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   19382篇
  免费   1400篇
  国内免费   361篇
耳鼻咽喉   106篇
儿科学   597篇
妇产科学   313篇
基础医学   1642篇
口腔科学   564篇
临床医学   1815篇
内科学   2696篇
皮肤病学   201篇
神经病学   1525篇
特种医学   1430篇
外科学   1855篇
综合类   1526篇
现状与发展   1篇
一般理论   2篇
预防医学   3707篇
眼科学   216篇
药学   1434篇
  3篇
中国医学   242篇
肿瘤学   1268篇
  2024年   48篇
  2023年   300篇
  2022年   426篇
  2021年   637篇
  2020年   706篇
  2019年   686篇
  2018年   624篇
  2017年   642篇
  2016年   672篇
  2015年   594篇
  2014年   1163篇
  2013年   1383篇
  2012年   1110篇
  2011年   1188篇
  2010年   867篇
  2009年   909篇
  2008年   870篇
  2007年   986篇
  2006年   827篇
  2005年   826篇
  2004年   735篇
  2003年   693篇
  2002年   522篇
  2001年   417篇
  2000年   341篇
  1999年   301篇
  1998年   279篇
  1997年   221篇
  1996年   180篇
  1995年   207篇
  1994年   201篇
  1993年   170篇
  1992年   202篇
  1991年   166篇
  1990年   105篇
  1989年   104篇
  1988年   117篇
  1987年   87篇
  1986年   76篇
  1985年   111篇
  1984年   75篇
  1983年   53篇
  1982年   65篇
  1981年   53篇
  1980年   44篇
  1979年   25篇
  1978年   40篇
  1977年   33篇
  1976年   17篇
  1975年   12篇
排序方式: 共有10000条查询结果,搜索用时 26 毫秒
221.
炔诺酮肟对大鼠抗着床抗早孕作用机理的形态学研究   总被引:1,自引:0,他引:1  
大鼠从妊娠第一天开始每日灌服炔诺酮肟4mg/kg,共3天。结果能引起早孕大鼠黄体细胞滑面内质网减少;脂滴大量积贮;抑制卵巢3β-羟基甾体脱氢酶活性,从而使卵巢孕酮生物合成受阻。药物还能引起早孕大鼠子宫蜕膜的病理改变,蜕膜细胞出现变性,坏死,宫腔内大量出血,白细胞浸润,胚胎发育不良,蜕膜细胞内糖原及碱性磷酸酶含量均下降。本文还讨论了药物引起卵巢孕酮生物合成受阻与蜕膜变化的关系。  相似文献   
222.
Prevalence of mental disorder in an urban population in central Sweden   总被引:1,自引:0,他引:1  
The principal reason for this epidemiological study was the lack of psychiatric morbidity studies in a predominantly urban population, by psychiatrists in direct interviews. The psychiatric examination, covering 1970-71, included a representative selection of 2,283 persons, 18-65 years old from "former" Stockholm County, and the 12-month prevalence of mental disorders was measured. The total of non-participants was 12%. Forty-seven percent had a psychiatric diagnosis - significantly more women (54%) than men (40%). Excluding the psychosomatic diagnoses, 31% of the population received a psychiatric diagnosis, which agrees closely with other contemporary studies of mental disorder in the Nordic countries. The primary diagnoses were: neuroses 26%, psychosomatic diagnoses 16%, schizophrenic/paranoid conditions or other psychoses 0.6%, affective disorders 0.2%, psychoorganic syndromes 1.2%, psychopathy 0.2%, character neurosis 1%, drug dependence 0.2% (as a primary or a secondary diagnosis 0.6%), alcoholism 1.4% (as a primary or a secondary diagnosis 3.1%) and mental retardation 0.4% (as a primary or a secondary diagnosis 0.8%).  相似文献   
223.
