995 resultados para 418


Relevância:

10.00% 10.00%

Publicador:

Resumo:

Gd_3Ga_5O_(12)稀土材料具有Ga~(3+)离子易于被其它离子部分取代的特点.Gd_3Sc_2Ga_3O_(12),Gd_3Lu_2Ga_3O_(12)和Gd_3In_2Ga_3O_(12)作为膜磁光材料YIG和Y_(3-x)Bi_xFe_5O_(12)的衬底引起关注. 这些材料可以通过固相反应、浮熔法、提拉法合成,但它们的高压合成未见报道.本文首次利用高温高压方法实现了Gd_3In_2Ga_3O_(12)的合成,并对其合成区进行了研究.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Cupric (II) ion transfer across the water/nitrobenzene interface facilitated by 2,2'-biqulnoline was investigated by cyclic voltammtry. Transfer process was controlled by diffusion. At [BQ](NB)>>[Cu2+](W), transfer ion was found to be 1:2 Cu2+-biquinoline

Relevância:

10.00% 10.00%

Publicador:

Resumo:

用循环伏安法研究了2.2’-联喹啉推动Cu2+在水/硝基苯界面的转移,提出了配合转移机理,并研究了配合反应过程的动力学,测定了Cu2+和2.2’-联喹啉形成的1:2配合物的界面热力学参数和配合物的形成速率常数k.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Ce~(3+)只有一个4f电子,基态能级为~2F_(5/2)和~2F(7/2),两能级差约为2200cm~(-1),Ce~(3+)不同于其它三价稀土离子,一般是d→f跃迁,特征发射为d→~2F_(5/2)和d→~2F_(7/2)跃迁引起的两宽带。CaF_2∶Ce~(3+)晶体中,当Ce~(3+)取代Ca~(2+)时,存在电荷补偿问题。Manthey讨论了CaF_2∶Ce~(3+)中间隙F~-充当电荷剂问题,Feofilov探讨了CaF_2∶Ce~(3+)的氧补偿问题,指出当有氧存在时,它

Relevância:

10.00% 10.00%

Publicador:

Resumo:

本文研究了丁基罗丹明 B-磷钼杂多酸-PVA_124超高灵敏显色反应,提出了测定痕量磷新的分光光度法,缔合物的最大吸收波长位于588nm 处,表观摩尔吸光系数ε值为1.1×10~6L·mol~(-1)·cm,研究了缔合物的组成比和红外光谱,并初步讨论了反应机理,本法直接用于钢、试剂和水样的分析,结果较为满意,测定下限分别可达4ppb(10ml 水)和2×10~(-6)%(1g 试剂)。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The worldwide shrimp culture is beset with diseases mainly caused by white spot syndrome virus (WSSV) and suffered huge economic losses, which bring out an urgent need to develop the novel strategies to better protect shrimps against WSSV. In the present study, CpG-rich plasmid pUC57-CpG, plasmid pUC57 and PBS were employed to pretreat shrimps comparatively to evaluate the protective effects of CpG ODNs on shrimps against WSSV. The survival rates, WSSV copy numbers, and antiviral associated factors (Dicer, Argonaute, STAT and ROS) were detected in Litopenaeus vannamei. There were higher survival proportion, lower WSSV copy numbers, and higher mRNA expression of Dicer and STAT in pUC57-CpG-pretreatment shrimps than those in pUC57- and PBS-pretreatment shrimps after WSSV infection. The Argonaute mRNA expression in pUC57-CpG-, pUC57- and PBS-pretreatment shrimps after WSSV infection was significantly higher than that of shrimps post PBS stimulation on the first day. The ROS levels in pUC57-CpG-pretreatment shrimps post secondary stimulation of PBS were significantly higher than those post WSSV infection on the first day. These results together demonstrated that pUC57-CpG induced partial protective immunity in shrimps against WSSV via intermediation of virus replication indirectly and could be used as a potential candidate in the development of therapeutic agents for disease control of WSSV in L. vannamei. (C) 2009 Elsevier Ltd. All rights reserved.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A hybrid coupled ocean-atmosphere model is designed, which consists of a global AGCM and a simple anomaly ocean model in the tropical Pacific. Retroactive experimental predictions initiated in each season from 1979 to 1994 are performed. Analyses indicate that: (1) The overall predictive capability of this model for SSTA over the central-eastern tropical Pacific can reach one year, and the error is not larger than 0.8 degrees C. (2) The prediction skill depends greatly on the season when forecasts start. However, the phenomenon of SPB (spring prediction barrier) is not found in the model. (3) The ensemble forecast method can effectively improve prediction results. A new initialization scheme is discussed.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

