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991.
Long records of monthly salinity observations along the axis of Chesapeake Bay, Delaware Bay, and Long Island Sound are used
to test a simple advection–dispersion model of the salt distribution in linearly tapered estuaries developed in a previous
paper. We subdivide each estuary into three to five segments, each with linear taper allowing a distributed input of fresh
water, and evaluate the dispersion in each segment. While Delaware Bay has weak dispersion and a classical sigmoidal salinity
structure, Long Island Sound and Chesapeake Bay are more dispersive and have relatively small gradients in the central stretches.
Long Island Sound is distinguished by having a net volume and salt flux out of its low-salinity end resulting in a smaller
range of salinity and increasing axial gradients at its head rather than the usual asymptotic approach to zero salinity. Estimates
of residence times based on model transport coefficients show that Long Island Sound has the most rapid response to fresh-water
flux variations. It also has the largest amplitude cycle in river discharge fluctuation. In combination, these cause the large
seasonal variation in the salinity structure relative to interannual variability in Long Island Sound as compared with Chesapeake
Bay and Delaware Bay. 相似文献
992.
On 19 April 2005, an oil spill occurred in southeastern Louisiana’s Barataria Bay estuary. We used a drop sampler to characterize
the marsh-edge nekton community. Thirty-six locations were sampled in pre- and post-spill time frames from March through May
2005. Before–after control–impact (BACI) analyses of the total number of individuals (fishes + decapod crustaceans), total
fishes, and sensitive species found significant interactions between the temporal (before/after) and spatial (control/impact)
treatments and indicated an effect of the oil spill. Nonparametric analyses detected varied faunal assemblages across temporal
treatments, but were similar in species composition among spatial treatments. While the BACI analyses showed event effects,
differences were not strongly detected in nonparametric analyses of community structure. Fish are mobile and left the spill
area after the disturbance, whereas the less mobile but more numerous benthic decapod crustaceans remained. The overall community
structure appears to be robust and quickly recovered from the localized spill event. 相似文献
993.
The occurrence and development of riparian forests, which were mainly dominated by mesophytes species related closely with
surface water. Since there was no water discharged to the lower reaches of Tarim River in the past three decade years, the
riparian forests degrade severely. The groundwater table, the saline content of the groundwater, as well as the content of
free proline, soluble sugars, plant endogenous hormones (abscisic acid (ABA), and cytokinins (CTK)) of the leaves and relative
rates of sap flow of the Populus euphratica Oliv. (arbor species), Tamarix ramosissima Ldb. (bush species), and Apocynum venetum L. (herb species) were monitored and analyzed at the lower reaches of the Tarim River in the study area where five positions
on a transect were fixed at 100 m intervals along a sampling direction from riverbank to the sand dunes before and after water
release. The physiological responses and acclimation strategies of three species to variations in water and salinity stress
were discussed. It was found that A. venetum population recovered to groundwater table ranging from −1.73 to −3.56 m, and when exposed to saline content of the groundwater
ranging from 36.59 to 93.48 m mol/L; P. euphratica appeared to be more sensitive to the elevation of groundwater table than the A. venetum and T. ramosissima at groundwater table ranging from −5.08 to −5.80 m, and when exposed to saline content of the groundwater ranging from 42.17
to 49.55 m mol/L. T. ramosissima tended to be the best candidate species for reclamation in this hyper-arid area because it responded to groundwater table
ranging from −1.73 to −7.05 m, and when exposed to saline content of the groundwater ranging from 36.59 to 93.48 m mol/L.
These results explained the distribution patterns of desert vegetation in the lower reaches of the Tarim River. Understanding
the relationships among ecological factors variables, physiological response and acclimation strategies of plant individuals
could provide guidance to sustainable management, reclamation and development of this and similar regions. 相似文献
994.
