全文获取类型
收费全文 | 452篇 |
免费 | 125篇 |
国内免费 | 42篇 |
专业分类
测绘学 | 91篇 |
大气科学 | 140篇 |
地球物理 | 268篇 |
地质学 | 45篇 |
海洋学 | 39篇 |
天文学 | 16篇 |
综合类 | 6篇 |
自然地理 | 14篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2018年 | 13篇 |
2017年 | 16篇 |
2016年 | 15篇 |
2015年 | 23篇 |
2014年 | 24篇 |
2013年 | 33篇 |
2012年 | 20篇 |
2011年 | 28篇 |
2010年 | 21篇 |
2009年 | 39篇 |
2008年 | 48篇 |
2007年 | 43篇 |
2006年 | 38篇 |
2005年 | 30篇 |
2004年 | 33篇 |
2003年 | 21篇 |
2002年 | 25篇 |
2001年 | 23篇 |
2000年 | 26篇 |
1999年 | 24篇 |
1998年 | 20篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 1篇 |
排序方式: 共有619条查询结果,搜索用时 46 毫秒
91.
使用高灵敏度的电容式微压波传感器对1998年4月11日16时发生在贵州省普定县的一次降冰雹过程的重力波进行观测,利用WRF(Weather Research and Forecast)中尺度模式对这一过程进行数值模拟,使用Morlet小波方法对模拟结果进行分析,得出这一过程中惯性重力波的分布和变化规律,并分析急流、地形及切变线对惯性重力波的影响.观测发现:在降冰雹前,每隔1~4小时出现一次短周期重力波阵性增强的现象.数值模拟结果显示:在低空降冰雹前几个小时有强的短周期重力波出现,其中周期较长的出现早、存在时间长,周期较短的出现晚、存在时间短;强的低空急流和风速垂直切变触发对流或湍流的发生和加强,对流或湍流又激发了80~200 min的短周期重力波;短周期重力波更容易向垂直方向传播,而长周期重力波倾向于水平方向传播.长周期重力波在降冰雹后周期有明显变短现象,随高度越加明显.由地形形成的重力波在最高山峰上空振幅最大. 相似文献
92.
93.
Taher Rajaee 《洁净——土壤、空气、水》2010,38(3):275-286
Simulation approaches employed in suspended sediment processes are important in the areas of water resources and environmental engineering. In the current study, neuro‐fuzzy (NF), a combination of wavelet transform and neuro‐fuzzy (WNF), multi linear regression (MLR), and the conventional sediment rating curve (SRC) models were considered for suspended sediment load (S) modeling in a gauging station in the USA. In the proposed WNF model, the discrete wavelet analysis was linked to a NF approach. To achieve this aim, the observed time series of river flow discharge (Q) and S were decomposed to sub time series at different scales by discrete wavelet transform. Afterwards, the effective sub time series were added together to obtain a useful Q and S time series for prediction. Eventually, the obtained total time series were imposed as inputs to the NF method for daily S prediction. The results illustrated that the predicted values by the proposed WNF model were in good agreement with the observed S values and gave better results than other models. Furthermore, the WNF model satisfactorily estimated the cumulative suspended sediment load and produced relatively reasonable predictions for extreme values of S, while NF, MLR, and SRC models provided unacceptable predictions. 相似文献
94.
95.
大容量气枪震源子波时频特性及其影响因素 总被引:3,自引:3,他引:0
通过分析福建街面水库气枪实验的近场水听器记录,研究气枪子波时频特性及其受沉放深度和工作压力的影响,并结合气泡模型解释气泡振荡过程。数据分析表明:①气枪子波由主脉冲和气泡脉冲组成。主脉冲振幅大,持时短,频带宽,通常应用于浅部探测;气泡脉冲能量集中在低频段,垂直穿透深,水平传播远,通常应用于深部探测。②随沉放深度的增加,主脉冲振幅变化很小,气泡脉冲振幅增加,初泡比减小,气泡周期减小,低频段主频增加。沉放深度为10m时,主脉冲振幅和初泡比最大,可应用于浅部探测;沉放深度为25m时,气泡脉冲振幅很大,初泡比最小,可应用于深部探测。③工作压力增加时,主脉冲振幅、气泡脉冲振幅、初泡比、气泡周期等随之增大,低频段主频则减小。 相似文献
96.
Marina Hruška William Corea Donald Seeburger William Schweller William H. Crane 《Mathematical Geosciences》2009,41(6):703-716
We describe a wavelet-transform-based method for automated segmentation of resistivity image logs that takes into account
the apparent dip in the data and addresses the problem of discriminating lithofacies boundaries from noise and intrafacies
variations. Our method can be applied to borehole measurements in general, but might have an advantage when applied to resistivity
image logs as it addresses explicitly the large variability in facies segments recorded with a high-resolution multiple-sensor
tool. We have developed an algorithm based on this method that might outperform other existing segmentation methods in the
cases of low to moderate dip. We made a detailed comparison of the segmentation from our method with the one done by a geologist
to delineate different lithofacies blocks in a well drilled in a deepwater depositional environment. Our results show considerable
success rates in reproducing the geologically defined lithofacies boundaries, and the generality of our procedure suggests
it could also be applied to other depositional environments. 相似文献
97.
