全文获取类型
收费全文 | 7331篇 |
免费 | 372篇 |
国内免费 | 34篇 |
专业分类
耳鼻咽喉 | 64篇 |
儿科学 | 283篇 |
妇产科学 | 163篇 |
基础医学 | 816篇 |
口腔科学 | 69篇 |
临床医学 | 756篇 |
内科学 | 1631篇 |
皮肤病学 | 138篇 |
神经病学 | 764篇 |
特种医学 | 215篇 |
外科学 | 944篇 |
综合类 | 31篇 |
一般理论 | 1篇 |
预防医学 | 702篇 |
眼科学 | 41篇 |
药学 | 489篇 |
中国医学 | 32篇 |
肿瘤学 | 598篇 |
出版年
2024年 | 11篇 |
2023年 | 64篇 |
2022年 | 106篇 |
2021年 | 193篇 |
2020年 | 120篇 |
2019年 | 172篇 |
2018年 | 199篇 |
2017年 | 160篇 |
2016年 | 201篇 |
2015年 | 181篇 |
2014年 | 271篇 |
2013年 | 352篇 |
2012年 | 489篇 |
2011年 | 559篇 |
2010年 | 263篇 |
2009年 | 248篇 |
2008年 | 440篇 |
2007年 | 475篇 |
2006年 | 447篇 |
2005年 | 438篇 |
2004年 | 409篇 |
2003年 | 377篇 |
2002年 | 365篇 |
2001年 | 140篇 |
2000年 | 152篇 |
1999年 | 119篇 |
1998年 | 57篇 |
1997年 | 43篇 |
1996年 | 30篇 |
1995年 | 24篇 |
1994年 | 32篇 |
1993年 | 31篇 |
1992年 | 60篇 |
1991年 | 54篇 |
1990年 | 49篇 |
1989年 | 38篇 |
1988年 | 46篇 |
1987年 | 40篇 |
1986年 | 34篇 |
1985年 | 43篇 |
1984年 | 30篇 |
1983年 | 19篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 19篇 |
1975年 | 11篇 |
1972年 | 10篇 |
1969年 | 11篇 |
1967年 | 11篇 |
排序方式: 共有7737条查询结果,搜索用时 15 毫秒
81.
Sexual risk behaviors associated with having older sex partners: a study of black adolescent females. 总被引:4,自引:0,他引:4
Ralph J DiClemente Gina M Wingood Richard A Crosby Catlainn Sionean Brenda K Cobb Kathy Harrington Susan L Davies Edward W Hook M Kim Oh 《Sexually transmitted diseases》2002,29(1):20-24
BACKGROUND: Volunteer black adolescent females from neighborhoods characterized by high rates of unemployment, substance abuse, violence, and sexually transmitted disease were studied to determine the frequency of condom use and unprotected vaginal sex with steady, older partners during various time periods over the previous 6 months. GOAL: To examine associations between having male sex partners who were typically older (by at least 2 years) and adolescent females' sexually transmitted disease (STD)/HIV-associated sexual risk behaviors. STUDY DESIGN: In this cross-sectional study, 522 sexually active black adolescent females completed a questionnaire and a structured interview, of which a portion assessed the age difference between the adolescents and their typical sex partners. The adolescents' ages, length of relationship and their use of hormonal contraception were identified as covariates. Adjusted odds ratios (AOR), their 95% confidence intervals, and respective P values were calculated to detect significant associations. RESULTS: Sixty-two percent of the adolescents reported their typical sex partners were at least 2 years older. These adolescents were more likely to report never using condoms during the most recent sexual encounter (AOR = 2.0), during the last five sexual encounters (AOR = 2.0), and during the past month (AOR = 2.2). Similarly, having older partners was associated with greater odds of reporting any unprotected vaginal sex in the past 30 days (AOR = 1.7) or the past 6 months (AOR = 1.5). CONCLUSION: Our findings suggest that many adolescent females have sex partners who are at least 2 years older and that their relationship dynamics do not favor the adoption and maintenance of behavior protective against STD or HIV infection. Prevention programs could include training designed to help adolescent females overcome barriers to safer sex with older male partners. 相似文献
82.
Fabrizio Rao Giancarlo Garuti Michele Vitacca Paolo Banfi Fabrizio Racca Renato Cutrera Martino Pavone Marina Pedemonte Matteo Schisano Stefania Pedroni Jacopo Casiraghi Andrea Vianello Valeria A Sansone UILDM Respiratory group 《Acta myologica》2021,40(1):8
Respiratory complications are common in the patient with muscular dystrophy. The periodic clinical and instrumental respiratory evaluation is extremely important. Despite the presence in the literature of updated guidelines, patient associations often report lack of knowledge of these pathologies, particularly in peripheral hospitals. The purpose of this work, inspired by the Italian Muscular Dystrophy Association (UILDM) is to improve management of respiratory problems necessary for the management of these patients complex. To this end, the main items that the specialist can meet in the follow-up of these pathologies have been analyzed and discussed, among which the respiratory basal evaluation, the criteria of adaptation to non-invasive ventilation, management of bronchial secretions, situations of respiratory emergency, indications for tracheostomy and the subject of advance directives of treatment (DAT).Key words: respiratory failure, muscular dystrophy, cough efficacy, spirometry, polygraphy, non-invasive ventilation, arterial blood gases, cough machine, invasive ventilation, tracheostomy, mechanical ventilation 相似文献
83.
