全文获取类型
| 收费全文 | 144篇 |
| 免费 | 2篇 |
| 国内免费 | 1篇 |
专业分类
| 测绘学 | 6篇 |
| 大气科学 | 10篇 |
| 地球物理 | 30篇 |
| 地质学 | 36篇 |
| 海洋学 | 16篇 |
| 天文学 | 16篇 |
| 自然地理 | 33篇 |
出版年
| 2022年 | 2篇 |
| 2021年 | 2篇 |
| 2020年 | 1篇 |
| 2019年 | 1篇 |
| 2018年 | 2篇 |
| 2017年 | 3篇 |
| 2016年 | 4篇 |
| 2015年 | 3篇 |
| 2014年 | 3篇 |
| 2013年 | 9篇 |
| 2012年 | 5篇 |
| 2011年 | 2篇 |
| 2010年 | 8篇 |
| 2009年 | 6篇 |
| 2008年 | 3篇 |
| 2007年 | 5篇 |
| 2006年 | 1篇 |
| 2005年 | 2篇 |
| 2004年 | 8篇 |
| 2003年 | 3篇 |
| 2002年 | 6篇 |
| 2001年 | 5篇 |
| 2000年 | 2篇 |
| 1999年 | 3篇 |
| 1998年 | 10篇 |
| 1997年 | 2篇 |
| 1996年 | 2篇 |
| 1995年 | 2篇 |
| 1993年 | 5篇 |
| 1992年 | 3篇 |
| 1991年 | 3篇 |
| 1990年 | 1篇 |
| 1989年 | 2篇 |
| 1987年 | 2篇 |
| 1986年 | 1篇 |
| 1985年 | 3篇 |
| 1984年 | 3篇 |
| 1983年 | 3篇 |
| 1982年 | 4篇 |
| 1981年 | 4篇 |
| 1980年 | 1篇 |
| 1977年 | 1篇 |
| 1976年 | 4篇 |
| 1971年 | 1篇 |
| 1961年 | 1篇 |
排序方式： 共有147条查询结果，搜索用时 343 毫秒
51.
Electrogeochemical sampling with
Reinhard W. Leinz Donald B. Hoover David L. Fey David B. Smith Thaxson Patterson 《Journal of Geochemical Exploration》1998,61(1-3)
Electrogeochemical extraction methods are based on the migration of ions in an electric field. Ions present in soil moisture are transported by an applied current into fluids contained in special electrodes placed on the soil. The fluids are then collected and analyzed. Extractions are governed by Faraday's and Ohm's laws and are modeled by the operation of a simple Hittorf transference apparatus. Calculations show that the volume of soil sampled in an ideal electrogeochemical extraction can be orders of magnitude greater than the volumes used in more popular geochemical extraction methods, although this has not been verified experimentally.
is a method of in-situ electrogeochemical extraction that was developed in the former Soviet Union and has been tested and applied internationally to exploration for buried mineral deposits. Tests carried out at the United States Geological Survey (
) indicated that there were problems inherent in the use of
technology. The cause of the problems was determined to be the diffusion of acid from the conventional electrode into the soil. The
electrode incorporates two compartments and a salt bridge in a design that inhibits diffusion of acid and enables the collection of anions or cations. Tests over a gold-enriched vein in Colorado and over buried, Carlin-type, disseminated gold deposits in northern Nevada show that there are similarities and differences between
results and those by partial extractions of soils which include simple extractions with water, dilute acids and solutions of salts used as collector fluids in the electrodes. Results of both differ from the results obtained by total chemical digestion. The results indicate that
responds to mineralized faults associated with disseminated gold deposits whereas partial and total chemical extraction methods do not. This suggests that faults are favored channels for the upward migration of metals and that
may be more effective in exploration for the deposits. It defines anomalies that are often narrow and intense, an observation previously made by
researchers. The field tests show that
is less affected by surface contamination. A test over the Mike disseminated gold deposit indicates that the method may not be effective for locating deposits with impermeable cover. Faradaic extraction efficiencies of 20–30%, or more, are frequently achieved with
and the method generally shows good reproducibility, especially in extraction of major cations. However, ions of other metals that are useful in exploration, including Au and As, may be collected in low and temporally variable concentrations. The reason for this variability is unclear and requires further investigation. 相似文献
Full-size image
Full-size image
Full-size image
Full-size image
Full-size image
Full-size image
Full-size image
Full-size image
Full-size image
Full-size image
52.
