全文获取类型
收费全文 | 337篇 |
免费 | 69篇 |
国内免费 | 27篇 |
专业分类
测绘学 | 88篇 |
大气科学 | 24篇 |
地球物理 | 161篇 |
地质学 | 78篇 |
海洋学 | 31篇 |
天文学 | 7篇 |
综合类 | 23篇 |
自然地理 | 21篇 |
出版年
2024年 | 2篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 17篇 |
2019年 | 12篇 |
2018年 | 7篇 |
2017年 | 13篇 |
2016年 | 15篇 |
2015年 | 9篇 |
2014年 | 19篇 |
2013年 | 22篇 |
2012年 | 17篇 |
2011年 | 17篇 |
2010年 | 14篇 |
2009年 | 13篇 |
2008年 | 16篇 |
2007年 | 24篇 |
2006年 | 33篇 |
2005年 | 17篇 |
2004年 | 21篇 |
2003年 | 13篇 |
2002年 | 13篇 |
2001年 | 7篇 |
2000年 | 14篇 |
1999年 | 11篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有433条查询结果,搜索用时 31 毫秒
371.
Summary The concept of diffracted rays introduced by Keller (1962) opened the way for a ray approach in the numerical modeling of
the diffraction phenomena frequently seen in the seismic field records. Unlike the computation of travel times, which has
never caused any difficulties being governed by the same eikonal equation as are the rays of ordinary seismic body waves,
the evaluation of the diffracted ray amplitude has been another story. In this paper we give a tutorial account of a highly
promising technique for the computation of the ray amplitude of seismic waves diffracted by linear edges on seismic interfaces
originally presented by Klem-Musatov (1980, 1995). We demonstrate the adequacy of this technique on a series of SH synthetic
traces containing diffracted arrivals, some of them diffracted more than once. Our computer program is based on a successful
combination of Klem-Musatov's approach with the zero order approximation of the Asymptotic Ray Theory (Červeny and Hron, 1980).
We showed in the paper that both techniqúes are ideally suited for such a combination, since the ray amplitude evaluation
in each of them is based on the same transport equation. In our tutorial review we present all formulae which are needed for
a practical implementation of the method and provide their physical interpretation, wherver possible, by using the numerical
examples presented in the paper. 相似文献
372.
Pavese et al. (1999) examined cation partitioning vs. temperature in a synthetic spinel of composition (Mg0.70 Fe0.23
3+) Al1.97 O4 using structure data obtained from in situ neutron powder diffraction. After imposing assumptions on the site assignment
of vacancies and Fe3+, they assigned the remaining cations by applying least-squares minimization to chemical constraints on site-occupancy sums,
site-scattering, chemical composition, and thermal expansion of the octahedral site. Their proposed site assignments exhibit
a sharp discontinuity in occupancy fractions versus temperature, a necessary consequence of their assumptions on vacancy assignments.
In this paper we reexamine the cation partitioning of the same spinel using the constrained least-squares formulation of OccQP (Wright et al. 2000), which optimizes site occupancies without ad hoc assumptions. We obtain strikingly different results,
supporting the general view that spinel undergoes a lambda transition at ∼1000 K. For all observed parameters, the residuals
obtained with the OccQP assignments are lower than those obtained with the Pavese et al. assignments, in some cases by more than 1 order of magnitude.
Received: 05 April 2000 / Accepted: 19 October 2000 相似文献
373.
Jiazheng Qin 《地震学报(英文版)》1992,5(3):563-578
In the light of the single scattering model of coda originating from local earthquakes, and based on the aftershock coda registered
respectively at the 4 short period stations installed near the foci shortly after theM7.6 Lancang andM7.2 Gengma earthquakes, this paper has tentatively calculated the rate of amplitude attenuation and theQ
c-value of the coda in the Lancang and Gengma areas using a newly-founded synthetic determination method. Result of the study
shows the rate of coda amplitude attenuation demonstrates remarkable regional differences respectively in the southern and
northern areas. The southern area presents a faster attenuation (Q
c=114), whereas the northern area shows a slower attenuation (Q
c=231). The paper also discusses the reasons causing such differences. Result of the study also suggests a fairly good linear
relation between the coda source factorA
o(f) and the seismic moment and the magnitude. Using the earthquake scaling law, the following formulas can be derived: lgM
0=lgA
0(f)+17.6,M
D=0.67lgA
0(f)+1.21 and logM
0=1.5M
D+15.79. In addition, the rates of amplitude attenuationβ
s andβ
m are respectively calculated using the single scattering and multiple scattering models, and the ratioβ
s/βm=1.20−1.50 is found for the results respectively from the two models. Finally, the mean free pathL of the S-wave scattering in the southern and northern areas are determined to be 54 km and 122 km respectively by the relations
which can distinguish between the inherentQ
i and scatteringQ
s, testify to this areas having lowQ-values correspond to stronger scatterings.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 71–82, 1992.
