have utilized social networking sites to promote their products, as the growth of the e-cigarette industry has paralleled that of Web 2.0. These online platforms are cost-effective and have unique technological features and user demographics that can be attractive for selective marketing. The popularity of multiple sites also poses a risk of exposure to social networks where e-cigarette brands might not have a presence.Objective
To examine the marketing strategies of leading e-cigarette brands on multiple social networking sites, and to identify how affordances of the digital media are used to their advantage. Secondary analyses include determining if any brands are benefitting from site demographics, and exploring cross-site diffusion of marketing content through multi-site users.Methods
We collected data from two e-cigarette brands from four social networking sites over approximately 2.5 years. Content analysis is used to search for themes, population targeting, marketing strategies, and cross-site spread of messages.Results
Twitter appeared to be the most frequently used social networking site for interacting directly with product users. Facebook supported informational broadcasts, such as announcements regarding political legislation. E-cigarette brands also differed in their approaches to their users, from informal conversations to direct product marketing.Conclusions
E-cigarette makers use different strategies to market their product and engage their users. There was no evidence of direct targeting of vulnerable populations, but the affordances of the different sites are exploited to best broadcast context-specific messages. We developed a viable method to study cross-site diffusion, although additional refinement is needed to account for how different types of digital media are used. 相似文献62.
Lucie S. Nogueira Patrícia Neves Ana C. Gomes Pedro Lavrador Luís Cunha-Silva Anabela A. Valente Isabel S. Gonalves Martyn Pillinger 《RSC advances》2018,8(29):16294
The synthesis of molybdenum(0) tricarbonyl and tetracarbonyl complexes of the form [Mo(CO)3(ptapzpy)Br] (1) and cis-[Mo(CO)4(ptapzpy)]Br (2) is reported, where ptapzpy = 2-(1-propyltrimethylammonium-3-pyrazolyl)pyridine. Preparation of these derivatives was accomplished either through thermal replacement of CO in Mo(CO)6 (for 1) or substitution under milder conditions of piperidine ligands in the precursor cis-[Mo(CO)4(pip)2] (for 2). The crystal structures of the ligand [ptapzpy]Br and complexes 1 and 2 were determined. Thermal treatment of 2 at 125–150 °C leads to mono decarbonylation and formation of 1. On the other hand, oxidative decarbonylation of 1 and 2 by reaction with tert-butylhydroperoxide (TBHP, 10 equiv.) gives a molybdenum oxide hybrid material formulated as [Mo3O9([ptapzpy]Br)2]·nH2O (3), which was characterised by FT-IR and Raman spectroscopy, thermogravimetric analysis, and 13C{1H} CP MAS NMR spectroscopy. Compounds 1–3 were effective (pre)catalysts for the epoxidation of cis-cyclooctene at 55 °C with aqueous H2O2 or TBHP (slightly better results were obtained with the former). The characterisation of the Mo-containing solids isolated after the catalytic reaction showed that poorly soluble β-octamolybdate salts, (L)x[Mo8O26], were formed from 1–3 with TBHP and from 1 with H2O2, while soluble oxoperoxo species were formed from 3 with H2O2. These findings helped to explain the different catalytic performances obtained.The oxidative decarbonylation and catalytic chemistry of molybdenum(0) tricarbonyl and tetracarbonyl complexes containing the same diimine ligand are compared. 相似文献
63.
Merlino Giovanni Smeralda Carmelo Gigli Gian Luigi Lorenzut Simone Pez Sara Surcinelli Andrea Marini Alessandro Valente Mariarosaria 《Journal of thrombosis and thrombolysis》2021,51(3):789-797
Journal of Thrombosis and Thrombolysis - No study investigated the possible detrimental effect of stress hyperglycemia on patients affected acute ischemic stroke (AIS) undergoing intravenous... 相似文献
64.
Valerio Rosato Antonio Ascione Riccardo Nevola Anna Ludovica Fracanzani Guido Piai Vincenzo Messina Ernesto Claar Carmine Coppola Luca Fontanella Rosa Lombardi Laura Staiano Giovanna Valente Maria Chiara Fascione Chiara Giorgione Annalisa Mazzocca Raffaele Galiero Pasquale Perillo Aldo Marrone Ferdinando Carlo Sasso Luigi Elio Adinolfi Luca Rinaldi 《Journal of viral hepatitis》2022,29(1):26-34
The long-term changes of liver stiffness (LS) in patients who achieve viral clearance after direct-acting anti-HCV therapy remain undefined. We conducted a multicentre prospective study to investigate this aspect. Patients with HCV infection treated with DAAs were enrolled from six Italian centres; they underwent clinical, biochemical, ultrasound and transient elastography evaluations before treatment (T0), 12 weeks (SVR12) and 24 months (T24) after the end of therapy. Among the 516 consecutive patients enrolled, 301 had cirrhosis. LS significantly decreased from T0 to SVR (14.3 vs 11.1 kPa, p = .002), with a progressive reduction until T24 (8.7 kPa, p < .001). However, only patients with steatosis and those who developed HCC did not experience a late improvement in LS. Multivariate analysis of baseline and follow-up variables identified steatosis as the only independent predictor of failure of LS improvement (OR 1.802, p = .013). ROC curve analysis of the association of LS with the risk of developing HCC showed that SVR12 ≥14.0 kPa had the highest accuracy (sensitivity 82%, specificity 99%; AUC: 0.774). Multivariate analysis revealed that LS was the only variable independently associated with an increased risk of developing HCC (OR 6.470, p = .035). Achieving an SVR was associated with a progressive, long-term decline of LS, suggesting a late improvement in liver fibrosis, besides the resolution of inflammation. Fatty liver and the development of HCC interfered with late reduction of LS. Patients with an LS ≥14 kPa at 12 weeks after the end of treatment were at higher risk for developing HCC. 相似文献
65.
