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   167篇
  免费   10篇
  2022年   2篇
  2020年   4篇
  2018年   1篇
  2017年   2篇
  2016年   4篇
  2015年   8篇
  2014年   6篇
  2013年   13篇
  2012年   6篇
  2011年   11篇
  2010年   5篇
  2009年   5篇
  2008年   9篇
  2007年   14篇
  2006年   11篇
  2005年   6篇
  2004年   9篇
  2003年   6篇
  2002年   9篇
  2001年   6篇
  2000年   3篇
  1999年   3篇
  1998年   3篇
  1997年   2篇
  1996年   1篇
  1995年   1篇
  1994年   1篇
  1993年   3篇
  1992年   2篇
  1990年   4篇
  1988年   2篇
  1987年   2篇
  1985年   2篇
  1982年   2篇
  1980年   3篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1973年   1篇
  1961年   2篇
排序方式: 共有177条查询结果,搜索用时 587 毫秒
31.
Exercise behavior, cardiorespiratory fitness, and obesity are strongly influenced by genetic factors. By studying young adult twins, we examined to what extent these interrelated traits have shared genetic and environmental etiologies. We studied 304 twin individuals selected from the population-based FinnTwin16 study. Physical activity was assessed with the Baecke questionnaire, yielding three indexes: sport index, leisure-time index, and work index. In this study, we focused on sport index, which describes sports participation. Body composition was determined using dual-energy X-ray absorptiometry and cardiorespiratory fitness using a bicycle ergometer exercise test with gas exchange analysis. The Baecke sport index was associated with high maximal oxygen uptake adjusted for lean body mass (Vo(2max)[adj]) (r = 0.40), with low body fat percentage (BF%) (r = -0.44) and low waist circumference (WC) (r = -0.29). Heritability estimates for the key traits were as follows: 56% for sport index, 71% for Vo(2max)[adj], 77% for body mass index, 66% for WC, and 68% for BF%. The association between sport index and Vo(2max) was mostly explained by genetic factors (70%), as were both the association between sport index and BF% (71%) and that between sport index and WC (59%). Our results suggest that genetic factors explain a considerable part of the associations between sports participation, cardiorespiratory fitness, and obesity.  相似文献   
32.
33.

Objectives

The aim of our study was to assess the effect of short-term cold exposure, typical in subarctic climate, on cardiac electrical function among untreated middle-aged hypertensive men.

Methods

We conducted a population-based recruitment of 51 hypertensive men and a control group of 32 men without hypertension (age 55–65 years) who underwent whole-body cold exposure (15 min exposure to temperature −10°C, wind 3 m/s, winter clothes). Conduction times and amplitudes, vectorcardiography, arrhythmias, and heart rate variability (autonomic nervous function) were assessed.

Results

Short-term cold exposure increased T-peak to T-end interval from 67 to 72 ms (p<0.001) and 71 to 75 ms (p<0.001) and T-wave amplitude from 0.12 to 0.14 mV (p<0.001) and from 0.17 to 0.21 mV (p<0.001), while QTc interval was shortened from 408 to 398 ms (p<0.001) and from 410 to 401 ms (p<0.001) among hypertensive men and controls, respectively. Cold exposure increased both low (from 390 to 630 ms2 (p<0.001) and 380 to 700 ms2 (p<0.001), respectively) and high frequency heart rate variability (from 90 to 190 ms2 (p<0.001) and 150 to 300 ms2 (p<0.001), respectively), while low-to-high frequency-ratio was reduced. In addition, the frequency of ventricular ectopic beats increased slightly during cold exposure. The cold induced changes were similar between untreated hypertensive men and controls.

Conclusions

Short-term cold exposure with moderate facial and mild whole body cooling resulted in prolongation of T-peak to T-end interval and higher T-wave amplitude while QTc interval was shortened. These changes of ventricular repolarization may have resulted from altered cardiac autonomic regulation and were unaffected by untreated hypertension.

