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排序方式: 共有4125条查询结果,搜索用时 15 毫秒
21.
珠江口伶仃洋锋的类别及其对沉积的影响 总被引:1,自引:0,他引:1
根据近年在珠江口伶仃洋的观测资料,对比国外有关河口锋的定义,归纳了伶仃洋内几种锋的现象,计有潮侵锋、岬角锋及湖水退急时的浅滩锋等。解释了锋生的原因与潮汐进退,特别与随潮入侵的咸水关系。文中也探讨了这些锋对沉积环境的影响,认为它是陆架水入侵河口地区的一种不容忽视的沉积动力过程。 相似文献
22.
利用牙鲆鳃细胞系分离和培养淋巴囊肿病毒 总被引:1,自引:4,他引:1
本文利用牙鲆鳃细胞系进行了养殖牙鲆淋巴囊肿病毒的分离及培养 ,并通过电镜对培养细胞中淋巴囊肿病毒的形态及感染循环进行了初步研究。将病鱼的淋巴囊肿组织无菌滤液接种牙鲆细胞系 ,细胞出现了明显的细胞病变 ( Cytopathic effect,CPE)。电镜观察在培养细胞的胞质中有病毒的包涵体 ,胞质中散在 6角形、5角形或圆形的病毒粒子 ,大小为 10 0~ 140 nm之间。在感染细胞的线粒体中也存在大量的病毒颗粒。 相似文献
23.
Many classes of environmental contaminants affect the reproductive function of animals through interactions with the endocrine system. The primary components affected by endocrine active compounds (EACs) are the steroid receptors and the enzymes responsible for steroidogenesis. This study sought to develop an in vitro model for assessing EAC effects in sea turtles by examining their ability to alter cytochrome P450 aromatase (CYP19) activity. Aromatase is the enzyme responsible for the conversion of testosterone to estradiol. This enzyme is critical in the sexual differentiation of reptiles which demonstrate temperature-dependent sex determination. An immortal testis cell line GST-TS from a green sea turtle was grown in culture at 30 degrees C in RPMI 1640 media. The cells were exposed to three known aromatase inducers; dexamethasone (Dex), 8Br-cyclic AMP, or human chronic gonadotropin (HCG) and one aromatase inhibitor 4-androstenol-dione (4-OHA). In addition, the GST-TS cells were exposed to 0.1-30 microM atrazine and 3-100 microM 4,4'-DDE. The inducing compounds that have been shown to increase aromatase activity in other systems failed to induce aromatase activity in the GST-TS cells, yet exposure to the inhibiting compound, 4-OHA, did result in a significant reduction. Atrazine (0.1, 1.0 and 10 microM) significantly induced aromatase activity following a 24 h exposure, and 4,4'-DDE inhibited the activity but only at cytotoxic concentrations (100 microM). Based on these results, this in vitro model can be useful in examining the endocrine effects of EACs in sea turtles. 相似文献
24.
南黄海表层沉积物中氮的区域地球化学特征 总被引:5,自引:0,他引:5
通过分级浸取分离的方法获得了南黄海表层沉积物不同形态的氮,首次探讨其分布的区域性特征:南黄海表层沉积物中各形态氮在不同测线上均呈现出波状分布。B测线的基本上呈现出中部海域高,两边海域低,而西部海域又略高于东部海域的趋势,D和E测线的基本上呈现出西高、东低的趋势,C测线的则呈现出西低、东高的趋势,F测线的变化趋势比较平缓,从整体上看,SOEF—N和TN的分布呈现出西部海区比东部海区低的趋势。受各测线上沉积物种类差异的影响,自北向南各形态氮的变化幅度逐渐减小,其中SOEF-N在各测线上的变化幅度最大,且自北向南降幅最大。受水动力及沉积物粒度的影响,不同形态氮在黄海槽内各站位沉积物中的含量较高。沉积物中各形态氮在不同测线上的分布还表明,陆源输入对南黄海沉积物中氮测线分布有较小的影响,海洋自生氮对南黄海表层沉积物中氮的形态、含量与分布具有重要影响。 相似文献
25.
激光扫描共聚焦显微镜具有成像清晰、获得三维图像、进行多标记观察等优势。本文扼要介绍了激光扫描共聚焦显微镜的原理和特点,着重阐述了激光扫描共聚焦显微镜在海洋动物配子发生;受精过程中细胞内Ca~(2 )变化、肌动蛋白转移和蛋白激酶变化;胚胎和幼体发育的三维成像等研究领域中的应用。并对LSCM在DNA含量、RNA含量等领域的定量、定性前景进行展望。 相似文献
26.
27.
A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined jets without excess streamwise momentum are considered. The numerical results of the Standard two-equation k-ε model show that the turbulent structure can be broadly categorised according to the jet-to-crossflow velocity ratio. For strong to moderate jet discharges, i.e. R> 4, the jet is characterized by a longitudinal transition through a bent-over phase during which the jet becomes almost parallel with the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 20-60. The similarity coefficients are only weakly dependent on R. The cross-section scalar field is kidney-shaped and bifurcated, vvith distinct double concentr 相似文献
28.
虾夷扇贝人工诱导雌核发育精子遗传失活及紫外线照射对精子形态结构影响的研究 总被引:4,自引:1,他引:4
在1698μWcm-2s^-1的紫外线照射强度下,虾夷扇贝雌核单倍体的最佳诱导时间为60s。从早期胚胎存活率可以观察到Hertwig效应的存在。随着照射时间增加,受精率明显下降,而受精卵在到达D形幼虫期之前便停止发育。扫描电镜显示,随着紫外线照射强度的增加。精子顶体和鞭毛结构趋向于受到更大程度的破坏,直到完全失去顶体和鞭毛。并指出这可能是造成受精率降低的主要原因。 相似文献
29.
The northern New England beach wrack community with special reference to the cosmopolitan amphipod crustacean, Orchestia platensis, was examined at estuarine and open coastal habitats. Beach wrack was dominated by the plant genera Ascophyllum, Zostera, Spartina and Chondrus, and was most abundant during spring and late summer. Animal community numbers, biomass and frequency in fresh to moderately decomposed wrack were dominated by O. platensis throughout the year at all habitats; oligochaetes and Collembola were also important. The abundance of O. platensis showed high spatial and temporal variability, with low abundance generally associated with decreased amounts of wrack during colder months. An exception was the winter presence of the species at one estuarine habitat, in patchy aggregations within gravel-cobble refuges. The abundance of O. platensis averaged 1280 (0.04 m2)−1, with a maximum of 7040 (0.04 m2)−1. The life cycle of O. platensis is bivoltine, with summer-hatched young reaching maturity within 1 month. Laboratory studies indicate females with up to 4 broods (30 days)−1, averaging 18 eggs brood−1.Orchestia platensis is omnivorous, eating fresh plant tissue, live oligochaetes, Limulus eggs and diatom ‘fuzz’. The rate of laboratory consumption of algae and Zostera was 0.05 mg plant mg−1 wet body weight day−1. Presumptive predators of O. platensis are juvenile green crab, Carcinus maenus, and the earwig. Anisolabis maritima. The mobility, aggregation and aggressiveness of O. platensis assist the species in establishing and maintaining populations in the rigorous wrack habitat. The general competitive superiority of O. platensis over its congener, O. gammarella, and the co-occurrence of these species on both eastern and western Atlantic shores is discussed. 相似文献
30.
WU Yu-xian 《四川测绘》2008,(6)
通过分析ArcGIS中的ArcMap、ArcCatalog和ArcToolbox的特点,简要讨论了它们在国家1︰50000 DLG更新中的应用。 相似文献