全文获取类型
收费全文 | 880篇 |
免费 | 192篇 |
国内免费 | 140篇 |
专业分类
测绘学 | 170篇 |
大气科学 | 154篇 |
地球物理 | 340篇 |
地质学 | 214篇 |
海洋学 | 111篇 |
天文学 | 43篇 |
综合类 | 147篇 |
自然地理 | 33篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 25篇 |
2021年 | 31篇 |
2020年 | 38篇 |
2019年 | 53篇 |
2018年 | 28篇 |
2017年 | 51篇 |
2016年 | 30篇 |
2015年 | 50篇 |
2014年 | 55篇 |
2013年 | 62篇 |
2012年 | 58篇 |
2011年 | 70篇 |
2010年 | 54篇 |
2009年 | 56篇 |
2008年 | 60篇 |
2007年 | 66篇 |
2006年 | 63篇 |
2005年 | 52篇 |
2004年 | 46篇 |
2003年 | 49篇 |
2002年 | 37篇 |
2001年 | 23篇 |
2000年 | 27篇 |
1999年 | 19篇 |
1998年 | 26篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 3篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1212条查询结果,搜索用时 671 毫秒
31.
32.
该文利用GMS 5原始数据、GMS 5展宽数据、FY-2A展宽数据和FY-2B展宽数据, 采用伪彩色增强和灰度直方图分析方法, 分别对这4种数据的红外、水汽、可见光通道图像进行了针对杂散光的对比分析以及对杂散信号来源分析。分析表明这三颗静止气象卫星的图像中都存在一定的杂散信号。该文提出了解决杂散光问题主要依靠优化辐射计光路设计; 地面系统在实时处理、展宽图像时采取简单剔除处理, 可以减小或消除图像冷空间区域的杂散信号, 但是去掉地球圆盘图像内部的杂散信号将非常困难。 相似文献
33.
用GPS秒信号锁定高频振荡器的方法研究 总被引:1,自引:0,他引:1
对用远距离传输的GPS秒信号锁定本地高频晶体振荡器的方法进行了探讨。介绍了高精度的时间数字转换器TDC(Time to Digital Converter)和对滤波的方法进行了探讨。为了降低成本又能够满足设计要求的精度,还考虑了双D/A转换的方法。有关的硬件系统已经通过了调试和一系列的测试和实验,在测量和控制精度方面,能达到设计的要求。此外,提出了这个系统有待解决的问题,如双D/A转换的非线性问题,Kalman滤波抗野值及继续提高精度的问题。 相似文献
34.
Feature removal and isolation in potential field data 总被引:1,自引:0,他引:1
35.
36.
37.
Quantifying flows along hydrological pathways by applying a new filtering algorithm in conjunction with master recession curve analysis 下载免费PDF全文
Ronan J. O'Brien Bruce D. Misstear Laurence W. Gill Paul M. Johnston Raymond Flynn 《水文研究》2014,28(26):6211-6221
Quantifying the proportion of the river hydrograph derived from the different hydrological pathways is essential for understanding the behaviour of a catchment. This paper describes a new approach using the output from master recession curve analysis to inform a new algorithm based on the Lyne and Hollick ‘one‐parameter’ signal analysis filtering algorithm. This approach was applied to six catchments (including two subcatchments of these) in Ireland. The conceptual model for each catchment consists of four main flow pathways: overland flow, interflow, shallow groundwater and deep groundwater. The results were compared with those of the master recession curve analysis, a recharge coefficient approach developed in Ireland and the semi‐distributed, lumped and deterministic hydrological model Nedbør‐Afstrømings‐Model. The new algorithm removes the ‘free variable’ aspect that is typically associated with filtering algorithms and provides a means of estimating the contribution of each pathway that is consistent with the results of hydrograph separation in catchments that are dominated by quick response pathways. These types of catchments are underlain by poorly productive aquifers that are not capable of providing large baseflows in the river. Such aquifers underlie over 73% of Ireland, ensuring that this new algorithm is applicable in the majority of catchments in Ireland and potentially in those catchments internationally that are strongly influenced by the quick‐responding hydrological pathways. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
38.
The isotopic composition of precipitation (D and 18O) has been widely used as an input signal in water tracer studies. Whereas much recent effort has been put into developing methodologies to improve our understanding and modelling of hydrological processes (e.g., transit‐time distributions or young water fractions), less attention has been paid to the spatio‐temporal variability of the isotopic composition of precipitation, used as input signal in these studies. Here, we investigated the uncertainty in isotope‐based hydrograph separation due to the spatio‐temporal variability of the isotopic composition of precipitation. The study was carried out in a Mediterranean headwater catchment (0.56 km2). Rainfall and throughfall samples were collected at three locations across this relatively small catchment, and stream water samples were collected at the outlet. Results showed that throughout an event, the spatial variability of the input signal had a higher impact on hydrograph separation results than its temporal variability. However, differences in isotope‐based hydrograph separation determined preevent water due to the spatio‐temporal variability were different between events and ranged between 1 and 14%. Based on catchment‐scale isoscapes, the most representative sampling location could also be identified. This study confirms that even in small headwater catchments, spatio‐temporal variability can be significant. Therefore, it is important to characterize this variability and identify the best sampling strategy to reduce the uncertainty in our understanding of catchment hydrological processes. 相似文献
39.
张永年 《测绘与空间地理信息》2016,(9)
在福建地区从事无人机低空数码航空摄影测量项目时,我们发现数传电台信号中断是无人机飞行的一个重大安全隐患。如不能实时掌握无人机飞行动态,出现异常状况时不能第一时间处理,极有可能出现安全事故,造成重大损失。本文通过具体案例说明,提出无人机信号传输中断的解决方案。 相似文献
40.
GRAPES(Globe and Regional Assimilation and Prediction System)变分系统能够同化常规资料和非常规卫星资料,这些被同化的资料究竟对同化系统得到的分析场有何影响,目前国内外尚未见相关的研究文献。为此,首次采用基于信息熵信号自由度思想,诊断风云三号B星(FY3B)红外分光计(Infrared Atmospheric Sounder,IRAS)资料对GRAPES分析场的影响。诊断过程中,采用数值逼近方法,统计2012年12月24日18时到2013年1月22日00时共114个时次IRAS资料对GRAPES分析场影响,结果表明,IRAS中高层通道亮温资料对GRAPES分析场影响比地表通道20观测亮温的影响大,地表通道8和9观测亮温对分析场影响较大。前24个GRAPES变分同化时次每个时次IRAS通道亮温对分析场影响的贡献率分析结果显示,高层通道和H_2O通道贡献率较大。个例分析结果表明,在同化探空资料基础上加入IRAS资料后,温度和湿度增量场变化幅度较大,表明IRAS资料对分析场有降温和增湿作用。 相似文献