全文获取类型
收费全文 | 1166篇 |
免费 | 201篇 |
国内免费 | 260篇 |
专业分类
测绘学 | 222篇 |
大气科学 | 277篇 |
地球物理 | 305篇 |
地质学 | 431篇 |
海洋学 | 121篇 |
天文学 | 39篇 |
综合类 | 82篇 |
自然地理 | 150篇 |
出版年
2024年 | 7篇 |
2023年 | 11篇 |
2022年 | 24篇 |
2021年 | 42篇 |
2020年 | 49篇 |
2019年 | 47篇 |
2018年 | 35篇 |
2017年 | 36篇 |
2016年 | 65篇 |
2015年 | 61篇 |
2014年 | 77篇 |
2013年 | 71篇 |
2012年 | 77篇 |
2011年 | 61篇 |
2010年 | 60篇 |
2009年 | 62篇 |
2008年 | 82篇 |
2007年 | 69篇 |
2006年 | 93篇 |
2005年 | 72篇 |
2004年 | 56篇 |
2003年 | 45篇 |
2002年 | 44篇 |
2001年 | 40篇 |
2000年 | 42篇 |
1999年 | 54篇 |
1998年 | 26篇 |
1997年 | 30篇 |
1996年 | 22篇 |
1995年 | 21篇 |
1994年 | 24篇 |
1993年 | 18篇 |
1992年 | 13篇 |
1991年 | 18篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 4篇 |
1973年 | 1篇 |
1971年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有1627条查询结果,搜索用时 515 毫秒
151.
152.
153.
Complex component analysis of shear-wave splitting: theory 总被引:2,自引:0,他引:2
154.
Anthropogenic activities create various contaminated leachate, which can migrate downward from the vadose zone to groundwater,
transferring contaminants, including some hazardous ones.
When these various sources of contamination influence the groundwater aquifer simultaneously, the effects of contamination
are enhanced.
The major concern of this study has been to determine whether the shape of a groundwater chlorograph might be the result of
such deterministic effects as accumulation of one or more particular processes of groundwater contamination, and how this
might relate to specific hydrological situations.
This study proposes a classification of groundwater contamination on the basis of properties of the main components of groundwater
quality graphs and the corresponding hydrogeological/environmental situation.
The study further suggests that contamination of groundwater in any hydrogeological situation (e.g. sea water) may be graphically
expressed.
A variety of chlorographs and nitrographs, representative of various groundwater aquifers sampled from a number of wells throughout
Israel attest to this.
The study thus indicates that groundwater quality graphs may be considered as a complementary tool for groundwater quality
control and better understanding aquifer situations. 相似文献
155.
A statistical study of the dependence between various critical fusion temperatures of a certain kind ofcoal and its chemical components is carried out.As well as using classical dependence techniques(multiple,stepwise and PLS regression,principal components,canonical correlation,etc.)together withthe corresponding inference on the parameters of interest,non-parametric regression and bootstrapinference are also performed. 相似文献
156.
大规模伸展构造是华北克拉通东部岩石圈减薄的重要表现形式。部分低角度韧性剪切带是地壳伸展变形后所展现的构造形式。本文研究了王格庄韧性剪切带的岩石学、几何学、运动学等特征显示:韧性剪切带走向近南北向,剪切带断层面倾向多变(倾向西、西南、西北方向)。大部分区域面理低角度倾向西,矿物拉伸线理近东西向,不对称旋转碎斑及S-C组构指示顶端指向西的剪切特征。结合研究区西侧与伸展构造相匹配的半地堑伸展盆地证据:本研究认为伸展构造的形成可能与西太平洋板块的后撤相关,即大规模伸展构造作用引发了华北克拉通东部的地壳减薄作用。 相似文献
157.
The carbonate factories, their controlling factors and their palaeoecological and sedimentological signals recorded in sedimentary successions are key elements for understanding the evolution of carbonate platform systems. Luis Pomar has dedicated most of his academic life to the study of carbonate rocks and carbonate factories. The idea for this special issue to celebrate Pomar’s career arose during a session at the 34th International Association of Sedimentologists meeting held in Rome, entitled ‘Understanding carbonate factories through palaeoecological and geochemical signals’. The proposal encountered great response among participants, and additional contributions followed an email invitation to other specialists. This issue contains a variety of papers on carbonate sedimentology and carbonate factories. Here, an introduction that contextualizes the papers and key concepts discussed in this thematic issue is provided. It reviews Luis Pomar’s major achievements in carbonate sedimentology and discusses the evolution of the concept of the carbonate factory and the series of palaeoecological and sedimentological signals used to characterize the wide spectrum of carbonate depositional systems found in the natural world. 相似文献
158.
