全文获取类型
收费全文 | 121篇 |
免费 | 16篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 36篇 |
地球物理 | 52篇 |
地质学 | 18篇 |
海洋学 | 12篇 |
天文学 | 1篇 |
综合类 | 2篇 |
自然地理 | 15篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 2篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 7篇 |
2012年 | 5篇 |
2011年 | 5篇 |
2010年 | 10篇 |
2009年 | 6篇 |
2008年 | 11篇 |
2007年 | 10篇 |
2006年 | 7篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 7篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有150条查询结果,搜索用时 15 毫秒
61.
62.
辽宁中部城市群度日的变化特征 总被引:2,自引:1,他引:2
利用1951—2006年辽宁中部城市群沈阳、抚顺、本溪、鞍山4城市逐日气温资料,分析各城市热度日HDD和冷度日CDD的变化规律,并探讨度日与平均气温及城市热岛强度等的关系。结果表明:辽宁中部城市群HDD和CDD最大值分别出现在1月和7月。4城市HDD年际变化均呈下降趋势;CDD年际变化沈阳和鞍山呈微弱的上升趋势,而抚顺和本溪呈微弱的下降趋势。自1950s始至21世纪的2006年,除抚顺外,其他各城市HDD年代际变化均表现为明显的下降趋势,而CDD年代际变化均表现为降—升—降的规律。年代HDD均值与年代平均气温呈反位相,而年代CDD均值与年代平均气温呈正位相,冬季HDD与城市热岛强度呈负相关。 相似文献
63.
64.
不同升温阈值下中国地区极端气候事件变化预估 总被引:5,自引:1,他引:5
本文基于耦合模式比较计划第五阶段(CMIP5)的18个全球气候模式的模拟结果,预估了全球平均气温在不同典型浓度路径(RCPs)下达到2℃、3℃和4℃阈值时,中国地区气温和降水的变化,并采用了具有稳定统计意义的27个极端气候指标定量评估了全球平均气温达到不同阈值时,中国地区极端气候事件的可能变化。结果表明,未来我国平均气温增幅将高于全球平均增暖,极端暖事件(如暖夜、暖昼、热带夜)明显增多,达到4℃阈值时,暖夜指数相比参考时段增加约49.9%。极端冷事件(如冷夜、冷昼、霜冻)减少。随全球气温升高,中国北方平均降水增多。在不同升温阈值下,中国地区降水的极端性都体现出增强的趋势,强降水事件发生频率(如中雨日数、大雨日数)和强度(如五日最大降水量、极端强降水量)都明显增加。随升温阈值的升高,这些变化幅度更大,在 RCP8.5 情景下全球升温 3℃和4℃时,中国平均五日最大降水分别增加 12.5mm和17.0mm。我国西南地区极端降水强度的增幅高于其他地区。 相似文献
65.
流域水系自动提取在西苕溪流域的应用 总被引:7,自引:0,他引:7
论述了如何基于栅格DEM自动提取流域自然水系的原理、方法和流程.以西苕溪中上游流域为例,根据DEM精度、上游集水区面积阈值和下垫面地形的不同,对所提取水系进行了比较.针对在平均地形坡度小于3°的平坦区域所提取水系与实际河网偏差较大的问题,提出了利用主干河道和平原水系数字化作为约束条件生成河网的新方法. 相似文献
66.
利用2006—2015年京津冀气象站的常规观测资料和同期NCEP/NCAR再分析资料,以秋冬季影响雾霾形成与消散的静稳大气和通透大气为研究对象,统计分析了气象因子的分布状况。结果表明:京津冀秋冬季降水对雾霾起不到冲刷作用,反而促进雾霾的形成与维持;京津冀秋冬季雾霾消散主要是风场因子的贡献。雾霾消散的大气状态可分为3种类型,在不同大气状态下,各风场因子对雾霾消散的贡献不同。采用迭代自组织数据类差最大值阈值分割法找出了各风场因子的最佳阈值。根据各风场因子对雾霾消散的敏感性和因子间的相关,筛选出3类大气状态下雾霾消散因子指标。采用指标叠套法对2016、2017年秋冬季大气进行检验,表明雾霾消散指标及其阈值能较好区分静稳大气和通透大气,对雾霾过程具有较好的指示意义;通过对derf2.0模式产品释用,可为延伸期雾霾过程客观化预测提供技术支撑。 相似文献
67.
