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991.
992.
An empirical projection method is described to predict the magnitudes and signs of two-bond 13C-13C spin-coupling constants (2JCC) in aldopyranosyl rings. The method has been applied primarily to the interpretation of 2JCCC values, although the behavior of 2JCOC has also been examined in light of the new approach, producing results which may prove useful in the conformational analysis of O-glycosidic linkages in oligosaccharides. High-level ab initio calculations of 2JCC values in model compounds were found to be in agreement with the predictions. 相似文献
993.
Eric L. Charnov 《Evolutionary ecology》1996,10(3):245-248
Summary ESS floral lifetimes satisfy the product theorem from sex allocation theory. The dimensionless time investment per flower is a symmetric function of two dimensionless gain : cost ratios, one for each gender function. 相似文献
994.
Elizabeth M. Hartgers G.H. Aalderink Paul J. Van den Brink Ronald Gylstra J. Wilfred F. Wiegman Theo C.M. Brock 《Aquatic Ecology》1998,32(2):135-152
Twelve indoor, plankton-dominated, freshwater microcosms (600 l) were used to study the effect of a mixture of herbicides
on structural and functional aspects of these ecosystems. The EC50, 72 h values of the most susceptible standard test alga
Selenastrum capricornutum (EC50, atrazine=54 μg l−1, EC50, diuron=15 μg l−1, EC50, metolachlor=56 μg l−1) were used as a starting
point for the dosage applied in the microcosms (dosages: 0, 0.01, 0.03, 0.1, 0.3, 1× EC50). The microcosms were exposed to
chronic levels for 28 days and subsequently monitored for 4 more weeks.
The following effects were observed: (1) direct effects became apparent from an initial drop in photosynthesis efficiency,
pH and oxygen concentration and a decrease in the abundance of several phytoplankton taxa at the 0.3 × EC50 treatment level
and higher. (2) Fourteen days post application an increase in the abundance of several phytoplankton taxa (Chlamydomonas sp.
and Stephanodiscus/Cyclotella) was observed; oxygen concentrations recovered while alkalinity, conductivity and total inorganic
nitrogen were elevated. (3) Effects on fauna were minor. Daphnia galeata showed a decreasing trend and the cyclopoid copepods
an increasing trend at the end of the experiment.
Multivariate statistical analyses demonstrated no effects of any treatment level on the zooplankton community. Effects were
reported for the phytoplankton community at dose levels of 0.3 × EC50 and higher. On species level the most sensitive taxon
was Chlorophyceae coccales. For this taxon a NOEC at the dose level of 0.01 × EC50 was calculated. This effect however was
relatively small in magnitude and merely based on an increase in numbers in the control and lowest treated microcosms rather
than a decrease in numbers in all other treatments. The standards based on algal toxicity data, as adopted by the Uniform
Principles, consist of a safety factors of 0.1 to be multiplied with the EC50. The NOEC of coccales was lower than 0.1 × EC50.
All other observed variables in this aquatic ecosystem were sufficiently protected against the mixture of herbicides by the
safety factor as proposed in the Uniform Principles.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
995.
Daniel Pauly 《Reviews in Fish Biology and Fisheries》1998,8(3):307-334
The extension into tropical areas of Beverton and Holt's yield per recruit approach for stock assessment represents a straightforward case of normal science, the common Kuhnian counterpart to his much rarer paradigm shifts. It is shown that the normal science which, in recent decades, has led to new methods for estimating growth, mortality and other statistics required for yield per recruit analyses in data-sparse environments, has not only enriched fisheries science and aquatic biology as a whole, but has also contributed to identify the limitations of the single-species research programme originally defined by Beverton and Holt. The most likely prospect for that programme, in the tropics and elsewhere, is to become a component of the multispecies, or rather ecosystem approach that is emerging, and to which Beverton and Holt will have contributed many of the concepts, and much of the rigour. 相似文献
996.
Dual and simultaneous sensitivity analysis for matched pairs 总被引:1,自引:0,他引:1
997.
998.
999.
1000.
内蒙古典型草原土壤固碳潜力及其不确定性的估算 总被引:1,自引:0,他引:1
以内蒙古锡林郭勒盟典型草原围封和放牧对照的实测数据为基础,比较了不同植物群落类型的碳储量和固碳量,并估算了重度退化草地完全恢复后的土壤固碳潜力.结果表明: 在局地尺度上,以羊草、大针茅和克氏针茅为优势种的3种植被类型的年均固碳量均随着围封年限的增加而减少.羊草和大针茅草原群落的碳储量显著高于克氏针茅草原群落,而在过牧导致的退化过程中,后者流失了更多的土壤有机碳,其固碳潜力高于前两者.在区域尺度上,内蒙古典型草原土壤表层0~20 cm的固碳潜力在-0.03×104~3.71×104 kg C·a-1范围内变化,总固碳潜力为12.1×108kg C·a-1.不确定性分析发现,忽略石砾含量不会造成土壤固碳潜力估算值的较大偏差,而气象数据空间插值造成的误差为±4.7×109 kg C·a-1.假设未来生长季降水的平均变化值为-3.2 mm·(10 a)-1时,土壤固碳潜力将减少1.07×108 kg C·(10 a)-1. 相似文献