全文获取类型
| 收费全文 | 4636篇 |
| 免费 | 427篇 |
| 国内免费 | 791篇 |
专业分类
| 测绘学 | 45篇 |
| 大气科学 | 183篇 |
| 地球物理 | 637篇 |
| 地质学 | 2010篇 |
| 海洋学 | 992篇 |
| 天文学 | 1411篇 |
| 综合类 | 156篇 |
| 自然地理 | 420篇 |
出版年
| 2024年 | 22篇 |
| 2023年 | 57篇 |
| 2022年 | 100篇 |
| 2021年 | 126篇 |
| 2020年 | 131篇 |
| 2019年 | 124篇 |
| 2018年 | 110篇 |
| 2017年 | 123篇 |
| 2016年 | 135篇 |
| 2015年 | 153篇 |
| 2014年 | 208篇 |
| 2013年 | 173篇 |
| 2012年 | 175篇 |
| 2011年 | 249篇 |
| 2010年 | 180篇 |
| 2009年 | 367篇 |
| 2008年 | 333篇 |
| 2007年 | 342篇 |
| 2006年 | 355篇 |
| 2005年 | 283篇 |
| 2004年 | 294篇 |
| 2003年 | 251篇 |
| 2002年 | 233篇 |
| 2001年 | 213篇 |
| 2000年 | 210篇 |
| 1999年 | 178篇 |
| 1998年 | 188篇 |
| 1997年 | 95篇 |
| 1996年 | 87篇 |
| 1995年 | 69篇 |
| 1994年 | 53篇 |
| 1993年 | 36篇 |
| 1992年 | 30篇 |
| 1991年 | 20篇 |
| 1990年 | 25篇 |
| 1989年 | 14篇 |
| 1988年 | 12篇 |
| 1987年 | 10篇 |
| 1986年 | 15篇 |
| 1985年 | 29篇 |
| 1984年 | 21篇 |
| 1983年 | 8篇 |
| 1982年 | 5篇 |
| 1981年 | 8篇 |
| 1979年 | 2篇 |
| 1978年 | 2篇 |
排序方式： 共有5854条查询结果，搜索用时 93 毫秒
991.
992.
Human Health Risk Assessment Model of Organic Pollution in Groundwater: Shijiazhuang Industrial Zone
In this study, a risk-based management model is developed and applied to an industrial zone. The models proposed by the United States Environmental Protection Agency and Han Bing have been improved by adding a residual ratio of volatile organic compounds (VOC) after boiling and deleting the related parameters in half-life. Using this improved model, an integrated process was used to assess human health risk level in the study area. Compared with water quality analysis, the results highlight the importance of applying an integrated approach for decision making on risk levels and water protection. The results of this study demonstrated that: (1) Compared with these permissible level standards in China (GB 3838-2002) and National Primary Drinking Water Regulations of the United States, the residents’ daily life had not been affected by the groundwater in this area (except for relative bad water quality of HB3-4 and HB3-6); (2) The typical detected organic contaminants of all groundwater samples were chloroform, carbon tetrachloride, trichloroethylene and tetrachloroethene, and the pollution sources were mainly industrial sources by preliminary investigations; (3) As for groundwater, the non-carcinogenic risk values of all samples do not exceed the permissible level of 1.0 and the carcinogenic risk values are relatively lower than the permissible level of 1.00E-06 to 1.00E-04; (4) Drinking water pathway of trichloroethylene and tetrachloroethylene mainly contribute to increasing the health risk of residents’ in study areas; (5) In terms of non-carcinogenic risk and carcinogenic risk, the health risk order for drinking water pathway and dermal contact pathway was: drinking water pathway > dermal contact pathway. 相似文献
993.
994.
995.
High quality marine source rock (HQMSR) is the key prerequisite for medium to large hydrocarbon accumulations. However, the forming mechanism remains unclear. On the basis of the in-vestigation for the geodynamic setting of the Middle-Upper Yangtze during the Early Cambrian in dif-ferent spatial scales and the analysis of trace elements, the main controlling factors of the development of high quality marine source rock are discussed, with specific consideration of the burial rate of the organic matter. The ... 相似文献
996.
Insoluble particle concentration in ice cores is commonly analyzed as a proxy for varia-tions in atmospheric mineral dust (aerosol concentration). However, recent studies have revealed that the mineral dust is not only a constituent of the particles but that biogenic organic particles are also contained. We microscopically analyzed insoluble particles in a shallow ice core drilled on a mountain glacier, the ürümqi Glacier No. 1, in eastern Tienshan, China. We distinguished different morphologi-cal particles... 相似文献
997.
Zhen Tao Quanzhou Gao Wenping Guo Zhengang Wang Yongling Zhang Chenji Xie Xiakun Huang Hongwei Zhong 《山地科学学报》2011,8(5):694-703
A whole year analysis of riverine dissolved organic carbon (DOC) concentrations in the Xijiang River (XJR), South China, showed that the mean riverine DOC concentration (1.24 mg L-1) in the XJR was notably lower than the averaged value (5.75 mg L-1) of the global riverine DOC concentration in several major rivers. There is an inconspicuous monthly fluctuation of the DOC signal in the XJR, but on a semi-yearly time scale, however, the riverine DOC concentration had significant difference between hydrological... 相似文献
998.
人工经济林在中国南方种植面积大,并有不断增加的趋势.人工经济林生态系统受人为周期性经营活动影响比较大,是重要的流动性碳库.因此,选择福建省建瓯市万木林自然保护区内本地条件基本一致的毛竹(Phyllostachys heterocycla)、柑橘(Citrus reticulata Blanco)和锥栗(Castanea henryi)作为研究对象,探讨其土壤有机碳含量及其垂直分布特征,结果表明:3种林地土壤剖面有机碳含量的变化范围分别为毛竹林5.91～19.18 g.kg-1、柑橘5.70～13.31g.kg-1、锥栗3.84～10.78 g.kg-1,3种林地土壤有机碳含量随着深度的增加呈现递减趋势;3种林地0～20 cm、20～40 cm层土壤有机碳含量与40～60 cm、60～80 cm、80～100 cm各层均存在显著性差异(P<0.05);3种林地间土壤有机碳储量均存在显著性差异(P<0.05);使用对数方程对3种林地土壤有机碳含量随土壤深度的变化进行拟合均达到显著水平(P<0.05);土壤有机碳含量与土壤全N、C/N比之间存在一定的相关性,特别是3种林地土壤有机碳含量均与土壤全N含量的相关性最好(... 相似文献
999.
基于HJ1A-HSI超光谱影像的耕地有机质遥感定量反演 总被引：5，自引：0，他引：5
以环境小卫星超光谱影像为主要数据源,在耕地有机质实测样本的支持下,开展光谱反射率及其变化形式与有机质的相关性分析,筛选耕地有机质响应的敏感波段与特征组合算法,利用多元回归分析方法,建立基于HSI影像的耕地有机质定量反演模型。研究结果表明,耕地有机质的HSI影像响应波段均位于可见光与近红外波段间,其中以540～860nm范围最佳,相关系数均在0.5左右;HSI反射率对数一阶微分预测模型精度最高,模型及其检验的决定系数都在0.7以上,均方根误差在0.2%左右,可用于顺义区耕地有机质全覆盖空间填图。因此,环境小卫星的超光谱影像对耕地有机质含量具有较好的光谱响应能力,其空间覆盖能力有助于开展县域尺度的耕地有机质遥感反演和空间填图。 相似文献
1000.