首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到19条相似文献,搜索用时 109 毫秒
1.
本文描述了一秋龄性腺成熟中华绒螯蟹(简称河蟹)的外部特征并与一秋龄未成熟及二秋龄成熟河蟹进行比较,同时给出了体重与壳宽的回归方程.保安湖的研究结果表明,对于一秋龄雌蟹,体重大于29.8g(壳宽为4.03cm)全部成熟,而体重小于13.1g(壳宽为3.00cm)均不成熟,体重在13、1-29.8g之间,既有成熟又有未成熟.对于一秋龄雄蟹,体重大于26.0g(壳宽3.91cm),全部成熟,而于12.0g壳宽2.66cm)均未成熟,体重在12.0-26.0g之间,既有成熟者又有未成熟个体.对一秋龄成熟河蟹成熟系数逐月变化的观察表明,在翌年3月份达到峰值,雌蟹为12. 32± 1. 75%,雄蟹为 4. 24± 0. 06%;此后,性腺迅速退化,至翌年七月上旬,卵巢退变成细索状结构.己无完整的卵粒.  相似文献   

2.
目的:探讨双源CT双能量成像技术在肾透明细胞癌和非透明细胞癌鉴别诊断中的应用价值。方法:选取我院2015年4月至2017年3月期间入院就诊,经超声、CT平扫怀疑肾占位性病变患者68例,所有患者均行双源CT扫描。对比分析肾透明细胞癌与非透明细胞癌双源CT成像特征,并比较肾透明细胞癌和非透明细胞癌皮髓期及实质期碘浓度和NIC(标准化碘浓度)、肾透明细胞癌不同病理分级碘浓度和NIC及双源CT双能量成像技术用于肾透明细胞癌和非透明细胞癌鉴别诊断灵敏度和特异度。结果:经手术病理确诊32例肾透明细胞癌和17例非透明细胞癌,经双源CT双能量成像技术扫描,透明细胞癌患者在皮髓期和实质期碘浓度及NIC均较非透明细胞癌患者高,组间统计差异显著(P<0.05);肾透明细胞癌在皮髓期及实质期,低级别(Ⅰ级、Ⅱ级)肾透明细胞癌患者碘含量及NIC均显著高于高级别(Ⅲ级、Ⅳ级)组,组间比较存在显著性差异(P<0.05)。此外,分析双源CT双能量成像技术用于肾透明细胞癌和非透明细胞癌鉴别诊断灵敏度和特异度发现:以实质期NIC界值0.70为标准时,对肾透明细胞癌及非透明细胞癌鉴别诊断的灵敏度(83.67%)和特异度最高(77.55%)。结论:双源CT双能量成像技术可通过将碘定量分析技术区分肾透明细胞癌和非透明细胞癌,且具有较高的灵敏度和特异度,同时还能为肾透明细胞癌病理分级提供依据。  相似文献   

3.
银鱼生产的发展是通过银鱼的引种来实现的,银鱼的引种主要是采取向水体投放受精卵的方式来完成,受精卵又是通过人工繁殖而获得银鱼的人工繁殖不同于常规养殖鱼类,因其一经捕起很快就会死亡而不能进行人工催产因此银鱼人工繁殖的亲本是在银鱼的繁殖季节从天然水体中捕捞而获得,而大量的性成熟好的、可以立即进行人工受精的亲本只能在产卵高峰期才能捕获得到.所以了解并掌握银鱼的性腺发育规律和产卵时期对银鱼的人工繁殖十分重要 1992年4月至1996年5月在湖北省徐家河水库对近太湖新银鱼的性腺发育规律和产卵时期进行了长期的研究,并从1995年5月至1996年4月(银鱼的一生)周年标本中逐月进行了组织切片通过对近太湖新银鱼(Neosalanx pseudotaihuensis)卵细胞的组织学研究表明该鱼为分批产卵类型根据卵巢外部形态和内部组织结构,建议将近太湖新银鱼的卵巢划分为六个阶段;从卵巢每月发育期趋势和卵细胞大小以及卵的成熟度得出近太湖新银鱼的产卵期为3-5月,其中4月中旬至5月中旬为产卵高峰期;根据体长频率分布来看,近太湖新银鱼产完最后一批卵就死亡,因此,它的寿命仅一年从其周年体长和成熟系数分布并结合秋季大捕捞大量样本的检查,得出近太湖新银鱼只有春季产卵群  相似文献   

