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71.
Migrating magmatism in the northern US Cordillera: in situ U–Pb geochronology of the Idaho batholith
Richard M. Gaschnig Jeffrey D. Vervoort Reed S. Lewis William C. McClelland 《Contributions to Mineralogy and Petrology》2010,159(6):863-883
New in situ laser ablation-inductively coupled plasma-mass spectrometry and sensitive high-resolution ion microprobe U–Pb
geochronology of zircons from the Idaho batholith and spatially overlapping Challis intrusions reveals a series of discrete
magmatic belts of different ages and compositions. Following the accretion of the Blue Mountains province to North America
along the Salmon River suture zone, two compositionally diverse belts of metaluminous plutons formed both adjacent to the
suture and well inboard of it. These were constructed from ~100 to 85 Ma and were followed by a voluminous pulse of peraluminous
magmatism, forming the bulk of the Atlanta lobe and largest fraction of the batholith between ~80 and 67 Ma. Around 70 Ma,
a later and more spatially restricted suite of metaluminous plutons formed around the Bitterroot lobe of the batholith. This
was followed by another pulse of voluminous peraluminous magmatism in the Bitterroot lobe, lasting from ~66 to 54 Ma. The
changes from low volume metaluminous to high volume peraluminous magmatism may reflect a combination of changes in the angle
and segmentation of the subducting Farallon plate and over thickening of the continental lithosphere. All of these features
were then cut by plutons and dikes associated with the Challis volcanic field, lasting from ~51 to 43 Ma. Inherited components
are pervasive in zircons from most phases of the batholith. While Precambrian components are very common, zircons also often
contain cores or mantles that are 5–20 million years older than their rims. This suggests that the early phases of the batholith
were repeatedly cannibalized by subsequent magmas. This also implies that the older suites may have been originally more aerially
extensive than their currently exposed forms. 相似文献
72.
Stephen Edward Lewis Robert A. Henderson Gerald R. Dickens Graham A. Shields Simon Coxhell 《Mineralium Deposita》2010,45(6):599-620
A significant resource of vanadium and molybdenum exists near Julia Creek, Australia, where the middle Cretaceous organic-rich
Toolebuc Formation lies between 0 and 25 m of the surface. We present and discuss a comprehensive geochemical study of the
Toolebuc Formation and its enclosing stratigraphy near Julia Creek to understand this ore deposit. V and Mo contents in fresh
facies are strongly associated with total organic carbon (TOC) contents, but not with Al or CaCO3; this suggests that V and Mo were originally concentrated in the organic fraction. However, chemical extractions using H2O2 indicate that Mo was originally concentrated in pyrite. The data also suggest that V was mobilised from organic matter during
early diagenesis and became associated with clays as little V was extracted by H2O2 in the fresh samples. TOC contents in the Toolebuc Formation were removed during weathering, residually enriching trace metals
including V and Mo, and as a result, the TOC relationship with V and Mo disintegrates. With weathering, both V and Mo predominantly
became associated with iron oxide/hydroxide phases (and possibly other unidentified phases) as these elements in the weathered
facies were highly soluble in the sodium citrate–sodium dithionite digestion. Large shale-hosted V and Mo deposits such as
Julia Creek offer a potentially viable alternative to the currently mined magnetite-hosted deposits. A thorough understanding
of the formation and host mineral phases for V and Mo of these shale deposits, however, is critical to ensure that these valuable
metals can be feasibly extracted. 相似文献
73.
Aseismic crustal-strain signals prior to the 2003 Mw 6.8 Chengkung, 2006 Mw 6.1 Taitung, and 2008 Mw 5.0 Antung earthquakes with epicenters located 20, 55 and 11 km, respectively, from the Antung radon-monitoring station have
been calculated using the radon anomalies recorded. Specifically, radon decreased from background levels of 791 ± 46, 762 ± 57,
and 735 ± 48 pCi/L to minima of 326 ± 9, 371 ± 9, and 480 ± 43 pCi/L prior to the 2003, 2006, and 2008 earthquakes, respectively.
The estimated aseismic crustal-strain maxima at the Antung hot spring during the rock dilation stage were 3.6, 2.7, and 1.3 ppm,
respectively. The v-shaped radon pattern recognized in all three anomalies is valuable for detecting the aseismic strain precursory
to disastrous earthquakes in the Antung hot spring which is situated in a brittle fractured aquifer of limited recharge surrounded
by ductile mudstone. 相似文献
74.
None of the prior studies implementing blended learning (BL) for GIS education has explored pedagogical theories to support BL design, and none coupled blended GIS learning practice with theories. Based on the theoretical framework of complex adaptive blended learning system (CABLS), this article presents a holistic and systematic view of BL for higher GIS education (termed as CABLS-GIS), where its key components are tightly integrated as an integral whole. The framework was implemented for an introductory-level GIS course to empirically evaluate the effectiveness of a BL design from students' perspectives. Most students involved in the implementation agreed that the BL enhanced their learning outcomes. They were mostly positive about the BL and motivated to use the BL materials. Incorporating more BL materials, especially practical ones, and active learning activities were suggested by them. A few negative comments about the BL suggested a thorough consideration of individual learners' characteristics. 相似文献
75.
Manuela Magliocchetti Steve J. Maddox Ed Hawkins John A. Peacock Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto de Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole A. Jackson Bryn Jones Ofer Lahav Ian Lewis Stuart Lumsden Peder Norberg Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,350(4):1485-1494
76.
