全文获取类型
收费全文 | 1025篇 |
免费 | 42篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 26篇 |
大气科学 | 109篇 |
地球物理 | 295篇 |
地质学 | 246篇 |
海洋学 | 109篇 |
天文学 | 177篇 |
自然地理 | 111篇 |
出版年
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 12篇 |
2018年 | 14篇 |
2017年 | 16篇 |
2016年 | 26篇 |
2015年 | 18篇 |
2014年 | 24篇 |
2013年 | 54篇 |
2012年 | 26篇 |
2011年 | 47篇 |
2010年 | 43篇 |
2009年 | 53篇 |
2008年 | 37篇 |
2007年 | 39篇 |
2006年 | 52篇 |
2005年 | 47篇 |
2004年 | 49篇 |
2003年 | 41篇 |
2002年 | 33篇 |
2001年 | 35篇 |
2000年 | 26篇 |
1999年 | 18篇 |
1998年 | 24篇 |
1997年 | 18篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1994年 | 21篇 |
1993年 | 13篇 |
1992年 | 23篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 18篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 13篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 6篇 |
排序方式: 共有1073条查询结果,搜索用时 703 毫秒
881.
882.
883.
The relationship between expressed attitudes and actual behaviour in the context of sustainable development is complex and difficult to apply in a policy-relevant manner. The household, however, represents a key ‘lens’ for understanding the environmental impact of consumption patterns and for instigating policy designed to change consumer behaviour. This paper assesses the use of a household diary approach as a means of framing and collecting household environmental data, and, critically, as an educational vehicle for bringing about behavioural change by encouraging reflexivity. Evaluating the success of the diary approach at instigating behavioural change, the paper concludes that the diary approach: (1) created awareness about pro-environmental behaviour where there was none; (2) extended existing awareness to a wider range of pro-environmental behaviours and range of household members, and; (3) induced change in pro-environmental behaviour. In particular, the paper argues that current research neglects the potential that participating in the research process may contribute to changing the outlook or behaviour of participants. 相似文献
884.
885.
Simulating the three-dimensional circulation and hydrography of Halifax Harbour using a multi-nested coastal ocean circulation model 总被引:2,自引:2,他引:0
Shiliang Shan Jinyu Sheng Keith Richard Thompson David Alexander Greenberg 《Ocean Dynamics》2011,61(7):951-976
Halifax Harbour is located on the Atlantic coast of Nova Scotia, Canada. It is one of the world’s largest, ice-free natural
harbours and of great economic importance to the region. A good understanding of the physical processes controlling tides,
flooding, transport and dispersion, and hydrographic variability is required for pollution control and sustainable development
of the Harbour. For the first time, a multi-nested, finite difference coastal ocean circulation model is used to reconstruct
the three-dimensional circulation and hydrography of the Harbour and its variability on timescales of hours to months for
2006. The model is driven by tides, wind and sea level pressure, air-sea fluxes of heat, and terrestrial buoyancy fluxes associated
with river and sewage discharge. The predictive skill of the model is assessed by comparing the model simulations with independent
observations of sea level from coastal tide gauges and currents from moored instruments. The simulated hydrography is also
compared against a new monthly climatology created from all available temperature and salinity observations made in the Harbour
over the last century. It is shown that the model can reproduce accurately the main features of the observed tides and storm
surge, seasonal mean circulation and hydrography, and wind driven variations. The model is next used to examine the main physical
processes controlling the circulation and hydrography of the Harbour. It is shown that non-linear interaction between tidal
currents and complex topography occurs over the Narrows. The overall circulation can be characterized as a two-layer estuarine
circulation with seaward flow in the thin upper layer and landward flow in the broad lower layer. An important component of
this estuarine circulation is a relatively strong, vertically sheared jet situated over a narrow sill connecting the inner
Harbour to the deep and relatively quiescent Bedford Basin. Local wind driven variability is strongest in winter as expected
but it is also shown that a significant part of the temperature and salinity variability is driven by physical processes occurring
on the adjacent inner continental shelf, especially during storm and coastal upwelling events. 相似文献
886.
Daisuke Hasegawa Jinyu Sheng David A. Greenberg Keith R. Thompson 《Ocean Dynamics》2011,61(11):1845-1868
The Bay of Fundy in eastern Canada has the highest tides in the world. Harnessing the tidal energy in the region has long
been considered. In this study, the effects of tidal in-stream energy extraction in the Minas Passage on the three-dimensional
(3D) tidal circulation in the Bay of Fundy (BoF) and the Gulf of Maine (GoM) are examined using a nested-grid coastal ocean
circulation model based on the Princeton Ocean Model (POM). The nested-grid model consists of a coarse-resolution (~4.5 km)
parent sub-model for the GoM and a high-resolution (~1.5 km) child sub-model for the BoF. The tidal in-stream energy extraction
in the model is parameterized in terms of nonlinear Rayleigh friction in the momentum equation. A suite of numerical experiments
are conducted to determine the ranges of extractable tidal in-stream energy and resulting effects on the 3D tidal circulation
over the Bay of Fundy and the Gulf of Maine (BoF-GoM) in terms of the Rayleigh friction coefficients. The 3D model results
suggest that the maximum energy extraction in the Minas Passage increases tidal elevations and tidal currents throughout the
GoM and reduces tidal elevations and circulation in the upper BoF, especially in the Minas Basin. The far-field effect of
tidal energy extraction in the Passage on the 3D tidal circulation in the BoF-GoM is examined in two cases of harnessing tidal
in-stream energy from (a) the entire water column and (b) the lower water column within 20 m above the bottom in the Passage.
The 3D model results demonstrate that tidal in-stream energy extraction from the lower water column has less impact on the
tidal elevations and circulation in the BoF-GoM than the energy extraction from the whole water column in the Minas Passage. 相似文献
887.
