全文获取类型
收费全文 | 1345篇 |
免费 | 30篇 |
国内免费 | 15篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 136篇 |
地球物理 | 370篇 |
地质学 | 546篇 |
海洋学 | 111篇 |
天文学 | 150篇 |
综合类 | 3篇 |
自然地理 | 58篇 |
出版年
2021年 | 12篇 |
2018年 | 25篇 |
2017年 | 14篇 |
2016年 | 25篇 |
2015年 | 18篇 |
2014年 | 34篇 |
2013年 | 40篇 |
2012年 | 33篇 |
2011年 | 52篇 |
2010年 | 37篇 |
2009年 | 49篇 |
2008年 | 54篇 |
2007年 | 36篇 |
2006年 | 46篇 |
2005年 | 38篇 |
2004年 | 34篇 |
2003年 | 31篇 |
2002年 | 47篇 |
2001年 | 19篇 |
2000年 | 20篇 |
1999年 | 17篇 |
1998年 | 27篇 |
1997年 | 19篇 |
1996年 | 19篇 |
1995年 | 23篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1991年 | 11篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 22篇 |
1984年 | 21篇 |
1983年 | 24篇 |
1982年 | 18篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 21篇 |
1978年 | 18篇 |
1977年 | 17篇 |
1976年 | 15篇 |
1975年 | 11篇 |
1974年 | 12篇 |
1973年 | 17篇 |
1970年 | 11篇 |
1959年 | 15篇 |
1956年 | 11篇 |
1954年 | 12篇 |
1948年 | 13篇 |
排序方式: 共有1390条查询结果,搜索用时 140 毫秒
151.
Pim de Klerk Andreas Haberl Andreas Kaffke Matthias Krebs Izolda Matchutadze Merten Minke Jenny Schulz Hans Joosten 《Quaternary Science Reviews》2009,28(9-10):890-910
The Kolkheti lowlands of western Georgia have a unique vegetation and a rich cultural history. Palynological and macrofossil analysis accompanied by AMS 14C-dates of the deposits of the Ispani 2 mire near Kobuleti allow the reconstruction of regional vegetation, environmental history and local peatland development within the context of Black Sea level and cultural changes. Comparison of two adjacent peatland cores confirms spatial differences in wetland development. Prior to 5400 cal yr BP, the Ispani basin was a floodplain of an active river system where overbank deposits with fluvially transported Castanea pollen were deposited. Subsequently, a lake or lagoon developed in which reeds expanded. These were succeeded by herb-rich open alder carrs. After 1900 cal yr BP, Carpinus and Fagus expanded on the dry grounds, where formerly Quercus was more abundant. Also Castanea declined. Local reedbeds, that burned regularly, succeeded the alder carr. After 1000 cal yr BP, a percolation bog developed resulting in the formation of 4 m of loose, porous, and largely undecomposed Sphagnum austinii peat with Molinia roots. The upper 50 cm of the analysed section show extensive human impact on the landscape during the 20th century. 相似文献
152.
Yasuhiro Hashimoto J. Patrick Henry Hans Böhringer 《Monthly notices of the Royal Astronomical Society》2007,380(2):835-838
We investigated the influence of environment on cluster morphology by examining the alignment of the cluster position angle with respect to the nearest neighbour cluster. The cluster position angle and ellipticity were measured using high spatial resolution X-ray data taken from the Chandra archive, while the nearest neighbour sample was extracted from the Abell cluster catalogue. We found high confidence for an alignment when neighbour distance (Dn) was less than 70 h −1 Mpc, while we found no significant variations of the confidence level at various values of Dn less than 70 h −1 Mpc. 相似文献
153.
Holger L. Fröhlich Lutz Breuer Hans‐Georg Frede Johan A. Huisman Kellie B. Vaché 《水文研究》2008,22(12):2028-2043
The link between spatiotemporal patterns of stream water chemistry and catchment characteristics for the mesoscale Dill catchment (692 km2) in Germany is explored to assess the catchment scale controls on water quality and to characterize water sources. In order to record the spatiotemporal pattern, ‘snapshot sampling’ was applied during low, mean and high flow, including 73 nested sites throughout the catchment. Water samples were analysed for the elements Li, B, Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Rb, Sr, Mo, Ba, Pb and U using inductively‐coupled‐plasma mass spectrometry, and for electric conductivity and pH. Principle component analysis and hierarchical cluster analysis were used to find typical element associations and to group water samples according to their hydrochemical fingerprints. This revealed regional hydrochemical patterns of water quality which were subsequently related to catchment attributes to draw conclusions about the controls on stream chemistry. It was found that various lithologic signals and anthropogenic point source inputs controlled the base flow hydrochemistry. During increased flows, stream waters were diluted causing additional hydrochemical variability in response to heterogeneous precipitation inputs and differences in aquifer storage capacities. The hydrochemical patterns further displayed in‐stream mixing of waters. This implied, that stream waters could be apportioned to the identified water sources throughout the catchment. The basin‐wide hydrochemical variability has the potential to outrange the tracer signatures typically inferred in studies at the hillslope scale and is able to strongly influence the complexity of the catchment output. Both have to be considered for further catchment scale tracer and modelling work. Despite the likelihood of non‐conservative behaviour, the minor and trace elements enhanced the rather qualitative discrimination of the various groundwater types, as the major cations were strongly masked by point source inputs. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
154.
