全文获取类型
收费全文 | 454篇 |
免费 | 92篇 |
国内免费 | 105篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 74篇 |
地球物理 | 122篇 |
地质学 | 209篇 |
海洋学 | 120篇 |
天文学 | 8篇 |
综合类 | 11篇 |
自然地理 | 87篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 19篇 |
2019年 | 16篇 |
2018年 | 3篇 |
2017年 | 13篇 |
2016年 | 13篇 |
2015年 | 26篇 |
2014年 | 25篇 |
2013年 | 27篇 |
2012年 | 25篇 |
2011年 | 44篇 |
2010年 | 17篇 |
2009年 | 36篇 |
2008年 | 35篇 |
2007年 | 28篇 |
2006年 | 23篇 |
2005年 | 29篇 |
2004年 | 23篇 |
2003年 | 20篇 |
2002年 | 20篇 |
2001年 | 22篇 |
2000年 | 14篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 22篇 |
1996年 | 24篇 |
1995年 | 12篇 |
1994年 | 16篇 |
1993年 | 17篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有651条查询结果,搜索用时 15 毫秒
611.
Guidelines to locate and protect high-quality groundwater in Baiyu Mountain area of China 总被引:1,自引:0,他引:1
Yunfeng Li Zhonghua Xu Jiangxia Wang Yaoguo Wu Guangcai Hou 《Environmental Geology》2005,47(5):647-652
The Baiyu Mountain area has the most shortage of water in the Ordos Basin of China. The majority of the groundwater is in the Luohe water-bearing formation, which is characterized by high total dissolved solids (TDS). The concentration of TDS can be as high as 10.45 g/l, which makes the water unsuitable for either potable or irrigation purpose. The dominant ions in the groundwater are SO2–4·Cl–. The maximum concentrations of SO2–4 and Cl– are 3,170 and 3,830 mg/l, respectively. The areas with low TDS groundwater are in Jingbian and Zhidan counties. However, nitrogen pollution caused by human and agriculture activities is a significant threat to the protection of fresh water in these counties. 相似文献
612.
山地降水垂直分布模式讨论 总被引:5,自引:1,他引:4
本文通过两个实例,讨论傅抱璞山地降水公式的优化计算问题,并提出另一种可能的高斯曲线型分布模式。 相似文献
613.
我国工业布局的变化趋势 总被引:7,自引:2,他引:5
解放以来,我国工业布局发生了重大的变化,积累了丰富的资料和经验。系统地分析、评价我国工业布局变化的规律和趋势是经济建设中的重大实践问题,也是经济地理学 相似文献
614.
地理环境对民族的形成、语言、习俗及地理分布具有深刻的影响作用。本文在依据一定的史实资料和实地调查的基础上,对我国赫哲族的源流和历史地域分布;赫哲语言和姓氏由来;赫哲族生产方式和习俗等与地理环境的关系,进行了研究探讨。赫哲族作为祖国大家庭中的一员,在长期民族融合的历史过程中,不同程度上仍然保留着本民族的固有特征。在地域分布上,各历史时期有相对稳定、集中的地域。而长期形成的生产、生活方式和习俗则反映了一个民族对地理环境适应与利用能力。 相似文献
615.
Hun-Bok Jung Seong-Taek Yun Bernhard Mayer Soon-Oh Kim Seong-Sook Park Pyeong-Koo Lee 《Environmental Geology》2005,48(4-5):437-449
Transport and sediment–water partitioning of trace metals (Cr, Co, Fe, Pb, Cu, Ni, Zn, Cd) in acid mine drainage were studied
in two creeks in the Kwangyang Au–Ag mine area, southern part of Korea. Chemical analysis of stream waters and the weak acid
(0.1 N HCl) extraction, strong acid (HF–HNO3–HClO4) extraction, and sequential extraction of stream sediments were performed. Heavy metal pollution of sediments was higher
in Chonam-ri creek than in Sagok-ri creek, because there is a larger source of base metal sulfides in the ores and waste dump
upstream of Chonam-ri creek. The sediment–water distribution coefficients (K
d) for metals in both creeks were dependent on the water pH and decreased in the order Pb ≈ Al > Cu > Mn > Zn > Co > Ni ≈ Cd.
