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排序方式: 共有239条查询结果,搜索用时 15 毫秒
51.
Climate Change During the Last Deglaciation in Antarctica 总被引:1,自引:0,他引:1
PA Mayewski MS Twickler SI Whitlow LD Meeker Q Yang J Thomas K Kreutz PM Grootes DL Morse EJ Steig ED Waddington ES Saltzman P Whung KC Taylor 《Science (New York, N.Y.)》1996,272(5268):1636-1638
Greenland ice core records provide clear evidence of rapid changes in climate in a variety of climate indicators. In this work, rapid climate change events in the Northern and Southern hemispheres are compared on the basis of an examination of changes in atmospheric circulation developed from two ice cores. High-resolution glaciochemical series, covering the period 10,000 to 16,000 years ago, from a central Greenland ice core and a new site in east Antarctica display similar variability. These findings suggest that rapid climate change events occur more frequently in Antarctica than previously demonstrated. 相似文献
52.
53.
Macías FA Simonet AM Pacheco PC Barrero AF Cabrera E Jiménez-González D 《Journal of agricultural and food chemistry》2000,48(7):3003-3007
A collection of 11 natural and synthetic podolactones have been tested as allelochemicals in a range between 10(-4) and 10(-9) M, and their potential use as natural herbicide models is discussed. Their effects on the germination and growth of the dicots Lactuca sativa (cv. Nigra and cv. Roman), Lepidium sativum, and Lycopersicon esculentum and the monocots Allium cepa, Hordeum vulgare, and Triticum aestivum as standard target species have been studied. An important inhibitory effect on the germination and growth of all tested species (average = 90%) was produced by compounds 9-11 at 10(-4) M. The specific structural requirements related to their activities are studied. On the basis of these results, their use as potential natural herbicide models is proposed. 相似文献
54.
Céspedes CL Lemus A Salazar JR Cabrera A Sharma P 《Journal of agricultural and food chemistry》2003,51(10):2923-2929
This work presents the herbicidal and plant growth regulatory activities of tertiary bismuthines containing heterocyclic aromatic rings of the general formula (2-C(4)H(3)X)(3)Bi, where X = S (3), O (1), or NMe (2). Toxicity against Artemia salina and herbicidal activity on Lactuca sativa, Trifolium pratense, and Lolium multiflorum were tested. In addition to the effects on mitochondrial respiration obtained from roots of Phaseolus vulgaris, these compounds also demonstrated partial radical scavenging properties against 2,2-diphenyl-1-picrylhydrazyl (DPPH). The furyl substituent is the most important structural requirement for the activity measurements observed in this study. 相似文献
55.
Morillo E Undabeytia T Cabrera A Villaverde J Maqueda C 《Journal of agricultural and food chemistry》2004,52(4):884-890
Adsorption-desorption studies of norflurazon on 17 soils of very different characteristics have been performed using a batch equilibration method and correlated to its mobility, activity, and persistence in soils. The influence of different soil properties and components on norflurazon adsorption was determined. The significant variables were organic matter (OM) content and iron and aluminum oxides, which accounted for 85 and 11% of the variability, respectively. Norflurazon desorption from soils was hysteretic in all cases, being more irreversible at the lowest herbicide concentrations adsorbed. The percentage of norflurazon eluted from columns of selected soils reached almost 100% in soils with sand content >80% and OM <1%, but in the soil which gave the highest sorption, herbicide residues were not detected at depths >16 cm. The herbicidal activity of norflurazon was followed by measuring its bleaching effect on soybean plants, and the herbicide concentration required to give 50% chlorophyll inhibition (CI(50)) was calculated. CI(50) was achieved on a sandy soil with 0.08 mg x kg(-)(1), whereas 1.98 mg x kg(-)(1) was necessary for the soil that presented maximum norflurazon adsorption. 相似文献
56.
Olalla M Fernández J Cabrera C Navarro M Giménez R López MC 《Journal of agricultural and food chemistry》2004,52(9):2715-2720
This paper presents the levels of copper and zinc determined in a total of 66 samples of the most widely consumed varieties of white and red grapes in Spain, as well as those of 60 samples of grape juice (39 from white varieties and 21 from red ones) chosen from the main commercial brands in the country. Atomic absorption spectroscopy was used as analytical technique, with electrothermal atomization after digestion of the sample with HNO(3)-H(2)O(2) for grapes and with HNO(3) for grape juice. The mean Zn contents obtained (0.0462 mg/100 g in grapes and 0.0460 mg/100 mL in grape juice) are lower than those provided by most of the more commonly used food composition tables. The mean Cu contents were 0.0515 mg/100 g in grapes and 0.0063 mg/100 mL in grape juice. On the basis of these data and the official data on consumption of grapes and grape juice in Spain, the contribution of both products to the recommended daily intake of zinc (15 and 12 mg/day for healthy adult men and women, respectively) is estimated to be approximately 0.1%, whereas for Cu, this supply represents rather more than 0.25% of the established ESADDI (1.5-3 mg/day in adults). The growing popularity of these products in recent years, on the basis of its nutritional properties and beneficial effects, requires additional data, and the present findings are of potential use to food composition tables. 相似文献
57.
