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211.
High resolution 3-cm weather radar was used to observe the three dimensional structure of a weak echo region of a severe convective storm in northern Minnesota, U.S.A. Observations show that a seemingly steady-state updraft in the lower portion of the storm broke into an unsteady structure in the upper levels. This is interpreted as indicating that precipitation loading gradually decelerated the upper reaches of the updraft, resulting in periodic breakout of a new updraft core on the inflow side. This periodic behavior of the updraft may be related to hailstreaks and what has been termed the multi-celled storm. 相似文献
212.
Martin I. Hoffert Yeong-Cherng Wey Andrew J. Callegari Wallace S. Broecker 《Climatic change》1979,2(1):53-68
The possibility of controlling atmospheric carbon dioxide accumulation and attendant climatic effects from fossil-fuel burning by diverting a fraction of the combustion product and injecting it into the deep-ocean, as proposed by Marchetti, is analyzed using an atmosphere/mixed layer/diffusive deep-ocean model for the carbon cycle. The model includes the nonlinear buffering of CO2 at the air/sea interface, and considers the long term trends associated with consuming an assumed fossil-fuel reserve equivalent to 7.09 × 1015 kg carbon as a logistic function of time as in the projections of Siegenthaler and Oeschger, except that atmospheric carbon dioxide levels are computed for five alternate strategies: (a) 100% injected into atmosphere, (b) 50% injected at oceanic depth of 1500 m and 50% into atmosphere, (c) 50% injected at sea floor (4000 m) and 50% into atmosphere, (d) 100% at 1500 m depth and (e) 100% at sea floor. Since no carbon leaves the system, all runs approached the same post-fossil fuel equilibrium after several thousand years, C
a
- 1150 ppm, almost four times the pre-fossil fuel value (- 300 ppm). But the transient response of these cases showed a marked variation ranging from a peak overshoot value of 2800 ppm in the year 2130 for 100% atmospheric injection to a slight decrease to the pre-fossil fuel 300 ppm lasting till 2300 with a subsequent slow approach to equilibrium for the 100% deep-ocean injection. The implications of these results for an oceanic injection strategy to mitigate the climatic impact of fossil-fuel CO2 is discussed, as are the ingredients of a second generation carbon cycle model for carrying out such forecasts on an engineering design basis. 相似文献
213.
R. G. Bill Jr. E. Chen R. A. Sutherland J. F. Bartholic 《Boundary-Layer Meteorology》1979,16(1):23-33
A steady-state, two-dimensional numerical model is used to simulate air temperatures and humidity downwind of a lake at night. Thermal effects of the lake were modelled for the case of moderate and low surface winds under the cold-air advective conditions that occur following the passage of a cold front. Surface temperatures were found to be in good agreement with observations. A comparison of model results with thermal imagery indicated the model successfully predicts the downwind distance for which thermal effects due to the lake are significant. 相似文献
214.
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217.
Stanley A. Mertzman Jr. 《Contributions to Mineralogy and Petrology》1979,70(1):81-88
Three contemporaneous yet mineralogically and chemically distinct lava series which range in composition from olivine basalt through basaltic andesite through two-pyroxene andesite, have been analyzed for their strontium isotopic composition. The Mammoth-Modoc lavas produce a mantle isochron which suggests derivation from a source approximately 243 m.y. old. The Medicine Lake shield-forming extrusives produce a minimum mantle isochron; the age of this source is likely greater than 760 m.y. old. Encompassing the entire time span of eruption for the two basalt-andesite series are a number of low potassium high alumina olivine tholeiite lavas which, when analyzed as a coherent group, produce a zero age. Lavas related to these three magma series have been extruded during the last 105 years and cover a limited geographic area. The isotope data suggest a model with substantial heterogeneity in the subcontinental lithosphere and asthenosphere, at least beneath the Medicine Lake Highland portion of the southern Cascade petrographic province.Contribution No. 126 相似文献
218.
219.
G. L. Nord Jr. 《Physics and Chemistry of Minerals》1980,6(2):109-128
Lunar and terrestrial orthopyroxenes (Mg,Fe,Ca)2Si2O6 contain varying abundances of coherent, Ca-enriched Guinier-Preston (G.P.) zones. G.P. zones 5–6 unit cells thick have been found in one lunar sample whereas all other examples (lunar and terrestrial) are only one unit-cell-thick. Electron diffraction maxima from the larger lunar G.P. zones indicate that d 100=18.52 Å whereas, d 100=18.2 Å for the host. This increase in the a direction corresponds to an increase in calcium content in the G.P. zones over that of the host of ~25 mol% Ca2Si2O6. Diffraction patterns of the hk0 net from an area containing G.P. zones show extra spots (h=2n+1) not observed in the host orthopyroxene (Pbca), that violate the a-glide of the host. The G.P. zones, therefore, have space group Pbc21 if it is assumed that the c-glide of pyroxene is retained and the space group of the G.P. zone is a subgroup of Pbca. The loss of the a-glide in the G.P. zones results in 4 distinct silica chains and 4 distinct cation sites M1A, M1B, M2A, M2B; by symmetry, equivalent M2A or M2B sites are clustered together in only one-half of the unit cell. As one-fourth of the divalent cations in the G.P. zones are calcium, ordering of Ca on M2A or M2B would produce a zone 9 Å thick extended parallel to (100) with the composition of Ca(Mg,Fe)Si2O6, but constrained by the host to the structure of orthopyroxene. This zone and the Ca-poor half-unit-cell then constitute an 18 Å thick G.P. zone. Heating experiments of varying duration indicate that the zones become unstable with respect to the host orthopyroxene at ~950°C for Wo0.6 and ~1,050°C for Wo2.5. The zones are interpreted in terms of the pyroxene subsolidus as a metastable phase having either a solvus relationship with orthopyroxene or originating as a distinct phase. The size, distribution, composition and structure of G.P. zones may be an important indicator of the low-temperature thermal history of orthopyroxene. 相似文献
220.
Dr. Roscoe R. Braham Jr. 《Pure and Applied Geophysics》1956,35(1):126-138
Summary Over the past several years, the University of Chicago has conducted a program of research into the physics and chemistry of cumulus cloud precipitation. From these measurements it has been possible to isolate the sublimation-coalescence mechanism (Bergeron process) from the condensation-coalescence mechanism and to estimate the relative role of each process in the formation of rain n cumulus clouds. It is found that size of cloud capable of raining is a strong function of geography, that the environment of the cloud is very important in determining the probability of rain and that liquid water content is one of the most important within-cloud parameters.An essential part of the research concerned cloud treatment. Definite, positive treatment effects were demonstrated for rain initiation through coalescence using water spray. No effects were detectable from dry ice seeding of subcooled clouds, although any such effects may have been obscured by sample size (27 cloud pairs).Text of paper presented before Physical Society and Royal Meteorological Society Joint Conference on Cloud Physics, London, England, Jan. 4–5, 1956. The research reported in this paper has been sponsored by the Geophysics Research. Directorate of the Air Force Cambridge Research Center, Air Research and Development Command under Contract Nos. AF 19 (604)-618 and AF 19 (604)-1388. 相似文献