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81.
82.
Yun Yuxing Liu Changhai Luo Yali Liang Xudong Huang Ling Chen Fei Rasmmusen Roy 《Climate Dynamics》2020,54(3):1469-1489
Climate Dynamics - Convection-permitting regional climate models have been shown to improve precipitation simulation in many aspects, such as the diurnal cycle, precipitation frequency, intensity... 相似文献
83.
In light of recent reductions in sulphur (S) and nitrogen (N) emissions mandated by Title IV of the Clean Air Act Amendments of 1990, temporal trends and trend coherence in precipitation (1984–2001 and 1992–2001) and surface water chemistry (1992–2001) were determined in two of the most acid‐sensitive regions of North America, i.e. the Catskill and Adirondack Mountains of New York. Precipitation chemistry data from six sites located near these regions showed decreasing sulphate (SO42?), nitrate (NO3?), and base cation (CB) concentrations and increasing pH during 1984–2001, but few significant trends during 1992–2001. Data from five Catskill streams and 12 Adirondack lakes showed decreasing trends in SO42? concentrations at all sites, and decreasing trends in NO3?, CB, and H+ concentrations and increasing trends in dissolved organic carbon at most sites. In contrast, acid‐neutralizing capacity (ANC) increased significantly at only about half the Adirondack lakes and in one of the Catskill streams. Flow correction prior to trend analysis did not change any trend directions and had little effect on SO42? trends, but it caused several significant non‐flow‐corrected trends in NO3? and ANC to become non‐significant, suggesting that trend results for flow‐sensitive constituents are affected by flow‐related climate variation. SO42? concentrations showed high temporal coherence in precipitation, surface waters, and in precipitation–surface water comparisons, reflecting a strong link between S emissions, precipitation SO42? concentrations, and the processes that affect S cycling within these regions. NO3? and H+ concentrations and ANC generally showed weak coherence, especially in surface waters and in precipitation–surface water comparisons, indicating that variation in local‐scale processes driven by factors such as climate are affecting trends in acid–base chemistry in these two regions. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
84.
It is shown that contortion and gravity are not interacting in the lowest possible order. The most convenient pairs of materials in the new Eötvös' experiments are also proposed. 相似文献
85.
86.
Jean L. Roy 《Precambrian Research》1983,19(4):319-348
More than half of the approximately 650 paleopoles reported from all Precambrian cratons have been obtained from North America. The observations have spurred a proliferation of apparent polar wander paths to support different hypotheses for the tectonic evolution of the continent. Many of the reasons for this development can be traced to the inadequacy of the data base with its average of only 1.6 poles 10 Ma?1 (as compared to 7 poles 10?1 Ma for the last 300 Ma). Even when it is assumed that a ·primary’ pole has been derived from each rock unit sampled, the total number of ·primary’ poles (excluding the 900–1200 Ma interval) yields an average of only 0.4 pole 10 Ma?1. An inspection of the data base shows a non-systematic sampling of a non-continuous (fragmented) paleomagnetic record with gaps as large as tens and even hundreds of Ma. More importantly, a search through the literature reveals that very few poles have an age known to better than 50 Ma and for many poles the age bracket could be as large as a few hundreds of Ma. This is partly owing to the fact that radiometric and paleomagnetic sites rarely originate from the same localities. It is shown that this limited data base with all its deficiencies and uncertainties cannot be used to support certain hypotheses, or for the drawing of a meaningful apparent polar path for the whole of the Precambrian. It appears that, because of the enormous time scale, Precambrian paleomagnetism should rather be directed towards the construction of segments of polar paths such as those in the 900–1200 Ma interval. Comparison of well dated contemporaneous segments from different parts (or structural provinces) could be used most effectively to delineate relative movements, if any, and reconstruct the mosaic of the past continent for certain time intervals. One of the recent developments of Precambrian paleomagnetism has been to show that the apparent pole did not remain constrained to the equatorial region, but made several excursions into high latitudes. 相似文献
87.
Spatially-flat cosmological models with interacting perfect fluid and zero-mass scalar field have been obtained under different equations of state and in presence of the scalar charge density associated with the Klein-Gordon equation assuming a special law of variation for the Hubble's parameter. 相似文献
88.
89.
Economic and social development indicators suggest that the small West African state of Sierra Leone is among the poorest
countries in the world. Sierra Leone’s economy and quality of life deteriorated rapidly during a decade of political instability
and civil war in the 1990s, when many people fled their homes and abandoned their livelihoods due to the rebel insurgency.
This paper examines the post-war reconstruction scenario in Sierra Leone and presents recent evidence from two rural communities
in the Eastern Province that were badly affected by the conflict. The paper considers the links between the farming and diamond
mining sectors, which, despite severe dislocation during the conflict period, have proved to be remarkably resilient. It is
argued that seasonal labour mobility associated with this dual economy has not only continued to be a key ingredient in sustaining
livelihood portfolios, but is actually an essential pre-condition for the creation of an enabling environment for sustainable
post-conflict return.
相似文献
Tony BinnsEmail: |
90.
This study aims to identify patterns in spatial distribution of Manta birostris along American East Coast by analyzing presence data using a suite of geostatistical techniques. Analysis of data from 1979 to 2008 revealed that the spatial patterns exhibited by the M. birostris include a strong clustering zone off the North Carolina from (however, not all years are represented in that range), Virginia and Maryland coast. Their presence is high near the coastal shelf edge and along the edge of the Gulf Stream. The mix of warm water and high chlorophyll concentration throughout the year in the region seem to create an ideal environment for this clustering pattern. However, in seasons with warmer water temperature, manta rays spread further north and inshore, possibly to avoid competition for prey. The results of geographic weighted regression indicate the role of sea surface temperatures on Manta presence or absence off the main current of the Gulf Stream near North Carolina and Virginia. Knowledge of the spatial distribution of M. birostris can assist in further protecting the species especially from dangers of by-catch and habitat degradation. 相似文献