首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 62 毫秒
1.
陆涛 《青海科技》2012,(4):71-73
青海省地大物博,是全国的五大牧区之一,是联合国教科文组织认定的"世界四大无公害超净区"之一,自然环境处于原始或半原始状态。这里辽阔的天然牧场,具有面积大、类型多、草质好的特点,适宜放牧各类牲畜,具有发展生态牧业的先天优越条件。青海省的天然草场面积占全国草场总面积的十分之一,在全国仅次于内蒙古、西藏和新疆,居于第四位。牧区面积占到了全省总土地面积的94.76%,可利用的草场5亿余  相似文献   

2.
中国车前属种子形态及其分类学意义   总被引:1,自引:0,他引:1  
本文研究了中国车前科Plantaginaceae车前属plantago2亚属8组17种及1变种植物的种子, 在扫描电子显微镜下的形态及亚显微结构(种皮纹饰).结果表明种子形态有四个类型:1,多角形类型;2.舟形类型;3.卵形类型;4.矩圆形类型。各个种的种子形态和种皮纹饰有着相当明显的区别。新种plantago densiflorus的建立应用了种子形态和种皮纹饰这一特征。车前种子形态分类与pilger用植物其他形态特征建立的车前属分类系统是一致的,因此,笔者支持Pilger的车前属分类系统。  相似文献   

3.
我国拥有53亿亩天然草场,仅次于苏联和澳大利亚,居世界第三位,是国家极其宝贵的资源。我国也保留了世界最丰富的天然草场类型和世界最大的野生牧草种质基因库。这些天然草场主要分布于大兴安岭—阴山山脉—贺兰山—横断山一线的西北,集中在少数民族聚居地区和边境地区。因此,在查清我国草场资源的基础上,科学地利用、保护好我国的草场资源,对  相似文献   

4.
甘肃省河西地区草场总面积约1.2亿亩,占河西土地总面积的30%,占全省草场总面积的1/2以上,是甘肃省草场的重要组成部分。河西地区草场主要分布在乌鞘岭以西的亚洲中部荒漠带上,草场类型较多,以山地草场为主。资料在查清河西地区草场类型和各类型草群组成的前提下,按草场产草量的高低将其划分为不同的级别,分级标准为表一所示。  相似文献   

5.
西藏高原湿地及保护发展战略研究   总被引:3,自引:0,他引:3  
刘务林 《西藏科技》2004,(10):37-39
西藏湿地总面积达600多万hm^2,主要是天然湿地,约占全区土地面积的4.9%,常见的类型有:湖泊湿地250多万hm^2;河流湿地23万多hm^2;沼泽和沼泽化草句湿地323万多hm^2;库塘湿地约1万hm^2。西藏自治区人民政府先后划定了具有(或有部分)湿地生态环境的自然保护区8个。在30年内优先考虑保护的重要湿地是:①生态环境有着重大影响;②湿地集中连片;③生物多样性较丰富;④生态环境较脆弱的区域。最重要的大约有33个湿地类型区域,面积达到225.49万hm^2。  相似文献   

6.
天然草场是国家宝贵的自然资源,是发展畜牧业的物质基础。我国天然草场不仅面积大,而且类型多。从全国看,大体上可划成三个草场区:东北西部、内蒙古中东部半湿润半干旱草原区;新疆、甘肃、宁夏、内蒙西部干旱荒漠及山地草原区和青藏高原高寒草甸、草原区。 内蒙古自治区及其东西部毗邻地区(以下简称本区)除内蒙古自治区外,主要包括黑龙江省呼伦贝尔盟及大兴安岭地区、吉林省哲里木盟及部分白城地区、辽宁省昭乌达盟、宁夏回族自治区阿拉善左旗和甘肃省阿拉善右旗和额济纳旗。据统计,天然草场总面积占本  相似文献   

7.
基于MODIS NDVI时序数据的青海省草地分级   总被引:1,自引:0,他引:1  
卫亚星  王莉雯  刘闯 《资源科学》2008,30(5):688-693
草地是陆地生态系统的重要组成部分,近几十年来,草地退化很严重,全球关注的荒漠化问题也主要是发生在草地上。本文使用MODIS NDVI数据分析了青海全省的草地状况,采用了一种密度分割的草场分级方法,将青海的草场分为10个等级,这10个等级中高一等级所代表的土地单元比低一等级所代表的土地单元草场状况好。研究结果表明,利用这种分级方法处理的图像能够较为准确地反映青海省的土地覆盖类型和一年内的物候变化规律。青海的草场可以分为3个等级,第一等是优良草场,第二等是普通草场,第三等是退化草场。每一等可以分为3级,第一等第一级的NDVI值在0.8-1.0之间,第一等第二级和第三级的NDVI值在0.7—0.8之间;第二等第一级的NDVI值在0.6-0.7之间,第二等第二级的NDVI值在0.5—0.6之间,第二等的第三级的NDVI值在0.4—0.5之间;第三等的第一级的NDVI值在0.3~0.4之间,第三等的第二级的NDVI值在0.2—0.3之间,第三等的第三级的NDVI值在0.1-0.2之间。本文提出的草地分级方法能够准确地给出冬春场和夏秋场的位置,从而可以根据NDVI值和鲜草产量模型确定产草量和理论载畜量,指导畜牧业生产。  相似文献   

