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991.
Beta-eucryptite as grown by the flux method has been investigated by in-situ cold- and hot-stage transmission electron microscopy
(TEM). Using electron diffraction and dark-field TEM imaging, we found no evidence for the merohedral twinning that accompanies
structural collapse at the β-to-α-quartz transition, suggesting a true hexagonal symmetry for the aluminosilicate framework
of β-eucryptite. Selected-area electron diffraction (SAED) patterns exhibited a variety of incommensurate structures along
the three a axes with an average modulation period of about 6.5 a. These modulated structures arise from superperiodic stacking parallel to (100) of two structural units with different Li
configurations. In-situ heating experiments show that the modulated structures undergo a reversible transition to the disordered
modification at elevated temperatures. This transition arises from positional order-disorder of Li ions along the main structural
channels. In addition, it appears that at constant low temperature, electron beam irradiation alone can induce a sequence
of transitions similar to those that are thermally induced from the ordered modification to modulated states.
Received: 12 November 1998 / Revised and accepted: 31 December 1998 相似文献
992.
993.
In an attempt to identify the molecular shocks associated with the entrainment of ambient gas by collimated stellar winds from young stars, we have imaged a number of known molecular outflows in H2 v=1-0 S(1) and wide-band K. In each flow, the observed H2 features are closely associated with peaks in the CO outflow maps. We therefore suggest that the H2 results from shocks associated with the acceleration or entrainment of ambient, molecular gas. This molecular material may be accelerated either in a bow shock at the head of the flow, or along the length of the flow through a turbulent mixing layer. 相似文献
994.
Elke Roediger Marcus Brüggen Matthias Hoeft 《Monthly notices of the Royal Astronomical Society》2006,371(2):609-618
We present a sample of 30 wide-angle tailed radio galaxies (WATs) that we use to constrain the jet speeds in these sources. We measure the distribution of the jet-sidedness ratios for the sample, and assuming that the jets are beamed, the jet speeds in the range (0.3–0.7) c are obtained. Whilst the core prominence of the sample, which ought to be a reliable indicator of beaming, shows little correlation with the jet sidedness, we argue that due to the peculiar nature of the WATs, core prominence is unlikely to be a good indicator of beaming in these sources. We further show that if the jets are fast and light, then the galaxy speeds required to bend the jets into C-shapes such as those seen in 0647+693 are reasonable for a galaxy in a merging or recently merged cluster. 相似文献
995.
Nesibe Köse Abdurrahim Aydın Ünal Akkemik Hüseyin Yurtseven Tuncay Güner 《Natural Hazards》2010,54(2):435-449
Many parts of our planet are exposed to natural disasters such as snow avalanches, floods and earthquakes. Detailed knowledge
on these natural disasters is crucial for human safety. On December 25–26, 1992, two avalanches occurred at Kayaarkası-Kastamonu
in northern Turkey. The first avalanche took place at night of 25–26 December and caused no damage. The second avalanche took
place at morning of 26 December, killed four people and did damage to properties. The purpose of the present study is to determine
the effects of the snow avalanches on tree rings and to investigate the boundaries and velocities of the avalanches using
a numerical simulation model and the tree-ring data. Increment cores from 71 trees in the avalanche-impacted area and the
control site were sampled to obtain individual standard chronologies. In the analyses, trees were grouped as (1) heavily damaged
by the avalanche, showing a decrease in tree-ring widths since the event, (2) trees heavily damaged by the avalanche, showing
an increase in tree-ring widths a couple of years later the event and (3) trees that were not damaged by the avalanche. In
this study, one of the most important results is the precise determination of the temporal and spatial patterns of the undocumented
avalanche (the first avalanche) event. Avalanches were numerically simulated using dynamical avalanche simulation software
ELBA+. Comparison of the simulation model with tree-ring analysis revealed valuable results about the boundaries of the zone
of influence of the avalanches. 相似文献
996.
Zusammenfassung Im System Fe–Mn–W–O wurden die heterogenen Gleichgewichte bei 1000°C ausgehend von allen binären und ternären Randsystemen untersucht. Im System Fe–Mn–W wurde die intermetallische Verbindung Mn5Fe2,7W2,3 gefunden. Im System Fe–Mn–O gibt es keine ternären Verbindungen, in den anderen Dreistoffsystemen nur FeWO4, Fe2WO6 und MnWO4. Mn2WO6 ließ sich bis pO2=100 atm nicht darstellen. Quaternäre Verbindungen fehlen völlig. ZnWO4 und NiWO4 sind gegen FeO und MnO nicht stabil und reagieren zu FeWO4 und MnWO4 plus ZnO und NiO. Hydrothermal konnte bei pH2O=2000 atm vollständige Mischbarkeit von FeWO4 und MnWO4 bis 160°C herab nachgewiesen werden. Die früher (Schröcke, 1960) durch Festkörperreaktionen festgestellte asymmetrische Mischungslücke im System FeWO4–NiWO4 konnte korrigiert werden,T
kj
=525°C,x
kr
=0.15 FeWO4. FeWO4–ZnWO4 und MnWO4–ZnWO4 sind bis mindestens 414°C, MnWO4 und NiWO4 bis mindestens 454°C herab vollständig mischbar.
