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   3282篇
  免费   240篇
  2023年   15篇
  2022年   23篇
  2021年   76篇
  2020年   45篇
  2019年   50篇
  2018年   68篇
  2017年   64篇
  2016年   100篇
  2015年   190篇
  2014年   186篇
  2013年   233篇
  2012年   321篇
  2011年   338篇
  2010年   194篇
  2009年   172篇
  2008年   188篇
  2007年   157篇
  2006年   123篇
  2005年   136篇
  2004年   158篇
  2003年   119篇
  2002年   97篇
  2001年   26篇
  2000年   18篇
  1999年   19篇
  1998年   32篇
  1997年   26篇
  1996年   20篇
  1995年   18篇
  1994年   11篇
  1993年   25篇
  1992年   11篇
  1991年   14篇
  1990年   9篇
  1989年   12篇
  1988年   13篇
  1987年   8篇
  1986年   11篇
  1985年   10篇
  1984年   17篇
  1983年   11篇
  1982年   18篇
  1981年   13篇
  1979年   10篇
  1978年   9篇
  1977年   11篇
  1976年   9篇
  1975年   10篇
  1973年   12篇
  1972年   11篇
排序方式: 共有3522条查询结果,搜索用时 109 毫秒
91.
Chromosomal abnormalities are seen in nearly 1% of live born infants. We report a 5-year-old boy with the clinical features of Down syndrome, which is the most common human aneuploidy. Cytogenetic analysis showed a mosaicism for a double aneuploidy, Down syndrome and XYY. The karyotype was 47, XY,+21[19]/48, XYY,+21[6]. ish XYY (DXZ1 × 1, DYZ1 × 2). Mosaic double aneuploidies are very rare and features of only one of the aneuploidies may predominate in childhood. Cytogenetic analysis is recommended even if the typical features of a recognized aneuploidy are present so that any associated abnormality may be detected. This will enable early intervention to provide the adequate supportive care and management.  相似文献   
92.
The orexigenic peptide ghrelin and the anorexigenic peptide nesfatin-1 are expressed by the same endocrine cell of the rat stomach, the X/A-like cell. However, data in humans are lacking, especially under conditions of obesity. We collected gastric tissue of obese patients undergoing sleeve gastrectomy and investigated the expression of nesfatin-1 and ghrelin in the gastric oxyntic mucosa by immunofluorescence. Nesfatin-1 immunoreactivity was detected in the human oxyntic mucosa in cells with an endocrine phenotype. A major portion of nesfatin-1 immunoreactive cells (78 %) co-localized with ghrelin indicating the occurrence in human X/A-like cells. In patients with very high body mass index (BMI 55–65 kg/m2), the number of nesfatin-1 immunoreactive cells/low-power field was significantly higher than in obese patients with lower BMI (40–50 kg/m2, 118 ± 10 vs. 82 ± 11, p < 0.05). On the other hand, the number of ghrelin immunoreactive cells was significantly reduced in obese patients with higher compared to lower BMI (96 ± 12 vs. 204 ± 21, p < 0.01). Also the ghrelin-acylating enzyme ghrelin-O-acyltransferase decreased with increasing BMI. In conclusion, nesfatin-1 immunoreactivity is also co-localized with ghrelin in human gastric X/A-like cells giving rise to a dual role of this cell type with differential effects on stimulation and inhibition of appetite dependent on the peptide released. The expression of these two peptides is differentially regulated under obese conditions with an increase of nesfatin-1 and a decrease of ghrelin immunoreactivity with rising BMI pointing towards an adaptive change of expression that may counteract further body weight increase.  相似文献   
93.
We present a comparison of feather stable isotope (δ13C, δ15N) patterns representing the habitat and diet conditions for two subspecies of willow warblers Phylloscopus trochilus that breed in parapatry, but winter in different regions of sub‐Saharan Africa. Previous analyses have shown that on average winter moulted innermost primaries (P1) show subspecific differences in δ15N values, although individuals show substantial variation for both δ13C and δ15N within the subspecies. We examined whether corresponding variation in the timing of the winter moult, as reflected by consistent intra‐wing correlations for individual's δ13C and δ15N values, could explain some of the previously observed isotopic variation. Further, differential subspecific adaptations to winter precipitation patterns across Africa might result in a variable degree of site fidelity or itinerancy during moult. We found no consistent trend in isotopic values from innermost to outermost primaries, thus inter‐individual variation in the timing of moult does not explain the subspecific isotopic variation for P1. Patterns in wing feather δ13C and δ15N values indicated that 41% of the individuals from both subspecies shifted their diet or habitats during winter moult. Importantly, despite well‐documented itinerancy in willow warblers during the winter, 59% of the individuals had feather isotope values consistent with stable use of habitats or diets during winter moult. Repeatability analyses suggest that individuals of both subspecies initiate moult in similar habitats from year‐to‐year while feeding on isotopically similar diets.  相似文献   
94.
Evaluation of rhythmic fluctuations of physical and mental variables should be of special significance for the understanding of students' performance and setting the schedules of school activities. The present study investigated the pattern of diurnal variation in oral temperature, sleepiness and performance of a group of adolescents undergoing a daytime school schedule. Eighteen girls (mean age 16 years-old), who attended the same class from 0715h to 1645h, were tested on seven days. They measured their oral temperature, quantified their sleepiness level by means of a visual analogue scale, and completed the following tests: letter cancellation test, addition test, and a simple motor task. One-way ANOVA statistics for repeated measures was used in order to verify the effect of test time on oral temperature, sleepiness and performance. Possible correlations between the level of sleepiness and performance were investigated by means of Spearman rank correlation. The results revealed significant time of day effect on all variables, except for the number of addition errors. Oral temperature values showed an increase from morning to afternoon. Letter cancellation, motor task and addition scores increased from early morning to late afternoon, showing rapid fluctuations throughout the day. Sleepiness level was negatively correlated with letter cancellation scores during the first three tests of the day. In agreement with other work, the diurnal variation of oral temperature, letter cancellation and addition test showed an improvement as the day progressed. Sleepiness, on the other hand, decreased throughout the day, with the highest level associated with the first test of the day, suggesting a circadian pattern of variation rather than a cumulative effect due to school activities.  相似文献   
95.

