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   16篇
  免费   1篇
  国内免费   4篇
  2023年   3篇
  2022年   1篇
  2021年   3篇
  2019年   2篇
  2017年   1篇
  2015年   2篇
  2014年   1篇
  2010年   1篇
  2008年   2篇
  2005年   1篇
  2003年   2篇
  2002年   1篇
  1993年   1篇
排序方式: 共有21条查询结果,搜索用时 15 毫秒
1.
Primates need to detect and recognize camouflaged animals in natural environments. Camouflage-breaking movements are often the only visual cue available to accomplish this. Specifically, sudden movements are often detected before full recognition of the camouflaged animal is made, suggesting that initial processing of motion precedes the recognition of motion-defined contours or shapes. What are the neuronal mechanisms underlying this initial processing of camouflaged motion in the primate visual brain? We investigated this question using intrinsic-signal optical imaging of macaque V1, V2 and V4, along with computer simulations of the neural population responses. We found that camouflaged motion at low speed was processed as a direction signal by both direction- and orientation-selective neurons, whereas at high-speed camouflaged motion was encoded as a motion-streak signal primarily by orientation-selective neurons. No population responses were found to be invariant to the camouflage contours. These results suggest that the initial processing of camouflaged motion at low and high speeds is encoded as direction and motion-streak signals in primate early visual cortices. These processes are consistent with a spatio-temporal filter mechanism that provides for fast processing of motion signals, prior to full recognition of camouflage-breaking animals.  相似文献   
2.
Three new compounds (1, 6, 9), with six known compounds (25, 78) were obtained from water-soluble extract of Cimicifuga dahurica (Turcz.) Maxim. by bioactivity-guided isolation. Their structures were elucidated by chemical and spectral analysis, including 1D, 2D NMR data and HRESIMS. H2O2-induced neurotoxicity on PC12 cells model were conducted to evaluate the neuro-protective capability of these compounds. The piscidic acid derivatives compounds 47 showed marked neuro-protective effect at certain concentration.  相似文献   
3.
张煜森  段彦博  吴哲元  刘洋  曹洋  雷雅凯 《生态学报》2023,43(20):8359-8374
通过分析郑州7·20暴雨事件中贾峪河山地丘陵区小流域的洪水过程,探究景观特征对洪水淹没强度影响的时空分布规律,并提出增强流域洪水韧性的规划建议,以缓解河南省山区所面临的社会经济发展、生态环境改善等问题。基于高分6号遥感数据、先进陆地观测卫星(ALOS,Advance Land Observing Satellite)相控阵L频段合成孔径雷达(PALSAR)的地表高程数据和小时降雨量数据,利用MIKE 21水动力模型构建贾峪河流域二维水文模型,分析其2021年7月20日0-24时期上、中、下游的洪水淹没深度和面积,并结合双变量空间自相关模型方法,探究洪水淹没强度与各景观组成和地形因素在时间和空间上的相关性的差异以及其空间聚类类型。研究表明:(1)贾峪河流域淹没面积在0-6时快速增长,于18时达到最大9.59km2,此时各区域淹没面积占比从大到小依次为下游18.88%、上游8.25%、中游12.03%,淹没深度在3m以上的面积占36.11%。(2)地形因素(平均Moran''s I=0.159)对洪水强度的影响大于土地类型(平均Moran''s I=0.096),主要影响因子相对高程、地形湿度指数、矿坑面积百分比、水体面积百分比、建设用地面积百分比、耕地面积百分比以及林地和草地面积百分比与洪水淹没强度之间的相关性随时间变化呈增大趋势,均在暴雨中后期18-24时达到最强。(3)交互探测结果表明,多因子叠加会增强各景观特征对洪水淹没强度的影响。上游影响洪水淹没强度的主要驱动力为矿坑和相对高程,中游和下游的主要影响为水体和地形湿度指数。(4)洪水淹没强度24时的平均值与景观特征指数之间的"高-高"和"高-低"地区的面积占比约0.47%-9.85%,主要分布在上游的中部山区和北部河道周围、中游的河道两侧和下游的河道以及常庄水库周边地区。研究结论建议在上游露天矿坑就地改造为蓄水池并恢复植被,中游和下游应提升河岸带绿地质量,增加下游城区绿色基础设施,减轻城市洪水风险。  相似文献   
4.
