全文获取类型
收费全文 | 446篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 24篇 |
地球物理 | 97篇 |
地质学 | 171篇 |
海洋学 | 28篇 |
天文学 | 82篇 |
自然地理 | 48篇 |
出版年
2021年 | 6篇 |
2020年 | 11篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 7篇 |
2014年 | 12篇 |
2013年 | 25篇 |
2012年 | 14篇 |
2011年 | 10篇 |
2010年 | 15篇 |
2009年 | 25篇 |
2008年 | 12篇 |
2007年 | 12篇 |
2006年 | 15篇 |
2005年 | 12篇 |
2004年 | 11篇 |
2003年 | 13篇 |
2002年 | 17篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1992年 | 8篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1970年 | 4篇 |
1962年 | 4篇 |
1961年 | 3篇 |
1960年 | 6篇 |
1959年 | 4篇 |
1956年 | 3篇 |
1955年 | 4篇 |
1952年 | 3篇 |
1940年 | 3篇 |
1937年 | 4篇 |
1936年 | 3篇 |
排序方式: 共有460条查询结果,搜索用时 15 毫秒
451.
T. Marke W. Mauser A. Pfeiffer G. Zängl D. Jacob U. Strasser 《Environmental Earth Sciences》2014,71(11):4849-4868
In the current study, two regional climate models (MM5 and REMO) driven by different global boundary conditions (the ERA40 reanalysis and the ECHAM5 model) are one-way coupled to the uncalibrated hydrological process model PROMET to analyze the impact of global boundary conditions, dynamical regionalization and subsequent statistical downscaling (bilinear interpolation, correction of subgrid-scale variability and combined correction of subgrid-scale variability and bias) on river discharge simulation. The results of 12 one-way coupled model runs, set up for the catchment of the Upper Danube (Central Europe) over the historical period 1971–2000, prove the expectation that the global boundaries applied to force the RCMs strongly influence the accuracy of simulated river discharge. It is, however, noteworthy that all efficiency criteria in case of bias corrected MM5 simulations indicate better performance under ERA40 boundaries, whereas REMO-driven hydrological simulations better correspond to measured discharge under ECHAM5 boundaries. Comparing the hydrological results achievable with MM5 and REMO, the application of bias-corrected MM5 simulations turned out to allow for a more accurate simulation of discharge, while the variance in simulated discharge in most cases was better reflected in case of REMO forcings. The correction of subgrid-scale variability within the downscaling of RCM simulations compared to a bilinear interpolation allows for a more accurate simulation of discharge for all model configurations and all discharge criteria considered (mean monthly discharge, mean monthly low-flow and peak-flow discharge). Further improvements in the hydrological simulations could be achieved by eliminating the biases (in terms of deviations from observed meteorological conditions) inherent in the driving RCM simulations, regardless of the global boundary conditions or the RCM applied. In spite of all downscaling and bias correction efforts described, the RCM-driven hydrological simulations remain less accurate than those achievable with spatially distributed meteorological observations. 相似文献
452.
In this study we experimentally determine phlogopite/melt partition coefficients of Ra and other trace elements in a lamproitic system. This work was achieved using an analytical technique (LA-ICP-MS) with low detection limits (~ 0.01 fg) permitting the measurement of the very low Ra concentrations feasible in experiments (~ 1 ppb). DRaphlogopite/melt was determined to 2.28 ± 0.44 and 2.84 ± 0.47 in two experiments, the ratio DRa/DBa is around 1.6. The compatibility of Ra in phlogopite results from an ionic radius being close to the apex of the lattice strain parabola for earth alkalis in the large XII-coordinated interlayer site of phlogopite. A re-evaluation of DRa and DRa/DBa for magmatic minerals containing appreciable Ra, yields DRamineral/melt ranging from ~ 2.6 for phlogopite down to 2–3 ? 10? 5 for pyroxenes, and DRa/DBamineral/melt from ~ 4 for leucite to 2 ? 10? 2 for orthopyroxene. The influence of melt composition on DRa/DBa is less than 10%. All investigated minerals have different DRa/DBa, strongly fractionating Ra from Ba. Thus, for magmatic systems, (226Ra)/Ba in the various minerals is not constant, these minerals do not form a straight line in the (226Ra)/Ba–(230Th)/Ba system at the time of crystallization and thus, there is no (226Ra)/Ba–(230Th)/Ba isochron at t0. 226Ra–230Th–Ba mineral dating is thus applicable only to model ages calculated from mineral–glass pairs with known DRa. 相似文献
453.
