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91.
92.
Endo T Yong-Un M Baker CS Funahashi N Lavery S Dalebout ML Lukoschek V Haraguchi K 《Marine pollution bulletin》2007,54(6):669-677
Levels of total mercury (T-Hg) were surveyed in red meat (n=73) and liver (n=3) from toothed whales, dolphins and porpoises (odontocetes) sold for human consumption in the coastal cities of South Korea. High concentrations of T-Hg were found in the liver products of finless porpoises (18.7 and 156 microg/wet g) and common dolphins (13.2 microg/wet g). The T-Hg concentrations in red meat products were highest in the false killer whale (9.66+/-12.3 microg/wet g, n=9), bottlenose dolphin (10.6+/-12.6 microg/wet g, n=3) and killer whale (13.3 microg/wet g, n=1), and lowest in Cuvier's beaked whale and the harbour porpoise (0.4-0.5 microg/wet g). Thus, most of the products that originated from odontocetes exceeded the safety limit of 0.5 microg/wet g for T-Hg set by the South Korean health authorities for the fishery industry. Pregnant women and other vulnerable sectors of the population living in South Korea should therefore limit their consumption of odontocete products. 相似文献
93.
94.
Impacts on agriculture following the 1991 eruption of Vulcan Hudson, Patagonia: lessons for recovery 总被引:1,自引:1,他引:0
Thomas Wilson Jim Cole Shane Cronin Carol Stewart David Johnston 《Natural Hazards》2011,57(2):185-212
Large explosive eruptions have the potential to distribute heavy ashfalls across large areas, resulting in physical and chemical impacts on agriculture, and economic and psycho-social impacts on rural communities. This study investigates how affected agriculture and rural communities have adapted, absorbed and mitigated impacts following a range of ashfall thicknesses (>2 m?C<1 mm) from the 12?C15 August 1991 eruption of Vulcan Hudson, one of the largest eruptions of the twentieth century. An estimated 1 million livestock died after the eruption due to pasture burial by ashfall and ongoing suppression of vegetation recovery. Horticulturalists suffered ongoing damage to crops from wind-blown ash and changes to soil properties increased irrigation and cultivation requirements. Real or perceived impacts on human health and impacts on farm productivity from the ashfall resulted in evacuation of farms and small towns in the short term. Long-term farm abandonment occurred in areas of heavy ashfall (upper Ibáñez valley) and highly stressed farming systems, even where ashfall was relatively thin (<50 mm), such as the Argentine steppe. The mono-agricultural system of sheep farming in the steppe region had few options other than destocking, proving less resilient than the diverse high-intensity horticultural and pastoral mix in irrigated valleys, which allowed more rapid adaption through diversification of production. Farms with natural advantages and greater investment in capital improvements led to greater damage potential initially (at least in cost terms), but ultimately provided a greater capacity for response and recovery. Better soils, climate and significantly greater access to technological improvements such as cultivation tools, irrigation and wind breaks were advantageous, such as at Chile Chico (Chile), Los Antiguos and Perito Moreno (Argentina). Cultivation increased chemical and physical soil fertility, especially when used in combination with fertilisation and irrigation. Appropriate use of seeds and cropping techniques within the new soil and growing conditions was important. Government agencies had a vital role in the dissemination of information for appropriate farm management responses, ash chemistry analysis, evacuations and welfare, and in the longer term to provide technical and credit assistance to facilitate recovery. 相似文献
95.