Theodore D. Kanellopoulos Michael O. Angelidis Dimitrios Georgopoulos Aristomenis P. Karageorgis 《Environmental Geology》2009,57(8):1729-1738
Evros River is the most important river flowing into the North Aegean Sea (eastern Mediterranean) in terms of freshwater discharge,
and the second largest one of Eastern Europe after the Danube River. Salinity and temperature measurements, together with
suspended particulate matter concentrations were obtained in various depths at 14 stations in the adjacent Alexandroupolis
Gulf during four seasons (June 1998, September 1998, February 1999 and March 2000) in order to investigate the particle dynamics
and distributions in the northern Aegean Sea. Analysis of the collected data, together with particle observations under the
scanning electron microscope and study of satellite images showed that, under certain circumstances driven by the hydrological
and wind regime of the area, the Evros River particulate matter, with the associated pollutants, can be transferred far away
from the estuary and implicitly comprise a hazardous factor for the environmental status of the northern Aegean Sea. This
fact, combined with the future construction of the Burgas-Alexandroupolis pipeline, may cause a negative impact on the studied
natural ecosystem. 相似文献
995.
The Valhalla uranium deposit, located 40 km north of Mount Isa, Queensland, Australia, is an albitite-hosted, Mesoproterozoic
U deposit similar to albitite-hosted uranium deposits in the Ukraine, Sweden, Brazil and Guyana. Uranium mineralisation is
hosted by a thick package of interbedded fine-grained sandstones, arkoses and gritty siltstones that are bound by metabasalts
belonging to the ca. 1,780 Ma Eastern Creek Volcanics in the Western Succession of the Mount Isa basin. Alteration associated
with U mineralisation can be divided into an early, main and late stage. The early stage is dominated by laminated and intensely
altered rock comprising albite, reibeckite, calcite, (titano)magnetite ± brannerite. The main stage of mineralisation is dominated
by brecciated and intensely altered rocks that comprise laminated and intensely altered rock cemented by brannerite, apatite,
(uranoan)-zircon, uraninite, anatase, albite, reibeckite, calcite and hematite. The late stage of mineralisation comprises
uraninite, red hematite, dolomite, calcite, chlorite, quartz and Pb-, Fe-, Cu-sulfides. Brannerite has U–Pb and Pb–Pb ages
that indicate formation between 1,555 and 1,510 Ma, with significant Pb loss evident at ca. 1,200 Ma, coincident with the
assemblage of Rodinia. The oldest ages of the brannerite overlap with 40Ar/39Ar ages of 1,533 ± 9 Ma and 1,551 ± 7 Ma from early and main-stage reibeckite and are interpreted to represent the timing
of formation of the deposit. These ages coincide with the timing of peak metamorphism in the Mount Isa area during the Isan
Orogeny. Lithogeochemical assessment of whole rock data that includes mineralised and unmineralised samples from the greater
Mount Isa district reveals that mineralisation involved the removal of K, Ba and Si and the addition of Na, Ca, U, V, Zr,
P, Sr, F and Y. U/Th ratios indicate that the ore-forming fluid was oxidised, whereas the crystal chemistry of apatite and
reibeckite within the ore zone suggests that F− and were important ore-transporting complexes. δ18O values of co-existing calcite and reibeckite indicate that mineralisation occurred between 340 and 380°C and involved a
fluid having δ18Ofluid values between 6.5 and 8.6‰. Reibeckite δD values reveal that the ore fluid had a δDfluid value between −98 and −54‰. The mineral assemblages associated with early and main stages of alteration, plus δ18Ofluid and δDfluid values, and timing of the U mineralisation are all very similar to those associated with Na–Ca alteration in the Eastern
Succession of the Mount Isa basin, where a magmatic fluid is favoured for this style of alteration. However, isotopic data
from Valhalla is also consistent with that from the nearby Mount Isa Cu deposit where a basinal brine is proposed for the
transport of metals to the deposit. Based on the evidence to hand, the source fluids could have been derived from either or
both the metasediments that underlie the Eastern Creek Volcanics or magmatism that is manifest in the Mount Isa area as small
pegmatite dykes that intruded during the Isan Orogeny. 相似文献
996.
