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排序方式: 共有699条查询结果,搜索用时 15 毫秒
1.
We analyze the effect of worker inflows on establishments’ productivity, using German data. Previous studies for other countries have found positive effects of hiring workers from superior (more productive or higher paying) firms. Ranking establishments by their median wage, we find that inflows from inferior establishments seem to increase hiring establishments’ productivity. Further empirical analyses suggest our findings are due to a positive selection of such inflows from their sending establishments. These workers might have to find a better job match in order to advance their careers, an interpretation supported by the finding that the effect is driven by workers with short tenure at their previous employer. Our findings reflect the increasingly assortative pattern of worker mobility in Germany found in a related strand of literature. 相似文献
2.
城市自生群落具有重要的生态服务功能与潜力,但因其外貌不被公众所接受而难以在城市公共空间中应用。将群落生态学和设计学相结合,探索一种介入栽培植物对城市自生群落进行改良,最终形成具有一定美学价值的植物群落的途径。实验以植物群落设计美学原理和种间竞争原理为依据,向已经演替1年的城市自生群落中引入63种栽培植物,按照分层的方式对群落进行改良。3年的观测结果表明,有61.9%的栽培植物可以在城市自生群落中定居并建立优势,能对76.7%的自生植物起到抑制作用,使55.8%的自生植物消失。相比城市自生群落,改良后的群落美观度提高29.4%,公众接受度提高24%,群落的物种丰富度提高至2.29倍。相比一般的人工植物群落,改良后的群落可以节约58.2%的建植成本,降低83.9%的浇水成本和67.8%的除草成本。实验证明改良设计是一种可行的群落设计途径,能有效提高群落的物种丰富度和美学价值,同时让自然参与群落设计过程,实现人与自然的合作。 相似文献
3.
赵亚杰 《中小企业管理与科技》2021,(9)
企业的经营生产离不开电力的供应,而现阶段我国的电力供应依靠发电厂供电,通过汽轮机等一系列机械设备来产生电能。就目前的情形来看,为了保证我国更好地发展,还需要加强对电力设备的保障,而汽轮机则是其中的重要环节。 相似文献
4.
文人园林营建过程中,园居植物的获取、选择、栽培以及品赏亦是一个较为复杂而必备的过程。江南常熟静圃(现名赵园)为晚清文人赵烈文所建。通过分析赵烈文撰写的《能静居日记》,并结合其他史料考证,在当时沿袭的文人审美标准下对同治四年至光绪十三年静圃中的植物应用过程及方式进行阐释,旨在获得关于晚清时期江南文人园林植物的历史性认识:静圃建园过程中植物主要通过苏州花肆购买、友人间赠送以及与种树人直接交易等方式获取;园中植物虽以地景、盆景区分,但种类选择与高濂、文震亨、李渔等给出的品赏范围并无明显差异;在定期维护的基础上,须保证后园可四时赏花,其中以春桃、夏荷、秋菊、冬梅为最,且植物的实用功能一直被延续。 相似文献
5.
Absentee landowners, or those who do not live on their forestland, own approximately 117 million acres of private forestland in the U.S. Thus, their land management decisions and activities influence the flow of forest-based goods and services. We explore the question of whether absentee family forest owners are less active land managers than resident landowners and whether membership in conservation organizations is associated with higher levels of land management activity by absentee owners. To examine these questions, we administered a mail survey to randomly-selected family forest landowners in Indiana. While we found some support for the contention that absentee owners are less active forestland managers than resident owners, we also found they are not necessarily inactive landowners. We found absentee owners were less likely to have: inspected their forestland for invasive plants, pulled or cut invasive plants, used herbicides to kill invasive plants, reduced fire hazard, or grazed livestock than resident owners. Absentee owners were more likely to be enrolled in the Indiana Classified Forest and Wildlands Program, a preferential forest property tax program. Absentee owners who are members of a conservation organization were more likely than absentee non-member owners to have undertaken a variety of land management activities, including: undertaking wildlife habitat improvement projects, inspecting their forestland for invasive plants, pulling or cutting invasive plants, enrolling in the Indiana Classified Forest and Wildlands program, and obtaining a management plan. 相似文献
6.
