全文获取类型
收费全文 | 2039篇 |
免费 | 119篇 |
国内免费 | 15篇 |
专业分类
测绘学 | 57篇 |
大气科学 | 144篇 |
地球物理 | 537篇 |
地质学 | 808篇 |
海洋学 | 281篇 |
天文学 | 211篇 |
综合类 | 14篇 |
自然地理 | 121篇 |
出版年
2023年 | 8篇 |
2022年 | 22篇 |
2021年 | 44篇 |
2020年 | 46篇 |
2019年 | 51篇 |
2018年 | 86篇 |
2017年 | 95篇 |
2016年 | 112篇 |
2015年 | 96篇 |
2014年 | 99篇 |
2013年 | 132篇 |
2012年 | 113篇 |
2011年 | 153篇 |
2010年 | 124篇 |
2009年 | 149篇 |
2008年 | 122篇 |
2007年 | 101篇 |
2006年 | 83篇 |
2005年 | 64篇 |
2004年 | 87篇 |
2003年 | 59篇 |
2002年 | 42篇 |
2001年 | 30篇 |
2000年 | 25篇 |
1999年 | 13篇 |
1998年 | 23篇 |
1997年 | 15篇 |
1996年 | 13篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 12篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1975年 | 5篇 |
1973年 | 4篇 |
1965年 | 3篇 |
1962年 | 2篇 |
排序方式: 共有2173条查询结果,搜索用时 15 毫秒
191.
Prof. G. Giacovazzo Dr. F. Scordari Dr. A. Todisco Prof. S. Menchetti 《Mineralogy and Petrology》1976,23(3):155-166
Summary The crystal structure of metavoltine from Sierra Gorda, Chile, has been solved from photographic X-ray data by the heavy atom method. The space group used wasP3 witha=9.575(5) andc=18.17(1)Å; cell content: K2Na6 (Fe
2+, Cu, Zn)Fe
6
3+
(SO4)12O2·18H2O. From the relatively small number and the somewhat poor quality of the X-ray data, the least squares refinement did not give very satisfactory results-especially so for the light atoms. Therefore, steric considerations and information from the Fourier maps were also used when choosing the final atomic coordinates. The salient features of the structure are clusters of Fe
3
3+
O(H2O)3(SO4)6 with Fe3+ in octahedral coordination, and Fe2+(H2O)6 octahedra. The Na+ ions show octahedral coordination, the K+ ions irregular nine coordination.
With 4 Figures 相似文献
Ein Kristallstrukturmodell für den Metavoltin von Sierra Gorda
Zusammenfassung Die Kristallstruktur des Metavoltins von Sierra Gorda (Chile) wurde aus photographischen Röntgendaten mit der Schweratommethode gelöst. Als Raumgruppe wurdeP3 mita 09,575(5) undc 0=18,17(1) Å verwendet; Zellinhalt K2Na6 (Fe 2+, Cu, Zn) Fe 6 3+ (SO4)12O2·18H2O.Wegen der relativ kleinen Zahl und der nicht sehr guten Qualität der Röntgendaten gab die Verfeinerung nach der Methode der kleinsten Quadrate keine sehr guten Ergebnissebesonders nicht für die leichten Atome. Deshalb wurden zur Festlegung der endgültigen Atomkoordinaten auch sterische Überlegungen und Informationen aus Fouriersynthesen herangezogen. Hervorstechende Züge der Struktur sind Gruppen Fe 3 3+ O(H2O)3(SO4)6 mit Fe3+ in oktaedrischer Koordination sowie Fe2+(H2O)6-Oktaeder. Die Na+-Ionen zeigen oktaedrische Koordination, die K+-Ionen unregelmäßige 9-Koordination.
With 4 Figures 相似文献
192.
193.
