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881.
Timely and accurately monitoring stand ages of deciduous rubber plantations is of great importance for ecological studies and plantations management. The re-establishment of rubber plantations usually experiences a short period (several years) of land clearance and transplantation of rubber seedlings, along with a noticeable landscape change from well-grown forest to bare land and sparse vegetation in situ. With Landsat times series (LTS) data of four commonly-used vegetation indices (VIs), namely the Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI), Normalized Difference Moisture Index (NDMI), and Normalized Burn Ratio (NBR), and three non-visible spectral bands, i.e. the near-infrared (NIR) and shortwave-infrared (SWIR1/2), in this study, an approach by combining the inter-annual defoliating and foliating features of rubber trees and the intra-annual landscape changes of rubber plantations was presented to detect and map stand ages of deciduous rubber plantations in an anti-chronological manner across Xishuangbanna between 1987 and 2018, one of the most intensive regions of deciduous rubber plantations within the tropics. The approach highlighted the repeated distribution of newly-cleared and replanted plot (NCRP) of rubber seedlings due to rubber management. It applied the bi-temporal VIs thresholds of zero of NBR and NDMI during the defoliation to foliation phases to delineate the stand ages of deciduous rubber plantations at an interval of five years, by combining a Landsat-based rubber map in 2018 and 32-year NCRPs as well as quadri-classified age-groups and seven sub-categories (i.e. ≤5 as infantile rubber plantations (IRP), 6–10 as young rubber plantations (YRP), 11–15 and 16–20 as mature rubber plantations (MRP), 21–25, 26–30, and ≥31 years as old rubber plantations (ORP)). The results showed that the areas of IRP, YRP, MRP, and ORP were 19.1 km2, 817.1 km2, 1681.7 km2, and 573.7 km2 in 2018, respectively. Spatially, the YRP are mainly around the outskirts of two county-level administrative centers (Jinghong and Mengla), while ORP primarily distributed along main roads. Nearly 53.9% of ORP, 51.8% of IRP, 47.3% of MRP and 46.3% of YRP were in Jinghong City, and Mengla County had 50.5% of YRP, 48.8% of MRP, 42.4% of IRP and 36.3% of ORP. This study demonstrates that the bi-temporal VIs thresholds method (i.e. NBRdefoliation <0, NDMIdefoliation <0, NBRfoliation <0, and NDMIfoliation <0) have great potential for detecting stand ages of deciduous rubber plantations. 相似文献
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l Some problems on the astronomical theory of ice ageThe astronomical theory of ice age, as the up todate solution for the global climatic changes in theQuaternary period, has been accepted by the most ofthe scientists in the world. However, there are stillsome arguable problems to need further research.Zhou Shangzhe (t994) pllt forward three questionslike as follows:The astronomical theory of ice age suggestedthat the ice age occurred when the eccentricity of theorbit of the earth was at its… 相似文献
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本文报道了内蒙古扎兰屯地区铜山组的碎屑锆石U-Pb年代学和Hf同位素分析结果,首次发现中国东北地区记录了泛非造山岩浆事件,并探讨了中国东北微陆块的构造归属.年代学研究表明:(1)扎兰屯地区铜山组碎屑岩最年轻锆石年龄峰值为569 Ma,与泛非造山岩浆活动(东、西冈瓦纳大陆碰撞-拼贴事件)的时代一致;其他3个峰期年龄为87... 相似文献
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The Mesozoic evolution of the Mongol-Okhotsk Ocean (MOO) has significantly affected the configuration of the modern Asian continent. Although a scissor-like closure of the MOO has long been proposed, when and how the MOO closed are still hotly debated, especially the timing of initial closure of the MOO in its western segment, hindering our understanding of both the evolution of the MOO and tectonics of the northern Asian continent. In order to uncover the timing of initial closure of the MOO, we performed a multidisciplinary study in sedimentology, detrital zircon U-Pb dating and paleomagnetic on the Late Triassic clastic strata from the Tarvagatay Block and the Amuria Block (AMB) on the both sides of the Mongol-Okhotsk Suture. The upper Triassic strata on both sides of the suture were dominated by plant fossil-bearing alluvial-fluvial facies sediments, which unconformably overlain pre-Triassic geological units, indicating a terrestrial setting after the closure of the MOO. Detrital zircon U-Pb dating results revealed consistent age distribution patterns for samples from both sides of the suture with a predominant peak at ∼253–251 Ma and a secondary peak at ∼359–357 Ma, representing two main arc magmatic events during the bidirectional subduction of the MOO in the Late Devonian-Early Carboniferous and Late Permian-Early Triassic. Coeval Late Triassic paleomagnetic poles were obtained from the northern AMB and Tarvagatay Block, revealing a comparable paleolatitude of the AMB (∼31–33°) and Tarvagatay Block (∼32–34°) in the Late Triassic, arguing for that the western segment of the MOO should have closed at the Late Triassic. The compilation of sedimentology, detrital zircon U-Pb dating, magmatic and paleomagnetic evidence provides integrated constraints on the Late Triassic initial closure of the MOO in its western segment. 相似文献
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