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151.
Steve Eales Frank Bertoldi Rob Ivison Chris Carilli Loretta Dunne Frazer Owen 《Monthly notices of the Royal Astronomical Society》2003,344(1):169-180
We have observed 23 sources from the Max-Planck Millimetre Bolometer (MAMBO) array 1200-μm survey with SCUBA at 850 μm, detecting 19 of the sources. The sources generally have low values for the ratio of 850- to 1200-μm flux. Two possible explanations for the low values are either that the sources are at very high redshifts or that the global properties of the dust in the MAMBO sources are different from the global properties of dust in low-redshift galaxies. If the former explanation is correct, we estimate that 15 of the MAMBO sources lie at z > 3 . 相似文献
152.
Lewis A. Owen Lyn Gualtieri Robert C. Finkel Marc W. Caffee Doug I. Benn Milap C. Sharma 《第四纪科学杂志》2001,16(6):555-563
The timing of glaciation in the Lahul Himalaya of northern India was ascertained using the concentrations of cosmogenic 10Be and 26Al from boulders on moraines and drumlins, and from glacially polished bedrock surfaces. Five glacial stages were identified: Sonapani I and II, Kulti, Batal and Chandra. Of these, cosmogenic exposure ages were obtained on samples representative of the Batal and Kulti glacial cycles. Stratigraphical relationships indicate that the Sonapani I and II are younger. No age was obtained for the Chandra glacial advance. Batal Glacial Stage deposits are found throughout the valley, indicating the presence of an extensive valley glacial system. During the Kulti Stage, glaciers advanced ca. 10 km beyond their current positions. Moraines produced during the Batal Stage, ca. 12–15.5 ka, are coeval with the Northern Hemisphere Late‐glacial Interstadial (Bølling/Allerød). Deglaciation of the Batal Glacial Stage was completed by ca. 12 ka and was followed by the Kulti Glacial Stage during the early Holocene, at ca. 10–11.4 ka. On millennial time‐scales, glacier oscillations in the Lahul Himalaya apparently reflect periods of positive mass‐balance coincident with times of increased insolation. During these periods the South Asian summer monsoon strengthened and/or extended its influence further north and west, thereby enhancing high‐altitude summer snowfall. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
153.
The large backscattering cross section of the particles composing the upper clouds on Venus suggests that a small quantity of high refractive index material is present in the clouds. We propose that this material is elemental sulfur and that sulfur also accounts for the absorption of uv-visible radiation at wavelengths outside of the SO2 absorption bands. A physical-chemical model of the clouds shows that sulfur, with a mass comparable to that of the observed Mode 1 particles, can be produced in oxygen-poor regions of the upper clouds and in rising air columns. Sulfur production from SO2 can be rapid, which explains the observed correlation between SO2 and the uv absorber. The sulfur is properly located to be the uv absorber uv absorber since its calculated concentration rapidly increases with depth in the upper clouds, but it is largely absent in the middle and lower clouds. Sulfur nucleation provides a means of generating the observed bimodal particle size distribution in the upper clouds. Chemical modeling shows that the sulfur vapor is rich in short-chain allotropes such as S3 and S4. These allotropes have absorption bands centered near 4000 and 5300 Å, respectively. We suggest that the sulfur particles on Venus are largely composed of S8, but also contain a few percent of S3 and S4. Such particles could account for the wavelength dependence of the albedo of Venus and for the solar energy deposition profile in the clouds. These allotropes are metastable and relax to S8 over periods of hours to days, providing a simple explanation for the relatively short lifetime of the uv absorber. 相似文献
154.
B.J. Buratti D.T. Britt M.D. Hicks R.H. Brown R.M. Nelson T.C. Owen B.R. Sandel N. Thomas 《Icarus》2004,167(1):129-135
Spectra of Asteroid 9969 Braille in the 1.25-2.6 μm region returned by the Deep Space 1 (DS1) Mission show a ∼10% absorption band centered at 2 μm, and a reflectance peak at 1.6 μm. Analysis of these features suggest that the composition of Braille is roughly equal parts pyroxene and olivine. Its spectrum between 0.4 and 2.5 μm suggests that it is most closely related to the Q taxonomic type of asteroid. The spectrum also closely matches that of the ordinary chondrites, the most common type of terrestrial meteorite. The geometric albedo of Braille is unusually high (pv=0.34), which is also consistent with its placement within the rarer classes of stony asteroids, and which suggests it has a relatively fresh, unweathered surface, perhaps due to a recent collision. 相似文献
155.
