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   15437篇
  免费   1207篇
  国内免费   23篇
耳鼻咽喉   80篇
儿科学   585篇
妇产科学   533篇
基础医学   1903篇
口腔科学   184篇
临床医学   2463篇
内科学   2601篇
皮肤病学   188篇
神经病学   1564篇
特种医学   315篇
外科学   1356篇
综合类   359篇
一般理论   25篇
预防医学   2360篇
眼科学   226篇
药学   1046篇
  4篇
中国医学   25篇
肿瘤学   850篇
  2024年   47篇
  2023年   217篇
  2022年   226篇
  2021年   411篇
  2020年   303篇
  2019年   417篇
  2018年   484篇
  2017年   297篇
  2016年   385篇
  2015年   408篇
  2014年   549篇
  2013年   733篇
  2012年   1234篇
  2011年   1225篇
  2010年   585篇
  2009年   514篇
  2008年   994篇
  2007年   1034篇
  2006年   982篇
  2005年   930篇
  2004年   898篇
  2003年   791篇
  2002年   717篇
  2001年   188篇
  2000年   133篇
  1999年   166篇
  1998年   139篇
  1997年   103篇
  1996年   89篇
  1995年   91篇
  1994年   81篇
  1993年   80篇
  1992年   114篇
  1991年   82篇
  1990年   68篇
  1989年   58篇
  1988年   58篇
  1987年   68篇
  1986年   63篇
  1985年   44篇
  1984年   33篇
  1983年   35篇
  1982年   37篇
  1981年   47篇
  1979年   32篇
  1974年   39篇
  1972年   40篇
  1971年   34篇
  1970年   39篇
  1969年   35篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Uptake of colorectal cancer screening remains suboptimal. Mailed fecal immunochemical testing (FIT) offers promise for increasing screening rates, but optimal strategies for implementation have not been well synthesized. In June 2019, the Centers for Disease Control and Prevention convened a meeting of subject matter experts and stakeholders to answer key questions regarding mailed FIT implementation in the United States. Points of agreement included: 1) primers, such as texts, telephone calls, and printed mailings before mailed FIT, appear to contribute to effectiveness; 2) invitation letters should be brief and easy to read, and the signatory should be tailored based on setting; 3) instructions for FIT completion should be simple and address challenges that may lead to failed laboratory processing, such as notation of collection date; 4) reminders delivered to initial noncompleters should be used to increase the FIT return rate; 5) data infrastructure should identify eligible patients and track each step in the outreach process, from primer delivery through abnormal FIT follow-up; 6) protocols and procedures such as navigation should be in place to promote colonoscopy after abnormal FIT; 7) a high-quality, 1-sample FIT should be used; 8) sustainability requires a program champion and organizational support for the work, including sufficient funding and external policies (such as quality reporting requirements) to drive commitment to program investment; and 9) the cost effectiveness of mailed FIT has been established. Participants concluded that mailed FIT is an effective and efficient strategy with great potential for increasing colorectal cancer screening in diverse health care settings if more widely implemented.  相似文献   
93.
Brazil is the most populous country in South America. Using 24 h dietary data, we compared the nutrient intakes of 4–13-year-olds to reference values and tested for regional and socioeconomic (SES) differences. A considerable proportion reported intakes below the Estimated Average Requirements (EAR) for vitamins E (78.1%, 96.5%), D (100% for both), and calcium (80.5%, 97.7%) for 4–8 and 9–13-year-olds, respectively. Few exceeded Adequate Intakes (AI) for potassium or fiber. Older children reported greater inadequacies and, while there was regional variability, patterns of inadequacy and excess tended to be similar. For vitamin C, the percent of children below EAR in the Northeast and Southeast was lower than in the South. Most children, regardless of SES, had energy intakes within the Acceptable Macronutrient Distribution Ranges (AMDRs) for carbohydrates and protein. Over a quarter reported total energy from fat less than the AMDR, and inversely associated with SES (low 50.9%, moderate 26.0%, and high 15.0%), but also exceeding the percentage of energy recommendation for saturated fat, increasing with SES (low 18.1%, moderate 38.9%, and high 48.8%). The contrast observed between the diets of young Brazilians and recommendations underscores the need for individual and regional environmental interventions to promote healthier dietary patterns.  相似文献   
94.
95.
96.

Introduction

African Americans' (AAs) late-onset Alzheimer's disease (LOAD) genetic risk profile is incompletely understood. Including clinical covariates in genetic analyses using informed conditioning might improve study power.

