首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 126 毫秒
1.
ThisworkisfundedbyagrantfromtheNationalKeyTaskProjectsof8thand9thFive-yearplanprogram.INTRODUCTIONInthepastyears,studiesonthevirusesofpenaeidshrimpshavemadegreatprogressinvari-ouscountries.Rightnow,aboutl4virusesofpenaeidshrimpswerefound,i.e.BP(Baculoviruspenaei,Couch,1974),MBV(Penaeusmonndonbaculovirus,Lightneretal.,1983)orPBV(Penaeusplebejusbaculovirus,Lesteretal.,1987),BMN(Baculovirusmidgutglandnecrosisvirus,Sanaetal.,1981),PHRV(Penaeushybridrod-shapedvirus,Owensetal.,199l),…  相似文献   

2.
ThisstudywassupportedbytheStateEducationalCommittee(SEC)ofChina.INTRODUCTIONThedissolvedorganiccarbon(DOC),ordissolvedorganicmatter(DOM),isoneofthemostimPortantorganiccarbonreservoiroftheworld,whichmayaffectthecontentofCO2intheatmospherewithatime-scaleof1OOO~1OOOOyears(Hedges,1992).Theratesofproduction,degradationortransPortationofDOCareseveralmaindynamicalparametersofDOCintheeu-photiclayer.Inthispaper,wefocusonthediurnalvariationsofDOCinordertoestimatetheseparameters.METso…  相似文献   

3.
1IntroductionAfterNittaandYamada(1989)andTren-berth(1990)haveinitiallydescribedthe1977climaticvariationovertheNorthPacificwithstep-likeshiftofwintermeansealevelpressurefield,thePacificinterdecadaloscillation(PDO)hasextensivelybeenstudied.TheworkaboutthecauseofPDOfromtheviewoftheNorthPacificincludesthermodynamicexplanationoflow-frequencysea-surfacetemperature(SST)affectedbyatmosphericrandomforcing(FrankignoulandHasselmann,1977),themeridionalchangeofthermaltransportbysubtropicalgyreandhen…  相似文献   

4.
Trachidermus fasciatus is a species of catadromous fish in China. In order to elucidate the phenomenon of their seaward propagation, comparative studies of kidney histological structure of this species collected from fresh-water (salinity 10), sea-water (salinity 32) and artificial sea-water (salinity 17.5, 22.5) have been made.  相似文献   

5.
1 IntroductionMicroorganism is an important constituentof the antarctic, arctic and deep sea ecosystemswhich are characterized as permanent lowtemperature. To adapt and survive in this ex-treme environment, these microorganisms pro-duce many distinctive substances such as poly-unsaturated fatty acids (PUFA), low-tempera-ture enzymes and novel pigments, etc. (Thomasand Dieckmann, 2002). Low-temperature en-zymes have a property of higher specific activ-ity (Kcat) at low temperature. Owing to…  相似文献   

6.
Oceanographical features on both sides of Balingtang Channel (17°55′-20°06′N, 122°55′-126°57′E) were comprehensively investigated on board of R/V "Experiment 3" in June. 1984. The pre-sent paper reports the chlorophyll data collected and primary productivity estimated there. Water sam-ples were taken with a glass bottle of Model HQM_(1-2)at the depth of 0, 10. 25, 50, 75, 100 and 150m, separately. Chlorophyll was determined according to the spectrophotometry proposed by UNESCO(1966) and calculated with the trichromatic equations of Jeffrey-Humphrey(1975). Estimations ofprimary productivity were carried out using a simplified equation (Q = 1.5) given by Cadee(1975).  相似文献   

7.
In this paper,the dynamic response of undersea -+towed systems is numerically simulated.Atwo body towed system is especially considered in detail.The factors influencing the heave oftowed-bodies,such as the weight of the towed-body(in sea water),the length and the weight(in sea water)per unit length of the cable between towed-bodies and towing ship,are investigated in detail.Calculationsshow that the two-body towed system can greatly increases the stability of the towed system.  相似文献   

8.
Tradescantia paludosa, a species from U.S. (1979), is known with its high sensitivityfor mutagen when used in Tradescantia micronucleus (MCN) bioassay. The sensitivity ofT. reflexa, a special clone of Tradescantia found in Qingdao, China (1980), to mutagens  相似文献   

