首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   435篇
  免费   27篇
  国内免费   2篇
儿科学   5篇
基础医学   93篇
口腔科学   2篇
临床医学   37篇
内科学   35篇
皮肤病学   53篇
神经病学   67篇
特种医学   33篇
外科学   46篇
综合类   3篇
一般理论   1篇
预防医学   23篇
眼科学   1篇
药学   50篇
肿瘤学   15篇
  2022年   4篇
  2021年   5篇
  2020年   9篇
  2019年   6篇
  2018年   10篇
  2017年   8篇
  2016年   12篇
  2015年   13篇
  2014年   28篇
  2013年   15篇
  2012年   35篇
  2011年   12篇
  2010年   14篇
  2009年   13篇
  2008年   20篇
  2007年   24篇
  2006年   20篇
  2005年   36篇
  2004年   17篇
  2003年   13篇
  2002年   20篇
  2001年   25篇
  2000年   16篇
  1999年   7篇
  1997年   5篇
  1994年   4篇
  1992年   3篇
  1991年   4篇
  1990年   2篇
  1989年   2篇
  1987年   2篇
  1985年   2篇
  1983年   3篇
  1981年   2篇
  1980年   3篇
  1979年   2篇
  1978年   4篇
  1977年   3篇
  1975年   3篇
  1974年   5篇
  1973年   3篇
  1972年   2篇
  1971年   3篇
  1970年   4篇
  1969年   2篇
  1968年   2篇
  1967年   3篇
  1966年   4篇
  1965年   2篇
  1952年   1篇
排序方式: 共有464条查询结果,搜索用时 375 毫秒
11.

Background

Low socioeconomic status (SES) exacerbates the high rate of smoking relapse in women following childbirth.

Purpose

This study examined multiple models of potential mechanisms linking SES and postpartum smoking relapse among women who quit smoking due to pregnancy.

Methods

Participants were 251 women enrolled in a randomized clinical trial of a new postpartum smoking relapse prevention intervention. Four models of the prepartum mechanisms linking SES and postpartum smoking relapse were evaluated using a latent variable modeling approach.

Results

Each of the hypothesized models were a good fit for the data. As hypothesized, SES indirectly influenced postpartum smoking relapse through increased prepartum negative affect/stress, reduced sense of agency, and increased craving for cigarettes. However, the model that included craving as the sole final pathway between SES and relapse demonstrated superior fit when compared with all other models.

Conclusions

Findings have implications for future interventions that aim to reduce postpartum relapse.  相似文献   
12.
BACKGROUND: In newborn screening with tandem mass spectrometry, multiple intermediary metabolites are quantified in a single analytical run for the diagnosis of fatty-acid oxidation disorders, organic acidurias, and aminoacidurias. Published diagnostic criteria for these disorders normally incorporate a primary metabolic marker combined with secondary markers, often analyte ratios, for which the markers have been chosen to reflect metabolic pathway deviations. METHODS: We applied a procedure to extract new markers and diagnostic criteria for newborn screening to the data of newborns with confirmed medium-chain acyl-CoA dehydrogenase deficiency (MCADD) and a control group from the newborn screening program, Heidelberg, Germany. We validated the results with external data of the screening center in Hamburg, Germany. We extracted new markers by performing a systematic search for analyte combinations (features) with high discriminatory performance for MCADD. To select feature thresholds, we applied automated procedures to separate controls and cases on the basis of the feature values. Finally, we built classifiers from these new markers to serve as diagnostic criteria in screening for MCADD. RESULTS: On the basis of chi(2) scores, we identified approximately 800 of >628,000 new analyte combinations with superior discriminatory performance compared with the best published combinations. Classifiers built with the new features achieved diagnostic sensitivities and specificities approaching 100%. CONCLUSION: Feature construction methods provide ways to disclose information hidden in the set of measured analytes. Other diagnostic tasks based on high-dimensional metabolic data might also profit from this approach.  相似文献   
13.

Background

Communication breakdowns and care coordination problems often cause preventable adverse patient care events, which can be especially acute in the trauma setting, in which ad hoc teams have little time for advanced planning. Existing teamwork curricula do not address the particular issues associated with ad hoc emergency teams providing trauma care.

Methods

Ad hoc trauma teams completed a preinstruction simulated trauma encounter and were provided with instruction on appropriate team behaviors and team communication. Teams completed a postinstruction simulated trauma encounter immediately afterward and 3 weeks later, then completed a questionnaire. Blinded raters rated videotapes of the simulations.

Results

Participants expressed high levels of satisfaction and intent to change practice after the intervention. Participants changed teamwork and communication behavior on the posttest, and changes were sustained after a 3-week interval, though there was some loss of retention.