A. V. Zernack S. J. Cronin V. E. Neall J. N. Procter 《International Journal of Earth Sciences》2011,100(8):1937-1966
The >25 ka volcaniclastic ring-plain succession in south-west Taranaki has been remapped to establish a much more detailed
understanding of the older stratigraphic record of Mt. Taranaki. Coastal cliff exposures show a range of volcaniclastic lithofacies,
including debris-avalanche and lahar deposits, and allow a detailed chronological reconstruction of past volcanic and sedimentary
events. Five new debris-avalanche deposits were identified, and their distribution in coastal cross-sections mapped. In addition,
four previously described units were renamed and their stratigraphic position and lateral extent redefined. Chronostratigraphic
control of the younger (<50 ka) sequence was obtained by radiocarbon dating of wood found within, or peat interbedded with,
the deposits. Emplacement ages of the older units were estimated from their stratigraphic position and underlying marine wave-cut
surfaces. Overall, at least 14 widespread debris-avalanche deposits occur within the <200 ka ring-plain record of Mt. Taranaki,
suggesting one major edifice failure on average every 14,000 years, with an increase in frequency since 40 ka. The stratigraphic
reconstruction of the ring-plain succession showed that the same pattern of deposition was repeatedly produced throughout
the existence of Mt. Taranaki. Depending on their sedimentological characteristics, the different volcanic and sedimentary
lithofacies can be related to phases of edifice-construction or collapse events. Based on the identified cyclic sedimentation
pattern, we present a new episodic stratigraphy that integrates existing and new lithostratigraphic units into a coherent
chronostratigraphic framework that can be applied to the entire volcanic and volcaniclastic succession at Mt. Taranaki. This
model takes into account the complex geological processes that have taken place on the volcano and provides a more uniform
stratigraphic terminology that could be applied to repeatedly collapsing stratovolcanoes elsewhere. 相似文献
96.
97.
Canonical discriminant function analysis was employed to discriminate between electron microprobe-determined titanomagnetite
and hornblende analyses from Egmont volcano and Tongariro Volcanic Centre. Data sets of 436 titanomagnetite and 206 hornblende
analyses from the two sources were used for the study. Titanomagnetite chemistry provided the best discrimination between
these two sources with classification efficiencies of 99% for sample averages and 95% for individual analyses. The difference
between sources for hornblende chemistry was less marked, but classification efficiencies of 100% for sample averages and
87% for individual analyses were achieved. Using the same methods a preliminary discrimination of individual Egmont volcano-sourced
tephras was attempted. Titanomagnetite chemistry enabled the discrimination of several individual tephras or at least pairs
of tephra units, but hornblende chemistry provided little discrimination. This technique provides an improvement on previous
methods for chemically distinguishing distal tephra from the two sources as well as potentially identifying individual tephras
from a particular source. A major advantage over previous discrimination techniques is that individual analyses can be classified
with a known probability of group membership (with groups such as volcano source or an individual tephra unit). Tephras in
a depositional environment where mixing is common such as within soil, loess and marine sequences, can be sourced or identified
more easily with classification of individual grains.
Received: 19 July 1995 / Accepted: 13 February 1996 相似文献
98.
Sonja Storm Phil Shane Axel K. Schmitt Jan M. Lindsay 《Earth and Planetary Science Letters》2011,301(3-4):511-520
Two mineralogically and chemically distinct rhyolite magmas (T1 and T3) were syn-erupted from the same conduit system during the 21.9 ka basalt intrusion-triggered Okareka eruption from Tarawera volcano, New Zealand. High spatial resolution U–Th disequilibrium dating of zircon crystals at the ~ 3–5 μm scale reveals a protracted yet discontinuous zircon crystallization history within the magmatic system. Both magma types contain zircon whose interiors predate the eruption by up to 200 ka. The dominant age peak in the T1 magma is ~ 30 ka with subordinate peaks at ~ 45, ~ 75, and ~ 100 ka, whereas the T3 magma has a dominant zircon interior age peak at ~ 90 ka with smaller modes at ~ 35 and ~ 150 ka. These patterns are consistent with isolated pockets of crystallization throughout the evolution of the system. Crystal rim analyses yield ages ranging from within error of the eruption age to at least ~ 90 ka prior to eruption, highlighting that zircon crystallization frequently stalled long before the eruption. Continuous depth profiling from crystal rims inward demonstrates protracted growth histories for individual crystals (up to ~ 100 ka) that were punctuated by asynchronous hiatuses of up to 30 ka in duration. Disparate zircon growth histories can result from localized thermal perturbations caused by mafic intrusions into a silicic reservoir. The crystal age heterogeneity at hand-sample scale requires considerable crystal transport and mixing. We propose that crystal mixing was achieved through buoyancy instabilities caused by mafic magma flow through crystal mush. A terminal pre-eruptive rejuvenation event was capable of mobilizing voluminous melts that erupted, but was too short (< 102–103 years) to result in extensive zircon growth. The contrasting, punctuated zircon histories argue against closed-system fractional crystallization models for silicic magmatism that require protracted cooling times following a mostly liquid starting condition. 相似文献
99.
