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排序方式: 共有189条查询结果,搜索用时 15 毫秒
61.
Trapping trials were conducted in two locations on the island of Hawaii with plastic‐matrix formulations of methyl eugenol (ME) (1‐2‐dimethoxy‐4‐allylbenzene) and cuelure (CL) [4‐(p‐acetoxyphenyl)‐2‐butanone] in traps with or without a toxicant (2, 2‐dichlorovinyl dimethyl phosphate, DDVP) against wild fly populations of oriental fruit fly, Bactrocera dorsalis (Hendel) and melon fly, Bactrocera cucurbitae (Coquillett) respectively. Both 5 g disks and 10 g cones of ME and 2 g plugs of CL caught flies for >9 months which varied relative to the population fluctuations. In all of these trials a one‐way entrance design trap caught more flies than the toxicant‐baited trap. The similar‐sized entrance holes (0.70 cm) of the latter may have slowed the dispersal of the toxicant vapour, thus causing flies to be repelled or killed outside the entrance to the trap when DDVP vapour was evolving at a maximum rate. The effect decreased as the toxicant aged. One‐way entrance traps are appropriate where toxicant traps are not allowed (e.g. organic farms), present a health hazard (e.g. yards with children), or would need to be replaced more frequently than lures. The results of these studies are discussed in relation to areawide fruit fly suppression programs where large populations of these flies are persistent, as well as to detection programs in areas where fruit flies have not established.  相似文献   
62.
DNA self-assembly has crucial implications in reading out the genetic information in the cell and in nanotechnological applications. In a recent paper, self-assembled DNA crystals displaying spectacular triangular motifs have been described (Zheng et al., 2009). The authors claimed that their data demonstrate the possibility to rationally design well-ordered macromolecular 3D DNA lattice with precise spatial control using sticky ends. However, the authors did not recognize the fundamental features that control DNA self-assembly in the lateral direction. By analysing available crystallographic data and simulating a DNA triangle, we show that the double helix geometry, sequence-specific cytosine–phosphate interactions and divalent cations are in fact responsible for the precise spatial assembly of DNA.  相似文献   
63.
This paper is the first within Fijian migration studies to discuss why indigenous Fijians migrate to the United Kingdom (UK) and the socio-economic challenges they face. The majority of these Fijians form a well-organised community based on similar principles as in Fiji (kinship, church, and chieftainship) and do their utmost to live ‘in the Fijian way’ (na ivakarau ni bula vakaviti), a lifestyle also known as living ‘in the manner of the land’ (i tovo vakavanua). I argue this way of life is a central aspect of being a Fijian person, which is characterised, amongst other things, by supporting kin as part of one's kinship obligations in the form of exchange and tribute. The tributes Fijian migrants make are predominantly in the form of services, goods, and especially monetary contributions towards church, communal, and ritual events to both kin in Fiji and in the UK. These monetary contributions regularly interfere with payments, such as utility bills and car insurances. As a consequence, electricity and phone lines are cut or cars are towed away. In Fiji, migrated relatives and friends are thought of as being millionaires, but this article illustrates that the reality is very different. Living costs in the UK are high and prioritising which bills to pay, how much one should contribute to church, communal, and ceremonial events, and how much money to remit to kin in Fiji can be very stressful. I discuss the pressures and motivation for these decisions in this article.  相似文献   
64.
Asexual reproduction has the potential to promote population structuring through matings between clones as well as through limited dispersal of related progeny. Here we present an application of three-gene identity coefficients that tests whether clonal reproduction promotes inbreeding and spatial relatedness within populations. With this method, the first two genes are sampled to estimate pairwise relatedness or inbreeding, whereas the third gene is sampled from either a clone or a sexually derived individual. If three-gene coefficients are significantly greater for clones than nonclones, then clonality contributes excessively to genetic structure. First, we describe an estimator of three-gene identity and briefly evaluate its properties. We then use this estimator to test the effect of clonality on the genetic structure within populations of yellow-cedar (Callitropsis nootkatensis) using a molecular marker survey. Five microsatellite loci were genotyped for 485 trees sampled from nine populations. Our three-gene analyses show that clonal ramets promote inbreeding and spatial structure in most populations. Among-population correlations between clonal extent and genetic structure generally support these trends, yet with less statistical significance. Clones appear to contribute to genetic structure through the limited dispersal of offspring from replicated ramets of the same clonal genet, whereas this structure is likely maintained by mating among these relatives.  相似文献   
65.
野外调查发现上海地区早春非耕地杂草共106种,隶属于29科88属.计测了261个样地1305个样方中杂草的生态重要值和6种主要环境因子,应用典范对应分析作出了反映106种杂草与6种环境因子关系的二维排序图,应用双向指示种分析对106种杂草进行了有生态学意义的定量分类.根据6种环境因子与前两个排序轴相关系数的大小,发现土壤水分、土壤翻耕程度、人迹出没程度、交通影响程度是影响上海地区早春非耕地杂草分布的主要环境因素;根据双向指示种分析,结合典范对应分析的结果,可以从106种早春中分出五个生态类群,即类群Ⅰ:湿生淤泥海边滩涂杂草类群,类群Ⅱ:相对干燥海边滩涂杂草类群,类群Ⅲ:干扰相对较小的人工林地杂草类群;类群Ⅳ:干旱、开阔、干扰较重环境中的杂草类群;类群Ⅴ:湿润、开阔、干扰较重的弃耕农田环境中的杂草类群.  相似文献   
66.