9.
Beta Distribution of Surface Elevation of Random Waves   总被引：2，自引：0，他引：2  
A probability density function (PDF) is derived of beta distribution with both λ3 (skewness) and λ4 (kurtosis) as parameters for weakly nonlinear wave surface elevation by use of a method recently proposed by Srokosz. This PDF not only has a simpler form than the well-known Gram-Charlier Series PDF derived by Longuet-Higgins. but also overcomes an obvious shortcoming of the latter that when the series is unsuitably truncated, the resulting PDF is locally negative. To test the derived beta PDF, laboratorial experiments of wind waves are conducted. The experimental data indicate that the theoretical requirements of the parameters in the beta PDF are fulfilled. The experimental results show that the present PDF is in better agreement with the measured data than the beta PDF only including parameter λ3, and also than the Gram-Charlier Series PDF truncated up to the term of H6.  相似文献   

10.
This paper studies the adsorption isotherm curves of four amino acids (glyucine,aspartic acid,glutamic acid and lysine)and the effects of existences of different concentrations of Cu(Ⅱ) on them.Both the adsorption isotherm of the amino acids on the kaolinite and that when the copper ion Cu(Ⅱ） exists belong to the Langmuir type.The slopes of these adsorption isotherm increase with the increasing concentrations of Cu(Ⅱ） added.It can be explained in terms of formation of the type(Ⅰ） ternary surface complexes in these systems.The regular pattern of the effects of copper ion Cu(Ⅱ) on the adsorption isotherm of amino acids on the kaolinite is identical with that of its effects on the exchange and adsorption percentage E(%)-pH on the kaolinite in the same system.  相似文献   

11.
褐藻多糖硫酸酯是一种含有硫酸基的水溶性杂聚糖,其化学组成对抗氧化活性有较大的影响。本文对三种褐藻来源的褐藻多糖硫酸酯及其降解产物化学组成和抗氧化活性进行了研究,阐明了不同来源褐藻多糖硫酸酯体外抗氧化活性的构效关系。实验结果表明:1)分子量对抗氧化活性有较大影响,但是对不同褐藻来源的褐藻多糖硫酸酯的影响趋势并不一致。2)岩藻糖、硫酸基和糖醛酸含量对清除超氧阴离子自由基的影响与分子量有一定的关系。对于低分子量样品,岩藻糖和硫酸基含量与抗氧化活性成正相关。3)岩藻糖和硫酸根的比值对羟基自由基的清除能力有一定影响,比值越大,羟基自由基的清除能力越强。分子量、岩藻糖、硫酸基和糖醛酸的含量对褐藻多糖硫酸酯的抗氧化活性的影响依次减小。本研究为褐藻多糖硫酸酯在抗氧化剂保健品和功能食品中的应用提供了基础数据,也为裙带菜、羊栖菜和铜藻的高值化利用提供了理论依据。  相似文献   

12.
采用过氧化氢法降解了相对分子质量约为141万±8.3万的海藻异枝麒麟菜(Eucheuma striatum Schmitz)硫酸多糖(ESPS),降解产物平均相对分子质量为4 819±440.降解后多糖的硫酸基(OSO2-3)质量分数稍有下降,由16.03%降至15.20%左右.同时,用体外模拟方法研究了降解前后ESPS对草酸钙(CaOxa)晶体生长的抑制作用,降解后的ESPS明显优于未降解多糖,其诱导生成的一水草酸钙(COM)晶体尺寸进一步减小,晶体数量减少,且棱角更为圆钝.表明低分子质量ESPS更能抑制CaOxa晶体的成核和生长.  相似文献   

13.
慢性肾衰的进程中伴随着肾脏炎症的发生,研究表明褐藻多糖硫酸酯具有抗炎作用,且对于慢性肾衰的早期治疗具有一定的作用。本文通过脂多糖(lipopolysaccharide,LPS)诱导,建立大鼠肾小球系膜细胞的炎症模型,用来源于海带的高分子质量褐藻多糖硫酸酯F1和低分子质量褐藻多糖硫酸酯F2对细胞进行处理,24 h后MTT法检测各组细胞活力,Griess法检测24 h及48 h后细胞培养液中NO的含量。结果表明,各组间细胞活力无明显差异;脂多糖可以诱导大鼠肾小球系膜细胞NO产量增加,F1和F2均可在一定程度上抑制脂多糖诱导的NO产量的增加,从而减轻细胞炎症反应。剂量为25μg/m L的F1和F2处理细胞48 h后,与模型组相比,F1和F2组细胞培养液中NO含量分别下降22.52%和38.65%,低分子质量褐藻多糖硫酸酯抗炎效果明显高于高分子质量褐藻多糖硫酸酯。  相似文献   

