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1.
网络时代的到来,对传统企业的组织结构、运作模式、管理方法均提出了严峻的挑战。传统的企业组织结构是适应大工业生产而形成的等级组织结构形式,它有很大的局限性;电子商务企业的组织结构是适应网络社会而形成扁平化、双向多对多、以信息为基础的新型组织结构形式。电子商务企业以其组织结构扁平化和中空化,决策分散化,运作虚拟化,灵活高效为特点,它将成为传统企业在电子商务发展阶段变革的方向和目标。 相似文献
2.
本矿床是我国金红石矿床重要的成因及工业类型,为具有特定化学成分的岩石在特定变质条件下形成的。本文通过对大量数据的处理,查明了化学成分与成矿的关系:高Al2O3、MgO、Fe2O3+FeO、K2O、P2O5、H2O+、MnO,低SiO2、CaO、Na2O、CO2、S等,利于钛富集;高TiO2、MgO、P2O5、S,低SiO2、CaO、K2O、Al2O3、Fe2O3/FeO,利于金红石形成;高Sc、Zr、Ni、Zn及La/Yb,低Y、Nb、Th、Cd、Ba、Be、ΣREE,利于金红石纯度提高。对研究矿床成因及寻找新的同类矿床等有重要意义 相似文献
3.
渤海湾水环境氮、磷营养盐分布特点 总被引:10,自引:2,他引:10
渤海是一个半封闭的陆架边缘海,主要由辽东湾、渤海湾、莱州湾及中央海区组成,面积为7.7×104 km2,平均水深18 m[1].近些年富含氮、磷营养盐的工农业废水的大量排放使得渤海湾营养盐结构发生了很大变化,同时导致渤海湾局部海域“赤潮”频繁发生.营养物质进入水体后,将会在水与沉积物之间发生迁移,其中一部分可以与钙、铁或铝络合形成沉淀,或吸附到矿物颗粒的表面而转移到沉积物中.近海沉积物可以看作营养物质的“蓄积库”.沉积物中营养物质的再生,对水体中营养盐的收支和营养盐循环动力学有着及其重要的作用[2]. 相似文献
4.
Management of a shallow temperate estuary to control eutrophication: The effect of hydrodynamics on the system’s nutrient loading 总被引:1,自引:0,他引:1
A.I. Lilleb J.M. Neto I. Martins T. Verdelhos S. Leston P.G. Cardoso S.M. Ferreira J.C. Marques M.A. Pardal 《Estuarine, Coastal and Shelf Science》2005,65(4):697-707
The Mondego estuary, a shallow warm-temperate intertidal system located on the west coast of Portugal, has for some decades been under severe ecological stress, mainly caused by eutrophication. Water circulation in this system was, until 1998, mainly dependent on tides and on the freshwater input of a small tributary artificially controlled by a sluice. After 1998, the sluice opening was effectively minimised to reduce the nutrient loading, and the system hydrodynamics improved due to engineering work in the upstream areas. The objective of the present study was to evaluate the effect of the mitigation measures implemented in 1998. Changes to the hydrodynamics of the system were assessed using precipitation and salinity data in relation to the concentrations of dissolved inorganic nutrients, as well as the linkage between dissolved N:P ratios and the biological parameters (phytoplankton chlorophyll a concentrations, green macroalgal biomass and seagrass biomass). Two distinctive periods were compared, over a ten year period: from January 1993 to January 1997 and from January 1999 until January 2003. The effective reduction in the dissolved N:P atomic ratio from 37.7 to 13.2 after 1998 is a result of lowered ammonia, but not the oxidised forms of nitrogen (nitrate plus nitrite), or increased concentrations of dissolved inorganic phosphorus. Results suggest that the phytoplankton is not nutrient limited, yet maximum and mean biomass of green macroalgae was reduced by one order of magnitude after the mitigation measures. This suggests that besides lowering the water residence time of the system, macroalgal growth became nitrogen limited. In parallel to these changes the seagrass-covered area and biomass of Zostera noltii showed signs of recovery. 相似文献
5.