Trial Registration

ClinicalTrials.gov NCT02007031  相似文献   
34.
Effects of ozone and/or drought on Norway spruce needles werestudied using light microscopy and electron microscopy. Saplingswere exposed to ozone in open-top chambers during 1992–1995and also to drought in the late summers of 1993–1995.Samples from current and previous year needles were collectedfive times during 1995. Ozone increased the numbers of peroxisomesand mitochondria, which suggests that defence mechanisms againstoxidative stress were active. The results from peroxisomes suggestthat the oxidative stress was more pronounced in the upper sideof the needles, and those from mitochondria that defence wasmore active in the younger needle generation. Possibly due tothe good nitrogen status and the active defence, no ozone-specificchloroplast alterations were seen. At the end of the season,older needles from ozone treatments had smaller central vacuolescompared with other needles. Cytoplasmic vacuoles around thenucleus were increased by ozone in the beginning of the experiment,and did not increase towards the end of the season as in thecontrols. These results from vacuoles may indicate that ozoneaffected the osmotic properties of the cells. Decreased numberand underdevelopment of sclerenchyma cells and proliferationof tonoplast were related to nutrient imbalance, which was enhancedby drought. Larger vascular cylinders and more effective starchaccumulation before and after the drought periods compensatedfor the reduced water status. Numbers of peroxisomes and mitochondriawere increased in the drought-exposed needles before the onsetof drought treatments of the study year, i.e. these changeswere memory effects. Interactions between ozone and droughtwere few.  相似文献   
35.

Objectives

Present study examines the relationship between the estimated risk of developing type 2 diabetes (T2D) and health-related quality of life (HRQoL). We quantify the association between Finnish Diabetes Risk Score (FINDRISC) and HRQoL, and examine the potential use of FINDRISC as tool to evaluate HRQoL indirectly.

Methods

We conducted a cross-sectional study comprising 707 Finnish people without a diagnosis of T2D between the ages of 51 and 75 years. The risk of developing T2D was assessed using the validated and widely used FINDRISC (range 0–26 points), and quality of life was measured using two preference-based HRQoL instruments (15D and SF-6D) and one health profile instrument (SF-36). Effects of the individual FINDRISC items and demographic and clinical characteristics, such as co-morbidities, on HRQoL were studied using multivariable Tobit regression models.

Results

Low HRQoL was significantly and directly associated with the estimated risk of developing T2D. An approximate 4–5 point change in FINDRISC score was observed to be associated with clinically noticeable changes in the preference-based instrument HRQoL index scores. The association between HRQoL and the risk of developing T2D was also observed for most dimensions of HRQoL in all applied HRQoL instruments. Overall, old age, lack of physical activity, obesity, and history of high blood glucose were the FINDRISC factors most prominently associated with lower HRQoL.