4.
洪湖日本沼虾的种群繁殖生物学   总被引:6,自引:0,他引:6  
1994年5月至1995年6月对洪湖日本沼虾的种群繁殖生物学进行了研究.洪湖日本沼虾的繁殖期为4月中旬至10月上旬,5月中旬至8月中旬为日本沼虾的繁殖高峰期,其中6月、8月雌虾抱卵率均在70%以上;日本沼虾群体中雄性总是少于雌性,月性比(♀/♂)变化于1.104-5.780之间,3—6月性比逐渐增高,7─10月性比则逐渐降低;在整个繁殖期.4─7月的抱卵虾均为前一年出生的大、中规格的个体,之后当年出生的个体在繁殖群体中逐渐占据优势;春季抱卵虾的绝对繁殖力和相对繁殖力都大于秋季抱卵虾,分别计算了绝对繁殖力、相对繁殖力与体长、体重的函数关系.本文还对日本沼虾群体性比的周年变化及其产卵次数进行了讨论.  相似文献   

5.
基于长江中下游成矿带铜、金矿床地质特征和氢、氧、硫、铅同位素研究,认 为两个系列铜、金矿床是不同动力学背景、不同时代的两个成矿流体系统演化的产物: 层状矿床组成的系列Ⅰ铜、金矿床形成于海西期拉张构造背景下,由热卤水沿同生断裂上升,经海底喷流(气)和热水沉积作用形成;与中酸性岩浆侵入活动有关的系列Ⅱ铜、金矿床形成于燕山期特提斯构造域和古太平洋构造域复合及与之相关联的地幔隆起和地壳减薄等深部过程耦合作用背景下的造山作用挤压-伸展转变期,是岩浆热液与部分大气降水混合形成的热液流体经复杂的水-岩作用和输运-化学耦合过程形成的.叠加 作用是区内大型矿床的重要形成条件.  相似文献   

6.
采用Cloudsat/CPR云雷达,FY2C/TBB亮温,Aura/MLS大气成分等卫星遥感资料,结合ECMWF气象分析资料和HYSPLIT4轨迹模式,研究了2009年6月一次东亚切断低压的暖区深对流和异常副热带锋面的结构和演变.分析表明,由于低压切断前的旧槽背景,在低涡的近成熟期,内部冷、暖锋降水偏弱,边沿的高空副热带锋面异常发展到对流层底部,低空西南暖湿水汽在副热带锋前聚集,形成千公里长的暖区深对流降水带.随着该锋面的快速东移,副热带锋区进入原暖区雨带,锋区热力间接次级环流的强上升支,加强了锋下冷侧(原暖湿区)的深对流,但该锋面阻挡了来自暖侧的水汽补充,降水结束.该异常副热带锋区还发生了强烈的平流层-对流层相互交换,在高空急流出口区的下方,平流层1.5PVU等位涡线向下入侵可达5.5 km(约500 hPa)处,锋下向上的深对流注入可达10 km,在入侵-注入混合区,臭氧和水汽的散点图上出现了二者浓度双高和双低的特殊气团.  相似文献   

7.
以艾比湖流域主要入湖河流为研究对象,在5月(丰水期)和8月(枯水期)分别沿博尔塔拉河(博河)和精河进行采样,采用平行因子模型(PARAFAC)和三维荧光区域积分法对水体三维荧光特性进行研究并对其与水质的关系在枯、丰水期下的变化进行探讨.结果表明①河流DOM在枯水期与丰水期都含有C1(240、425 nm) UVC类腐殖质,C2(225、290 nm)紫外区内络氨酸类有机物,C3(230/280、330 nm)蛋白类有机物,C4(265、260 nm)腐殖质类共4种组分.通过对水体三维荧光进行区域积分可以看出DOM荧光成分的占比在不同时期的变化.博河在枯水期时EEM光谱中的区域Ⅲ富里酸含量低于丰水期,枯水期时区域Ⅱ芳香类蛋白质、区域Ⅳ可溶性微生物代谢物以及区域Ⅴ类腐殖质酸高于丰水期;对于精河来说,区域Ⅱ芳香类蛋白质和区域Ⅳ可溶性微生物代谢物在枯水期的含量高于丰水期,区域Ⅲ富里酸和区域Ⅴ类腐殖质酸的含量枯水期低于丰水期,这表明水体腐质化程度较高.②本研究选取了一些常规的荧光指数来描述枯、丰水期水体的荧光指数特性.经研究发现,精河的荧光指数、自生源指数和腐殖化指数在不同时期的变化幅度较小,而博河的变化幅度较大.③将荧光指数与水质参数进行相关性分析并建模,结果表明枯水期自生源指数(BIX)与化学需氧量呈显著正相关,相关系数R=0.688;丰水期时BIX与铵态氮浓度呈显著负相关,相关系数R=-0.493.通过对比分析艾比湖主要入湖河流的三维荧光光谱特性与水质在枯、丰水期时的关系进一步表明水体中DOM的特性以及在枯、丰水期下的差异,为艾比湖流域的治理改善提供一定的理论支持和参考依据.  相似文献   

8.