This study is partly supported by the Seismological Science Foundation of the State Seismological Bureau of China, and the
present English version of the paper is translated from its Chinese original by Wenyi Xia, Seismological Bureau of Yunnan
Province. 相似文献
374.
地震转换波测深中二次反射波震相的识别和利用 总被引:1,自引:0,他引:1
二次反射波震相的识别和利用对于进一步发展地震转换波测深法有重要意义。本文利用合成地震图方法,分析研究了短周期远震三分量初始30秒记录中主要震相的运动学和动力学特征。文中集中分析了PPP和PPS型二次波震相的振幅、波形和到时差等特征,及其与震中距、界面两侧波速差、界面结构和介质吸收等因素的关系。讨论了综合利用PS波和二次波震相的到时差资料测定介质速度参数的方法,并介绍了应用实例。 相似文献
375.
在对单项观测资料进行概率化的基础上,以唐山地区和乌鲁木齐地区为研究区,计算分析了多种前兆观测资料的合成缺信量,结果表明在强震和中强震发生前,合成缺信量的低值异常过程是比较明显的。进行这项研究对于综合识别多种前兆变化图象及在实际预报中的应用均有一定的意义。 相似文献
376.
377.
378.
Ankita Jain 《国际地球制图》2017,32(9):1017-1033
Estimation of vegetation covered soil moisture with satellite images is still a challenging task. Several models are available for soil moisture retrieval in which water cloud model (WCM) is most common. But, it requires an estimation of accurate vegetation parameterization. Thus, there is a need to develop such an approach for soil moisture retrieval which minimize these limitations. Therefore, this paper deals with the soil moisture retrieval using fully polarimetric SAR data by fusing the information from different bands. Various polarimetric indices and observables were critically analysed, and found that the index; SPAN (total scattered power) gives better information of vegetation cover as compared to other indices/observables. Based on this, WCM model has been modified using SPAN as parameter and soil moisture content were retrieved. 相似文献
379.
Utilizing remote sensing techniques to extract soil properties can facilitate several engineering applications for large-scale monitoring and modeling purposes such as earthen levees monitoring, landslide mapping, and off-road mobility modeling. This study presents results of statistical analyses to investigate potential correlations between multiple polarization radar backscatter and various physical soil properties. The study was conducted on an approximately 3 km long section of earthen levees along the lower Mississippi river as part of the development of remote levee monitoring methods. Polarimetric synthetic aperture radar imagery from UAVSAR was used along with an extensive set of in situ soil properties. The following properties were analyzed from the top 30–50 cm of soil: texture (sand and clay fraction), penetration resistance (sleeve friction and cone tip resistance), saturated hydraulic conductivity, field capacity, permanent wilting point, and porosity. The results showed some correlation between the cross-polarized (HV) radar backscatter coefficients and most of these properties. A few soil properties, like clay fraction, showed similar but weaker correlations with the co-polarized channels (HH and VV). The correlations between the soil properties and radar backscatter were analyzed separately for the river side and land side of the levee. It was found that the magnitude and direction of the correlation for most of the soil properties noticeably differed between the river and the land sides. The findings of this study can be a good starting point for scattering modelers in a pursuit of better models for radar scattering at cross polarizations which would include more diverse set of soil parameters. 相似文献
380.
R. Domínguez-Mora M.L. Arganis-Juárez A. Mendoza-Reséndiz E. Carrizosa-Elizondo B. EchavarrÍa-Soto 《Atmósfera》2013,26(1):27-43
A first procedure to generate synthetic storms, which preserves the statistical characteristics of the historical daily precipitation events registered in 49 stations located within the basin of Mexico City is presented. This procedure (a variation of the Svanidze method) implicitly supposes that the correlation between the maximum rainfall and its spatial distribution is meaningless. However, the obtained results did not validate that hypothesis. For this reason a second procedure was developed, which allows to consider the correlation between maximum rainfall and spatial distribution. This second procedure allowed reproducing the statistical characteristics of the daily rainfall for each station and also its spatial distribution, as shown in this work. 相似文献