全文获取类型
收费全文 | 790篇 |
免费 | 186篇 |
国内免费 | 293篇 |
专业分类
测绘学 | 83篇 |
大气科学 | 128篇 |
地球物理 | 174篇 |
地质学 | 518篇 |
海洋学 | 157篇 |
天文学 | 27篇 |
综合类 | 72篇 |
自然地理 | 110篇 |
出版年
2024年 | 16篇 |
2023年 | 21篇 |
2022年 | 81篇 |
2021年 | 78篇 |
2020年 | 63篇 |
2019年 | 76篇 |
2018年 | 75篇 |
2017年 | 64篇 |
2016年 | 74篇 |
2015年 | 88篇 |
2014年 | 68篇 |
2013年 | 78篇 |
2012年 | 67篇 |
2011年 | 56篇 |
2010年 | 47篇 |
2009年 | 23篇 |
2008年 | 23篇 |
2007年 | 22篇 |
2006年 | 25篇 |
2005年 | 21篇 |
2004年 | 19篇 |
2003年 | 17篇 |
2002年 | 21篇 |
2001年 | 23篇 |
2000年 | 18篇 |
1999年 | 23篇 |
1998年 | 13篇 |
1997年 | 20篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1978年 | 2篇 |
排序方式: 共有1269条查询结果,搜索用时 15 毫秒
111.
Near-source noise suppression of AMT by compressive sensing and mathematical morphology filtering 总被引:5,自引:0,他引:5
Guang Li Xiao Xiao Jing-Tian Tang Jin Li Hui-Jie Zhu Cong Zhou Fa-Bao Yan 《应用地球物理》2017,14(4):581-589
In deep mineral exploration, the acquisition of audio magnetotelluric (AMT) data is severely affected by ambient noise near the observation sites; This near-field noise restricts investigation depths. Mathematical morphological filtering (MMF) proved effective in suppressing large-scale strong and variably shaped noise, typically low-frequency noise, but can not deal with pulse noise of AMT data. We combine compressive sensing and MMF. First, we use MMF to suppress the large-scale strong ambient noise; second, we use the improved orthogonal match pursuit (IOMP) algorithm to remove the residual pulse noise. To remove the noise and protect the useful AMT signal, a redundant dictionary that matches with spikes and is insensitive to the useful signal is designed. Synthetic and field data from the Luzong field suggest that the proposed method suppresses the near-source noise and preserves the signal well; thus, better results are obtained that improve the output of either MMF or IOMP. 相似文献
112.
HouMao Wang Chong Wang YongMei Wang XiaoXin Zhang Cong Huang ShaoLin Liang 《中国科学:地球科学(英文版)》2017,60(9):1732-1738
Fabry-Perot Interferometer(FPI) has been used widely for wind measurements of the middle and upper atmosphere.To date, most of FPIs have been based on full-closed circular fringe, which needs 15–25 min to obtain a group of wind velocity(zonal and meridional). However, it is hard to improve the temporal resolution because full-closed circular fringe in several directions cannot be easily imaged onto the same Charge-Coupled Device(CCD) with enough airglow intensity. In this paper, a data processing method is proposed for non-full circular fringe of FPI, which can support CCD with enough area of observations in several directions simultaneously. The method is focused on the center determination of non-full fringe. It includes radial cross-section, peak coordinate determination, and center calculation. Based on the calculated center, the fringe is annular summed. Then its radius is determined subsequently using Gaussian fitting. Finally, the wind is retrieved from the fringe radius. For validation, fringes from two ground-based FPIs were used, which are deployed in Kelan(38.71°N, 111.58°E) and Xinglong(40.40°N, 117.59°E) in China. The results retrieved from non-full fringes of FPIs were compared with that from full-closed circular fringe. The averaged wind deviation between them demonstrates reasonable difference with 5.38 ms~-(1) for 892.0 nm airglow emission, 5.81 ms~-(1) for 630.0 nm emission, and 3.03 ms~-(1) for 557.7 nm emission. Besides, wind results of Xinglong FPI are compared roughly with measurements of meteor radar which is deployed in Ming Tombs of Beijing(40.3°N,116.2°E). Good agreement demonstrates that this method is robust enough for FPI wind retrieval of mesosphere and thermosphere. 相似文献
113.
选取2013-2017年吉林测震台网记录的部分地震,按测震台网运行管理细则对地震编目的要求,需对地震波形进行WA仿真处理后测量震级。对比仿真前后震级,发现仿真后量取的震级普遍较大,偏差在0.3以内。因此,地震编目需严格按照细则执行,地震速报使用仿真震级更加准确,而且掌握震级偏差可为新旧震级资料的连续性提供参考依据。 相似文献
114.
115.
