全文获取类型
收费全文 | 6006篇 |
免费 | 1237篇 |
国内免费 | 1666篇 |
专业分类
测绘学 | 1018篇 |
大气科学 | 901篇 |
地球物理 | 1152篇 |
地质学 | 3121篇 |
海洋学 | 1166篇 |
天文学 | 198篇 |
综合类 | 560篇 |
自然地理 | 793篇 |
出版年
2024年 | 47篇 |
2023年 | 110篇 |
2022年 | 386篇 |
2021年 | 475篇 |
2020年 | 362篇 |
2019年 | 406篇 |
2018年 | 401篇 |
2017年 | 335篇 |
2016年 | 362篇 |
2015年 | 375篇 |
2014年 | 424篇 |
2013年 | 471篇 |
2012年 | 497篇 |
2011年 | 441篇 |
2010年 | 451篇 |
2009年 | 386篇 |
2008年 | 394篇 |
2007年 | 363篇 |
2006年 | 342篇 |
2005年 | 280篇 |
2004年 | 258篇 |
2003年 | 186篇 |
2002年 | 236篇 |
2001年 | 202篇 |
2000年 | 127篇 |
1999年 | 114篇 |
1998年 | 57篇 |
1997年 | 80篇 |
1996年 | 65篇 |
1995年 | 51篇 |
1994年 | 44篇 |
1993年 | 34篇 |
1992年 | 33篇 |
1991年 | 25篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1964年 | 1篇 |
1958年 | 1篇 |
1957年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有8909条查询结果,搜索用时 78 毫秒
51.
52.
Rapid economic developments in East Asian countries have inevitably resulted in environmental degradation in the surrounding seas, and concern for both the environment and protection from pollutants is increasing. Identification of sources of contaminants is essential to environmental pollution management. In this study, the provenance of anthropogenic lead (Pb), a major pollutant of Yellow Sea sediments, was determined for river mouth sediments, including those of the Changjiang, Huanghe, Han, and Geum Rivers, and for age-determined shelf core sediments through the measurement of Pb isotope ratios in the HCl-leached fraction using multi-collector inductively coupled plasma-mass spectrometry (MC ICP/MS). Anthropogenic Pb has accumulated in shelf core sediments since 1910, and its isotope ratios were estimated as 0.863–0.866 and 2.119–2.125 for 207Pb/206Pb and 208Pb/206Pb, respectively, from the mixing relationships of the two endmembers. River mouth sediments exhibited enough distinction in anthropogenic Pb isotope ratios to be discriminated: 0.874 (2.144) in the Huanghe, 0.856 (2.129) in the Han, 0.857 (2.122) in the Geum, and 0.854 (2.101) in the Changjiang for 207Pb/206Pb (208Pb/206Pb), respectively. Although isotope ratios of geogenic Pb in sediments dating before 1910 showed narrow ranges (0.842–0.845 and 2.088–2.100 for 207Pb/206Pb and 208Pb/206Pb, respectively), distinct isotope ratios in each core permitted source identification of sediments in the Yellow Sea based on geographic locations and the geogenic Pb of each river. By comparing the isotope ratios of the estimated anthropogenic Pb to source-related materials, the provenances of anthropogenic Pb in Chinese river sediments were presumed to be Chinese coal or ore, which is also a major source of atmospheric particulate Pb. The anthropogenic Pb in the shelf core sediments in the northern Yellow Sea originated from northern Chinese cities such as Beijing and Tianjin through atmospheric pathways. Pb isotope ratios indicated that Pb in Korean river sediments was characteristic of local Korean ores. 相似文献
53.
There are 4 species of Littorinidae on the intertidal hard bed in the Jiulong River Estu-ary. They are Littorina scabra, L. brevicula, Nodilittorina pyramidalis pyramidalis and N.millegrana. Of these species, L. scabra is a dominant species. According to the results of in-vestigation, we find distribution patterns of the Littorinidae on intertidal hard bed in theestuary as follows: (1)There is no Littorinid species at Haicheng Station. (2)There is only Lit- 相似文献
54.
55.
56.
阐述了岛屿综合的内容和原则。介绍了双向缓冲区算法的概念并给出了双向缓冲区算法的定义,研究并证明了双向缓冲区算法的特性。分析了利用双向缓冲区算法综合海图岛屿的原理,并通过实验验证利用双向缓冲区算法综合海图岛屿具有较好的效果。 相似文献
57.
地质灾害治理工程项目管理是地质灾害管理的具体体现和实施过程,其基本任务是根据地质灾害管理目标和管理方法,组织实施防治工程,保障取得预期的减灾成果。就镇江市地质灾害治理工程项目管理目前现状,从规范文件、招标机构、管理工具、管理经验、干扰因素、风险评价、人员素质等方面进行粗浅分析,并针对存在的问题提出相应的对策,借以提高镇江市地质灾害治理工程项目管理的能力和水平,以便今后地质灾害治理项目管理更好地完善和发展。 相似文献
58.
59.
60.