共查询到18条相似文献，搜索用时 421 毫秒
1.
对雷州半岛旱地蔗田杂草进行２ａ的调查,结果表明,全年共有１８科４８种杂草相继发生为害,以禾本科、菊科、莎草科和苋科为主,并经过杂草防除分析了除草剂的使用方法。 相似文献
2.
毒草型退化草地具有群落演替特点,通过高光谱遥感技术反演毒杂草分布与退化草地群落结构能对该类退化草地进行有效监测,而光谱特征分析是毒杂草与优良牧草遥感识别的基础。本文选取了三江源区毒草型退化草地的8种典型毒杂草和4种优良牧草的地面实测高光谱数据作为研究样本,经过SG平滑、包络线去除、导数变换和光谱参量化对毒杂草种和优良牧草种的光谱特征进行了分析,并通过马氏距离法提取其特征识别波段。结果表明：① 8种典型毒杂草和4种优良牧草的 “近红外峰值”差异较大,其中鹅绒萎陵菜的“近红外峰值”达到60.07%,而最小者早熟禾仅为17.53%;② 经包络线去除处理后,植被光谱曲线中吸收谷和反射峰光谱差异更加明显,且可减少环境背景对植被光谱的影响,如沼泽草甸的鹅绒委陵菜和驴蹄草,其“绿峰幅值”分别为6.46%和6.89%,经处理后其“绿峰指数”分别为0.2866和0.3671,而在2种环境下生长的同一草种（狼毒草1和狼毒草2）的峰谷特征差异不明显;③ 基于马氏距离法提取的毒杂草与优良牧草的敏感识别波段主要分布在680~750 nm和900~1000 nm波长范围内,以醉马草与矮嵩草为例,其基于反射率的敏感识别波段为713.1~737.1 nm和934.6~965.6 nm。该研究可为利用高光谱遥感进行大面积毒杂草草种识别和植被群落生长监测提供重要科学依据,对于三江源区毒杂草的监测防治和畜牧业的可持续发展具有重要意义。 相似文献
3.
4.
5种除草剂对白鲢鱼种急性毒性试验 总被引：1，自引：0，他引：1
以白鲢(Hypophthalmicthysmolitris)为实验材料,研究常用除草剂对鱼类的毒性效应。结果表明:采用直线回归法求得的96hLC50值分别为:2,4_D丁酯0.185mg/L,可信限0.138~0.247mg/L;丁草胺0.080mg/L,可信限0.067~0.097mg/L;使它隆3.80mg/L,可信限2.68~5.40mg/L;艾割18.60mg/L,可信限14.80~23.32mg/L;嗪草酮108.80mg/L,可信限91.46~129.72mg/L。对鱼类安全浓度分别为0.019mg/L,0.38mg/L,0.008mg/L,1.86mg/Land10.88mg/L。 相似文献
5.
5种除草剂对白鲢鱼种急性毒性试验 总被引：1，自引：0，他引：1
以白鲢（Hypophthalmicthys molitris）为实验材料，研究常用除草剂对鱼类的毒性效应。结果表明：采用直线回归法求得的96h LC50值分别为：2，4-D丁酯0．185mg/L，可信限0．138～0．247mg／L；丁草胺0．080mg/L，可信限0．067～0．097mg/L；使它隆3．80mg/L，可信限2．68—5．40mg／L；艾割18．60mg／L，可信限14．80～23．32mg/L；嗪草酮108．80mg/L，可信限91．46～129．72mg／L。对鱼类安全浓度分别为0．019mg／L，0．38mg／L，0.008mg／L，1.86mg／L and 10．88mg／L。 相似文献
6.
7.
“远看像个村，进去不是村。荒坑汇污流，荒地杂草生。蚊蝇嗡嗡叫，耗子满地跑”。这是临颖县当地农民对一些荒芜、苍凉“空心村”现状自编的顺口溜。 相似文献
8.
