全文获取类型
收费全文 | 289篇 |
免费 | 12篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 34篇 |
地球物理 | 47篇 |
地质学 | 84篇 |
海洋学 | 23篇 |
天文学 | 73篇 |
自然地理 | 38篇 |
出版年
2022年 | 1篇 |
2021年 | 11篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 8篇 |
2014年 | 7篇 |
2013年 | 22篇 |
2012年 | 26篇 |
2011年 | 19篇 |
2010年 | 13篇 |
2009年 | 27篇 |
2008年 | 15篇 |
2007年 | 13篇 |
2006年 | 12篇 |
2005年 | 13篇 |
2004年 | 14篇 |
2003年 | 11篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有302条查询结果,搜索用时 15 毫秒
251.
252.
Rachel Warren Jeff Price Andreas Fischlin Santiago de la Nava Santos Guy Midgley 《Climatic change》2011,106(2):141-177
In a meta-analysis we integrate peer-reviewed studies that provide quantified estimates of future projected ecosystem changes
related to quantified projected local or global climate changes. In an advance on previous analyses, we reference all studies
to a common pre-industrial base-line for temperature, employing up-scaling techniques where necessary, detailing how impacts
have been projected on every continent, in the oceans, and for the globe, for a wide range of ecosystem types and taxa. Dramatic
and substantive projected increases of climate change impacts upon ecosystems are revealed with increasing annual global mean
temperature rise above the pre-industrial mean (ΔTg). Substantial negative impacts are commonly projected as ΔTg reaches and exceeds 2°C, especially in biodiversity hotspots. Compliance with the ultimate objective of the United Nations
Framework Convention on Climate Change (Article 2) requires that greenhouse gas concentrations be stabilized within a time
frame “sufficient to allow ecosystems to adapt naturally to climate change”. Unless ΔTg is constrained to below 2°C at most, results here imply that it will be difficult to achieve compliance. This underscores
the need to limit greenhouse gas emissions by accelerating mitigation efforts and by protecting existing ecosystems from greenhouse-gas
producing land use change processes such as deforestation. 相似文献
253.
Rachel Stubbington Paul J. Wood Ian Reid 《Aquatic Sciences - Research Across Boundaries》2011,73(4):499-511
A key ecological role hypothesized for the hyporheic zone is as a refugium that promotes survival of benthic invertebrates
during adverse conditions in the surface stream. Many studies have investigated use of the hyporheic refugium during hydrological
extremes (spates and streambed drying), and recent research has linked an increase in the abundance of benthic invertebrates
within hyporheic sediments to increasing biotic interactions during flow recession in a temporary stream. This study examined
spatial variability in the refugial capacity of the hyporheic zone in two groundwater-dominated streams in which flow permanence
varied over small areas. Two non-insect taxa, Gammarus pulex and Polycelis spp. were common to both streams and were investigated in detail. Hydrological conditions in both streams comprised a four-month
period of flow recession and low flows, accompanied by reductions in water depth and wetted width. Consequent declines in
submerged benthic habitat availability were associated with increases in population densities of mobile benthic taxa, in particular
G. pulex. The reduction in the spatial extent of the hyporheic zone was minimal, and this habitat was therefore a potential refugium
from increasing biotic interactions in the benthic sediments. Concurrent increases in the hyporheic abundance and hyporheic
proportion of a taxon’s total (benthic + hyporheic) population were considered as evidence of active refugium use. Such evidence
was species-specific and site-specific, with refugium use being observed only for G. pulex and at sites dominated by downwelling water. A conceptual model of spatial variability in the refugial capacity of the hyporheic
zone during habitat contraction is presented, which highlights the potential importance of the direction of hydrologic exchange. 相似文献
254.
