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排序方式: 共有6919条查询结果,搜索用时 15 毫秒
61.
AG Loeser Z Shen DS Dessau DS Marshall CH Park P Fournier A Kapitulnik 《Science (New York, N.Y.)》1996,273(5273):325-329
Angle-resolved photoemission experiments reveal evidence of an energy gap in the normal state excitation spectrum of the cuprate superconductor Bi2Sr2CaCu2O8+delta. This gap exists only in underdoped samples and closes around the doping level at which the superconducting transition temperature Tc is a maximum. The momentum dependence and magnitude of the gap closely resemble those of the dx2-y2 gap observed in the superconducting state. This observation is consistent with results from several other experimental techniques, which also indicate the presence of a gap in the normal state. Some possible theoretical explanations for this effect are reviewed. 相似文献
62.
Z Chen M Mitchell M Segev TH Coskun DN Christodoulides 《Science (New York, N.Y.)》1998,280(5365):889-892
"Dark beams" are nonuniform optical beams that contain either a one-dimensional (1D) dark stripe or a two-dimensional (2D) dark hole resulting from a phase singularity or an amplitude depression in their optical field. Thus far, self-trapped dark beams (dark solitons) have been observed using coherent light only. Here, self-trapped dark incoherent light beams (self-trapped dark incoherent wavepackets) were observed. Both dark stripes and dark holes nested in a broad partially spatially incoherent wavefront were self-trapped to form dark solitons in a host photorefractive medium. These self-trapped 1D and 2D dark beams induced refractive-index changes akin to planar and circular dielectric waveguides. The experiments introduce the possibility of controlling high-power coherent laser beams with low-power incoherent light sources such as light emitting diodes. 相似文献
63.
64.
65.
G.F. Dong Y.O. Yang X.M. Song L. Yu T.T. Zhao G.L. Huang Z.J. Hu J.L. Zhang 《Aquaculture Nutrition》2013,19(4):543-554
A 6‐week growth trial was conducted to investigate the effect of dietary supplementation with maggot meal (MGM) and soybean meal (SBM) on the growth performance and antioxidant responses of gibel carp (GC) and darkbarbel catfish (DC). The basal diet was formulated to contain 114 g kg−1 fish meal (FM) and 200 g kg−1 SBM. The basal diet was supplemented with either 280 g kg−1 FM (Control), 390 g kg−1 MGM or 450 g kg−1 SBM to obtain three isonitrogenous (crude protein: 380 g kg−1) and isocaloric (gross energy: 16 kJ g−1) diets. For GC, a significant decrease in specific growth rate (SGR) was only observed in fish fed the SBM diet compared with the control (P < 0.05). Principal components analysis (PCA) of GC showed a higher similarity in antioxidant response to dietary supplementation with MGM and SBM proteins between liver and intestine, but the DC did not. The present results suggest that supplementing 390 g kg−1 MGM protein to basal diet cause an enhancement of the antioxidant capacity in GC, but supplementing 390 g kg−1 MGM and 450 g kg−1 SBM proteins to basal diets resulted in a significant attenuation of the antioxidant capacity in DC. 相似文献
66.
This study aimed to investigate the optimum dietary carbohydrate/lipid (CHO/L) ratio for fingerling blunt snout bream Megalobrama amblycephala (average initial weight: 6.61 ± 0.03 g). Six isonitrogenous and isoenergetic diets were formulated to contain various CHO/L ratios ranging from 1.62 to 24.20. Each diet was tested in four replicates for 10 weeks. Specific growth rate (SGR), feed conversion ratio and nitrogen and energy retention all improved significantly (P < 0.05) as dietary CHO/L ratios decreased from 24.20 to 5.64 but showed little difference (P > 0.05) as dietary CHO/L ratios ranged from 2.45 to 5.64. Hepatosomatic index increased significantly (P < 0.05) as dietary CHO/L ratios increased, whereas intraperitoneal fat ratio showed an opposite trend (P < 0.05). Opposite to moisture content, lipid content of whole body and carcass all increased significantly (P < 0.05) as dietary CHO/L ratios decreased. Liver lipid content showed little difference (P > 0.05) among all the treatments, while liver glycogen content increased significantly (P < 0.05) with increasing CHO/L ratios. High dietary carbohydrate enhanced the activities of liver hexokinase, pyruvate kinase and glucose‐6‐phosphate dehydrogenase but did not induce hyperglycaemia. Based on the second‐order polynomial regression analysis of SGR, the optimal dietary carbohydrate and lipid contents for fingerling blunt snout bream were 291.7 and 81.4 g kg−1, respectively, with a corresponding dietary CHO/L ratio of 3.58. 相似文献
67.