Verticillium fungicola, the type species of Verticillium sect. Albo-erecta, and related taxa were studied using morphological and molecular techniques. Sequences of the ITS region and SSU rDNA suggest that V. fungicola is very close to members of the genus Lecanicillium and unrelated to other species that were originally accommodated in the same section. New combinations in Lecanicillium are proposed for Verticillium fungicola and its var. flavidum at species rank, L. f. var. aleophilum is retained as a variety. These taxa can be distinguished from each other by optimum and maximum temperatures for growth, in addition to ITS sequence differences. Morphologically, L. flavidum is also distinct by repeated branching of the conidiophores, whereas the two varieties of L. fungicola have a simple conidiophore axis.  相似文献   
67.
目的:进一步探讨经皮穿刺椎弓根途径椎体成形术与传统保守治疗方法的临床比较差异,从而为临床相关实践提供借鉴和参考依据。方法:2014年12月至2015年5月医院临床收治的胸腰椎椎体转移肿瘤患者共计88例,根据治疗方法分成研究组(经皮穿刺椎弓根途径椎体成形术组)和对照组(传统保守治疗方法组),每组患者44例。观察和比较两组患者实施不同治疗后的临床满意度。结果:研究组患者手术1d、1个月、3个月、6个月和1年后的临床满意度均显著的高于对照组,且组间比较差异均有统计学意义(P0.05)。结论:经皮穿刺椎弓根途径椎体成形术治疗胸腰椎椎体转移肿瘤的临床综合效果显著,与传统保守治疗方法相比较可有效改善和提高患者的生活质量。  相似文献   
68.
The site condition of cultivated land greatly influences the utilization and management of cultivated land resources and is an element that is disturbed tremendously by urbanization. Since the rejuvenation of the northeast old industrial base strategy in 2003, urbanization in northeast China has progressed rapidly. The excessive urban sprawl has profoundly changed land use structure in the peri-urban area of the black soil region, and the subsequent site condition changes will impede the full utilization of cultivated land resources. This study used the suburb of Changchun Kuancheng District as an empirical case, and employed a patch-scale site assessment system to analyze dynamic changes in cultivated land site conditions at a typical rural-urban interface of the black soil region from 2004 to 2014. Cultivated land loss and land use changes were prominent in the study area and the land conversion rate was shown to be accelerating. Most of the occupied cultivated land was converted to urban areas such as industrial land or urban settlements. However, a part of the occupied cultivated land was left unutilized, which indicates how the urban sprawl is jeopardizing benefits of both urban development and cultivated land protection. Besides direct occupation of cultivated land resources, urbanization has led to a loss of cultivated land with good site conditions and a deterioration of the site conditions of unconverted cultivated land in the peri-urban area. Urbanization has fragmented peri-urban cultivated land, increased farming distance and brought more frequent anthropogenic disturbances. On the other hand, it has also improved transportation conditions and the local ecological environment. As site condition is believed to be closely related to both cultivated land loss and cultivation abandonment, the deterioration will aggravate the loss of cultivated land resources in a disguised form.  相似文献   
69.
栽培大麦,纤毛鹅观草,属间杂种,酯酶,过氧化物酶 ISOZYME ANALYSIS OF F5 AND BCiF4 FROM CULTIVATED BARLEY ( HORDEUM VULGARE ) ~ ROEGNERIA CILIARIS LI Wan-Ji LI Yi-Ping L1U Fang Abstract Esterase and peroxidase isozymes were analysed in the variants including 4 types, 16 lines of Fs, BC1F4 and the parents derived from cultivated barley ( Hordeum vulgare cv. Arupo) x Roegneria ciliaris (Trin.) Nevski in young roots, shoots, spikes and seeds. The zymogram patterns of esterase and peroxidase demonstrated that the 16 lines of F5 and BC1F4 had all or most bands of the cultivated barley parent cv. "Arupo", 1 to 3 bands from the male R. ciliaris, and new hybrid isozyme bands in various amount. Some bands of parent "Arupo" were lost. It suggested that the genetic substances come from R. ciliaris were stably inherited to the progenies of selfing and backcrossing, and there were some variations among the lines. There was certain relationship between isozyme variance and plant characters. Thus, in identifying the translocation lines by isozyme analysis, it would be preferable to study the various organ-specific isozymes or to trace one type of isozyme pattern in consequence.  相似文献   
70.
In this paper we consider the setting where a group of n judges are to independently rank a series of k objects, but the intended complete rankings are not realized and we are faced with analyzing randomly incomplete ranking vectors. In this paper we propose a new testing procedure for dealing with such data realizations. We concentrate on the problem of testing for no differences in the objects being ranked (i.e., they are indistinguishable) against general alternatives, but our approach could easily be extended to restricted (e.g., ordered or umbrella) alternatives. Using an improvement of a preliminary screening approach previously proposed by the authors, we present an algorithm for computation of the relevant Friedman‐type statistic in the general alternatives setting and present the results of an extensive simulation study comparing the new procedure with the standard approach of imputing average within‐judge ranks to the unranked objects.  相似文献   
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