共查询到13条相似文献,搜索用时 8 毫秒
1.
Yilin Dong 《Growth and change》2020,51(4):1542-1561
The objective of this paper is to estimate the relationship between agglomeration economies and the birth of new firms in U.S. manufacturing sectors during 2004–2012. I examine the variations in Marshallian factors across MSAs and across counties within MSAs. My findings support the existence of Marshallian agglomeration forces: input sharing, labor market pooling, and knowledge spillovers, with input–output linkages particularly important. I then examine the variations in Marshallian factors across regions and find regional differences are not very strong. In addition, large-sized firms appear to be more responsive to a supplier-customer relationship. Moreover, my empirical results provide evidence that firms in highly concentrated industries react more to input linkage and labor pooling. 相似文献
2.
Godfrey Baldacchino 《Asia Pacific viewpoint》1998,39(3):267-279
Try valiantly though they might, small (often island) territories cannot possibly follow the hard-and-fast logic of industrialisation marked out for them by larger economies. Instead, they have worked out for themselves an alternative resort to manufacturing industry; they have done so on the basis of a pragmatism in part derived from the handicaps imposed by the architecture of global capitalism and colonialism. This ‘hands on’ approach involves: (1) the exploitation of the rentier status of a microstate as a base or platform for ‘merchandise’; (2) the provision of goods (apart from services) for privileged export purposes, particularly aimed at captured markets (such as tourists and small state diasporas); (3) the expansion into small, knowledge-based industries; and (4) the parallel preservation of part-time small scale, cottage industry, often in relation to self employment. In all four cases, the common denominator and main argument proposed is that manufacturing in micro-states is best seen as an extension of services, rather than the other way round as is generally proposed. 相似文献
3.
摘 要:在城市各类防灾系统中,应急避难绿地是一种既能为城市提供自然空间又有助于防灾救援的有效手段。通过对应急避难绿地的概念及其建设条件等内容的分析,结合黄山市屯溪区规划布局特点、灾害类型以及城区防灾避难工作现状调查,提出建立屯溪区绿地避难场所的必要性和规划设计建议。 相似文献
4.
Sun Dihua Liu Weining Liu Fei 《保鲜与加工》1998,(4):73-78
Based on the fundamental principle of the fractal theory, the fractal characteristics of the decision making mapping model for manufacturing and its modeling process are discussed. The principle of modeling for defcision-making mapping models by the fractal theory is proposed. 相似文献
5.
E. M. M. Paul 《Euphytica》1984,33(2):347-354
Summary An investigation was carried out into the genotypic variation in the response to temperature of leaf area in tomatoes. Differences between genotypes in the response of the area of a leaf to contrasting temperature regimes were found, and this was due to variation in the number of epidermal cells. The epidermal cell size showed little response to temperature. The results are discussed in relation to the potential for selection for improved leaf area and the development of a rapid screening test for cold tolerance.Guestworker Project Group Tomato Physiology. 相似文献
6.
Green Area Duration during the Grain Filling Period of an Argentine Wheat Cultivar as Influenced by Sowing Date, Temperature and Sink Strength 总被引:1,自引:0,他引:1
The effects of sowing date, air temperature during the grain filling period, sink-strength, and then-interactions on the wheat green area (leaves, leaf sheaths and peduncles) duration from anthesis to total senescence were determined under field conditions at Buenos Aires (Argentina). The individual grain weight was determined as an average of either all grains or basal grains of the spikelets 7 and 8 through the treatments.
The delayed sowing date reduced the period of leaf senescence when it was regarded as calendar time between anthesis to maturity, but it did not affect that period regarded as thermal time. Similarly, the increased temperature has also increased the rate of senescence. On the other hand, the sink strength did not affect the green area duration; since neither the rate nor the period of senescence was altered.
Similarly, both sowing date and mean temperature decreased the individual grain weight, but the sink strength did not affected the weight of the basal grains, which could be interpreted as the effects of the other two factors were independent to the availability of assimilates per grain.
The effect of increased grain filling temperature on reducing grain weight did not operate via reducing the availability of assimilates although it also reduced the total grain area duration. We observed that the increased temperature decreased the individual grain weight of the basal grains at any source sink ratio. 相似文献
The delayed sowing date reduced the period of leaf senescence when it was regarded as calendar time between anthesis to maturity, but it did not affect that period regarded as thermal time. Similarly, the increased temperature has also increased the rate of senescence. On the other hand, the sink strength did not affect the green area duration; since neither the rate nor the period of senescence was altered.
Similarly, both sowing date and mean temperature decreased the individual grain weight, but the sink strength did not affected the weight of the basal grains, which could be interpreted as the effects of the other two factors were independent to the availability of assimilates per grain.
The effect of increased grain filling temperature on reducing grain weight did not operate via reducing the availability of assimilates although it also reduced the total grain area duration. We observed that the increased temperature decreased the individual grain weight of the basal grains at any source sink ratio. 相似文献
7.
