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121.
John W. Johnston Todd A. Thompson Douglas A. Wilcox Steve J. Baedke 《Journal of Paleolimnology》2007,37(3):349-364
A common break was recognized in four Lake Superior strandplain sequences using geomorphic and sedimentologic characteristics.
Strandplains were divided into lakeward and landward sets of beach ridges using aerial photographs and topographic surveys
to identify similar surficial features and core data to identify similar subsurface features. Cross-strandplain, elevation-trend
changes from a lowering towards the lake in the landward set of beach ridges to a rise or reduction of slope towards the lake
in the lakeward set of beach ridges indicates that the break is associated with an outlet change for Lake Superior. Correlation
of this break between study sites and age model results for the strandplain sequences suggest that the outlet change occurred
sometime after about 2,400 calendar years ago (after the Algoma phase). Age model results from one site (Grand Traverse Bay)
suggest an alternate age closer to about 1,200 calendar years ago but age models need to be investigated further. The landward
part of the strandplain was deposited when water levels were common in all three upper Great Lakes basins (Superior, Huron,
and Michigan) and drained through the Port Huron/Sarnia outlet. The lakeward part was deposited after the Sault outlet started
to help regulate water levels in the Lake Superior basin. The landward beach ridges are commonly better defined and continuous
across the embayments, more numerous, larger in relief, wider, have greater vegetation density, and intervening swales contain
more standing water and peat than the lakeward set. Changes in drainage patterns, foreshore sediment thickness and grain size
help in identifying the break between sets in the strandplain sequences. Investigation of these breaks may help identify possible
gaps in the record or missing ridges in strandplain sequences that may not be apparent when viewing age distributions and
may justify the need for multiple age and glacial isostatic adjustment models.
This is the third in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were
presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University
of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue.
The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged. 相似文献
122.
Fernando Saboya Jr. Maria da Glória Alves Wendell Dias Pinto 《Engineering Geology》2006,86(4):211-224
Generally, the process of land occupation in urban areas involves spaces that are not suitable for construction. In most cases these areas are subject to landslides. Therefore it is mister the development of models to evaluate the susceptibility of occurrence of landslides in these areas. For this, Fuzzy Logic is used herein for modeling such areas where landslides are susceptible to occur and, therefore, a direct evaluation is important. The possibility of capturing the judgment and the modeling of linguistic variables are the main advantages of using Fuzzy Logic. These models are capable to capture the factors directly affecting the slope stability and also the inter-relationship amongst them. These factors were chosen by experts to whom a questionnaire was sent. Fuzzy Logic was then used to transform the linguistic variables into fuzzy number, allowing thus, the calculation of failure potential index (FPI). Herein the MAX-MIN Mamdani strategy for the inference of the rule base was used. This methodology has been applied to identify the susceptibility of landslides in a chaotic occupied urban area of Itaperuna City in northeastern of Rio de Janeiro, Brazil, where some occurrences have been reported. 相似文献
123.
Benjamin H. Passey Thure E. Cerling Todd F. Robinson Stephen K. Krueger 《Geochimica et cosmochimica acta》2005,69(16):4101-4116
Mammalian teeth are invaluable archives of ancient seasonality because they record along their growth axes an isotopic record of temporal change in environment, plant diet, and animal behavior. A major problem with the intra-tooth method is that intra-tooth isotope profiles can be extremely time-averaged compared to the actual pattern of isotopic variation experienced by the animal during tooth formation. This time-averaging is a result of the temporal and spatial characteristics of amelogenesis (tooth enamel formation), and also results from laboratory sampling. This paper develops and evaluates an inverse method for reconstructing original input signals from time-averaged intra-tooth isotope profiles. The method requires that the temporal and spatial patterns of amelogenesis are known for the specific tooth and uses a minimum length solution of the linear system Am = d, where d is the measured isotopic profile, A is a matrix describing temporal and spatial averaging during amelogenesis and sampling, and m is the input vector that is sought. Accuracy is dependent on several factors, including the total measurement error and the isotopic structure of the measured profile. The method is shown to accurately reconstruct known input signals for synthetic tooth enamel profiles and the known input signal for a rabbit that underwent controlled dietary changes. Application to carbon isotope profiles of modern hippopotamus canines reveals detailed dietary histories that are not apparent from the measured data alone. Inverse methods show promise as an effective means of dealing with the time-averaging problem in studies of intra-tooth isotopic variation. 相似文献
124.
125.
