全文获取类型
收费全文 | 118篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 15篇 |
地球物理 | 28篇 |
地质学 | 54篇 |
海洋学 | 11篇 |
天文学 | 5篇 |
自然地理 | 13篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 3篇 |
2017年 | 8篇 |
2016年 | 6篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 13篇 |
2012年 | 7篇 |
2011年 | 6篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 6篇 |
2007年 | 11篇 |
2006年 | 1篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1991年 | 3篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1982年 | 2篇 |
1978年 | 1篇 |
1921年 | 2篇 |
1920年 | 1篇 |
排序方式: 共有130条查询结果,搜索用时 15 毫秒
31.
32.
Lindsay P. Keller Scott Messenger George J. Flynn Sue Wirick 《Geochimica et cosmochimica acta》2004,68(11):2577-2589
Eight interplanetary dust particles (IDPs) exhibiting a wide range of H and N isotopic anomalies have been studied by transmission electron microscopy, x-ray absorption near-edge structure spectroscopy, and Fourier-transform infrared spectroscopy. These anomalies are believed to have originated during chemical reactions in a cold molecular cloud that was the precursor to the Solar System. The chemical and mineralogical studies reported here thus constitute direct studies of preserved molecular cloud materials. The H and N isotopic anomalies are hosted by different hydrocarbons that reside in the abundant carbonaceous matrix of the IDPs. Infrared measurements constrain the major deuterium (D) host in the D-enriched IDPs to thermally labile aliphatic hydrocarbon groups attached to macromolecular material. Much of the large variation observed in D/H in this suite of IDPs reflects the variable loss of this labile component during atmospheric entry heating. IDPs with elevated 15N/14N ratios contain N in the form of amine (-NH2) functional groups that are likely attached to other molecules such as aromatic hydrocarbons. The host of the N isotopic anomalies is not as readily lost during entry heating as the D-rich material. Infrared analysis shows that while the organic matter in primitive anhydrous IDPs is similar to that observed in acid residues of primitive chondritic meteorites, the measured aromatic:aliphatic ratio is markedly lower in the IDPs. 相似文献
33.
We analyzed the isotopic patterns found in the tooth enamel of modern feral horses from Shackleford Banks, North Carolina (USA), which has a temperate climate and supports primarily C4 grasslands. Enamel δ13C values averaged −4.1‰ with a standard deviation (1σ) of 1.7‰, which corresponds to an average diet of 66 ± 12% C4 plants. Our results differ from dietary reconstructions from 1978 to 1981, which found that horses consumed 91% C4 plants. This suggests that horses have increased their consumption of C3 forbs, likely as a result of the removal of cattle, sheep, and goats from the island. Shackleford surface waters had δ18O values that averaged −3.3 ± 0.5‰ and −1.3 ± 1.8‰ on the western and eastern ends of the island, respectively. Tooth enamel samples averaged 27.3 ± 1.5‰ and displayed the same range of δ18O values as surface waters. The variability of both δ18O and the δ13C values among individuals within this population demonstrates that horses from relatively homogenous temperate environments can display a wide range of isotopic values. Given the observed range of isotopic values for modern horses, we suggest that researchers use the mean values of multiple (≥9) equids when attempting to reconstruct average paleodiets and/or paleoenvironmental conditions. 相似文献
34.
35.
The Miller Range 090340 and 090206 meteorites: Identification of new brachinite‐like achondrites with implications for the diversity and petrogenesis of the brachinite clan
下载免费PDF全文
![点击此处可从《Meteoritics & planetary science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Cyrena Anne Goodrich Noriko T. Kita Stephen R. Sutton Sue Wirick Juliane Gross 《Meteoritics & planetary science》2017,52(5):949-978
Miller Range (MIL) 090340 and MIL 090206 are olivine‐rich achondrites originally classified as ureilites. We investigate their petrography, mineral compositions, olivine Cr valences, equilibration temperatures, and (for MIL 090340) oxygen isotope compositions, and compare them with ureilites and other olivine‐rich achondrites. We conclude that they are brachinite‐like achondrites that provide new insights into the petrogenesis of brachinite clan meteorites. MIL 090340,6 has a granoblastic texture and consists of ~97 modal % by area olivine (Fo = molar Mg/[Mg+Fe] = 71.3 ± 0.6). It also contains minor to trace augite, chromite, chlorapatite, orthopyroxene, metal, troilite, and terrestrial Fe‐oxides. Approximately 80% by area of MIL 090206,5 has a granoblastic texture of olivine (Fo 72.3 ± 0.1) plus minor augite and chromite, similar to MIL 090340 but also containing minor plagioclase. The rest of the section consists of a single crystal of orthopyroxene (~11 × 3 mm), poikilitically enclosing rounded grains of olivine (Fo = 76.1 ± 0.6), augite, chromite, metal, and sulfide. Equilibration temperatures for MIL 090340 and MIL 090206, calculated from olivine‐spinel, olivine‐augite, and