ObjectivesBisphenol A (BPA) is used in the electrical, mechanical, medical, and food industries. Previous studies have suggested that BPA is an endocrine disruptor. Regulation of BPA has led to increased use of bisphenol F (BPF) and bisphenol S (BPS). However, few studies have investigated the associations of BPF and BPS with thyroid dysfunction in children. Our study investigated the associations of prenatal BPA and early childhood BPA, BPF, and BPS exposure with thyroid function in 6-year-old children.MethodsPrenatal BPA concentrations were measured during the second trimester of pregnancy in an established prospective birth cohort. We measured urinary BPA, BPF, and BPS concentrations and thyroid hormone levels (thyroid-stimulating hormone, total T3, and free T4) in 6-year-old children (n=574). We examined the associations between urinary bisphenol concentrations and percentage change of thyroid hormone concentrations using multivariate linear regression. We also compared thyroid hormone levels by dividing the cohort according to BPA, BPF, and BPS concentrations.ResultsThe associations between prenatal BPA and total T3 levels were statistically significant in all models, except for girls when using a crude model. The associations between urinary BPA and BPS concentrations and levels of all thyroid hormones were not statistically significant. However, we observed that lower free T4 levels (−1.94%; 95% confidence interval, −3.82 to −0.03) were associated with higher urinary BPF concentrations in girls only.ConclusionsOur findings identified significant associations between prenatal BPA exposure and total T3 levels in all children and between BPF exposure and free T4 levels in girls only.  相似文献   
224.
Polyphenols are a group of phytochemicals with potential health-promoting effects. They are classified as flavonoid (flavonols, flavanols, flavones, flavanones, isoflavones, and anthocyanins) and non-flavonoid molecules (phenolic acids, hydroxycinnamic acids, lignans, stilbenes, and tannins). Although an increasing number of trials have shown a correlation among polyphenol consumption and a reduction in risk factors for chronic diseases, discrepancies in explaining their positive effects have been found in terms of the bioavailability. In fact, polyphenols show a low bioavailability due to several factors: interaction with the food matrix, the metabolic processes mediated by the liver (phase I and II metabolism), intestine and microbiota. On the other hand, the biological activities of phenol compounds may be mediated by their metabolites, which are produced in vivo, and recent studies have confirmed that these molecules may have antioxidant and anti-phlogistic properties. This review discusses the studies performed in vivo, which consider the polyphenol bioavailability and their different food sources. Factors influencing the biological effects of the main classes of polyphenols are also considered.  相似文献   
225.
Low intakes of fruits and vegetables have resulted in suboptimal intakes of several micronutrients, including vitamin C. This cross-sectional study used data from 84,902 children/adults (≥1 y) who completed a 24-h dietary recall as part of the United States National Health and Nutrition Examination Survey (1999–2018). Mean vitamin C intakes from foods/beverages were calculated as were trends in major food/beverage sources of vitamin C. Percentages below the Estimated Average Requirement (EAR) were estimated. Overall, mean vitamin C consumption declined by 23% (97–75 mg/d; p-value for trend < 0.001). 100% fruit juice was the leading source of vitamin C (25.6% of total or 21.7mg/d), but this declined by 48% (25–13 mg/d; p-value for trend < 0.001). Whole fruit increased among children/adolescents (+75.8%;10–17 mg/d; p-value for trend < 0.001), but not adults, while the vegetable contribution was generally unchanged. The proportion of the population below the EAR increased by 23.8% on a relative scale or 9 percentage points on an absolute scale (38.3–47.4%). Declines in vitamin C intake is driven largely by decreases in fruit juice coupled with modest increases in whole fruit. Due to associations between vitamin C intake and numerous health outcomes these trends warrant careful monitoring moving forward.  相似文献   
226.
