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   2308篇
  免费   106篇
  国内免费   14篇
耳鼻咽喉   29篇
儿科学   63篇
妇产科学   20篇
基础医学   261篇
口腔科学   98篇
临床医学   208篇
内科学   359篇
皮肤病学   20篇
神经病学   222篇
特种医学   130篇
外科学   373篇
综合类   3篇
一般理论   6篇
预防医学   188篇
眼科学   136篇
药学   218篇
肿瘤学   94篇
  2023年   5篇
  2022年   16篇
  2021年   18篇
  2020年   25篇
  2019年   32篇
  2018年   30篇
  2017年   38篇
  2016年   46篇
  2015年   41篇
  2014年   64篇
  2013年   103篇
  2012年   117篇
  2011年   135篇
  2010年   85篇
  2009年   86篇
  2008年   163篇
  2007年   137篇
  2006年   167篇
  2005年   168篇
  2004年   162篇
  2003年   126篇
  2002年   138篇
  2001年   43篇
  2000年   22篇
  1999年   32篇
  1998年   39篇
  1997年   30篇
  1996年   22篇
  1995年   30篇
  1994年   27篇
  1993年   15篇
  1992年   14篇
  1991年   18篇
  1990年   11篇
  1989年   18篇
  1988年   12篇
  1987年   15篇
  1986年   16篇
  1985年   27篇
  1984年   21篇
  1983年   22篇
  1982年   15篇
  1981年   23篇
  1980年   10篇
  1979年   9篇
  1978年   6篇
  1977年   6篇
  1976年   4篇
  1972年   5篇
  1967年   3篇
排序方式: 共有2428条查询结果,搜索用时 15 毫秒
71.
It is a common practice in Northern countries that children aged about 2 weeks to 2 years take their daytime sleep outdoors in prams in winter. The aim was to evaluate the thermal insulation of clothing of infants sleeping outdoors in winter. Clothing data of infants aged 3.5 months was collected, and sleep duration, skin and microclimate temperatures, humidity inside middle wear, air temperature and velocity of the outdoor environment were recorded during sleep taken outdoors (n = 34) and indoors (n = 33) in families’ homes. The insulation of clothing ensembles was measured by using a baby-size thermal manikin, and the values were used for defining clothing insulation of the observed infants. Required clothing insulation for each condition was estimated according to ISO 11079. Clothing insulation did not correlate with ambient air temperature. The observed and required insulation of the study group was equal at about −5°C, but overdressing existed in warmer and deficiency in thermal insulation in colder temperatures (r s 0.739, p < 0.001). However, even at −5°C a slow cooling (ca. 0.012°C/min) of mean skin temperature (T sk) was observed. When the difference between observed and required insulation increased, the cooling rate of T sk increased linearly (r s 0.605, p < 0.001) and the infants slept for a shorter period (r s 0.524, p = 0.001). The results of this study show the difficulty of adjusting systematically the optimal thermal insulation for outdoor sleeping infants during northern winter. Therefore, the necessity for guidelines is obvious. The study provides information for adequate cold protection of infants sleeping in cold conditions.  相似文献   
72.

Background  

In a previous study we observed an increasing trend in candidemia in Finland in the 1990s. Our aim was now to investigate further population-based secular trends, as well as outcome, and evaluate the association of fluconazole consumption and prophylaxis policy with the observed findings.  相似文献   
73.
74.

Background

Self-rated health is an independent predictor of mortality. However, general health checks in populations unselected for disease or risk factors have not been shown to reduce mortality or morbidity.

Aim

To describe new comorbidities and cardiovascular risk factors in apparently healthy people and to relate this to their self-rated health.

Design and setting

A targeted screening programme identified 462 middle-aged people with cardiovascular risk factors without previously diagnosed chronic disease in a Finnish community in 2005–2006.

Method

Home blood pressure monitoring, oral glucose tolerance test, estimated glomerular filtration rate, and ankle brachial index were used to detect previously undiagnosed conditions. The Short-Form Health Survey and Beck’s Depression Inventory were completed by participants before the diagnostic tests were performed.

Results

The prevalence of previously undiagnosed disease was: hypertension 113/462 (24% [95% confidence interval {CI} = 21% to 29%]), diabetes 19/462 (4% [95% CI = 2% to 6%]), renal insufficiency 23/462 (5% [95% CI = 3% to 7%]), and peripheral arterial disease 17/462 (4% [95% CI = 2% to 5%]). Of the 139 participants who regarded their health as ‘fair–poor’, 60 (43%) had a previously undetected condition affecting their vasculature.

