共查询到20条相似文献，搜索用时 31 毫秒
1.
Winfree AT 《Science (New York, N.Y.)》1973,181(4103):937-939
Ferric ions catalyze the oxidation of malonate by bromate in acid solution, sometimes at a spatially uniform, steady rate, but sometimes in a self-regenerating three-dimensional wave which resembles a rotating scroll, often with its axis closed in a ring. In cross section perpendicular to the axis, one sees an involute spiral emerging from a thin cylindrical core. This "dissipative structure" organizes reaction stages periodically in space and time everywhere except along its rotation axis, which may therefore be a thermodynamically unique locus. 相似文献
2.
以新疆某铁矿及其周边区域作为研究对象,运用2007—2016年多时相TM/ETM+、OLI影像,分析铁矿及其周边区域植被覆盖度指数(fractional vegetation cover, FVC)及植被生长状况指数(vegetation condition index, VCI),评价研究区植被覆盖度、植被生长状况时空变化特征及铁矿开采对周边环境的影响,为矿区环境治理提供决策支持。结果表明,FVC及VCI指数能够较好地反映出研究区植被覆盖度及植被生长状况等级不高且铁矿区域几乎无植被生长的实际状况,为研究区生态风险防范提供理论支持。2007—2016年,研究区整体植被覆盖度及植被生长状况呈波动上升趋势,较低植被覆盖度等级和植被生长状况较差等级同时向较好等级发展。FVC及VCI较高等级主要分布在南坡及西南坡。但铁矿面积逐年增大,铁矿开采对其所在区域及周边区域造成了严重的植被退化和生态破坏,极易导致水土流失及山体滑坡等灾害的发生,应及时采取防控措施。 相似文献
3.
Hazen RM 《Science (New York, N.Y.)》1983,219(4588):1065-1067
Unit cell parameters of synthetic zeolite 4A were measured at several pressures to 40 kilobars with both water and an alcohol mixture as hydrostatic pressure media. Compression in water was normal, with no observed phase transitions. Compression in alcohols was twice as great as in water, and three volume discontinuities were observed. These volume changes in alcohol were rapid with increasing pressure but sluggish in reverse. High-pressure "phases," all of which are dimensionally cubic, are progressively more compressible at high pressure. These unusual high-pressure phenomena, which indicate significant interactions between zeolite 4A and the hydrostatic media, are consistent with differences in zeolite adsorption of water alcohols. 相似文献
4.
5.
Ground-based imaging of Jupiter at visible and infrared wavelengths has been used to build up a time sequence of cloud feature variations. The global cloud configuration seen by Voyager 1 appears markedly different than that seen by Pioneer 10 and 11. In the context of historical data, these two different cloud distributions are not unique but part of a continuous spectrum of global variations. The most recent global changes occurred in a pattern which has been a characteristic trend observed many times before. 相似文献
6.
硅酸盐细菌对磷矿石风化作用机理的探讨 总被引：1，自引：0，他引：1
[目的]以1株硅酸盐细菌为例研究微生物对磷矿石的风化作用。[方法]在装有100目磷矿石粉的液体培养基中接种硅酸盐细菌,按不同时间取样处理后,用原子吸收光谱仪测定培养液上清液中Ca2+的质量浓度,磷钼比色法测定水溶性磷(DP)的质量浓度;细菌作用后的残留物用电子探针、透射电镜和能谱仪进行分析。[结果]结果表明,硅酸盐细菌对磷矿石粉风化后,培养液中Ca2+和DP的质量浓度随作用时间延长而增加,细菌作用后的矿粉颗粒浑圆,边缘模糊不清,菌体及有机物对矿物有较强的剥蚀作用。[结论]经分析认为细菌对磷矿石的风化作用源自细菌生长导致的机械破坏作用、胞外分泌物的生化降解作用以及多种因素之间的协同作用。 相似文献
7.
