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71.
Issam Mouayn 《Pure and Applied Geophysics》2007,164(5):957-974
We have derived, evaluated, and compared two empirical methods for computing duration magnitude M
D
from 25 short-period vertical component stations of the Northern Morocco Seismic Network (NMSN). M
D
has been scaled to IGN (Insituto Geograpfico National, Spain) body-wave magnitude (mb
IGN
), using a set of 479 shallow (less than 30 km) earthquakes recorded from March 1992 to February 2001, with 2.5 ≤ mb
IGN
≤ 5.4. In the first approach: Individual Network Calibration, we determined an individual M
D
formula for each station. In the second approach: Global Network Calibration, we used a single relationship to compute M
Dij
(from the jth observation for the i-th earthquake) magnitudes at 25 selected stations as: M
Dij
= − 0.14 +1.63 log10 (τ
ij
)+0.031(Δij)+cSta
j
. Residuals (M
Dij
− mb
IGN
) for both techniques were thereafter deduced. Comparison between the two approaches provided the principal results: (1) The
mean correlation between estimated magnitude; M
Dij
and reference magnitude; mb
IGN
is about 89.9% for the individual calibration method, and near 95% for global calibration method in which station corrections
cSta
j
were introduced, (2) Residuals (M
Dij
− mb
IGN
) are relatively large, and are ranging between − 0.60 and 0.60 magnitude units, for the individual calibration method, whereas
they vary in the range − 0.38 to 0.40, for the global calibration method with corrections; cSta
j
. (3) A random distribution of residuals (M
Dij
− mb
IGN
) is observed for each station in the case of the individual approach. Thus, the resulting average of these residuals is almost
equal to zero. Using a global calibration without corrections results in negative residuals for a group stations and positive
residuals for another an group indicating respectively that sites corresponding to these groups have a tendency to underestimate,
or overestimate observed magnitude values. 相似文献
72.
73.
多波束勘测的特殊地形处理 总被引:3,自引:2,他引:1
海底特殊地形在多波束勘测后处理时经常遇到但又极易被忽视,导致具有重要地学和工程意义的特殊地形未能被反映在成果图上。通过分析后处理中的常见问题,提出了利用水深残差法搜索定位多波束海量数据中存在的局部特殊地形,进而提取特殊地形的水深浅点和深点的处理方法。该方法在国家海洋勘测专项中取得了很好的应用效果。 相似文献
74.
1982—2015年中国气候变化和人类活动对植被NDVI变化的影响 总被引:14,自引:1,他引:13
基于中国603个气象站的地表气温和降水观测资料以及GIMMS NDVI3g数据,采用变化趋势分析和多元回归残差分析等方法研究了1982—2015年中国植被NDVI变化特征及其主要驱动因素(即气候变化和人类活动)的相应贡献。结果表明:① 1982—2015年中国植被恢复明显,在选择的32个省级行政区中,山西、陕西和重庆的生长季NDVI增加最快,仅上海生长季NDVI呈减小趋势。② 气候变化和人类活动的共同作用是中国植被NDVI呈现整体快速增加和巨大空间差异的主要原因,其中气候变化对各省生长季NDVI变化的影响在-0.01×10 -3~1.05×10 -3 a -1之间,而人类活动的影响在-0.32×10 -3~1.77×10 -3 a -1之间。③ 气候变化和人类活动分别对中国近34年来植被NDVI的增加贡献了40%和60%;人类活动贡献率超过80%的区域主要集中在黄土高原中部、华北平原以及中国东北和西南等地;人类活动贡献率大于50%的省份有22个,其中贡献率最大的3个地区为上海、黑龙江和云南。研究结果建议应更加重视人类活动在植被恢复中的作用。 相似文献
75.
76.
77.
Fresnel volumes provide a suitable tool for estimating the resolution limits or accuracy of tomographic methods based only on the arrival times of these seismic waves, which penetrate the deep interior of the Earth. The standard definition of the Fresnel volume was modified to include effects of multipathing, i.e., multivalued travel times. Computations were performed in the IASP91 model for three representative epicentral distances and two prevailing signal periods. Preliminary results have been obtained. They place a rather strong restriction on the resolution limits of tomographic methods, depending on the prevailing period, due to the relatively large fatness of PKP Fresnel volumes. 相似文献
78.
着重介绍了一种数值力学方法薄板加权残值法用于处理近景摄影测量问题。通过实验证实这种方法在减少已知点数、改正近景像片的系统误差及提高解算精度方面的有效性。实验中采用了各种标准图型的模拟数据 ,并结合生产实例 ,从各个方面进行了探讨 ,得出了可靠的结果 相似文献
79.
Discussion on the influence of truncation of ground motion residual distribution on probabilistic seismic hazard assessment 总被引:1,自引:0,他引:1
Recent studies on assessment of a very low annual probability of exceeding (APE) ground motions, 10-4 or less, have highlighted the importance of the upper bound of ground motions when very low probability results are acquired. The truncation level adopted in probabilistic seismic hazard analysis (PSHA) should be determined by an aleatory uncertainty model (i.e., distribution model) of ground motions and the possible maximum and minimum ground motion values of a specific earthquake. However, at the present ... 相似文献
80.
Elizabeth Vanacore 《地震学报(英文版)》2011,(1):87-99
SKS and SKKS waveforms from 16 events occurring between 2003 and 2005 in the Tonga Trench that were recorded by the BOLIVAR array are analyzed to determine the structure of the D layer beneath the Galapagos Islands.248 differential travel-time residuals of SKKS-SKS are measured and reveal a region of positive residuals of differential travel times in the northeast portion of the sampled region.Analyzing correlation statistics between the measured SKKS-SKS residuals and the observed absolute travel time dela... 相似文献