Maria Bianca Cita Luca Capraro Neri Ciaranfi Enrico Di Stefano Fabrizio Lirer Patrizia Maiorano Maria Marino Isabella Raffi Domenico Rio Rodolfo Sprovieri Simona Stefanelli Gian Battista Vai 《《幕》》2008,31(4):408-419
The name Calabrian was introduced in the geological literature by the French stratigrapher Maurice Gignoux in 1910, and later described in his important monograph (633 pages) "Les formations marines pliocknes et quaternaires de l'ltalie du sud et de la Sicile "published in 1913. Detailed data were provided on several sections (Santa Maria di Catanzaro, Caraffa, Monasterace, Palermo) and on their fossil content. The Calabrian Stage has commonly been used for over fifty years as the oldest subdivision of the Qua- ternary, notably in the time scales of Berggren & van Cou- vering (1974) and Haq & Eysinga (1987). However, after the GSSP for the Pliocene/Pleistocene boundary (P/P) was approved by INQUA in 1982 and ratified by lUGS in 1984 at the Vrica section of Calabria, there was a decline in the usage of the stage name, and an increasing tendency by many Quaternary workers to question the boundary stratotype. This was because there was increasing evidence that it did not correspond to the beginning of the "ice age". In doing so, they were not complying with the recommendations presented at the 18th International Geological Congress (IGC) in London, 1948 (Oakley, 1950). 相似文献
194.
Maria Bianca Cita 《《幕》》2008,31(2):251-254
Eight marine stages for the Quaternary have been defined in Italy starting from 1872 (Sicilian of Doderlein) to 1979 (Selinuntian of Ruggieri and Sprovieri). The definition of all these stages was based essentially on invertebrate paleontology, initially from the study of pelecypods and gastropods, but also of corals, ostracods, benthic foraminifers and, more recently, on planktonic foraminifers and calcareous nannofossils. The 1948 International Geological Congress held in London decided to search for a locality in Italy to define the Neogene/Quaternary boundary in correspondence with the first appearance of the "northern guests" in the Mediterranean. The Vrica section of Calabria was selected for defining the GSSP of the Pleistocene in 1984. 相似文献
195.
Melissa L. Northcott Michael N. Gooseff John E. Barrett Lydia H. Zeglin Cristina D. Takacs‐Vesbach John Humphrey 《水文研究》2009,23(9):1255-1267
Water is a limiting factor for life in the McMurdo Dry Valleys (MDV), Antarctica. The active layer (seasonally thawed soil overlying permafrost) accommodates dynamic hydrological and biological processes for 10–16 weeks per year. Wetted margins (visually wetted areas with high moisture content) adjacent to lakes and streams are potential locations of great importance in the MDV because of the regular presence of liquid water, compared with the rest of the landscape where liquid water is rare. At 11 plots (four adjacent to lakes, seven adjacent to streams), soil particle size distribution, soil electrical conductivity, soil water content and isotopic signature, width of the wetted margin, and active layer thaw depth were characterised to determine how these gradients influence physicochemical properties that determine microbial habitat and biogeochemical cycling. Sediments were generally coarse‐grained in wetted margins adjacent to both lakes and streams. Wetted margins ranged from 1·04 to 11·01 m in average length and were found to be longer at lakeside sites than streamside. Average thaw depths ranged from 0·12 to 0·85 m, and were found to be deepest under lake margins. Lake margins also had much higher soil electrical conductivity, steeper topographic gradients, but more gradual soil moisture gradients than stream margins. Patterns of soil water δ18O and δD distribution indicate capillary action and evaporation from wetted margins; margin pore waters generally demonstrated isotopic enrichment with distance from the shore, indicating evaporation of soil water. Lake margin pore waters were significantly more negative in DXS (DXS = δD‐8δ18O) than streamside pore waters, indicating a longer history of evaporation there. Differences between lake and stream margins can be explained by the more consistent availability of water to lake margins than stream margins. Differences in margin characteristics between lakes and streams have important consequences for the microbial habitat of these margins and their functional role in biogeochemical cycling at these terrestrial–aquatic interfaces. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
196.
197.
198.
199.
200.