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排序方式: 共有108条查询结果,搜索用时 46 毫秒
1.
Leptin   总被引:39,自引:0,他引:39  
Leptin is an adipocyte hormone that signals nutritional status to the central nervous system (CNS) and peripheral organs. Leptin is also synthetized in the placenta and in gastrointestinal tract, although its role in these tissues is not yet clear. Circulating concentrations of leptin exhibit pulsatility and circadian rhythmicity. The levels of plasma leptin vary directly with body mass index and percentage body fat, and leptin contributes to the regulation of body weight. Leptin plasma concentrations are also influenced by metabolic hormones, sex, and body energy requirements. Defects in the leptin signaling pathway result in obesity in animal models. Only a few obese humans have been identified with mutations in the leptin gene or in the leptin receptor; however, most cases of obesity in humans are associated with high leptin levels. Thus, in humans obesity may represent a state of leptin resistance. Minute-to-minute fluctuations in peripheral leptin concentrations influence the activity of the hypothalamic-pituitary-ovarian and hypothalamic-pituitary-adrenal axes, indicating that leptin may be a modulator of reproduction, stress-related endocrine function, and behavior. This suggests potential roles for leptin or its antagonists in the diagnosis, pathophysiology and treatment of several human diseases.  相似文献
2.
齐鸿雁  薛凯  张洪勋 《生态学报》2003,23(8):1576-1582
应用磷脂脂肪酸谱图分析技术对微生物群落进行定量分布,克服了传统的微生物培养方法和显微技术的局限性。介绍了磷脂脂肪酸谱图分析方法及其在微生物生态学领域中的应用,包括对微生物群落的生物量、群落结构、营养状况和新陈代谢活动等方面的研究。  相似文献
3.
脂质营养对中华绒螯蟹幼体肝胰腺超微结构的影响   总被引:12,自引:0,他引:12       下载免费PDF全文
江洪波  陈立侨  周忠良  温小波 《动物学研究》2001,22(1):64-68,T001,T002
采用透射电镜技术研究了中华绒螯蟹(Eriocheir sinensis)各期幼体肝胰腺的超微结构,结果表明,蟹的肝胰腺腺管上皮由E,F,B和R4种细胞组成,其中E细胞为胚胎细胞,能分化成其他3种细胞;B,R和F细胞均呈,高柱状,腔面有发达的微绒毛,基底部有基膜,呈明显的极性分布;B细胞粗面内质网丰富,胞质中有1-2个大液泡,起分泌作用,属分泌液;F细胞内含发达的粗面内质网,还可见酶原颗粒;R细胞胞质中有丰富的滑面内质网、游离的核糖体和脂肪滴,主要起贮存养人的作用。细胞的连接有紧密连接和中间连接2种方式。与脂质营养缺乏时相比,脂质营养充足的幼体其肝胰腺超微结构有如下特点:R细胞质中有连多的脂肪滴,线粒体呈饱满的圆形或椭圆形,且膜未见有内陷或萎缩,滑面内质网膨胀成小泡状结构。  相似文献
4.
雪尿分析技术是北方冬季有蹄类种群营养状况评价的可靠性指数。本通过对兴隆镇小东林场和三江自然保护区1999及2000年冬季狍50个雪尿、尿液样本采集及分析,用以评价在不同类型的栖息地中狍冬季的营养状况,结果表明:雪尿分析可以评价狍冬季的营养状况及其变化;雪尿中较低的尿素氮与肌酸酐的比率表明两地区狍基本上处于营养不良早期阶段,反映了食物资源可利用性低、食物营养质量低造成外源蛋白质和能量摄人不足,而使狍大量消耗体脂肪,并通过对尿液化学成分的重吸收利用而保持其在尿液中排出量最低,使机体内源蛋白质分解代谢处于较低状态;三江1999年冬季狍营养状况相对较差,而2000年情况较好;幼体及亚成体处于营养不良中期阶段。  相似文献
5.
氮沉降是当前全球变化的一个重要方面,它对各类森林生态系统和植物的影响及其机制的研究是当前国际生态学界关注的问题之一。探讨了南亚带森林两种优势树种荷木(Schimasuperba)和黄果厚壳桂(Cryptocaryaconcinna)幼苗的养分状况对模拟氮沉降增加的响应。实验随机分为对照(Control)、T5、T10、T15和T305个样方,每个样方包括3个重复。所施氮肥为NH4NO3,每次溶解在10L自来水中,5个样方喷施的浓度分别为0、0.12、0.24、0.36和0.72mol·L-1。每月喷施2次,5个样方一年喷施的总氮量分别相当于氮沉降率0、5、10、15和30g·m-2·a-1。经过11个月的处理,土壤中速效氮水平明显提高,而pH值下降。两种幼苗叶、枝干和根的氮含量随处理水平的增加而升高,但P、K、Ca和Mg的含量与对照相比普遍下降。荷木幼苗的单株氮贮量除T5处理外,所有处理样方均高于对照,但以T10样方最高;黄果厚壳桂幼苗的单株氮贮量随处理水平增加而增加,在T15样方达最大值,之后下降。氮处理引起两种幼苗体内的氮分配到枝干的比例增加,但分配到叶中的比例下降。两种幼苗叶、枝和根3器官中N与其他营养元素的比值随氮处理水平增加而显著增加。  相似文献
6.