本文利用2013年6月至2015年10月北京南苑观象台两年多午后臭氧探空资料,初步分析了北京城区大气混合层内臭氧浓度的垂直分布规律以及典型天气条件下大气边界层臭氧的变化特征.主要结果有:(1)季节平均而言,地表至对流层中部(8 km)的臭氧浓度在夏季最高,冬季最低,相差50~130 μg·m-3,最大差异在边界层.总体而言,对流层臭氧浓度随高度有比较缓慢的增加,但是边界层内臭氧浓度的垂直结构随季节有比较大的差异:夏季混合层中部存在一个臭氧浓度极大值,这与夏季比较强的光化学生成臭氧有关;而在冬季地面臭氧浓度很低,平均值小于40 μg·m-3,说明冬季地面是臭氧很强的汇.(2)臭氧浓度季节内变率的季节差异也十分明显,夏季最大、冬季最小.季节内变率在从边界层向自由对流层过渡区域最小(夏季为24 μg·m-3,冬季仅为10 μg·m-3),在边界层内变率较大,夏季可达64 μg·m-3(冬季为30 μg·m-3),这也说明边界层化学过程明显影响臭氧浓度的变化.(3)我们从所有白天样本中严格筛选了部分混合层样本,并把臭氧浓度在由混合层向自由大气过渡时的垂直分布分成了三类,即臭氧浓度随高度增大(Ⅰ型)、减小(Ⅱ型)以及基本稳定不变(Ⅲ型);臭氧垂直结构类型有明显的季节特征,夏季主要是Ⅱ型,而冬季则以Ⅰ型为主.(4)此外,我们还针对一些典型天气过程(强风、静稳雾天和PM2.5污染)边界层内臭氧的变化特征进行了分析,结果表明:强风切变产生的机械对流引起的充分混合,有利于高层臭氧向低层输送,使得混合层内臭氧浓度的垂直梯度明显减小,同时混合层高度较高,达3 km以上;在高湿度静稳天气控制下,大气混合层较稳定,对北京上空污染物的垂直扩散十分不利:颗粒物浓度升高,削弱到达近地层的太阳辐射,从而降低臭氧的生成效率,混合层内臭氧浓度与混合层厚度都处于较低水平.

  相似文献   

9.
水合物合成及导热系数测定   总被引:6,自引:0,他引:6       下载免费PDF全文
设计了一套实验装置,结合瞬态面热源法来测量混合气水合物导热系数及含混气水合物的沙子多孔介质的有效导热系数.在-10℃~5℃,压力6.6MPa下,含体积比甲烷90.01%,乙烷5.03%,丙烷4.96%的混合气与0.971mol/m3十二烷基磺酸钠水溶液生成的水合物的导热系数约为0.55W/(m·K),并且其值随温度的上升而增高,呈玻璃体导热特性.由于“爬壁”效应的存在,混合气与饱含SDS水溶液的沙子多孔介质反应生成含混合气水合物的沙子多孔介质的有效导热系数(约1.2W/(m·K))显著低于含四氢呋喃水合物的沙子多孔介质的值(约1.9W/(m·K)).虽然本实验使用了SDS来加速和促进水合反应的进行,但是水合物样品中依然存在游离水,因此本研究采用了温度振荡法来进一步促进含SDS水溶液的水合反应进行,研究发现当浴槽温度在-10℃~4℃间周期变化时,游离水在水的相变温度区附近转变为水合物,通过几个周期的温度振荡,样品中的游离水被完全消耗掉.最后通过对含不同浓度SDS的四氢呋喃水合物导热系数测试,讨论了实验中加入SDS对水合物导热系数的影响,结果认为本实验中加入的SDS量对测试结果影响很小(±1.5%).  相似文献   

