全文获取类型
收费全文 | 1372篇 |
免费 | 208篇 |
国内免费 | 260篇 |
专业分类
测绘学 | 140篇 |
大气科学 | 136篇 |
地球物理 | 293篇 |
地质学 | 593篇 |
海洋学 | 365篇 |
天文学 | 41篇 |
综合类 | 109篇 |
自然地理 | 163篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 32篇 |
2021年 | 30篇 |
2020年 | 22篇 |
2019年 | 29篇 |
2018年 | 26篇 |
2017年 | 31篇 |
2016年 | 76篇 |
2015年 | 36篇 |
2014年 | 133篇 |
2013年 | 128篇 |
2012年 | 107篇 |
2011年 | 98篇 |
2010年 | 98篇 |
2009年 | 112篇 |
2008年 | 98篇 |
2007年 | 72篇 |
2006年 | 86篇 |
2005年 | 73篇 |
2004年 | 71篇 |
2003年 | 66篇 |
2002年 | 48篇 |
2001年 | 44篇 |
2000年 | 42篇 |
1999年 | 46篇 |
1998年 | 37篇 |
1997年 | 32篇 |
1996年 | 25篇 |
1995年 | 27篇 |
1994年 | 23篇 |
1993年 | 19篇 |
1992年 | 14篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有1840条查询结果,搜索用时 31 毫秒
11.
Improved spatial delineation of streambed properties and water fluxes using distributed temperature sensing 下载免费PDF全文
Landon J. S. Halloran Hamid Roshan Gabriel C. Rau Martin S. Andersen R. Ian Acworth 《水文研究》2016,30(15):2686-2702
A new method was developed for analysing and delineating streambed water fluxes, flow conditions and hydraulic properties using coiled fibre‐optic distributed temperature sensing or closely spaced discrete temperature sensors. This method allows for a thorough treatment of the spatial information embedded in temperature data by creating a matrix visualization of all possible sensor pairs. Application of the method to a 5‐day field dataset reveals the complexity of shallow streambed thermal regimes. To understand how velocity estimates are affected by violations of assumptions of one‐dimensional, saturated, homogeneous flow and to aid in the interpretation of field observations, the method was also applied to temperature data generated by numerical models of common field conditions: horizontal layering, presence of lateral flow and variable streambed saturation. The results show that each condition creates a distinct signature visible in the triangular matrices. The matrices are used to perform a comparison of the behaviour of one‐dimensional analytical heat‐tracing models. The results show that the amplitude ratio‐based method of velocity calculation leads to the most reliable estimates. The minimum sensor spacing required to obtain reliable velocity estimates with discrete sensors is also investigated using field data. The developed method will aid future heat‐tracing studies by providing a technique for visualizing and comparing results from fibre‐optic distributed temperature sensing installations and testing the robustness of analytical heat‐tracing models. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
12.
13.
In this study, a methodology for clustering 18 lakes in Alberta, Canada using the data of 19 water quality parameters for a period of 11 years (1988–2002) is presented. The methods consist of (i) principal component analysis (PCA) to determine the dominant water quality parameters, (ii) cluster analysis techniques to develop the characteristics of the clusters, and (iii) pattern‐match lakes to determine the appropriate cluster for each of the lakes. The PCA revealed that three principal components (PCs) were able to explain ~88% of the variability and the dominant water quality parameters were total dissolved solids, total phosphorus, and chlorophyll‐a. We obtained five clusters for the period 1994–1997 by using the dominant parameters with water quality deteriorating as the cluster number increased from 1 to 5. Upon matching cluster patterns with the entire dataset, it was observed that some of the lakes belonged to the same cluster all the time (e.g., cluster 1 for lakes Elkwater, Gregg, and Jarvis; cluster 3 for Sturgeon; cluster 4 for Moonshine; and cluster 5 for Saskatoon), while others changed with time. This methodology could be applied in other regions of the world to identify the most suitable source waters and prioritize their management. It could be helpful to analyze the natural controlling processes, pollution types, impact of seasonal changes and overall quality of source waters. This methodology could be used for monitoring water bodies in a cost effective and efficient way by sampling only less number of dominant parameters instead of using a large set of parameters. 相似文献
14.
针对王铺渡槽上部墩柱结构出现的大开度贯穿性裂缝,课题组经过全面分析和多方案综合对比,采用裂缝化灌、碳纤维加固、外表面刷涂水性环保型乳胶漆外墙涂料作为防护的综合措施对原工程进行有效的加固处理,并结合水利工程的自身特点改进了加固技术工艺,取得了显著的经济和社会效益. 相似文献
15.
16.
PHC桩在动力打桩过程中,往往会因为锤击数或锤击能量过高而发生桩头或桩身损坏,引起的挤土效应和振动效应也会对周围环境造成不良影响.PHC桩桩端加环可减少沉桩过程中桩侧土体摩阻力的影响,结合某电厂工程综合试桩工作,通过对沉桩总锤击数、最终贯入度、土塞高度、打桩振动测试及高应变检测结果的分析,指出桩端加环对保证PHC桩的完... 相似文献
17.
18.
19.
结合沈阳市地理信息公共服务平台数据更新项目,研究地理共享平台数据的更新方式、更新技术以及更新发布一体化流程等关键技术。采用增量更新技术矢量数据,基于历史要素与现势要素节点、分线段的位置关系,检测并提取数据库中更新的要素;利用分词检测方法检测地名信息的匹配度,进行地名数据的更新;基于地名与路网数据,对公交数据进行检测、采集、优化等流程,完成公交数据的更新;并建立平台数据更新与发布一体化流程。经过作业流程控制与编写辅助程序,极大提高数据更新的速度与质量控制水平。 相似文献
20.