黔东北黑色泥岩盆地中菱锰矿的品位普遍偏低,高品位的块状菱锰矿 在横向 上和垂向上并非稳定存在,弄清菱锰矿的空间分布规律可以为勘探开发提供指导。文章首先 从区域尺度分析了菱锰矿矿床分布与黑色泥岩盆地内部次级洼陷的关系,然后以杨家湾锰矿 床为例,分析了同一次级洼陷内锰品位与含锰岩系厚度和矿层厚度的相关性。最后选取次级 洼陷内的典型探井,从矿石的结构特征和矿物共生组合规律等微观尺度,研究了菱锰矿矿床 的垂向非均质性,探讨了黑色泥岩盆地中菱锰矿富集的控制因素。研究表明,菱锰矿主要赋 存于有机质含量较高的大塘坡组一段底部,锰矿品位与矿层厚度呈正相关,高品位的锰矿主 要为泥晶结构的块状菱锰矿,平面上主要分布于黑色泥岩盆地的次级洼陷沉积中心;锰矿层 在横向上并非稳定的均质沉积,从洼陷中心到洼陷边缘,菱锰矿的品位逐渐降低;锰矿层与 粉砂质泥页岩交互沉积,具有很强的垂向非均质性。 相似文献
8.
针对科技论文中如何正确判断“年”、“天”是否为时间单位的问题, 通过实例对科技论文中如何正确使用时间“年”、“天”进行了详细分析, 指出“年”、“天”用于计量时, 为时间单位, 应用单位符号a、d;而用于表示时序、计数、习惯时间及特定的时间段等情况时, “年”、“天”并不是表达精确的时间长度, 不是时间单位, 不能使用单位符号, 应使用汉字“年”、“天”。 相似文献
9.
10.
11.
利用新育成的大穗型籼二系杂交稻组合光优５８进行了高产栽培示范试验,获得了１０５３０ｋｇ／ｈｍ＾２的高产,比汕优６３增产７．８％,并总结出“前促中控后重”的大穗高产栽培策略和培育多蘖壮秧、增蔸增苗,重视后期管理,以壮秧保大穗,以增蔸增苗来增穗,以加强后期管理来提高结实率和粒重的大穗高产栽培技术。 相似文献
12.
More than 40 base metal porphyry ore deposits in southwestern North America are associated with the Laramide orogeny (about 90 million to 50 million years ago). Rhenium-osmium dates on molybdenite, a rhenium-enriched sulfide common in many of the deposits, reveal that in individual deposits mineralization occurs near the final stages of magmatic activity irrespective of the time of inception, magnitude, or duration of magmatism. Deposits that differ widely in location and in the extent and timing of magmatism have nearly identical ages for mineralization. Rhenium-osmium-ages suggest that mineralization occurred during two distinct intervals from about 74 million to 70 million years ago and from 60 million to 55 million years ago. Most deposits that formed in the oldest interval are within the older Precambrian basement of northwestern Arizona, whereas the younger deposits are restricted to the younger Precambrian basement in southern Arizona and northern Mexico. Synchronous, widespread mineralization indicates that similar crust-mantle interaction occurred on a regional scale for ore deposits once thought to be the product of localized processes. 相似文献
13.
Reduction of permeability in granite at elevated temperatures 总被引：1，自引：0，他引：1
The addition of hydrothermal fluids to heated, intact granite leads to permeability reductions in the temperature range of 300 degrees to 500 degrees C, with the rate of change generally increasing with increasing temperature. The addition of gouge enhances the rate of permeability reduction because of the greater reactivity of the fine material. Flow rate is initially high in a throughgoing fracture but eventually drops to the level of intact granite. These results support the fault-valve model for the development of mesothermal ore deposits, in which seals are formed at the base of the seismogenic zone of high-angle thrust faults. The lower temperature results yield varying estimates of mineral-sealing rates at shallower depths in fault zones, although they generally support the hypothesis that such seals develop in less time than the recurrence interval for moderate to large earthquakes on the San Andreas fault. 相似文献
14.
毛竹枯梢病症状、病原形态与生物学研究 总被引：15，自引：2，他引：13
本文报道毛竹枯梢病的症状发生、病原形态与生物学特性的系统研究。研究结果表明,枝枯、梢枯和株枯是宏观的病状表现形式,微观病症的产生部位具有特殊表现,棘状子实体产生于侵染点节叉处。竹喙球菌子囊壳扁球形,深埋在病组织中,黑色长喙外露,从孔口溢出淡黄色子囊孢子角。分生孢子器扁圆形,大部分外露,顶部涌出黑色分生孢子丝。菌落在PDA加竹杆煮汁培养基生长最好,菌落白色,气生菌丝发达。菌体最适生长温度为25～28℃,最适pH值5—6。子囊孢子萌发与营养关系不密切,萌发具有自身抑制现象。子囊孢子室温干燥贮存15天即丧失萌发力。 相似文献
15.