Increasing sugar-sweetened beverages (SSB) consumption and associated health impacts warrant health-policy action. We assessed associations of socioeconomic and lifestyle variables with adolescents’ consumption of regular soda (RSD), sport (SD), and energy (ED) drinks. Cross-sectional study of 3930 Spanish adolescents (2089 girls, 1841 boys) aged 13–18 years). We compared frequency of consuming each SSB type (European Food Safety Authority questionnaire) with sociodemographic and lifestyle variables (standardized questions). RSD, SD, and ED were consumed at least weekly by 72.7%, 32.3%, and 12.3% of participants, respectively, and more frequently (p < 0.001) by boys, compared to girls. Multivariate ordinal logistic regression showed inverse association between RSD, SD, and ED consumption and parental occupation-based socioeconomic status (p < 0.01). Daily smoking was associated (p < 0.001) with higher ED (OR 3.64, 95% CI 2.39–5.55) and RSD (OR 2.15, 95% CI 1.56–2.97) consumptions. SD intake was associated inversely with smoking (OR 0.60, 95% CI 0.40–0.89, p = 0.012) and directly with physical activity (OR 2.93, 95% CI 2.18–3.95, p < 0.001). School performance was lower among ED (OR 2.14, 95% CI, 1.37–3.35, p = 0.001) and RSD (OR 1.81, 95% CI 1.24–2.64, p = 0.002) consumers, compared to SD. Maleness and low socioeconomic status predicted SSB consumption. Smoking and low school performance were associated with higher ED and RSD intakes.  相似文献   
227.
BackgroundSchool meals are associated with improved food security status and dietary intake. Children receiving free and reduced-price school meals lose access to these meals during the summer. The association between food security status and dietary intake in these children during summer is unclear.ObjectiveTo examine the association between food security status (high, marginal, low, and very-low food security) among children and intake of select dietary factors during summer in children certified for free and reduced-price school meals by age group (3 to 4 years, 5 to 8 years, 9 to 12 years, and 13 to 17 years).DesignCross-sectional analysis.Participants/settingSecondary data from 11,873 children aged 3 to 17 years in the control group of the US Department of Agriculture Summer Electronic Benefit Transfer for Children Demonstration Project.Main outcome measuresConsumption of total fruits and vegetables; fruits and vegetables, excluding fried potatoes; whole grains; added sugars; added sugars, excluding cereals; added sugars from sugar-sweetened beverages; and dairy products assessed using questions from the 2009-2010 National Health and Nutrition Examination Survey Multifactor Diet Screener.Statistical analysisMultiple linear regression.ResultsFor the majority of age groups, marginal food security, low food security, and very-low food security were associated with lower fruit and vegetable consumption and low food security and very-low food security were associated with lower dairy consumption, with children from households with very-low food security having the lowest consumption. Children from households with very-low food security consumed 0.73 (95% CI –0.93 to –0.53) to 0.99 (95% CI –1.59 to –0.39) cup equivalents less per day of fruits and vegetables and 0.49 (95% CI –0.65 to –0.34) to 0.68 (95% CI –1.07 to –0.29) cup equivalents less per day of dairy compared with children from households experiencing high food security.ConclusionsLower food security was associated with reduced consumption of fruits and vegetables and dairy products during summer in children from low-income households.  相似文献   
228.
目的描述12~36月龄幼儿胃肠道功能情况,探讨潜在影响因素。方法2018年9月—2019年1月在北京市朝阳区某社区卫生服务中心招募12~36月龄幼儿385名,收集幼儿及母亲基本信息,采用简版《婴幼儿胃肠道症状问卷》评估幼儿胃肠道功能。问卷共10个问题,反映幼儿胃肠道症状(6个问题)和相关行为(4个问题)。胃肠道功能总评分为10~60分,其中胃肠道症状6~36分、胃肠道相关行为4~24分,评分越高提示胃肠功能越弱;将总评分等于或高于第二个三分位数(17分)定义为轻度胃肠不适。采用多因素logistic回归分析幼儿轻度胃肠不适的可能影响因素。结果幼儿胃肠道功能总评分、症状评分和相关行为评分的中位数(四分位数间距)分别为13.0(11.0~19.0)分、6.0(6.0~10.0)分和6.0(5.0~8.0)分。小月龄(12~17月龄14.5分,18~23月龄13.0分)比大月龄(24~29月龄12.0分,30~36月龄12.5分)、母亲为初产妇(14.0分)比经产妇(12.0分)的幼儿中位胃肠道功能总评分高(P<0.05)。轻度胃肠不适幼儿124名(32.2%),母亲为初产妇(36.8%)比母亲为经产妇(21.8%)的幼儿轻度胃肠不适发生率显著升高(P=0.004)。多因素logistic回归分析显示,12~17月龄幼儿与30~36月龄幼儿相比(调整OR,2.32;95%CI,1.14~4.71)、母亲为初产妇的幼儿与经产妇的幼儿相比(调整OR,2.05;95%CI,1.19~3.52),轻度胃肠不适风险显著升高。幼儿性别、分娩方式、母乳喂养时长和母亲分娩年龄对轻度胃肠不适发生风险无显著影响。结论幼儿胃肠道功能整体较好,幼儿月龄及母亲产次影响幼儿胃肠功能,小月龄及母亲为初产妇的幼儿易发生轻度胃肠不适。  相似文献   
229.
