岳西县改造中低产田初步尝试     

管叔其  张祎  查旵松  刘中柱 《山地学报》1993,(3)

岳西是典型的贫困山区县,由于低产土壤分布广,自然灾害频繁,物化投入少等原因导致粮食生产水平低,广大群众没有摆脱贫困。通过耕作制度改革,优化种植结构等措施,已取得显著效果。对于山区低温冷害类型和生理机制等方面研究,也取得较大进展,同时也闯出一条具有山区特色发展高效农业的路子。  相似文献   

Wind-determined sediment distribution and Holocene sediment yield in a small,Danish, kettle lake     

Bent Vad Odgaard 《Journal of Paleolimnology》1993,8(1):3-13

Sediment distribution was mapped by multiple corings in a small oligotrophic lake in northwestern Denmark. Sediment cores along a representative West-East transect were dated by ¹⁴C and correlated using pollen, mineral magnetics and general lithology. Estimates of whole-lake Holocene sediment accumulation were used to calculate sediment yield (terrestrial erosion). Results indicate that: 1) sediment yield was low 10000–5000 BP and increased strongly 5000–2500 BP and again 2500–1200 BP, 2) sediment focusing and waves and currents induced by strong winds were the major processes controlling sediment distribution throughout the Holocene; 3) the dominant wind direction of strong winds has been westerly throughout the Holocene; and 4) the lake was probably more productive in the last 5000 years than in the period from 10000 to 5000 BP.  相似文献   

几种屈服函数的比较   总被引：5，自引：0，他引：5  

沈珠江 《岩土力学》1993,14(1):41-50

应用等向压缩试验和三轴剪切试验2种参数测定方法和5种屈服函数计算了单向压缩、单剪和软土地基固结变形3个算例。计算结果表明,计算参数定义方法影响最大,屈服函数的影响比较次要,而且在π平面上选用较复杂的函数未必比简单的圆形函数更好。  相似文献   

Sediment yield and delivery in the blanket peat moorlands of the southern Pennines     

J. C. Labadz  T. P. Burt  A. W. R. Potter 《地球表面变化过程与地形》1991,16(3):255-271

In contrast to much previous research on blanket peat moorland, which has concentrated upon studies of the form and causes of gully erosion, this paper attempts to investigate sediment transport and to estimate both short-term and long-term sediment yields in such terrain. The research was conducted on Wessenden Head Moor to the west of Huddersfield, Yorkshire, where automatic stream sampling continued over a period of two years. Use of corrected rating curves (Ferguson, 1988) provided a mean estimate of sediment yield over this period of 55 t km^?2 yr^?1. In addition an estimate of longer-term sediment yield was derived from four reservoir sediment surveys in the Wessenden Valley. Total yield was 203.69 t km^?2 yr^?1, including an organic fraction of 38.82 t km ^?2 yr^?1. Stream sampling at three sites on Shiny Brook, including headwaters and the outflow to the reservoir, suggested that there is great temporal and spatial variability in mineral and organic inputs to the reservoirs. Although not excessive in gravimetric terms, the low density of peat means that there is a serious erosion problem. Estimates of erosion rates for the peat gully network at Shiny Brook appear to confirm earlier evidence concerning the relatively recent occurrence of this erosion, within the last two centuries.  相似文献   

EFFECT　OF　FINE　PARTICLES　ON　THE　VERTICAL　CONCENTRATION　DISTRIBUTION　AND　TRANSPORT　RATE　OF　COARSE　PARTICLES     

WAN Zhaohui  SONG Tiancheng 《国际泥沙研究》1994,(1)

ＥＦＦＥＣＴＯＦＦＩＮＥＰＡＲＴＩＣＬＥＳＯＮＴＨＥＶＥＲＴＩＣＡＬＣＯＮＣＥＮＴＲＡＴＩＯＮＤＩＳＴＲＩＢＵＴＩＯＮＡＮＤＴＲＡＮＳＰＯＲＴＲＡＴＥＯＦＣＯＡＲＳＥＰＡＲＴＩＣＬＥＳＷＡＮＺｈａｏｈｕｉ；ＳＯＮＧＴｉａｎｃｈｅｎｇＡｂｓｔｒａｃｔ：...  相似文献   

常用流域水文模型若干问题探讨   总被引：5，自引：0，他引：5       下载免费PDF全文

张国祥 《水科学进展》1994,5(3):248-253

简要介绍了三个国内常用的水文模型,探讨了这三个模型中的蒸发、下渗、产汇流机制,并剖析了模型中存在的问题.  相似文献   

Seismic yield determination of Soviet underground nuclear explosions at the Shagan River test site   总被引：4，自引：0，他引：4  

Frode Ringdal  Peter D. Marshall  Ralph W. Alewine 《Geophysical Journal International》1992,109(1):65-77

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Observations of teleseismicP wave coda for underground explosions     

Christopher S. Lynnes  Thorne Lay 《Pure and Applied Geophysics》1988,128(1-2):231-249