Methods

We conducted a genome-wide association study (GWAS) in AAs employing informed conditioning in 1825 LOAD cases and 3784 cognitively normal controls. We derived a posterior liability conditioned on age, sex, diabetes status, current smoking status, educational attainment, and affection status, with parameters informed by external prevalence information. We assessed association between the posterior liability and a genome-wide set of single-nucleotide polymorphisms (SNPs), controlling for APOE and ABCA7, identified previously in a LOAD GWAS of AAs.

Results

Two SNPs at novel loci, rs112404845 (P = 3.8 × 10?8), upstream of COBL, and rs16961023 (P = 4.6 × 10?8), downstream of SLC10A2, obtained genome-wide significant evidence of association with the posterior liability.

Discussion

An informed conditioning approach can detect LOAD genetic associations in AAs not identified by traditional GWAS.  相似文献   
97.
Tickborne diseases (TBDs) such as Lyme disease result in ≈500,000 diagnoses annually in the United States. Various methods can reduce the abundance of ticks at small spatial scales, but whether these methods lower incidence of TBDs is poorly understood. We conducted a randomized, replicated, fully crossed, placebo-controlled, masked experiment to test whether 2 environmentally safe interventions, the Tick Control System (TCS) and Met52 fungal spray, used separately or together, affected risk for and incidence of TBDs in humans and pets in 24 residential neighborhoods. All participating properties in a neighborhood received the same treatment. TCS was associated with fewer questing ticks and fewer ticks feeding on rodents. The interventions did not result in a significant difference in incidence of human TBDs but did significantly reduce incidence in pets. Our study is consistent with previous evidence suggesting that reducing tick abundance in residential areas might not reduce incidence of TBDs in humans.  相似文献   
98.
A novel Hendra virus variant, genotype 2, was recently discovered in a horse that died after acute illness and in Pteropus flying fox tissues in Australia. We detected the variant in flying fox urine, the pathway relevant for spillover, supporting an expanded geographic range of Hendra virus risk to horses and humans.  相似文献   
99.
There is limited research on the intake of non-nutritive sweeteners (NNS) among preschool-aged children. Canada’s Food Guide suggests limiting intake of NNS for all population groups and Health Canada recommends that young children (<2 years) avoid consuming beverages containing NNS. The aim of this study was to investigate the frequency and type of non-nutritive sweetener (NNS) intake in preschool-aged children participating in the Guelph Family Health Study pilots. Parents (n = 78 families) completed 3-day food records (n = 112 children; n = 55 females, n = 57 males; 3.6 years ± 1.3). Nineteen children (17%) reported consumption of foods or beverages containing NNS. Food sources with NNS included: freezies, oral nutritional supplements, flavored water, carbonated drinks, sugar free jam and protein powder. The majority of NNS contained in these foods were identified as stevia leaf extract, acesulfame K, sucralose, monk fruit extract and aspartame. Future research should continue to study NNS intake patterns longitudinally in children and examine the association of NNS intake with diet quality and health outcomes.  相似文献   
100.
Ciguatera poisoning is a global health concern caused by the consumption of seafood containing ciguatoxins (CTXs). Detection of CTXs poses significant analytical challenges due to their low abundance even in highly toxic fish, the diverse and in-part unclarified structures of many CTX congeners, and the lack of reference standards. Selective detection of CTXs requires methods such as liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS) or high-resolution MS (LC–HRMS). While HRMS data can provide greatly improved resolution, it is typically less sensitive than targeted LC–MS/MS and does not reliably comply with the FDA guidance level of 0.1 µg/kg CTXs in fish tissue that was established for Caribbean CTX-1 (C-CTX-1). In this study, we provide a new chemical derivatization approach employing a fast and simple one-pot derivatization with Girard’s reagent T (GRT) that tags the C-56-ketone intermediate of the two equilibrating C-56 epimers of C-CTX-1 with a quaternary ammonium moiety. This derivatization improved the LC–MS/MS and LC–HRMS responses to C-CTX-1 by approximately 40- and 17-fold on average, respectively. These improvements in sensitivity to the GRT-derivative of C-CTX-1 are attributable to: the improved ionization efficiency caused by insertion of a quaternary ammonium ion; the absence of adduct-ions and water-loss peaks for the GRT derivative in the mass spectrometer, and; the prevention of on-column epimerization (at C-56 of C-CTX-1) by GRT derivatization, leading to much better chromatographic peak shapes. This C-CTX-1–GRT derivatization strategy mitigates many of the shortcomings of current LC–MS analyses for C-CTX-1 by improving instrument sensitivity, while at the same time adding selectivity due to the reactivity of GRT with ketones and aldehydes.  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