Conclusion

Out of the screen-detected apparently healthy cardiovascular risk subjects, one in three had undiagnosed hypertension, diabetes, peripheral arterial disease, or renal insufficiency. Those individuals experiencing ill health tended to be at high risk of cardiovascular problems.  相似文献   
75.
Blood O2 carrying capacity affects aerobic capacity (VO2max). Patients with type 1 diabetes have a risk for anaemia along with renal impairment, and they often have low VO2max. We investigated whether total haemoglobin mass (tHb-mass) and blood volume (BV) differ in men with type 1 diabetes (T1D, n = 12) presently without complications and in healthy men (CON, n = 23) (age-, anthropometry-, physical activity-matched), to seek an explanation for low VO2max. We determined tHb-mass, BV, haemoglobin concentration ([Hb]), and VO2max in T1D and CON. With similar (mean ± SD) [Hb] (144 vs. 145 g l?1), T1D had lower tHb-mass (10.1 ± 1.4 vs. 11.0 ± 1.1 g kg?1, P < 0.05), BV (76.8 ± 9.5 vs. 83.5 ± 8.3 ml kg?1, P < 0.05) and VO2max (35.4 ± 4.8 vs. 44.9 ± 7.5 ml kg?1 min?1, P < 0.001) than CON. VO2max correlated with tHb-mass and BV both in T1D (r = 0.71, P < 0.01 and 0.67, P < 0.05, respectively) and CON (r = 0.54, P < 0.01 and 0.66, P < 0.001, respectively), but not with [Hb]. Linear regression slopes were shallower in T1D than CON both between VO2max and tHb-mass (2.4 and 3.6 ml kg?1 min?1 vs. g kg?1, respectively) and VO2max and BV (0.3 and 0.6 ml kg?1 min?1 vs. g kg?1, respectively), indicating that T1D were unable to reach similar VO2max than CON at a given tHb-mass and BV. In conclusion, low tHb-mass and BV partly explained low VO2max in T1D and may provide early and more sensitive markers of blood O2 carrying capacity than [Hb] alone.  相似文献   
76.
To compare different MRI sequences for the detection of lesions and the evaluation of response to chemotherapy in patients with diffuse large B‐cell lymphoma (DLBCL), 18 patients with histology‐confirmed DLBCL underwent 3‐T MRI scanning prior to and 1 week after chemotherapy. The MRI sequences included T1‐weighted pre‐ and post‐contrast, T2‐weighted with and without fat suppression, and a single‐shot echo‐planar diffusion‐weighted imaging (DWI) with two b values (0 and 800 s/mm2). Conventional MRI sequence comparisons were performed using the contrast ratio between tumor and normal vertebral body instead of signal intensity. The apparent diffusion coefficient (ADC) of the tumor was measured directly on the parametric ADC map. The tumor volume was used as a reference for the evaluation of chemotherapy response. The mean tumor volume was 374 mL at baseline, and decreased by 65% 1 week after chemotherapy (p < 0.01). The T2‐weighted image with fat suppression showed a significantly higher contrast ratio compared with images from all other conventional MRI sequences, both before and after treatment (p < 0.01, respectively). The contrast ratio of the T2‐weighted image with fat suppression decreased significantly (p < 0.01), and that of the T1‐weighted pre‐contrast image increased significantly (p < 0.01), after treatment. However, there was no correlation between the change in contrast ratio and tumor volume. The mean ADC value was 0.68 × 10–3 mm2/s at baseline; it increased by 89% after chemotherapy (p < 0.001), and the change in ADC value correlated with the change in tumor volume (r = 0.66, p < 0.01). The baseline ADC value also correlated inversely with the percentage change in ADC after treatment (r = ?0.62, p < 0.01). In conclusion, this study indicates that T2‐weighted imaging with fat suppression is the best conventional sequence for the detection of lesions and evaluation of the efficacy of chemotherapy in DLBCL. DWI with ADC mapping is an imaging modality with both diagnostic and prognostic value that could complement conventional MRI. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
77.
The Arctic mutation (APP E693G) is unique, since it is located within the amyloid-beta (Abeta) sequence and leads to Alzheimer's disease (AD). Arctic Abeta peptides more easily form Abeta protofibrils in vitro, but little is known about the pathogenic mechanism of the Arctic mutation in vivo. Here, we analyzed APP transgenic mice with both the Swedish and Arctic mutations (tg-APPArcSwe) and transgenic mice with the Swedish mutation alone (tg-APPSwe). Intense intraneuronal Abeta-immunoreactive staining was present in young tg-APPArcSwe mice, but not in tg-APPSwe mice. Intracellular Abeta aggregates in tg-APPArcSwe were strongly stained by antibodies recognizing the N-terminus of Abeta, while those recognizing the C-terminus of Abeta stained weakly. The Abeta aggregates inside neurons increased with age and predated extracellular Abeta deposition in both tg-APPArcSwe and tg-APPSwe mice. Senile plaque deposition was markedly accelerated in tg-APPArcSwe mice, as compared to tg-APPSwe mice. We conclude that the Arctic mutation causes AD by facilitating amyloidosis through early accumulation of intracellular Abeta aggregates in association with a rapid onset of senile plaque deposition.  相似文献   
78.