Jean-François Ghienne Max Deynoux Giänreto Manatschal Jean-Loup Rubino 《Comptes Rendus Geoscience》2003,335(15):1091-1100
In the Gargaf area, the stratigraphic architecture of the Late-Ordovician glacial drift results from successive glacial erosion events, with the location of the main glacial valleys partly controlled by inherited Panafrican structural trends, and by the existence of glacio-isostatically induced fault-related depocentres. Four laterally discontinuous, depositional units correspond to the filling of palaeovalleys. Each of the corresponding basal bounding surfaces was incised during a major ice front advance, reaching at least the northern Gargaf (>28°S). The bulk of the glacial record is made up of fluvial to shallow-marine sediments deposited in relatively distal glacial environments. Each unit, which recorded a glacial-interglacial climatic cycle, can be used for correlation throughout the Murzuq Basin and even at the scale of the North Gondwana platform. To cite this article: J.-F. Ghienne et al., C. R. Geoscience 335 (2003). 相似文献
454.
455.
Unconventional PGE occurrences and PGE mineralization in the Great Dyke: metallogenic and economic aspects 总被引:4,自引:0,他引:4
B. Stribrny F. -W. Wellmer K. -P. Burgath T. Oberthür M. Tarkian T. Pfeiffer 《Mineralium Deposita》2000,35(2-3):260-280
Platinum group elements (PGE) are strategic materials because 96–99% of the world production is derived from just five mining
districts and because they cannot be replaced as catalysts in many chemical processes. In order to lessen the strategic character
of PGE, both conventional deposits and unconventional PGE mineralizations were investigated in an attempt to locate viable
deposits which would diversify the supplier base. In the Great Dyke, conventional PGE mineralization occurs in the form of
pristine sulfide ores mined underground and oxidic surface ores. New observations such as bimodal distributions of the PGE
in the Main Sulfide Zone (MSZ), elevated Pt/Pd ratios in the oxidized MSZ compared to the sulfidic part and distinct differences
between the platinum group mineral (PGM) assemblages of the MSZ and stream sediments of adjacent rivers emphasize the fact
that even though the Great Dyke seems to be the second or third largest PGE occurrence in the world, the complicated PGE distributions
and supergene redistributions should be kept in mind during planning and mine operation. Investigations of unconventional
PGE occurrences in ophiolites, Alaskan-type intrusions, porphyry copper deposits and in the Kupferschiefer show that economically
exploitable PGE concentrations can be expected in a broader variety of host rocks than considered favourable in the past.
In the Albanian Mirdita ophiolite average contents of 860 ppb Pt and 60 ppb Pd were detected. Flotation concentrates of porphyry
copper deposits, for example from Mamut, Malaysia, Santo Tomas, Philippines, Elacite, Bulgaria, and Ok Tedi, Papua New Guinea,
contain between 827 and 1860 ppb Pd + Pt. In selected profiles of the Polish Kupferschiefer average contents of 255 ppb Pt,
94 ppb Pd, 2.4 ppm Au and 13.0 ppm Ag were analysed. The distribution of the PGE resources in the world and the annual production
rates, however, underline the fact that the chances for a significant change in the supplier base are relatively low. The
Bushveld Complex will remain the largest producer, followed by Noril'sk-Talnakh, Sudbury and Stillwater. If the operations
in the Great Dyke reach their planned capacities, the Great Dyke will rank in third place among the PGE-producing deposits
in the world.