Transluminal angioplasty was performed as an urgent treatment in 9 patients with unstable angina, refractory to medical therapy and ST elevation during pain. All had a coronary stenosis greater than 50% (89 +/- 12%; range 60-99%). The left anterior descending coronary artery was affected in 6 patients, the right coronary artery in 1 patient, the circumflex in 1 patient and 1 patient had two stenosis on both the left anterior descending and the first diagonal branch. A reduction of the luminal stenosis greater than 20% was obtained in all (residual stenosis 30 +/- 11%; range 11-40%). During a follow-up of 6-20 months, two patients only showed recurrence of chest pain. A maximal ergometric test was negative in all patients after 1, 3 and 6 months. A second arteriography, performed in 7 patients after 3-6 months, demonstrated a mean stenosis of 35% (range 30-40%). Transluminal coronary angioplasty is a feasible and effective therapeutic approach in patients with unstable angina and ST elevation, when a significant coronary stenosis is present. 相似文献
66.
67.
Bruna de Athayde Casadei Snia T.de O. Lara‐Mendes Camila de Freitas M. Barbosa Christiane Valente Araújo Cristina Almeida de Freitas Vinícius C. Machado Caroline C. Santa‐Rosa 《Australian endodontic journal : the journal of the Australian Society of Endodontology Inc》2020,46(1):101-106
Procedural accidents are eventualities that may occur during endodontic treatment because of lack of attention to detail or even unforeseeable situations. Knowledge of the root canal anatomy and its variations is a prerequisite for successful endodontic treatment. This case report describes an endodontic treatment where there was an intercurrence, generating deviation and perforation, which was solved with the aid of guided endodontics. A 37 years old, ASA1, was referred to the clinic for localisation and treatment of a calcified canal of the second right upper premolar. The tomographic images revealed the presence of only one canal and deviation with apical perforation. With the help of CBCT and CAD/CAM, it was possible to perform the guided access technique even after deviation and root perforation. Once again, this technique proved to be safe and predictable, allowing for a favourable prognosis in the long term. 相似文献
68.
Fernando H. Y. Cesena Viviane A. Valente Raul D. Santos Mrcio S. Bittencourt 《Arquivos brasileiros de cardiologia》2020,115(3):440
Background Differences between the updated versions of the Brazilian Guideline on Dyslipidemias and the American Heart Association (AHA)/American College of Cardiology (ACC) Cholesterol Guideline regarding cardiovascular risk stratification and statin eligibility are unknown.Objectives To compare cardiovascular risk categorization and statin eligibility based on the Brazilian guideline with those based on the AHA/ACC guideline in primary prevention patients.Methods We retrospectively analyzed individuals aged 40-74 years without high-risk conditions, with LDL-c 70 to < 190 mg/dL, not on lipid-lowering drugs, who underwent routine clinical assessment. Cardiovascular risk was stratified according to the Brazilian and the AHA/ACC guidelines. Subjects were considered eligible for statin therapy if LDL-c was at least 30 mg/dL above the target for the cardiovascular risk (Brazilian guideline) or the 10-year atherosclerotic cardiovascular disease risk was ≥7.5% (AHA/ACC guideline). A p-value < 0.05 was considered statistically significant.Results The study sample consisted of 18,525 subjects (69% male, age 48 ± 6 years). Among subjects considered at intermediate or high risk by the Brazilian guideline, over 80% would be in a lower risk category by the AHA/ACC guideline. Among men, 45% and 16% would be statin eligible by the Brazilian and the AHA/ACC guidelines criteria, respectively (p < 0.001). Among women, the respective proportions would be 16% and 1% (p < 0.001). Eighty-two percent of women and 57% of men eligible for statins based on the Brazilian guideline criterion would not be eligible according to the AHA/ACC guideline criterion.Conclusions Compared with the AHA/ACC guideline, the Brazilian guideline classifies a larger proportion of primary prevention patients into higher-risk categories and substantially increases statin eligibility. (Arq Bras Cardiol. 2020; 115(3):440-449) 相似文献
69.
70.