Quantifying the variability and allocation patterns of aboveground carbon stocks across plantation forests is central in deriving accurate and reliable knowledge and understanding of the extent to which these species contribute to the global carbon cycle and towards minimizing climate change effects. The principal objective of this study was to quantify the variability and allocation patterns of aboveground carbon stocks across Pinus and Eucalyptus plantation forests, tree-structural attributes (i.e. stems, barks, branches and leaves) and age groups, using models developed based on remotely sensed data. The results of this study demonstrate that aboveground carbon stocks significantly (α = 0.05) vary across different plantation forest species types, structural attributes and age. Pinus taeda and Eucalyptus grandis species contained aboveground carbon stocks above 110 t C ha−1, and Eucalyptus dunii had 20 t C ha−1. Across plantation forest tree structural attributes, stems contained the highest aboveground carbon stocks, when compared to barks, branches and leaves. Aboveground carbon stock estimates also varied significantly (α = 0.05) with stand age. Mature plantation forest species (i.e. between 7 and 20 years) contained the highest aboveground carbon stock estimates of approximately 120 t C ha−1, when compared to younger species (i.e. between 3 and 6 years), which had approximately 20 t C ha−1. The map of aboveground carbon stocks showed distinct spatial patterns across the entire study area. The findings of this study are important for understanding the contribution of different plantation forest species, structural attributes and age in the global carbon cycle and possible climate change moderation measures. Also, this study demonstrates that data on vital tree structural attributes, previously difficult to obtain, can now be easily derived from cheap and readily-available satellite data for inventorying carbon stocks variability. 相似文献
159.
Zheng-Gang Li Yan-Hui Dong Ji-Qiang Liu Ling Chen 《International Geology Review》2015,57(5-8):978-997
Seamounts are an integral part of element recycling in global subduction zones. The published trace element and Pb-Sr-Nd isotope data for basaltic lavas from three key segments (Central Lau Spreading Ridge (CLSR), Eastern Lau Spreading Ridge (ELSR), and Valu Fa Ridge (VFR)) of the Lau back-arc basin were compiled to evaluate the contribution of Louisville seamount materials to their magma genesis. Two geochemical transitions, separating three provinces with distinct geochemical characteristics independent of ridge segmentation, were identified based on abrupt geochemical shifts. The origin of the geochemical transitions was determined to be the result of drastic compositional changes of subduction components added into the mantle source, rather than the transition from Indian to Pacific mid-ocean ridge basalt (MORB) mantle, or due to variable mantle fertilities. The most likely explanation for the drastic shifts in subduction input is the superimposition of Louisville materials on ‘normal’ subduction components consisting predominantly of aqueous fluids liberated from the down-going altered oceanic crust and minor pelagic sediment melts. Quantitative estimation reveals that Louisville materials contributed 0–74% and 21–83% of the Th budget, respectively, to CLSR and VFR lavas, but had no definite contribution to the lavas from the ELSR, which lies farthest away from the subducted Louisville seamount chain (LSC). The spatial association of the subducted LSC with the Louisville-affected segments suggests that the Louisville signature is regionally but not locally available in the Tonga subduction zone. Besides, the preferential melting of subducted old Cretaceous LSC crust instead of the old normal Pacific oceanic crust at similar depths implies that elevated temperature across the subduction interface or seamount erosion and rupture were required to trigger melting. A wider implication of this study, thus, is that seamount subduction may promote efficiency of element recycling in subduction zones. 相似文献
160.
A conceptual coupled ocean-atmosphere model was used to study coupled ensemble data assimilation schemes with a focus on the role of ocean-atmosphere interaction in the assimilation. The optimal scheme was the fully coupled data assimilation scheme that employs the coupled covariance matrix and assimilates observations in both the atmosphere and ocean. The assimilation of synoptic atmospheric variability that captures the temporal fluctuation of the weather noise was found to be critical for the estimation of not only the atmospheric, but also oceanic states. The synoptic atmosphere observation was especially important in the mid-latitude system, where oceanic variability is driven by weather noise. The assimilation of synoptic atmospheric variability in the coupled model improved the atmospheric variability in the analysis and the subsequent forecasts, reducing error in the surface forcing and, in turn, in the ocean state. Atmospheric observation was able to further improve the oceanic state estimation directly through the coupled covariance between the atmosphere and ocean states. Relative to the mid-latitude system, the tropical system was influenced more by ocean-atmosphere interaction and, thus, the assimilation of oceanic observation becomes more important for the estimation of the ocean and atmosphere. 相似文献