Perilous rock is a dominant geological hazard in Three Gorges Reservoir area of P. R. China. The Taibaiyan cliff at Wanzhou is a representative case of massive perilous rocks in the area. Using this cliff as an example, the conditions triggering massive perilous rocks were studied and described. This included examining the following three conditions: alternating layers of mudstone and sandstone; steep landforms such as cliffs or scarps; and intense rainfall. The massive development mechanism for perilous rocks was discussed, including micro chained pattern gradual and interval evolution from the bottom to the summit of the cliffs individually as perilous rock, and a macro chained pattern evolving stage by stage from the cliff face backward up the mountain. In some respects, rock cells below sandstone in cliffs serves as the pulsating valve of the massive development mechanism for perilous rock. In any micro chained pattern, perilous rock situated on summits is the easiest to rupture due to the fissure pressure. For any single perilous rock, two load compositions were derived. In addition, methods for analyzing perilous rock stability were established in detail using the limit equilibrium principle. Two key techniques, a union scheme that both supports and anchors and a union scheme that nails and anchors, are proposed in light of the massive development mechanism for perilous rock. 相似文献
8.
M. Belhaj Fraj H. Falentin-Guyomarc'h H. Monod C. DE Vallavieille-Pope W. E. Weber 《Plant Breeding》2003,122(5):385-391
Two polymorphic microsatellite markers were selected to identify 24 bread wheat cultivars commonly grown in France and to estimate the proportions of cultivar and hybrid grains in the harvests of four 4‐cultivar mixtures (CM 1‐4) planted in equal proportions in farmers’ fields. This technology was used not only to determine whether a mixture comprises the declared cultivars, but also whether there is any contamination with other cultivars, to identify the contaminants and to estimate their proportions. At harvest, the cultivar proportions ranged from 15 to 37%. Only in the mixture CM2 (‘Malacca’, ‘Somme’, ‘Renan’ and ‘Soissons’), did the cultivars contribute equally to the harvest. The other cultivar mixtures CM1 (‘Malacca’, ‘Somme’, ‘Renan’ and ‘Camp Remy’), CM3 (‘Malacca’, ‘Texel’, ‘Apache’ and ‘Aligre’) and CM4 (‘Malacca’, ‘Somme’, ‘Apache’ and ‘Virtuose’) showed significantly unequal cultivar proportions with ‘Somme’ dominating ‘Renan’ and ‘Camp Remy’ in CM1, and ‘Apache’ dominating ‘Malacca’ and ‘Aligre’ in CM3 and ‘Malacca’ in CM4. Similar cultivar proportions were measured with gliadin and glutenin markers in the mixtures CM3 and CM4, confirming the results with microsatellites. No contamination was found. Hybrids accounted for between 1.3 and 6.3% of the grains produced in the four cultivar mixtures. 相似文献
9.
Flavonoids as Flower Pigments: The Formation of the Natural Spectrum and its Extension by Genetic Engineering 总被引:17,自引:0,他引:17
G. Forkmann 《Plant Breeding》1991,106(1):1-26
Preharvest aflatoxin contamination of maize (Lea mays L.) gram by Aspergillns spp. is a concern to both producers and consumers of maize. Aflatoxms are carcinogenic to animals and have been linked to liver cancer in humans. The most desirable solution for eliminating or reducing aflatoxin contamination is to identify and/or develop sources of resistance. However, only a few genetic studies, which utilized a limited amount of genetic material, have been conducted. A thorough review and consolidation of information from these studies was deemed necessary. The purpose of this paper is to present a current, critical review on aspects of infection by Aspergillus, role of insects, inoculation techniques, and sources and genetics of resistance as they relate to aflatoxin production in maize. Damage to maize kernels by insects, especially the European corn borer (Ostrinia nubilalis Hübner), fall armyworm (Spodoptera frugiperda J. E. Smith), and corn ear-worm (Helicoverpa zea Boddie), has been associated with high aflatoxin levels. Artificial inoculation techniques that damage maize kernels generally result in the highest and most consistent aflatoxin levels. Although, a relatively large amount of maize germplasm has been screened for resistance and varying levels of resistance have been identified, additional germplasm needs to be systematically evaluated. To date, there are no known genotypes with complete resistance. Results from the few genetic studies indicated that additive genetic effects controlled resist-Preharvest aflatoxin contamination of maize (Zea mays L.) gram by Aspergillns spp. is a concern to both producers and consumers of maize. Aflatoxms are carcinogenic to animals and have been linked to liver cancer in humans. The most desirable solution for eliminating or reducing aflatoxin contamination is to identify and/or develop sources of resistance. However, only a few genetic studies, which utilized a limited amount of genetic material, have been conducted. A thorough review and consolidation of information from these studies was deemed necessary. The purpose of this paper is to present a current, critical review on aspects of infection by Aspergillus, role of insects, inoculation techniques, and sources and genetics of resistance as they relate to aflatoxin production in maize. Damage to maize kernels by insects, especially the European corn borer (Ostrinia nubilalis Hübner), fall armyworm (Spodoptera frugiperda J. E. Smith), and corn ear-worm (Helicoverpa Zea Boddie), has been associated with high aflatoxin levels. Artificial inoculation techniques that damage maize kernels generally result in the highest and most consistent aflatoxin levels. Although, a relatively large amount of maize germ-plasm has been screened for resistance and varying levels of resistance have been identified, additional germplasm needs to be systematically evaluated. To date, there are no known genotypes with complete resistance. Results from the few genetic studies indicated that additive genetic effects controlled resistance to aflatoxin contamination in maize. Aflatoxin production on maize grain appeared to be greatly influence by the environment. Further genetic studies, utilizing additional germplasm, are warranted for a better understanding of the nature of resistance to asflatoxin contamination in maize. Future research needs and plans relative to resistance to aflatoxin contaminaton in maize are presented. 相似文献
10.
