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   14607篇
  免费   1033篇
  国内免费   22篇
耳鼻咽喉   94篇
儿科学   585篇
妇产科学   452篇
基础医学   2001篇
口腔科学   214篇
临床医学   2118篇
内科学   2652篇
皮肤病学   126篇
神经病学   1326篇
特种医学   303篇
外国民族医学   1篇
外科学   1444篇
综合类   187篇
一般理论   15篇
预防医学   1872篇
眼科学   146篇
药学   790篇
中国医学   14篇
肿瘤学   1322篇
  2024年   19篇
  2023年   107篇
  2022年   166篇
  2021年   358篇
  2020年   263篇
  2019年   419篇
  2018年   406篇
  2017年   327篇
  2016年   348篇
  2015年   346篇
  2014年   492篇
  2013年   779篇
  2012年   1152篇
  2011年   1208篇
  2010年   665篇
  2009年   608篇
  2008年   1024篇
  2007年   1031篇
  2006年   956篇
  2005年   937篇
  2004年   844篇
  2003年   725篇
  2002年   743篇
  2001年   159篇
  2000年   120篇
  1999年   129篇
  1998年   127篇
  1997年   114篇
  1996年   85篇
  1995年   107篇
  1994年   72篇
  1993年   72篇
  1992年   70篇
  1991年   65篇
  1990年   66篇
  1989年   68篇
  1988年   46篇
  1987年   54篇
  1986年   29篇
  1985年   27篇
  1984年   34篇
  1983年   35篇
  1982年   32篇
  1981年   29篇
  1980年   14篇
  1979年   16篇
  1978年   15篇
  1977年   16篇
  1974年   18篇
  1973年   16篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The 32-mile Detroit River and surrounding tributaries have been designated as a Great Lakes Area of Concern due to pollution from decades of municipal and industrial discharges, sewer overflows and urban development. Key pollutants in fish samples from the Detroit River include mercury, polychlorinated biphenyls (PCBs), dichlorodiphenyldichloroethylene (DDE), dioxins and furans. A biomonitoring study was conducted to assess exposures to these persistent toxic substances in Detroit urban shoreline anglers who may be at high exposure risk due to consumption of locally caught fish. Using a modified venue-based sampling approach, 287 adult shoreline anglers along the Detroit River were recruited and participated in the program. Study participants provided blood and urine specimens and completed a questionnaire following informed consent. We examined percentile estimates for total blood mercury, PCBs, DDE, and dioxin-like total toxic equivalency (TEQ) concentrations among study participants. Multiple linear regression was used to identify important predictors of contaminant concentrations. Participants consumed a median of 64 Detroit River caught fish meals in the past year. The Detroit urban anglers’ median total blood mercury concentrations was 3.2 times higher than that for the general adult U.S. population. PCB concentrations among the Detroit anglers aged 18–39 years were higher than the U.S. population of the same race/ethnicity. Elevated levels of DDE and total TEQ concentrations were not observed in the cohort. Eating more locally caught fish was associated with higher total blood mercury and serum PCB concentrations. The biomonitoring data served to inform public health officials and help guide environmental public health actions to reduce harmful exposures.  相似文献   
992.
OBJECTIVES: Clinicians are told to use the number needed to treat (NNT) to compare the benefits of therapeutic strategies, and researchers are asked to report results this way, generally without considering differences among the studies from which these were derived. METHODS: The crude NNT currently advocated is compared to the NNT standardized for a common outcome, follow-up time, study population and comparator. An NNT model for cardiovascular disease is described as an example that addresses differences among studies of secondary prevention of cardiovascular disease. Crude NNTs are compared to those obtained from the model. RESULTS: Follow-up in the 18 trials identified varied from 1.0 to 6.2 years; rates of cardiovascular events in the untreated subgroups ranged from 4.8% to 45.9%. The crude NNTs were more variable (9.1-163.7) than those obtained from the model (9.1-75.2). The effect of standardization was substantial in some cases, with proportional changes ranging from a 91% decrease to a 223% increase. CONCLUSION: Using an NNT model to account for differences in study design allows for more meaningful comparisons.  相似文献   
993.