Damiano Gianelle Alberto Romanzin Fabrizio Clementel Loris Vescovo Stefano Bovolenta 《国际农业可持续发展杂志》2018,16(1):64-73
The effect of different supplementary feeding rates for grazing cattle on high-altitude pastures dynamics was evaluated. A field experiment was carried out during three years in a subalpine pasture area of the Eastern Alps. The investigated pasture area was 40?ha, located between 1820 and 2230?m?a.s.l. Two paddocks were chosen in the experiment and two herds of 12 cattle each were kept in the two enclosures for 5 weeks. For the first herd (HS), the supplementary feeding rate was 4.8?kg?OM?head?1 per day, while for the second herd (LS), the rate was 1.6?kg?OM?head?1 per day. The amount of herbage consumed by each cattle was determined using the n-alkane technique. To monitor the pasture vegetation dynamics, eight metal exclusion cages were placed in each paddock to determine herbage growth, utilization rates, vegetation composition and animal grazing selectivity. Grazing behaviour of dairy cattle, in terms of herbage intake and species selection was affected by the different feeding rates. Cattle grazing Paddock HS consumed 1.9?kg?OM?day?1 of herbage less than Paddock LS. In the LS paddock, cattle grazed higher phytomass rates. When the animals were fed by higher concentrate rates, a more selective grazing seemed to significantly increase the pasture necromass component. The lower grazing selectivity favoured the development of species as Nardus stricta and Deschampsia caespitosa, which are well known for their low palatability. Distinct vegetation dynamic patterns were observed, with a reduction of hair grass and an increase of legumes in the Paddock LS. 相似文献
7.
8.
以贵阳市黔灵山公园为研究对象,选取24个植物景观单元。以生态适宜、景观适宜、社会适宜为准则层,建立山地公园植物景观景观适宜性评价体系。运用主成分分析确定评价指标权重,克服以往植物景观评价赋权重的主观性,建立山地公园植物景观景观适宜性评价模型,得到不同植物景观的景观适宜性指数。结果表明:黔灵山公园在适宜范围内的植物景观有10个,占评价单元总数的41.6%,适宜性较差的有14个,乔灌比(数量)在1:11.2~1.7:1之间的植物群落景观适宜性较好。根据评价结果,提出了3点山地公园植物景观营建策略,以期为山地公园植物景观评价及营建提供理论指导。 相似文献
9.
本文以猪八戒网为研究对象,结合已往研究成果与猪八戒网调研结果,并将管理熵理论进一步应用于众包情境下,构建综合激励体系,从而测度激励体系协同激励效果。研究表明:目前猪八戒网接包绩效激励系统处于一定的有序状态,各激励指标的激励效果相对良好;二级体系内部指标协同效应较差,应注意"环境公平""品牌效应"与"信息转换机制"三项二级指标对激励系统稳定的干扰;"程序公平"和"交互公平"两项三级指标熵流值为正,对接包绩效产生显著抑制作用。通过测度激励系统的激励效果,有助于及时遏制正熵并提高激励负熵,进而实现总激励熵的下降,对激励盲点的发现与激励措施的动态维护具有重要意义。 相似文献
10.
通过对上海近30年的气候因子汇总分析,结合对上
海世博公园主要绿化树种生长状况调查和年度生物量计算,通
过典型相关性分析发现,极端高低温、强风和暴雨等5个气候
因子对树木的生长产生了不同程度的影响,有些因子严重阻碍
了树木的正常生长,成为障碍因子。经过10年的绿化实践验
证,上海世博公园对骨干树种的选择,以乡土树种为主,群落
结构较为稳定,且气候障碍因子对乡土树种的影响较小。在引
种外来树种时,采用气候相似植物区系法,结合植物耐寒、耐
热带图,把种源地划分为2个气候带和3个植物区系,并确定了
最南引种线,成功引种了红花槭等20种观花色叶乔木树种。 相似文献