全文获取类型
收费全文 | 401篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 27篇 |
地球物理 | 103篇 |
地质学 | 111篇 |
海洋学 | 27篇 |
天文学 | 113篇 |
综合类 | 1篇 |
自然地理 | 30篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 9篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 10篇 |
2016年 | 9篇 |
2015年 | 10篇 |
2014年 | 9篇 |
2013年 | 13篇 |
2012年 | 19篇 |
2011年 | 13篇 |
2010年 | 15篇 |
2009年 | 35篇 |
2008年 | 16篇 |
2007年 | 19篇 |
2006年 | 21篇 |
2005年 | 16篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 2篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 8篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1971年 | 2篇 |
排序方式: 共有423条查询结果,搜索用时 15 毫秒
371.
372.
Spatial patterns of primary production on the shelf, slope and basin of the Western Arctic in 2002 总被引:3,自引:0,他引:3
Victoria Hill Glenn Cota 《Deep Sea Research Part II: Topical Studies in Oceanography》2005,52(24-26):3344
In the spring and summer of 2002 primary production in the Chukchi Sea was measured, using 14C uptake experiments. Our cruise track encompassed the shelf and continental slope area of the Chukchi and Beaufort Seas progressing into deep water over the Canada Basin. The study area experienced upwards of 90% ice cover during the spring, with ice retreating into the basin during the summer. Production in the spring was light-limited due to ice cover, with average euphotic zone production rates of <0.3 g C m−2 d−1. Values of 8 g C m−2 d−1 were observed in association with surface bloom conditions during the initial ice breakup. Considerable nutrient reduction in the surface waters took place between the spring and summer cruise, and although not observed, this was attributed to a spring bloom. Decreased ice cover and increased clarity of surface waters in the summer allowed greater light penetration. The highest rates of production during the second cruise were found at 25–30 m, coincident with the top of the nutricline. Daily euphotic zone productivity in the summer averaged 0.78 g C m−2 d−1 on the shelf and 0.32 g C m−2 d−1 on the edge of the Canada basin. These data provide an estimated annual production of 90 g C m−2 yr−1 in the study area. 相似文献
373.
All of the data acquired at Jupiter by the Infrared Radiometers on board Pioneers 10 and 11 are presented in the form of images with geometric control. The images are compared with 5-μm and visible images taken in the same time frame. The association of dark (blue or brown) and light (white or red) areas with warm and cool areas (at 5, 20, and 45 μm) respectively, extends to nearly all features observed on the planet. Where the normal association of light and dark visible markings with the zonal velocity breaks down (e.g., at the latitude of the South Equatorial Belt during the Pioneer encounters), the infrared emission seems to follow the visible cloud structure rather than the zonal velocity structure. Exceptions to the general rule involve 20-μm radiation, which reflects conditions in the altitude range 0.1–0.3 bar. For example, a comparison between Pioneer 10 and 11 images suggests that the South Equatorial Belt became brighter at 20 μm, but remained constant at other wavelengths between the two encounters. 相似文献
374.
Spectra from the Voyager 1 IRIS experiment confirm the existence of enhanced infrared emission near Jupiter's north magnetic pole in March 1979. The spectral characteristics of the enhanced emission are consistent with a Planck source function. A temperature-pressure profile is derived for the region near the north magnetic pole, from which quantitative abundance estimates of minor species are made. Some species previously detected on Jupiter, including CH3D, C2H2 and C2H6, have been observed again near the pole. Newly discovered species, not previously observed on Jupiter, include C2H4, C3H4, and C6H6. All of these species except CH3D appear to have enhanced abundances at the north polar region with respect to midlatitudes. Upper limits are determined for C4H2 and C3H8. The quantitative results are compared with model calculations based on ultraviolet results from the IUE satellite. The plausibility of the C6H6 identification in discussed in terms of the literature on C2H2 polymerization. The relation of C6H6 to cuprene is also discussed. 相似文献
375.