大型海藻孔石莼抑制浮游微藻生长的原因初探--种群密度及磷浓度的作用 总被引:8,自引:0,他引:8
本文以磷浓度和种群密度为变量 ,以亚心形扁藻为浮游微藻代表 ,采用实验生态学手段研究了大型海藻孔石莼与浮游微藻 (亚心形扁藻 )间的竞争。结果显示 ,不论营养盐浓度如何 ,高密度的孔石莼皆能显著抑制浮游微藻的生长。分析显示 ,高密度的孔石莼压制浮游微藻生长的原因 ,不是由于对氮、磷等营养盐的竞争所致 ,而可能是其他原因所致。 相似文献
6.
根据1988年7月调查资料讨论了台湾海峡中北部海域夏季上升流区各种形态磷的分布特征。结果表明,上升流中心区(即海坛岛东侧一带水域)具有低温、高盐、低溶解氧;DIp,TDP,PP,TP较高;DOP较低(0.27);及DIP/DOP比值(约为1)较高的特性。DOP是该海域磷的主要形态(占TP的49.2%),其含量分布及其形态转化与生物活动直接相关,是该海域生物生产力高的体现。 相似文献
7.
Modelling nitrogen and phosphorus cycles and dissolved oxygen in the Zhujiang Estuary Ⅰ. Model development 总被引:1,自引:0,他引:1
wrmcrloxHuman activities related to the population growth and developrnent of industry and rnwhci-pality have led to the incrouing hadings of various POllutants into estudries during the past fewdecades. These increasing edlutant lOadings have caused declined estuallne hedth which can bemereured by a vdriety of indices. In order to obtain solutions to environrnent problerns, re-sources manageTnnt apencies are supporting a holistic approach to envirorirnental management.An effcient strategy t… 相似文献
8.
A surface panel method treating a boundary-value problem of the Dirichlet type with the free surface is presented to design a three-dimensional body corresponding to a prescribed pressure distribution. The free surface boundary condition is linearized with respect to the oncoming flow, and computed by four-point finite difference scheme. Sample designs for submerged spheroids and Wigley hull are carried out to demonstrate the stable convergence, the effectiveness and the robustness of the method. The design of a 5500TEU container carrier is performed with respect to reduction of the wave resistance. To reduce the wave resistance, calculated pressure on the hull surface is modified to have the lower fluctuation, and is applied as a Dirichlet type dynamic boundary condition on the hull surface. The designed hull form is verified to have the lower wave resistance than the initial one not only by computation but also by experiment. 相似文献
9.
根据1992年12月(冬季)和1993年7月(夏季)对大鹏澳海域24h定点连续观测和夏季大面调查,统计了该海域各种形态磷的变化范围和平均含量;计算了各种形态磷分别占总磷(TP)和总溶解磷(TDP)的百分比;讨论了各种形态磷之间的相互关系;分析了影响TP和TDP分布的环境因素。 相似文献
10.
Effect of emersion and immersion on the porewater nutrient dynamics of an intertidal sandflat in Tokyo Bay 总被引:2,自引:0,他引:2
Tomohiro Kuwae Eiji Kibe Yoshiyuki Nakamura 《Estuarine, Coastal and Shelf Science》2003,57(5-6):929-940
Porewater nutrient dynamics during emersion and immersion were investigated during different seasons in a eutrophic intertidal sandflat of Tokyo Bay, Japan, to elucidate the role of emersion and immersion in solute transport and microbial processes. The water content in the surface sediment did not change significantly following emersion, suggesting that advective solute transport caused by water table fluctuation was negligible. The rate of change in nitrate concentration in the top 10 mm of sediments ranged from −6.6 to 4.8 μmol N l−1 bulk sed. h−1 during the whole period of emersion. Steep nutrient concentration gradients in the surface sediment generated diffusive flux of nutrients directed downwards into deeper sediments, which greatly contributed to the observed rates of change in porewater nutrient concentration for several cases. Microbial nitrate reduction within the subsurface sediment appeared to be strongly supported by the downward diffusive flux of nitrate from the surface sediment. The stimulation of estimated nitrate production rate in the subsurface layer in proportion to the emersion time indicates that oxygenation due to emersion caused changes in the sediment redox environment and affected the nitrification and/or nitrate reduction rates. The nitrate and soluble reactive phosphorus pools in the top 10 mm of sediment decreased markedly during immersion (up to 68% for nitrate and up to 44% for soluble reactive phosphorus), however, this result could not be solely explained by molecular diffusion. 相似文献