首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   48篇
  免费   10篇
  国内免费   9篇
测绘学   3篇
大气科学   3篇
地球物理   15篇
地质学   20篇
海洋学   13篇
天文学   2篇
综合类   3篇
自然地理   8篇
  2022年   2篇
  2021年   3篇
  2020年   1篇
  2018年   3篇
  2015年   5篇
  2014年   5篇
  2013年   4篇
  2012年   2篇
  2011年   3篇
  2010年   3篇
  2009年   3篇
  2008年   7篇
  2007年   5篇
  2004年   6篇
  2003年   1篇
  2002年   2篇
  2001年   4篇
  1998年   2篇
  1996年   1篇
  1995年   2篇
  1992年   1篇
  1988年   2篇
排序方式: 共有67条查询结果,搜索用时 15 毫秒
11.
Pseudocycnus appendiculatus Heller is described and recorded, for the first time from New Zealand, on Thunnus alalunga (Bonnaterre, 1788). Pseudocycnus spinosus Pearse, 1951 and P. thynnus Brandes, 1955 are thought to be synonyms of P. appendiculatus. Other species previously placed in the genus are discussed and the action of Yamaguti (1963) in removing them to other genera supported. It is suggested that the family Pseudocycnidae Yamaguti, 1963 cannot be differentiated from the family Dichelesthiidae Bassett‐Smith, 1898.  相似文献   
12.
13.
The distribution of selected heavy metals, including some radionuclides, metalloids and non-metals was determined in stream sediments in a region influenced by abandoned copper mining and ore processing activities. A considerable amount of the ore processing waste with a very complex composition and highly elevated concentrations of zinc, sulfur, lead, copper, arsenic, and a lot of other elements in the range between 100 and 1,000 mg/kg (Sb, Mn, Ni, Cr, Cd, Hg, and Ag) was piled up on mine dumps. The dispersion of the pollutants originating from this source and their environmental impact were investigated. Both, sediments and original waste material were studied to indicate the pathways and the mobilization behavior of different pollutants. For this purpose, the process of the elution of pollutants by application of different fractionation schemes was studied. The capabilities of different analytical techniques are shown for the analysis of solid samples (X-ray fluorescence spectrometry, Gamma-spectrometry) and liquid ones (ICP-atomic emission spectrometry, ICP-mass spectrometry and different techniques of atomic absorption). Additionally, the coupling of ion chromatography and ICP-MS detection was used to study the distribution of arsenic species in the sediment cores of a lake which acts as a natural sink for the region.  相似文献   
14.
陶鹍  杨汝良 《测绘学报》2003,32(1):63-66
根据残余点生成机理,建立了残余点发生概率与干涉回波信号相关性内在联系的数学模型。据此,提出了以残余点的数目作为衡量干涉复图像整体配准质量的定量尺度。实验结果表明,该方法简便精确,尤其适用于系统基线较长时配准结果的比较、择优,从而能最大程度地减小数字高程模型中因配准精度欠佳所引起的误差。  相似文献   
15.
煤燃烧过程中微量元素的迁移和富集   总被引:5,自引:0,他引:5  
煤中微量元素在燃烧过程中产生迁移与富集。大部分元素在煤的燃烧产物中得以富集,一些挥发性强的元素将扩散到大气中。在飞灰中,大部分环境有害元素的富集程度与其粒度成反比,即在细粒飞灰中更加富集,由此对人体健康的潜在危害也更大。在我国,大型燃煤电厂的环境问题值得重视,同时大量的民用炉灶产生的环境污染更加严重,值得进一步研究与治理。  相似文献   
16.
利用吉林农安和桦甸、广东茂名、海南长昌以及黑龙江达连河等5个产地的油页岩样品进行脱油残渣的烧制和不同条件下的成瓷条件实验,通过XRD、XRF分析及烧失率的变化,初步获得了5个产地油页岩的化学成分、矿物含量、废渣成分及烧瓷后的矿物成分等.结果表明:不同油页岩中黏土矿物的种类差异在不同程度上会影响油页岩的含油率.  相似文献   
17.
