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11.
Geotechnical and Geological Engineering - The physical and chemical characteristics of water critically influence the mechanical and chemical breakdown of rocks. The physical properties of rocks,... 相似文献
12.
R. Hasan 《洁净——土壤、空气、水》1988,16(6):573-578
The present investigation gives the turnover value and productivity of macrophytes like Eichhornia crassipes, Hydrilla verticillata, Ceratophyllum demersum, Potamogeton crispus and Azolla pinnata for the year 1978 at Koylaghat site of the Champanala channel, a southern side spill channel of the river Ganges. The average annual production of all the macrophytes comes to 3.925 g/m2 · d, which is better than the world average of rice cultivated fields. All the important macrophytes in the present investigation are replaced annually. In contrast to pond and reservoir ecosystems, where the productivity of macrophytes is highest in the rainy season, in the Champanala channel the most of the macrophytes are absent from July to December and maximal productivity was about 4 g/m2 · d from February to April. The difference in the development of macrophytes in standing and flowing waters results from the fact that in the rainy season increasing flow velocity, sudden fluctuations in water column depth and other destabilising factors produce unfavourable conditions for macrophytes in flowing waters. 相似文献
13.
ABSTRACTAdvances in open data science serve large-scale model developments and, subsequently, hydroclimate services. Local river flow observations are key in hydrology but data sharing remains limited due to unclear quality, or to political, economic or infrastructure reasons. This paper provides methods for quality checking openly accessible river-flow time series. Availability, outliers, homogeneity and trends were assessed in 21 586 time series from 13 data providers worldwide. We found a decrease in data availability since the 1980s, scarce open information in southern Asia, the Middle East and North and Central Africa, and significant river-flow trends in Africa, Australia, southwest Europe and Southeast Asia. We distinguish numerical outliers from high-flow peaks, and integrate all investigated quality characteristics in a composite indicator. We stress the need to maintain existing gauging networks, and highlight opportunities in extending existing global databases, understanding drivers for trends and inhomogeneity, and in innovative acquisition methods in data-scarce regions. 相似文献
14.
The NASA Office of Space Science has established a series of archivalcenters where science data acquired through its space science missionsis deposited. The availability of high quality data to the generalpublic through these open archives enables the maximization of sciencereturn of the flight missions. The Astrophysics Data Centers CoordinatingCouncil, an informal collaboration of archival centers, coordinates datafrom five archival centers distiguished primarily by the wavelength rangeof the data deposited there. Data are available in FITS format. Anoverview of NASA's data centers and services is presented in this paper.A standard front-end modifyer called Astrowbrowse is described. Othercatalog browsers and tools include WISARD and AMASE supported by theNational Space Scince Data Center, as well as ISAIA, a follow on toAstrobrowse. 相似文献
15.
Priya Hasan 《Astrophysics and Space Science》2007,312(1-2):63-77
Using HST/ACS images in four bands F435W, F606W, F775W and F850LP, we identify optical counterparts to the X-ray sources in
the Chandra Deep Field South in the GOODS South field. A detailed study has been made of these sources to study their morphological
types. We use methods like decomposition of galaxy luminosity profiles, color maps and visual inspection of 192 galaxies which
are identified as possible optical counterparts of Chandra X-ray sources in the CDFS-GOODS field. We find that most moderate
luminosity AGN hosts are bulge dominated in the redshift range (z≈0.4–1.3), but not merging/interacting galaxies. This implies probable fueling of the moderate luminosity AGN by mechanisms
other than those merger driven. 相似文献
16.
S.I. Recca E.R.D. Scott K. Keil R.N. Clayton T.K. Mayeda G.I Huss E. Jarosewich K.S. Weeks F.A. Hasan D.W.G. Sears R. Wieler P. Signer 《Meteoritics & planetary science》1986,21(2):217-229
The Ragland, New Mexico chondrite was found in 1978, and consists of a single stone of 12.16 kg that broke into three pieces. The stone is moderately weathered and has a pronounced chondritic texture. Bulk composition favors an LL classification, and modal analysis and oxygen isotopic composition are consistent with this. The thermoluminescence sensitivity of 0.056 ± 0.020 normalized to Dhajala, compositional variability of olivine (mean Fa 18.3, σ = 10.1) and low-Ca pyroxene (mean Fs 14.6, σ = 6.7), and Ca concentrations in olivine indicate metamorphic subtype 3.4 ± 0.1. The isotopically heavy oxygen composition, which is characteristic of subtypes 3.0–3.1, may be a primary characteristic and not a result of weathering. Low concentrations of radiogenic 40Ar and planetary 36Ar suggest noble gas loss. 相似文献
17.