Todd H. Skaggs 《Advances in water resources》2011,34(10):1335-1342
Critical path analysis (CPA) is a method for estimating macroscopic transport coefficients of heterogeneous materials that are highly disordered at the micro-scale. Developed originally to model conduction in semiconductors, numerous researchers have noted that CPA might also have relevance to flow and transport processes in porous media. However, the results of several numerical investigations of critical path analysis on pore network models raise questions about the applicability of CPA to porous media. Among other things, these studies found that (i) in well-connected 3D networks, CPA predictions were inaccurate and became worse when heterogeneity was increased; and (ii) CPA could not fully explain the transport properties of 2D networks. To better understand the applicability of CPA to porous media, we made numerical computations of permeability and electrical conductivity on 2D and 3D networks with differing pore-size distributions and geometries. A new CPA model for the relationship between the permeability and electrical conductivity was found to be in good agreement with numerical data, and to be a significant improvement over a classical CPA model. In sufficiently disordered 3D networks, the new CPA prediction was within ±20% of the true value, and was nearly optimal in terms of minimizing the squared prediction errors across differing network configurations. The agreement of CPA predictions with 2D network computations was similarly good, although 2D networks are in general not well-suited for evaluating CPA. Numerical transport coefficients derived for regular 3D networks of slit-shaped pores were found to be in better agreement with experimental data from rock samples than were coefficients derived for networks of cylindrical pores. 相似文献
126.
Jacinto GS Sotto LP Senal MI San Diego-McGlone ML Escobar MT Amano A Miller TW 《Marine pollution bulletin》2011,63(5-12):243-248
Herein we present results from one of the first extensive bay-wide oceanographic surveys of Manila Bay, wherein 31 stations were sampled during the northeast monsoon (cold and dry season). A band of hypoxic bottom water (dissolved oxygen<2.8 mg/L) spanned the midsection of the bay from east to west. Bottom nitrate concentrations (5.7-16.8 μM; avg. 11.1 μM) and total organic carbon values in sediments (1.7-3.1%; avg. 2.4%) were high in the midsection, which coincided with the band of hypoxic bottom water. Physical processes and site-specific accumulation of organic material likely lead to hypoxic conditions in Manila Bay, even during the northeast monsoon period when the water column is relatively well mixed. The results of this study complement the previously reported widespread hypoxia that occurs during the rainy season. Thus, hypoxia may be pervasive in the bay throughout the year, although it varies in intensity and spatial extent. 相似文献
127.
Deformation and fluid pressure during constant-rate pumping tests were characterized by sensitivity analyses using a theoretical model of a deformable fracture, and by conducting and analyzing field tests at a site underlain by fractured biotite gneiss in western South Carolina, USA. The sensitivity analysis indicates that displacement is a hysteretic function of fluid pressure during constant-rate pumping tests, and the signals are affected by properties of the fracture (normal stiffness, aperture, and heterogeneities in the fracture plane) and enveloping rock (elastic modulus and permeability). The field tests used a removable borehole extensometer to measure axial displacements in the pumping well. The field results are generally similar to simulations, and the hydraulic and mechanical properties obtained by inversion of the pumping test results are essentially the same as results from hydromechanical slug tests. The observed displacements early in the pumping tests are less than, whereas late in the test they are greater than predicted values assuming a uniform fracture. This difference can be explained as a consequence of preferential flow within the fracture. These results indicate that displacements in a wellbore are sensitive to details of fracture connectivity and preferential flow that are difficult to detect through the pressure signal alone. 相似文献
128.
129.
When globally mapping the observed photospheric magnetic field into the corona, the interaction of the solar wind and magnetic
field has been treated either by imposing source surface boundary conditions that tacitly require volume currents outside
the source surface (Schatten, Wilcox, and Ness, 1969) or by limiting the interaction to thin current sheets between oppositely
directed field regions (Wolfson, 1985). Yet observations and numerical MHD calculations suggest the presence of non-force-free
volume currents throughout the corona as well as thin current sheets in the neighborhoods of the interfaces between closed
and open field lines or between oppositely directed open field lines surrounding coronal helmet-streamer structures. This
work presents a model including both horizontal volume currents and streamer sheet currents. The present model builds on the
magnetostatic equilibria developed by Bogdan and Low (1986) and the current-sheet modeling technique developed by Schatten
(1971). The calculation uses synoptic charts of the line-of-sight component of the photospheric magnetic field measured at
the Wilcox Solar Observatory. Comparison of an MHD model with the calculated model results for the case of a dipole field
and comparison of eclipse observations with calculations for CR 1647 (near solar minimum) show that this horizontal current-current-sheet
model reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces coronal helmet
structures better than the current-sheet model. 相似文献
130.
Reflectance spectra of Mercury, covering the spectral range of ~0.3–1.1 μm obtained during 1963–1976, were examined for any correlations with surface terrain. Mercury's 6.1385°/day rotational rate, the phases of the planet around maximum elongations, and bidirectional reflectance spectroscopy theory were used to identify the surface area associated with each spectrum. Data from 1974–1975, re-reduced with improved standard star flux ratios, show a weak absorption band in the near infrared not see in earlier analyses. Older spectra suggest that the western longitudes of the unimaged side of Mercury are similar to the rest of the planet. Spectra of the intercrater plains in the 0–90° quadrant suggest a possible absorption band. Spectra of areas dominated by Caloris Basin with the encompassing smooth plains may show Fe2+ abundances in the soil comparable to lunar highlands soil. No striking differences between spectra of intercrater plains and spectra of smooth plains are found. The absorption features seen in spectra of Mercury are generally weaker than features seen in lunar spectra. 相似文献