Theoretical arguments point to and recent observations confirm the existence of clouds in Titan's atmosphere, yet we possess very little data on their particle size, composition and formation mechanism. A time-dependent microphysical model is used to study the evolution of ice clouds in Titan's atmosphere. The model simulates nucleation, condensational growth, evaporation, coagulation, and transport of particles in a column of atmosphere. A variety of cloud compositions are studied, including pure ethane clouds, pure methane clouds, and mixed methane-ethane clouds (all with tholin cores). The abundance of methane cloud particles may be limited by the number of ethane coated tholin nuclei rather than the number of tholins with hydrocarbon coatings. However, even the condensation of methane onto these relatively sparse ethane/tholin cloud particles is sufficient to keep the methane close to saturation. Typical methane supersaturations are of order 0.06 on the average. For simulations which take into account recent lab measurements indicating it is relatively easy for methane to nucleate onto tholin particles without an ethane-layer present, the three types of clouds (methane, ethane, and mixed) exist simultaneously. Pure methane clouds are the most abundant cloud type and serve to lower the supersaturation to about 0.04. Cloud production does not require a continuous surface source of methane. However, clouds produced by mean motions are not the visible methane clouds seen in recent Cassini and ground-based observations. Ethane clouds in the troposphere almost instantaneously nucleate methane to form mixed clouds. However, a thin ethane ‘haze’ remains just above the tropopause for some scenarios and the mixed clouds at the tropopause remain ?50% ethane by mass. Also, evaporation of methane from the mixed cloud particles near the surface leaves a thicker layer of ethane cloud particles at ∼10 km. Nevertheless, the precipitation rate of methane to Titan's surface is between 0.001 and 0.5 cm/terrestrial-year, depending on various initial conditions such as critical saturation, size and abundance of cloud condensation nuclei, surface sources and eddy diffusion. 相似文献
156.
The possibilities of lightning generation on other planets are considered, and the basic conditions that exist in terrestrial clouds during lightning discharges and the various theories of charge separation are reviewed. Recent measurements of cloud structure and whistlers, as well as optical observation of lightning on Jupiter, suggest that charge separation and lightning discharges occur on other planets in ways similar to those in which they occur on Earth. Using these terrestrial ideas, it is concluded that lightning on Venus will probably be found in clouds that are located in regions of convection such as those observed downwind of the subsolar point. It is also possible that if volcanoes on Venus are erupting, they too can produce lightning discharges in their plumes although it seems unlikely that this process can account for the observed rate of discharge. Jovian lightning is most probably generated in the lower water-ice clouds. These clouds are of moderate temperatures and have strong convection and large mass loading, all important ingredients for electrical buildup. Lightning is all but ruled out for Mars, even though some electrification is possible owing to the large dust storms on that planet. 相似文献
157.
During the last two minutes before closest approach of Deep Space 1 to Comet 19P/Borrelly, a long exposure was made with the short-wavelength infrared (SWIR) imaging spectrometer. The observation yielded 46 spectra covering 1.3-2.6 μm; the footprint of each spectrum was ∼160 m × width of the nucleus. Borrelly's highly variegated and extremely dark 8-km-long nucleus exhibits a strong red slope in its short-wavelength infrared reflection spectrum. This slope is equivalent to J-K and H-K colors of ∼0.82 and ∼0.43, respectively. Between 2.3-2.6 μm thermal emission is clearly detectable in most of the spectra. These data show the nucleus surface to be hot and dry; no trace of H2O ice was detected. The surface temperature ranged continuously across the nucleus from ?300 K near the terminator to a maximum of ∼340 K, the expected sub-solar equilibrium temperature for a slowly rotating body. A single absorption band at ∼2.39 μm is quite evident in all of the spectra and resembles features seen in nitrogen-bearing organic molecules that are reasonable candidates for compositional components of cometary nuclei. However as of yet the source of this band is unknown. 相似文献
158.
A. Owen 《Geophysical Journal International》1980,62(1):59-75
Summary. Two-dimensional numerical models are used to examine the tidal regime of the Bristol Channel. The effect of including S2 in addition to M2 in the models on both the tidal elevations and the residual Eulerian circulation is investigated. The spatial distribution of the maximum spring currents and the time of their occurrence are also computed.
The Eulerian and Lagrangian residual circulations are compared and the effect of model grid size on the former is examined.
Finally the spatial distribution of energy dissipation within, and the total flux of energy into, the Bristol Channel are given. 相似文献
The Eulerian and Lagrangian residual circulations are compared and the effect of model grid size on the former is examined.
Finally the spatial distribution of energy dissipation within, and the total flux of energy into, the Bristol Channel are given. 相似文献
159.
160.
Christopher Potter Peggy Gross Vanessa Genovese Marie-Louise Smith 《Carbon balance and management》2007,2(1):1-11