全文获取类型
收费全文 | 808篇 |
免费 | 26篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 31篇 |
大气科学 | 55篇 |
地球物理 | 181篇 |
地质学 | 322篇 |
海洋学 | 52篇 |
天文学 | 164篇 |
自然地理 | 33篇 |
出版年
2021年 | 6篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2017年 | 15篇 |
2016年 | 23篇 |
2015年 | 17篇 |
2014年 | 25篇 |
2013年 | 30篇 |
2012年 | 15篇 |
2011年 | 34篇 |
2010年 | 42篇 |
2009年 | 39篇 |
2008年 | 29篇 |
2007年 | 31篇 |
2006年 | 29篇 |
2005年 | 33篇 |
2004年 | 24篇 |
2003年 | 26篇 |
2002年 | 29篇 |
2001年 | 23篇 |
2000年 | 10篇 |
1999年 | 17篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1991年 | 18篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1983年 | 8篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1972年 | 6篇 |
1966年 | 7篇 |
1964年 | 6篇 |
1962年 | 5篇 |
1960年 | 6篇 |
1952年 | 5篇 |
1948年 | 5篇 |
排序方式: 共有838条查询结果,搜索用时 31 毫秒
111.
Time variable Earth’s gravity field from SLR satellites 总被引:4,自引:4,他引:0
112.
113.
114.
115.
Winter-to-spring temperature dynamics in Turkey derived from tree rings since AD 1125 总被引:2,自引:1,他引:1
Ingo Heinrich Ramzi Touchan Isabel Dorado Liñán Heinz Vos Gerhard Helle 《Climate Dynamics》2013,41(7-8):1685-1701
In the eastern Mediterranean in general and in Turkey in particular, temperature reconstructions based on tree rings have not been achieved so far. Furthermore, centennial-long chronologies of stable isotopes are generally also missing. Recent studies have identified the tree species Juniperus excelsa as one of the most promising tree species in Turkey for developing long climate sensitive stable carbon isotope chronologies because this species is long-living and thus has the ability to capture low-frequency climate signals. We were able to develop a statistically robust, precisely dated and annually resolved chronology back to AD 1125. We proved that variability of δ13C in tree rings of J. excelsa is mainly dependent on winter-to-spring temperatures (January–May). Low-frequency trends, which were associated with the medieval warm period and the little ice age, were identified in the winter-to-spring temperature reconstruction, however, the twentieth century warming trend found elsewhere could not be identified in our proxy record, nor was it found in the corresponding meteorological data used for our study. Comparisons with other northern-hemispherical proxy data showed that similar low-frequency signals are present until the beginning of the twentieth century when the other proxies derived from further north indicate a significant warming while the winter-to-spring temperature proxy from SW-Turkey does not. Correlation analyses including our temperature reconstruction and seven well-known climate indices suggest that various atmospheric oscillation patterns are capable of influencing the temperature variations in SW-Turkey. 相似文献
116.
Marco Micheli Detlef Koschny Gerhard Drolshagen Olivier Hainaut Fabrizio Bernardi 《Earth, Moon, and Planets》2014,113(1-4):1-13
In this work we summarize the initial results of a targeted effort of the ESA NEO Coordination Centre to obtain additional observational data in order to eliminate or reduce the impact probability estimate of a subset of the known near-Earth objects representing the highest fraction of the total known impact risk, as measured by the Palermo Scale. 相似文献
117.