Soil and sand fine particles, which may be resuspended as fine dust in the atmosphere, contain a variety of anthropogenic and natural organic components. Samples of fine soil and sand particles (sieved to <125 μM) were collected from the Riyadh area in the summer of 2003 and extracted with a mixture of dichloromethane and methanol (3:1, v:v). The derivatized total extracts were analyzed by gas chromatography–mass spectrometry in order to characterize the composition and sources of the organic components. Both anthropogenic and natural biogenic inputs were the major sources of the organic compounds in these extracts. Discarded plastics and vehicular emission products were the major anthropogenic sources in the fine particles from populated areas of the city. Their tracers were plasticizers, UCM, n-alkanes, hopanes and traces of steranes. Vegetation was the major natural source of organic compounds in samples from outside Riyadh and included n-alkanols, n-alkanoic acids, n-alkanes, methyl alkanoates, sterols and triterpenoids. Carbohydrates had high concentrations (42–54%) in all samples and indicate sources from decomposition of cellulose and/or the presence of viable microbiota such as bacteria and fungi. The results were also compared with the data obtained in winter 2002 and showed that anthropogenic inputs were higher in summer than in winter, whereas the opposite trend was observed for natural inputs.  相似文献   
18.
褐藻渣是褐藻工业产生的固体废弃物,直接排放到环境中容易破坏水体生态平衡.本研究用硅胶固定的褐藻渣吸附重金属Cu2+,并对其吸附特征进行了检测.结果表明,吸附pH,Cu2+初始浓度以及吸附时间对吸附过程均有很大的影响.该吸附材料对初始浓度在2.0 mmol/L以下的Cu2+溶液吸附率可达85%,25℃时最大吸附容量在0....  相似文献   
19.
高冉  饶竹  郭晓辰 《岩矿测试》2021,40(6):973-986
地下水中多种农药快速检测是全面表征地下水水质、确保地下水安全的重要技术支撑。本文结合现有检测标准和文献中农药需分类分别前处理和测试的问题,采用气相色谱-质谱仪,通过对水样前处理方法和气相色谱-质谱分析条件进行选择和优化,建立了地下水中91种农药气相色谱-质谱同时测定的快速分析方法。经优化,目标物采用脉冲不分流进样,Zebron Multiresidue-2色谱柱分离,分段选择离子扫描,内标法定量,多数农药在1.0~1000μg/L浓度范围内线性良好,相关系数在0.9901~0.9997之间。水样经二氯甲烷液液萃取浓缩后上机测试,各农药方法检出限为3.1~12.5ng/L,平均加标回收率在54.3%~129%之间,相对标准偏差(RSD)为1.2%~20%。本方法快速、简单,准确度高,不仅显著提高了地下水中多种类农药残留分析效率,降低了分析成本;而且方法更适合大批量地下水样品的快速筛查,从而保证了样品分析的时效性。该方法已成功应用于全国地下水污染调查专项。  相似文献   
20.
保护性耕作是攻克黑土地保护和利用的核心技术之一。研究立足中国科学院黑土区农业生态重点试验室保护性耕作长期定位试验基地,系统梳理总结了农田黑土土壤生物多样性对保护性耕作的响应特征。与传统耕作相比,保护性耕作显著增加各生物类群(微生物、线虫、跳虫、螨类及蚯蚓)的物种丰富度(1%~8%)、数量(25%~57%)和生物量(30%~50%),提高食物网网状结构的复杂性及各营养级间的连通性(14%~32%),促进土壤生物在固土蓄水、土壤碳固存、氮素高效利用以及稳定作物产量四方面生态功能的可持续性发挥。研究结果表明,实施保护性耕作可有效利用土壤生物的功能潜力,实现东北黑土区农田生态系统的健康发展、服务国家粮食安全产业带建设和现代农业发展。  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