BACKGROUND: The amount of dietary fat required for optimal bioavailability of carotenoids in plant matrices is not clearly defined. OBJECTIVE: The objective was to quantify the appearance of carotenoids in plasma chylomicrons after subjects ingested fresh vegetable salads with fat-free, reduced-fat, or full-fat salad dressings. DESIGN: The subjects (n = 7) each consumed 3 salads consisting of equivalent amounts of spinach, romaine lettuce, cherry tomatoes, and carrots with salad dressings containing 0, 6, or 28 g canola oil. The salads were consumed in random order separated by washout periods of > or =2 wk. Blood samples were collected hourly from 0 to 12 h. Chylomicrons were isolated by ultracentrifugation, and carotenoid absorption was analyzed by HPLC with coulometric array detection. RESULTS: After ingestion of the salads with fat-free salad dressing, the appearance of alpha-carotene, beta-carotene, and lycopene in chylomicrons was negligible. After ingestion of the salads with reduced-fat salad dressing, the appearance of the carotenoids in plasma chylomicrons increased relative to that after ingestion of the salads with fat-free salad dressing (P < 0.04). Similarly, the appearance of the carotenoids in plasma chylomicrons was higher after the ingestion of salads with full-fat than with reduced-fat salad dressing (P < 0.02). CONCLUSIONS: High-sensitivity HPLC with coulometric array detection enabled us to quantify the intestinal absorption of carotenoids ingested from a single vegetable salad. Essentially no absorption of carotenoids was observed when salads with fat-free salad dressing were consumed. A substantially greater absorption of carotenoids was observed when salads were consumed with full-fat than with reduced-fat salad dressing.  相似文献   
994.
Evidence about the total cost of health, absence, short-term disability, and productivity losses was synthesized for 10 health conditions. Cost estimates from a large medical/absence database were combined with findings from several published productivity surveys. Ranges of condition prevalence and associated absenteeism and presenteeism (on-the-job-productivity) losses were used to estimate condition-related costs. Based on average impairment and prevalence estimates, the overall economic burden of illness was highest for hypertension ($392 per eligible employee per year), heart disease ($368), depression and other mental illnesses ($348), and arthritis ($327). Presenteeism costs were higher than medical costs in most cases, and represented 18% to 60% of all costs for the 10 conditions. Caution is advised when interpreting any particular source of data, and the need for standardization in future research is noted.  相似文献   
995.
Dietary nitrites and nitrates, nitrosatable drugs, and neural tube defects   总被引:3,自引:0,他引:3  
BACKGROUND: Amine-containing (nitrosatable) drugs can react with nitrite to form N-nitroso compounds, some of which are teratogenic. Data are lacking on whether dietary intake of nitrates and nitrites modifies the association between maternal nitrosatable drug exposure and neural tube defects (NTDs) in offspring. METHODS: We examined nitrosatable drug exposure and NTD-affected pregnancies in relation to dietary nitrite and total nitrite intake in a case-control study of Mexican American women. We interviewed 184 women with NTD-affected pregnancies and 225 women with normal live births, including questions on periconceptional drug exposures and dietary intake. For 110 study participants, nitrate was also measured in the usual source of drinking water. RESULTS: Women who reported taking drugs classified as nitrosatable were 2.7 times more likely to have an NTD-affected pregnancy than women without this exposure (95% confidence interval [CI] = 1.4-5.3). The effect of nitrosatable drugs was observed only in women with higher intakes of dietary nitrite and total nitrite (dietary nitrite + 5% dietary nitrate). Women within the highest tertile (greater than 10.5 mg/day) of total nitrite were 7.5 times more likely to have an NTD-affected pregnancy if they took nitrosatable drugs (95% CI = 1.8-45.4). The association between nitrosatable drug exposure and NTDs was also stronger in women whose water nitrate levels were higher. CONCLUSIONS: Findings suggest that effects of nitrosatable drug exposure on risk for neural tube defects in offspring could depend on the amounts of dietary nitrite and total nitrite intake.  相似文献   
996.