14.
主要采用傅里叶红外光谱(fourier transform infrared spectroscopy, FTIR)、气相色谱(gas chromatography, GC)和凝胶渗透色谱(gel permeation chromatography, GPC)方法对5种海藻粗多糖的单糖组成、官能团、分子量进行了初步分析。结果显示5种海藻粗多糖均含有木糖和岩藻糖, 其中南方团扇藻多糖含有较为丰富的山梨糖, 属于大分子量均一性多糖, 而孔石莼多糖分子量分布较宽, 均一性较差。红外光谱分析结果表明, 5种粗多糖均为酸性多糖, 棒叶蕨藻、琼枝麒麟菜和匍枝马尾藻多糖具有明显的硫酸基团吸收峰, 琼枝麒麟菜多糖存在呋喃糖和吡喃糖, 并且吡喃糖苷键可能存在β和α两种类型。明胶氯化钡实验结果指出南方团扇藻多糖的硫酸基团含量为38.43%(±2.38%), 明显高于其他几种海藻多糖, 而棒叶蕨藻多糖的硫酸基团含量最低, 仅为8.92%(±1.04%)。  相似文献   

15.
经Tris-HCl缓冲液浸提、硫酸铵分级沉淀盐析、DEAE-Sepharose Fast Flow离子交换层析和Sephadex G-75凝胶过滤层析等步骤,从菲律宾蛤仔内脏团中分离得到碱性磷酸酶,SDS-PAGE显示为单一条带,提纯倍数为14.42,比活力达到131.08U/mg。酶学性质研究表明:该酶亚基分子量约44kD,最适反应温度为45℃,最适pH值为9.0,米氏常数Km为0.098mmol/L,最大反应速度Vmax为1.01μmol/(mL·min)。Ca2+、Mg2+对酶活力表现出显著的激活作用。  相似文献   

16.
采用人肠道微生物体外厌氧发酵技术,研究人肠道微生物对不同分子量岩藻聚糖硫酸酯的降解利用。分别将五个志愿者的肠道微生物接种到以高分子量和低分子量岩藻聚糖硫酸酯为唯一碳源的培养基中,酵解48h后,采用TLC和PAGE分析分子量变化,PMP-HPLC分析单糖组成变化,GC分析短链脂肪酸的生成情况。结果发现:在人肠道微生物体外降解岩藻聚糖硫酸酯的体系中,岩藻聚糖硫酸酯寡糖和低分子量组分(10—20k Da)含量显著降低,而且酵解产物的单糖组成没有变化,说明被人肠道微生物彻底降解利用;而人肠道微生物对高分子量岩藻聚糖硫酸酯(20k Da)的降解和利用度很低,产物的半乳糖和甘露糖的比例明显下降。低分子量和高分子量岩藻聚糖硫酸酯在酵解后均生成短链脂肪酸乙酸、丙酸和丁酸,但在高分子量岩藻聚糖硫酸酯发酵液中还生成了支链脂肪酸(异丁酸、异戊酸)和戊酸。研究结果表明,人肠道微生物能够彻底降解利用复杂的海带岩藻聚糖硫酸酯寡糖和低分子量组分,但是对高分子量岩藻聚糖硫酸酯的降解率很低。单糖分析说明人肠道微生物能够降解和利用多糖中的所有单糖,产生有利于肠道健康的短链脂肪酸,但是只有低分子量岩藻聚糖硫酸酯能够抑制支链脂肪酸生成。  相似文献   

17.
利用微滤和超滤技术研究了九龙江河口区表层水中铀及其同位素组成的粒级分布和地球化学行为.结果表明,溶解态(<0.4μm)中低分子量组分(<10 000 u)占主要份额,胶体态(10 000 u~0.4μm)238U所占比例不足1%,且随盐度的增加其所占份额逐渐降低.溶解态、低分子量组分和胶体态238U的比活度与盐度之间存在良好的线性正相关关系,证实它们在九龙江河口区呈现保守行为.在颗粒态(>0.4μm)中,各粒级组分238U所占份额主要受控于相应颗粒物的浓度,在盐度小于20的区域,各粒级颗粒组分238U占颗粒态的份额有如下变化次序:10~53μm>2~10μm>0.4~2μm>大于53μm,而在盐度大于30的近外海站位,该次序发生一些变化:0.4~2μm>10~53μm>2~10μm>大于53μm,最小粒级颗粒组分238U的贡献有所增加,反映了自生铀贡献的加强.九龙江河口区表层水中溶解态(包括低分子量组分和胶体态)的234U/238U)A.R.均大于1,显示出234U过剩的特征,而各粒级颗粒组分中的234U/238U)A.R.则接近于平衡值(1.0).这一现象与陆地岩石风化过程中水体对铀的淋滤释出量及234U的优先浸出有关.对232Th/238U质量比的研究显示,溶解态及其所包括的低分子量组分和胶体态的232Th/238U质量比均小于1,而颗粒态及其所包括的4个粒级组分中的232Th/238U质量比均大于1,反映了向外海输送过程中铀、钍地球化学行为的差异.  相似文献   

