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101.
Mixing in a two-layer stably stratified fluid by a turbulent jet was studied by a laboratory experiment. A non-swirling jet was discharged vertically downwards in a confined fluid system consisting initially of a top layer of fresh water and a bottom layer of salt water. In total, 16 experimental cases were considered, where the diameter and exit velocity of the jet were varied together with the density difference between the top and bottom layer. Vertical density profiles were determined from conductivity measurements. A three-layer density structure developed in all cases with an intermediate layer that grew in size with time elapsed as fresh and salt water were mixed. The mixing efficiency, defined as the percentage of the supplied kinetic jet energy that is used for increasing the potential energy of the fluid system, was related to a densimetric Froude number based on the intermediate layer depth. Overall, the calculated jet mixing efficiency displayed higher values than comparable efficiencies for destratification with air-bubble plumes. 相似文献
102.
103.
Magnetic lineations in the Pacific Jurassic quiet zone 总被引:1,自引:0,他引:1
Steven C. Cande Roger L. Larson John L. LaBrecque 《Earth and Planetary Science Letters》1978,41(4):434-440
Magnetic anomalies of low amplitude (<100 gammas) are present in the Jurassic magnetic quiet zone of the western Pacific Ocean. These small anomalies are lineated and can be correlated among the Phoenix, Hawaiian and Japanese lineation patterns. Thus, they represent seafloor spreading that recorded some sort of magnetic field phenomena prior to magnetic anomaly M25 at 153 m.y. B.P. The most likely possibility is that they represent a series of late Jurassic magnetic field reversals that occurred during a period of anomalously low magnetic field intensity. We propose a time scale of magnetic reversals between 153 and 158 m.y. B.P. to account for these anomalies and suggest that the dipole magnetic field intensity increased by a factor of about four from 160 to 140 m.y. B.P. in the late Jurassic. 相似文献
104.
Analytical heat transfer calculations are used to relate geological surface evidence to conditions that should exist in magma chambers for the purpose of improving estimates of possible commercial heat extraction rates. These calculations indicate that an upward-melting magma system necessarily is approximately equidimensional and that injected magmas with very high aspect (L/D) ratios are likely formed by a forced intrusion process which involves little if any melting or natural convection. Calculations along with surface heat flow measurements suggest that steady-state heat extraction rates for emplaced heat exchangers in currently suspected shallow magma chambers will probably be below 10 kW m−2, a value that is low by engineering standards. 相似文献
105.
A palaeomagnetic study of dolerites spread over a large area in the coastal part of Ångermanland, central Sweden, introduces a palaeopole close to poles obtained from Jotnian or post-Jotnian dolerites in Finland, implying that all these rocks belong to the same intrusive phase. 相似文献
106.
R. E. Larson D. J. Bressan K. W. Marlow T. A. Wojciechowski J. L. Heffter 《Pure and Applied Geophysics》1979,117(5):874-882
The concentrations of airborne fission products were observed to be air mass dependent during a cruise of the USNSHayes from Norfolk, Va to Athens, Greece in May–June 1977. Minimum concentrations of fission products, radon, and CCN (cloud condensation nuclei) were measured in maritime air which had previously transited northern North America. Higher fission products, radon, and CCN concentrations were measured in recent, continental air traceable to mid North America or central Europe. These data are consistent with either entrainment by strong winds of previously precipitated fission products (the continental effect) or greater transfer of fission products from the stratosphere to low levels by tropospheric folding. 相似文献
107.