Weng  Wei  Di  Shengdi  Xing  Shitong  Sun  Zhengguo  Shen  Zheyuan  Dou  Xiaojie  He  Shouyu  Tang  Huibin  Min  Jikang 《Molecular and cellular biochemistry》2021,476(6):2503-2512

The balance of osteoblasts and marrow adipocytes from bone marrow mesenchymal stem cells (BM-MSCs) maintains bone health. Under aging or other pathological stimuli, BM-MSCs will preferentially differentiate into marrow adipocytes and reduce osteoblasts, leading to osteoporosis. Long non-coding RNA differentiation antagonizing non-protein coding RNA (DANCR) participates in the osteogenic differentiation of human BM-MSCs, but the mechanism by which DANCR regulates the osteogenic differentiation of human BM-MSCs has not been fully explained. We observed that DANCR and prospero homeobox 1 (PROX1) were downregulated during osteogenic differentiation of human BM-MSCs, while miR-1301-3p had an opposite trend. DANCR overexpression decreased the levels of alkaline phosphatase, RUNX2, osteocalcin, Osterix in BM-MSCs after osteogenic induction, but DANCR silencing had the opposite result. Moreover, DANCR sponged miR-1301-3p to regulate PROX1 expression. miR-1301-3p overexpression reversed the suppressive role of DANCR elevation on the osteogenic differentiation of human BM-MSCs. Also, PROX1 elevation abolished the promoting role of miR-1301-3p overexpression on the osteogenic differentiation of human BM-MSCs. In conclusion, DANCR suppressed the osteogenic differentiation of human BM-MSCs through the miR-1301-3p/PROX1 axis, offering a novel mechanism by which DANCR is responsible for the osteogenic differentiation of human BM-MSCs.

  相似文献   
5.
Notch signaling determines and reinforces cell fate in bilaterally symmetric multicellular eukaryotes. Despite the involvement of Notch in many key developmental systems, human mutations in Notch signaling components have mainly been described in disorders with vascular and bone effects. Here, we report five heterozygous NOTCH1 variants in unrelated individuals with Adams-Oliver syndrome (AOS), a rare disease with major features of aplasia cutis of the scalp and terminal transverse limb defects. Using whole-genome sequencing in a cohort of 11 families lacking mutations in the four genes with known roles in AOS pathology (ARHGAP31, RBPJ, DOCK6, and EOGT), we found a heterozygous de novo 85 kb deletion spanning the NOTCH1 5′ region and three coding variants (c.1285T>C [p.Cys429Arg], c.4487G>A [p.Cys1496Tyr], and c.5965G>A [p.Asp1989Asn]), two of which are de novo, in four unrelated probands. In a fifth family, we identified a heterozygous canonical splice-site variant (c.743−1 G>T) in an affected father and daughter. These variants were not present in 5,077 in-house control genomes or in public databases. In keeping with the prominent developmental role described for Notch1 in mouse vasculature, we observed cardiac and multiple vascular defects in four of the five families. We propose that the limb and scalp defects might also be due to a vasculopathy in NOTCH1-related AOS. Our results suggest that mutations in NOTCH1 are the most common cause of AOS and add to a growing list of human diseases that have a vascular and/or bony component and are caused by alterations in the Notch signaling pathway.  相似文献   
6.
The Hani terrace paddyfield in Yunnan Province, China is categorized as a ‘constructed wetland’ under the Lamsar Convention classification. The Hani terrace paddyfield ranges from an altitude of 144 to 2000 m above sea level (ASL) in the southern slopes of the Ailao Mountains, angling down at a range of 15° to 75°. In this study, we investigated the ecosystem of the terrace paddyfields in the Mengpin and Quanfuzhuang administrative villages located at the center of the cultural heritage conservation district in the Hani terrace paddyfield. The Hani terrace paddyfield ecosystem structure is “forest-village-terrace paddyfield-river” in the order of descending altitude. Soil and water samples were sequentially taken from forests, villages and the terrace paddyfields to be able to study the vertical characteristics of Hani's terrace paddyfields. PO4-P and NH3-N in water were measured to test for water contamination. Seven soil nutrient factors were tested, including organic material (OM), char and nitrogen ratio (C/N), pH, total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), and available potassium (AK). Soil quality was also evaluated using the characteristics of the soil nutrient factors. Vertical changes in the landscape, wetland types, wetland plants, hydrology and soil nutrients were characterized. Results showed that: (1) Hani's terrace paddyfield can be divided into five types of wetlands; the rice varieties and cultivation patterns vary in each type of wetland. (2) Hani's terrace paddyfield has a great capacity for water conservation and a strong ability to purify contaminants. The impoundage of Hani's terrace paddyfield is about 5050 m3/hm2. Contaminants in the terrace paddyfield soils decrease exponentially with the decline in altitude. (3) Comparison of soil quality in five different land use types indicates decreasing soil quality from forest to terrace land to terrace paddyfield to water source. Except for headwater soil, single factors such as OM, TN and TP, and the comprehensive soil quality in individual sampling zones tend to increase with altitude elevation. Comprehensive soil quality in the Quanfuzhuang sampling zone is better than in the Mengpin sampling zone. Finally, a comparison of Hani's terrace paddyfield with plain paddyfields and natural wetlands highlighted the vertical characteristics of Hani's terrace paddyfield. __________ Translated from Acta Ecologica Sinica, 2006, 26(7): 2115–2124 [译自: 生态学报]  相似文献   
7.
