全文获取类型
收费全文 | 961篇 |
免费 | 23篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 21篇 |
大气科学 | 45篇 |
地球物理 | 262篇 |
地质学 | 290篇 |
海洋学 | 60篇 |
天文学 | 250篇 |
综合类 | 2篇 |
自然地理 | 58篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 13篇 |
2020年 | 13篇 |
2019年 | 20篇 |
2018年 | 30篇 |
2017年 | 27篇 |
2016年 | 31篇 |
2015年 | 38篇 |
2014年 | 32篇 |
2013年 | 34篇 |
2012年 | 51篇 |
2011年 | 58篇 |
2010年 | 45篇 |
2009年 | 69篇 |
2008年 | 56篇 |
2007年 | 59篇 |
2006年 | 44篇 |
2005年 | 47篇 |
2004年 | 43篇 |
2003年 | 35篇 |
2002年 | 38篇 |
2001年 | 30篇 |
2000年 | 24篇 |
1999年 | 17篇 |
1998年 | 18篇 |
1997年 | 12篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 13篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1964年 | 1篇 |
排序方式: 共有988条查询结果,搜索用时 15 毫秒
51.
A structural and geophysical approach to the study of fractured aquifers in the Scansano-Magliano in Toscana Ridge, southern Tuscany, Italy 总被引:1,自引:0,他引:1
Roberto Francese Francesco Mazzarini Andrea Bistacchi Gianfranco Morelli Giorgio Pasquarè Nicola Praticelli Henry Robain Nigel Wardell Annalisa Zaja 《Hydrogeology Journal》2009,17(5):1233-1246
Fresh water availability has recently become a serious concern in the Italian Apennines, as various activities rely on a predictable supply. Along the ridge between Scansano and Magliano in Toscana, in southern Tuscany, the situation is further complicated by contamination of the nearby alluvial aquifers. Aquifers locally consist of thin fractured reservoirs, generally within low-permeability formations, and it can be difficult to plan the exploitation of resources based on conventional techniques. An integrated study based on geological data investigated the link between tectonics and groundwater circulation, to better define the hydrological model. After the regional identification of fault and fracture patterns, a major structure was investigated in detail to accurately map its spatial position and to understand the geometry and properties of the associated aquifer and assess its exploitation potential. The subsurface around the fault zone was clearly imaged using ground probing radar, two-dimensional and three-dimensional resistivity tomography, and three-dimensional shallow seismic surveys. The vertical and horizontal contacts between the different geological units of the Ligurian and Tuscan series were resolved with a high degree of spatial accuracy. Three-dimensional high-resolution geophysical imaging proved to be a very effective means of characterising small-scale fractured reservoirs. 相似文献
52.
The paper presents a strainhardening constitutive model for unsaturated soil behaviour based on energy conjugated stress variables in the framework of superposed continua. The proposed constitutive law deals with hydro‐mechanical coupling phenomena. The main purpose is to develop within a consistent framework a model that can deal with possible mechanical instabilities occurring in partially saturated materials. The loss of capillary effects during wetting processes can, in fact, play a central role in unstable processes. Therefore, it will be shown that the bonding effects due to surface tensions can be described in a mathematical framework similar to that employed for bonded geomaterials to model weathering or diagenesis effects, either mechanically or chemically induced. The results of several simulations of common laboratory tests on partially saturated soil specimens are shown. The calculated behaviour appears to be in good qualitative agreement with that observed in the laboratory. In particular it is shown that volumetric collapse phenomena due to hydraulic debonding effects can be successfully described by the model. Finally, it will be highlighted the ability of the model to naturally capture the transition to a fully saturated condition and to deal with possible mechanical instabilities in the unsaturated regime. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
53.
Mark Cropper Silvia Zane Roberto Turolla Luca Zampieri Matteo Chieregato Jeremy Drake Aldo Treves 《Astrophysics and Space Science》2007,308(1-4):161-166
We report XMM-Newton observations of the isolated neutron star RBS1774 and confirm its membership as an XDINS. The X-ray spectrum is best fit
with an absorbed blackbody with temperature kT=101 eV and absorption edge at 0.7 keV. No power law component is required. An absorption feature in the RGS data at 0.4 keV
is not evident in the EPIC data, but it is not possible to resolve this inconsistency. The star is not seen in the UV OM data
to m
AB
∼21. There is a sinusoidal variation in the X-ray flux at a period of 9.437 s with an amplitude of 4%. The age as determined
from cooling and magnetic field decay arguments is 105–106 yr for a neutron star mass of 1.35–1.5 M⊙.
相似文献
54.
55.
56.
57.
Roberto Bugiolacchi Urs Mall Susan McKenna-Lawlor Kjell Brønstad Finn Søraas Rolf B. Pedersen 《Icarus》2011,213(1):43-63
Newly acquired, sequentially spaced, high-resolution near-infrared spectra across the central section of crater Copernicus’ interior have been analyzed using a range of complementary techniques and indexes.We have developed a new interpretative method based on a multiple stage normalization process that appears to both confirm and expand on previous mineralogical estimations and mapping. In broad terms, the interpreted distribution of the principle mafic species suggests an overall composition of surface materials dominated by calcium-poor pyroxenes and minor olivine but with notable exceptions: the southern rim displays strong ca-rich pyroxene absorption features and five other locations, the uppermost northern crater wall, opposite rim sections facing the crater floor, and the central peak Pk1 and at the foot of Pk3, show instead strong olivine signatures.We also propose impact glass an alternative interpretation to the source of the weak but widespread olivine-like spectral signature found in low-reflectance samples, since it probably represents a major regolith constituent and component in large craters such as Copernicus.The high quality and performance of the SIR-2 data allows for the detection of diagnostic key mineral species even when investigating spectral samples with very subdued absorption features, confirming the intrinsic high-quality value of the returned data. 相似文献
58.
59.
Water quality and relationship between superficial and ground water in Rome (Aniene River basin,central Italy) 总被引:1,自引:1,他引:0
Francesco La Vigna Simone Ciadamidaro Roberto Mazza Laura Mancini 《Environmental Earth Sciences》2010,60(6):1267-1279
Chemical, physical, and biological features of streams and ground water of the North-Eastern area of Rome are jointly analyzed
in order to assess the status of water resources. Ground water was investigated with classical survey methods (pH, temperature,
and electric conductivity). Microbiological pollution, faunal composition, and stream surrounding area conditions of surface
waters were studied, in order to quantify the residual value of these ecosystems from both a human and an environmental point
of view. Results show a general impairment of the system and the comparison between superficial waters and shallow ground
waters makes it possible to detect the presence of a connection between the two levels. This relationship occurs as an exchange
from superficial waters (streams and rivers) to the shallow aquifers. Where superficial waters are contaminated, as in the
Tor Sapienza stream, pollutants move to the shallow aquifers too, due to the decreased pressure of the over-exploited aquifer.
Moreover, uncontrolled drilling activity, diffused in urban areas, makes it possible the connection between shallow and deep
ground water. Notwithstanding this, the mixing between superficial and deep ground water system in Rome is not very widespread
and, apparently, limited to restricted areas. 相似文献
60.