全文获取类型
收费全文 | 2935篇 |
免费 | 566篇 |
国内免费 | 857篇 |
专业分类
测绘学 | 97篇 |
大气科学 | 229篇 |
地球物理 | 838篇 |
地质学 | 2112篇 |
海洋学 | 374篇 |
天文学 | 17篇 |
综合类 | 187篇 |
自然地理 | 504篇 |
出版年
2024年 | 10篇 |
2023年 | 39篇 |
2022年 | 81篇 |
2021年 | 76篇 |
2020年 | 91篇 |
2019年 | 100篇 |
2018年 | 75篇 |
2017年 | 106篇 |
2016年 | 90篇 |
2015年 | 104篇 |
2014年 | 141篇 |
2013年 | 157篇 |
2012年 | 204篇 |
2011年 | 165篇 |
2010年 | 142篇 |
2009年 | 221篇 |
2008年 | 190篇 |
2007年 | 255篇 |
2006年 | 227篇 |
2005年 | 196篇 |
2004年 | 207篇 |
2003年 | 172篇 |
2002年 | 178篇 |
2001年 | 138篇 |
2000年 | 130篇 |
1999年 | 123篇 |
1998年 | 119篇 |
1997年 | 117篇 |
1996年 | 78篇 |
1995年 | 90篇 |
1994年 | 85篇 |
1993年 | 66篇 |
1992年 | 39篇 |
1991年 | 36篇 |
1990年 | 28篇 |
1989年 | 21篇 |
1988年 | 24篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4358条查询结果,搜索用时 359 毫秒
61.
旅游空间合作研究进展 总被引:6,自引:0,他引:6
该文回顾了旅游业空间结构的研究进展,总结出我国旅游业空间结构研究集中在旅游资源分布描述及区划、旅游空间结构演替和区域关系研究、区域旅游开发与规划研究等领域。并从理论研究和个案研究两个方面介绍了我国旅游空间合作研究状况。 相似文献
62.
63.
64.
65.
66.
Exploring some relationships between biological soil crusts, soil aggregation and wind erosion 总被引:5,自引:0,他引:5
A portable wind tunnel was used to test the contribution of biological and physical elements to overall soil aggregation on a soil dominated by biological soil crusts in south-eastern Australia. After moderate disturbance and simulated wind erosion, 90% of surface aggregates on the loamy soil and 76% on the sandy soil were dominated by biological elements (cryptogams). Lower levels of biological bonding were observed on the severely disturbed treatment. Linear regression indicated a significant positive relationship (r2=0·72) between biological soil crust cover and dry aggregation levels greater than 0·85mm. To maintain sediment transport below an erosion control target of 5gm−1s−1 for a 65kmh−1 wind at 10m height, a crust cover of approximately 20% is required. When a multiple regression model which sequentially fitted biological crust cover and dry aggregation greater than 0·85mm was applied to the data, dry aggregation accounted for more of the variation in sediment transport rate than biological crust cover. These data were used to develop a conceptual model which integrates crust cover and dry aggregation, and provides a useful framework within which to predict the likely impacts of changes in soil crust cover and aggregation. 相似文献
67.
Microcoleus vaginatus isolated from a desert algal crust of Shapotou was cultured in BG-11 medium containing 0.2 mol l−1 NaCl or 0.2 mol l−1 NaCl plus 100 mg l−1 sucrose, extracellular polymeric substances (EPS) or hot water-soluble polysaccharides (HWP), respectively. Photosynthetic oxygen evolution rates, photosystem II activity (Fv/Fm) and dark respiration of NaCl-stressed cells were enhanced significantly by the added sucrose or EPS under salt stress conditions (0.2 mol l−1 NaCl). Compared with cells treated with salt alone, sodium contents in cells reduced significantly; the content of cellular total carbohydrate did not change, and intracellular sucrose, water-soluble sugar increased significantly following the addition of exogenous carbohydrates. Sucrose synthase (SS) activity of NaCl-stressed cells increased following the addition of sucrose, and sucrose phosphate synthase (SPS) activity of NaCl-stressed cells increased following the addition of exogenous sucrose, EPS or HWP compared with cells stressed with NaCl only. The results suggested that the extruded EPS might be re-absorbed by cells of M. vaginatus as carbon source, they could increase salt tolerance of M. vaginatus through the changes of carbohydrate metabolism and the selective uptake of sodium ions. 相似文献
68.
地下物探在有色金属矿山寻找隐伏矿体的应用 总被引:4,自引:0,他引:4
介绍了地下地球物理找矿方法在几个典型有色金属矿山进行生产找矿的实例,根据对不同深度的面积工作获得的系列直流电法、电磁法异常的计算分析,分别提出解释推断及施工建议,经工程验证,取得了显著的地质效果。 相似文献
69.
70.
根据新提供的Pb同位素组成及岩石地球化学研究成果,本文进一步证实了位于北秦岭北界的明港地区发育的早中生代安山玄武质火山角砾岩岩筒所携带的下地壳捕虏体属于南秦岭。所恢复的南秦岭下地壳剖面自下而上为:底侵成因的变辉长岩-基性麻粒岩(其中含有榴辉岩及辉石岩的透镜体)-酸性麻粒岩。秦岭造山带总体的岩石因模型为:南秦岭(扬子块体)向北拆离俯冲,北秦岭地壳向华北仰冲,华北岩石因呈楔状插入秦岭造山带,拆离面约在中、下地壳之间。南秦岭俯冲岩片延伸的范围在平面上有可能达到400km。 相似文献