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911.
Late Devonian (Famennian) marine successions globally are typified by organic-rich black shales deposited in anoxic and euxinic waters and the cessation of shelf carbonate sedimentation. This global ‘carbonate crisis’, known as the Hangenberg Event, coincides with a major extinction of reef-building metazoans and perturbations to the global carbon cycle, evidenced by positive carbon-isotope excursions of up to 4‰. It has been suggested that authigenic carbonate, formed as cements in sedimentary pore spaces during early burial diagenesis, is a significant mass fraction of the total global carbon burial flux, particularly during periods of low oxygen concentration. Because some authigenic carbonate could have originated from remineralization of organic carbon in sediments, it is possible for this reservoir to be isotopically depleted and thereby drive changes in the carbon isotopic composition of seawater. This study presents bulk isotopic and elemental analyses from fine-grained siliciclastics of the Late Devonian–Early Mississippian Bakken Formation (Williston Basin, USA) to assess the volume and isotopic composition of carbonates in these sediments. Carbonate in the Bakken black shales occurs primarily as microscopic disseminated dolomite rhombs and calcite cements that, together, comprise a significant mass-fraction (ca 9%). The elemental composition of the shales is indicative of a dynamic anoxic to sulphidic palaeoenvironment, likely supported by a fluctuating chemocline. Despite forming in an environment favourable to remineralization of organic matter and the precipitation of isotopically depleted authigenic carbonates, the majority of carbon isotope measurements of disseminated carbonate fall between −3‰ and +3‰, with systematically more depleted carbonates in the deeper-water portions of the basin. Thus, although there is evidence for a significant total mass-fraction of carbonate with contribution from remineralized organic matter, Bakken authigenic carbonates suggest that Famennian black shales are unlikely to be sufficiently 13C-depleted relative to water column dissolved inorganic carbon to serve as a major lever on seawater isotopic composition. 相似文献
912.
ZHANG Tao WANG Bin LI Dedong NIU Ben SUN Jie SUN Yifei YANG Xiaoguang LUO Juan HAN Jian 《《地质学报》英文版》2020,94(1):189-197
The Cambrian Kuanchuanpu Formation in southern Shaanxi, China is a critical window for the understanding of the Cambrian explosion, because of abundant and various exceptionally preserved metazoans and embryo fossils yielded. The efficiency of traditional sample manually selecting with microscopes is quite low and hinder the discoveries of new species, thus recognition and classification of microfossils by artificial intelligence (AI) is substantially in the request. In this paper, we develop a procedure for fossil area segmentation in common multi-typed mixed photos by improved watershed algorithm. And for better fossil recognition, previous histogram of oriented grandient (HOG) algorithm is replaced by scale invariant feature transform (SIFT), which is feasible for the segmented images and increase the accuracy significantly. Thus, the scope of application of AI fossil recognition can be extended form single fossil image to multi-typed mixed images and the reliability is also secured, as the result of our test presents a high (at least 84%) accuracy of fossil recognition. 相似文献
913.
Sabiha Tlig-Zouari Lotfi RabaouiHosni Fguiri Moctar DiawaraOum Kalthoum Ben Hassine 《Estuarine, Coastal and Shelf Science》2010
The present study focuses on horizontal spatial variability of benthic macrofauna associated with Patella ferruginea. Thirty-six samples collected at 12 transects belonging to 4 midlittoral sites along the rocky Tunisian coastline, were examined. A total of 44 species belonging to 5 taxa were found. Multivariate analysis applied on gathered data did not show a horizontal spatial variability at small scale (between transects), but at large scale, between sites as well as sectors. Thus, three groups of communities were identified (GI: Korbous and El Haouaria; GIIa: Zembra Island and GIIb: Kelibia). The distribution of species abundance within these groups revealed that crustaceans were the most abundant taxon, due to the overwhelming dominance of Chthamalus stellatus. This substratum appeared to create favourable micro-habitats for the installation of molluscs including gastropods. Regarding the low diversity index (H') and evenness (J), they seemed to reflect a disturbance and a demographic unbalance within these communities. The heterogeneity of substrate surface, created by C. stellatus specimens appeared to be caused by various complex interactions established between the key components of these communities in particular suspension feeders, predators, herbivorous molluscs and macroalgae. Thus, the dynamic status of each of these communities is the result of these complex interactions. 相似文献
914.