全文获取类型
收费全文 | 8104篇 |
免费 | 661篇 |
国内免费 | 174篇 |
专业分类
测绘学 | 338篇 |
大气科学 | 941篇 |
地球物理 | 2538篇 |
地质学 | 2981篇 |
海洋学 | 595篇 |
天文学 | 889篇 |
综合类 | 191篇 |
自然地理 | 466篇 |
出版年
2023年 | 11篇 |
2022年 | 16篇 |
2021年 | 47篇 |
2020年 | 50篇 |
2019年 | 54篇 |
2018年 | 518篇 |
2017年 | 433篇 |
2016年 | 362篇 |
2015年 | 215篇 |
2014年 | 201篇 |
2013年 | 265篇 |
2012年 | 765篇 |
2011年 | 584篇 |
2010年 | 247篇 |
2009年 | 332篇 |
2008年 | 294篇 |
2007年 | 266篇 |
2006年 | 257篇 |
2005年 | 938篇 |
2004年 | 974篇 |
2003年 | 752篇 |
2002年 | 273篇 |
2001年 | 152篇 |
2000年 | 133篇 |
1999年 | 82篇 |
1998年 | 91篇 |
1997年 | 65篇 |
1996年 | 55篇 |
1995年 | 34篇 |
1994年 | 27篇 |
1993年 | 33篇 |
1992年 | 23篇 |
1991年 | 40篇 |
1990年 | 24篇 |
1989年 | 22篇 |
1987年 | 18篇 |
1986年 | 11篇 |
1985年 | 20篇 |
1984年 | 26篇 |
1983年 | 20篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 20篇 |
1975年 | 17篇 |
1973年 | 10篇 |
1971年 | 11篇 |
排序方式: 共有8939条查询结果,搜索用时 15 毫秒
121.
红壤丘陵区农业开发中的生态环境效应及其调控 总被引:3,自引:0,他引:3
文章以江西余江县为例。通过实验研究,历史资料对比分析及邻近参照等方法。研究红壤区农业开发中的生态环境效应。农业开发引起的微观环境效应在于改变土壤水分及其运动状况,加速土壤物质迁移及降低土壤肥力质量;区域性效应是植被减少,农业面源污染,水土流失扩大及气候异常;全球性影响除区域集聚效应外,则是农业活动中产生的温室气体对全球气候的影响等,采取的调控对策主要是:保持合理开发,适当减轻土地压力,优化农业开发模式,更新农业耕作技术。强化环境整治与生态建设。 相似文献
122.
This is the second part of a contribution to the debate on the possibilities of leveraging economic globalisation — through incorporation in international production networks and global commodity chains (GCCs) — as a strategy for developing countries to industrialise and advance their position in the world economy. In the first part, we analysed the experience of the East Asian apparel industry and addressed the issues of sustaining positions, upgrading to more rewarding roles, and advancing to less dependent positions within production networks and GCCs. We developed an analytical framework at both the firm and industry levels, and subsequently identified alternative firm- and industry-level strategies and trajectories. The present paper deals with these issues in the context of the Singapore apparel industry. Based on extensive empirical research, we demonstrate that although the East Asian experience of upgrading and repositioning within the GCC is to some extent emulated in the case of the Singapore apparel industry, the outcomes have been less favourable in terms of the depth, extent and strength of these trajectories. The differing outcomes can be explained in terms of different (systemic) conditions in the Singapore business environment, including the agency of local players, the geography of sourcing networks, and the role of the state and prevailing business attitudes. Our conclusions merit continued attention in both research and policy circles on the development of capabilities at the firm level, and the role of local business and institutional environments in local industry development processes under globalisation. 相似文献
123.
124.
Data and model uncertainty estimation for linear inversion 总被引:1,自引:0,他引:1
Kasper van Wijk John A. Scales William Navidi Luis Tenorio 《Geophysical Journal International》2002,149(3):625-632
125.
126.
Pore‐ice sublimation is a prerequisite for aeolian activity in cold environments where surface sediments hold significant amounts of frozen water. Few quantitative studies have defined the rate of grain release from cemented surfaces by pore‐ice sublimation. In 1996–1997, controlled field experiments at Presqu'ile Beach, Ontario, were implemented to measure sediment release from frozen surfaces. The release rates were compared to the local wind regime, ambient temperature and humidity. In additional field experiments, the effect of sediment water content on grain release by sublimation was examined. From the experimental results, an equation which predicts grain release based on local wind speed, ground temperature, humidity, and surface water content is proposed. Predicted release rates show reasonable agreement with natural deflation measured on the beach at Presqu'ile Provincial Park. 相似文献
127.
Shear wave statics using receiver functions 总被引:1,自引:0,他引:1
128.
129.
130.
Simon J. van Donk Xuewen Huang Edward L. Skidmore Alan B. Anderson Dick L. Gebhart Valerie E. Prehoda Elizabeth M. Kellogg 《Journal of Arid Environments》2003,54(4):687-703
Military training activities reduce vegetation cover, disturb crusts, and degrade soil aggregates, making the land more vulnerable to wind erosion. The objective of this study was to quantify wind erosion rates for typical conditions at the Marine Corps Air Ground Combat Center, Twentynine Palms, CA, U.S.A. Five Big Spring Number Eight (BSNE) sampler stations were installed at each of five sites. Each BSNE station consisted of five BSNE samplers with the lowest sampler at 0·05 m and the highest sampler at 1·0 m above the soil surface. Once a month, sediment was collected from the samplers for analysis. Occurrence of saltating soil aggregates was recorded every hour using Sensits, one at each site. The site with the most erosion had a sediment discharge of 311 kg m−1 over a period of 17 months. Other sites eroded much less because of significant rock cover or the presence of a crust. Hourly sediment discharge was estimated combining hourly Sensit count and monthly sediment discharge measured using BSNE samplers. More simultaneously measured data are needed to better characterize the relationship between these two and reconstruct a detailed time-series of wind erosion. This measured time-series can then be used for comparison with simulation results from process-based wind erosion models such as the Wind Erosion Prediction System (WEPS), once it has been adapted to the unique aspects of military lands. 相似文献