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排序方式: 共有882条查询结果,搜索用时 268 毫秒
61.
The larvae of Glaucopsyche lygdamus (Lepidoptera: Lycaenidae) secrete substances that attract ants. In two field sites in Colorado, tending ants protect caterpillars of G. lygdamus from attack by braconid and tachinid parasitoids. This protection may have been an important feature in the evolution of the association between lycaenid larvae and ants. 相似文献
62.
Gaffen DJ Santer BD Boyle JS Christy JR Graham NE Ross RJ 《Science (New York, N.Y.)》2000,287(5456):1242-1245
Trends in global lower tropospheric temperature derived from satellite observations since 1979 show less warming than trends based on surface meteorological observations. Independent radiosonde observations of surface and tropospheric temperatures confirm that, since 1979, there has been greater warming at the surface than aloft in the tropics. Associated lapse-rate changes show a decrease in the static stability of the atmosphere, which exceeds unforced static stability variations in climate simulations with state-of-the-art coupled ocean-atmosphere models. The differential temperature trends and lapse-rate changes seen during the satellite era are not sustained back to 1960. 相似文献
63.
Microwave spectrometer on the nimbus 5 satellite: meteorological and geophysical data 总被引:1,自引:0,他引:1
Staelin DH Barrett AH Waters JW Barath FT Johnston EJ Rosenkranz PW Gaut NE Lenoir WB 《Science (New York, N.Y.)》1973,182(4119):1339-1341
The Nimbus 5 microwave spectrometer has been used to measure thermal radiation in five frequency bands between 22.235 and 58.8 gigahertz, and has yielded both the temperature profile and, over ocean, the vapor and liquid water content of the terrestrial atmosphere, even in overcast conditions. Information has also been obtained on geophysical parameters that affect the surface emissivity, such as ice type, sea roughness, and snow cover. The experiment demonstrates the considerable potential of passive microwave sensing of meteorological and geophysical parameters. 相似文献
64.
Rats receiving occasional brief electric shocks pressed a bar, which caused them to be injected with amobarbital sodium, more frequently than the control rats to which they were yoked and which were injected when their partners pressed but whose own bar activated only a recorder. This differential effect was not shown by pairs run without shocks. 相似文献
65.
瑞安市梅屿乡大棚番茄基地是我省颇具规模的番茄基地,常年种植大棚番茄600hm^2。该基地一直以来,以种植一季番茄为主,因连年种植,造成土壤板结、养分失调、病害严重,生产效益不太理想。近年来,当地农民积极探索高产高效的栽培模式,应用水稻、番茄水旱轮作、粮经结合的种植模式,使侵害番茄的病菌大幅度减少,病害发生减轻,生产效益大幅度提高。据2004年调查:该模式亩产番茄5869h,产值10564元。纯收入达7037元,是常规种植(品种为“合作903”)的2.38倍,还增收粮食613kg,实现粮经双丰收。该种植模式的推广,既解决了蔬菜基地农民的口粮问题,又为实现大棚番茄可持续、稳定发展找到了有效途径。现将其技术要点介绍如下。 相似文献
66.
GARY NE 《Science (New York, N.Y.)》1961,133(3463):1479-1480
The termination of mandibular gland secretion by gland removal in living mated queen honey bees (Apis mellifera L.) caused approximately 85 percent loss of queen attractiveness to worker bees. The secretion of attractants in virgin queens increased with age. Old virgins were as attractive as mated queens. A rapid assay for queen attractiveness is described. 相似文献
67.
为探究滴水湖引水河段生态浮床和滨岸带组合型生态工程建成初期对入湖水质的改善效果,于2010年春季设点对引水河进行营养盐浓度、透明度、叶绿素等理化指标和浮游植物种类数量的测定,并用综合营养状态指数法评价水体富营养化状况。结果表明:(1) 工程河段水体TN、TP、Chl-a 、NH-3N水平较上游明显降低,浮床和滨岸带组合工程对TN去除率为47.9%,TP为46.8%;(2) 浮游植物密度变化与温度呈极显著正相关、与TN/TP呈极显著负相关,其密度单因子评价显示各点均达富营养化水平;(3)样点水体的综合评分范围为54.58~72.75,综合评分均值为64.07,处于中度富营养水平,其中样点1为重度富营养化;(4) Shannon-Wiener多样性指数显示滨岸带工程下游样点受污程度降低,与Pielou均匀度指数比较表明,调查水体绝大部分为中污和重污染,2类指数评价相似度为52.4%。考虑滴水湖周边潜在污染源较多、换水周期长,浮游植物群落结构尚不稳定等特征,对湖区及其周边水系的长期监测和评估可以为人工湖相关研究提供重要参考。 相似文献
68.
Schubert EF Hunt NE Micovic M Malik RJ Sivco DL Cho AY Zydzik GJ 《Science (New York, N.Y.)》1994,265(5174):943-945
One-dimensional microcavities are optical resonators with coplanar reflectors separated by a distance on the order of the optical wavelength. Such structures quantize the energy of photons propagating along the optical axis of the cavity and thereby strongly modify the spontaneous emission properties of a photon-emitting medium inside a microcavity. This report concerns semiconductor light-emitting diodes with the photon-emitting active region of the light-emitting diodes placed inside a microcavity. These devices are shown to have strongly modified emission properties including experimental emission efficiencies that are higher by more than a factor of 5 and theoretical emission efficiencies that are higher by more than a factor of 10 than the emission efficiencies in conventional light-emitting diodes. 相似文献
69.
Cotton FA Gruhn NE Gu J Huang P Lichtenberger DL Murillo CA Van Dorn LO Wilkinson CC 《Science (New York, N.Y.)》2002,298(5600):1971-1974
We report a class of molecules with extremely low ionization enthalpies, one member of which has been determined to have a gas-phase ionization energy (onset, 3.51 electron volts) lower than that of the cesium atom (which has the lowest gas-phase ionization energy of the elements) or of any other known closed-shell molecule or neutral transient species reported. The molecules are dimetal complexes with the general formula M2(hpp)4 (where M is Cr, Mo, or W, and hpp is the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine), structurally characterized in the solid state, spectroscopically characterized in the gas phase, and modeled with theoretical computations. The low-energy ionization of each molecule corresponds to the removal of an electron from the delta bonding orbital of the quadruple metal-metal bond, and a strong interaction of this orbital with a filled orbital on the hpp ligands largely accounts for the low ionization energies. 相似文献
70.
Frequently repeated strain measurements near Palmdale, California, during the period from 1971 through 1980 indicate that, in addition to a uniform accumulation of right-lateral shear strain (engineering shear, 0.35 microradian per year) across the San Andreas fault, a 1-microstrain contraction perpendicular to the fault that accumulated gradually during the interval 1974 through 1978 was aseismically released between February and November 1979. Subsequently (November 1979 to March 1980), about half of the contraction was recovered. This sequence of strain changes can be explained in terms of south-southwestward migration of a slip event consisting of the south-southwestward movement of the upper crust on a horizontal detachment surface at a depth of 10 to 30 kilometers. The large strain change in 1979 corresponds to the passage of the slip event beneath the San Andreas fault. 相似文献