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941.
Six Tautenburg astrograph plates have been used to derive proper motions for 12 740 stars in the region of the Great Nebula
in Orion. The Oricat catalog of proper motions and B and R photometry has been compiled, incorporating as well data from other published catalogs. The proper motions presented in different
catalogs are compared. The Oricat catalog is useful for studies of features of the structure and kinematics of star clusters
and groups. 相似文献
942.
A test of the photometric calibration accuracy for the guide-star catalog (Master Catalog) of the Spectrum-UV project (World
Space Observatory—Ultraviolet) has been performed using CCD observations in a spectral band close to that of the guide sensor
system of the T-170M space telescope. The mean photometric uncertainty of the Master Catalog at 14
m
–17
m
is 0.23
m
; variations in this uncertainty over the sky are within a factor of two. About 2% of the stars in the Master Catalog were
found to have photometric errors in excess of 2
m
. We analyze the correspondence of large photometric errors to flags of the Master Catalog. 相似文献
943.
M. A. Yudovskaya V. V. Distler N. V. Rodionov A. V. Mokhov A. V. Antonov S. A. Sergeev 《Geology of Ore Deposits》2011,53(1):27-57
The formation conditions and age of the Sukhoi Log gold deposit are considered on the basis of new isotopic-geochemical data.
The U-Pb isotopic study of zircon and monazite from high-grade ore and host black slates at the Sukhoi Log deposit was carried
out with SIMS technique using a SHRIMP II instrument. Two generations of monazite are distinguished on the basis of optical
and scanning electron microscopy, cathodoluminescence, and micro X-ray spectroscopy. Monazite I is characterized by black
opaque porphyroblasts with microinclusions of minerals pertaining to metamorphic slates and structural attributes of pre-
and synkinematic formation. Monazite II occurs only within the ore zone as transparent crystals practically free of inclusions
and as rims around monazite I. The REE contents are widely variable in both generations. Porphyroblastic monazite I differs
in low U and Th (0.01–0.7 wt % ThO2) contents, whereas transparent monazite II contains up to 4 wt % ThO2. The average weighted U-Pb isotopic age of monazite
I is 650 ± 8.1 Ma (MSWD = 1.6; n = 9) and marks the time of metamorphism or catagenesis. The U-Pb age estimates of synore monazite II cover the interval of
486 ± 18 to 439 ± 17 Ma. Zircons of several populations from 0.5 to 2.6 Ga in age are contained in the ore. Most detrital
zircon grains have porous outer rims composed of zircon and less frequent xenotime with numerous inclusions of minerals derived
from slates. The peaks of 206Pb/238U ages in the most abundant zircon populations fall on 570 and 630 Ma and correspond to the age of newly formed metamorphic
mineral phases. The discordant isotopic ages indicate that the U-ThPb isotopic system of ancient detrital zircons was disturbed
470–440 Ma ago in agreement with isotopic age of monazite II and the Rb-Sr whole -rock isochron age of black slates (447 ±
6 Ma). The new data confirm the superimposed character of the gold-quartz-sulfide mineralization at the deposit. Black shales
of the Khomolkho Formation of the Bodaibo Synclinorium were affected by metamorphism over a long period; the peaks of metamorphism
and catagenesis are dated at 570 and 650–630 Ma. The high-temperature ore formation was probably related to a hidden granitic
pluton emplaced 450–440 Ma ago, that is, 200 Ma later than the events of greenschist metamorphism. Hercynian granitoid magmatism
(320–270 Ma) did not exert a substantial effect on the U-Th-Pb isotopic system in accessory minerals from the ore and could
not have been a major source of ore-forming fluids. 相似文献
944.
The domal structures of the Erzgebirge in Saxony, Germany, which control localization of the Variscan hydrothermal U, Sn,
W, and base-metal deposits, started to form in the Late Riphean in the course of folding, regional metamorphism, and granitization
and were eventually created at the end of the Paleozoic, when an enormous mass of granitic melts was emplaced and cooled.
As is illustrated by the world’s largest Schlema-Alberoda vein uranium deposit, the fractures that determined the localization
of ore-bearing veins were formed in the outer contact zones of the Variscan granites related to domal uplifts. Beyond the
zones of contact metamorphism, the orientation of ore-bearing fractures changes, their morphology simplifies, the amplitude
of displacements decreases, and most fractures pinch out. Such a zoning is explained by development of faults around growing
granitic domes. 相似文献
945.
