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   1643篇
  免费   169篇
  2023年   9篇
  2022年   24篇
  2021年   30篇
  2020年   21篇
  2019年   22篇
  2018年   33篇
  2017年   25篇
  2016年   45篇
  2015年   78篇
  2014年   80篇
  2013年   110篇
  2012年   133篇
  2011年   122篇
  2010年   71篇
  2009年   85篇
  2008年   116篇
  2007年   93篇
  2006年   115篇
  2005年   95篇
  2004年   96篇
  2003年   114篇
  2002年   87篇
  2001年   19篇
  2000年   16篇
  1999年   27篇
  1998年   17篇
  1997年   11篇
  1996年   7篇
  1995年   8篇
  1994年   9篇
  1993年   7篇
  1992年   3篇
  1991年   6篇
  1990年   7篇
  1989年   3篇
  1988年   3篇
  1986年   5篇
  1985年   6篇
  1984年   5篇
  1980年   3篇
  1979年   3篇
  1978年   4篇
  1972年   2篇
  1971年   7篇
  1968年   3篇
  1967年   2篇
  1966年   2篇
  1963年   2篇
  1962年   2篇
  1959年   2篇
排序方式: 共有1812条查询结果,搜索用时 15 毫秒
891.
892.

Background

Intake of monounsaturated fatty acids has been reported to reduce oxidative stress, insulin resistance and related inflammatory processes and may thus protect from skin photoaging. The objective of this study was to investigate the association between the risk of photoaging, monounsaturated fatty acids intake and the sources of monounsaturated fatty acids.

Methodology/Principal Findings

A cross sectional study was conducted within the framework of the SUVIMAX cohort. The survey included 1264 women and 1655 men aged between 45 and 60 years old. Dietary monounsaturated fatty acids intakes were estimated by dietary source through at least ten 24-h diet records completed during the first 2.5 years of the follow-up period. Severity of facial skin photoaging was graded by trained investigators at baseline during a clinical examination using a 6-grade scale illustrated by photographs. A lower risk of severe photoaging was associated with higher intakes of monounsaturated fatty acids from olive oil in both sexes. Strikingly, no association was found with intake of monounsaturated fatty acids from animal sources whether from dairy products, meat or processed meat.

Conclusion/Significance

These findings support the beneficial effect of dietary olive oil or healthy diet habits associated with olive oil consumption on the severity of facial photoaging.  相似文献   
893.
Epidermodysplasia verruciformis (EV) is characterized by persistent cutaneous lesions caused by a specific group of related human papillomavirus genotypes (EV-HPVs) in otherwise healthy individuals. Autosomal recessive (AR) EVER1 and EVER2 deficiencies account for two thirds of known cases of EV. AR RHOH deficiency has recently been described in two siblings with EV-HPV infections as well as other infectious and tumoral manifestations. We report here the whole-exome based discovery of AR MST1 deficiency in a 19-year-old patient with a T-cell deficiency associated with EV-HPV, bacterial and fungal infections. MST1 deficiency has recently been described in seven patients from three unrelated kindreds with profound T-cell deficiency and various viral and bacterial infections. The patient was also homozygous for a rare ERCC3 variation. Our findings broaden the clinical range of infections seen in MST1 deficiency and provide a new genetic etiology of susceptibility to EV-HPV infections. Together with the recent discovery of RHOH deficiency, they suggest that T cells are involved in the control of EV-HPVs, at least in some individuals.  相似文献   
894.
895.
Subcutaneous fat tissues from an indigenous fat-type breed and an intensively-lean selected breed were studied in juvenile pigs. Combining DIGE with bioinformatics and target analyses of key genes, enzymes or terminal routes, this study identifies metabolic and homeostatic processes, response to organic substances, and acute-phase responses as the main pathways whose proteins were regulated in association with adiposity. Breed-related differences in abundance and activities of malic enzyme and glucose-6-phosphate dehydrogenase NADPH-supplying enzymes suggested up-regulation of the lipogenic pathway to dispose for a greater adiposity. Over-abundance in the lipolytic protein carboxylesterase-1 was revealed in fat-type piglets. A panel of pro- and anti-inflammatory proteins such as serpins, had an altered abundance in the fat-type piglets, suggesting adverse consequences of fat accumulation even in early post-weaning stages. Propensity to low-grade inflammation in fat pigs was reinforced by the up-regulation of genes encoding pro-inflammatory cytokines IL6 and TNF-α in these piglets. Differential abundance in annexin-A5 and pericentrin suggested a positive regulation of cell apoptosis in lean piglets. Our results are relevant in the context of data linking the accretion of body lipids to the physiology and pathology of adipose tissue in models other than rodents for a better control of human health and nutrition.  相似文献   
896.
897.

Background:

Increases in life expectancy make it important to remain healthy for as long as possible. Our objective was to examine the extent to which healthy behaviours in midlife, separately and in combination, predict successful aging.

Methods:

We used a prospective cohort design involving 5100 men and women aged 42–63 years. Participants were free of cancer, coronary artery disease and stroke when their health behaviours were assessed in 1991–1994 as part of the Whitehall II study. We defined healthy behaviours as never smoking, moderate alcohol consumption, physical activity (≥ 2.5 h/wk moderate physical activity or ≥ 1 h/wk vigorous physical activity), and eating fruits and vegetables daily. We defined successful aging, measured over a median 16.3-year follow-up, as good cognitive, physical, respiratory and cardiovascular functioning, in addition to the absence of disability, mental health problems and chronic disease (coronary artery disease, stroke, cancer and diabetes).