John R. Moeller G. Wayne Minshall Kenneth W. Cummins Robert C. Petersen C.E. Cushing James R. Sedell R.A. Larson Robin L. Vannote 《Organic Geochemistry》1979,1(3):139-150
Transport of dissolved organic carbon (DOC) in four river systems in different physiographic regions of the United States was related to link magnitude by a power function, log Y = ?0.84 + 1.24 log X. Multiple linear regression indicated that discharge, watershed area, and link magnitude explained almost all variation in DOC transport. For purposes of ecosystem comparison, link magnitude appeared superior to other classification systems, such as stream order.In two of the river systems, the largest fraction of DOC was transported in the spring. A third has a winter transport maximum; the last had bimodal spring and fall maxima.Streams transporting similar total amounts of DOC may vary widely in DOC concentration (mg. 1?1). Particulate organic matter concentration was not simply related to that of DOC.Ranges and means of DOC concentration, mean DOC: POC ratios, annual load of transported DOC as well as annual watershed DOC output were tabulated for 45 streams and rivers, representing a broad range of stream systems and physiographic regions. Mean DOC concentration for these 45 waterways ranged from 0.7 to 28 mg. 1?1. The very low DOC values are found in undisturbed streams; many of the higher values are associated with larger streams influenced by human activities. Most DOC outputs fell within the range 0.21–5.42 metric tons. km?2.yr?1; mean DOC:POC ranged between 0.09 and 70.A comparison was made among several biomes of the ratio of experted DOC to watershed gross and net primary production. DOC, while playing a major role in aquatic ecosystem organic budgets, appears to be of little significance in the nutrient balance of watersheds. 相似文献
108.
J.M. Herndon M.W. Rowe E.E. Larson D.E. Watson 《Earth and Planetary Science Letters》1976,29(2):283-290
Thermomagnetic analysis was made on samples of all known C3 and C4 chondrites in a controlled oxygen atmosphere. Considerable variation was noted in the occurrence of magnetic minerals, comparable to the variation observed earlier in the C2 chondrites. Magnetite was found as the only major magnetic phase in samples of only three C3 chondrites (2–4 wt.%) and the Karoonda C4 chondrite (7.7 wt.%). The magnetite content of these three C3 chondrites is only about one-third that observed in the C1 and C2 chondrites which were found to contain magnetite as the only magnetic phase. Five C3 chondrites were observed to undergo chemical change during heating, producing magnetite: this behavior is characteristic of troilite oxidation. Upper limits on initial magnetite content of about 1–9% were established for these meteorites. Samples of the remaining five C3 chondrites and the Coolidge C4 chondrite were found to contain both magnetite and metallic iron. In two samples, iron containing ≤2% Ni was observed, while in the other four, the iron contained 6–8 wt.% Ni. In addition to containing both magnetite and iron metal, three of these samples reacted during heating to form additional magnetite. Variations in the magnetic mineralogy and, hence by inference bulk mineralogy, of C3 and C4 chondrites indicate a more complex genesis than is evident from whole-rock elemental abundance patterns. 相似文献
109.
D.E. Watson E.E. Larson J.M. Herndon M.W. Rowe 《Earth and Planetary Science Letters》1975,27(1):101-107
Samples of all eighteen of the known C2 chondrites have been analyzed thermomagnetically. For eleven of these, initial Fe3O4 content is low (generally <1%) and theJs-T curves are irreversible. The heating curves show variable greater (up to 10 times) than it is initially. This behavior is attributed to the production of magnetite from a thermally unstable phase — apparently FeS. Four of the remaining seven C2 chondrites contain Fe3O4 as the only significant magnetic phase: initial magnetite contents range from 4 to 13%. The remaining three C2 chondrites contain iron or nickel-iron in addition to Fe3O4. These seven C2 chondrites show little evidence of the breakdown of a thermally unstable phase. 相似文献
110.
Cobalt, like Mg, may cause the precipitation of aragonite rather than calcite in aqueous solutions due to the adsorption and crystal poisoning of calcite by a hydrated ion. Solutions containing NaCl and CaCl2, having the ionic strength and Ca content of seawater (35‰ salinity), were spiked with known amounts of CoCl2. Calcium carbonate was precipitated by the addition of 0.7 ml of 1 M Na2CO3. All experimental runs were made at 25°C, and all products were examined by X-ray diffraction. At low concentrations of Co (< 5·?4M) calcite and vaterite formed. At concentrations from 5·10?4 M to 2·10?3M, the products consisted of combinations of calcite and vaterite; aragonite and calcite; aragonite and vaterite; calcite, vaterite and aragonite. In solutions of 3·10?3M CoCl2, most precipitates were aragonite with only one sample containing a small amount of calcite. All precipitates from 5·10?3M CoCl2 solutions either contained aragonite or were amorphous. Solutions with concentrations of 1 · 10?2M CoCl2 produced only amorphous precipitates. All precipitates contained an amorphous violet phase, assumed to be basic cobaltous carbonate (2CoCO3·Co(OH)2·H2O). 相似文献