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711.
712.
针对云南省因土地利用结构变化,自然环境遭到破坏,导致许多物种极度濒危甚至灭绝、生物多样性遭到严重破坏的问题,本文利用最大熵模型(MaxEnt)对云南9种特色优先保护物种进行了环境适宜性分析。首先以资源环境承载力及国土空间开发适宜性为基础,筛选出具有云南特色的9个优先保护物种,然后对各物种的最优生存环境进行了预测。研究结果表明,云南省9种优先保护物种现存分布区总计0.21万km2。经最大熵模型(MaxEnt)预测可知,最优适生分布区可达5.45万km2,是现存分布区的25倍。 相似文献
713.
A number of isolated islands of Leymus chinensis + herbosa community were investigated in fragmented habitat islands, by Braun-Blanquet field survey approach, in a degenerated
meadow in the Songnen Plain, China in 2007. These islands were classified as large, medium, and small scales on the basis
of the island area (100–1000m2, large island; 50–100m2, middle island; 10–50m2, small island). Each scale of the investigation involved eight islands. The responses of β-diversity patterns of plant taxon to the habitat fragmentation at local community and metacommunity levels were analyzed
on different scales of 24 isolated islands. The results indicated that at the local community level, there were 57 species
belonging to 20 families and 49 genera in large islands, 49 species belonging to 16 families and 40 genera in middle islands,
and 27 species belonging to eight families and 23 genera in small islands. β-diversity indexes for species, genus and family in large, middle, and small islands varied greatly, and the highest value
of the indexes was not noted in the largest island. However, the average of the data obtained at the three scales showed that
across large islands, Whittaker indexes were low and Bray-Curtis similarity indexes were high, while across small islands,
Whittaker indexes were high and Bray-Curtis similarity indexes were low. At the metacommunity level, Whittaker indexes for
species and genus showed a great significantly negative double logarithmic correlation (p<0.01) with the island area, whereas the Bray-Curtis indexes for species, genus and family showed a great significantly positive
double logarithmic correlation (p<0.01) with the island area. At both local community and metacommunity levels, turnovers of species and genus could respond
more sensitively to spatial changes of plant diversity patterns than that of family. Hence, the species and the genus could
be used for the analysis of β-diversity patterns of plant community. 相似文献
714.
715.
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717.
Short-term geomorphic and hydrologic effects of subsidence induced by longwall mining under Burnout Creek, Utah were evaluated.
During the year after longwall mining, 0.3–1.5 m of subsidence was measured near impacted reaches of the mountain stream channel.
The major channel changes that occurred in a 700-m reach of Burnout Creek that was subsided from 1992 to 1993 were: (1) increase
in lengths of cascades and to a lesser extent glides; (2) increases in pool length, numbers and volumes; (3) increase in median
particle diameter of bed sediment in pools; and (4) some constriction in channel geometry. Most of the changes appeared short-lived,
with channel recovery approaching pre-mining conditions by 1994. In a 300-m reach of the South Fork that was subsided from
1993 to 1994, only channel constriction was observed, although any impacts on pool morphology may have been confounded by
heavy grazing in the riparian reaches during the dry summer of 1994. Similar near-channel sedimentation and loss of pool volume
between 1993 and 1994 were noted throughout Burnout Creek and in adjacent, unmined James Creek. Subsidence during the 3-year
period had no effect on baseflows or near-channel landslides.
Received: 10 April 1998 · Accepted: 21 September 1998 相似文献
718.
M.F. Carreño M.A. Esteve J. MartinezJ.A. Palazón M.T. Pardo 《Estuarine, Coastal and Shelf Science》2008
In recent decades wetlands associated with the Mar Menor lagoon (SE Spain) have undergone several hydrological and biological changes as a consequence of increased water inputs from agricultural drainage off the watershed. Changes in the vegetal communities were studied by means of supervised classification of Landsat images, and TM and ETM+ sensors during the period 1984–2000, and a series of land cover maps was created. Changes in the wetland area during this period were analysed and a good fit was found with the total area of irrigated lands in the watershed. The series of land cover maps also allowed the study of the internal composition of the vegetal communities in each wetland. Important changes were detected, with an expansion of reedbeds and a significant reduction in the area occupied by priority habitats according to the Habitats Directive. 相似文献
719.
Subdivision of Permian Fossil Communities and Habitat Types in Northeast Sichuan, South China 总被引:1,自引:0,他引:1
Recent achievement in hydrocarbon exploration In Northeast Sichuan (四川) demonstrated that Permian calcareous and argillaceous deposits are the major contributing source rocks. Reevaluation on the hydrocarbon potential of the Permian strata over the whole Yangtze region is thus to be desired. A comprehensive corroboration was carried out at the Shangsi (上寺) Section, Guangyuan (广元), Northeast Sichuan, which is believed to be another promising area in South China. This article deals with the ecological and depositionai conditions of the Permian strata in the section, including the Chihsla, Maokou (茅口), Wujiaping (吴家坪), and Dalong (大隆) formations, which share some similarities with those occurring in the broad Yangtze carbonate platforms. Five fossil communities of Mizzia-Permocalculus, Hayasakaia, Inozoan, Ostracod, and Crinoid were identified in the Yangtze region and described in detail including their components and occurrence. On the basis of the fossil communities and depositional features, 23 habitat types, mainly occurring from inner to outer shelves, were recognized at the Shangsi Section in order to reconstruct the depositional conditions and accordingly to evaluate the paleoproductivity. In addition, the subdivision of Chihsia Formation in the section was revised, which would be of significance for the reconstruction of the Chihsian paleogeography in the study area. 相似文献