8.
基于决策树分类的云南省迪庆地区景观类型研究   总被引:3,自引:0,他引:3  
李亚飞  刘高焕  黄翀 《资源科学》2011,33(2):328-334
决策树分类是基于空间数据挖掘和知识发现的监督分类方法。本研究利用遥感TM数据和DEM数据,构建分类决策树,并通过ENVI软件实现决策树分类,得到迪庆地区的景观类型分布图。同时利用传统的监督分类的方法进行分类,得到该地区景观类型分布图。利用野外实地采样的数据对两种分类方法进行精度评价,结果表明,两种分类方法的总体分类精度分别为85.5%和67.4%,决策树分类方法的总体分类精度比传统监督分类提高了近20%。在此基础上,研究云南省迪庆地区的景观类型分布状况,可得到以下结论:迪庆地区的景观类型主要有河谷灌丛面积约占5.5%,针叶林面积约占36.16%,亚高山灌丛草甸面积约占3.4%,高山冰雪面积约占3.7%,裸地面积约占25.4%,水体面积约占4.4%。除裸地和水体外,其他景观基本都沿着山体按海拔高度和坡向分布,其中面积最大的为针叶林景观。这与该地区高山峡谷地貌吻合。  相似文献   

9.
矢志开发终见成效许明国(湖北省石首市委政策研究室.434400)湖北石首市地处长江荆江河段,境内河床经过两次自然裁弯和一次人工裁弯,形成南碾子、北碾子、中洲子、沙滩子4个故道区,历经多年淤积和开发后已成为独特的自然生态经济区。该区总面积3.07万ha...  相似文献   

10.
罗培  谌柯  刘辉  曾凡伟 《资源科学》2007,29(4):179-186
根据1885年、2004年的土地利用现状图、土地详查资料以及实地收集数据,在GIS技术支持下,利用数学模型分析了南充市高坪区近20年间土地利用变化及其动因。研究表明:20年来,研究区土地利用类型的面积变化为12 050hm2,占该区总土地面积的14.84%,主要表现为园地、城市工业用地和交通用地的增加和未利用地和耕地的减少;区域土地利用空间格局发生较大变化,斑块数目增加2 921个,斑块面积均有由大到小的变化趋势,土地利用类型多样性和破碎度增加,优势度降低;除园地、交通用地以外,其他土地类型都有分散分布的趋势;不同的土地利用类型重心在不同的方向上有不同的移动距离; 影响城郊农业区土地利用变化的因素主要是城市化和政策导向。  相似文献   

11.
This study examined how students who had no prior experience with videoconferencing would react to the use of videoconferencing as an instructional medium. Students enrolled in seven different courses completed a questionnaire at the beginning of the semester and again at the end of the semester. Students at the origination and remote sites did not differ in their reactions toward videoconferencing but there was a significant difference for gender. Women reacted less favorably to videoconferencing. Compared to the beginning of the semester, students reported significantly less positive attitudes toward taking a course through videoconferencing at the end of the semester. There were no significant differences in students' attitudes toward videoconferencing across courses at the beginning of the semester but there were significant differences across the courses at the end of the semester. The results suggest the need for better preparation for both students and instructors.  相似文献   

12.
Ajoint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology and his co-workers from Norway, US and Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells, suggesting that China's projected climate warming could decrease the pest's numbers. The study was published in Proceedings of theNational Academy of Sciences on 17 September, 2007.  相似文献   

13.
A computer-mediated group is a complex entity whose members exchange many types of information via multiple means of communication in pursuit of goals specific to their environment. Over time, they coordinate technical features of media with locally enacted use to achieve a viable working arrangement. To explore this complex interaction, a case study is presented of the social networks of interactions and media use among members of a class of computer-supported distance learners. Results show how group structures associated with project teams dominated who communicated with whom, about what, and via which media over the term, and how media came to occupy their own communication niches: Webboard for diffuse class-wide communication; Internet Relay Chat more to named others but still for general communication across the class; and e-mail primarily for intrateam communication. Face-to-face interaction, occurring only during a short on-campus session, appears to have had a catalytic effect on social and emotional exchanges. Results suggest the need to structure exchanges to balance class-wide sharing of ideas with subgroup interactions that facilitate project completion, and to provide media that support these two modes of interaction.  相似文献   

