Evidence for late tertiary volcanic activity in the northern black hills, South dakota

Rhyolitic volcanic rock in the northern Black Hills has a potassium-argon isotopic age of 10.5 +/- 1.5 million years. This is considerably younger than any previously reported igneous activity in this or adjacent areas and indicates that the renewed uplift of the Black Hills, which occurred after the Oligocene epoch, was also accompanied by some volcanism.     

福建中、晚稻主栽品种(组合)抗瘟性研究

对福建省２３个中、晚稻主栽品种进行了两年苗期人工接种在病区４个鉴定点采取田间自然艉发对叶瘟和惠颈瘟的鉴定,综合评定为中抗以上的品种有荆糯６号、汕优１０号、特优６８９、汕优７０、特优７０、汕优明８６等６个品种;根据抗谱分析,汕优１０号抗性最强、抗谱最广,其次为荆糯６号、特优６８９,后３个品种抗性较弱,抗谱较窄。文中对２ａ抗性鉴定不一致的品种以发病重的一年代表该品种的抗性作了论证;分析了２ａ抽穗期降雨     

The acraman impact structure: source of ejecta in late precambrian shales, South australia

A major probable impact structure occurs in middle Proterozoic dacitic volcanics in the Gawler Ranges, central South Australia. The structure has an inner depressed area about 30 kilometers in diameter that contains the Lake Acraman salina, an intermediate depression or ring about 90 kilometers in diameter, and a possible outer ring approximately 160 kilometers in diameter. Outcrops of dacite in Lake Acraman are intensely shattered and contain shatter cones and multiple sets of shock lamellac in quartz grains. The Acraman structure is the largest probable impact structure known in Australia and is the likely source of dacitic ejecta found in late Precambrian marine shales some 300 kilometers to the east.     

Multiple microtektite horizons in upper eocene marine sediments: no evidence for mass extinctions

Microtektites have been recovered from three horizons in eight middle Eocene to middle Oligocene marine sediment sequences. Five of these occurrences are coeval and of latest Eocene age (37.5 to 38.0 million years ago); three are coeval and of early late Eocene age (38.5 to 39.5 million years ago); and three are of middle Oligocene age (31 to 32 million years ago). In addition, rare probable microtektites have been found in sediments with ages of about 36.0 to 36.5 million years. The microtektite horizon at 37.5 to 38.0 million years can be correlated with the North American tektite-strewn field, which has a fission track age (minimum) of 34 to 35 million years and a paleomagnetic age of 37.5 to 38.0 million years. There is no evidence for mass faunal extinctions at any of the microtektite horizons. Many of the distinct faunal changes that occurred in the middle Eocene to middle Oligocene can be related to the formation of the Antarctic ice sheet and the associated cooling phenomena and intensification of bottom currents that led to large-scale dissolution of calcium carbonate and erosion, which created areally extensive hiatuses in the deep-sea sediment records. The occurrence of microtektite horizons of several ages and the lack of evidence for faunal extinctions suggest that the effects of extraterrestrial bolide impacts may be unimportant in the biologic realm during middle Eocene to middle Oligocene time.     

Isotopic paleoceanography of the Caribbean and East pacific: role of panama uplift in late neogene time

Comparisons of carbon isotopic data on benthic foraminifera from Deep Sea Drilling Project sites 502 (western Caribbean) and 503 (eastern Pacific) indicate that the difference between the Atlantic and the Pacific in the per mil enrichment in carbon-13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago, when the difference reached the modern level (1 per mil). Comparisons of planktonic foraminiferal oxygen isotopic data for the Caribbean and the Pacific suggest that the salinity of Caribbean surface waters began increasing 4 million years ago, possibly in response to shoaling of the Panama isthmus. These results suggest that modern circulation patterns in the Caribbean and eastern Pacific developed by 3 million years ago in concert with changing tectonic, climatic, and biogeographic patterns.     

