传统图书馆向数字图书馆的跨越     

王春侠 《安徽农业大学学报》2005,(4):139-141

随着知识经济时代的到来和数字技术的普及，数字图书馆也应运而生。数字图书馆以其独特的优势为人们提供广泛、快捷、先进的服务。为此，要求传统图书馆必须与时俱进，尽快实现向数字图书馆的跨越。  相似文献   

河北省耕地功能供需转型时空演变及利用分区     

徐磊    胡浩  尹士  杨静园  马立军 《水土保持研究》2023,30(3):403-412

[目的]以河北省县域为研究单元,测算耕地多功能供需转型的幅度与速度,探寻耕地多功能利用的优化路径。[方法]基于土地利用现状数据及社会经济数据,采用价值量法测算2000年、2010年、2018年各单元耕地功能供需水平,利用四象限模型实现河北省县域耕地利用分区。[结果]研究期内,河北省绝大部分县域耕地功能供给量和需求量增加,耕地功能供给量分布为东高西低; 耕地功能需求量集中分布于环京津的沧州市、廊坊市和唐山市。河北省耕地功能供给转型幅度高值区为承德市、秦皇岛市和唐山市,耕地功能需求转型幅度高值区为京津周边的沧州市、廊坊市和唐山市; 河北省大多县域耕地功能供需转型速度逐步提升,从空间分布看承德市耕地功能供给转型速度快,廊坊市和唐山市耕地功能需求转型速度快。[结论]河北省耕地功能供需匹配由盈余转为赤字,耕地利用分区研究为高供给高需求、高供给低需求、低供给高需求和低供给低需求4类耕地功能区提供优化路径。  相似文献   

中国农牧交错带生态评价研究   总被引：10，自引：6，他引：4  

王志伟  王平  王迅  张学通  陈全功 《草业科学》2009,26(4):64-73

中国农牧交错带是我国农业种植区与草原畜牧区相连接的生态过渡地带,又称半农半牧区或生态脆弱带。农牧交错带是一个独特而重要的产业界面,是我国最大的气候、生态过渡带,在我国经济、社会发展和环境保护方面具有重要的战略地位。本文对中国农牧交错带生态安全评价的研究是以农牧交错系统特殊的生态状况为基础,考虑到现有的自然环境压力、社会经济压力以及人类的积极影响,选择目前与潜在的压力、对生态系统的影响以及经济社会的响应3个方面作为指标体系和评价标准,对中国农牧交错带生态环境因子以及生态总体状况进行安全评估。因此,根据农牧交错带的特点,基于压力状态响应概念模型,建立了生态安全评价指标体系,以及相应的选取标准,将为农牧交错带生态安全评价研究和生态环境管理实践提供理论基础。  相似文献   

旺长期烤烟叶片的叶绿素荧光特性与激发能分配   总被引：1，自引：1，他引：0  

刘德育  于方玲  孙冰玉  贺国强  元野  赵光伟  李恒全  孙广玉 《核农学报》2010,24(3):623-627

以烤烟品种龙江911为试验材料,研究了烤烟植株上、中、下3个部位叶片实际光化学效率(ΦPSⅡ)和PSⅡ最大光能转化效率(Fv/Fm)的日变化,以及激发能的分配特性。结果表明,烤烟叶片Fv/Fm和实际光化学效率(ΦPSⅡ)中午降低,PSⅡ功能下调,有明显的光抑制。在光合有效辐射(PPFD)逐渐增强过程中,Fv/Fm和ΦPSⅡ降低,非光化学猝灭(NPQ)增加,激发能由PSⅠ向PSⅡ分配的比例增加,说明引起烤烟光抑制的原因除了NPQ之外,分配给PSⅡ能量增加是光抑制非常重要的因素。PPFD逐渐减小时,光抑制逐渐减缓,光化学效率恢复,激发能分配不平衡性系数(β/α-1)下降,PSⅡ能量负荷减轻,失活的PSⅡ恢复活性。  相似文献   

两系小麦不育系BNS雄性育性的转换   总被引：2，自引：0，他引：2  

周美兰  茹振刚  骆叶青  罗丕  李青  郭小孔  周萍 《核农学报》2010,24(5):887-894

于2006-2009年在湖南长沙采用分期播种方法以两系小麦不育系BNS和对照百农矮抗58、农大211、农大3688和杨麦13为试验材料,研究了BNS雄性育性在南方生态区域的转换规律。结果表明:随播种期的推迟,BNS雄性育性表现为完全败育→高度不育→部分可育→完全可育的育性转换规律;雄性完全败育阶段以花粉典型败育为主;3月中、下旬开花阶段,花粉完全败育;4月上旬开花阶段,雄性育性发生转变,4月中旬开花阶段,花粉可育。雄性育性的转换伴随着开花习性发生转换。  相似文献   

香蕉粉喷雾干燥工艺优化   总被引：10，自引：4，他引：6  

陈启聪  黄惠华  王娟  胡凯  曾霖霖 《农业工程学报》2010,26(8):331-337

为了改善香蕉粉的喷雾干燥效果,优化喷雾干燥工艺,该文研究了进风温度、助干剂添加量、热空气流量、压缩空气流量的变化对香蕉汁喷雾干燥效果的影响,并采用Box-Behnken响应曲面法优化喷雾干燥条件,分析进风温度、热空气流量、压缩空气流量的变化对出风温度和产品得率的影响规律。结果显示：当进风温度为170.0℃、热空气流量为36.08 m3/h、压缩空气流量为489.70 L/h时,出风温度为76～80℃,产品得率最高,达44.28%,所制备的香蕉粉含水率低于5%,符合固体饮料标准。由此说明,通过响应曲面优化得到的喷雾干燥工艺能有效应用于加工香蕉粉。  相似文献   