Lake Kitagata, Uganda, is a hypersaline crater lake with Na–SO4–Cl–HCO3–CO3 chemistry, high pH and relatively small amounts of SiO2. EQL/EVP, a brine evaporation equilibrium model (Risacher and Clement 2001), was used to model the major ion chemistry of the evolving brine and the order and masses of chemically precipitated sediments.
Chemical sediments in a 1.6-m-long sediment core from Lake Kitagata occur as primary chemical mud (calcite, magadiite [NaSi7O13(OH)3·3H2O], burkeite [Na6(CO3)(SO4)2]) and as diagenetic intrasediment growths (mirabilite (Na2SO4·10H2O)). Predicted mineral assemblages formed by evaporative concentration were compared with those observed in salt crusts along
the shoreline and in the core from the lake center. Most simulations match closely with observed natural assemblages. The
dominant inflow water, groundwater, plays a significant role in driving the chemical evolution of Lake Kitagata water and
mineral precipitation sequences. Simulated evaporation of Lake Kitagata waters cannot, however, explain the large masses of
magadiite found in cores and the formation of burkeite earlier in the evaporation sequence than predicted. The masses and
timing of formation of magadiite and burkeite may be explained by past groundwater inflow with higher alkalinity and SiO2 concentrations than exist today. 相似文献
946.
A. A. Stepashko 《Russian Journal of Pacific Geology》2011,5(1):1-12
The role of the lateral structure of the lithospheric mantle in the seismotectonics and seismicity of the southern part of
the Russian Far East has been investigated. The positions of the epicenters of all the major earthquakes in Sakhalin (M ≥
6.0), as well as in the Amur region and the Primorye zones (M ≥ 5.0), are defined by the boundaries of the Anyui block of
highly ferruginous mantle, which lies at the base of the Sikhote-Alin area. Three cycles of large earthquakes are recognized
in the region: the end of the 19th-beginning of the 20th century, the mid-20th century, and end of the 20th-beginning of the
21st century. In the seismic zone of the Amur region (hereafter, the Amur seismic zone), the epicenters of the large earthquakes
in each cycle migrate from the SW to NE along the Tan-Lu fault megasystem at a rate of 30–60 km/yr. The specific features
of the seismicity of the region are explained by the repeated arrival of strain waves from the west. The waves propagate in
the upper part of the mantle and provoke the activation of the deep structure of the region. The detailed analysis of the
earthquakes in the Sikhote-Alin area (M ≥ 4.0) in 1973–2009 confirmed the clockwise tectonic rotation of the mantle block.
The characteristics of the Primorye zone of deep-focus seismicity at the Russia-China boundary are stated. Since 1973, 13
earthquakes with M ≥ 6.0 have been recorded in the zone at a depth of 300–500 km. This number of earthquakes is at least twice
as many as the number of large deep-focus earthquakes elsewhere in the Sea of Japan-Sea of Okhotsk transition zone. The unique
genesis of the Primorye seismic zone is related to the additional compression in the seismofocal area due to the creeping
of the Anyui mantle block onto the subduction zone during its rotation. The geodynamic implications of the seismotectonic
analysis are examined, and the necessity of division of the Amur plate into three geodynamically independent lithospheric
blocks is substantiated. 相似文献
947.
Kita-Uebaru natural rock slope failure and its back analysis 总被引:1,自引:2,他引:1
A large landslide occurred in Kita-Uebaru (or Asato) area of Nakagusuku village in Okinawa Island (Japan) on 10 June 2006
after a rainy period of about 9 days. The total rainfall was 126 mm from June 8 till the time of the landslide this period.
This landslide destroyed several buildings and roads, and the total travel distance of the landslide was about 110 m. In this
article, the authors were concerned with the initiation conditions of Kita-Uebaru landslide and post-failure motions of the
landslide body. The observations made in the landslide area, structural geology analyses and outcomes of geotechnical investigations
are described first. Then, possible causes of the landslide are investigated through back analyses using as inputs the geological
structure and the strength properties of planes of discontinuities involved in the sliding processes. The final part of the
article is concerned with the simulation of post-failure motions of the landslide body. The results of the investigations
and back analyses indicate that the failure plane was bi-planar and the heavy torrential rainy period for about 3 days was
the main cause of initiation of the landslide. The mechanical model presented in this article was capable of capturing the
overall features of the landslide body following the initiation of the failure. 相似文献
948.