T. M. Wilson J. W. Cole C. Stewart S. J. Cronin D. M. Johnston 《Bulletin of Volcanology》2011,73(3):223-239
Tephra fall from the August 1991 eruption of Volcán Hudson affected some 100,000 km2 of Patagonia and was almost immediately reworked by strong winds, creating billowing clouds of remobilised ash, or ‘ash storms’.
The immediate impacts on agriculture and rural communities were severe, but were then greatly exacerbated by continuing ash
storms. This paper describes the findings of a 3-week study tour of the diverse environments of southern Patagonia affected
by ash storms, with an emphasis on determining the impacts of repeated ash storms on agriculture and local practices that
were developed in an attempt to mitigate these impacts. Ash storms produce similar effects to initial tephra eruptions, prolonged
for considerable periods. These have included the burial of farmland under dune deposits, abrasion of vegetation and contamination
of feed supplies with fine ash. These impacts can then cause problems for grazing animals such as starvation, severe tooth
abrasion, gastrointestinal problems, corneal abrasion and blindness, and exhaustion if sheep fleeces become laden with ash.
In addition, ash storms have led to exacerbated soil erosion, human health impacts, increased cleanup requirements, sedimentation
in irrigation canals, and disruption of aviation and land transport. Ash deposits were naturally stabilised most rapidly in
areas with high rainfall (>1,500 mm/year) through compaction and enhanced vegetation growth. Stabilisation was slowest in
windy, semi-arid regions. Destruction of vegetation and suppression of regrowth by heavy tephra fall (>100 mm) hindered the
stabilisation of deposits for years, and reduced the surface friction which increased wind erosivity. Stabilisation of tephra
deposits was improved by intensive tillage, use of windbreaks and where there was dense and taller vegetative cover. Long-term
drought and the impracticality of mixing ash deposits with soil by tillage on large farms was a barrier to stabilising deposits
and, in turn, agricultural recovery. The continuing ash storms motivated the partial evacuation of small rural towns such
as Chile Chico (Chile) and Los Antiguos (Argentina) in September–December 1991, after the primary tephra fall in August 1991.
Greatly increased municipal cleanup efforts had to be sustained beyond the initial tephra fall to cope with the ongoing impacts
of ash storms. Throughout the 1990s, ash storms contributed to continued population migration out of the affected area, leaving
hundreds of farms abandoned on the Argentine steppe. The major lesson from our study is the importance of stabilisation of
ash deposits as soon as possible after the initial eruption, particularly in windy, arid climates. Suggested mitigation measures
include deep cultivation of the ash into the soil and erecting windbreaks. 相似文献
100.
Akira Nagano Kazuyuki Uehara Toshio Suga Yoshimi Kawai Hiroshi Ichikawa Meghan F. Cronin 《Journal of Oceanography》2014,70(4):389-403
Hydrographic data in the Kuroshio Extension (KE) region from 2008 to 2010 show large year-to-year variability in near-surface salinity, including a very large anomalous event in February 2010. During this event, the deep winter mixed layer in the southern KE region had higher salinity than had existed during the previous summer in September 2009. Our analysis shows that advection from the Philippine Sea along the western branch of the North Pacific subtropical gyre, taking approximately 9 months, resulted in this large salinity anomaly in February 2010 and contributes to the interannual salinity variability in the southern KE region. 相似文献