降温方法对不同采收期鸭梨采后果心褐变和膜脂组分的影响   总被引：5，自引：2，他引：3  

闫师杰  梁丽雅  陈计峦  李晓丹  胡小松 《农业工程学报》2010,26(8):356-362

为了探讨缓慢降温抑制采后鸭梨果实褐变的机理,研究了不同降温方法对不同采收期鸭梨果心膜脂脂肪酸组分、含量、膜相变温度、脂氧合酶（LOX）活性以及果心褐变的影响。结果表明：鸭梨果心含有月桂酸、豆蔻酸、棕榈酸、棕榈油酸、珠光酸、硬脂酸、油酸、亚油酸、亚麻酸,其中含量较多的是亚油酸、棕榈酸和油酸。缓慢降温提高了早采鸭梨果心的亚麻酸和亚油酸相对含量及不饱和脂肪酸与饱和脂肪酸比值（U/S）,降低了果心的膜相变温度,明显抑制了果心LOX活性和褐变。推迟采收提高了鸭梨果心的U/S值,降低了膜相变温度,但由于采收期晚,果实衰老较快,后期果心LOX活性快速升高,膜脂过氧化严重,导致晚采果更容易褐变。总之,适当早采结合缓慢降温可以提高鸭梨果心膜脂不饱和脂肪酸含量和U/S值,抑制果心褐变。  相似文献   

DNA barcoding reveals clear delineation between spawning sites for neritic versus oceanic fishes in the Gulf of Mexico     

Makenzie Burrows  Jeremy S. Browning  Mya Breitbart  Steven A. Murawski  Ernst B. Peebles 《Fisheries Oceanography》2019,28(2):228-239

We combined research‐vessel cruises of opportunity with DNA barcoding to survey planktonic, percomorph fish eggs at 40 stations distributed across and around the Gulf of Mexico (GoM). The objectives were (a) to determine whether eggs of fishes that are potential candidates for the daily egg production method (DEPM) can be readily barcoded, (b) to identify taxa that are spawning in the GoM, (c) to determine encounter rates for eggs of economically valuable taxa, and (d) to characterize individual egg taxa as being primarily neritic, primarily oceanic, or primarily mixed (i.e., both neritic and oceanic). Of the 1,144 eggs that were individually barcoded, 709 (62%) were definitively identified to species (62 species from 42 families), with an additional 20 taxa identified to genus or subfamily level. The eggs of 15 economically important species were identified, most of which had intermediate encounter rates and moderately dispersed spatial distributions, as indicated by an index of aggregation. SIMPROF analysis of stationwise cluster analysis identified eight significant groups within the 35 stations that yielded percomorph eggs; a corresponding specieswise analysis identified six groups of stations as having a neritic egg community and two groups as having an oceanic community, with a community transition located at the shelf break. Although the neritic and oceanic stations did not share important species, it remains possible that coastal pelagic species have mixed neritic–oceanic distributions. Together, these results indicate DEPM fish‐egg surveys based on DNA barcoding are feasible at the large marine ecosystem scale.  相似文献   

Atmospheric forcing drives recruitment variation in the Dungeness crab (Cancer magister), revisited     

A. L. Shanks 《Fisheries Oceanography》2013,22(4):263-272

For 12 yr (1997–2001, 2006–2012) daily abundance of Cancer magister megalopae was measured in Coos Bay, Oregon. Before 2007 from 2000 to 80 000 megalopae were caught annually. In 2007, catch jumped and has since varied from 164 000 to 2.3 million. The step change in catch size appears related to a shift to negative Pacific Decadal Oscillation (PDO) values. Late season catches, which cannot be due to local spawning, are negatively correlated to the PDO, suggesting that these megalopae derive from north of the California Current. During periods of lower and higher catches, annual returns of megalopae were significantly negatively correlated to the day of the year of the spring transition and positively correlated to the amount of upwelling during the settlement season. The size of the Oregon commercial catch lagged 4 yr to allow for growth of recruits into the fishery is set by the number of returning megalopae; the relationship is parabolic. At lower returns, the population is recruitment limited, but at higher returns, density‐dependent effects predominate and set the commercial catch. Lagged commercial catches in Washington and Northern and Central California were also related to the number of megalopae returning to Coos Bay, suggesting that the forces causing variation in larval success are coast wide. If high return rates are due to a PDO regime shift, then for years to decades the commercial catch may be set by density‐dependent effects following settlement and the huge numbers of returning megalopae may impact benthic community structure.  相似文献   

水泵全特性曲线的预测及对数值分析的影响     

黄亚  周建旭 《排灌机械工程学报》2021,39(8):777-783

为了准确评估泵系统水力过渡过程特性并实施合理有效的水锤防护,基于水泵全特性曲线的Suter曲线表达形式,提出基于牛顿插值算法的水泵全特性曲线预测方法,进一步给出一种利用水泵基本特性曲线来修正水泵全特性曲线的数值变换方法.通过与常用的水泵全特性曲线预测拟合方法的比较,以及在泵站系统过渡过程计算中的应用分析,结果表明:基于...  相似文献