植被覆盖度是生态环境变化的重要指标,也是遥感反演的关键参数。盐碱地植被覆盖度的准确测量对研究地表植被蒸腾、土壤水分蒸发及土壤退化、盐碱化等具有重要意义。过绿指数(Excess Green index,ExG)对绿色植被比较敏感,能突显植被信息,去除土壤、阴影的干扰。通过对吉林西部盐碱地玉米、高粱、绿豆、杂草、土壤数字图像特征分析,利用改进过绿指数(Modified Excess Green index,MExG)算法计算植被和土壤的MExG值;并确定区分植被和土壤的MExG阈值为40,进而计算植被覆盖度。本文采用监督分类的最大似然法对比验证MExG自动提取结果,并对两种方法计算的玉米、高粱、绿豆和杂草的覆盖度,分别进行目视判读和t检验。研究表明,MExG自动提取方法具有客观性强,处理时间短,分类精度高等优点,是计算不同植被类型覆盖度的有效方法。 相似文献
9.
10.
孙红玲 《资源导刊(河南)》2007,(12)
"乱石滩,杂草积水漫河畔.漫河畔,洛水潺潺,怎灌新田?炎夏机声隆隆忙,敢叫滩地变良田.变良田,秋透新叶,民露笑颜."这首《忆秦娥·记鱼泉开发》是宜阳县柳泉镇鱼泉村土地开发项目的真实写照. 相似文献
11.
邓遂 《广东海洋大学学报》2013,(5):16-21
临海社会转型性家庭贫困现象在临海社会转型过程中出现,主要表现为因海洋资源枯竭及海洋市场洗牌所导致的家庭贫困、因临海经济开发而衍生的家庭贫困等类型。临海社会转型性家庭贫困是临海家庭的社会适应能力与临海社会急剧变迁之间的矛盾产物,富有浓郁的社会公平性问题色彩,它制约了临海社会的顺利转型。在消除临海社会转型性家庭贫困生成的某些宏观社会原因的前提下,发展临海地区文化教育与职业教育,进而提高临海家庭社会适应能力,是消除临海社会转型性家庭贫困现象的关键。 相似文献
12.
为了研究寻找一般平衡问题的公共解集中共有元素的迭代方法,及无穷非扩张映像族的不动点问题.通过在Hilbert空间中构造非扩张序列Ti得出了一种关于Wn算子的新黏性逼近迭代算法,在一定条件下,得出了其强收敛定理. 相似文献
13.
华夏家谱GIS的数据组织与系统架构 总被引：1，自引：0，他引：1
华夏文明源远流长,家谱、正史与方志共同构成了中华文明史的三个重要成分,其中,家谱以家族中的个人信息为基本记录单元,以人与人之间的关系为框架,形成了富有中国特色的对家族从空间分布到时间演化的完整描述体系,家谱资料的蕴含信息和记录粒度是其他历史资料所不能比拟的。家谱GIS扩展了现有家谱信息描述的概念,通过强化其中蕴含的空间信息,以家族谱系为基础,在空间信息技术的支持下,重构个人的空间活动,重现一个家族的兴衰、繁衍与变迁,实现从宏观到微观角度家族历史的全面地反映。本文分析了家谱与GIS的关系,提出了家谱GIS构建所必须的统一的历史地理时空描述框架;在此基础上分析了家谱中信息的组织模式,设计了的家谱的核心数据模型;在Web2.0理念下,以公众参与的开放式系统构建为基础,设计了家谱GIS的系统架构并进行了系统实现。 相似文献
14.
15.
应用正规族理论及Zalcman引理,推广了Yuntong Li和Yongxing Gu一个亚纯函数正规性的定理,得到了下面的定理,即：设罗为复平面上一区域D上的亚纯函数族,k,n≥k＋2为正整数,a为非零有穷复数,L（f^n）的表达式为a0（f^n）^k）＋a1（f^n）^（k-1）＋…＋ak（fn）,其中a0≠0,a1,…,ak为复数,对任意的f,g∈F,L（fn）,L（gn）在D内分担a,则矿在D上正规． 相似文献
16.