鲁中地区登海超试一号适宜收获期研究初报

选用近几年在鲁中地区表现突出的玉米高产品种登海超试一号,6月9日播种,安排6个收获期,完全随机区组设计,通过比较它们的百粒重和单产,得出登海超试一号玉米适宜收获期在10月1日前后。     

中、晚粳稻区白背飞虱为害损失及其防治指标研究

为明确五（２）代白背飞虱对粳稻的为害损失,确定合理的防治指标, 作者于１９９６～１９９７ 年在中、晚粳水稻品种武育粳 ３ 号和 Ｓｏ１５ 上,通过接虫笼罩法结合小区、大田试验,研究不同虫量对水稻产量的影响以及五（２）代白背飞虱的增殖规律、为害损失和防治指标⒚结果表明,中、晚粳稻不同生育期,不同虫口密度的白背飞虱的增长速度不一样⒚同一生育期,低密度的增殖速度要大于高密度,但总虫量高密度处理显著高于低密度区⒚五（２）代白背飞虱百丛虫量与水稻产量损失呈极显著正相关⒚因此,当五（２）代白背飞虱早发或中等以上发生时,必须用药防治⒚控制其危害,防治指标为 １８０～２５０ 头⒚     

Single-grain 40Ar-39Ar ages of glauconies: implications for the geologic time scale and global sea level variations

The mineral series glaucony supplies 40% of the absolute-age database for the geologic time scale of the last 250 million years. However, glauconies have long been suspected of giving young potassium-argon ages on bulk samples. Laser-probe argon-argon dating shows that glaucony populations comprise grains with a wide range of ages, suggesting a period of genesis several times longer ( approximately 5 million years) than previously thought. An estimate of the age of their enclosing sediments (and therefore of time scale boundaries) is given by the oldest nonrelict grains in the glaucony populations, whereas the formation times of the younger grains appear to be modulated by global sea level.     

Autoradiography: technique for drastic reduction of exposure time to alpha particles

High-speed, gross, alpha autoradiographs can be made if silver-activated zinc sulfide is used as an intensifier in conjunction with high-speed film. The intensifier is interposed between the sample and film. This technique requires about 1/1000 of the exposure time required with Kodak NTB plates. The gross autoradiographs have greater contrast but slightly less resolution than conventional plates.     

家庭生命周期对农户规模经营意愿的影响分析——基于长江中游三省稻农的调查与分析

借鉴家庭生命周期理论,利用长江中游地区3省711个样本农户家庭的数据,揭示家庭生命周期对农户规模经营意愿的影响机制。研究发现:1)相比于空巢期家庭,处于其他生命周期阶段的农户家庭愿意进行规模经营的可能性更高;2)户主个人特征年龄、文化程度、健康状况,农户家庭特征户主是否外出就业、人均耕地面积,外在环境特征山地丘陵地形、农地块均面积、种粮政策支持感知、农村道路交通设施满意度是影响农户规模经营意愿的关键因素;3)不同家庭生命周期阶段农户规模经营意愿影响因素存在显著差异。有鉴于此,本研究认为对于空巢期阶段家庭,政府应该给予养老政策支持,鼓励其转出土地。处于抚养期和稳定期阶段农户家庭具备较强的人力资源禀赋与意愿成为适度规模经营主体,政府应加大对这些农户农业生产经营能力培训与政策支持力度。进一步改善农业生产外在环境条件,提高农户生产积极性与规模经营意愿。     

长江中游早灿代二晚抗灾补种的生理特性与配套技术

论述了早籼代二晚抗灾补种稳产高产生理特性及其控制的技术指标，并提出了选用高产、优质、抗病、生育期适宜的品种，育秧与直播相结合，秧龄15－18d，7月25日以前插秧，合理密植等配套栽培技术。     