Mit 6 Abbildungen 相似文献
Heterogeneous equilibria in the Wolframite group
Summary In the system Fe–Mn–W–O solid state equilibria at 1000°C were determined beginning with all binary and ternary bordering systems. In the system Fe–Mn–W the ternary phase Mn5Fe2.7W2.3 was found. In the system Fe–Mn–O there does not exist any ternary phase. In the other systems only FeWO4, Fe2WO6 and MnWO4 exist. Mn4WO6 could not be synthesized up to 100 atm partial pressure of oxygen. Quaternary phases do not exist. ZnWO4 and NiWO4 are not stable in coexistence with FeO and MnO oxides. Reaction products are always FeWO4 or MnWO4 with ZnO or NiO. Hydrothermal studies at pH2O=2000 atm showed complete solid solution in the system FeWO4–MnWO4 down to 160°C.Schröcke (1960) found an asymmetrical miscibility gap in the system FeWO4–NiWO4 by means of solid state reactions. Now this miscibility gap has been corrected: Critical temperature 525°C, critical composition 0,15 FeWO4. Complete miscibility exists in the systems FeWO4–ZnWO4 and MnWO4–ZnWO4 down to at least 414°C, in the system MnWO4–NiWO4 down to at least 454°C.
Mit 6 Abbildungen 相似文献
997.
Regolith breccia Northwest Africa 7533: Mineralogy and petrology with implications for early Mars 下载免费PDF全文
Roger H. Hewins Brigitte Zanda Munir Humayun Alexander Nemchin Jean‐Pierre Lorand Sylvain Pont Damien Deldicque Jeremy J. Bellucci Pierre Beck Hugues Leroux Maya Marinova Laurent Remusat Christa Göpel Eric Lewin Marion Grange Allen Kennedy Martin J. Whitehouse 《Meteoritics & planetary science》2017,52(1):89-124
Northwest Africa 7533, a polymict Martian breccia, consists of fine‐grained clast‐laden melt particles and microcrystalline matrix. While both melt and matrix contain medium‐grained noritic‐monzonitic material and crystal clasts, the matrix also contains lithic clasts with zoned pigeonite and augite plus two feldspars, microbasaltic clasts, vitrophyric and microcrystalline spherules, and shards. The clast‐laden melt rocks contain clump‐like aggregates of orthopyroxene surrounded by aureoles of plagioclase. Some shards of vesicular melt rocks resemble the pyroxene‐plagioclase clump‐aureole structures. Submicron size matrix grains show some triple junctions, but most are irregular with high intergranular porosity. The noritic‐monzonitic rocks contain exsolved pyroxenes and perthitic intergrowths, and cooled more slowly than rocks with zoned‐pyroxene or fine grain size. Noritic material contains orthopyroxene or inverted pigeonite, augite, calcic to intermediate plagioclase, and chromite to Cr‐bearing magnetite; monzonitic clasts contain augite, sodic plagioclase, K feldspar, Ti‐bearing magnetite, ilmenite, chlorapatite, and zircon. These feldspathic rocks show similarities to some rocks at Gale Crater like Black Trout, Mara, and Jake M. The most magnesian orthopyroxene clasts are close to ALH 84001 orthopyroxene in composition. All these materials are enriched in siderophile elements, indicating impact melting and incorporation of a projectile component, except for Ni‐poor pyroxene clasts which are from pristine rocks. Clast‐laden melt rocks, spherules, shards, and siderophile element contents indicate formation of NWA 7533 as a regolith breccia. The zircons, mainly derived from monzonitic (melt) rocks, crystallized at 4.43 ± 0.03 Ga (Humayun et al. 2013 ) and a 147Sm‐143Nd isochron for NWA 7034 yielding 4.42 ± 0.07 Ga (Nyquist et al. 2016 ) defines the crystallization age of all its igneous portions. The zircon from the monzonitic rocks has a higher Δ17O than other Martian meteorites explained in part by assimilation of regolith materials enriched during surface alteration (Nemchin et al. 2014 ). This record of protolith interaction with atmosphere‐hydrosphere during regolith formation before melting demonstrates a thin atmosphere, a wet early surface environment on Mars, and an evolved crust likely to have contaminated younger extrusive rocks. The latest events recorded when the breccia was on Mars are resetting of apatite, much feldspar and some zircons at 1.35–1.4 Ga (Bellucci et al. 2015 ), and formation of Ni‐bearing pyrite veins during or shortly after this disturbance (Lorand et al. 2015 ). 相似文献
998.