Thomas M. Soniat Eileen E. Hofmann John M. Klinck Eric N. Powell 《International Journal of Earth Sciences》2009,98(1):99-114
The eastern oyster (Crassostrea virginica) is affected by two protozoan parasites, Perkinsus marinus which causes Dermo disease and Haplosporidium nelsoni which causes MSX (Multinucleated Sphere Unknown) disease. Both diseases are largely controlled by water temperature and salinity and thus are potentially sensitive to climate variations resulting from the El Niño-Southern Oscillation (ENSO), which influences climate along the Gulf of Mexico coast, and the North Atlantic Oscillation (NAO), which influences climate along the Atlantic coast of the United States. In this study, a 10-year time series of temperature and salinity and P. marinus infection intensity for a site in Louisiana on the Gulf of Mexico coast and a 52-year time series of air temperature and freshwater inflow and oyster mortality from Delaware Bay on the Atlantic coast of the United States were analyzed to determine patterns in disease and disease-induced mortality in C. virginica populations that resulted from ENSO and NAO climate variations. Wavelet analysis was used to decompose the environmental, disease infection intensity and oyster mortality time series into a time–frequency space to determine the dominant modes of variability and the time variability of the modes. For the Louisiana site, salinity and Dermo disease infection intensity are correlated at a periodicity of 4 years, which corresponds to ENSO. The influence of ENSO on Dermo disease along the Gulf of Mexico is through its effect on salinity, with high salinity, which occurs during the La Niña phase of ENSO at this location, favoring parasite proliferation. For the Delaware Bay site, the primary correlation was between temperature and oyster mortality, with a periodicity of 8 years, which corresponds to the NAO. Warmer temperatures, which occur during the positive phase of the NAO, favor the parasites causing increased oyster mortality. Thus, disease prevalence and intensity in C. virginica populations along the Gulf of Mexico coast is primarily regulated by salinity, whereas temperature regulates the disease process along the United States east coast. These results show that the response of an organism to climate variability in a region is not indicative of the response that will occur over the entire range of a particular species. This has important implications for management of marine resources, especially those that are commercially harvested. 相似文献
98.
99.
根据波茨坦地磁场模型(POMME6.2),研究喜马拉雅东构造结周围地区地壳磁异常的空间分布、磁异常随高度的衰减特征.利用二维小波变换方法对地表磁异常进行分解,分析小波细节组合和逼近信号的异常特点.讨论磁异常与地质构造的联系.结果表明,研究区内地壳磁异常分布相当不均匀.喜马拉雅—东构造结—龙门山—大巴山地区分布着较强的负磁异常;四川盆地为正磁异常,其他地区磁异常较弱.东构造结对周围地区磁异常有重要影响,它及其周围地区的地壳磁异常都是在负磁或弱磁异常背景上,叠加着中短波长的正负磁异常.这些中小尺度磁异常由中、上层地壳磁性物质产生,走向与地质构造基本一致.沿金沙江、红河断裂带分布着清晰的弱磁异常带.龙门山断裂带、丽江—小金河断裂带和红河断裂带是磁异常强弱过渡带.青蒇高原中部东西向的磁异常,在东构造结弧顶地区呈弧形分布.青藏高原中部和滇中地块带状、团状磁异常具有相同的衰减规律. 相似文献
100.
基于飞艇的时间域地空电磁探测系统,具有勘探深度大、效率高、空间分辨率高、飞行控制容易等优势.但在低空飞行测量过程中,飞艇飞行高度、航迹、姿态等受风向、大气气流、地形、地面局部温度场变化等影响而发生变化,导致固定在艇囊前端的接收线圈发生运动,切割大地磁场,产生了电磁噪声、运动噪声、基线漂移等,从而影响电磁数据的电阻率成像质量.因此,研究地空电磁信号中多种噪声的去除方法,对数据的反演解释非常重要.由于地空电磁信号中有效信号频带与部分噪声频带相重叠,使用传统滤波或消噪方法具有一定局限性.因此,本文提出一种综合小波去噪法:根据地空电磁信号的特点,采用sym8小波基;基于小波多分辨率分析原理,利用小波高尺度近似分量估计基线漂移,以校正电磁数据中的基线;基于小波阈值收缩原理,采用5层小波分解、极小极大阈值配合硬收缩函数的消噪方法,来压制数据中的其余噪声.最后,通过异常环模型的理论响应和实测数据进行算法的验证,结果表明这种综合消噪法对多种噪声均有很好的抑制作用,是一种实用有效的时间域地空电磁数据消噪方法. 相似文献