14.
Aresearch group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol--a chemical found in the skins of red grapes and in red wine--can improve the sensitivity of mice to the hormone insulin, according to a report in the October,2007 issue of Cell Metabolism. As insulin resistance is often characterized as the most critical factor contributing to the development of Type 2 diabetes, the findings“provide a potential new therapeutic approach for preventing or treating” both conditions, the researchers said.  相似文献   

15.
Electronic data interchange (EDI) provides means for interorganizational communication, creates network externalities, requires an advanced information technology (IT) infrastructure, and relies on standards. In the diffusion of such innovations, institutional involvement is imperative. Such institutions contain governmental agencies, national and global standardization organizations, local government, and nonprofit private organizations like industry associations. The last type of organizations we call intermediating institutions. They intermediate or coordinate ("inscribe") the activities of a group of would-be adopters. Unfortunately, little is known of how these organizations shape the EDI diffusion trajectory. In this article we examine one specific type of intermediating organizations?industry associations?and how they advanced the EDI diffusion process in the grocery sectors of Hong Kong, Denmark and Finland. We identify six institutional measures, placed into a matrix formed by the mode of involvement (influence vs. regulation) and the type of diffusion force (supply push vs. demand pull), that can be mobilized to further the EDI diffusion. Industry associations were found to be active users of all these measures to varying degrees. Their role was critical especially in knowledge building, knowledge deployment, and standard setting. Furthermore, institutional involvement varied due to policy and cultural contingencies and power dependencies.  相似文献   

16.
The increasing prospects of digital piracy has prompted the perceived need by electronic publishers to adopt technical systems of protection, and governments to reform their copyright laws. This article is a preliminary study of the management of intellectual property by electronic publishers, defined as those involved in the production of online databases, and CD-ROMs. It focuses on three main issues: (1) how electronic publishers view the increasing threat of piracy; (2) the methods of protection employed to protect intellectual property in digital format; and (3) the importance of technological protection of intellectual property in electronic publications. The analysis is based on a sample of 23 UK electronic publishers. The interviews revealed an interesting assortment of protection methods and did not show that technological protection was a preferred way. Instead, the means of protection, in addition to copyright law, comprised niche markets, pricing, trust, bad publicity, and nontechnical and technical means.  相似文献   

17.
Long-standing conflict between domain name registrants and trademark holders prompted the Internet Corporation for Assigned Names and Numbers (ICANN) to create a global, mandatory arbitration procedure known as the Uniform Dispute Resolution Policy (UDRP). The UDRP has been used in 2166 cases involving 3938 domain names as of 1 November 2000. The policy gives the initiator of a complaint, generally a trademark holder, the right to choose which ICANN-accredited dispute resolution service provider (RSP) will handle the case. During the preparation of the UDRP,some feared that complainant selection would lead to "forum shopping" that might bias the results. This article performs a statistical assessment of the forum-shopping thesis and finds support for it. There are statistically significant differences in the various RSPs' propensity to take away names from defendants; there are also major differences in the number of cases brought to each RSP. RSPs who take away names have the larger share of cases. The study examines other variables that might explain differences in market share, such as price, the plaintiff's nationality, or the time taken to decide a case. It finds that nationality and time also are correlated with market share. The study concludes that shopping for a favorable outcome is an important factor in the UDRP.  相似文献   

18.
Prof. Raymond C.K. Chen, a neuropsychologist with the CAS Institute of Psychology, has made novel progress in his studies of schizophrenia. His work has been reported by a recent issue of Behavioural Neurology.  相似文献   

19.
Active biological molecules and functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery, disease diagnosis and therapy, and new nanodevice construction.  相似文献   

20.
<正>In Xishuangbanna,one of China’s most biodiverse regions,landscape has changed dramatically during the past three decades due to the conversion of tropical rainforest to rubber plantations.In steep areas,terraces are often constructed before planting rubber trees,which causes two important changes in the soil:the destabilization of soil in the bench terraces and the increased vulnerability of unvegetated riser faces to erosion.Few studies have documented the nature and intensity of erosion on bench terraces.Prof.LIU Wenjie and his colleagues from the Xishuangbanna Tropical Botanical Garden(XTBG)conducted a study in Menglun County(21°5′39″N,101°15′55″E),Xishuangbanna to evaluate the influence  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号