The Hani terrace paddyfield in Yunnan Province,China is categorized as a 'constructed wetland' under the Lamsar Convention classification.The Hani terrace paddyfield ranges from an altitude of 144 to 2000 m above sea level (ASL) in the southern slopes of the Ailao Mountains,angling down at a range of 15°to 75°.In this study,we investigated the ecosystem of the terrace paddyfields in the Mengpin and Quanfuzhuang administrative villages located at the center of the cultural heritage conservation district in the Hani terrace paddy-field.The Hani terrace paddyfield ecosystem structure is "forest-village-terrace paddyfield-river" in the order of descending altitude.Soil and water samples were sequen-tially taken from forests,villages and the terrace paddy-fields to be able to study the vertical characteristics of Hani's terrace paddyfields.PO4-P and NH3-N in water were measured to test for water contamination.Seven soil nutrient factors were tested,including organic material (OM),char and nitrogen ratio (C/N),pH,total nitrogen (TN),total phosphorus (TP),available phosphorus (AP),and available potassium (AK).Soil quality was also eval-uated using the characteristics of the soil nutrient factors.Vertical changes in the landscape,wetland types,wetland plants,hydrology and soil nutrients were characterized.Results showed that:(1) Hani's terrace paddyfield can be divided into five types of wetlands; the rice varieties and cultivation patterns vary in each type of wetland.(2) Hani's terrace paddyfield has a great capacity for water conservation and a strong ability to purify contaminants.The impoundage of Hani's terrace paddyfield is about 5050 m3/hm2.Contaminants in the terrace paddyfield soils decrease exponentially with the decline in altitude.(3) Comparison of soil quality in five different land use types indicates decreasing soil quality from forest to ter-race land to terrace paddyfield to water source.Except for headwater soil,single factors such as OM,TN and TP,and the comprehensive soil quality in individual sampling zones tend to increase with altitude elevation.Comprehensive soil quality in the Quanfuzhuang sam-pling zone is better than in the Mengpin sampling zone.Finally,a comparison of Hani's terrace paddyfield with plain paddyfields and natural wetlands highlighted the vertical characteristics of Hani's terrace paddyfield.  相似文献   
8.
北京市居住区林木健康评价   总被引:2,自引:1,他引:1  
为了揭示北京市居住区林木健康变化特征及影响因素,提供北京市居住区林木健康经营对策。对北京市85个居住区林木进行健康特征调查,在建立林木健康评价模型评价林木健康状况的基础上,采用方差分析法和多重比较法分析不同类型居住区林木健康差异。结果表明:不同类型居住区林木健康指标差异显著(P0.05),各指标变化规律不完全一致;不同类型居住区地表覆盖情况、光污染程度、树干倾斜度、栽植截干、树势、冠形、干形等方面普遍较差。北京市居住区林木健康指数在0.60—0.80之间,健康等级呈现右偏正态分布特点,健康林木比例为3. 65%,亚健康林木(56. 07%)最多,其次是中等健康林木(36.68%),不健康林木有3.50%,濒死林木仅占0.10%。居住区林木健康指数在不同区域和不同来源间差异不显著(P0.05),在不同时期间差异显著(P0.05),健康指数大小分别为:三—四环=四—五环五—六环二环内=二—三环;福利房商品房保障房;2009—2013年2003—2008年=1998—2002年=1991—1997年1956—1990年。北京市居住区林木生长处于亚健康状态,潜在影响因子如地表覆盖情况、光污染程度、树干倾斜度等指标是限制北京市居住区林木生长的重要因子。适当减小夜间照明影响、增加有机地表覆盖、避免过度的修枝截干和加强林木养护管理是当前北京市居住区林木健康生长的保障。  相似文献   
9.
10.
Brazzein is a small, intensely sweet protein. As a probe of the functional properties of its solvent-exposed loop, two residues (Arg-Ile) were inserted between Leu18 and Ala19 of brazzein. Psychophysical testing demonstrated that this mutant is totally tasteless. NMR chemical shift mapping of differences between this mutant and brazzein indicated that residues affected by the insertion are localized to the mutated loop, the region of the single alpha-helix, and around the Cys16-Cys37 disulfide bond. Residues unaffected by this mutation included those near the C-terminus and in the loop connecting the alpha-helix and the second beta-strand. In particular, several residues of brazzein previously shown to be essential for its sweetness (His31, Arg33, Glu41, Arg43, Asp50, and Tyr54) exhibited negligible chemical shift changes. Moreover, the pH dependence of the chemical shifts of His31, Glu41, Asp50, and Tyr54 were unaltered by the insertion. The insertion led to large chemical shift and pKa perturbation of Glu36, a residue shown previously to be important for brazzein's sweetness. These results serve to refine the known sweetness determinants of brazzein and lend further support to the idea that the protein interacts with a sweet-taste receptor through a multi-site interaction mechanism, as has been postulated for brazzein and other sweet proteins (monellin and thaumatin).  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