梅花品种"美人"叶片离体再生体系建立 总被引:1,自引:0,他引:1
以“美人’梅离体培养的叶片为材料进行愈伤组织诱导再生研究,诱导过程分两步,第一步是愈伤组织的诱导,诱导过程中生长素2,4-D起了决定性的作用,并且以液体培养基为佳,而且暗培养的愈伤组织再分化率明显高于光培养。具体培养基为1/2WPM+5mg/L 2,4-D;第二步是在愈伤组织诱导出之后,进一步诱导愈伤组织再生出植物,在经过7d液体培养基的诱导之后将离体叶片转入1/2WPM+1.0mg/L 6-BA+0.1mg/L NAA+8mg/L AgNO3+100mg/L水解乳蛋白培养,再分化率可以达到24.25%。愈伤组织分化出苗之后,进一步诱导生根,“美人”梅最佳生根培养基是1/2WPM+0.5mg/L NAA。 相似文献
11.
福建沿海地区乡村旅游游客旅游行为特征研究——以泉州双芹村旅游区为例 总被引:1,自引:0,他引:1
乡村旅游对中国统筹城乡发展、大力建设社会主义新农村、构建和谐社会意义巨大。乡村旅游游客旅游行为研究,是乡村旅游发展的一个关键问题,必须高度重视。作者以问卷调查为主要手段,以福建泉州双芹村乡村旅游区为案例,在分析国内外有关乡村旅游游客旅游行为研究现状的基础上,对乡村旅游游客的旅游决策行为、旅游偏好行为、旅游空间行为、客主交互效应和旅游体验评价认知等旅游前、中、后的行为进行研究,总结了福建沿海地区乡村旅游游客的旅游行为特征,并提出了该地区乡村旅游发展的相关建议。 相似文献
12.
Summary The production of self-seed was investigated in apple and pear with the aid of viable and compatible mentor/ pioneer pollen in relation to the proportion of self-imcompatible pollen present in the pollen cloud.Treatments consisted of mixtures of compatible and self-incompatible pollen at ratios of 1:1, 1:2 and 1:9 applied once or twice or followed by self-pollination. Selfing only, whether once or twice, produced virtually no fruits or seeds, while mixed pollinations did. Generally, fruit set tended to decrease and the self-seed to increase with increasing amounts of self pollen in the pollinations.The pioncer-pollen method (compatible in advance of self pollen) appeared more effective than the mentor pollen method (compatible and self pollen mixed). The use of viable instead of dead mentor/pioneer pollen causes competition for the ovules with the self pollen, but has the advantage that, in addition to some self-seed, other seeds are formed which, e.g. in apple, are necessary to keep the fruits on the tree until harvest.Fruit set was moderately reduced at ratios of compatible pollen to self pollen not exceeding 1:9 with pear and 1:5 with apple which constitute maximal ratios in practice as regards pollinator trees: trees of the main cultivar. In fruit orchards and probably in nature with other species, the interaction between compatible and self pollen may result in more self-seed, and so suggests that inbreeding played a greater part in the evolution of self-incompatible species, than the meager results of articial self-pollination imply. 相似文献
13.
A better understanding of the fate of fertilizer nitrogen (N) is critical to design appropriate N management strategies in plastic-mulched croplands. We evaluated the effects of plastic mulch on urea-N recovery by crops and loss from soil in furrow-ridge plots, with and without maize (Zea mays L.) cropping, in a semi-arid rain-fed site in China. We applied the same rate of urea-N (281 kg ha−1) to all treatments during the preparation of the furrow-ridges in 2011 and 2012 but 15N-labeled the urea in 2011 only. We used transparent film to cover all soil surfaces in the mulched treatments and seeded maize in furrows in treatments with crop. In 2011, plastic mulch increased the total N uptake in the aboveground biomass of maize by 53%, whereas it decreased the in-season labeled-N uptake by 19%, compared to non-mulched treatment. At harvest in 2011, in mulched treatments the total labeled-N remaining in the 0−170 cm soil layer was 25% greater whereas unaccounted labeled-N was 69% less, than in non-mulched treatments, regardless of whether maize was cropped. In 2012 the effect of mulch on total maize N uptake was comparable to that in 2011, but the residual soil labeled-N uptake by maize was 63% higher in mulched compared to non-mulched treatment. At harvest in 2012, plastic mulch increased total labeled-N remaining in the 0−170 cm depth in cropped soils and unaccounted labeled-N in non-cropped soils, compared with no mulch. Our results indicate that plastic mulch profoundly changes the fate of urea-N in maize production in cold and dry croplands. 相似文献