Kakela PJ 《Science (New York, N.Y.)》1981,212(4491):132-136
Following World War II, Americans feared their iron ore supplies were depleted. The steel industry attempted to increase supplies by exploring foreign countries for new, high-grade hematite ores and experimenting with technology that upgraded low-grade domestic taconite ores into acceptable, but apparently uneconomical, pellets. Government did little at first, but the Korean War renewed fears of domestic resource exhaustion. Congress quickly enacted loan guarantees, rapid tax write-offs, and other tax policies that helped commercialize taconite pellets for national defense. These policies lingered long after the Korean War ended. Other policies bolstering taconite were enacted on the state level well after taconite had replaced hematite as industry's ore of choice. Understanding how government policies helped to develop pelletized lean iron ore may help in thinking about current policy suggestions aimed at easing our energy crisis or other mineral shortages. For taconite, too much government help came too late. 相似文献
16.
17.
采用盆栽试验方法,研究了不同培养基质条件(10cm土5cm尾矿、8cm土7cm尾矿、5cm土10cm尾矿)下,接种丛枝菌根真菌和不接种丛枝菌根真菌(对照)两种处理对玉米生物量及植株中营养元素吸收的影响。结果表明,无论接种与否,植株的生物量都随覆土厚度增大而增大;与非菌根植物相比,接种菌根真菌的植株可以吸收更多的营养元素,而向地上部运移的Na较少,抑制了植株积累过量的Na盐;地上部Zn和Cu的含量受接种菌根的影响不大,而接种菌根降低了地上部Mn的含量。植株生物量及其植株体内的营养元素含量,接种菌根真菌后,覆土少的(覆5cm厚的土壤于10cm厚的尾矿上)相应高于不接种且覆土厚(覆10cm厚的土壤于5cm厚的尾矿上)的,说明接种菌根可以抵消由于覆土少而导致的植株生物量降低,并且对尾矿充填复垦土壤的植被重建具有重要作用。 相似文献
18.
Neurons in rhesus monkey visual cortex: systematic relation between time of origin and eventual disposition 总被引：36，自引：0，他引：36
P Rakic 《Science (New York, N.Y.)》1974,183(123):425-427
Autoradiographic evidence after injection of tritiated thymidine indicates that cell position in the laminae of the monkey visual cortex is systematically related to time of cell orgin. The earliest-formed neurons, destined for the deepest stratum, arise at about embryonic day 45, and the last ones, destined for the outermost cell stratum, form at about day 102; cells of intervening layers are generated at intervening times. No neocortical neurons are produced in the last two prenatal months or after birth. Compared to cortical neurons in rodents, those in the monkey arise earlier, and the "inside-out" relation of cell position to time of origin is more rigid. 相似文献
19.
Precipitation of sulfide ores and organic matter: sulfate reactions at pine point, Canada 总被引：1，自引：0，他引：1
Bitumen is a common associate of carbonate-hosted lead-zinc deposits. On the Pine Point lead-zinc property, Northwest Territories, Canada, there are two forms of bitumen. Unaltered bitumens have atomic hydrogen/carbon ratios of about 1.4, sulfur contents of about 7.8 percent, and sulfur isotope ratios ( section sign(34)S) of approximately +4.6 per mil. Altered bitumens occur in proximity to sulfide ore bodies and white sparry dolomite. Their hydrogen/carbon ratios are about 1.02, the sulfur contents average 22 percent, and the section sign(34)S values are about +12.4 per mil. These data indicate that some bitumen has participated in the thermochemical reduction of sulfate to produce hydrogen sulfide required to precipitate the ores. Mass balance considerations show that the amount and degree of alteration of bitumen is more than adequate to account for the reduced sulfur species (lead, zinc, and iron sulfides) deposited at Pine Point. These reactions may provide an important means of generating the large volumes of sulfide necessary to precipitate ore bodies in carbonate rocks. 相似文献
20.
屠乃美 《湖南农业大学学报(自然科学版)》1989,(4)
本研究结果表明:水稻光周期诱导质变在主茎与分蘖间及分蘖之间均不能够互相传导;造成两段抽穗现象的原因,初步认为是由两批穗的穗分化始期的差异所致,而与幼穗分化进度无关。 相似文献