ObjectivesThe recently developed Hospital Frailty Risk Score (HFRS) allows ascertainment of frailty from administrative data. We aimed to compare the HFRS against the widely used FRAIL Scale and Frailty Index.DesignPopulation-based cohort study linked to Western Australian Hospital Morbidity Data Collection and Death Registrations.Setting and ParticipantsThe Health in Men Study with frailty determined at Wave 2 (2001/2004), mortality in the 1-year period following Wave 2, and disability at Wave 3 (2008). Participants were 4228 community-based men aged ≥75 years, followed until Wave 3.MeasurementsWe used multivariable regression to determine the association between each frailty measure and outcomes of length of stay (LOS), death, and disability. We also determined if the additional cases of frailty identified by one measure over the other was associated with these outcomes.ResultsOf 4228 men studied, the HFRS (n = 689) identified fewer men as frail than the FRAIL Scale (n = 1648) and Frailty Index (n = 1820). In the fully adjusted models, all 3 frailty measures were associated with longer LOS and mortality, whereas only the FRAIL Scale and Frailty Index were significantly associated with disability. The additional cases of frailty identified by the FRAIL Scale and Frailty Index had longer LOS and greater risks of death and disability. The fully adjusted hazard ratio for death among the additional cases of frailty identified by the FRAIL Scale (compared to being not frail on both HFRS and FRAIL Scale) was 2.14 (95% CI 1.48-3.08).Conclusions and ImplicationsThe HFRS is associated with adverse outcomes. However, it identified approximately 60% fewer men who were frail than the FRAIL Scale and Frailty Index, and the additional cases identified were also at high risks of adverse outcomes. Users of the HFRS should be aware of the differences with other frailty measures.  相似文献   
230.
BackgroundWomen with disabilities experience elevated risks for pregnancy complications and report barriers accessing prenatal care. Emerging evidence highlights the significant role primary care providers play in promoting preventive services like prenatal care.ObjectiveTo examine the relationship between continuity of primary care (COC) and prenatal care adequacy among women with disabilities.MethodsWe conducted a population-based study using health administrative data in Ontario, Canada. The study population included 15- to 49-year-old women with physical (n = 106,555), sensory (n = 32,194), intellectual/developmental (n = 1515), and multiple (n = 6543) disabilities who had a singleton livebirth or stillbirth in 2003–2017 and ≥ 3 primary care visits < 2 years before conception. COC was measured using the Usual Provider of Care Index. Nominal logistic regression was used to compute adjusted odds ratios (aOR) for prenatal care adequacy, measured using the Revised-Graduated Prenatal Care Utilization Index, for women with low versus moderate/high COC, controlling for other social and medical characteristics.ResultsWomen with disabilities with low COC, versus those with moderate/high COC, had increased odds of no (aOR 1.42, 95% CI 1.29–1.56), inadequate (aOR 1.19, 95% CI 1.16–1.23), and intensive prenatal care (aOR 1.22, 95% CI 1.19–1.25) versus adequate. In additional analyses, women with low COC and no/inadequate prenatal care were the most socially disadvantaged among the cohort, and those with low COC and intensive prenatal care had the greatest medical need.ConclusionImproving primary care access for women with disabilities, particularly those experiencing social disadvantage, could lead to better prenatal care access.  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