Nutrient supply and fertilizer experiments in view of N saturation   总被引:5,自引:0,他引:5  
New types of forest damage associated with Mg (and K) deficiency can be corrected by proper fertilization using fast release Mg (and K) fertilizers or Mg limestone. Sufficient Mg and K supply provided by former fertilizer applications inhibited the appearance of typical deficiency symptoms in areas where unfertilized control trees are now characterized by yellowing. In these areas N input rates vary appreciably. Addition of N fertilizers, particularly in the form of NH4-N, can induce nutrient imbalances as was demonstrated for Mg and K. From these disorders relative growth reductions may result. However, sustained negative effects will probably only occur when large doses are applied or when atmospheric N input rates are high. Increased N uptake due to N fertilization indicated that the investigated sites were not saturated with N.Needle analysis is a very simple as well as valuable tool to characterize the nutritional status of forest tress and stands when it is carried out correctly. Nutrient ratios should receive the attention they deserve, rather than concentrate exclusively on the evaluation of absolute nutrient contents.  相似文献
7.
Human capital, wealth, and nutrition in the Bolivian Amazon   总被引:4,自引:0,他引:4  
We analyze anthropometric variables of a society of forager-horticulturalists in the Bolivian Amazon (Tsimane') in 2001-2002. Community variables (e.g., inequality, social capital) explain little of the variance in anthropometric indices of nutritional status, but individual-level variables (schooling, wealth) are positively correlated with nutritional status. Dietary quality (foods high in animal proteins), access to foraging technology, and traditional knowledge of medicinal plants are related to better anthropometric indices.  相似文献
8.
A perturbation of zinc metabolism has been noted in subjects with obesity. The present work intends to investigate whether the zinc nutritional status is associated with hyperinsulinemia in obesity. A study was carried out in a group of obese children and adolescents (n=23) and compared to a control group (n=21), both between 7 and 14 yr of age. Software analyzed diet information from 3-d food records. Body composition was evaluated by body mass index (BMI), bioelectrical impedance, and skinfold measurements. Zinc nutritional status was evaluated by Zn determination in plasma, erythrocyte, and 24-h urine, by atomic absorption spectrophotometry (λ=213.9 nm). Insulin was measured by radioimmunoassay (Linco Res). Diets consumed by both groups had marginal concentrations of zinc. Zinc concentrations in plasma and erythrocytes were significantly lower in the obese group. Urinary zinc excretion and serum insulin were significantly higher in the same group, although the insulinemia and the parameters of zinc nutritional status were not significantly correlated. As a result, considering that zinc is part of the synthesis and secretion of this hormone, an assessment is necessary of the possible participation of the oligoelement in the mechanisms of insulin resistance, commonly present in obese patients.  相似文献
9.
Zinc nutritional status in obese children and adolescents   总被引:4,自引:0,他引:4  
Studies in animals and humans have corroborated that zinc (Zn) metabolism is altered in obesity. The present work intends to evaluate the Zn nutritional status in obese children and adolescents by the determination of some biochemical parameters and analyses of the diets. The investigation was carried out in a group of obese children and adolescents (n=23) and compared to a control group (n=21), both between 7 and 14 yr of age. A software analyzed diet information from 3-d food records. Body composition was evaluated by body mass index, bioelectrical impedance, and skinfold measurements. Zinc nutritional status was evaluated by Zn determination in plasma, erythrocyte, and 24-h urine, by atomic absorption spectrophotometry (γ=213.9 nm). Diets consumed by both groups had marginal concentrations of zinc. Zinc concentrations in plasma and erythrocytes were significantly lower in the obese group. Urinary zinc excretion was significantly higher in the same group. The results allowed one to conclude that zinc nutritional status in obese individuals is altered.  相似文献
10.
王丽华  王发园  景新新  李帅  刘雪琴 《生态学报》2015,35(15):5254-5261
纳米氧化锌是应用最广的人工纳米颗粒(nanoparticles, NPs)之一,具有一定生物毒性。丛枝菌根(arbuscular mycorrhizal, AM)真菌能与陆地上80%以上的高等植物形成丛枝菌根共生体,并能改善宿主植物矿质营养,提高其抗逆性。然而纳米ZnO与丛枝菌根的关系尚不清楚。通过温室沙培盆栽试验,研究了施加不同水平纳米ZnO(0、500、1000、2000、3000 mg/kg)和接种AM真菌Acaulospora mellea对大豆生长及营养状况的影响。结果表明,3000 mg/kg的纳米ZnO显著抑制大豆植株生长,表现出植物毒性,在其他水平时没有显著影响。纳米ZnO在施加水平500、1000 mg/kg时没有抑制AM真菌对大豆根系的侵染,但是高施加水平(>2000 mg/kg)时对AM真菌产生毒害,几乎完全抑制大豆根系菌根侵染。接种AM真菌仅在500 mg/kg纳米ZnO时显著促进大豆生长,增加大豆植株对P、K、N的吸收,降低根系Zn含量。纳米ZnO可能会持续释放锌离子,并抑制大豆根系对矿质营养元素的吸收,从而产生生物毒性,而AM真菌与大豆根系的共生可起到有益作用。  相似文献
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