慢性镉暴露对小鼠血常规的影响

本试验探究了慢性镉暴露对小鼠血常规的影响。结果表明,与正常小鼠比较,镉中、高剂量组淋巴细胞值增高,中剂量组增高具有统计学意义(P0.05);高剂量组红细胞体积分布宽度与红细胞平均体积较正常组显著性降低(P0.05);高剂量镉暴露降低了血小板计数、血小板比容。因此,在长期低浓度镉暴露下,红细胞比容和淋巴细胞计数可有潜力成为镉毒性的早期预警指标,外周血淋巴细胞比其他血液指标更敏感。     

Spatiotemporal self-organization in a surface reaction: from the atomic to the mesoscopic scale

Scanning tunneling microscopy data revealed the atomic processes in propagating reaction fronts that occur in the catalytic oxidation of hydrogen on Pt(111). The fronts were also characterized on mesoscopic length scales with respect to their velocity and width. Simulations on the basis of a reaction-diffusion model reproduce the experimental findings qualitatively well. The quantitative comparison reveals the limitations of this traditional approach to modeling spatiotemporal pattern formation in nonlinear dynamics.     

长江中游早籼代二晚抗灾补种的生理特性与配套技术

论述了早籼代二晚抗灾补种稳产高产生理特性及其控制的技术指标 ,并提出了选用高产、优质、抗病、生育期适宜的品种 ,育秧与直播相结合 ,秧龄 15～ 18d ,7月 2 5日以前插秧 ,合理密植等配套栽培技术     

适宜华南地区园林种植观花树木资源的调查

据不完全统计,华南地区有显著观花特色的树种共有60科168属315种.对这些观花树种的形态、花色、花期、园林应用频率等方面进行了分类,并重点介绍几种值得推广的观花树种,为华南地区园林设计观花树种的选择提供资料.     

From signals to patterns: space, time, and mathematics in developmental biology

We now have a wealth of information about the molecular signals that act on cells in embryos, but how do the control systems based on these signals generate pattern and govern the timing of developmental events? Here, I discuss four examples to show how mathematical modeling and quantitative experimentation can give some useful answers. The examples concern the Bicoid gradient in the early Drosophila embryo, the dorsoventral patterning of a frog embryo by bone morphogenetic protein signals, the auxin-mediated patterning of plant meristems, and the Notch-dependent somite segmentation clock.     

From sharecropping to crop-rent: women farmers changing agricultural production relations in rural South Asia

This paper explores changing production relations in agriculture in context of increasingly widespread and longer-duration male outmigration, as against previous, short-duration and seasonal migration. It investigates how de facto women-heads of households (WHHs) are changing a resilient crop-sharing system in absence of adequate access to productive assets, formal training or experience in farming, and while contributing labour to farming and coping with gendered demands on their time. Based on qualitative inquiry in one of the poorest parts of South Asia, the Eastern Gangetic Plains, the paper shows that a section of WHHs are replacing sharecropping arrangements with fixed-value rental arrangements that resemble commercial contracts. The paper ends with a discussion on the implications of this emerging development.     

Radiohalos in coalified wood: new evidence relating to the time of uranium introduction and coalification

The discovery of embryonic halos around uranium-rich sites that exhibit very high (238)U/(206)Pb ratios suggests that uranium introduction may have occurred far more recently than previously supposed. The discovery of (210)Po halos derived from uranium daughters, some elliptical in shape, further suggests that uranium-daughter infiltration occurred prior to coalification when the radionuclide transport rate was relatively high and the matrix still plastically deformable.     

河北省肉牛“北繁南育”生产模式的建立

采用对比试验及典型调查试验的方法,对河北省肉牛养殖结构的区域化进行了研究。结果表明：河北省北部丰宁、隆化和南部的临漳、大厂母牛每产一头犊牛的成本分别为５２２．４９,４９３．０６和８６８．７０,１１７６．７２元。在北部以放牧为主的饲养条件和南部放牧加补饲的条件下,１２月龄犊牛体重分别为２３０ｋｇ以下和２８０ｋｇ以上,存在显著差异。在两种气候条件下,舍饲育肥均可达到较快增重。６,１８,３０月龄牛调至农