全文获取类型
收费全文 | 857篇 |
免费 | 27篇 |
国内免费 | 25篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 118篇 |
地球物理 | 202篇 |
地质学 | 252篇 |
海洋学 | 247篇 |
天文学 | 39篇 |
综合类 | 14篇 |
自然地理 | 23篇 |
出版年
2023年 | 3篇 |
2022年 | 9篇 |
2021年 | 23篇 |
2020年 | 14篇 |
2019年 | 17篇 |
2018年 | 45篇 |
2017年 | 46篇 |
2016年 | 73篇 |
2015年 | 50篇 |
2014年 | 52篇 |
2013年 | 63篇 |
2012年 | 53篇 |
2011年 | 70篇 |
2010年 | 65篇 |
2009年 | 50篇 |
2008年 | 39篇 |
2007年 | 38篇 |
2006年 | 34篇 |
2005年 | 34篇 |
2004年 | 21篇 |
2003年 | 29篇 |
2002年 | 15篇 |
2001年 | 13篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有909条查询结果,搜索用时 31 毫秒
741.
Victor Balagansky Andrey Shchipansky Alexander I. Slabunov Il’ya Gorbunov Sergey Mudruk Mikhail Sidorov 《International Geology Review》2015,57(11-12):1543-1565
This paper addresses the relationships between relic amphibole-eclogite facies (AE) eclogites and their host units, Archaean amphibolites, enveloped by Archaean tonalite–trondhjemite–granodiorite (TTG) gneisses, in the Kuru-Vaara study area in the northern Belomorian Province. According to observational constraints, the crystallization of the relic peak omphacite + Mg-garnet ± kyanite assemblage and the subsequent replacement of omphacite by clinopyroxene–plagioclase symplectite occurred before the earliest deformational, metamorphic, and migmatization events that are recorded in the amphibolites. The amphibolites and their TTG hosts have a shared deformational and metamorphic history that is composed of the Archaean and Palaeoproterozoic periods. This history favours the conclusion that the AE metamorphism recorded in the relic eclogites within the amphibolites occurred during the Mesoarchaean to Neoarchaean periods. The deformation and metamorphism of the amphibolite facies of the second period resulted from the Lapland–Kola collisional orogeny at 1.91–1.93 Ga, which led to eclogite–high-pressure granulite (E–HPG) facies conditions in the lowermost portions of the over-thickened crust in Belomorian Province (the southwestern foreland of the Lapland–Kola collisional orogen). The Palaeoproterozoic E–HPG overprint was reported from the Palaeoproterozoic Gridino mafic dikes. Although the ages of the oldest low Th/U zircons are close to the time of the Lapland–Kola collision, the low Th/U 1.9–1.8 Ga zircons reflect a zircon response to regional fluid infiltration in the eclogites during slow exhumation following the Lapland–Kola orogeny and do not record any metamorphic event. Contrary to the Palaeoproterozoic E–HPG overprint, the areal occurrence of the 2.7–2.8 Ga AE eclogites with mid-ocean ridge basalt-like chemistry and their paragenetic link with the TTG gneisses suggest a tectonic regime that involves subduction. This research favours concepts suggesting that the modern-style plate tectonics has operated in some places, at least since the late Mesoarchaean. 相似文献
742.
Samaddar Subhajyoti Choi Junho Misra Bijay Anand Tatano Hirokazu 《Natural Hazards》2015,75(2):1531-1554
Natural Hazards - Recent decades have seen an increasing recognition and consensus among researchers and planners in disaster management in the need to foster social learning... 相似文献
743.
744.
745.
Soil moisture state and variability control many hydrological and ecological processes as well as exchanges of energy and water between the land surface and the atmosphere. However, its state and variability are poorly understood at spatial scales larger than the fields (i.e. 1 km2) as well as the ability to extrapolate field scale to larger spatial scales. This study investigates soil moisture profiles, their spatial organization, and physical drivers of variability within the Walnut Creek watershed, Iowa, during Soil Moisture Experiment 2005 and relates the watershed scale findings to previous field‐scale results. For all depths, the watershed soil moisture variability was negatively correlated with the watershed mean soil moisture and followed an exponential relationship that was nearly identical to that for field scales. This relationship differed during drying and wetting. While the overall time stability characteristics were improved with observation depth, the relatively wet and dry locations were consistent for all depths. The most time stable locations, capturing the mean soil moisture of the watershed within ± 0·9% volumetric soil moisture, were typically found on hill slopes regardless of vegetation type. These mild slope locations consistently preserve the time stability patterns from field to watershed scales. Soil properties also appear to impact stability but the findings are sensitive to local variations that may not be well defined by existing soil maps. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
746.
