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   854篇
  免费   29篇
  2023年   5篇
  2022年   7篇
  2021年   26篇
  2020年   25篇
  2019年   22篇
  2018年   21篇
  2017年   13篇
  2016年   20篇
  2015年   28篇
  2014年   39篇
  2013年   54篇
  2012年   55篇
  2011年   85篇
  2010年   44篇
  2009年   33篇
  2008年   62篇
  2007年   58篇
  2006年   58篇
  2005年   44篇
  2004年   42篇
  2003年   35篇
  2002年   31篇
  2001年   20篇
  2000年   11篇
  1999年   10篇
  1998年   2篇
  1997年   6篇
  1996年   3篇
  1995年   1篇
  1994年   4篇
  1993年   2篇
  1992年   2篇
  1991年   1篇
  1990年   3篇
  1988年   2篇
  1987年   2篇
  1986年   2篇
  1972年   1篇
  1968年   1篇
  1967年   1篇
  1964年   1篇
  1962年   1篇
排序方式: 共有883条查询结果,搜索用时 15 毫秒
1.
In a previous study, our laboratory showed that young dogs born at sea level (SL) and raised from 2.5 mo of age to beyond somatic maturity at a high altitude (HA) of 3,100 m show enhanced resting lung function (Johnson RL Jr, Cassidy SS, Grover RF, Schutte JE, and Epstein RH. J Appl Physiol 59: 1773-1782, 1985). To examine whether HA-induced adaptation improves pulmonary gas exchange during exercise and whether adaptation is reversible when animals return to SL before somatic maturity, we raised 2.5-mo-old foxhounds at HA (3,800 m) for 5 mo (to age 7.5 mo) before returning them to SL. Lung function was measured under anesthesia 1 mo and 2 yr after return to SL and during exercise approximately 1 yr after return. In animals exposed to HA relative to simultaneous litter-matched SL controls, resting circulating blood and erythrocyte volumes, lung volumes, septal volume estimated by a rebreathing technique, and lung tissue volume estimated by high-resolution computed tomography scan were persistently higher. Lung diffusing capacity, membrane diffusing capacity, and pulmonary capillary blood volume estimated at a given cardiac output were significantly higher in animals exposed to HA, whereas maximal oxygen uptake and hematocrit were similar between groups. We conclude that relatively short exposure to HA during somatic maturation improves long-term lung function into adulthood.  相似文献   
2.
The effect of varied supply of P (2.5× 10−5 to 6× 10−4 M) and Zn (0 to 10−6 M) on uptake and concentrations of P and Zn was studied in cotton ( Gossypium hirsutum L. cv. Deltapine 15/21) grown in nutrient solution under controlled environmental conditions. At a given Zn supply, increasing levels of P had no significant effect on the concentrations of total Zn in plants. However, increasing levels of P induced or enhanced visual Zn deficiency symptoms when the Zn concentration in the nutrient solution was low. The concentrations of water-soluble Zn in roots and shoots constituted 60% of the total Zn concentrations for plants grown with low P and 30% for plants grown with high P. The concentration of water-soluble Zn in leaves, but not total Zn, was closely correlated with visual Zn deficiency symptoms, levels of chlorophyll, super oxide dismutase and membrane permeability. The critical deficiency concentration of water-soluble Zn in cotton leaves was in the range of 6 to 7 μg (g dry weight)−1 or about 1.0 μg (g fresh weight)−1. The results show that high P concentrations in plant tissue decrease the physiological availability of Zn. Water-soluble Zn in the tissue appears to be a suitable indicator for Zn nutritional status in general and phosphorus-induced Zn deficiency in particular. Also in field-grown orange trees (Citrus sinensis) visual Zn deficiency symptoms in leaves were closely related to the concentration of water-soluble Zn.  相似文献   
3.
In rat pancreatic islets, tumoral islet cells (RINm5F line), parotid gland, and in human erythrocytes, but not in rat hepatocytes, the production of 3H2O from D-[2-3H]glucose is 20-30% lower than from D-[5-3H]glucose. This coincides with the production of tritiated lactic acid from D-[2-3H]glucose and may be attributable to an intramolecular hydrogen transfer in the phosphoglucoisomerase reaction. It is concluded that the production of 3H2O from D-[2-3H]glucose is not a reliable tool to assess the total rate of hexose phosphorylation.  相似文献   
4.
