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21.
Rob N. J. Comans Cornelis H. Van Der Weijden Simon P. Vriend 《Environmental Geology》1987,9(2):119-128
A hydrogeochemical study of the impact of land use on the composition of natural waters in the Vouzela region in northern
Portugal was carried out during the summer of 1983. Water samples were collected from spring and major streams in the area
and analyzed for major constituents and some trace elements. Analysis of variance and subsequent pairwise contrast tests demonstrated
that waters from agricultural areas are significantly enriched in constiluents such as Na, K, Ca, Mg, Sr, Cl, SO4, and NO3. High concentrations of these ions in agricultural areas are the result of both the application of fertilizers and enhanced
evaporation by the intensive irrigation of agricultural lands. Constitutents such as H4SiO4, HCO3, F, and probably Li, which are typically related to mineral weathering, were not affected by land use. In waters from forested
areas the concentration of most constituents was about 20% higher than in waters from uncultivated areas with mainly a grass
cover. This reflects the difference in the evapotranspiration of these two vegetation types. The chemistry of the Rio Zela
clearly reflects differences in land use in the Rio Zela valley. 相似文献
22.
Z.A. Der W.D. Rivers T.W. McElfresh A. ODonnell P.J. Klouda M.E. Marshall 《Physics of the Earth and Planetary Interiors》1982,30(1):12-25
A worldwide study of short-period teleseismic body wave spectra shows that the high frequency falloff rates of spectra are correlated with the tectonic type of the source and receiver regions and with source depth. The data indicate, in a consistent manner, that the main cause for such variations is the lateral variation of Q in the upper mantle as well as change of Q with depth. Using the internal consistency checks provided by redundancies in the data set other effects such as crustal, site dependent distortion of the spectra, source effects and instrument non-linearity can be ruled out as significant factors influencing the estimates obtained. The results indicate high attenuation in the upper mantle under tectonic regions and new oceans. Long-period regional attenuation studies indicate similar variations in mantle Q among the types of regions mentioned but yield significantly lower Q estimates in all areas. The short- and long-period attenuation results can be reconciled only by assuming a frequency dependent Q that increases with frequency along all types of paths, such that the relative differences in Q along various types of paths retain the same sign over the short- and long-period bands. 相似文献
23.
An electrical substation consists of a complex set of equipment items that are interconnected through conductor buses or cables. If the connections are not sufficiently flexible, significant dynamic interaction may occur between the connected equipment items during a seismic excitation. This interaction is believed to be responsible for some of the observed substation equipment damage in recent earthquakes. This paper investigates the interaction between two equipment items connected by a linear spring‐dashpot or spring‐dashpot‐mass element representing a conductor bus. It is found that the interaction between the two equipment items may significantly amplify the response of the higher‐frequency equipment item. The influences of various key parameters on the interaction effect are quantified. Means for reducing the adverse interaction effect are described. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
24.
The extent of the deposition and of the preservation of the Blouberg Formation and Waterberg Group was at least partially controlled by brittle reactivation along the Palala Shear Zone. The Palala Shear Zone in the Blouberg area (Northern Province, South Africa) is characterised by granulite-grade gneiss, and formed by sinistral transpressional collision between the Southern Marginal Zone (Kaapvaal Craton) and the Central Zone of the Limpopo Belt. The Limpopo collision is thought to have occurred either at 2.0 Ga or at 2.7 Ga with reactivation at 2.0 Ga. Deposition of the Blouberg Formation was characterised by syn-sedimentary tectonism, which is reflected by a sudden upward coarsening in sedimentary rocks, and by the presence of a strongly folded and thrusted lower member. Bedding orientations and slickenside lineation orientations suggest that vergence was towards the south, and such a tectonism can be inferred to have produced a highland area to the north, bound on the southern margin by the southern strand of the Melinda Fault. The presence of an inferred northerly upland area is supported by palaeocurrent directions and the preservational extent of the Setlaole and Makgabeng Formations of the Waterberg Group (post-Blouberg Formation). The extent and stratigraphy of the overlying Mogalakwena Formation suggests that these strata onlapped northwards over the denuding highlands. Younger Sibasa basalts of the Soutpansberg Group have been dated at ca. 1.85 Ga. Blouberg and Waterberg strata can therefore be interpreted as syn- and post-tectonic sedimentary rocks, respectively, following a ca. 2.0 reactivation event along the Palala Shear Zone. It is difficult to reconcile the succession of geological events at Blouberg with a ca. 2.0 Ga Limpopo orogeny, and thus sedimentary strata in the study area support a 2.7 Ga date for Limpopo collision, with syn-Blouberg tectonism relating to ca. 2.0 reactivation within the previously assembled Limpopo Belt. 相似文献
25.
