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991.
An experimental study has been carried out to determine the partition coefficients of tungsten between aqueous fluids and
granitic melts at 800 °C and 1.5 kb with natural granite as the starting material. The effects of the solutions on the partition
coefficients of tungsten show a sequence of P > CO
3
2−
> B > H2O. The effects are limited (generallyK
D
< 0.3) and the tungsten shows a preferential trend toward the melt over the aqueous fluid. The value ofK
D
increases with increasing concentration of phosphorus; theK
D
increases first and then reduces with the concentration of CO
3
2−
when temperature decreases, theK
D
between the solution of CO
3
2−
and the silicate melt increases, and that between the solution of B4O
7
2−
and the silicate melt decreases. The partition coefficients of phosphorus and sodium between fluids and silicate melts have
been calculated from the concentrations of the elements in the melts. TheK
D
value for phosphorus is 0.38 and that for sodium is 0.56. Evidence shows that the elements tend to become richer and richer
in the melts. 相似文献
992.
To better understand the movement and transport of water and pollution through the coarse gravel unsaturated zone, the presented
research was conducted to estimate water flow and transport processes with a tracing experiment in a lysimeter in the Selniška
Dobrava. A combined tracing experiment was performed with deuterated water and the fluorescent dye—uranine. The fastest and
dominant flow velocities were calculated based on injection time, the first tracer appearance time and the time of highest
concentration. Mean flow velocity and vertical dispersion were estimated by an analytical best-fit method using one-dimensional
convection–dispersion model. Deuterium was confirmed as an ideal conservative tracer and a more suitable tracer than dye (uranine)
for the study of water flow in the unsaturated zone of a coarse gravel aquifer. The retardation factor of the dye as compared
with deuterium was 1.13–1.75, which is in agreement with previously published results. Artificial tracers, especially deuterated
water, were also identified as a very useful tool to assess other properties and differences in water flow in the unsaturated
zone of a coarse gravel aquifer such as velocity and dispersion. 相似文献
993.
Vadim S. Kamenetsky Andrey A. Gurenko 《Contributions to Mineralogy and Petrology》2007,153(4):465-481
The origin of compositional heterogeneities among the magmas parental to mid-ocean ridge basalts (MORB) was investigated using
a single rock piece of the olivine-phyric basalt from 43°N, Mid-Atlantic Ridge (AII D11-177). The exceptional feature of this
sample is presence of very primitive olivine crystals (90–91 mol% Fo) that are significantly variable in terms of CaO (0.15–0.35 wt%).
A population of low-Ca olivine (0.15–0.25 wt% CaO) is also notably distinct from high-Ca olivine population in AII D11-177,
and primitive MORB olivine in general, in having unusual assemblage of trapped mineral and glass inclusions. Mineral inclusions
are represented by high-magnesian (Mg# 90.7–91.1 mol%) orthopyroxene and Cr-spinel, distinctly enriched in TiO2 (up to 5 wt%, c.f. <1 wt% in common MORB spinel). Glass inclusions associated with orthopyroxene and high-Ti Cr-spinel have
andesitic compositions (53–58 wt% SiO2). Compared to the pillow-rim glass and “normal” MORB inclusions, the Si-rich glass inclusions in low-Ca olivine have strongly
reduced Ca and elevated concentrations of Ti, Na, K, P, Cl, and highly incompatible trace elements. Strong variability is
recorded among glass inclusions within a single olivine phenocrysts. We argue that the observed compositional anomalies are
mineralogically controlled, and thus may arise from the interaction between hot MORB magmas and crystal cumulates in the oceanic
crust or magma chamber. 相似文献
994.
Shin-Ichi Machida Hisako Hirai Taro Kawamura Yoshitaka Yamamoto Takehiko Yagi 《Physics and Chemistry of Minerals》2007,34(1):31-35
High-pressure Raman studies of methane hydrate were performed using a diamond anvil cell in the pressure range of 0.1–86 GPa
at room temperature. Raman spectra of the methane molecules revealed that new softened intramolecular vibration mode of ν
1 appeared at 17 GPa and that the splitting of vibration mode of ν
3 occurred at 15 GPa. The appearance of these two modes indicates that an intermolecular attractive interaction increases between
the methane molecules and the host water molecules and between the neighboring methane molecules. These interactions might
result in the exceptional stability of a high-pressure structure, a filled ice Ih structure (FIIhS) for methane hydrate, up
to 40 GPa. At 40 GPa, a clear change in the slope of the Raman shift versus pressure occurred, and above 40 GPa the Raman
shift of the vibration modes increased monotonously up to 86 GPa. A previous XRD study showed that the FIIhS transformed into
another new high-pressure structure at 40 GPa. The change in the Raman spectra at 40 GPa may be induced by the transition
of the structure. 相似文献
995.
Sven-Ulf Weber Michael Grodzicki Werner Lottermoser Günther J. Redhammer Gerold Tippelt Johann Ponahlo Georg Amthauer 《Physics and Chemistry of Minerals》2007,34(7):507-515
Natural alexandrite Al2BeO4:Cr from Malyshevo near Terem Tschanka, Sverdlovsk, Ural, Russia, has been characterized by 57Fe Mössbauer spectroscopy, electron microprobe, X-ray single-crystal diffractometry and by electronic structure calculations in order to determine oxidation state and location of iron. The sample contains 0.3 wt% of total iron oxide. The 57Fe Mössbauer spectrum can be resolved into three doublets. Two of them with hyperfine parameters typical for octahedrally coordinated high-spin Fe3+ and Fe2+, respectively, are assigned to iron substituting for Al in the octahedral M2-site. The third doublet is attributed to Fe3+ in hematite. Electronic structure calculations in the local spin density approximation are in reasonable agreement with experimental data provided that expansion and/or distortion of the coordination octahedra are presumed upon iron substitution. The calculated hyperfine parameters of Fe3+ are almost identical for the M1 and M2 positions, but the calculated ligand-field splitting is by far too large for high-spin Fe3+ on M1. 相似文献
996.