Stephen R. Lewis Peter L. Read Barney J. Conrath John C. Pearl Michael D. Smith 《Icarus》2007,192(2):327-347
The Thermal Emission Spectrometer aboard the Mars Global Surveyor spacecraft has produced an extensive atmospheric data set, beginning during aerobraking and continuing throughout the extended scientific mapping phase. Temperature profiles for the atmosphere below about 40 km, surface temperatures and total dust and water ice opacities, can be retrieved from infrared spectra in nadir viewing mode. This paper describes assimilation of nadir retrievals from the spacecraft aerobraking period, LS=190°–260°, northern hemisphere autumn to winter, into a Mars general circulation model. The assimilation scheme is able to combine information from temperature and dust optical depth retrievals, making use of a model forecast containing information from the assimilation of earlier observations, to obtain a global, time-dependent analysis. Given sufficient temperature retrievals, the assimilation procedure indicates errors in the a priori dust distribution assumptions even when lacking dust observations; in this case there are relatively cold regions above the poles compared to a model which assumes a horizontally-uniform dust distribution. One major reason for using assimilation techniques is in order to investigate the transient wave behavior on Mars. Whilst the data from the 2-h spacecraft mapping orbit phase is much more suitable for assimilation, even the longer (45–24 h) period aerobraking orbit data contain useful information about the three-dimensional synoptic-scale martian circulation which the assimilation procedure can reconstruct in a consistent way. Assimilations from the period of the Noachis regional dust storm demonstrate that the combined assimilation of temperature and dust retrievals has a beneficial impact on the atmospheric analysis. 相似文献
77.
Over the last century, afforestation in Ireland has increased from 1% of the land area to 10%, with most plantations on upland drained blanket peatlands. This land use change is considered to have altered the hydrological response and water balance of upland catchments with implications for water resources. Because of the difficulty of observing these long‐term changes in the field, the aim of this study was to utilize a hydrological model to simulate the rainfall runoff processes of an existing pristine blanket peatland and then to simulate the hydrology of the peatland if it were drained and afforested. The hydrological rainfall runoff model (GEOtop) was calibrated and validated for an existing small (76 ha) pristine blanket peatland in the southwest of Ireland for the 2‐year period, 2007–2008. The current hydrological response of the pristine blanket peatland catchment with regard to streamflow and water table (WT) levels was captured well in the simulations. Two land use change scenarios of afforestation were also examined, (A) a young 10‐year‐old and (B) a semi‐mature 15‐year‐old Sitka Spruce forest. Scenario A produced similar streamflow dynamics to the pristine peatland, whereas total annual streamflow from Scenario B was 20% lower. For Scenarios A and B, on an annual average basis, the WT was drawn down by 16 and 20 cm below that observed in the pristine peatland, respectively. The maximum WT draw down in Scenario B was 61 cm and occurred in the summer months, resulting in a significant decrease in summer streamflow. Occasionally in the winter (following rainfall), the WT for Scenario B was just 2 cm lower than the pristine peatland, which when coupled with the drainage networks associated with afforestation led to higher peak streamflows. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
78.
Geraint F. Lewis † Rodrigo A. Ibata 《Monthly notices of the Royal Astronomical Society》2002,337(1):26-33
There is growing evidence that the majority of the energy density of the Universe is not baryonic or dark matter, but rather it resides in an exotic component with negative pressure. The nature of this 'quintessence' influences our view of the Universe, modifying angular diameter and luminosity distances. Here, we examine the influence of a quintessence component upon gravitational lens time-delays. As well as a static quintessence component, an evolving equation of state is also considered. It is found that the equation of state of the quintessence component and its evolution influence the value of the Hubble constant derived from gravitational lenses. However, the differences between evolving and non-evolving cosmologies are relatively small. We undertake a suite of Monte Carlo simulations to examine the potential constraints that can be placed on the universal equation of state from the monitoring of gravitational lens systems, and demonstrate that at least an order of magnitude more lenses than currently known will have to be discovered and analysed to accurately probe any quintessence component. 相似文献
79.
D. A. Robinson A. Binley N. Crook F. D. Day‐Lewis T. P. A. Ferré V. J. S. Grauch R. Knight M. Knoll V. Lakshmi R. Miller J. Nyquist L. Pellerin K. Singha L. Slater 《水文研究》2008,22(18):3604-3635
We want to develop a dialogue between geophysicists and hydrologists interested in synergistically advancing process based watershed research. We identify recent advances in geophysical instrumentation, and provide a vision for the use of electrical and magnetic geophysical instrumentation in watershed scale hydrology. The focus of the paper is to identify instrumentation that could significantly advance this vision for geophysics and hydrology during the next 3–5 years. We acknowledge that this is one of a number of possible ways forward and seek only to offer a relatively narrow and achievable vision. The vision focuses on the measurement of geological structure and identification of flow paths using electrical and magnetic methods. The paper identifies instruments, provides examples of their use, and describes how synergy between measurement and modelling could be achieved. Of specific interest are the airborne systems that can cover large areas and are appropriate for watershed studies. Although airborne geophysics has been around for some time, only in the last few years have systems designed exclusively for hydrological applications begun to emerge. These systems, such as airborne electromagnetic (EM) and transient electromagnetic (TEM), could revolutionize hydrogeological interpretations. Our vision centers on developing nested and cross scale electrical and magnetic measurements that can be used to construct a three‐dimensional (3D) electrical or magnetic model of the subsurface in watersheds. The methodological framework assumes a ‘top down’ approach using airborne methods to identify the large scale, dominant architecture of the subsurface. We recognize that the integration of geophysical measurement methods, and data, into watershed process characterization and modelling can only be achieved through dialogue. Especially, through the development of partnerships between geophysicists and hydrologists, partnerships that explore how the application of geophysics can answer critical hydrological science questions, and conversely provide an understanding of the limitations of geophysical measurements and interpretation. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
80.