The CQC rule for modal combination is extended to include the quasi-static contribution of truncated modes and the effects of input narrow-bandedness and cut-off frequency. A simple measure of the error in approximating a high-frequency modal response by its quasi-static contribution is derived. The extended rule is applicable to structures with high-frequency modes and to seismic inputs which may not be regarded as wide band. Numerical examples demonstrate the significance of input bandwidth and cut-off frequency on modal cross-correlation coefficients, and on the error resulting from truncation of high-freqeuncy modes. 相似文献
26.
Summary The method of predictive deconvolution is described and applied to seismograms from the 1963 Lake Superior experiment. The process is successful in removing shot-generated reverberations and sometimes reveals seismic phases which are not easily identifiable on the original seismograms. 相似文献
27.
Transition from elliptic to hyperbolic orbits in the two-body problem with slowly decreasing mass is investigated by means of asymptotic approximations.Analytical results by Verhulst and Eckhaus are extended to construct approximate solutions for the true anomaly and the eccentricity of the osculating orbit if the initial conditions are nearly-parabolic. It becomes clear that the eccentricity will monotonously increase with time for all mass functions satisfying a Jeans-Eddington relation and even for a larger set of functions. To illustrate these results quantitatively we calculate the eccentricity as a function of time for Jeans-Eddington functionsn=0(1) 5 and 18 nearly-parabolic initial conditions to find that 93 out of 108 elliptic orbits become hyperbolic. 相似文献
28.
The results of the spectral classification of newly discovered M-type variables obtained as part of an H-alpha survey of Galactic dark cloud regions are presented. The survey was carried out with the 40 Schmidt camera of Byurakan Observatory, and the spectra of the variable stars for the classification were obtained with the Observatory's 2.6-m telescope. The observational material allowed register of late M-type variables as well as their brightness variations. Among the 97 newly discovered M-type stars, 22 show brightness variations. The results of the spectral classification of these new variables show that 21 out of 22 are red giants, and in all probability they are Mira Ceti type long period variables. 相似文献
29.
The Inclusion of Stakeholder Knowledge and Perspectives in Integrated Assessment of Climate Change 总被引:1,自引:0,他引:1
Over the past few decades Integrated Assessment (IA) has emerged as an approach to link knowledge and action in a way that
is suitable to accommodate uncertainties, complexities and value diversities of global environmental risks. Responding to
the complex nature of the climate problem and to the changing role of climate change in the international climate policy process,
the scientific community has started to include stakeholder knowledge and perspectives in their assessments. Participatory
Integrated Assessment (PIA) is in its early stage of development. Methodology varies strongly across PIA projects. This paper
analyzes four recent IA projects of climate change that included knowledge or perspectives from stakeholders in one-way or
another. Approaches and methods used turn out to differ in whether stakeholders are involved actively or passively, whether
the approach is bottom-up or top-down, and whether the different functions in the IA process are open or closed to stakeholder
input. Also, differences can be seen in the degree to which boundaries are pre-set that limit the roles and domains of competencies
attributed to each scientific or non-scientific participant (so-called boundary work). The paper discusses pros and cons of
the various approaches identified, and outlines heuristics and considerations to assist those who plan, design or fund new
IA processes with stakeholder input on what approaches best to choose in view of the objectives for stakeholder involvement,
in view of the role that the IA plays in the overall risk management process and in view of considerations regarding boundary
work. 相似文献
30.
The Woodlands Formation (uppermost Pretoria Group) of eastern Botswana overlies thick quartzites of the Sengoma Formation (Magaliesberg Formation) and comprises a lower unit of interbedded mudrocks and fine-grained recrystallised quartzitic sandstones, succeeded by chaotic and very coarse-grained inferred slump deposits. Within the adjacent western region of South Africa, interbedded mudrocks and quartzitic sandstones stratigraphically overlying the Magaliesberg Formation are now assigned to the lower Woodlands Formation. Within the entire region, interference folding produced by northeast-southwest (F1 and F3) and northwest-southeast (F2) compression, and concomitant faulting characterised inversion of the Pretoria Group basin. This deformation is of pre-Bushveld age and affected all units in the Pretoria Group, including the uppermost Silverton, Magaliesberg and Woodlands Formations, and intrusive Marico Hypabyssal Suite (pre-Bushveld) mafic sills. The Nietverdiend lobe of the Bushveld Complex, intrusive into this succession, was not similarly deformed. Movement along the major Mannyelanong Fault in the northwest of the study area post-dated Transvaal Basin inversion, after which the “upper Woodlands” chaotic slump deposits were formed. The latter must thus belong to a younger stratigraphical unit and is possibly analogous to apparently syntectonic sedimentary rocks (Otse Group) in the Otse Basin of eastern Botswana. 相似文献