P. Beck E. Quirico A. Garenne Q.‐Z. Yin L. Bonal B. Schmitt G. Montes‐Hernandez G. Montagnac R. Chiriac F. Toche 《Meteoritics & planetary science》2014,49(11):2064-2073
Sutter's Mill is a regolith breccia composed of both heavily altered clasts and more reduced xenoliths. Here, we present a detailed investigation of fragments of SM18 and SM51. We have characterized the water content and the mineralogy by infrared (IR) and thermogravimetric analysis (TGA) and the structure of the organic compounds by Raman spectroscopy, to characterize the secondary history of the clasts, including aqueous alteration and thermal metamorphism. The three methods used in this study suggest that SM18 was significantly heated. The amount of water contained in phyllosilicates derived by TGA is estimated to be approximately 3.2 wt%. This value is quite low compared with other CM chondrites that typically range from 6 to 12 wt%. The infrared transmission spectra of SM18 show that the mineralogy of the sample is dominated by a mixture of phyllosilicate and olivine. SM18 shows an intense peak at 11.2 μm indicative of olivine (Fig. 1). If we compare SM18 with other CM and metamorphosed CM chondrites, it shows one of the most intense olivine signatures, and therefore a lower proportion of phyllosilicate minerals. The Raman results tend to support a short‐duration heating hypothesis. In the ID/IG versus FWHM‐D diagram, SM18 appears to be unusual compared to most CM samples, and close to the metamorphosed CM chondrites Pecora Escarpment (PCA) 91008 and PCA 02012. In the case of SM51, infrared spectroscopy reveals that olivine is less abundant than in SM18 and the 10 μm silicate feature is more similar to that of moderately altered CM chondrites (like Murchison or Queen Alexandra Range [QUE] 97990). Raman spectroscopy does not clearly point to a heating event for SM51 in the ID/IG versus FWHM‐D diagram. However, TGA analysis suggests that SM51 was slightly dehydrated as the amount of water contained in phyllosilicates is approximately 3.7 wt%, which is higher than SM18, but still lower than phyllosilicate water contents in weakly altered CM chondrites. Altogether, these results confirm that fragments with different secondary histories are present within the Sutter's Mill fall. The dehydration that is clearly observed for SM18 is attributed to a short‐duration heating based on the similarity of its Raman spectra to that of PCA 91008. Because of the brecciated nature of Sutter's Mill and the presence of adjacent clasts with different thermal histories, impacts that can efficiently fragment and heat porous materials are the preferred heat source. 相似文献
118.
Clive R. Neal Matthew D. Hacker Gregory A. Snyder Lawrence A. Taylor Yun-Gang Liu Roman A. Schmitt 《Meteoritics & planetary science》1994,29(3):349-361
Abstract— The petrogenesis of Apollo 12 mare basalts has been examined with emphasis on trace-element ratios and abundances. Vitrophyric basalts were used as parental compositions for the modelling, and proportions of fractionating phases were determined using the MAGFOX program of Longhi (1991). Crystal fractionation processes within crustal and sub-crustal magma chambers are evaluated as a function of pressure. Knowledge of the fractionating phases allows trace-element variations to be considered as either source related or as a product of post-magma-generation processes. For the ilmenite and olivine basalts, trace-element variations are inherited from the source, but the pigeonite basalt data have been interpreted with open-system evolution processes through crustal assimilation. Three groups of basalts have been examined: (1) Pigeonite basalts — produced by the assimilation of lunar crustal material by a parental melt (up to 3% assimilation and 10% crystal fractionation, with an “r” value of 0.3). (2) Ilmenite basalts — produced by variable degrees of partial melting (4–8%) of a source of olivine, pigeonite, augite, and plagioclase, brought together by overturn of the Lunar Magma Ocean (LMO) cumulate pile. After generation, which did not exhaust any of the minerals in the source, these melts experienced closed-system crystal fractionation/accumulation. (3) Olivine basalts — produced by variable degrees of partial melting (5–10%) of a source of olivine, pigeonite, and augite. After generation, again without exhausting any of the minerals in the source, these melts evolved through crystal accumulation. The evolved liquid counterparts of these cumulates have not been sampled. The source compositions for the ilmenite and olivine basalts were calculated by assuming that the vitrophyric compositions were primary and the magmas were produced by non-modal batch melting. Although the magnitude is unclear, evaluation of these source regions indicates that both be composed of early- and late-stage Lunar Magma Ocean (LMO) cumulates, requiring an overturn of the cumulate pile. 相似文献
119.
120.