热带气旋气候数学模型的预报应用 总被引:5,自引:2,他引:3
使用西太平洋海温格点资料,选取若干个因子,组成多个复合因子,建立权重方程,使得单因子的相关系数信度检验0.05提高到复合因子的信度检验0.01,权重方程的信度检验提高到0.001。用权重方程产生的突变的高阶非线性预报方程,其Y与X的相关系数比1阶线性方程提高5%左右。自1999年至今,热带气旋年、月频数气候预测的模型投入到实际预报应用,其预报准确律达到75%~90%。使用非线性预报模型作了逐日气压、逐日雨量的气候预测。将沿海气压场、雨量场的气候预测结果用于分析、制作热带气旋登陆中国以及广东地区的时段、地段的气候预报,准确率达80%~90%。 相似文献
116.
风云三号C星(FY-3C卫星)空间环境监测器(SEM)可监测轨道高度上的高能带电粒子(质子、电子和重离子)辐射环境及其引起的辐射剂量和表面充电等空间天气效应,是空间天气监测预警业务不可或缺的自主数据源之一。为验证FY-3C卫星高能粒子探测数据的有效性,需开展数据的定量检验工作。本文采用与同类卫星同类数据进行交叉比对的方式来进行检验。首先,根据一定的假设条件,对比对数据进行归一化处理,尽量消除不同卫星间观测时间、空间(星下点经、纬度和高度)、方向和能量范围等差异对高能粒子分布的影响,然后进行比对,最后计算比对数据间的相关系数、斜率和标准偏差等统计参数,并据此评价比对数据的一致性。通过空间天气平静期高能质子和高能电子与NOAA-18和FY-3B卫星数据的交叉比对可以看出,FY-3C卫星高能粒子数据与比对卫星数据具有较好的一致性。由于工作原理和技术指标相同,FY-3C与FY-3B卫星高能粒子数据的一致性更好,也证明了载荷技术状态的稳定性。通过对太阳质子事件和高能电子暴的观测实例证明,FY-3C卫星高能粒子数据能够准确地反映空间天气扰动事件的特征和强度。以上结果表明,FY-3C卫星高能粒子数据可信度较高,能够用于空间天气监测、预警以及研究工作。 相似文献
117.
以西南某典型岩溶区为例,解析示踪试验在岩溶管道连通性以及获取水文地质参数中的应用。选择落水洞为投放点,分别从落水洞西侧和东侧寻找地下水出露点作为接收点,判别落水洞地下径流的实际去向以及落水洞与接收点之间的水力联系。结合Qtracer2软件对示踪试验成果进行定量解析,确定示踪剂回收率、地下水平均流速、最快流速,估算出岩溶管道结构特征和水文地质参数。结果表明:落水洞与接收点JS01、JS03之间不存在直接水力联系;落水洞与接收点JS02存在水力联系且岩溶管道极为发育,含水介质不均匀,地下水运移路径较为通畅,为典型的紊流流态;落水洞地下径流的主要方向是由西向东,但在丰水期雨量较大期间,接收点JS04能够接收到荧光素钠,说明丰水期水位上涨后两者间会有水力联系,导致部分水量向落水洞西侧排泄。 相似文献
118.
YANG Kai ZHANG Bing WANG Xuben HE Lanfang YANG Hongyu WANG Pengwan TANG Jialin DENG Jixin ZHANG Cong 《《地质学报》英文版》2020,94(5):1531-1546
The Lower Silurian Longmaxi Formation in the south of Sichuan is a key player in the exploration and development of shale gas in China. Due to a highly complex topographic area, electromagnetic methods (EM) become important exploration means in this area. Many studies have been conducted on the shale mineral composition and electrical properties of shale, however, the correlation between sedimentary environments and the electrical properties of shale remain poorly understood. The electrical properties and sedimentary environment of the organic-rich shale of the Longmaxi Formation have been studied by means of X-ray diffraction, organic geochemistry, scanning electron microscopy and complex resistivity measurements. The discovered high quartz content of the Longmaxi Formation shale results in low resistivity. Deep-water shelf biogenic quartz contributes lower resistivity more than that of shallow-water terrigenous quartz. The deep-water anoxic and organic sedimentary environment led to major enrichment of pyrite, leading to a high polarization effect in shale. We present the correlation between the lithofacies types and electrical properties of Longmaxi Formation. The mixed siliceous shale lithofacies is the most favorable among the three lithofacies, which is characterized by high total organic carbon (TOC) content, high brittleness mineral content, high polarization and low resistivity (“three high and one low”). This feature is an effective identification of shale gas reservoirs by electromagnetic prospecting. Our study can provide constraints on electrical parameters of rocks for electromagnetic “sweet spot” exploration of shale gas, and so this has important geological significance to shale gas exploration and development. 相似文献
119.
数字化地形图地形原始数据的采集理论及方法 总被引:1,自引:0,他引:1
随着我国公路建设任务的日渐繁重,缩短勘测设计周期、提高工作效率变得尤为重要。在这一要求下,数字化地形图的直接应用就成为了一个重要的突破口。本文阐述了数字地形图原始地形数据的获取,着重论述了利用纸质地形图进行数字矢量化获取数据的方法,以此作为构建数字地形图的基础数据,以期为公路勘测设计提供帮助。 相似文献
120.