In the present investigation, an effort has been made to identify the critical sub-watersheds for the development of best
management plan for a small watershed of Eastern India using a hydrological model, namely, AVSWAT2000. A total of 180 combinations
of various management treatments including crops (rice, maize ground nut and soybean), tillage (zero, conservation, field
cultivator, mould board plough and conventional practices) and fertilizer levels (existing half of recommended and recommended)
have been evaluated. The investigation reveled that rice cannot be replaced by other crops such as groundnut, maize, mungbean,
sorghum and soybean since comparatively these crops resulted in higher sediment yield. The tillage practices with disk plough
have been found to have more impact on sediment yield and nutrient losses than conventional tillage practices for the existing
level of fertilizer. Sediment yield decreased in the case of zero tillage, conservation tillage, field cultivator, moldboard
plough, and conservation tillage as compare to conventional tillage. Lowest NO3–N loss was observed in zero tillage in all the fertilizer treatments, whereas field cultivator, moldboard plough and disk
plough resulted in increase of NO3–N loss. As compared to conventional tillage, the losses of soluble phosphorus were increased in moldboard plough. The losses
of organic nitrogen were also increased as fertilizer dose increased. After zero tillage the conservation tillage preformed
better in all the fertilizer treatments as per loss of organic nitrogen and organic phosphorus is concerned. It can be concluded
that the sediment yield was found to be the highest in the case of disk plough followed by moldboard plough, field cultivator,
conventional tillage, field cultivator and least in zero tillage practices. The nutrient losses were found to be in different
order with tillage practices, resulted highest in disk plough tillage practices. In view of sediment yield and nutrient losses,
the conservation tillage practice was found to be the best as the sediment yield is less than the average soil loss whereas
nutrient loss is within the permissible limit. 相似文献
997.
Justus E. E. van Beusekom Sabine Diel-Christiansen 《International Journal of Earth Sciences》2009,98(2):269-280
Phytoplankton plays a dominant role in shelf biogeochemistry by producing the major part of organic matter. Part of the organic
matter will reach the sediment where diagenetic processes like denitrification, apatite formation or burial will remove nutrients
from the biogeochemical cycle. In this article current knowledge on the decadal plankton variability in the North Sea is summarized
and possible implications of these changes for the biogeochemistry of the North Sea are discussed. Most of the observed interdecadal
dynamics seem to be linked to large-scale oceanographic and atmospheric processes. Prominent changes in the North Sea ecosystem
have taken place around 1979 and 1988. In general, the phytoplankton color (CPRS indicator of phytoplankton biomass) reached
minimum values during the end of the 1970s and has increased especially since the mid 1980s. Changes with a similar timing
have been identified in many time series from the North Sea through the entire ecosystem and are sometimes referred to as
regime shifts. It is suggested that the impact of global change on the local biogeochemistry is largely driven by the phyto-
and zooplankton dynamics during spring and early summer. At that time the extent of zooplankton–phytoplankton interaction
either allows that a large part of the new production is settling to the sediment, or that a significant part of the new production
including the fixed nutrients is kept within the pelagic system. The origin of the extent of the phytoplankton–zooplankton
interaction in spring is probably set in the previous autumn and winter. In coastal areas, both large-scale atmospheric and
oceanographic changes as well as anthropogenic factors influence the long-term dynamics. Due to eutrophication, local primary
production nowadays still is up to five times higher than during pre-industrial conditions, despite a decreasing trend. Recently,
introduced species have strengthened the filter feeder component of coastal ecosystems. Especially in shallow coastal seas
like the Wadden Sea, this will enhance particle retention, shift organic matter degradation to the benthic compartment and
enhance nutrient removal from the biogeochemical cycle by denitrification or apatite formation. 相似文献
998.