The classical integral formula for determining the indirect effect in connection with the Stokes–Helmert method is related
to a planar approximation of the sea level. A strict integral formula, as well as some approximations to it, are derived.
It is concluded that the cap- size truncated integral formulas will suffer from the omission of some long-wavelength contributions,
of the order of 50 cm in high mountains for the classical formula. This long-wavelength information can be represented by
a set of spherical harmonic coefficients of the topography to, say, degree and order 360. Hence, for practical use, a combination
of the classical formula and a set of spherical harmonics is recommended.
Received: 10 March 1998 / Accepted: 16 November 1998 相似文献
999.
The paper addresses the individual and collective contribution of different forcing factors (tides, wind waves, and sea-level rise) to the dynamics of sediment in coastal areas. The results are obtained from simulations with the General Estuarine Transport Model coupled with a sediment transport model. The wave-induced bed shear stress is formulated using a simple model based on the concept that the turbulent kinetic energy (TKE) associated with wind waves is a function of orbital velocity, the latter depending on the wave height and water depth. A theory is presented explaining the controls of sediment dynamics by the TKE produced by tides and wind waves. Several scenarios were developed aiming at revealing possible trends resulting from realistic (observed or expected) changes in sea level and wave magnitude. The simulations demonstrate that these changes not only influence the concentration of sediment, which is very sensitive to the magnitude of the external forcing, but also the temporal variability patterns. The joint effect of tides and wave-induced bed shear stress revealed by the comparison between theoretical results and simulations is well pronounced. The intercomparison between different scenarios demonstrates that the spatial patterns of erosion and deposition are very sensitive to the magnitude of wind waves and sea-level rise. Under a changing climate, forcing the horizontal distribution of sediments adjusts mainly through a change in the balance of export and import of sediment from the intertidal basins. The strongest signal associated with this adjustment is simulated North of the barrier islands where the evolution of sedimentation gives an integrated picture of the processes in tidal basins. 相似文献
1000.
Ann-Sofi Smedman Sven-Erik Gryning Karl Bumke Ulf H gstr m Anna Rutgersson Ekaterina Batchvarova Gerhard Peters Barbara Hennemuth Bengt Tammelin Reijo Hyv nen Anders Omstedt Daniel Michelson Tage Andersson Marco Clemens 《Journal of Atmospheric & Ocean Science》2005,10(3):163-191
Precipitation and evaporation budgets over the Baltic Sea were studied in a concerted project called PEP in BALTEX (Pilot study of Evaporation and Precipitation in the Baltic Sea), combining extensive field measurements and modelling efforts. Eddy-correlation-measurements of turbulent heat flux were made on a semi-continuous basis for a 12 month period at four well-exposed coastal sites in the Baltic Proper (the main basin of the Baltic Sea). Precipitation was measured at land-based sites with standard gauges and on four merchant ships travelling between Germany and Finland with the aid of specially designed ship rain gauges (SRGs). The evaporation and precipitation regime of the Baltic Sea was modelled for a 12 month period by applying a wide range of numerical models: the operational atmospheric High Resolution Limited Area Model (HIRLAM, Swedish and Finnish versions), the German atmospheric REgional-scale MOdel, REMO, the operational German Europe Model (only precipitation), the oceanographic model PROBE-Baltic, and two models that use interpolation of ground-based data, the Swedish MESAN model of SMHI and a German model of IFM-GEOMAR Kiel. Modelled precipitation was compared with SRG measurements on board the ships. A reasonable correlation was obtained, but the regional-scale models and MESAN gave some 20% higher precipitation over the sea than is measured. Bulk parameterisation schemes for evaporation were evaluated against measurements. A constant value of CHN and CEN with wind speed, underestimated large fluxes of both sensible and latent heat flux. The limited area models do not resolve the influence of the height of the marine boundary layer in coastal zones and the entrainment (on the surface fluxes), which may explain the observed low correlations between modelled and measured latent heat fluxes. Estimates of evaporation, E, and precipitation, P, for the entire Baltic Proper were made with several models for a 12 month period. While the annual variation was well represented by all predictions, there are still important differences in the annual means. Evaporation ranges from 509 to 625 mm year-1 and precipitation between 624 and 805 mm year-1 for this particular 12 month period. Taking the results of model verification from the present study into account, the best estimate of P-E is about 100 ± 50 mm for this particular 12 month period. But the annual mean of P-E varies considerably from year to year. This is reflected in simulations with the PROBE-Baltic model for an 18 year period, which gave 95 mm year-1 for the 12 month period studied here and 32 mm year-1 as an average for 18 years. 相似文献