Context

Despite their widespread use in medical school selection, there remains a lack of clarity on exactly what situational judgement tests (SJTs) measure.

Objectives

We aimed to develop an SJT that measures integrity by combining critical incident interviews (inductive approach) with an innovative deductive approach. The deductive approach guided the development of the SJT according to two established theoretical models, of which one was positively related to integrity (honesty–humility [HH]) and one was negatively related to integrity (cognitive distortions [CD]). The Integrity SJT covered desirable (HH‐based) and undesirable (CD‐based) response options. We examined the convergent and discriminant validity of the Integrity SJT and compared the validity of the HH‐based and CD‐based subscores.

Methods

The Integrity SJT was administered to 402 prospective applicants at a Dutch medical school. The Integrity SJT consisted of 57 scenarios, each followed by four response options, of which two represented HH facets and two represented CD categories. Three SJT scores were computed, including a total, an HH‐based and a CD‐based score. The validity of these scores was examined according to their relationships with external integrity‐related measures (convergent validity) and self‐efficacy (discriminant validity).

Results

The three SJT scores correlated significantly with all integrity‐related measures and not with self‐efficacy, indicating convergent and discriminant validity. In addition, the CD‐based SJT score correlated significantly more strongly than the HH‐based SJT score with two of the four integrity‐related measures.

Conclusions

An SJT that assesses the ability to correctly recognise CD‐based response options as inappropriate (i.e. what one should not do) seems to have stronger convergent validity than an SJT that assesses the ability to correctly recognise HH‐based response options as appropriate (i.e. what one should do). This finding might be explained by the larger consensus on what is considered inappropriate than on what is considered appropriate in a challenging situation. It may be promising to focus an SJT on the ability to recognise what one should not do.  相似文献   
997.
Introduction Obesity is a global problem that is challenging to prevent and expensive to treat. Early childhood interventions show promise in establishing lifelong healthy eating patterns, however a better understanding of how parental feeding practices develop is needed. The study aimed to investigate maternal perception of infant weight and its relationship to feeding practices and infant dietary intake. Methods A questionnaire was completed by 263 Queensland mothers of infants aged between 5 and 13 months. Logistic regression was used to describe the association between maternal feeding practices (restriction, pressure-to-eat, monitoring), parenting style (warmth, hostility), infant weight concern and infant dietary intake. Correlation and linear regression were used to identify relationships between maternal feeding practices, parenting style, infant weight concern and infant weight. Results Mothers were found to be more concerned about underweight than overweight, misjudge infants as being underweight and failed to recognise overweight infants. Underweight concern was associated with infant weight (r?=??0.27, p?<?0.01), early introduction of solids (OR 0.24, CI 0.11–0.51) and pressure-to-eat (r?=?0.19, p?<?0.01). Pressure-to-eat was associated to maternal perception of infant weight (r?=???0.21, p?<?0.01), infant weight (r?=???0.17, p?<?0.05) and lower fruit and vegetable intake (OR 0.50, CI 0.27–0.92). Restrictive feeding practices were correlated to overweight concern (r?=?0.08, p?<?0.05). Discussion Maternal infant weight perception and concerns are related to control feeding practices which can be detrimental to infant dietary intake. Inability to recognise healthy weight may ignite these concerns or fail to address infant feeding risk factors. Discussing healthy growth should be a fundamental component of strategies to support healthy infant feeding and eating.  相似文献   
998.
999.

Background

Diet and obesity influence prostate cancer risk and progression–effects that may be mediated through the gut microbiome.

Objective

Our aim was to explore relationships among diet, gut microbes, and Gleason sum in overweight and obese prostate cancer patients enrolled in a presurgical weight-loss trial.

Design

Randomized controlled trial (NCT01886677) secondary analysis.

Participants/setting

In 2013-2014, 40 prostate cancer patients in the southeastern United States were randomized and allocated equally to weight-loss and wait-list control arms while they awaited prostatectomy; stool samples were collected on a subset of 22 patients.

Intervention

Registered dietitian nutritionists and exercise physiologists provided semi-weekly in-person and telephone-based guidance on calorie-restricted diets and exercise to promote an approximate weight loss of 0.91 kg/wk.

Main outcome measures

Baseline and follow-up 24-hour dietary recalls were conducted and analyzed (using the Automated Self-Administered 24-hour dietary recall system; National Cancer Institute, Bethesda, MD) for macronutrients, micronutrients, and food groups. Microbiome analysis targeting the V4 region of the 16S ribosomal RNA gene was performed on fecal samples. Biopsy Gleason sum data were accessed from diagnostic pathology reports.

Statistical analyses performed

Associations between dietary factors and operational taxonomic units were determined by β-diversity analysis. Wilcoxon signed rank, and Mann-Whitney U testing assessed within- and between-arm differences. Associations between Gleason sum and operational taxonomic units, and diet and operational taxonomic units, were analyzed using Spearman correlations.

Results

At baseline, Proteobacteria (median 0.06, interquartile range 0.01 to 0.16) were abundant, with four orders positively associated with Gleason sum. Gleason sum was associated with Clostridium (ρ=.579; P=0.005) and Blautia (ρ=?0.425, P=0.049). Increased red meat consumption from baseline was associated with Prevotella (ρ=?.497; P=0.018) and Blautia (ρ=.422; P=0.039). Men who increased poultry intake had decreased Clostridiales abundance (P=0.009).

Conclusions

This hypothesis-generating study provides a starting point for investigating the relationships between the fecal microbiome, diet, and prostate cancer. Adequately powered studies are required to further explore and validate these findings.  相似文献   
1000.
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