J. Escuder Viruete A. Pérez-Estaún D. Weis 《International Journal of Earth Sciences》2009,98(2):407-425
The nature of the oceanic crust produced through rifting and oceanic spreading between North and South America during the
Late Jurassic is a key element for the Caribbean plate tectonic model reconstruction. Located in the Cordillera Central of
Hispaniola, the Loma La Monja volcano-plutonic assemblage (LMA) is composed of gabbros, dolerites, basalts, and oceanic sediments,
as well as metamorphic equivalents, which represent a dismembered fragment of this proto-Caribbean oceanic crust. Petrologic
and geochemical data show that the LMA have a relatively broad diversity in composition, which represent the crystallization
products of a typical low-pressure tholeiitic fractionation of mid-ocean ridge basalts (MORB)-type parental magmas, ranging
from N- to E-MORB. Three geochemical groups have been distinguished in the volcanic sequence: LREE-flat to slightly LREE-enriched
basalts of groups II and III occur interlayered in the lower stratigraphic levels; and LREE-depleted basalts of group I in
the upper levels. Mantle melt modeling suggests that group III magmas are consistent by mixing within a mantle melt column
of low-degree (<1%) melts of a deep garnet lherzolite source and high-degree (>15%) melts of a shallow spinel source, and
groups II and I magmas are explained with moderate to high (14–18%) and very high (>20%) fractional melting degrees of a shallower
spinel mantle source, respectively. Thus, upward in the volcanic sequence of the LMA, the magmas represent progressively more
extensive melting of shallower sources, in a plume-influenced spreading ridge of the proto-Caribbean oceanic crust. Nb/Y versus
Zr/Y systematics combined with recent plate tectonic model reconstructions reveal that Caribbean Colombian oceanic plateau
fragments in Hispaniola formed through melting of heterogeneous mantle source regions related with distinct plumes during
at least from Aptian–Albian (>96 Ma) to Late Campanian. 相似文献
999.
With the global container population exceeding 25 million TEU (Twenty-foot Equivalent Unit) and the annual production of new
boxes exceeding 3 million TEU it is estimated that around 1.5 million TEU of empty containers are sitting in yards and depots
around the world waiting for use. Although utilization rates have improved since 2004, container utilization depends on the
very dynamic nature of container transportation, and the container building and leasing industries. Owing primarily to the
chronic trend of increasing trade imbalances across the oceans, and despite recent trends along some trade routes, the empty
container management problem has become a major issue for the container shipping industry during the last decade. This paper
examines and analyzes empty container logistics at a global, interregional, regional and local level. Special consideration
is given to key factors affecting the empty container logistics management and strategies implemented by ocean carriers and
other stakeholders to better manage empty containers.
相似文献
Maria BoileEmail: |
1000.
Pan Wu Changyuan Tang Congqiang Liu Lijun Zhu TingQuan Pei Lijuan Feng 《Environmental Geology》2009,57(7):1457-1467
The chemical characteristics, formation and natural attenuation of pollutants in the coal acid mine drainage (AMD) at Xingren
coalfield, Southwest China, are discussed in this paper based on the results of a geochemical investigation as well as geological
and hydrogeological background information. The chemical composition of the AMD is controlled by the dissolution of sulfide
minerals in the coal seam, the initial composition of the groundwater and the water–rock interaction. The AMD is characterized
by high sulfate concentrations, high levels of dissolved metals (Fe, Al, Mn, etc.) and low pH values. Ca2+ and SO4
2− are the dominant cation and anion in the AMD, respectively, while Ca2+ and HCO3
− are present at significant levels in background water and surface water after the drainage leaves the mine site. The pH and
alkalinity increase asymptotically with the distance along the flow path, while concentrations of sulfate, ferrous iron, aluminum
and manganese are typically controlled by the deposition of secondary minerals. Low concentrations of As and other pollutants
in the surface waters of the Xingren coalfield could be due to relatively low quantities being released from coal seams, to
adsorption and coprecipitation on secondary minerals in stream sediments, and to dilution by unpolluted surface recharge.
Although As is not the most serious water quality problem in the Xingren region at present, it is still a potential environmental
problem.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献