Dynamic Global Vegetation Models (DGVMs) provide a state-of-the-art process-based approach to study the complex interplay between vegetation and its physical environment. For example, they help to predict how terrestrial plants interact with climate, soils, disturbance and competition for resources. We argue that there is untapped potential for the use of DGVMs in ecological and ecophysiological research. One fundamental barrier to realize this potential is that many researchers with relevant expertize (ecology, plant physiology, soil science, etc.) lack access to the technical resources or awareness of the research potential of DGVMs. Here we present the Land Sites Platform (LSP): new software that facilitates single-site simulations with the Functionally Assembled Terrestrial Ecosystem Simulator, an advanced DGVM coupled with the Community Land Model. The LSP includes a Graphical User Interface and an Application Programming Interface, which improve the user experience and lower the technical thresholds for installing these model architectures and setting up model experiments. The software is distributed via version-controlled containers; researchers and students can run simulations directly on their personal computers or servers, with relatively low hardware requirements, and on different operating systems. Version 1.0 of the LSP supports site-level simulations. We provide input data for 20 established geo-ecological observation sites in Norway and workflows to add generic sites from public global datasets. The LSP makes standard model experiments with default data easily achievable (e.g., for educational or introductory purposes) while retaining flexibility for more advanced scientific uses. We further provide tools to visualize the model input and output, including simple examples to relate predictions to local observations. The LSP improves access to land surface and DGVM modelling as a building block of community cyberinfrastructure that may inspire new avenues for mechanistic ecosystem research across disciplines.  相似文献   
5.
Rotifera from north and northeast Anatolia (Turkey)   总被引:1,自引:1,他引:0  
Samples from 21 freshwater sites in Turkey yielded 91 different species of Rotifera, 42 of which are new to the Turkish fauna. Lepadella costatoides n. sp. is described and L. costata Wulfert is redescribed. L. christineae Koste is synonymised with L. quinquecostata (Lucks). Remarks on the intraspecific variability of some species of Lecane are given. L. pomiformis Edmondson is added to the synonymy of L. pyriformis (Daday). The synonymy of the latter with L. paraclosterocerca Pennak is confirmed.  相似文献   
6.
Objective:To translate and validate into Greek, the SARC-F questionnaire, a screening tool for sarcopenia.Methods:Questionnaire was back-translated and culturally adapted into Greek according to guidelines proposed by the World Health Organization. A convenience sample of 197 Greek elderly people (71.6±7.8 years, 68.5% women) was recruited, 64 of which were classified as persons at risk of sarcopenia according to the SARC-F. Internal consistency, test-retest and inter-rater reliability were evaluated. Validity (sensitivity, specificity, predictive positive value and predictive negative value) was assessed against the definition from the European Working Group of Sarcopenia in Older People (EWGSOP2), which is considered gold standard. Receiver-operating characteristic analysis was also performed to calculate the area under the curve.Results:SARC-F demonstrated high internal consistency (Cronbach’s alpha of 0.93) and excellent inter-rater and test-retest reliability, with intraclass correlation coefficient (ICC) of 0.91 (95% CI 0.79-0.96), and 0.93 (95% CI 0.91-0.95), respectively. According to the definition of sarcopenia from the EWGSOP2, 53 (26.85) participants were identified as probable sarcopenic and 23 (11.6%) as sarcopenic. Sensitivity of the tool for sarcopenia was 34.4 and specificity was 93.2. Positive predictive values were 26.4 and negative predictive values were 66.6%.Conclusion:Τhe SARC-F was successfully adapted into Greek language. The Greek SARC-F revealed low sensitivity but high specificity with EWGSOP2 sarcopenia definitions, indicating that it can detect with precision the absence of sarcopenia.  相似文献   
7.
8.
Dissection of the genetic basis of wheat ionome is crucial for understanding the physiological and biochemical processes underlying mineral accumulation in seeds, as well as for efficient crop breeding. Most of the elements essential for plants are metals stored in seeds as chelate complexes with phytic acid or sulfur‐containing compounds. We assume that the involvement of phosphorus and sulfur in metal chelation is the reason for strong phenotypic correlations within ionome. Adjustment of element concentrations for the effect of variation in phosphorus and sulfur seed content resulted in drastic change of phenotypic correlations between the elements. The genetic architecture of wheat grain ionome was characterized by quantitative trait loci (QTL) analysis using a cross between durum and wild emmer wheat. QTL analysis of the adjusted traits and two‐trait analysis of the initial traits paired with either P or S considerably improved QTL detection power and accuracy, resulting in the identification of 105 QTLs and 617 QTL effects for 11 elements. Candidate gene search revealed some potential functional associations between QTLs and corresponding genes within their intervals. Thus, we have shown that accounting for variation in P and S is crucial for understanding of the physiological and genetic regulation of mineral composition of wheat grain ionome and can be implemented for other plants.  相似文献   
9.
Yazici  R.  Yilmaz  M.  Yazicioğlu  O. 《Journal of Ichthyology》2021,61(3):452-459
Journal of Ichthyology - In this study, vertebrae, otoliths (asteriscus and lapillus), sectioned lapillus and pectoral fin rays were evaluated for age determination of Silurus glanis L., 1758...  相似文献   
10.
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