Minor tin, tungsten, tantalum and beryllium mineralization occurs near Mount Isa in pegmatites along the eastern rim of the Queen Elizabeth pluton, a multi-phase pluton in the Proterozoic Sybella Granite batholith of northwest Queensland. The Queen Elizabeth pluton and adjacent metamorphic rocks were explored by Mount Isa Mines Limited during 1980–1983 to assess the tin potential of the area.An orientation study was carried out over an existing tin deposit, using stream-sediment, soil and rock-chip sampling, magnetometer and scintillometer surveys and percussion drilling. This defined the geophysical and geochemical features of the deposit, and indicated that monazite and cassiterite had related distributions and could be used as heavy-mineral tracers. Broader exploration used stream-sediment and rock-chip sampling, and airborne magnetic and gamma-ray spectrometry surveys.The eastern rim of the Queen Elizabeth pluton was found to be enriched in thorium and tin, and an area of approximately 2000 × 400 m with anomalously high tin values in bedrock was delineated in a part of the pluton not previously known to be mineralized. An economic assessment led to relinquishment of the area at that stage. Although no new areas of economic mineralization were found, the study indicated that in this region the thorium gamma-ray response can be used in regional airborne surveys to define areas of prime interest for tin exploration, and that monazite in stream sediments can be used as a heavy-mineral tracer for pegmatitic tin mineralization. 相似文献
53.
Jennifer M. Galloway R. Timothy Patterson Christine T. Doherty Helen M. Roe 《Journal of Paleolimnology》2007,38(4):569-588
Pollen and diatoms preserved in the radiocarbon dated sediments of Two Frog Lake in the Seymour-Belize Inlet Complex of the
central mainland coast of British Columbia document postglacial climate change. Two Frog Lake was isolated from the sea prior
to 11,040 ± 50 yr BP (13,030 cal. yr BP) when the climate was cool and dry, and open Pinus contorta woodlands covered the landscape. These woodlands were replaced by a mixed conifer forest ca. 10,200 yr BP (ca. 12,300 cal.
yr BP) when the climate became moister. A relatively dry and warm early Holocene climate allowed Pseudotsuga menziesii to migrate northward to this site where it grew with Picea, Tsuga heterophylla and Alnus. The climate became cooler and moister at ca. 8,000 yr BP (ca. 9,200 cal. yr BP), approximately 500–1,000 years prior to
sites located south of Two Frog Lake and on the Queen Charlotte Islands, but contemporary with sites on the northern mainland
coast of British Columbia and south coastal Alaska. Climate heterogeneity in central coastal British Columbia appears to have
occurred on a synoptic scale, suggesting that atmospheric dynamics linked to a variable Aleutian Low pressure system may have
had an important influence on early Holocene climate change in the Seymour-Belize Inlet Complex. The transition to cooler
and moister conditions facilitated the expansion of Cupressaceae and the establishment of a modern-type coastal temperate
rainforest dominated by Cupressaceae and T. heterophylla. This was associated with progressive lake acidification. Diatom changes independent of vegetation change during the late
Holocene are correlative with the mid-Neoglacial period, when cooler temperatures altered diatom communities. 相似文献
54.
Daniel J. Rolfe Carole A. Haswell Joseph Patterson 《Monthly notices of the Royal Astronomical Society》2000,317(4):759-772
The eclipsing nova-like cataclysmic variable star V348 Pup exhibits a persistent luminosity modulation with a period 6 per cent longer than its 2.44-h orbital period ( P orb ). This has been interpreted as a 'positive superhump' resulting from a slowly precessing non-axisymmetric accretion disc gravitationally interacting with the secondary. We find a clear modulation of mid-eclipse times on the superhump period, which agrees well with the predictions of a simple precessing eccentric disc model. Our modelling shows that the disc light centre is on the far side of the disc from the donor star when the superhump reaches maximum light. This phasing suggests a link between superhumps in V348 Pup and late superhumps in SU UMa systems. Modelling of the full light curve and maximum entropy eclipse mapping both show that the disc emission is concentrated closer to the white dwarf at superhump maximum than at superhump minimum. We detect additional signals consistent with the beat periods between the implied disc precession period and both and 相似文献
55.
56.
R. Silvotti A. Bonanno A. Frasca S. Bernabei R. Janulis R. Østensen S.-L. Kim B.-G. Park J. Xiaojun J. Guo Z. Liu M.D. Reed R.S. Patterson K.M. Gietzen P.J. Clark G.W. Wolf Y. Lipkin L. Formiggini E. Leibowitz T.D. Oswalt M. Rudkin K. Johnston 《Astrophysics and Space Science》2004,289(3-4):445-448
I present a model for the formation and evolution of a massive disk galaxy, within a growing dark halo whose mass evolves according to cosmological simulations of structure formation. The galactic evolution is simulated with a new 3D chemo-dynamical code, including dark matter, stars and a multi-phase ISM. We follow the evolution from redshift z = 4.85 until the present epoch. The energy release by massive stars and supernovae prevents a rapid collapse of the baryonic matter and delays the maximum star formation until redshift z ≈ 1. The galaxy forms radially from inside-out and vertically from top-to-bottom. The feedback of stars leads to turbulent motions and large-scale flows in the ISM. As one result the galactic disk is significantly enriched by chemical elements synthesized in bulge stars. 相似文献
57.