Kesang Wangchuk 《山地科学学报》2016,13(3):455-464
This study was carried out to investigate if on-farm cut vs. grazed pastures differed in soil fertility and species density in the temperate Himalayan highlands. Soil fertility and species relative density were measured from 30 cut and 30 grazed dairy pastures. In both types of pasture, soil pH, available phosphorus (P) and exchangeable potassium (K) were negatively correlated with pasture age and slope. In cut pasture, cocksfoot (Dactylis glomerata) and pasture age were positively correlated, whereas in grazed pasture, they were negatively correlated. In grazed pasture, unsown species and pasture age were positively correlated. Soil available P was significantly greater in cut pastures whereas soil exchangeable K was significantly greater in grazed pastures. In terms of species density, cut pasture had greater densities of cocksfoot and Italian ryegrass (Lolium multiflorum), whereas grazed pasture showed greater densities of white clover, sedge and local grass. Our study suggests that, if there are no improvements in the current method of pasture management, the cut pastures in the future are likely to have a simple pasture mixture constituting only cocksfoot and white clover (Trifolium repens). Whereas in grazed pasture, the pasture mixture is likely to be comprised of white clover and unsown species such as sedge, local grass and broadleaf weeds. 相似文献
17.
《山地科学学报》2020,17(10):2447-2458
South Sinai includes Egypt's highest mountains that resemble an ecological island surrounded by desert. The present study aims to analyse the vegetation physiognomy along the altitudinal and environmental gradients in the main wadi beds in South Sinai mountainous region. This includes determining the natural, native-weed and alien vegetation in representative stands in this region, analysing their vegetation in terms of species composition, abundance and life forms and determining the national and global distribution of the associated species. This investigation also aims to describe the prevailing plant communities and assess the role of environmental conditions that affect the vegetation in this region. Thus, thirty-two stands were chosen during March-June 2018 to reflect the prevailing altitude and environmental gradients. Total species was 316(229 genera and 61 families): 186 species were perennials(58.9%), while 130 were annuals(41.1%). In addition, 152 species were native weeds(48.1% of total species), 31 were aliens(9.8%), along with 133 natural species(42.1%). Eight species were recorded as endemic to Egypt: Anarrhinum pubescens, Euphorbia sanctae-catharinae, Hypericum sinaicum, Origanum syriacum subsp. sinaicum, Phlomis aurea, Primula boveana, Rosa arabica and Solanum sinaicum. In addition, 10 species were recorded as near-endemics to Egypt and other adjacent countries: Allium desertorum, Asclepias sinaica, Centaurea scoparia, Fagonia mollis var. hispida, Hyoscyamus boveanus, Iphiona mucronata, Micromeria sinaica, Pterocephalus sanctus, Salvia deserti and Stachys aegyptiaca. In the present study, 33 species are threatened and categorized as follows: 8 endangered, 8 vulnerable and one indeterminate, while the rest were evaluated by the authors as rares. The rich plant diversity of this region is due to its extensive mountainous massif, which supports many microhabitats. The high elevations in this region hinder the dispersal process of propagules, a situation which often tends to increase endemic and near-endemic species. The current results were discussed and compared with some related previous studies. 相似文献
18.
采用问卷方法调查湛江市中小企业的治理状况,分析湛江市中小企业治理模式的选择原因,并为提高中小企业治理水平提出建议。湛江市中小企业的治理结构以高度集中的家族治理为特征。中小企业选择家族治理的原因在于对财产权、经营权控制的考虑以及经营风险和交易成本的考虑。加强治理文化建设,改善治理环境,完善职业经理人市场,逐步引导中小企业治理从家族治理向外部专业化治理转化,有助于湛江市中小企业的发展。 相似文献