K
d values for Al, Cu and Zn were very sensitive to changes in pH. The results of sequential extraction indicated that among
non-residual fractions, Fe–Mn oxides are most important for retaining trace metals in the sediments. Therefore, the precipitation
of Fe(–Mn) oxides due to pH increase in downstream sites plays an important role in regulating the concentrations of dissolved
trace metals in both creeks. For Al, Co, Cu, Mn, Pb and Zn, the metal concentrations determined by 0.1 N HCl extraction (Korean
Standard Method for Soil Pollution) were almost identical to the cumulative concentrations determined for the first three
weakly-bound fractions (exchangeable + bound to carbonates + bound to Fe–Mn oxides) in the sequential extraction procedure.
This suggests that 0.1 N HCl extraction can be effectively used to assess the environmentally available and/or bioavailable
forms of trace metals in natural stream sediments. 相似文献
616.
617.
Heavy metal contamination and their distribution in different size fractions of the surficial sediment of Haihe River, China 总被引:3,自引:0,他引:3
Heavy metal contamination and their distribution in different size fractions of the surficial sediment in Haihe River, China have been investigated. These results reveal that the heavy metal contamination of Haihe River is closely related to the contaminating sources along the river and has the order: Cd > Cu > Pb > Cr. The contents of these heavy metals in the sediment of Haihe River are at least two times higher than their background values and the highest contaminating metal, Cd, is 15.5 times higher than its background value and determined in the urban area of Tianjin city. The surficial sediments of Haihe River, with 70% particles smaller than 20 μm, belong to sandy clay containing about 28% clay and 42% silt. Electron micrographs and x-ray analysis show that the concentrations of heavy metals depend on the particle size of sediments. The highest concentrations for most metals exist in fine-grained sediments, which are mainly composed of silicates, oxides, and hydroxides of Si, Fe, and Al. In contrast, lower levels of heavy metals are usually found in the coarse sandy sediments, which are composed of quartz, feldspar, and other rocky substances. Based on the results in the present study of the surficial sediments of Haihe River, the contents of Cr, Cu, Pd, and Cd in finer sediments are 2.4, 3.9, 2.8, and 3.6 times higher than those in coarse sandy sediments, respectively. Obviously, because of rapid industrial development in this area during the last few decades, the surficial sediments of Haihe River, especially those finer fractions, have been seriously contaminated by heavy metals. 相似文献
618.
苏北盆地油气富集与分布的主控因素 总被引:3,自引:0,他引:3
根据烃源岩及沉积体系的分布、断裂的发育与分布、盖层的发育状况、圈闭形成时期等因素与油气富集特征的分析,认为苏北盆地各凹陷的油气富集程度与其烃源岩的发育程度有关,油气藏的形成及分布与断层密切相关,断层是控制油气成藏与富集的主要因素之一;紧邻生烃中心的长期隆起区是油气运移的指向区,控制油气的聚集成藏;区域盖层阻止油气往上覆层运移,其下伏储集层段为油气富集层段,缺乏统一区域性盖层的层段,局部盖层发育与否直接影响油气富集程度;沉积体系的分布控制油气的分布和富集地区。 相似文献
619.
620.
地面雨滴谱观测技术及特征研究进展 总被引:4,自引:0,他引:4
雨滴谱是反映降水微观物理过程和宏观动力结构的主要指标之一.通过分析雨色斑滴谱,可以深入了解降水的发展和演变过程,揭示降水机制.传统雨滴谱测量包括动力学法、滤纸色斑法、面粉团法、快速摄影法和浸润法等,但是普遍存在精度低、工作量大、实时性差、成本高及无法自动完成测量分类等缺点.以雨滴谱仪为代表的新型雨滴谱测量技术包括冲击雨滴谱仪、光学雨滴谱仪和声学雨滴谱仪以及雷达技术等克服了这些缺点,在降水粒子观测和降水物理研究中发挥了重要的作用.综合概述了描述雨滴谱的主要分布模型及其适用条件.归纳分析了不同降水云系(对流云、层状云和层积云降水)、不同降水类型(大陆云和海洋云降水)及不同高度处观测的降水的雨滴谱特征.从学科发展趋势和社会需求的角度,概述了有关雨滴谱研究中存在的主要问题和发展趋势. 相似文献