×Tritordeum (Ascherson et Graebner, an amphiploid between Triticum turgidum conv. durum and Hordeum chilense), and chromosome substitution lines of tritordeum where chromosomes 2 H
ch or 3 H
ch
H. chilense were replaced with chromosome 2 D of T. aestivum or 3 H
v chromosome of H. vulgare, respectively, were used to assess the effect of specific chromosomes on the rachis. ×Tritordeum has brittle rachis while the 2 D(2 H
ch) and 3 H
v (3 H
ch) substitution lines have non-brittle rachis. Both lines also have compact spikes, a character highly desirable for the improvement
of tritordeum threshability. Different combinations of 2 D and 3 H
v translocations were developed in tritordeum. In this article we present information on the identification and characterisation
of all these introgression lines by the fluorescent in situ hybridisation. 相似文献
58.
59.
Héctor Castillo-Juárez Juan Carlos Quintana Casares Cesáreo Cabrera Villela Hugo Horacio Montaldo 《Aquaculture (Amsterdam, Netherlands)》2007,273(1):42-49
To estimate family BLUP breeding values and the heritability of body weight at harvest size (BW) in the Pacific white shrimp, Penaeus (Litopenaeus) vannamei, an experiment was conduced using information from two farm units of a Mexican hatchery and two shrimp population densities at each location. Data consisted of 12,658 shrimps that were siblings from 48 sires and 77 dams with a nested dam-sire structure. Shrimps were individually weighed at an average age of 130 days post-hatching. BW phenotypic mean (S.D.) was 18.2 (2.4) g, with values ranging from 8.4 to 30.0 g. Data were analyzed using univariate and multivariate models that considered BW within location by density pond environment as a different trait and included or not a common full-sib effect (c). The multivariate animal model included fixed effects of days from hatching and sex. For univariate models that included c effects, BW heritability (S.E.) estimates ranged from 0.24 (0.14) to 0.35 (0.18) across environments (heritability was zero in one environment). For multivariate models (excluding the environment with zero heritability) the heritabilities increased and ranged from 0.37 (0.06) to 0.45 (0.09). Standard errors of heritabilities and c effects were both drastically reduced in the multivariate analysis. Pairwise genetic correlations between environments were from 0.80 (0.08) to 0.86 (0.04). These differences may be indicative of genotype-environment interaction for BW at 130 days post-hatching. Statistical problems found to separate c from additive genetic effects both in univariate models were reduced using multivariate models. Correlation between family raw phenotypic means and family BV means from the multivariate analysis was 0.93 indicating a rather low risk of miss selecting superior families if BLUP solutions were neglected using replicated environment data. It is also concluded that use of incorrect statistical models or unreplicated data may lead to biased or inaccurate estimates of genetic parameters in shrimp breeding programs. 相似文献
60.
A chickpea F2 population of 593 plants derived from the intraspecific cross ILC3279 × WR315 was genotyped for markers closely linked to
quantitative trait loci (QTLs) for ascochyta blight resistance (QTLAR1 and QTLAR2 located on linkage group 4 and QTLAR3 on linkage group 2). All the markers located on linkage group 4 exhibited strongly distorted segregation with respect to
the expected Mendelian inheritance, towards the male parental line. This skewed segregation was also observed in a second
F2 population of 50 plants derived from the same cross, confirming the presence of a region of distorted segregation on this
linkage group and its heritability. The most skewed markers were SC-Y17 and TA72, which were tightly linked to each other,
indicating that they may both be closely associated with the genetic factor responsible for segregation distortion in chickpea.
To attempt to explain the non-Mendelian segregation, by identifying factors to which it could be attributed, three different
chi-square tests were carried out to test different hypotheses using the data obtained from examining co-dominant markers
associated with segregation distortion. According to our results, the distorted segregation could be caused by gametophytic
factors that affect either male or female gametes. Pollen fertility and meiosis were also analysed to determine their relationship
with segregation distortion; however, these not seem to be inducing factors in the non-Mendelian segregation reported in this
study. 相似文献