The earlyP wave coda (5–15 sec after the first arrival) of underground explosions at the Nevada Test Site is studied in the time domain using 2082 teleseismic short-period recordings, with the intent of identifying near-source contributions to the signals in the frequency range 0.2–2.0 Hz. Smaller magnitude events tend to have relatively high coda levels in the 0.4–0.8 Hz frequency band for both Yucca Flat and Pahute Mesa explosions. Coda complexity in this low-frequency passband is negatively correlated with burial depth for Pahute Mesa events but is only weakly correlated with depth for Yucca Flat events. Enhanced excitation of relatively long-period scattered waves for smaller, less deeply buried events is required to explain this behavior. Coda complexity in the 0.8–1.1 Hz band is positively correlated with magnitude and depth for Pahute Mesa events, but has no such dependence for Yucca Flat events. This may result from systematic variations between the spectra of direct signals and coda arrivals caused bypP interference for the largest events, all of which were detonated at Pahute Mesa. Another possible explanation is a frequency-dependent propagation effect on the direct signals of the larger events, most of which were located in the center of the mesa overlying strong lateral velocity gradients in the crust and upper mantle. Event average complexity varies spatially for both test sites, particularly in the 0.8–1.1 Hz band, providing evidence for frequency-dependent focussing or scattering by near-source structure. Both the direct arrivals and the early coda have strong azimuthal amplitude patterns that are produced by defocussing by mantle heterogeneity. The direct arrivals have stronger coherent azimuthal patterns than the early coda for Pahute Mesa events, indicating more pronounced deep crustal and shallow mantle defocussing for the direct signals. However, for Yucca Flat events the direct arrivals have less coherent azimuthal patterns than the coda, suggesting that a highly variable component of near-source scattering preferentially affecting the downgoing energy is superimposed on a pattern produced by mantle heterogeneity that affects the entire signal. This complicated behavior of the direct arrivals may be the result of triplications and caustics produced by the complex basement structure known to underlie the Yucca Flat test site. The presence of strong azimuthal patterns in the early coda indicates that source strength estimates based on early coda are subject to biases similar to those affecting estimates based on direct arrivals.  相似文献   

Improvements in resource recovery at Stauffer's Big Island Mine     

J. F. T. Agapito  R. V. Hunter 《Geotechnical and Geological Engineering》1988,6(3):195-214

Summary Significant increases in extraction ratio on the order of 6 to 8%, equivalent to as much as 142 t/m of panel advance, have occurred at the Big Island Mine during the last five years with the help of a practical rock mechanics program. This increase in resource recovery has also contributed to improvements in productivity. Both conventional and continuous machine mining have been used to mine two flat-laying trona beds at depths of 250 and 260 m in the Green River Formation in southwestern Wyoming.Conventional room and pillar mining originally was conducted in panels with extraction ratios of 58 to 60%. The use of yield pillars has allowed the panel extraction to increase to 66%. Continuous machine mining was introduced recently, with a 64% extraction ratio using long, narrow pillars and wide rooms. Further improvements in resource recovery seem feasible in the light of present mining experience.The rock mechanics program consisted of field instrumentation to determine the pillar and roof response to mining, and computer modelling to evaluate and help determine the stability of various layouts, which were then adopted for mining.  相似文献   

多情景土壤水分胁迫对固城夏玉米产量的定量影响评估     

谭方颖  李昊  王建林  宋迎波  谭凯炎  任三学 《气象科技》2020,48(4):600-606

基于河北省固城生态与农业气象试验站2013—2015年夏玉米田间水分控制试验资料,分多情景模拟自然环境,研究了水分充足条件下夏玉米穗粒重随发育进程(DVS)的变化特征,对比分析了不同持续时间、不同发育阶段、不同程度水分胁迫对产量的影响,并建立了不同情景水分胁迫下土壤相对湿度与产量的定量关系模型。结果表明,在水分充足条件下,夏玉米穗粒重随DVS的增加呈现"慢—快—慢"的增长特征,其中乳熟—乳熟后10d的增长幅度和增长速率均为最大;水分胁迫发生在抽雄后10d—乳熟阶段,粒重减少最明显。夏玉米产量与出苗—拔节(阶段Ⅰ)、拔节—抽雄(阶段Ⅱ)、抽雄—成熟(阶段Ⅲ)以及[阶段Ⅰ+阶段Ⅱ]和[阶段Ⅱ+阶段Ⅲ]5个不同时段土壤相对湿度均呈线性显著正相关关系,其关系模型表明,水分胁迫程度越严重、持续时间越长,产量减少幅度越大,不同阶段、相同胁迫程度和持续时间对产量的影响总体表现为:阶段Ⅰ阶段Ⅱ阶段Ⅲ[阶段Ⅰ+阶段Ⅱ][阶段Ⅱ+阶段Ⅲ],以上阶段土壤相对湿度下降10%,产量分别减少89.7g/m2、122.7g/m2、129.8g/m2、133.7g/m2和144.4g/m2,减幅为22.8%～36.8%。  相似文献