10.
长江中下游燕山期中酸性-酸性火山-侵入杂岩大家公认为具有偏碱性到碱性特点,但对富碱原因即碱质来石源则存在不同意见,大多数人认为壳幔亮混源,碱质来源于富集地幔的部分熔融,也受到地壳物质的混染.另一种意见强调富碱是由于岩浆侵位或分异过程中受到蒸发岩(特别是膏盐层)的混染与同化。笔者根据长江中下游有关岩体的大量岩石化学分析数据.分地区、分岩体、也按时代对其K2O、Na2O、CaO、MgO与SiO2的相关性作了直观性对比分析,事实表现出Na2O对SiO2几乎完全没有相关性,Na2O对SiO2可以说是独立变化的;K2O与MgO对SiO2具有不同程度的相关性;而CaO-SiO2则具有明显的直线性相关。据此提出:除了原始岩浆具有的碱质外,在岩浆分导过程中不时地有外来碱质加入,这些外来的碱质主要由中、下三叠统中的膏盐层提供。文中根据岩浆硫的δ34S值偏高、膏盐层主要矿物的自由能在高温下熔融及分解温度与低温下在水中的溶解度、石膏矿山的矿泉水中K+、Na+、C1+、SO32-等的浓度,以及斜长石的环带构造方面作了论证.  相似文献   

11.
Effluents from brown coal mines are frequently rich in iron, the water being red-brown in colour and turbid. For several years a fish farm in the Lusatia (Brandenburg, Germany) has used such mine effluents for rearing rainbow trout. The total iron content of this water varies between 5 and 10 mg/l with pH ranging from 6.7 to 7.4. Water turbidity is high with a transparency of 10 to 40 cm at the most due to the substantial ferric hydroxide concentrations. Until 1989 trout have been reared in net cages within concrete settling basins destined for settling the ferric hydroxide mud. The cages were stocked with fingerlings in autumn, reaching portion size in the spring of the following year. Specific growth rate was 0.98% per day, comparable to that of trout in another farm unpolluted by iron but stocked at higher densities. The results show that fingerling rainbow trout may live in water containing more than 5 mg/l total iron but in the absence of Fe2+. These concentrations of water-borne iron seem to have only a limited detrimental effect on fish growth and feed conversion and do not prevent trout culture in principle.  相似文献   

12.
We analyzed Hg, Zn and Cu concentrations in the liver and muscle of tiger sharks (Galeocerdo cuvier) from the coast of Ishigaki Island, Japan. The Hg concentration in the muscle increased proportionally with body length in the tiger sharks, whereas that in the liver increased rapidly after maturity (defined by a length of over 2.7 m). Muscle Hg levels were higher than liver concentrations in immature sharks, with the inverse trend observed in mature sharks. Notably, the Zn and Cu concentrations in the liver tended to decrease with increasing body length. This rapid increase in hepatic Hg concentration concurrent with the onset of maturity in sharks may result from the continuous intake of Hg via food and the slower growth of mature sharks. The high concentrations of the essential metals Zn and Cu in immature sharks may be explained by the physiological demands related to rapid growth.  相似文献   

13.
金刚  李钟杰 《湖泊科学》1999,11(1):52-56
极大螺旋藻藻体SOD聚丙烯酰胺梯度凝胶电泳呈现4条同工酶带,H2O2明显抑制该酶活性,KCN对酶活性无影响,确认为Fe-SOD。经硫酸铵分部盐析,离子交换柱层析及凝胶过滤,纯化到电泳单斑点均一程度。纯化的Fe-SOD分子量为39.3KD,亚基分子量为20KD,金属元素分析表明,每个亚基含0.55个Fe原子。该酶在紫外区最大吸收峰值为275.8nm,该酶氨基酸组成与蓝,绿藻和高等植物的Fe-SOD相  相似文献   

14.
Patterns and levels of chlorinated aromatic contaminants (DDTs, PCBs, non-ortho PCBs and PCDD/Fs) in blubber tissue were compared among six sample groups of male harbour porpoises (Phocoena phocoena) from the Baltic Sea, the Kattegat-Skagerrak Seas and the west coast of Norway. A principal component and classification analysis showed that mature harbour porpoises from the Baltic had significantly different contaminant patterns than animals from the Kattegat-Skagerrak and Norway. ANOVAs showed that mature porpoises from the Baltic had higher levels of ΣPCB and several individual PCBs and PCDD/Fs than the Kattegat-Skagerrak and the Norwegian samples and higher ΣDDT than the Norwegian. A comparison between immature porpoises showed that Baltic animals had higher levels of ΣPCDD/F than the corresponding sample from the Kattegat-Skagerrak. The levels of ΣDDT, ΣPCB and Σnon-ortho PCB were significantly higher in animals collected during 1978–81 compared to animals collected in 1988–90 indicating a temporal decline of these organochlorines in the Kattegat-Skagerrak Seas. The contaminant levels recorded in the Baltic Sea are a serious cause for concern and could have management implications for the already threatened harbour porpoises in this area.  相似文献   