Objectives: Our aim was to describe the occurrence of dental fear among Finnish children of different ages and to ascertain how oral health and family characteristics are associated with dental fear. Methods: The subject groups were aged 3, 6, 9, 12, and 15 years in two middle‐sized cities, and the 1474 participants were distributed over fairly equal samples of each age. A questionnaire given to each child to be filled out at home enquired about social background, oral hygiene habits, diet, and dental fear. Oral health status was examined clinically and radiographically by two calibrated dentists. Multiple logistic regression analyses were performed for each age group in order to study the associations between dental fear and selected factors. Results: Dental fear was higher among 12‐ and 15‐year‐old children than among the younger ones. Pain, drilling, and local anesthesia were reported to be the most frightening aspects. Excluding the 12‐year‐olds, children whose family members reported dental fear were more likely to report dental fear than children whose family members did not report dental fear. Six‐ and 12‐year‐olds who had experienced caries were more likely to report dental fear than were caries‐free children. Among 6‐year‐olds, father's education modified the effect of a child's caries experience on child dental fear. Frequent intake of sugary items and a limit on eating candies to only one day per week were associated with higher dental fear. Conclusions: Fear of dental treatment is still fairly common among Finnish children, and the factors associated with it differ with the age of the child.  相似文献   
79.
Short-term fluctuations in systolic blood pressure (SBP) and heart rate (HR) and their inter-relationship were analysed in a group of normotensive middle-aged men (n = 16) using a multivariate autoregressive modelling technique. This study is the first to evaluate the beat-to-beat variability of SBP and HR in a group of real normotensive subjects. Direct intra-arterial blood pressure was registered together with ECG using an ambulatory tape recording technique (the Oxford method). Power spectrum density estimated (PSD) were used as a measure of the variability. PSDs were calculated over 3-min periods for four basic physiological conditions: during sleep and in the supine, sitting and standing positions. The inter-relationship between the blood pressure and heart rate variabilities was analysed using a closed-loop model. In agreement with results presented earlier in the literature, the beat-to-beat variation in SBP and HR was concentrated in three typical power spectrum regions: the high-frequency (HF = 0.15-0.35 Hz) region (respiration), the mid-frequency (MF = 0.075-0.15 Hz) region (vasomotor oscillation) and the low-frequency (LF = 0.02-0.075 Hz) region (thermoregulation). The variability changes considerably between different situations, especially that of the MF region. The variability was most prominent in the MF region and in the standing position. The variability was generally smallest in the HF region and in sleep. The results also demonstrate that the beat-to-beat variability in SBP and HR can considerably affect one another.  相似文献   
80.
The modulatory role of protein kinase C (PK-C)- and Gi-protein-mediated signal transduction systems was studied in the cyclic variation of follicle-stimulating hormone (FSH)-stimulated cAMP production of rat seminiferous tubules. FSH (Metrodin, Serono, 30 mg/1) stimulated cAMP production 10-fold (p < 0.01) in a 3 h incubation of 5 mm segments of seminiferous tubules of stages II–VI of the epithelial cycle, but only 2-fold (p < 0.01) in stages VII–VIII. The PK-C activator 12-O-tetradecanoylphorbol 13-acetate (TPA, 100 nmol/1) suppressed the FSH effect on cAMP output by 50–70% (p < 0.01) in stages II–VI, but had no effect in stages VII–VIII. If the tubular segments were preincubated for 3 h in the presence of pertussis toxin (PT, 100 μg/1), the FSH-stimulated cAMP production of stages VII-VIII increased by 100–200% (p < 0.01), and now they also became responsive to the TPA suppression. Conversely, no effect of PT was observed in stages II–VI. Cholera toxin (CT, 100 μg/1) and forskolin (Fk, 100 μmol/1) nearly similarly stimulated the cAMP production in both stages studied (about 10-fold, p < 0.01), and TPA and PT potentiated the effects in a non-additive fashion. In conclusion, both Gi-protein and PK-C-mediated mechanisms modulate cAMP production of rat seminiferous tubules. A clear cyclic variation can only be demonstrated in FSH-stimulated cAMP production, but not if the Gs-protein or adenylate cyclase are directly stimulated. Upon FSH stimulation, the low cAMP production in stages VII–VIII is mainly due to the Gi-protein-mediated inhibition. In contrast, the absence (or non-function) of this inhibition mechanism explains the brisk cAMP response to FSH in stages II–VI. PK-C activation suppresses FSH-stimulated cAMP production only if it is not inhibited by the Gi-protein-mediated mechanism (stages II–VI), probably by inhibiting the FSH-receptor-Gs-protein association. It also increases CT and Fk-stimulated cAMP production, in this case inactivating the Gi-protein.  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