Edward J. Olsen T.E. Bunch Eugene Jarosewich Albert F. Noonan Glenn I Huss 《Meteoritics & planetary science》1977,12(2):109-124
Happy Canyon [found: 1971, 34° 46.5′N, 101° 33.6′W, Texas] consists of about 85 vol. % enstatite (Fs 0.4%), 5 to 10 vol % plagioclase (An 26%), and 5 vol % diopside (Fs 0.9%). In addition, there are minor remnants of metal (Ni 6.35 wt %, Si-free) and troilite (with 5.10 wt % Cr and 1.15 wt % Ti) that have survived extensive terrestrial weathering. The meteorite has a cumulate texture, uniform-size euhedral, prismatic crystals of enstatite (0.3 to 0.4 mm long) with interstitial plagioclase, diopside, troilite, and metal. The enstatite crystals are dominantly disordered and occur in alignments that suggest flow. There are no chondrules or remnants of chondrules. The enstatite crystals contain internal negative crystal voids, which are charactieristic of enstatite achondrites, as well as internal branching submicron rivulet dislocations. The bulk composition is that of an E6 enstatite chondrite, however, it has the texture of a crystal cumulate; achondritic, but unlike that of enstatite achondrites. Glass of a granitic composition occurs mainly in the mesostasis and is compositionally like the glass found inside pyroxene crystals in the Cumberland Falls enstatite achondrite. Happy Canyon is most simply explained as an E6 composition that has melted and reprecipitated at a slightly higher oxidation state, at some depth (> 7 km), possibly in the core volume of a small, asteroidal-size parent body. In terms of classification, it occupies the gap between the recrystallized enstatite chondrites and the igneous, crystalline, unbrecciated enstatite achondrites like Shallowater. Happy Canyon is a new type of enstatite achondrite 相似文献
376.
The assumption that five men witnessed the formation of the lunar crater Giordano Bruno on June 18, 1178, is analyzed. The difficulties inherent in this interpretation are discussed. The only tenable solution — that of a meteor passing before the moon — is presented. 相似文献
377.
378.
Robert N. Clayton Glenn J. MacPherson Ian D. Hutcheon Andrew M. Davis Lawrence Grossman Toshiko K. Mayeda Carol Molini-Velsko John M. Allen Ahmed El Goresy 《Geochimica et cosmochimica acta》1984,48(3):535-548
We have discovered two FUN inclusions, CG-14 and TE, among a group of five forsterite-rich inclusions in Allende, two of which are described for the first time herein. All five consist of euhedral forsterite and spinel crystals poikilitically enclosed by fassaite. Forsterite and spinel are usually segregated from one another, sometimes into a spinel-rich mantle and a forsterite-rich core. Some inclusions contain vesicles, indicating that they were once molten. The crystallization sequence inferred from textures is: spinel, forsterite, fassaite and, finally, Mg-rich melilite. One concentrically-zoned inclusion contains melilite in its mantle whose composition lies on the opposite side of the liquidus minimum in the melilite binary from that in its core. This suggests that segregation of forsterite from spinel in all of these inclusions could be due to volatilization of MgO and SiO2 relative to Al2O3 and CaO from the outsides of droplets. CG-14 is relatively uniformly enriched in refractory elements relative to Cl chondrites by a factor similar to that for Ca-, Al-rich coarse-grained inclusions except for Ca, Al and Hf which are unusually low. No Ce anomaly such as found in FUN inclusions Cl and HAL is present in CG-14. Whole-rock samples of CG-14 and TE are more strongly mass-fractionated in oxygen relative to “normal” Allende inclusions than the FUN inclusion EK 1-4-1 and less so than Cl. Relative to bulk Allende, both inclusions have strongly massfractionated magnesium and silicon and 25Mg excesses or deficits of 24Mg or 26Mg. CG-14 has a 29Si excess or a deficit of 28Si or 30Si. Volatilization loss cannot be responsible for the magnesium and silicon isotope fractionations, as this would require prohibitively large mass loss from these magnesium-rich inclusions. The remarkable similarity in textures between FUN and non-FUN inclusions implies similar thermal histories, arguing against different rates of evaporative loss of major elements. Sputtering alone may be insufficient to account for the magnitude and direction of oxygen isotope fractionation in FUN inclusions. 相似文献
379.
Georges Calas Gordon E. Brown Jr. Glenn A. Waychunas Jacqueline Petiau 《Physics and Chemistry of Minerals》1987,15(1):19-29
Selected results of x-ray absorption spectroscopy (XAS) studies of amorphous silicates and minerals are presented in order to show their utility in providing short-and, in certain cases, medium-range structural and bonding information for cations and anions. EXAFS and XANES studies of amorphous silicates are reviewed with the objective of illustrating variations in structural environments of the various types of glass-forming cations, including Si, Al, Na, K, Ca, Ti, Fe, Yb, and U. Al is shown to occur in tetrahedral coordination in all aluminosilicate glasses examined, including peraluminous compositions. The weakly bonded Na and Ca cations are shown to occur in sites with observed coordination numbers (ranging from 6 to 7) and distances similar to those predicted by molecular dynamics simulations. Elements like Ti, which form bonds of intermediate strength, may show some order beyond the first coordination shell at low concentrations in silicate glasses. EXAFS studies of Yb and U in silicate glasses at trace to minor concentration levels provide unique structural information about the environments of these cations. K-edges and XANES of transition element sulfides, third-row tetrahedral oxyanions, and oxygen in minerals are interpreted in terms of band theory or molecular orbital theory. 相似文献
380.