Conclusions

Brief training exercises can change teamwork and communication behaviors on ad hoc trauma teams.  相似文献   
14.
15.
Objectives. The purpose of this study was to address current gaps in the literature by examining the associations of fast food restaurant (FFR) density around the home and FFR proximity to the home, respectively, with body mass index (BMI) among a large sample of African American adults from Houston, Texas.Methods. We used generalized linear models with generalized estimating equations to examine associations of FFR density at 0.5-, 1-, 2-, and 5-mile road network buffers around the home with BMI and associations of the closest FFR to the home with BMI. All models were adjusted for a range of individual-level covariates and neighborhood socioeconomic status. We additionally investigated the moderating effects of household income on these relations. Data were collected from December 2008 to July 2009.Results. FFR density was not associated with BMI in the main analyses. However, FFR density at 0.5, 1, and 2 miles was positively associated with BMI among participants with lower incomes (P ≤ .025). Closer FFR proximity was associated with higher BMI among all participants (P < .001), with stronger associations emerging among those of lower income (P < .013) relative to higher income (P < .014).Conclusions. Additional research with more diverse African American samples is needed, but results supported the potential for the fast food environment to affect BMI among African Americans, particularly among those of lower economic means.Obesity and its associated health conditions are a growing problem in the United States, with obesity prevalence having more than doubled since the 1960s.1 The health care cost of Americans’ growing waistlines is substantial and expected to top $860 billion by 2030.2 Racial/ethnic disparities in obesity are of particular concern for the nation’s health, with African Americans experiencing the highest prevalence of obesity relative to other racial/ethnic groups.1 The National Health and Nutrition Examination Survey from 2009 to 2010 indicated that 38.8% of African American men and 58.5% of African American women were obese compared with 36.2% of non-Hispanic White men and 32.2% of non-Hispanic White women.3 Racial/ethnic disparities have also been cited for body mass index (BMI), with the gap in BMI growth widening between African Americans and Whites in recent decades.4To better understand the factors associated with these trends, researchers and policymakers are paying increased attention to the retail food environment. The growing availability of low-cost, calorie-dense consumables from fast food restaurants (FFRs) is one of the factors implicated in the nation’s rising BMI.5–7 The availability of FFRs may be particularly relevant to the growing racial/ethnic disparities in BMI because several studies support a higher density of FFRs among predominately African American neighborhoods relative to predominately White neighborhoods.8–11 Moreover, at least 1 study reports stronger relations between fast food availability and fast food consumption among non-White versus White populations.12 Thus, African Americans may be more likely to consume fast food if it is available, and it may be more available to them because FFRs tend to be clustered in African American neighborhoods. Not surprisingly, greater fast food consumption is associated with higher BMI.13–15Several studies examined associations between the availability of fast food and BMI. Fast food availability was most commonly conceptualized as the density of FFRs near a person’s home, work, or school environment. Findings about the associations of FFR density with BMI and overweight or obesity status, however, were mixed,5,11 with some studies supporting positive associations,16–19 and others citing null results.14,20 Less commonly, studies conceptualized fast food availability as the proximity of the closest FFR to a person’s home. Studies taking this approach yielded mixed results regarding relations between FFR proximity and fast food consumption,21,22 as well as between FFR proximity and BMI or obesity status.11,23 Unfortunately, most of these studies focused predominately on White populations, and many had methodological limitations (e.g., self-reported BMI) that could have contributed to mixed results.5,11 We found only a single study that focused on an all-African American sample, which yielded null results regarding associations between FFR density and BMI.24 Although this study had several strengths, including a sample of more than 4500 African Americans and investigator-measured BMI, limitations included only 1 conceptualization of FFR availability (FFR density), and the use of Euclidean distances (“as the crow flies”) in density buffer calculation, which may be less realistic than buffers based on road networks (i.e., the only places along which FFRs can be found).5 In addition, we found no previous studies that examined whether associations between FFR availability and BMI were moderated by household income. Because reasons cited for frequent fast food consumption include both accessibility and affordability,6 it might be that relations of FFRs and BMI are stronger among those of lower economic means for whom fast food might be more affordable than other dining options. Therefore, additional research is needed to better understand the relations of fast food availability and BMI among African Americans.The purpose of this study was to address current gaps in the literature by examining the associations of FFR density around the home and FFR proximity to the home, respectively, with BMI among a large sample of African American adults from Houston, Texas. We additionally investigated the moderating effects of household income on these relations.  相似文献   
16.