two‐pyroxene thermometry range from ~800 to 930 °C. In both samples, symplectic intergrowths of Ca‐poor orthopyroxene + opaque phases (Fe‐oxides, sulfide, metal) occur as rims on and veins/patches within olivine. Before terrestrial weathering, the opaques were probably mostly sulfide, with minor metal. All petrologic properties of MIL 090340 and MIL 090206 are consistent with those of brachinite clan meteorites, and largely distinct from those of ureilites. Oxygen isotope compositions of olivine in MIL 090340 (δ18O = 5.08 ± 0.30‰, δ17O = 2.44 ± 0.21‰, and Δ17O = ?0.20 ± 0.12‰) are also within the range of brachinite clan meteorites, and well distinguished from ureilites. Olivine Cr valences in MIL 090340 and the granoblastic area of MIL 090206 are 2.57 ± 0.06 and 2.59 ± 0.07, respectively, similar to those of three brachinites also analyzed here (Brachina, Hughes 026, Nova 003). They are higher than those of olivine in ureilites, even those containing chromite. The valence systematics of MIL 090340, MIL 090206, and the three analyzed brachinites (lower Fo = more oxidized Cr) are consistent with previous evidence that brachinite‐like parent bodies were inherently more oxidized than the ureilite parent body. The symplectic orthopyroxene + sulfide/metal assemblages in MIL 090340, MIL 090206, and many brachinite clan meteorites have superficial similarities to characteristic “reduction rims” in ureilites. However, they differ significantly in detail. They likely formed by reaction of olivine with S‐rich fluids, with only minor reduction. MIL 090340 and the granoblastic area of MIL 090206 are similar in modal mineralogy and texture to most brachinites, but have higher Fo values typical of brachinite‐like achondrites. The poikilitic pyroxene area of MIL 090206 is more typical of brachinite‐like achondrites. The majority of their properties suggest that MIL 090340 and MIL 090206 are residues of low‐degree partial melting. The poikilitic area of MIL 090206 could be a result of limited melt migration, with trapping and recrystallization of a small volume of melt in the residual matrix. These two samples are so similar in mineral compositions, Cr valence, and cosmic ray exposure ages that they could be derived from the same lithologic unit on a common parent body. 相似文献
36.
Caritg Séverine Burkhard Martin Ducommun Romain Helg Urs Kopp Lionel Sue Christian 《地学学报》2004,16(1):27-37
We document two phases of folding within the central part of the Late Palaeozoic Anti‐Atlas chain of Morocco. A first generation of SW–NE folds involve a horizontal shortening of 10–20%, accommodated by polyharmonic buckle folding of contrasting wavelengths in Ordovician Jbel Bani quartzites and Devonian Jbel Rich carbonates. A second generation of folds with similar style and wavelengths in an E–W direction lead to complex interference patterns. Dome and basins are developed within the Jbel Rich and within Lower Cambrian dolomites. Both folding phases are related to thick‐skinned uplift of Precambrian basement in a Laramide style. In contrast to the typical Rocky Mountain foreland style, however, cover deformation in the Anti‐Atlas is mostly decoupled from the undying basement along thick incompetent horizons such as the Lower Cambrian Lie‐de‐Vin and Silurian shales. 相似文献
37.
Distinctive diatom assemblages may be associated with tsunami sediments and may often contrast with the assemblages found within sediments underlying the tsunami deposit as well as those associated with the modern coastal environment. Sediments associated with the 1998 tsunami that destroyed much of the Sissano lagoon area in northern Papua New Guinea have been investigated. Surface sediments from three transects across the sediment spit near Warapu have been examined for diatom content and preservation. The preservation is variable, and the data show an, often chaotic, assemblage that can be attributed to the tsunami waves incorporating and depositing diatoms from distinctive habitat zones during their runup and subsequent backwash. The diatoms identified within the Warapu sediments indicate an origin from within the inter-tidal and offshore area rather than from the beach–sand spit complex. The sand deposits disclose a high percentage, in excess of 75%, of broken diatom valves, and a predominance of centric (circular) species due to preferential preservation. The study demonstrates that the application of diatom biostratigraphy to modern tsunami deposits can be used in conjunction with other stratigraphical lines of evidence to interpret the source and provenance of historical and palaeo-tsunami deposits. 相似文献
38.
Delegates at the simultaneous National Astronomy Meeting, UK Solar Physics meeting and Spring MIST meeting were impressed by the warm welcome and efficient organization from the hosts, the University of Central Lancaster in Preston. The meetings were successful in terms of the number of participants and the breadth and depth of science discussed, but also in terms of the spread of that science across the media. 相似文献
39.
40.