Shulin Liu Tao Wang Guangting Chen Jian Guo Xian Xue Shaoxiu Ma 《Environmental Geology》2008,53(6):1225-1233
The characteristics of sand and dust movement over different sandy grasslands in China’s Otindag Sandy Land were explored
based on field observations and laboratory analyses. Threshold wind speeds (the speed required to initiate sand movement)
at a height of 2 m above the ground were estimated in the field for different surface types. Threshold wind speed above shifting
dunes in the study area is about 4.6 m s−1 at this height. This value was smaller than values observed above other surfaces, resulting in a greater risk of blowing
sand above these dunes. Differences in sand transport rates (STR) as a function of the severity of desertification resulted
primarily from differences in surface vegetation cover and secondarily from the soil’s grain-size distribution. STR increased
exponentially with increasing near-bed wind velocity. Under the same wind conditions, STR increased with increasing severity
of desertification: from 0.08 g cm−2 min−1 above semi-fixed dunes to 8 g cm−2 min−1 above semi-shifting dunes and 25 g cm−2 min−1 above shifting dunes. Vegetation’s affect on STR was clearly large. Different components of sand and dust were trapped over
different lands: mostly sand grains but little dust were trapped above shifting dunes, but much dust was collected over semi-shifting
and semi-fixed dunes. Human disturbance is likely to produce dust even from fixed dunes as a result of trampling by animals
and vehicle travel. In addition, spring rainfall decreased the risk of sand and dust movement by accelerating germination
of plants and the formation of a soil crust. 相似文献
68.
C. Martínez Navarrete J. Grima Olmedo J. J. Durán Valsero J. D. Gómez Gómez J. A. Luque Espinar J. A. de la Orden Gómez 《Environmental Geology》2008,54(3):537-549
The European Water Framework Directive (WFD) has driven the protection of groundwater and characterization of water bodies.
Development of appropriate and efficient approaches which consider the special features of the hydrologic regime is essential.
The results of different projects that have been carried out to integrate characterization and protection of water bodies
are summarized herein. In the Les eaux de la Mediterranée (AQUAMED) Project, applicability to the Mediterranean Region of
guidelines provided by the European Commission to facilitate the WFD implementation has been verified. The Background criteria
for the identification of groundwater thresholds (BRIDGE) Project developed a methodology to establish threshold values of
pollutants contributing to the chemical status of groundwater bodies. This method has been applied to pollutants used to classify
groundwater bodies as at risk of not achieving objectives of the WFD. Selected features of protection areas for drinking water
and safeguard zones are analyzed, as well as the possibility of using wellhead protection areas. 相似文献
69.
采用舟山海域1962—2015年的4个气象观测站资料、2014—2015年2 a的逐时自动气象数据和浮标站数据,统计分析了舟山海雾特征,结果表明:海雾总是在大尺度背景条件和一定的气象水文条件下发生;海雾春季最多,秋季最少,一天中多发生在夜间和早晨,又以下半夜到早晨最多,雾散一般在11∶00以后;海雾按天气形势可分4型,不同类型其季节变化和日变化存在差异;浓雾发生的要素特征为,气温5~27℃,海温9~27℃,气温露点差0~4℃,90%的浓雾发生在2 m相对湿度≥95%、气海温差-3.7~3.2℃时,浓雾风向主要落在东南风和偏南风之间,平均风力一般在1~5级;利用要素阈值对WRF能见度模式进行订正检验,发现对提高浓雾的定性预报准确率有较明显的作用。 相似文献
70.
Chao Chen Kate Z. Guyton 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(4):487-494
The objectives of this paper are to (1) reexamine the data that were used to support the conclusion of a threshold effect
for 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline (MeIQx)-induced initiation and carcinogenicity at low doses in the rat
liver, and (2) discuss issues and uncertainties about assessing cancer risk at low doses. Our analysis is part of an effort
to understand proper interpretation and modeling of data related to cancer mechanisms and is not an effort to develop a risk
assessment for this compound. The data reanalysis presented herein shows that the low-dose initiation activity of MeIQx, which
can be found in cooked meat, cannot be dismissed. It is argued that the threshold effect for carcinogenic agents cannot be
determined by statistical non-significance alone; more relevant biological information is required. A biologically motivated
procedure is proposed for data analyses. The concept and procedure that are appropriate for analyzing MeIQx data are equally
applicable to other compounds with comparable data.
The ideas and approaches in this presentation are those of the authors and do not necessarily represent the positions or policies
of the USEPA. 相似文献