全文获取类型
收费全文 | 5722篇 |
免费 | 1048篇 |
国内免费 | 879篇 |
专业分类
测绘学 | 992篇 |
大气科学 | 573篇 |
地球物理 | 1311篇 |
地质学 | 2800篇 |
海洋学 | 790篇 |
天文学 | 8篇 |
综合类 | 479篇 |
自然地理 | 696篇 |
出版年
2024年 | 35篇 |
2023年 | 81篇 |
2022年 | 165篇 |
2021年 | 243篇 |
2020年 | 246篇 |
2019年 | 273篇 |
2018年 | 201篇 |
2017年 | 261篇 |
2016年 | 292篇 |
2015年 | 288篇 |
2014年 | 421篇 |
2013年 | 416篇 |
2012年 | 387篇 |
2011年 | 425篇 |
2010年 | 347篇 |
2009年 | 377篇 |
2008年 | 388篇 |
2007年 | 416篇 |
2006年 | 380篇 |
2005年 | 285篇 |
2004年 | 246篇 |
2003年 | 210篇 |
2002年 | 194篇 |
2001年 | 189篇 |
2000年 | 144篇 |
1999年 | 133篇 |
1998年 | 126篇 |
1997年 | 91篇 |
1996年 | 87篇 |
1995年 | 63篇 |
1994年 | 68篇 |
1993年 | 52篇 |
1992年 | 37篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 17篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有7649条查询结果,搜索用时 78 毫秒
901.
选取山东省3个洞体应变台2007-2011年观测数据,分析资料的完整性、内在质量及干扰因素.结果表明:①观测资料连续性和完整性较好;②仪器零漂满足设计指标要求;③M2波振幅因子相对误差和相对噪声水平达到Ⅰ类应变台标准;④仪器更新后观测质量提升;⑤洞体应变观测主要受仪器调修、气压、降雨和观测环境变化等因素影响. 相似文献
902.
Tropical rivers display profound temporal and spatial heterogeneity in terms of environmental conditions. This aspect needs to be considered when designing a monitoring program for water quality in rivers. Therefore, the physico-chemical composition and the nutrient loading of the Upper Mara River and its two main tributaries, the Amala and Nyangores were monitored. Initial daily, and later a weekly monitoring schedule for 4 months spanning through the wet and dry seasons was adopted. Benthic macro-invertebrates were also collected during the initial sampling to be used as indicators of water quality. The aim of the current study was to investigate the physico-chemical status and biological integrity of the Upper Mara River basin. This was achieved by examining trends in nutrient concentrations and analyzing the structure, diversity and abundance of benthic macro-invertebrates in relation to varying land use patterns. Sampling sites were selected based on catchment land use and the level of human disturbance, and using historical records of previous water quality studies. River water pH, dissolved oxygen, electrical conductivity (EC), temperature, and turbidity were determined in situ. All investigated parameters except iron and manganese had concentration values within allowable limits according to Kenyan and international standards for drinking water. The Amala tributary is more mineralized and also shows higher levels of pH and EC than water from the Nyangores tributary. The latter, however, has a higher variability in both the total phosphorus (TP) and total nitrogen (TN) concentrations. The variability in TP and TN concentrations increases downstream for both tributaries and is more pronounced for TN than for TP. Macro-invertebrate assemblages responded to the changes in land use and water quality in terms of community composition and diversity. The study recommends detailed continuous monitoring of the water quality at shorter time intervals and to identify key macro-invertebrate taxa that can be used to monitor changes of the water quality in rivers of the Mara basin as a result of anthropogenic changes. 相似文献
903.
904.
Innovative Germicidal UV and Photocatalytic System Dedicated to Aircraft Cabin Eliminates Volatile Organic Compounds and Pathogenic Micro‐Organisms
下载免费PDF全文
![点击此处可从《洁净——土壤、空气、水》网站下载免费的PDF全文](/ch/ext_images/free.gif)
905.
906.
907.
908.
909.
910.