A. Kawachi Y. Hayami J. Jimbo S. Kamei T. Kifune H. Kubo J. Kushida S. LeBohec K. Miyawaki M. Mori K. Nishijima J. R. Patterson R. Suzuki T. Tanimori S. Yanagita T. Yoshikoshi A. Yuki 《Astroparticle Physics》2001,14(4):1492-269
A new imaging atmospheric Cherenkov telescope with a light-weight reflector has been constructed. Light, robust, and durable mirror facets of containing carbon fiber reinforced plastic laminates were developed for the telescope. The reflector has a parabolic shape (f/1.1) with a 30 m2 surface area, which consists of 60 spherical mirror facets. The image size of each mirror facet is 0°.08 (FWHM) on average. The attitude of each facet can be adjusted by stepping motors. After the first in situ adjustment, a point image of about 0°.14 (FWHM) over 3° field of view was obtained. The effect of gravitational load on the optical system was confirmed to be negligible at the focal plane. The telescope has been in operation with an energy threshold for γ-rays of 300 GeV since May 1999. 相似文献
58.
Bernhard Jenny Bojan Šavrič Tom Patterson 《International journal of geographical information science》2013,27(6):935-952
There are two problems with current cylindrical projections for world maps. First, existing cylindrical map projections have a static height-to-width aspect ratio and do not automatically adjust their aspect ratio in order to optimally use available canvas space. Second, many of the commonly used cylindrical compromise projections show areas and shapes at higher latitudes with considerable distortion. This article introduces a new compromise cylindrical map projection that adjusts the distribution of parallels to the aspect ratio of a canvas. The goal of designing this projection was to show land masses at central latitudes with a visually balanced appearance similar to how they appear on a globe. The projection was constructed using a visual design procedure where a series of graphically optimized projections was defined for a select number of aspect ratios. The visually designed projections were approximated by polynomial expressions that define a cylindrical projection for any height-to-width ratio between 0.3:1 and 1:1. The resulting equations for converting spherical to Cartesian coordinates require a small number of coefficients and are fast to execute. The presented aspect-adaptive cylindrical projection is well suited for digital maps embedded in web pages with responsive web design, as well as GIS applications where the size of the map canvas is unknown a priori. We highlight the projection with a height-to-width ratio of 0.6:1, which we call the Compact Miller projection because it is inspired by the Miller Cylindrical projection. Unlike the Miller Cylindrical projection, the Compact Miller projection has a smaller height-to-width ratio and shows the world with less areal distortion at higher latitudes. A user study with 448 participants verified that the Compact Miller – together with the Plate Carrée projection – is the most preferred cylindrical compromise projection. 相似文献
59.
Lynn M. Patterson 《The Professional geographer》2013,65(3):451-454
The objectives are to (1) quantify, map, and analyze vegetation cover distributions and changes across Accra, Ghana, for 2002 and 2010; and (2) examine the statistical relationship between vegetation cover and a housing quality index (HQI) for 2000 at the neighborhood level. Pixel-level vegetation cover maps derived using threshold classification of 2002 and 2010 QuickBird normalized difference vegetation index images have very high overall accuracies and yield an estimate of 5.9 percent vegetation cover reduction over the study area between 2002 and 2010. A high degree of variance in vegetation cover for individual dates is explained by HQI at the neighborhood level, although minimal covariability between absolute or relative vegetation cover change and HQI for 2000 was observed. 相似文献
60.
Brent Lennox Ian Spooner Timothy Jull William P. Patterson 《Journal of Paleolimnology》2010,43(1):15-27
A high-resolution, multi-proxy lake sediment record was used to establish the timing of Holocene environmental change in Canoran Lake, southwest Nova Scotia, Canada. Proxies include %C, δ15N, δ13C, HI, magnetic susceptibility, and pollen. Canoran Lake is a small, shallow (11 m) lake with two ephemeral inlets and an outlet. The site was deglaciated at ca. 15,300 cal (calibrated) year BP and elevated %C values indicate the establishment of a productive aquatic environment that is consistent with Allerød warming. The Allerød was interrupted by rapid air temperature cooling during the Younger Dryas (ca. 12,900–11,600 cal year BP). The Early Hypsithermal (ca. 11,600–8,500 cal year BP) was relatively warm and wet. A slight increase in clastic input occurred between 9,100 and 8,500 cal year BP but δ15N, δ13C, and HI values imply that the lithostratigraphic response may not be indicative of climate-induced change. The strong proxy response between 8,500 and 8,000 cal year BP was likely due to cooling and drying coincident with the 8.2 k year event. The climate was relatively warm and dry during the Late Hypsithermal (ca. 8,000–3,500 cal year BP). None of the proxies’ exhibit notable change during the 5,500 cal year BP hemlock decline, indicating that ecological change was likely due to a pathogen attack. Post-Hypsithermal (modern) climate was characterized by an increase in precipitation and a decrease in air temperatures from ca. 3,500 to 700 cal year BP (top of core). 相似文献