The solar atmosphere is magnetically structured and highly dynamic. Owing to the dynamic nature of the regions in which the
magnetic structures exist, waves can be excited in them. Numerical investigations of wave propagation in small-scale magnetic
flux concentrations in the magnetic network on the Sun have shown that the nature of the excited modes depends on the value
of plasma β (the ratio of gas to magnetic pressure) where the driving motion occurs. Considering that these waves should give rise to
observable characteristic signatures, we have attempted a study of synthesised emergent spectra from numerical simulations
of magneto-acoustic wave propagation. We find that the signatures of wave propagation in a magnetic element can be detected
when the spatial resolution is sufficiently high to clearly resolve it, enabling observations in different regions within
the flux concentration. The possibility to probe various lines of sight around the flux concentration bears the potential
to reveal different modes of the magnetohydrodynamic waves and mode conversion. We highlight the feasibility of using the
Stokes-V asymmetries as a diagnostic tool to study the wave propagation within magnetic flux concentrations. These quantities can
possibly be compared with existing and new observations in order to place constraints on different wave excitation mechanisms. 相似文献
18.
Thermal convection is the motor of Earth dynamics and therefore is the link between plate motions, hotspots, seismic velocity variations in the mantle, and anomalies of the gravity field. Small scale mantle anomalies, such as plumes, do, however, generally escape detection by tomographic methods. It is attempted to approach the problem of detection in a somewhat statistical manner. Correlations are sought between spherical harmonic expansions of the fields under study: the hotspot distribution, mantle velocity variations, gravity, heat flow. Using spherical harmonic representations of global fields implies integration and averaging over the whole globe. Thus, although relationships may remain masked in the space domain by a multitude of effects, tendencies may become visible in the spectra or in appropriate averages.The main results are the following: There is a significant long wavelength (n=2,3) negative correlation between the hotspot density and the P-wave velocity variation in the lower mantle. Positive hotspot density of degree 2 to 9 generally correlates with low seismic velocity in all depths of the upper mantle and with positive gravity. This fits well with plume-type convection. These results are also confirmed regionally for a number of individual mid-ocean ridges and hotspots. The hotspot density and the free air anomalies are distinctly positive above regions of low velocity extending to great depth. The effect is not distinct at ridges with shallow velocity anomalies. In a general way, we suggest that the antipodal upwellings (Pacific, Africa) are divided by downwelling currents around the shrinking Pacific. Plate boundaries can easily move away from their past connections with the deeper mantle. Small scale plume currents seem to be depicted in the hotspot expansion. © 1999 Elsevier Science Ltd. All rights reserved. 相似文献
19.
20.
Geochemical background in soils: a linear process domain? An example from Istria (Croatia) 总被引:1,自引:1,他引:0
Definition of geochemical background in exploration and environmental geochemistry has always been regarded as contingent
upon scale and investigated locality but mostly under assumption that hosts of processes that produce the data more or less
conform individually to Gaussian law of “central tendencies”. Recently, understanding of pedogenesis as synergetic process
being characterized by non-linear dynamics renders thermodynamic approach directly applicable in assessment of geochemical
thresholds, with concepts of linearity and normality set alongside in solving the problems of soil geochemistry. Seen from
this perspective the work is an attempt to relate conceptual fundamentals of non-linear dynamical theory to basic statistical
methods in order to elucidate the nature and origins of element subpopulations hidden in the original geochemical data from
the soils of Istrian Peninsula (western Croatia). To this purpose the two major groups of soils were selected for analysis
depending on the type of bedrock as one of the main soil-forming factors. Geochemical data were subjected to the trimming
procedure by which the outliers were removed from the total data collective and attributed to non-linear causes precluding
simple cause-and-effect relationships as the sine qua non of Gaussian distribution. Geochemical background is then defined as the normal range of data of the remaining (trimmed) dataset
indicating the “thermodynamic branch” of the specific soil processes as opposed to outliers being described as dissipative
structures. 相似文献