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961.
LARS NIELSEN ADAM SCHACK VON BROCKDORFF MORTEN BJERAGER FINN SURLYK 《Sedimentology》2009,56(3):695-708
Bryozoan mounds from the middle Danian (Lower Palaeocene) of the Danish Basin represent a possibly new class of non‐cemented skeletal mounds. The sedimentology and palaeoecology of the mounds have recently been studied in detail. Three‐dimensional images of middle Danian bryozoan mound structures in the Limhamn limestone quarry, south‐west Sweden, obtained from combined reflected ground‐penetrating radar signals and outcrop analysis provide new information about the architecture and growth development of such mounds. The mounds are composed of bryozoan limestone and dark‐grey to black flint bands which outline mound geometries. Ground‐penetrating radar data sections are collected over a 120 m by 60 m grid of data lines with trace spacing of 0·25 m, providing a depth penetration of 7 to 12 m and a vertical resolution of ca 0·30 m. The ground‐penetrating radar images outline the geometry of the internal layering of the mounds which, typically, have widths and lengths of 30 to 60 m and heights of 5 to 10 m. Mound architecture and growth show great variability in the ground‐penetrating radar images. Small‐scale mound structures with a palaeorelief of only a few metres may constitute the basis for growth of larger mounds. The outermost beds of the individual mounds are commonly characterized by sub‐parallel to parallel reflections which have a circular to slightly oval appearance in map view. The mounds are mainly aggrading and do not show clear signs of pronounced lateral migration during growth, although some mound structures indicate a preferential growth direction towards the south. Growth patterns interpreted from the ground‐penetrating radar images suggest that the palaeocurrents in the study area may have shown great variability, even on a small scale. This observation is in contrast to results from studies of extensive, slightly older early Danian mound complexes exposed in coastal cliffs at Stevns Klint and Karlby Klint located 50 and 200 km away from the study area, respectively. At these locations the mounds show a remarkably uniform development and typically are asymmetrical, clearly showing migration directions towards the south. These differences in mound geometry may be the result of differences in the current systems and water depths that existed during formation of the early and middle Danian mounds, respectively. The mounds at Limhamn were located closer to the basin margin in shallower water than those at Stevns Klint and Karlby Klint. In addition, the difference in mound architecture may be due to the occurrence of non‐layered, irregular coral mounds intercalated with the bryozoan mounds at Limhamn. 相似文献
962.
Thomas W. Schmidlin 《Natural Hazards》2009,50(1):13-25
There were 407 deaths from wind-related tree failures in the United States, 1995–2007. The most common cause of the deadly
fallen tree was a thunderstorm (41%), followed by nonconvective high winds (35%), tropical cyclones (14%), tornadoes (7%),
and snow and ice (3%). Most (62%) of the deaths were males while the median age was 44 years. The most common location of
the fatality was in a vehicle struck by the tree or a vehicle that crashed into a downed tree on the road (44%), followed
by persons outdoors (38%), in mobile homes (9%), and in frame houses (9%). Persons killed by wind-related tree failures during
tropical cyclones and tornadoes were more commonly at home (40%) when struck than those killed at home by thunderstorm and
nonconvective high winds (13%). Seasonality of the deaths varied by weather type with deaths in thunderstorms clustered during
May–August, nonconvective high winds October–April, tropical cyclones August–October, tornadoes in April and November, and
snow and ice December–April. Regional patterns result from frequency of the wind events, population density, and tree cover.
Suggestions are made for hazard reductions. 相似文献
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966.
一种基于序列影像匹配的独立树冠可视化方法 总被引:2,自引:1,他引:1
介绍采用非量测相机与序列影像匹配实现独立树冠3维重建的方法。主要包括从影像提取特征点:使用多基线影像与金字塔分层相关技术进行特征点匹配;解算影像的相对方位参数;由前方交会求出各特征点的模型坐标;由模型坐标构造树冠表面三角网;由纹理映射得到树冠3维模型景观图,实现树木可视化的真3维表达。 相似文献
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以雅鲁藏布江源区为研究对象,以Landsat5 TM图像为数据源,根据不同草地类型的波段组合特征,结合源区1∶100万植被类型图、DEM和NDVI数据,构建草地判别规则,利用决策树分类法对雅鲁藏布江源区草地类型进行遥感识别。研究结果表明:①不同类型草地因其生境不同,利用不同波段组合特征进行草地类型识别能够达到较好的效果;②与传统的监督分类法相比,基于波段组合特征的决策树分类法具有较高的识别精度(总体精度提高了15.4%,Kappa系数提高了0.225);③在海拔4 400~5 000 m区域内,固沙草草原面积最大,其次为矮嵩草和小嵩草混生草甸,再次为变色锦鸡儿和金露梅灌丛,藏北嵩草草甸面积最小。 相似文献
969.
GPS-RTK技术给测绘业带来了一次革命,它快速、精确的定位方式使得其应用于测绘的各个领域,本文以河南省新乡市凤泉山区1∶1000数字地形图测绘为例对GPS-RTK在数字化测图中的应用进行具体的介绍。 相似文献
970.