Serum immunoglobulin (Ig)G anti-nuclear antibodies (ANA) detected by indirect immunofluorescence (IF) microscopy remains a hallmark of systemic lupus erythematosus (SLE). Whether or not IF-ANA status varies over time is controversial. We therefore designed a prospective study with longitudinal follow-up of patients with recent-onset SLE. The study population consisted of 54 recently diagnosed SLE cases, all meeting the 1982 American College of Rheumatology (ACR) and/or the 2012 Systemic Lupus International Collaborating Clinics (SLICC) criteria. Clinical follow-up data, including disease activity, organ damage and sera, were collected from clinical onset of SLE and onwards, in most cases yearly (0‒96 months). IF-ANA was analysed on human epithelial cells-2 (HEp-2) cells and categorized regarding staining patterns. Using an addressable laser bead assay (FIDIS™ Connective profile), we measured IgG-ANA fine specificities against Ro52/SSA, Ro60/SSA, Sjögren’s syndrome type B antigen (La/SSB), Smith antigen (Sm), Smith antigen/ribonucleoprotein (Sm/RNP), U1 RNP (U1RNP), dsDNA, ribosomal-P protein and histone. At baseline, all patients were judged ANA-positive at an abnormal titre corresponding to the 95th percentile of healthy blood donors, but seven of 54 patients (13%) lost ANA-positivity over time. Homogeneous (AC-1; 46%) and speckled (AC-4 or 5; 31%) were the most frequently observed patterns at inclusion, whereas 7% switched pattern at least once during follow-up. Established associations between ANA fine specificities and clinical data were confirmed. Levels of anti-Sm/RNP, but not of anti-dsDNA, correlated with clinical disease activity [modified SLE disease activity 2000 (mSLEDAI-2K)]. Our data indicate that a considerable proportion of Swedish patients with SLE lose ANA-positivity over time, whereas consistent staining patterns were frequent. The clinical and mechanistic relevance of ANA seroconversion remains uncertain. Further prospective evaluations in larger SLE populations with more diverse ethnicities are warranted.  相似文献   
17.
BACKGROUND: Carnitine is applied to ameliorate ischemia-reperfusion (I/R) injury of several organs. However, application to hepatic I/R injury is not frequently reported. The aim of this study was to elucidate the effect of exogenous carnitine administration to ameliorate the warm hepatic I/R injury. MATERIALS AND METHODS: Male Wistar rats were divided into two groups, a carnitine group (Car);100 mg/kg of l-carnitine administration and a control group (C); vehicle administration. Thirty minutes after administration, the left hepatic lobes were given 60-min ischemia and then reperfused. Plasma alanine aminotransferase (ALT), aspartate aminotransferase (AST), glutamate dehydrogenase (GLDH), tumor necrosis factor (TNF)-alpha, and lipoperoxides (LPO) were measured. Hepatic adenosine triphosphate (ATP) concentration was also measured. The hepatic blood flow was estimated using a Laser Doppler. The presence of apoptosis in the livers was evaluated by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. RESULTS: In group Car, the blood flow of the left hepatic lobes was better recovered during the reperfusion period than in group C (P < 0.0001). Plasma levels of ALT, AST, GLDH, and TNF-alpha at 1 h after reperfusion were not significantly different between the groups. Although there were no statistical significances, ALT, AST, and TNF-alpha levels in group Car at 24 h after reperfusion tended to be higher than in group C. Plasma LPO levels were not different between the two groups. Also hepatic ATP concentration was not different between the two groups. TUNEL positive liver cells were visible only in group Car at 24 h after reperfusion, but not in the controls. CONCLUSIONS: Although carnitine administration improved the hepatic blood flow during the reperfusion period, we could not demonstrate a protective effect to the hepatic warm I/R injury.  相似文献   
18.
We characterised task‐related top‐down signals in monkey auditory cortex cells by comparing single‐unit activity during passive sound exposure with neuronal activity during a predictable and unpredictable reaction‐time task for a variety of spectral‐temporally modulated broadband sounds. Although animals were not trained to attend to particular spectral or temporal sound modulations, their reaction times demonstrated clear acoustic spectral‐temporal sensitivity for unpredictable modulation onsets. Interestingly, this sensitivity was absent for predictable trials with fast manual responses, but re‐emerged for the slower reactions in these trials. Our analysis of neural activity patterns revealed a task‐related dynamic modulation of auditory cortex neurons that was locked to the animal's reaction time, but invariant to the spectral and temporal acoustic modulations. This finding suggests dissociation between acoustic and behavioral signals at the single‐unit level. We further demonstrated that single‐unit activity during task execution can be described by a multiplicative gain modulation of acoustic‐evoked activity and a task‐related top‐down signal, rather than by linear summation of these signals.  相似文献   
19.
20.
BACKGROUND: This study examined the characteristics, tobacco use patterns over time, and predictors of tobacco cessation among concomitant users of cigarettes and smokeless tobacco. METHODS: Participants were employed adults residing in the southeastern United States who participated in the Working Well cancer prevention trial. Participants were assessed at baseline and followed-up 4 years later. RESULTS AND CONCLUSIONS: The study yielded several key findings: (a) the prevalence of concomitant smoking and smokeless tobacco use was high among males and nonexistent among females, (b) the characteristics of concomitant users were relatively distinct from those of both smokers and smokeless tobacco users, (c) concomitant users exhibited substantial variability in their tobacco use patterns and were less likely to stop using tobacco than were smokers or smokeless tobacco users, (d) indicators of nicotine dependence predicted tobacco cessation for both smokers and smokeless tobacco users, but were largely unrelated to tobacco cessation among concomitant users, and (e) demographics, environmental variables, and measures derived from the transtheoretical model were not consistent predictors of tobacco cessation after controlling for nicotine dependence.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号