Microdiamond and graphite occur in quartzofeldspathic rocks (saidenbachites) of the central Erzgebirge in Saxony. Zircon from such rocks contains not only relatively high but also variable amounts of early formed graphite and later crystallized diamond, however no carbonate. Six purified zircon concentrates were analysed by mass spectrometry for δ13C(PDB) values which were between −24 and −33‰. The carbon inclusions resulted in C contents of the concentrates as high as 0.5 wt%. It is hypothesized that the observed δ13C signature results from organic material in the sedimentary protoliths of the saidenbachites probably deposited not earlier than Mid‐Devonian. This material was transformed to graphite during early metamorphism and subsequently to diamond after an anatectic event at great depths (>150 km). During these processes, the δ13C signature of the carbon did not (significantly) change. 相似文献
155.
156.
157.
A compilation of phytoplankton species abundance data from the spring bloom along the northern Norwegian coast and in the
Barents Sea shows that the quantitatively most important species are the prymnesiophyte Phaeocystis pouchetii and the common cold water to temperate diatoms Chaetoceros socialis, Skeletonema costatum sensu lato, Fragilariopsis oceanica, Thalassiosira spp., Chaetoceros furcellatus, Chaetoceros compressus, Chaetoceros debilis and Bacterosira bathyomphala. The relative abundance of diatoms and Phaeocystis varied highly and apparently stochastically between years. P. pouchetii occurred during all stages of the spring bloom and sometimes completely dominated the phytoplankton community. Along the
Norwegian coast, the importance of P. pouchetii increased northwards. The species composition in coastal fjords at 70° N is surprisingly similar to that of shelf waters
in the Barents Sea (up to 80° N). An exception is S. costatum sensu lato which was seldom observed in Arctic waters. Small flagellates (<10 μm) other than dinoflagellates and P. pouchetii are also important among the Barents Sea spring phytoplankton. Associations of species seem rigid over time and are dominated
by C. socialis and P. pouchetii in northern waters. Biogeographical categories of spring bloom species in relation to environmental conditions are discussed. 相似文献
158.
Following an earlier climatological study of North Pacific Polar Lows by employing dynamical downscaling of NCEP1 reanalysis in the regional climate model COSMO-CLM, the characteristics of Polar Low genesis over the North Pacific under different global warming scenarios are investigated. Simulations based on three scenarios from the Special Report on Emissions Scenarios were conducted using a global climate model (ECHAM5) and used to examine systematic changes in the occurrence of Polar Lows over the twenty first century. The results show that with more greenhouse gas emissions, global air temperature would rise, and the frequency of Polar Lows would decrease. With sea ice melting, the distribution of Polar Low genesis shows a northward shift. In the scenarios with stronger warming there is a larger reduction in the number of Polar Lows. 相似文献
159.
Barbados is a small Caribbean island located on the crest of an accretionary prism about 125 km east of the Lesser Antilles volcanic island arc. The oldest strata, Eocene sandstones and shales, are overlain by Oligocene–Miocene chalks and marls, in turn overlain by Pleistocene reef and lagoonal limestones that cover about 85 % of the island. The Eocene sediments, which crop out in the Scotland District of Barbados, are prone to soil creep and landslides covering tens to hundreds of hectares. The largest historic landslide, the “Boscobel Landslip,” occurred on 01 October 1901. We used nineteenth-century and more modern topographic and geologic maps, air photographs, and various archival and petrophysical data, to supplement reconnaissance of the landslide in the field. We identified about ten million cubic meters of the displaced material of the landslide, as well as the meteorological and geological conditions that contributed to the Boscobel Landslip. Similar landslides would pose a presently unquantified hazard to inhabitation and future development in the Scotland District. 相似文献
160.
Large‐scale simulations of flow in deformable porous media require efficient iterative methods for solving the involved systems of linear algebraic equations. Construction of efficient iterative methods is particularly challenging in problems with large jumps in material properties, which is often the case in geological applications, such as basin evolution at regional scales. The success of iterative methods for this type of problems depends strongly on finding effective preconditioners. This paper investigates how the block‐structured matrix system arising from single‐phase flow in elastic porous media should be preconditioned, in particular for highly discontinuous permeability and significant jumps in elastic properties. The most promising preconditioner combines algebraic multigrid with a Schur complement‐based exact block decomposition. The paper compares numerous block preconditioners with the aim of providing guidelines on how to formulate efficient preconditioners. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献