Conclusions

The findings may help the health care professionals to substantiate the possible improvement in glucose metabolism and HRQoL potentially achieved by lifestyle changes, and better convince people at high risk of T2D to take action towards healthier lifestyle habits. FINDRISC may also provide an accurate proxy for HRQoL, and thus by estimating the risk of T2D with the FINDRISC, information about patients’ HRQoL may also be obtained indirectly, when it is not feasible to use HRQoL instruments.  相似文献   
36.
The amount of total ribosome assemblies extractable from the vegetative buds of 2 m high Scots pine ( Pinus sylvestrís L.) plants remained more or less constant throughout the sampling period from September to May. The stability of the ribosomes, the shape of the polysome profiles obtained after sucrose density gradient centrifugation and the clustering of material as seen in the scanning electron micrographs suggested the presence of storage formations during the winter.
All samples of isolated ribosomes were able to synthesize proteins in vitro. During midwinter the translation capacity, when calculated on a ribosome unit basis, was about one third of that found in September and May. This reflects not only the occurrence of storage formation during the winter, but also the amount of initiated translation processes at any given time. The decrease in the in vitro translation capacity in the autumn ceases around the end of November. Ribosome activity starts to increase as early as the end of January or beginning of February. It seems that the reactions are triggered either by an endogenous clock or by the change in the daylength.  相似文献   
37.
OBJECTIVE--To investigate the effect of overweight on premature mortality and work disability in young and middle aged Finns. DESIGN--Prospective cohort study based on data collected in the multiphasic health examinations by the Social Insurance Institution of Finland from 1966 to 1972 and follow up until 1982. SETTING--34 Communities throughout Finland. SUBJECTS--12,053 Women and 19,076 men who were employed and aged 25-64 at baseline. MAIN OUTCOME MEASURES--Mortality and work disability pensions from all and specified causes. RESULTS--Body mass index was a weak predictor of death but a strong predictor of early work disability, which increased linearly with body mass index. After adjustment for age, geographical region, occupation, and smoking the relative risks of work disability for women and men with a body mass index greater than or equal to 30 kg/m2 were, respectively, 2.0 (95% confidence interval 1.8 to 2.3) and 1.5 (1.3 to 1.7) when compared with those of subjects with body mass index less than 22.5 kg/m2. The increased risks were due to an excess of cardiovascular and musculoskeletal diseases but not of mental diseases. One fourth of all disability pensions from cardiovascular and musculoskeletal causes in women and half as many in men could be attributed to overweight (body mass index greater than 25 kg/m2) alone. CONCLUSIONS--Though modest overweight has little impact on mortality it predicts severe functional impairment. A considerable proportion of work disability pensions could probably be prevented by efficient weight control.  相似文献   
38.
We have isolated the birch homologue (BP8) for the carrot embryogenic gene DC8 by heterologous hybridization. The birch BP8 gene encodes a putative protein of 53 kDa, showing 52% sequence identity with the DC8 gene at the amino acid level. The putative BP8 protein contains 20 repeats of 11 amino acids and thus belongs to the group of LEA proteins isolated from such plants as carrot, cotton and wheat. Northern hybridization of mRNA isolated from birch cells representing different stages of somatic embryogenesis and non-embryogenetic material with a PB8 probe gave no signals, suggesting a low expression level of the BP8 gene.  相似文献   
39.
Nurseries would benefit greatly if frost hardiness (FH) of seedlings could be predicted by some environmental variable or by bud development in spring. We investigated the FH of 1-year-old Norway spruce (Picea abies (L.) Karst.) seedlings of local origin. The seedlings were stored frozen until incubated in the growth chamber at six different temperature sums (TSs) (0, 55, 88, 142, 185 and 240 d.d., >5°C) from mid-February to mid-March. FH of the buds, stems and previous year needles was assessed on three occasions. When the TS was 88 d.d. or less, buds exhibited only microscopic signs of development, even when seedlings tolerated temperatures below −10°C. As TS increased, primordial needles and primordial stems of buds grew while FH weakened, especially in previous year needles. When the TS was at least 142 d.d., all plant parts were frost hardy to approximately −6°C. Monitoring TS and bud development can help predict FH of Norway spruce seedlings in spring. However, more studies with seedlings of different ages and from multiple locations are necessary to appreciate the generality of our results.  相似文献   
40.
The purpose of this study is to evaluate whether sample preservation can affect the yield of nucleic acid extracts from environmental samples. Storage of microbial samples was studied using three sediment types of varying carbon contents (10–57% carbon of dry weight). Four different storage solutions were tested at three temperatures. Freezing of samples at ?20 °C or ?80 °C, either without preservative or in phenol–chloroform solution, retained nucleic acid quantities very efficiently. Storage of samples in phenol–chloroform solution at +4 °C also gave good yields except for sediment with extremely high-carbon content. Ethanol and RNAlater® preservation decreased nucleic acid yields drastically at all temperatures. To study how sample preservation may affect the result of microbial community analysis, one type of sediment was selected for length heterogeneity-PCR analysis and PCR cloning of the 16S rRNA genes. Ethanol and RNAlater® preservation caused a slight bias towards certain microbial types in the community analyses shown by underrepresentation of Bacteroidetes, Betaproteobacteria and Gammaproteobacteria-affiliated peak sizes and overrepresentation of Actinobacteria, Chloroflexi and Alphaproteobacteria-affiliated peak sizes. Based on the results of this study, preservation in phenol–chloroform solution can be recommended as an alternative storage method when freezing is not possible such as during extended field sampling; however, ethanol and RNAlater® may cause serious problems when used as preservatives for environmental samples containing humic acids.  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