18.
测定褐藻羊栖菜中的岩藻聚糖硫酸酯 (F 2 )的中性单糖组成和硫酸基含量 ,发现F 2主要由岩藻糖、半乳糖、葡萄糖、甘露糖和少量的木糖、鼠李糖等组成 ,硫酸基含量为 3 4.6%。采用温和的溶剂法将F 2脱硫 ,比较其脱硫前后硫酸基含量和中性单糖组成的差异 ,其脱硫产物F 2d的硫酸基含量为 5 .6% ,除岩藻糖含量略有降低外 ,其他中性单糖组成相似 ,测定结果表明脱硫基本完全且效果较好。另外 ,本文选用改良的甲基化方法 ,并通过红外光谱扫描验证了甲基化反应完全。对F 2脱硫前后部分甲基化糖醇乙酸酯的GC MS进行分析比较 ,得出F 2的结构信息 ,包括其主链和支链的构成、连接方式和硫酸基取代位置等。  相似文献   

19.
Surface water was collected from the Jiulong Estuary for determination of activity concentrations of uranium isotopes in different size fractions, namely, greater than 53, 10 -53, 2 - 10, 0.4 -2 μm, 10 000 u -0.4 μm and less than 10 000 u fractions by microfihration and cross-flow uhrafiltration technologies. Results indicated that most of the dissolved uranium （ 〈 0.4 μm） exis- ted in the low molecular mass fraction （ 〈 10 000 u）, and the colloidal uranium-238 （10 000 u -0.4 μm） only contributed less than 1% of the dissolved uranium-238. The fractions of colloidal uranium in the dissolved phases decreased with the increasing sa- linity. A positive linear relationship between uranium-238 activities and salinities was observed for the dissolved, colloidal and low molecular mass fractions, indicating a conservative behavior of uranium in the Jiulong Estuary. In the particulate phases （ 〉 0.4 μm）, the partitioning of uranium isotopes among different size fractions was controlled by the partitioning of particle concentrations. In the regions with salinities below 20, the partitioning of uranium-238 among different size fractions was as follows： 10 - 53 μm 〉 2 - 10 μm 〉 0.4 - 2 μm greater than above 53 μm. However, the order at the offshore station with salinities above 30 changed as follows ： 0.4 - 2 μm 〉 10 - 53 μm 〉 2 - 10 μm greater than above 53 μm. The fraction of the 0.4 - 2 μm particles increased at the offshore station, suggesting the increased contribution of the authigenic uranium. The activity ratio of uranium-234 to uranium-238 in the dissolved phases, including the low molecular mass fraction and the colloidal fraction, was larger than unity, showing the occurrence of excess uranium-234. In contrast, the activity ratio of uranium-234 to uranium-238 in all size fractions of the particulate phase was close to the equilibrium value （1.0）. The observed different values of the activity ratio of uranium-234 to uranium-238 in the dissolved phase and the partic  相似文献   

20.
Marine macroalgal sulfated fucose-containing polysaccharides, like fucoidan, have drawn significant attention due to their biotechnological potentials, such as anti-cancer, antioxidant, and anti-cholinesterase activities. The fucoidan derived from brown macroalgae Sargassum angustifolium species (FSA) was investigated for its cytotoxic effects and alterations in cell proliferation, and cell cycle-related gene expression in the present study occurred on NB4 cell line. The results showed that FSA would induce p53, p21, pro-apoptotic genes and increase expression of the p15 gene as a cell arrest marker. Also, FSA inhibited the anti-apoptotic effect of the Bcl-2 gene and decreased dnmt-1 gene expression. FSA significantly exhibited potent 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (p<0.05) with an IC50 value of 0.157 mg/mL and showed moderate anti-acetylcholinesterase activity with an IC50 value of 1.20 μg/mL. These results indicated the potential of FSA for the development of therapeutic or preventive agents of cancer and Alzheimer’s disease mainly through cytotoxic effect and AChE (acetylcholinesterase) inhibition as well as additional antioxidant capacities.  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