Bolivia is a country with high levels of poverty and inequality among its peoples and regions. For the nation and its urban
and rural areas, trends in the social and spatial distribution of poverty (and extreme poverty) are identified from 1976 to
2003 using UBN data with minor support where appropriate from poverty lines. The main survey between 1992 and 2001 uses composite
and selected UBN to track detailed poverty change for the country’s nine departments, its ten largest cities and a selection
of other smaller urban and rural municipalities. Because of rising background increases in population in the various surveyed
administrative units, many instances of relative reductions in poverty are accompanied by rising absolute increases. Marked
spatial variations in poverty and development in the country over the last several decades are identified as the main driver
for the country’s quickening pace of rural–urban migration. As a result, the paper concludes by assessing two different but
closely related views. One investigation tests the notion that because more poor people have been living in Bolivia’s cities
than in its rural areas since the mid to late 1990s, rapid rural–urban migration has simply shifted the locus of poverty from
the countryside to the cities in a process called, the ‘urbanisation of poverty.’ A second, more challenging, investigation
assesses the view that the flow of poor rural people to the better serviced urban areas of Bolivia has actually acted to alleviate
national poverty levels. 相似文献
997.
Roger H. Mitchell Malcolm Alexander Lachlan M. D. Cranswick Ian P. Swainson 《Physics and Chemistry of Minerals》2007,34(10):705-712
The cell dimensions and crystal structures of the fluoroperovskite NaMgF3 (neighborite), synthesized by solid state methods, have been determined by powder neutron diffraction and Rietveld refinement
over the temperature range 300–3.6 K using Pt metal as an internal standard for calibration of the neutron wavelength. These
data show that Pbnm NaMgF3 does not undergo any phase transitions to structures of lower symmetry with decreasing temperature. The cell dimensions and
atomic coordinates together with polyhedron volumes and distortion indices are given for Pbnm NaMgF3 at 25 K intervals from 300 to 3.6 K. Decreases in the a and c cell dimensions reach a saturation point at 50 K, whereas the b dimension becomes saturated at 150 K. The distortion of the structure of Pbnm NaMgF3 from the aristotype cubic
structure is described in terms of the tilting of the MgF6 octahedra according to the tilt scheme a
−
a
−
c
+
. With decreasing temperature the antiphase tilt (a
−) increases from 14.24° to 15.39°, whereas the in-phase tilt (c
+
) remains effectively constant at ∼10.7°. Changes in the tilt angles are insufficient to cause changes in the coordination
sphere of Na that might induce a low temperature phase transition. The structure of Pbnm NaMgF3 is also described in terms of normal mode analysis and displacements of the condensed normal modes are compared with those
of Pbnm KCaF3. 相似文献
998.
Isabelle Letard Philippe Sainctavit Catherine Deudon 《Physics and Chemistry of Minerals》2007,34(2):113-120
Pyrrhotite (Fe7S8) is a natural iron sulphide that can participate in rock magnetisation. Its electronic structure is not yet surely described.
X-ray magnetic circular dichroism (XMCD) at Fe L2,3 edges on Fe7S8, coupled with multiplet calculations, shows that iron is present only as Fe2+ in this magnetic iron sulphide. It reveals a strong magnetic orbital moment. XMCD at Fe and S K edges shows the quite strong
polarization of both Fe and S in Fe7S8. 相似文献
999.
Sebastian Hinsken Kamil Ustaszewski Andreas Wetzel 《International Journal of Earth Sciences》2007,96(6):979-1002
Eocene to Early Oligocene syn-rift deposits of the southern Upper Rhine Graben (URG) accumulated in restricted environments.
Sedimentation was controlled by local clastic supply from the graben flanks, as well as by strong intra-basinal variations
in accommodation space due to differential tectonic subsidence, that in turn led to pronounced lateral variations in depositional
environment. Three large-scale cycles of intensified evaporite sedimentation were interrupted by temporary changes towards
brackish or freshwater conditions. They form three major base level cycles that can be traced throughout the basin, each of
them representing a stratigraphic sub-unit. A relatively constant amount of horizontal extension (ΔL) in the range of 4–5 km has been estimated for the URG from numerous cross-sections. The width of the rift (L
f
), however, varies between 35 and more than 60 km, resulting in a variable crustal stretching factor between the bounding
masterfaults. Apart from block tilting, tectonic subsidence was, therefore, largely controlled by changes in the initial rift
width (L
0). The along-strike variations of the graben width are responsible for the development of a deep, trough-like evaporite basin
(Potash Basin) in the narrowest part of the southern URG, adjacent to shallow areas in the wider parts of the rift such as
the Colmar Swell in the north and the Rhine Bresse Transfer Zone that delimits the URG to the south. Under a constant amount
of extension, the along-strike variation in rift width is the principal factor controlling depo-centre development in extensional
basins. 相似文献
1000.