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991.
INTRODUCTIONFromthe1990’s,thescallop,C.farreri,culturedinthenorthernChinaSea,deterioratedinsize,healthandoutputbecauseofhighstockingdensities,shortageofnaturalfoodanddiseases.Massmortalityof50%-90%occurredinJiaozhouBay,Qingdao,andSishiliwanBay,Yantai,fromJulyto… 相似文献
992.
993.
US regional and state migration data from the 1940s–80s, when members of the baby boom generation aged into their years of peak labor force mobility, suggest ways in which changing age composition regulates geographical mobility and interregional migration. Labor supply pressure plays a key role in the dynamics of the national migration system. A “delayed mobility” effect in the 1980s similar to the delayed fertility of the baby boom cohorts appears to be a result of the depressed rates of mobility experienced by members of this generation when they flooded regional labor markets with record numbers of entrants in the 1970s. Recent temporal shifts in age-specific volumes of interregional migration help predict the future pace of migration based upon the projected age distribution of the nation. 相似文献
994.
大坂山“铬矿物”产出于灰绿色中细粒石英闪长岩中,笔者从区域地质特征、岩石学、岩石化学、地球化学、同位素等方面对石英闪长岩进行了较全面的研究后认为,该套岩石成因为壳幔混合型,构造环境为北祁连加里东洋盆收缩阶段板块俯冲作用下形成的火山弧,岩石成岩时代为早奥陶世,铬矿物形成深度约30km,受区域性岩石圈断裂带控制。 相似文献
995.
矿山废石淋溶对水环境的影响 总被引:3,自引:1,他引:2
为了研究废石堆砌对水环境的影响,通过对废石做淋溶实验,分析了出入水的水质变化规律,对废石衍生环境效应的过程、机制、影响因素方面进行讨论,揭示了人们容易忽视的酸性水中硫酸根、总硬度、微量金属离子的动力学变化机理,指出矿山废石对水环境的污染不至限于使水质酸化,硫酸根、总硬度也会大幅度提高,废石堆放应充分考虑当地的地理气候及水文条件,合理堆放,减少污染。 相似文献
996.
We present new infrared (2-4 μm) spectroscopic observations of Vesta obtained in 2001, 2003, and 2004. Together with previously published work, these present a picture of how Vesta's spectrum changes with sub-Earth latitude and longitude. Vesta's albedo and 2-μm band vary regularly with its rotational phase. While establishing the continuum level for Vesta in the 3-μm region is not straightforward, Vesta appears to have a spectrum consistent with the HED meteorites and not requiring a 3-μm water of hydration band. We cannot formally rule out a shallow (∼1%) band, however. We place limits on the extent to which solar-wind implantation and contamination by CM-like impactors has changed the surface spectrum of Vesta. 相似文献
997.
We have used the spectra obtained by the Composite Infrared Spectrometer (CIRS) onboard the Cassini spacecraft to search for latitudinal variation in the 15N/14N ratio on Jupiter. We found no variations statistically significant given the observational and model uncertainties. The absence of latitudinal variations demonstrates that 15NH3 is not fractionated in Jupiter's atmosphere, and that the measured 15N/14N represents Jupiter's global value. Our mean value for the global jovian 15N/14N ratio of (2.22±0.52)×10−3 agrees with previous measurements made by Fouchet et al. (2000, Icarus 143, 223-243) and Owen et al. (2001, Astrophys. J. 553, L77-L79). We argue that the jovian isotopic 15N/14N ratio must represent the solar nitrogen isotopic composition. The solar 15N/14N ratio hence significantly differs from the terrestrial value: (15N/14N)⊕=3.68×10−3. This supports the proposition that terrestrial nitrogen originates from a nitrogen reservoir isolated from the main nitrogen reservoir in the proto-solar nebula. The origin and carrier of this isolated reservoir are still unknown. 相似文献
998.
饮用矿泉水作为一种新型饮料已被广大群众所接受,但真正进入国内、国际市场的数量与其丰富的资源形势不相匹配。原因是我国目前评价指标与国际通用指标尚不接轨。本文对其中一些问题提出质疑,试图修正现行评价指标和改善管理制度,以推动我国饮用矿泉水的进一步开发。 相似文献
999.
We report on PFS-MEX (Planetary Fourier Spectrometer on board Mars Express) limb observations of the non-Local Thermodynamic Equilibrium emission by CO and CO2 isotopic molecules. The CO emission is observed peaking at altitudes lower than the CO2 emission peak. Two orbits have been considered, which explore latitudes from 75 to 15° N, located in local time at 11:30 and 06:40, and with Ls=138° and 168°, respectively. In general in the season considered (northern summer) the emission intensity increases going to lower latitudes. The peak emission height is also decreasing with decreasing latitude. The CO2 isotopic molecules are emitting radiance out of proportion with respect to the normal isotopic abundance, which surely indicates a strong contribution from a large number of much weaker CO2 bands, a result that will demand careful theoretical modeling. By comparison with Hitran data base we can identify, among the emitting bands, the second hot band for the 626 and 636 molecule, while for the 628 and 627 emission from the third hot bands are very possible. Other minor bands or lines are also observed in emission for the first time in Mars. In one of the two orbits considered, the orbit 1234 of MEX, we also observe at altitudes 80-85 km scattered radiation, with indication of CO2 ice aerosols as scattering centers. At the same altitude the Pathfinder descending measurements show a temperature that allows CO2 condensation. Pathfinder measurements were at 03:00 local time, while our observations are for orbit 1234 showing CO2 ice signature at 11:30 local time. These non-LTE limb emissions, with their unprecedented spectral resolution in this portion of the near infrared and their sensitivity and geographical coverage, will represent in our opinion an excellent data set for testing current theoretical models of the martian upper atmosphere. 相似文献
1000.
本文在阐明关中盆地环境水文地质条件的基础上,论述了关中盆地潜水化学特征及其成因,并着重对盆地潜水化学变化的几个主要问题,诸如常规组份的升高及水化学类型的改变、潜水硬度的升高、硝酸盐的富集及微量重金属元素的污染等进行了分析。讨论了上述问题的因果及今后工作意见。 相似文献