全文获取类型
收费全文 | 151篇 |
免费 | 34篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 13篇 |
地球物理 | 68篇 |
地质学 | 57篇 |
海洋学 | 19篇 |
天文学 | 7篇 |
综合类 | 5篇 |
自然地理 | 22篇 |
出版年
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 9篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 9篇 |
2013年 | 9篇 |
2012年 | 16篇 |
2011年 | 5篇 |
2010年 | 7篇 |
2009年 | 9篇 |
2008年 | 8篇 |
2007年 | 12篇 |
2006年 | 11篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1988年 | 1篇 |
1987年 | 4篇 |
排序方式: 共有191条查询结果,搜索用时 140 毫秒
111.
The signal of the nucleus was digitally extracted from six images of the innermost coma of this comet, obtained with the Hubble
Space Telescope’s Wide-Field Planetary Camera 2 in the planetary mode between October 23, 1995 and October 17, 1996. Two different
anisotropic, power-type laws were used to filter out the contribution from the dust coma: one peaking at the center of the
elliptical surface brightness distribution (law A), the other peaking at its focus (law B). The nuclear R magnitudes in the
Cousins system, reduced to a zero phase angle and to 1 AU from Earth and the Sun with a phase coefficient of 0.035 mag/deg
and an inverse square distance power law, are found to average 9.46 ± 0.07 and 9.48 ± 0.18 when law A and law B are applied,
respectively. These results become 9.49 ± 0.07 and 9.51 ± 0.17, when the nucleus signal on the October 1995 image is assumed
to consist of a sum of the contributions from two unresolved nuclear components. In either scenario, no systematic variations
are apparent in the nuclear brightness with time, which suggests the absence of any significant contamination of the extracted
nuclear signal by the coma. Assuming a geometric albedo of 4 percent, the corresponding effective nuclear diameter amounts
to 71 ± 4 km (formal error). This result substantially exceeds the size estimates published by Weaver et al., which are based
only on the October 1995 observation and which were obtained with the help of a different reduction method. Runs in which
a power-type law fitting the contribution from the coma was assumed to hold all the way to a small fraction of a pixel from
the nucleus led to distinctly inferior solutions and yielded spurious values ll70 km for the nuclear diameter.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
112.
为了确定金矿采空区的位置,对其隐患进行治理,首次应用高精度重力方法.在研究区布设了两条比例尺为1∶100的高精度重力测量剖面,使用加拿大Scintrex公司的CG-5AutoGrav型重力仪, 测取重力异常数据,并采用欧拉反褶积方法实施反演解释,确定了采空塌陷区域及稳定地段.研究结果表明:高精度重力测量应用于金矿采空区探测是行之有效的,用欧拉反褶积方法解释重力异常数据是一种快速、高效、人为干预少的好方法. 相似文献
113.
在对现存的图像盲解卷积恢复算法进行阐述的基础上,介绍了一种根据概率统计理论推导的极大似然图像恢复算法.该算法通过用共轭梯度法对一个误差函数进行最小化来实现.并且在运算的过程中,加入了一些先验知识,如非负性和有限支持域等约束. 相似文献
114.
115.
本文利用面积广、勘探深度大的重磁数据通过增强型局部相位边界识别方法和优化欧拉反褶积法获得东海陆架盆地的构造特征,为油气勘探提供基础资料。增强型局部相位边界识别法是重磁数据一阶和二阶水平导数的比值函数,能有效地均衡不同深度地质体的边界响应,从而同时显示不同深度构造的边界,提高对较深层构造的分辨率;优化欧拉反褶积法有效地降低了背景异常的干扰,从而可获得更加准确的构造反演结果。理论模型研究表明,增强型局部相位边界识别法可更加准确和清晰地划分边界信息,优化欧拉反褶积法可获得更加准确和收敛的反演结果。综合利用增强型局部相位边界识别和优化欧拉反褶积法对东海陆架断裂构造分布进行划分,获得了分析区域构造背景和评估油气潜力的基础资料。 相似文献
116.
117.
Further improvement of temporal resolution of seismic data by autoregressive (AR) spectral extrapolation 总被引:1,自引:0,他引:1
Hakan Karsl 《Journal of Applied Geophysics》2006,59(4):324-336
Seismic data have still no enough temporal resolution because of band-limited nature of available data even if it is deconvolved. However, lower and higher frequency information belonging to seismic data is missing and it is not directly recovered from seismic data. In this paper, a method originally applied by Honarvar et al. [Honarvar, F., Sheikhzadeh, H., Moles, M., Sinclair, A.N., 2004. Improving the time-resolution and signal–noise ratio of ultrasonic NDE signals. Ultrasonics 41, 755–763.] which is the combination of the most widely used Wiener deconvolution and AR spectral extrapolation in frequency domain is briefly reviewed and is applied to seismic data to improve temporal resolution further. The missing frequency information is optimally recovered by forward and backward extrapolation based on the selection of a high signal–noise ratio (SNR) of signal spectrum deconvolved in signal processing technique. The combination of the two methods is firstly tested on a variety of synthetic examples and then applied to a stacked real trace. The selection of necessary parameters in Wiener filtering and in extrapolation are discussed in detail. It is used an optimum frequency windows between 3 and 10 dB drops by comparing results from these drops, while frequency windows are used as standard between 2.8 and 3.2 dB drops in study of Honarvar et al. [Honarvar, F., Sheikhzadeh, H., Moles, M., Sinclair, A.N., 2004. Improving the time-resolution and signal–noise ratio of ultrasonic NDE signals. Ultrasonics 41, 755–763.]. The results obtained show that the application of the purposed signal processing technique considerably improves temporal resolution of seismic data when compared with the original seismic data. Furthermore, AR based spectral extrapolated data can be almost considered as reflectivity sequence of layered medium. Consequently, the combination of Wiener deconvolution and AR spectral extrapolation can reveal some details of seismic data that cannot be observed in raw signal or which lost during the previous processing. 相似文献
118.
预条件共轭梯度反褶积方法是结合稀疏反褶积的实现,运用优化的预条件共轭梯度法,完成反射系数的反演。用该方法处理地震资料时可提高资料频率,展宽有效频率宽度。但由于地震信号具有时变性,因此本文将该反褶积过程中的子波用多尺度时变子波代替。由数值算例可以看出,该方法可取得较好的实用效果。 相似文献
119.
120.
总结了遥感影像数据获取、传输和存储过程中引起影像退化的原因。根据信号处理中的概率统计理论,推导出了一种可以不依赖目标成像模型的遥感影像去模糊算法。实验结果表明,该算法具有较强的影像恢复能力和抗噪能力,对于缺乏点扩散函数先验知识的模糊遥感影像更加适用。 相似文献