The compression index is a one of the important soil parameters that is essential to geotechnical designs. As the determination of the compression index from consolidation tests is relatively time-consuming, empirical formulas based on soil parameters can be useful. Over the decades, a number of empirical formulas have been proposed to relate the compressibility to other soil parameters, such as the natural water content, liquid limit, plasticity index, specific gravity, and others. Each of the existing empirical formulas yields good results for a particular test set, but cannot accurately or reliably predict the compression index from various test sets. In this study, an alternative approach, an artificial neural network (ANN) model, is proposed to estimate the compression index with numerous consolidation test sets. The compression index was modeled as a function of seven variables including the natural water content, liquid limit, plastic index, specific gravity, and soil types. Nine hundred and forty-seven consolidation tests for soils sampled at 67 construction sites in the Republic of Korea were used for the training and testing of the ANN model. The predicted results showed that the neural network could provide a better performance than the empirical formulas. 相似文献
747.
Graphite-bearing rocks and graphites from the Precambrian metamorphic sequence of the Pestpaksha ore occurrence, Murmansk
district, have been studied by the X-ray method. It was determined that the rocks have a complex polycomponent composition.
Graphite is associated with garnet-quartz, pyroxene-amphibole, and biotite-quartz with an admixture of pyrrhotite, kyanite,
chlorite, and other minerals. In terms of mineral composition, the studied samples are subdivided into five groups. The structural
characteristics of graphite—parameters a
0 and c
0, the degree of structural perfection (U), the content of rhombohedral phase (R), and others—were found to be different for
each group. The U value varies from 1.04 to 1.56 (with predominant values from 1.4 to 1.5), while the content of rhombohedral
phase in samples is no more than 18%. This fact indicates a relatively high 3D order, which is typical of graphites from metamorphic
rocks. Graphites from metasomatites have the lowest U value, while those from weathering zones are characterized by a small
value of the coherent scattering domain (CSD). It was established that interplanar spacing d
002 of graphite correlates with depth, while the degree of ductility and flexibility of the graphite is defined by conditions
of its retrograde metamorphism. 相似文献
748.
Meteorological stations, which measure all the required meteorological parameters to estimate reference evapotranspiration (ETo) using the Food and Agriculture Organization Penman?CMonteith (FAO56-PM) method, are limited in Korea. In this study, alternative methods were applied to estimate these parameters, and the applicability of these methods for ETo estimation was evaluated by comparison with a complete meteorological dataset collected in 2008 in Korea. Despite differences between the estimation and observation of radiation and wind speed, the comparison of ETo showed small differences [i.e., mean bias error (MBE) varying ?0.22 to 0.25?mm?day?1 and root-mean-square-error (RMSE) varying 0.06?C0.50?mm?day?1]. The estimated vapor pressure differed considerably from the observed, resulting in a larger discrepancy in ETo (i.e., MBE of ?0.50?mm?day?1 and RMSE of 0.60?C0.73?mm?day?1). Estimated ETo showed different sensitivity to variations of the meteorological parameters??in order of vapor pressure?>?wind speed?>?radiation. It is clear that the FAO56-PM method is applicable for reasonable ETo estimation at a daily time scale especially in data-limited regions in Korea. 相似文献
749.
750.
The impact of transient eddies on extratropical seasonal-mean prediction and predictability was examined using DEMETER seasonal prediction data. Two distinct groups were found among the seven DEMETER models based on the simulated properties of their climatological state: (1) models of a strong jet stream and strong transient activity (strong transient models), which is close to the observed intensity, and (2) models of a weak jet stream and weak transient activity (weak transient models). In addition to climatology, the strong transient models tend to predict strong Pacific North American (PNA) patterns, whereas the weak transient models predict weak PNA patterns. Here we demonstrate that these differences mainly result from differences in the eddy feedback intensity. Due to synoptic eddy feedback, the strong transient models exhibit not only strong signal variance but also strong noise variance compared with those of the weak transient models. Interestingly two groups of models show the potential predictability of deterministic forecast, measured by the signal to noise ratio, which is similar to each other. However, the strong transient models produce the error to spread ratio smaller than that of the weak transient models, implying that the former models produce a more reliable spread for the probabilistic forecast. This study implies that a better representation of transient statistics is needed to improve the extratropical predictability of the dynamical seasonal prediction. 相似文献