在胶州湾内、东海与南海通过现场实验(营养盐添加实验与稀释实验)的方法,对N(N0_3~--N、NH_4~+-N)、P、Fe、Si营养盐以及小型浮游动物对浮游植物生长的调控机制进行了初步研究。同时还在胶州湾内开展了上、下行效应的比较研究,主要结果如下:1 在胶州湾内共进行了25次富营养现场实验与12次稀释实验,网采浮游植物(20-200μm)与微型浮游植物(2-20μm)是叶绿素a生物量的主要组成部分,比较而言,在周年的水平上,微型浮游植物比网采浮游植物更多的支配着浮游植物群落的叶绿素a生物量。在营养盐添加实验中,培养后期浮游植物群落也都是网采浮游植物与微型浮游植物占叶绿素a生物量的优势地位。胶州湾是营养盐含量较高,且营养盐变化不规律的海区,但胶州湾各季节的DIN/P基本都大于16:1的Redfield比值。营养盐添加实验的结果显示,在湾内,似乎在秋季无营养盐限制浮游植物生长的情况发生;而在冬、春季发生Si限制的可能性很大;除Fe外,在夏季似乎N(NO_3~--N、NH_4~+-N)、P、Si营养盐限制都有可能发生,但无明显的规律性。在周年的水平上,Si似乎是最主要的限制性营养盐,而P与N都可能产生次级营养盐限制。营养盐添加实验中分级叶绿素的结果显示,网采浮游植物与微型浮游植物在冬、春季一般会经历较显著的Si限制作用,在夏季N似乎对网采浮游植物与微型浮游植物的生长有更重要的调控作用。超微型浮游植物的生长似乎主要受到P的调控。在胶州湾内,网采浮游植物的生长似主要受到上行效应的调控,而下行效应似是控制超微型浮游植物生长的主要机制。从整个浮游植物群落(<200μm)的周年变化情况来看,在控制浮游植物的生物量上,似乎下行效应比上行效应更有效。 2在东海,除402站(122°33'E、30°45'N)位于长江口,受到显著的陆源输入影响外(特别是该站有相当高的SiO_3~(2-)-Si含量),418站(127°30'E、27°55'N)、Y136站(128°、30°27')与E064(125°14'E、25°48'N)站都位于开放海区,营养盐含量都很低。1999年的航次,表层的硝酸盐与铵盐含量都比1998年的航次高,但另外三种常量营养盐含量都低。402站有较高比例的网采浮游植物与微型浮游植物叶绿素a生物量,相应的超微型浮游植物占总叶绿素a生物量的比例则显著低于其它三站。位于陆架区的Y136站,其微型浮游植物叶绿素a生物量则显著低于沿岸海区,但超微型浮游植物叶绿素a生物量则显著增加,占总叶绿素a的50%以上。处于开放海区的418站与E064站,网采浮游植物叶绿素a生物量所占的比例已经很低,而无一例外的是超微型浮游植物叶绿素a生物量贡献了总叶绿素a生物量的大部分。但在培养后期,各组处理中网采浮游植物占总叶绿素a生物量的比例都高于初始值。营养盐添加实验的结果显示,沿岸海水中,从比例上看,浮游植物的生长似乎更需要N而不是P,但是太高的N/P添加对浮游植物生长的促进作用反不如适中的N/P的添加;在418站,各种营养盐的添加对浮游植物的生长都有促进作用(Fe除外),但P的作用更显著一些,在添加的两种N源中,NH_4~+-N的作用比NO_3~--N的作用更显著;在E064站,培养中各实验组的总叶绿素a生物量都有不同程度的增加,但NH_4~+-N与NO_3~--N的作用更显著;Y136站的实验结果与E064站相似,也是NH_4~+-N与NO_3~--N的作用更显著,而且该站Si的作用还比较显著(强于P)。在开放海区,1998年夏季,似乎是P限制着浮游植物群落的生长,但在1999年春季则可能是N限制着浮游植物的生物量。稀释实验的结果显示,在长江口附近的402站与开放海区的E064站浮游植物的生长率都显著高于大陆架的Y136站。小型浮游动物的摄食率则无明显的空间变化趋势,除开放海区的E064站显著高外,其它三站摄食率接近。这一结果与浮游物的群落组成,浮游植物的群落组成以及光照、温度等条件有关。营养盐添加实验与稀释实验的结果都证实,更可能是营养盐通过上行效应,而不是小型浮游动物实施下行效应控制着网采浮游植物的的生长;在东海的实验区域似乎是上行效应控制着微型浮游植物的种群数量变动,从营养盐添加实验的结果看,由于时间的不同,似乎有春季N限制与夏季P限制的季节交替;超微型浮游植物的生长也主要受到营养盐的控制,似乎也有春季N限制与夏季P限制的季节交替;摄食对微型浮游植物的生长有一定的调控作用,但这一调控机制并不是十分有效。