J. W. Huang L. X. Tian Z. Y. Du H. J. Yang Y. J. Liu 《Fish physiology and biochemistry》2007,33(2):167-172
This study was conducted to evaluate the effects of dietary thiamin on the physiological status of the juvenile grouper, Epinephelus coioides. Graded levels of thiamin (0.08, 0.50, 2.12, 3.15, 4.63, 12.37 mg thiamin kg−1 diet) were fed to grouper juveniles (mean weight: 16.97 ± 0.14 g) for 10 weeks. Although fish fed the thiamin-deficient (TD)
diet showed no obvious symptoms of thiamin deficiency or increased mortality, those fed the lowest doses of thiamin (0.08
and 0.50 mg thiamin kg−1 diet) had significantly decreased transketolase activity in the liver. In addition, the level of liver thiobarbituric acid
reactive substances in fish fed the TD diet was 33–67% higher than that in fish with the thiamin-supplemented diet. There
were no significant differences in superoxide dismutase activity between the different groups of fish. 相似文献
68.
Different effects of single and repeated application of various rates of phosphogypsum to a crusty meadow chernozemic high-sodium
solonetz with soda salinization formed in the zone of insufficient moistening in the forest-steppe zone of Western Siberia
(the Ishim-Irtysh interfluve area) with the mean annual precipitation of 325 mm are revealed. Repeated phosphogypsum application
provided a higher saturation of the soil exchange complex with exchangeable calcium, deeper desalinization of the soil profile,
and more intensive removal of the exchange products beyond the 1-m-thick layer as compared to a single phosphogypsum application.
The soil reclamation results in the soil profile’s differentiation into three zones with respect to the salt content: the
desalinization, transit, and accumulation zones. The greater the ameliorant rate, the higher the soil desalinization upon
a single application of phosphogypsum. Upon the repeated phosphogypsum application, the zones of desalinization and salt transit
are thicker irrespectively of the ameliorant rate. Despite the additional salt application, the degree of salinization in
the upper 2 m does not increase. Data of the long-term investigations show that a single gypsum application exerts a favorable
and long-term ameliorative effect. In the solonetz repeatedly ameliorated with phosphogypsum at the rates of 8 and 16 t/ha,
the amount of the reacted phosphogypsum considerably exceeds the applied calculated rate and is almost equal to that upon
a single application of phosphogypsum at the double rate (32 t/ha). It has been shown that not only the repeatedly applied
phosphogypsum but also the soil calcium participates in the exchange reactions. This makes it possible to apply smaller rates
of the ameliorant or calculate its rate for the upper 10-cm-thick layer. 相似文献
69.
Daniel E. León Henry Zúñiga-Benítez Gustavo A. Peñuela Héctor D. Mansilla 《Water, air, and soil pollution》2017,228(9):361
This study presents the main results about the removal of the antibiotic cefotaxime (CTX) under simulated sunlight radiation using heterogeneous photocatalysis with titanium dioxide (TiO2) and zinc oxide (ZnO) in aqueous solutions. The effects of pH and catalyst initial load on pollutant removal were assessed considering the response surface methodology and a central composite circumscribed experimental design, which allowed to determine the optimized conditions that lead to a higher substrate elimination. Experimental results indicated that evaluated parameters have a significant effect on antibiotic removal in both TiO2 and ZnO suspensions. In addition, the role of photogenerated holes, hydroxyl, and superoxide anion radicals on CTX degradation was evaluated to clarify the reaction mechanism. Finally, analysis of the dissolved organic carbon content in solutions and the antibacterial activity of treated samples showed that photocatalytic treatments were able to reduce a considerable portion of the organic matter present in the systems and its antimicrobial activity. 相似文献
70.
Low-molecular-weight organic acids play an important role in the mobilization of soil phosphorus (P). The molybdate blue colorimetric
method, based on the formation of P molybdenum blue compound, is commonly used for analysis of phosphate in soil and environmental
samples. However, some organic acids can act as a ligand to bond with molybdenum acid, which subsequently interfere with the
colorimetric reaction. The recoveries of P were inhibited by the addition of oxalic (>2 mM) and citric acids (>3 mM) both
in standard P solutions and soil extracts, but formic and maleic acids did not interfere with the P determination. The inhibition
of oxalic and citric acids on P recovery remained even at higher level of P (up to 100 μg P 100 ml−1) though such interferences decreased by increasing P concentration. Comparison between oxalic and citric acids revealed the
more pronounced interference by the addition of oxalic acid. The results suggested that the interference of organic acids
with P determination is related to the types of organic acids and the ratio of organic acid ligands to P anions in the solutions.
Thus, analysis of P using the molybdate blue colorimetric method should be undertaken cautiously in the presence of relative
strong ligands like oxalic and citric acids. 相似文献