Geochemical processes controlling the spatial distribution of selenium in soil and water,west central South Dakota,USA 总被引:8,自引:0,他引:8
Selenium (Se) is essential in the human diet, but has a low threshold for toxic concentration. It is recommended that nutrients
such as Se should be consumed through foods as part of a normal diet. Se concentrations in crops and meat depend on the amount
of labile Se in the soil where crops and forage are grown. Therefore, managing agriculture for optimal Se in grain crops and
forage requires an understanding of the distribution and mobility of Se. Elevated concentrations of Se occur in waters, soils,
and forage 120 km west of Pierre in west central South Dakota, USA. The research site lies in an elevated, dissected plain
where soils developed on gently dipping Pierre Shale. Soils were sampled along catena transects and waters collected from
soil, ponds, and shallow borings in areas of known elevated forage and crop Se. Soil extracts from saturated-paste extraction
and acid (aqua regia and hydrofluoric acid) extraction were analyzed. Selenate was the dominant Se species in both acid and
saturated-paste extracts; selenite and organic Se were below detection (<0.2 ppb) in the same soil extracts. On average, 98% of soil Se was not water-soluble. The distribution of total Se shows much less spatial variation than water-soluble
Se in the areas sampled. Se shows correlation with organic carbon in soils and waters, suggesting its association with organic
carbon. Ca shows some correlation to Se in acid extracts, but not in saturated-paste extracts or in waters. Total Se shows
no significant correlation to Na, Mg, and total S in the soils. Se in saturated-paste extracts and water samples shows good
correlations with Na, Mg, and SO4, suggesting that evaporitic Na–Mg–sulfate minerals may temporarily concentrate water-soluble Se in shallow soils. The dissolution
and precipitation of these Na–Mg–sulfate salts together with pH and oxidation–reduction conditions apparently control water-soluble
Se distribution and mobilization in shallow subsurface environments. 相似文献
949.
María Teresa Rodríguez-Salazar Ofelia Morton-Bermea Elizabeth Hernández-Álvarez Rufino Lozano Victor Tapia-Cruz 《Environmental Earth Sciences》2011,62(5):899-905
This research presents and discusses information concerning the spatial distribution of heavy metals (Pb, Cu, Zn, Ba, Co,
Cr, Ni and V) in the urban environments of Mexico City using geographical information system and statistical analysis. Superficial
soil samples (n = 146) were analyzed. The highest contamination indices were found in the north and center zone of the metropolitan area.
In contrast, the surrounding rural fields show a lower impact grade. The higher concentrations of Pb, Cu, Zn and Ba were observed
as being related to high vehicular traffic, nevertheless other elements such as Co, Cr, Ni and V do not show anthropogenic
influence and their content can be attributed to the parental rock. The results are compared with previous surveys carried
out in 2003 in order to evaluate temporal deposition trends. No changes were found on reported concentrations except for Cu
and Zn, whose concentration has increased in later years. The results suggest that spatial distribution analysis and results
in comparison with previous studies could be useful for the management and sustainable development of the metropolitan area
of Mexico City. 相似文献
950.
B. Panteleit K. Hamer R. Kringel W. Kessels H. D. Schulz 《Environmental Earth Sciences》2011,62(1):77-91
Geochemical processes, occurring in a stable transition zone between saltwater and freshwater, were simulated in a 2D, multi-layer
flow chamber experiment. Mixing, calcite dissolution, and oxidative degradation of organic matter were identified as the main
controlling factors. The results of the chamber experiment were compared to field data and verified by thermodynamic modeling.
Similarity in most ion distributions suggests the general applicability of the experimental method. Differences in the redox
conditions between field and experiment were reflected by the oxidants involved in the mineralization of organic carbon; while
field data show evidence of sulfate reduction, the presence of oxygen in the laboratory experiment resulted in the reoxidation
of sulfides. 相似文献