15.
16.
Marine bivalves such as oysters are widely used as bioindicators to monitor marine coastal pollution. This study aimed to use B-esterase activity responses in oysters (Crassostrea gigas) cultured in Ebro Delta bays to monitor environmental effects of pesticides. The B esterases investigated were acetylcholinesterase, propionylcholinesterase, and carboxylesterase and their activities were measured in adductor muscle and gills from oysters transplanted in Ebro Delta bays where the are traditionally grown. Enzyme activities were related with physico-chemical parameters and pesticide levels measured in water. Cholinesterase activities measured in gills were unaffected across sites and periods. Conversely, carboxylesterase activities in oyster gills varied across periods and sites and were negatively correlated with residue levels of organophoshporous and carbamate pesticides in water. Therefore, inhibition of carboxylesterase activities can be considered a good indicator of exposure to anti-cholinergic pesticides in oysters.  相似文献   

17.
Periods of summertime low flows are often critical for fish. This study quantified the impacts of forest clear‐cutting on summertime low flows and fish habitat and how they evolved through time in two snowmelt‐dominant headwater catchments in the southern interior of British Columbia, Canada. A paired‐catchment analysis was applied to July–September water yield, the number of days each year with flow less than 10% of mean annual discharge, and daily streamflow for each calendar day. The postharvest time series were divided into treatment periods of approximately 6–10 years, which were analysed independently to evaluate how the effects of forestry changed through time. An instream flow assessment using a physical habitat simulation‐style approach was used to relate streamflow to the availability of physical habitat for resident rainbow trout. About two decades after the onset of logging and as the extent of logging increased to approximately 50% of the catchments, reductions in daily summertime low flows became more significant for the July–September yield (43%) and for the analysis by calendar day (11–68%). Reductions in summertime low flows were most pronounced in the catchment with the longest postharvest time series. On the basis of the temporal patterns of response, we hypothesize that the delayed reductions in late‐summer flow represent the combined effects of a persistent advance in snowmelt timing in combination with at least a partial recovery of transpiration and interception loss from the regenerating forests. These results indicate that asymptotic hydrological recovery as time progresses following logging is not suitable for understanding the impacts of forest harvesting on summertime low flows. Additionally, these reductions in streamflow corresponded to persistent decreases in modelled fish habitat availability that typically ranged from 20% to 50% during the summer low‐flow period in one of the catchments, suggesting that forest harvest may have substantial delayed effects on rearing salmonids in headwater streams.  相似文献   

18.
Tropical high Andes lakes are aquatic ecosystems with peculiar limnological characteristics that are related to their geographical location and high altitude, yet they remained understudied. We present the results of a standardized survey of morphometric, physico-chemical and biotic variables in 32 high altitude lakes of the Cordillera del Tunari (Eastern Andes of Bolivia). Based on the variables measured, we identified three lake types. One group of lakes differed from the other lakes by a relatively high pH and biological productivity (as evidenced from higher densities of phytoplankton, zooplankton, and fish). A second group of lakes consisted of relatively large and deep water bodies with neutral to slightly acid pH and with a relatively high occurrence of the large cladoceran Daphnia pulex. The third group contained relatively small, shallow, and acid lakes with no Daphnia. Rainbow trout occurred in more than half of the lakes and catch yields were very variable. Overall, the abundances of different organism groups tended to be positively associated (e.g. phytoplankton, copepods, rotifers, fish) indicating the existence of a major productivity gradient. We found no negative associations between trout catches and densities of any of the major zooplankton groups, suggesting moderate to low top-down effects of trout on the zooplankton communities.  相似文献   

19.
Small streams are ecosystems mainly controlled by physical factors. Minor differences in these factors can affect periphyton, which are key functional communities in these ecosystems. Eight different environmental conditions combining two types of current, two flow velocities and two light intensities were produced and controlled in artificial channels. Their impact on young and mature periphyton was investigated during a 6-week exposure period. The two different levels of light intensity produced early effects on the algal community. In young periphyton, the lower level of light intensity enhanced the number of algal cells, and this community appeared to be significantly structured by light. As the periphyton matured, the effects of physical factors became more marked. At this later stage, both the bacterial and algal communities began to be affected. Both function (primary production) and structure began to respond to differences in light and in flow velocity. Small differences in low-level environmental factors, such as light and flow, had an effect both on the structure of periphyton and its functional capacities. Keeping in mind the close link between diversity and function in microbial communities, periphyton confronted to various environmental stresses (pollution, flooding) in the field may behave differently due to minor differences in physical factors.  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