Received: 12 September 1998 / Accepted: 7 December 1999 相似文献
456.
Two very high-frequency radars (VHFR) operating on the Opal coast of eastern English Channel provided a nearly continuous 35-day long dataset of surface currents over a 500 km2 area at 0.6–1.8 km resolution. Argo drifter tracking and CTD soundings complemented the VHFR observations, which extended approximately 25 km offshore. The radar data resolve three basic modes of the surface velocity variation in the area, that are driven by tides, winds and freshwater fluxes associated with seasonal river discharge. The first mode, accounting for 90% of variability, is characterized by an along-shore flow pattern, whereas the second and third modes exhibit cross-shore, and eddy-like structures in the current velocity field. All the three modes show the dominant semi-diurnal variability and low-frequency modulation by the neap-spring tidal cycle. Although tidal forcing provides the major contribution to variability of local currents, baroclinicity plays an important role in shaping the 3D velocity field averaged over the tidal cycle and may strongly affect tracer dynamics on larger time scales. An empirical orthogonal function (EOF) decomposition and a spectral rotary analysis of the VHFR data reveal a discontinuity in the velocity field occurring approximately 10 km offshore which was caused by the reversal in the sign of rotation of the current vector. This feature of local circulation is responsible for surface current convergence on ebb, divergence on flood and strong oscillatory vertical motion. Spectral analysis of the observed currents and the results of the Agro drifter tracking indicate that the line of convergence approximately follows the 30-m isobath. The most pronounced feature of the radar-derived residual circulation is the along-coast intensification of surface currents with velocity magnitude of 0.25 m/s typical for the Regions of Freshwater Influence (ROFI). The analysis has provided a useful, exploratory examination of surface currents, suggesting that the circulation off the Opal coast is governed by ROFI dynamics on the hypertidal background. 相似文献
457.
458.
Christopher Bone Bart Johnson Max Nielsen‐Pincus Eric Sproles John Bolte 《Transactions in GIS》2014,18(2):161-182
Agent‐based modeling provides a means for addressing the way human and natural systems interact to change landscapes over time. Until recently, evaluation of simulation models has focused on map comparison techniques that evaluate the degree to which predictions match real‐world observations. However, methods that change the focus of evaluation from patterns to processes have begun to surface; that is, rather than asking if a model simulates a correct pattern, models are evaluated on their ability to simulate a process of interest. We build on an existing agent‐based modeling validation method in order to present a temporal variant‐invariant analysis (TVIA). The enhanced method, which focuses on analyzing the uncertainty in simulation results, examines the degree to which outcomes from multiple model runs match some reference to how land use parcels make the transition from one land use class to another over time. We apply TVIA to results from an agent‐based model that simulates the relationships between landowner decisions and wildfire risk in the wildland‐urban interface of the southern Willamette Valley, Oregon, USA. The TVIA approach demonstrates a novel ability to examine uncertainty across time to provide an understanding of how the model emulates the system of interest. 相似文献
459.
The simplest magnetic model for the upper 20 km of crust in central Ireland is of two layers. A thin, weakly magnetic upper layer carrying a number of magnetic bodies that can be related to surface geology overlies a magnetic crustal zone whose gross magnetization increases towards the north. The deeper trace of the lapetus Suture in central Ireland forms the boundary between a more magnetic northern crustal area and a less magnetic southern area. A pre-Carboniferous major dextral offset of this suture boundary occurs in the Limerick area. The suture is traced beneath the Dingle peninsula in the far south-west of Ireland. In east-central Ireland, between the Iapetus Suture and Southern Upland Line, the crust contains a large, south-dipping magnetic body with no surface expression, which produces the Virginia magnetic anomaly. The development of magnetic bodies — in particular, volcanic rocks of Carboniferous age — has been controlled by regional stress patterns. The major volcanic centre at Limerick lies at the intersection of two major Caledonian block fault systems just to the north of the surface trace of the Hercynian Front. 相似文献
460.