Objectives

To investigate the associations of environmental MS risk factors with clinical and MRI measures of progression in high-risk clinically isolated syndromes (CIS) after the first demyelinating event.

Methods

We analyzed 211 CIS patients (age: 28.9±7.8 years) enrolled in the SET study, a multi-center study of high-risk CIS patients. Pre-treatment samples were analyzed for IgG antibodies against cytomegalovirus (anti-CMV), Epstein Barr virus (EBV) early nuclear antigen-1 (EBNA-1), viral capsid antigen (VCA), early antigen-diffuse (EA-D), 25 hydroxy-vitamin D3 and cotinine levels and HLA DRB1*1501 status. The inclusion criteria required evaluation within 4 months of the initial demyelinating event, 2 or more brain MRI lesions and the presence of two or more oligoclonal bands in cerebrospinal fluid. All patients were treated with interferon-beta. Clinical and MRI assessments were obtained at baseline, 6, 12, and 24 months.

Results

The time to first relapse decreased and the number of relapses increased with anti-CMV IgG positivity. Smoking was associated with increased number and volume of contrast-enhancing lesions (CEL) during the 2-year period. The cumulative number of CEL and T2 lesions during the 2-year period was greater for individuals in the highest quartile of anti-EBV VCA IgG antibodies. The percent loss of brain volume was increased for those in the highest quartile of with anti-EBV VCA IgG antibodies.

Conclusions

Relapses in CIS patients were associated with CMV positivity whereas anti-EBV VCA positivity was associated with progression on MRI measures, including accumulation of CEL and T2 lesions and development of brain atrophy.  相似文献   
96.

Background

In patients who remain virologically suppressed in plasma with triple-drug ART a switch to protease inhibitor monotherapy maintains high rates of suppression; however it is unknown if protease inhibitor monotherapy is associated to a higher rate of neurocognitive impairment.

Methods

In this observational, cross-sectional study we included patients with plasma virological suppression (≥1 year) without concomitant major neurocognitive confounders, currently receiving for ≥1 year boosted lopinavir or darunavir as monotherapy or as triple ART. Neurocognitive impairment was defined as per the 2007 consensus of the American Association of Neurology. The association between neurocognitive impairment and protease inhibitor monotherapy, adjusted by significant confounders, was analysed.

Results

Of the 191 included patients - triple therapy: 96, 1–2 years of monotherapy: 40 and >2 years of monotherapy: 55 - proportions (95% CI) with neurocognitive impairment were: overall, 27.2% (20.9–33.6); triple therapy, 31.6% (22.1–41.0); short-term monotherapy, 25.0% (11.3–38.7); long-term monotherapy: 21.4% (10.5–32.3); p = 0.38. In all groups, neurocognitive impairment was mildly symptomatic or asymptomatic by self-report. There were not significant differences in Global Deficit Score by group. In the regression model confounding variables for neurocognitive impairment were years on ART, ethnicity, years of education, transmission category and the HOMA index. Adjusted by these variables the Odds Ratio (95% CI) for neurocognitive impairment of patients receiving short-term monotherapy was 0.85 (0.29–2.50) and for long-term monotherapy 0.40 (0.14–1.15).

Conclusions

Compared to triple drug antiretroviral therapy, monotherapy with lopinavir/ritonavir or darunavir/ritonavir in patients with adequate plasma suppression was not associated with a higher rate of asymptomatic neurocognitive impairment than triple drug ART.  相似文献   
97.
98.
99.
100.
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