Robert John Chapman James Keith Mortensen William P. LeBarge 《Mineralium Deposita》2011,46(8):881-903
Between 1978 and 2009, approximately 430,000 oz of placer gold were obtained from the Indian River and Black Hills Creek,
which equates to roughly 20% of the production for the entire Yukon Territory during that period. The area is unglaciated,
exposure is poor, and there are few known lode gold occurrences present. The technique of microchemical characterization of
placer gold grains has been applied to illuminate the style(s) of source mineralization and their relationship to placer gold
from the Klondike gold district immediately to the north. A total of 2,613 placer gold grains from 22 localities were characterised
in terms of the Au, Ag, Cu, and Hg content of their alloy and associated suite of opaque mineral inclusions. A combination
of alloy and inclusion mineralogy was used to define gold signatures which augmented the previous classification of orogenic
gold in the Klondike. Gold type 3b (8–25% Ag) is the main component of the placers in lower Dominion Creek but is augmented
and eventually replaced by type 3a gold (10–40% Ag) in placers in the main Indian River valley, probably through erosion of
gold-bearing veins in the valley floor. Type 4 gold exhibits highly variable Ag which may contain Hg to a maximum of 11 wt.%.
This gold type also hosts a distinctive inclusion assemblage of complex polymetallic sulphides, tellurides, sulfotellurides,
and sulfosalts and has previously been ascribed to local low sulfidation epithermal mineralization. Placer gold in drainages
radiating from Eureka Dome exhibits various proportions of types 3 and 4 gold depending on location, but type 3 gold forms
the major component in Black Hills Creek and northerly flowing tributaries of the Indian River with the exception of Eureka
and Montana creeks. Type 5 gold is found only in placers in the middle and lower Indian River. It is distinguished by slightly
elevated (0.05–0.17%) Cu in the gold alloy, together with low (5–9%) Ag contents. Inclusions of Bi minerals, Cr-bearing magnetite
and molybdenite within type 5 gold suggest derivation from an intrusion-related source. Candidates for such a source include
undiscovered lode occurrences associated with Cretaceous age intrusions to the south of the Indian River, or deformed Cu-Au
(−Mo) porphyry occurrences which are known to be present in the same area. This analysis of placer gold has indicated that
the contribution of low sulfidation epithermal gold from Eureka Creek to the larger placers of the Indian River is minor.
Consequently, the placer gold inventory of the Indian River is primarily orogenic in origin. Similarly, the characterization
of placer gold in Blackhills Creek strongly suggests an orogenic source. This study has demonstrated for the first time that
orogenic lode gold mineralization extends a considerable distance to the south of the southern Klondike goldfield. This information
contributes to the regional models of gold mineralization in an area which is currently the focus of intensive exploration. 相似文献
888.
Geochemical correlation of ash-fall beds with conventional tephrochronologic methods is not feasible when original glass composition is altered. Thus, alternative correlation methods may be required. Initial studies of heavily altered Paleozoic tephra (K-bentonites) have suggested the potential for employing trace-element concentrations in apatite as ash-fall bed discriminators. To further test the utility of apatite trace-element tephrochronology, we analyzed apatite phenocrysts from unaltered volcanic rocks with an electron microprobe: nine samples from rocks erupted during the Quaternary and one sample from a rock erupted during the Paleogene. The resulting apatite trace-element data provide unique bed discriminators despite within-crystal variability. Each of the volcanic rocks studied possesses unique trends in Mg, Cl, Mn, Fe, Ce and Y concentrations in apatite. The results from this study establish an important tephrochronologic method that can be applied to nearly all portions of the Phanerozoic stratigraphic record and greatly assist development of an advanced timescale. In addition to establishing a fingerprint for a particular eruption, apatite chemistry provides useful information about the source magma. 相似文献
889.
The processes that govern the predictability of decadal variations in the North Atlantic meridional overturning circulation (MOC) are investigated in a long control simulation of the ECHO-G coupled atmosphere?Cocean model. We elucidate the roles of local stochastic forcing by the atmosphere, and other potential ocean processes, and use our results to build a predictive regression model. The primary influence on MOC variability is found to come from air?Csea heat fluxes over the Eastern Labrador Sea. The maximum correlation between such anomalies and the variations in the MOC occurs at a lead time of 2?years, but we demonstrate that the MOC integrates the heat flux variations over a period of 10?years. The corresponding univariate regression model accounts for 74.5% of the interannual variability in the MOC (after the Ekman component has been removed). Dense anomalies to the south of the Greenland-Scotland ridge are also shown to precede the overturning variations by 4?C6?years, and provide a second predictor. With the inclusion of this second predictor the resulting regression model explains 82.8% of the total variance of the MOC. This final bivariate model is also tested during large rapid decadal overturning events. The sign of the rapid change is always well represented by the bivariate model, but the magnitude is usually underestimated, suggesting that other processes are also important for these large rapid decadal changes in the MOC. 相似文献
890.
Roberto E. San Juan-Farfán Lkhamsuren Bayarjargal Björn Winkler Eiken Haussühl Miguel Avalos-Borja Keith Refson Victor Milman 《Physics and Chemistry of Minerals》2011,38(9):693-700
We have measured the pressure-induced change in the lattice dynamics of diaspore, α-AlO(OH), by in situ Raman spectroscopy
up to 25 GPa. The spectra are evaluated by density functional perturbation theory-based atomistic model calculations. The
assignment of calculated to experimentally observed Raman bands is based on the calculation of Raman intensities. We discuss
the accuracy of the approach employed for these calculations and explain the relative magnitudes of mode Grüneisen parameters. 相似文献