3 在南海的航次中,表层硝酸盐的平均浓度较低,经常检测不出,但表层磷酸盐、铵盐与硅酸盐的浓度要比东热带太平洋等贫营养海区高。4 断面沿经度横跨大洋,其表层各种营养盐的平均浓度均低于2断面与5断面,(硝酸盐一般都在检测限之下,铵盐与磷酸盐的平均值分别为0.20与0.12 μM),属于营养盐较低的海区;2断面表层各种营养盐的平均浓度最高(硝酸盐、铵盐与磷酸盐分别为0.29、1.17与O.19μM);5断面表层平均的营养盐含量介于2断面与4断面之间,但硝酸盐含量经常在检测限之下。K206与K508站在培养实验的初始时刻都是超微型浮游植物占总叶绿素a生物量的大部分,但K409站网采浮游植物、微型浮游植物与超微型浮游植物的叶绿素a生物量分别占总叶绿素a生物量的30%左右。培养中,各组处理中网采浮游植物叶绿素a生物量占总叶绿素a生物量的比例都增加。K409站位于南海中央,该站浮游植物对各种营养盐的添加都有显著的响应效果;K206站位于2断面中部巴士海峡处,本站除P的添加效果较明显外,另外几种营养盐的富营养效果都不显著;K508站磷酸盐与硝酸盐的添加效果较明显。总的来说,各种营养盐的添加对浮游植物的生长都有促进作用,但磷酸盐的作用似乎更显著一些。实验结果可能更反应了N、P、Fe这几种营养盐的共同限制作用。Si限制不如其它几种营养盐显著。南海Fe的限制情况也不严重。各站浮游植物摄食率(g)与生长率(u)的空间变化都不显著。各站的g/u都在0.4左右,说明在南海小型浮游动物的摄食压力比较一致。K409站与K508站浮游植物的生长率显著高于K206站。小型浮游动物的摄食率与浮游植物生长率的变化趋势一致,都是中部的K409站与南边的K508站高于北边的K206站。这可能是各采样站点浮游动物种类组成不同的结果。网采浮游植物似乎主要受到各种营养盐的限制,其中P的作用最显著,N也较显著,随地域不同,间或有Fe的限制作用发生。在南海的中部,可能存在N、P、Fe营养盐对微型浮游植物的共同限制作用,但在北部,可能有微弱的P限制作用,而在大洋的南部,几乎无营养盐限制微型浮游植物的生长,摄食在控制微型浮游植物的生物量上并不是十分有效。超微型浮游植物的生长似乎同时受到营养盐与小型浮游动物摄食的控制,营养盐添加实验的结果显示可能P对超微型浮游植物的生长促进作用最大,同时进行的稀释实验证实,小型浮游动物的摄食活动在调节超微型浮游植物的生长上也相当有效。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Six steroids have been isolated from ethanolic extract of green alga Chaetomorpha basiretorsa Setchell by a combination of repeated normal phase silica gel and Sephadex LH-20 gel column chromatography as well as recrystallization. Using spectroscopic methods including MS and NMR, their structures were determined as beta-lawsaritol (1), saringosterol (2), 24-hydroperoxy-24-vinyl-cholesterol (3), beta-stigmasterol (4), stigmast-4-en-3 alpha, 6 beta-diol (5), 29-hydroxystigmasta-5, 24 (28)-dien-3 beta-ol (6). All these compounds were obtained from this genus for the first time and they were inactive (IC50 > 10 mu g /ml) against KB, Bel-7402, PC-3M, Ketr 3 and MCF-7 cell lines.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