Results:

At the end of follow-up, 549 participants had died and 953 qualified as aging successfully. Compared with participants who engaged in no healthy behaviours, participants engaging in all 4 healthy behaviours had 3.3 times greater odds of successful aging (95% confidence interval [CI] 2.1–5.1). The association with successful aging was linear, with the odds ratio (OR) per increment of healthy behaviour being 1.3 (95% CI 1.2–1.4; population-attributable risk for 1–4 v. 0 healthy behaviours 47%). When missing data were considered in the analysis, the results were similar to those of our main analysis.

Interpretation:

Although individual healthy behaviours are moderately associated with successful aging, their combined impact is substantial. We did not investigate the mechanisms underlying these associations, but we saw clear evidence of the importance of healthy behaviours for successful aging.Increases in life expectancy make remaining free of disease and in good functional health for as long as possible an important objective for the present and future generations.1 Most research in this domain has focused on risk factors for single health outcomes, such as mortality, chronic diseases or functioning. However, good health at older ages is a multidimensional concept, having been defined variously with reference to absence of disease and good functional status.25 There is considerable research on disability outcomes at older ages,2,68 but less attention has been paid to successful aging combining favourable functioning outcomes with good mental health and the absence of chronic diseases and disability.913Smoking, alcohol consumption, poor diet and physical inactivity are among the top 10 leading risk factors for death and disability in intermediate- and high-income countries.14 There is increasing interest in the combined effect of these behaviours on health. Studies show that people who engage in multiple unhealthy behaviours have a higher risk of death,1523 chronic disease2430 and poor cognitive function than people who do not engage in as many unhealthy behaviours.31 However, whether healthy behaviours determine good functional status at older ages, combined with the absence of chronic diseases, remains unknown.Our objective was to examine the extent to which individual and combined healthy behaviours in midlife predict successful aging about 16 years later, at 60 years of age or older. We used a comprehensive definition of successful aging that included having good mental health, having good cognitive, physical and cardiorespiratory function, and being free of disability and chronic disease (coronary artery disease, stroke, diabetes and cancer).  相似文献   
898.
Quantifying the vocal repertoire of a species is critical for subsequent analysis of signal functionality, geographic variation, and social relevance. However, the vocalizations of free‐ranging common dolphins (Delphinus sp.) have not previously been described from New Zealand waters. We present the first quantitative analysis of whistle characteristics to be undertaken on the New Zealand population. Acoustic data were collected in the Hauraki Gulf, North Island from 28 independent dolphin group encounters. A total of 11,715 whistles were collected from 105.1 min of recordings. Seven whistle contours were identified containing 29 subtypes. Vocalizations spanned from 3.2 to 23 kHz, with most whistles occurring between 11 and 13 kHz. Whistle duration ranged from 0.01 to 4.00 s (mean ± SD; 0.27 ± 0.32). Of the 2,663 whistles analyzed, 82% have previously been identified within U.K. populations. An additional six contours, apparently unique to New Zealand Delphinus were also identified. Data presented here offer a first insight into the whistle characteristics of New Zealand Delphinus. Comparisons with previously studied populations reveal marked differences in the whistle frequency and modulation of the New Zealand population. Interpopulation differences suggest behavior and the local environment likely play a role in shaping the vocal repertoire of this species.  相似文献   
899.
Species of filamentous brown algae in the family Ectocarpaceae are significant members of fouling communities. However, there are few systematic studies on the influence of surface physico-chemical properties on their adhesion. In the present paper the development of a novel, laboratory-based adhesion bioassay for ectocarpoid algae, at an appropriate scale for the screening of sets of experimental samples in well-replicated and controlled experiments is described. The assays are based on the colonization of surfaces from a starting inoculum consisting of multicellular filaments obtained by blending the cultured alga Ectocarpus crouaniorum. The adhesion strength of the biomass after 14 days growth was assessed by applying a hydrodynamic shear stress. Results from adhesion tests on a set of standard surfaces showed that E. crouaniorum adhered more weakly to the amphiphilic Intersleek? 900 than to the more hydrophobic Intersleek? 700 and Silastic? T2 coatings. Adhesion to hydrophilic glass was also weak. Similar results were obtained for other cultivated species of Ectocarpus but differed from those obtained with the related ectocarpoid species Hincksia secunda. The response of the ectocarpoid algae to the surfaces was also compared to that for the green alga, Ulva.  相似文献   
900.
Phyllotaxis, the regular arrangement of leaves and flowers around the stem, is a key feature of plant architecture. Current models propose that the spatiotemporal regulation of organ initiation is controlled by a positive feedback loop between the plant hormone auxin and its efflux carrier PIN-FORMED1 (PIN1). Consequently, pin1 mutants give rise to naked inflorescence stalks with few or no flowers, indicating that PIN1 plays a crucial role in organ initiation. However, pin1 mutants do produce leaves. In order to understand the regulatory mechanisms controlling leaf initiation in Arabidopsis (Arabidopsis thaliana) rosettes, we have characterized the vegetative pin1 phenotype in detail. We show that although the timing of leaf initiation in vegetative pin1 mutants is variable and divergence angles clearly deviate from the canonical 137° value, leaves are not positioned at random during early developmental stages. Our data further indicate that other PIN proteins are unlikely to explain the persistence of leaf initiation and positioning during pin1 vegetative development. Thus, phyllotaxis appears to be more complex than suggested by current mechanistic models.  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