全文获取类型
| 收费全文 | 618篇 |
| 免费 | 71篇 |
| 国内免费 | 71篇 |
专业分类
| 测绘学 | 31篇 |
| 大气科学 | 57篇 |
| 地球物理 | 184篇 |
| 地质学 | 227篇 |
| 海洋学 | 71篇 |
| 天文学 | 3篇 |
| 综合类 | 36篇 |
| 自然地理 | 151篇 |
出版年
| 2024年 | 1篇 |
| 2023年 | 4篇 |
| 2022年 | 12篇 |
| 2021年 | 8篇 |
| 2020年 | 9篇 |
| 2019年 | 8篇 |
| 2018年 | 12篇 |
| 2017年 | 18篇 |
| 2016年 | 26篇 |
| 2015年 | 31篇 |
| 2014年 | 27篇 |
| 2013年 | 25篇 |
| 2012年 | 31篇 |
| 2011年 | 25篇 |
| 2010年 | 26篇 |
| 2009年 | 32篇 |
| 2008年 | 41篇 |
| 2007年 | 34篇 |
| 2006年 | 44篇 |
| 2005年 | 27篇 |
| 2004年 | 29篇 |
| 2003年 | 24篇 |
| 2002年 | 27篇 |
| 2001年 | 33篇 |
| 2000年 | 25篇 |
| 1999年 | 27篇 |
| 1998年 | 23篇 |
| 1997年 | 18篇 |
| 1996年 | 13篇 |
| 1995年 | 23篇 |
| 1994年 | 21篇 |
| 1993年 | 19篇 |
| 1992年 | 11篇 |
| 1991年 | 6篇 |
| 1990年 | 8篇 |
| 1989年 | 4篇 |
| 1987年 | 6篇 |
| 1984年 | 1篇 |
| 1983年 | 1篇 |
排序方式： 共有760条查询结果，搜索用时 15 毫秒
101.
102.
103.
We studied the physicochemical and molecular changes of compost during its maturation within 60, 90, and 150 days after the composting process. Moreover, the changes were also studied in compost residues after sequential removal of lipidic compounds. Infrared DRIFT spectrometry and 13C‐CPMAS‐NMR spectroscopy indicate that the molecular composition of compost changes dramatically during the stabilization period. The most decomposable components, mainly represented by bioavailable lipidic and peptidic structures, were progressively mineralized passing from 60 days to longer periods of compost stabilization. At increasing maturity stages, the composition of organic matter underwent a progressive enrichment in stable hydrophobic and ligno‐cellulosic material. The sequential extraction of lipidic compounds allowed an improved characterization of substrates and confirmed the outlined progressive transformation of compost. Compost may well be chosen on the basis of selected characteristics for environmental applications. 相似文献
104.
With the degeneration of environment and acceleration of urbanization,human environment has attracted great attention worldwide.This paper sets up the Human Settlements Environment Index(HEI) model and evaluates the natural environment suitability for Human Settlements in China based on GIS technology.The results show that the HEI of China decreases from southeast to northwest in general,HEI is significantly correlated with population density at grid size and the correlation coefficient(r) between them reaches 0.93,which indicates that natural environment suitability for Human Settlements has a significant influence on population distribution.Most people in China mainly concentrate in areas with high natural environment suitability.The total suitable area is 430.47×104 km2,which accounts for nearly 45% of the total land area in China,while the proportion of people living in the area reaches 96.56%.With a population density of 18 people per square kilometer,the critical area is the transitional region for people to live in China.The critical area covers 225.11×104 km2 with a population of 41.12 million.The non-suitable area covers 304.42×104 km2 with a population of only 2.49 million. 相似文献
105.
基于GIS的中国人居环境自然适宜性评价 总被引：13，自引：4，他引：9
With the degeneration of environment and acceleration of urbanization, human environment has attracted great attention worldwide. This paper sets up the Human Settle-ments Environment Index (HEI) model and evaluates the natural environment suitability for Human Settlements in China based on GIS technology. The results show that the HEI of China decreases from southeast to northwest in general, HEI is significantly correlated with population density at grid size and the correlation coefficient (r) between them reaches 0.93, which indicates that natural environment suitability for Human Settlements has a significant influence on population distribution. Most people in China mainly concentrate in areas with high natural environment suitability. The total suitable area is 430.47×104> km2, which ac-counts for nearly 45% of the total land area in China, while the proportion of people living in the area reaches 96.56%. With a population density of 18 people per square kilometer, the critical area is the transitional region for people to live in China. The critical area covers 225.11×104 km2 with a population of 41.12 million. The non-suitable area covers 304.42×104 km2 with a population of only 2.49 million. 相似文献
106.
The ecological tidal model simulates the cycling of carbon, nitrogen, phosphate, and silicate and describes the tidal, diurnal,
and annual dynamics of the back barrier area of the island Spiekeroog in the German Bight. The region is characterized by
strong tidal currents and extensive tidal flats. It is strongly influenced by the conditions in the southern part of the German
Bight. This model study investigates the dependence of the model behavior on the boundary conditions and the forcing. The
effect of short- and long-term sea level rise on nutrient and plankton dynamics is analyzed. As the model is set up as semi-Lagrangian
with only a coarse approximation of the hydrodynamics, the seasonal and intratidal variability in the biogeochemical cycling
can only be reproduced qualitatively. By varying the boundary conditions, the intrinsic dynamics of the back barrier area
can be separated from boundary condition effects. This study shows that any agreement between model results and field data
cannot be expected without correct boundary conditions. The seasonal variability is of major importance, while higher-frequency
variability only plays a minor role. 相似文献
107.
在分析辽宁能源状况和水资源量与分布状况及生态环境现状的基础上,揭示了经济发展与生态环境方面存在的矛盾,针对辽宁的能源利用率低、水环境安全受到威胁、区域环境污染集中等问题,结合辽宁实际情况,对此进行了探讨并提出了对策与建议。 相似文献
108.
109.
邓永光 《华东地质学院学报》2000,23(3):214-221
人类生存环境的变化是人类共同关心的环境问题之一,最直接影响环境变化的自然因素有气候变化、海平面和陆地的升降等,通过对有关广西沿海海平面和地壳运动资料的研究,初步分析了地壳运动对沿海地区产生的不良环境变化。 相似文献
110.