Vaccaro O Cardoni O Cuomo V Panarelli W Laurenzi M Mancini M Riccardi G Zanchetti A;Gubbio Study Research Group 《Clinical endocrinology》2003,58(3):316-322
BACKGROUND: There is substantial but not conclusive evidence that insulin resistance is related to left ventricular mass (LVM) in hypertensive individuals. To what extent this association is mediated by the relationship between plasma insulin and body size and build is still debated, and is poorly explored in nonhypertensive people. OBJECTIVE: To explore the relationship between insulin or insulin resistance and LVM in a population-based sample of nonhypertensive participants of the Gubbio Study. METHOD: Echocardiographic LVM was determined in 91 nondiabetic, nonhypertensive individuals aged 45-54 years, participating in a population-based screening. LVM normalized for height2.7 was used in the analyses; LV hypertrophy was defined as a value of > or = 50 g/m2.7 in men or > or = 47 g/m2.7 in women. Fasting plasma insulin and glucose were measured and the Homeostasis Model Assessment (HOMA) index was used as a measure of insulin resistance. RESULTS: LVM was positively and significantly correlated with body mass index (BMI) (P < 0.01), waist circumference (P < 0.01) and HOMA index (P < 0.05), whereas correlations with plasma glucose and triglycerides did not reach statistical significance (P = 0.07 for both); all correlations were offset after adjusting for BMI. Fasting plasma insulin and HOMA index were not significantly different in subjects with or without LV hypertrophy (70.8 +/- 27.8 vs. 77.7 +/- 29.6 pmol/l and 2.2 +/- 1.0 vs. 2.6 +/- 1.4, respectively). Bivariate analysis performed stratifying participants above or below the 75th percentile of the sex-specific distribution for BMI (29.1 and 29.4 kg/m2 for males and females, respectively) and plasma insulin (84 pmol/l for either gender), did not result in appreciable differences in LVM due to insulin levels. Similar results were obtained replacing the HOMA index for insulin in the analysis. CONCLUSION: In nonhypertensive individuals left ventricular mass is not associated with plasma insulin independently of body mass index. 相似文献
84.
Chronic heart failure (CHF) is a leading cause of morbidity and mortality. Although a precise definition for a cut-off value of hemoglobin level for anemia is still lacking, it has recently been found to be a common complication in CHF, occurring in 10-20% of patients. There are several possible pathogenetic mechanisms for anemia in CHF, and a precise underlying cause is found in only a minority of patients. In CHF, more than 50% of anemia cases are considered to be 'anemia in chronic illness'. In CHF patients, low hemoglobin values directly relate to poor peak oxygen consumption, disabling symptoms, and impaired survival. Recent pilot studies showed that correction of anemia with erythropoietin and iron may lead to improvement in symptoms and exercise capacity. These issues need to be tested in larger, double-blind, randomized, placebo-controlled trials before anemia treatment becomes routine in patients with CHF. 相似文献
85.
Müller T Werblowsky TL Florio GM Berne BJ Flynn GW 《Proceedings of the National Academy of Sciences of the United States of America》2005,102(15):5315-5322
A simple model system for the 2D self-assembly of functionalized organic molecules on surfaces was examined in a concerted experimental and theoretical effort. Monolayers of 1-halohexanes were formed through vapor deposition onto graphite surfaces in ultrahigh vacuum. Low-temperature scanning tunneling microscopy allowed the molecular conformation, orientation, and monolayer crystallographic parameters to be determined. Essentially identical noncommensurate monolayer structures were found for all 1-halohexanes, with differences in image contrast ascribed mainly to electronic factors. Energy minimizations and molecular dynamics simulations reproduced structural parameters of 1-bromohexane monolayers quantitatively. An analysis of interactions driving the self-assembly process revealed the crucial role played by small but anisotropic electrostatic forces associated with the halogen substituent. While alkyl chain dispersion interactions drive the formation of a close-packed adsorbate monolayer, electrostatic headgroup forces are found to compete successfully in the control of both the angle between lamella and backbone axes and the angle between surface and backbone planes. This competition is consistent with energetic tradeoffs apparent in adsorption energies measured in earlier temperature-programmed desorption studies. In accordance with the higher degree of disorder observed in scanning tunneling microscopy images of 1-fluorohexane, theoretical simulations show that electrostatic forces associated with the fluorine substituent are sufficiently strong to upset the delicate balance of interactions required for the formation of an ordered monolayer. The detailed dissection of the driving forces for self-assembly of these simple model systems is expected to aid in the understanding of the more complex self-assembly processes taking place in the presence of solvent. 相似文献
86.
R A Martino A S Kissack J H Stuckey F Kavaler V J Fisher 《The American journal of cardiology》1969,24(4):537-543
87.
88.
Bravo G Duguet AM Dubois MF Delpierre C Vellas B 《Journal of cross-cultural gerontology》2008,23(3):239-253
The authors first describe the rules enacted in Quebec and France to protect adults with decisional impairment who may be approached by investigators to participate in research protocols. They then present two consecutive postal surveys conducted among Quebec and French researchers in aging and designed to (1) assess their knowledge of the legal provisions implemented to protect decisionally incapable adults, (2) elicit their opinions regarding the person best suited to provide substitute consent for research participation, and (3) document their conduct related to obtaining consent for prospective subjects with impaired decisional capacity. Knowledge of the legislation governing substitute consent was poor, even more so among French than Quebec researchers (p < 0.001). In both samples, the majority of respondents felt that the substitute decision-maker does not have to be legally appointed when the study poses little risk to the participant. Practice data revealed a certain discrepancy between the conduct of researchers in aging and the legal provisions regarding consent for research purposes that prevail in their jurisdictions. These findings underscore the need to better educate clinical investigators about existing measures to protect prospective subjects who lack decisional capacity. They also provide some support for allowing close relatives to consent to research participation on behalf of older adults who are unable to consent by themselves and have not been appointed a legal representative. 相似文献
89.