用所建立的高效液相色谱-荧光检测法测定了罂粟籽和火锅汤料中的罂粟碱。采用的色谱柱为RP—C18柱(250mm×4.6mm i.d.,5μm);检测激发波长为285nm,发射波长为355nm;流动相为甲醇-0.02mol/L乙酸铵(体积比为70:30),流速0.8mL/min。实验结果表明,罂粟碱的进样量为1×10^-4 - 0.1μg时其质量浓度与相应峰面积有良好的线性关系,最低检测限(以信噪比大于3计)达到0.02ng。罂粟籽中罂粟碱的回收率为99.0%~100.8%。方法快速准确,简便灵敏,分离度高,能够满足有关食品中罂粟碱的检测要求。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

基于1997~1999年野外实验,对高寒草甸小云雀和黄嘴朱顶雀两种雀形目鸟的窝雏数进行增减处理。结果表明,对照组的幼鸟生长率和离巢体重都大于增加组,说明窝雏数增加后,幼鸟质量下降。随着窝雏数增加,这两种幼鸟生长率显著下降(小云雀:r = -0.965, P = 0.035 < 0.05;朱顶雀:r = -0.828, P = 0.022 < 0.05)。窝雏数改变对小云雀幼鸟出飞重影响不显著(r = -0.418, P = 0.528 > 0.05),而对黄嘴朱顶雀有显著的影响(r = -0.901,P = 0.014 < 0.05)。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

对青海海北地区高山草甸主要植物群落小嵩草(K obresia pygmaea) 草甸、矮嵩草(K. humilis) 草甸、藏嵩草(K. tibetica) 沼泽化草甸地上生物量动态和能量分配的研究结果表明, 不同植物群落年地上净生产量及其年际动态和主要植物类群生物量季节动态具明显的差异, 其生物量季节动态可由如下模型表示: W i = Ki/(1 + exp (A i - B it) )   植物群落地上、地下生物量的垂直分布呈典型的金字塔和倒金字塔模式。小嵩草草甸、矮嵩草草甸和藏嵩草沼泽化草甸的地上净生产量依次为368.4g·m – 2·a- 1、418.5 g·m – 2·a- 1和518.4 g·m – 2·a- 1, 所固定的太阳能值依次为6655.16kJ·m – 2·a- 1、7610.09 kJ·m – 2·a- 1、9488.77 kJ·m – 2·a- 1。光能利用率分别为0.1097%、0.1256%、0.1568%。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Pollen morphology of 40 species of Rheum, belonging to eight sections, was investigated under LM and SEM. Four new exine patterns were found in the species: a) microcchinate-foveolate, b) rugulate, c) verrucate-perforate, and d) verrucaterugulate ornamentation. In addition, two patterns, the Rheum-type pollens with microechinate-perforate and fine-reticulate, as previously described, were also confirmed in the present study. Based on above study the evolution trends of pollen morphology in the taxa involved were discussed phylogenetically as below. As microechinate-perforate exine pattern existed commonly, the pattern is, therefore, regarded as the most primitive among all the six types. The fine-reticulate type was thought as a derivative type, deriving from the basic micro echinate-foveolate-perforate pattern, and followed by the rugulate and verrucate-perforate ornamentation. The verrucate-rugulate ornamentation should be the most advanced. More than one pollen type often exist in most of the sections in Rheum. The pollen morphology of Rheum was strongly correlated with its geographical and ecological distribution. Three medicinally important species R. officinale, R. palmation and R. tanguticum can be palynologically distinguished by their ornamentations.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

含量不断升高,封闭填埋场种植的玉米果实有一部分汞含量超过了食用标准,这些都说明填埋场的运行会给周围的生态环境带来一定的汞污染风险。