Contourites within a deep-water sequence stratigraphic framework 总被引:2,自引:2,他引:0
Rachel Brackenridge Dorrik A. V. Stow F. Javier Hern��ndez-Molina 《Geo-Marine Letters》2011,31(5-6):343-360
Sequence stratigraphy has proven to be an extremely useful predictive tool in the search for hydrocarbons along the continental margins. However, of the several models in use, none includes the effects of alongslope processes in deep-water. This paper, therefore, is a first attempt to place contourite depositional systems (CDSs) firmly within a sequence stratigraphic framework, based on detailed examination of over 20 CDSs worldwide. It also presents a new view of how sea level variation influences bottom current generation and intensity. Two key controls on contourite drift formation are identified: sediment influx and bottom current velocity. Sea level directly influences the sediment influx to a basin and, therefore, the contourite response fits nicely into the downslope sequence stratigraphy model. Bottom current velocity variations in response to sea level are more complex, and two key controls are identified: (1) oceanic gateways can effectively constrict and accelerate water masses and are therefore closely associated with CDS evolution; fluctuating sea level will affect the water exchange through a gateway; (2) changing rates of bottom-water generation: some water masses appear more vigorous during periods of lowstand, whereas others appear more sluggish. In order to accommodate this variation, two new sequence stratigraphy models are herein presented, comprising both downslope and alongslope processes. The first model reveals a CDS where bottom current activity is markedly more vigorous during times of sea level highstand, whereas the second model indicates margin evolution where bottom-water currents are most vigorous during times of sea level lowstand. It is recognised that there are additional controlling factors linked to sea level variation which can significantly modify the distribution and development of contourite elements. 相似文献
255.
At Dromedary Massif, Southern Victoria Land, Antarctica, a suite of coarse-grained granite dykes cross-cuts a gabbro pluton which has been partially metamorphosed at amphibolite facies. During regional deformation, strain has been inhomogeneously distributed through the gabbro pluton and has been concentrated in granite dykes. In zones of relatively high strain, the granite dykes have developed a mylonitic fabric. A high strain gradient between granitic mylonite and metagabbroic host rock has induced isochemical mylonitization of the margin of the host. This grain size reduction allowed chemical diffusion between granitic and metagabbroic mylonites, resulting in a marginal zone of biotite-rich mylonite with intermediate composition. Biotite-rich mylonite decoupled from metagabbroic mylonite and flowed with granitic mylonite. Continued folding and transposition of granitic mylonite and biotite-rich mylonite has produced compositionally banded mylonite zones through thorough and irreversible mixing of the two lithologies. 相似文献
256.
257.
258.
Water forms an essential resource for life on earth because all living things on earth depend on water for life activities. However, with the increase in the human population, which is coupled with intense urbanization and agricultural activities, global water pollution has increased over the past decades. In China, agricultural activities that occure mainly in the planting fields have been listed as the main source of surface water and groundwater pollution. This review focuses on the major factors that influence pollution from planting fields in China mainly as a result of farming activities such as flood irrigation, excessive application of fertilizers and pesticides, and poor management practices. At present, good results are achieved by adopting soil fertilization test formula, biodegradable pesticides, proper irrigation, and agroforestry interventions. In the future, pollution from planting fields as a non‐point source of water pollution can be improved and resolved by perfect nutrient management, best management practices, organic amendments, restoring water environment, and intelligent assessment management. 相似文献
259.
Ariyeh H. Maller Avishai Dekel Rachel Somerville 《Monthly notices of the Royal Astronomical Society》2002,329(2):423-430
We model the acquisition of spin by dark-matter haloes in semi-analytic merger trees. We explore two different algorithms: one in which halo spin is acquired from the orbital angular momentum of merging satellites, and another in which halo spin is gained via tidal torquing on shells of material while still in the linear regime. We find that both scenarios produce the characteristic spin distribution of haloes found in N -body simulations, namely, a log-normal distribution with mean ≈ 0.04 and standard deviation ≈ 0.5 in the log. A perfect match requires fine-tuning of two free parameters. Both algorithms also reproduce the general insensitivity of the spin distribution to halo mass, redshift and cosmology seen in N -body simulations. The spin distribution can be made strictly constant by physically motivated scalings of the free parameters. In addition, both schemes predict that haloes that have had recent major mergers have systematically larger spin values. These algorithms can be implemented within semi-analytic models of galaxy formation based on merger trees. They yield detailed predictions of galaxy properties that strongly depend on angular momentum (such as size and surface brightness) as a function of merger history and environment. 相似文献
260.