全文获取类型
收费全文 | 439篇 |
免费 | 19篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 32篇 |
地球物理 | 155篇 |
地质学 | 166篇 |
海洋学 | 35篇 |
天文学 | 50篇 |
综合类 | 1篇 |
自然地理 | 16篇 |
出版年
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 8篇 |
2014年 | 16篇 |
2013年 | 15篇 |
2012年 | 7篇 |
2011年 | 19篇 |
2010年 | 17篇 |
2009年 | 24篇 |
2008年 | 22篇 |
2007年 | 13篇 |
2006年 | 14篇 |
2005年 | 18篇 |
2004年 | 15篇 |
2003年 | 9篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 19篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1951年 | 1篇 |
排序方式: 共有463条查询结果,搜索用时 359 毫秒
251.
Joël Lancelot Gérard Sarazin Claude J. Allegre 《Contributions to Mineralogy and Petrology》1971,32(4):315-333
Stratiform deposits found in mesozoic sedimentary layers, in Marocco and in France, have been analysed to determine lead and sulphur isotopic compositions.For the sulphur, the results indicate a low temperature formation, and are in good agreement with synsedimentary theories. The lead isotopic compositions are anomalous: J type for french galenas, B type for these of Marocco. The authors propose that the lead of these galenas have had a continental origin; the two different histories of the continental areas explain the galena anomalous compositions; two factors are particulary important: the age of the crust formation, and after that, the time of separation of lead from uranium and thorium in the continental crust. 相似文献
252.
Claude J. Allègre Francis Albarède Marc Grünenfelder Dr. Viktor Köppel 《Contributions to Mineralogy and Petrology》1974,43(3):163-194
Based on regular arrays in a U-Pb diagram of data points of zircons from polymetamorphic rocks of the Alps quantitative models are developed that include several episodic lead losses, continuous lead losses during discrete periods and combinations of both.The data from the Alps can be explained by assuming an initial age of the zircons of 2000 and/or 2500–2600 m.y. and three episodic lead losses 520–580 m.y., 300 m.y. and 30 m.y. ago with regionally varying intensities of the events as can be seen from the efficiency parameters which define the shape of the discordia. On the other hand, zircon data from North American basement rocks satisfy a model assuming a discrete interval of continuous lead loss that starts with the time of uplift of the rocks.The Th-U-Pb diagrams are valuable for recognising whether the history of the zircons and their host rock is a complex one or not which is not always noticeable in a U-Pb diagram. 相似文献
253.
In the calc-alkaline rocks of Peru, the rubidium content and the K/Ba, Rb/Sr ratios increase, while the strontium content and the K/Rb, Ba/Rb ratios decrease according to the distance of the trench. It is suggested that theses variations are related to a fractionation of plagioclase and contamination with differential migration of mobile elements. A comparative study between andesites of various localities shows in Peru an enrichment in Rb, Sr and Ba and a disparition of the Rb-Ba correlation; this last observation looks characteristic of continental margin andesites. The shoshonitic rocks differ from the andesites by a high content of Sr and Ba. The genetic relationships between these two kinds of rocks are discussed. It appears that the shoshonites are originated from a different magmatic source. 相似文献
254.
In the East of Montagne Noire (South Massif Central), the granitic Mendic massif and the porphyroïds have been dated as 510±20 m.y. with a corresponding initial ratio of 0.706±0.001. Within the limits of the analytical errors, we cannot distinguish between two separate isochrons. The Mendic-porphyroïds represents a volcano-plutonic association. The age of 510 m.y. is somewhat younger than the one determined on the orthogneisses of the Central zone (530 m.y.). It can be connected to a post-orogenic magmatism of the cadomian orogenesis. At last the Sr of the minerals of the Mendic massif has been partially remobilised during the hercynian orogeny (285 m. y.). 相似文献
255.
By means of flame spectrometry, K and Rb were measured in minerals and rocks belonging to several ignimbrite suite in Toscane, (Italy). 相似文献
256.
257.
U-Th chronology and paleoceanographic record in a Fe-Mn crust from the NE Atlantic over the last 700 ka 总被引:1,自引:0,他引:1
Christelle Claude Guenter Suhr Albrecht W. Hofmann 《Geochimica et cosmochimica acta》2005,69(20):4845-4854
Hydrogenetic ferromanganese crusts (Fe-Mn crusts) provide a secular record of the variations of seawater composition responding to changes in ocean circulation and erosion processes. In this respect, the acquisition of an absolute and reliable chronology in Fe-Mn crusts is a prerequisite. Here we combine four different and complementary chronometers (10Be, 230Thex, 230Thex/232Th, 234U/238U) in a Fe-Mn crust dredged at ∼2000 m depth in the east Atlantic to first establish a reliable chronology over the Quaternary period. Then, we use EDS chemical analysis to look for correlation between major element chemistry and climate changes. (230Thex), (230Thex/232Th), and Be data give very consistent growth rates. In particular, the good match between (230Thex) and (230Thex/232Th) data indicates that at the location of crust 121DK, 230Th and 232Th fluxes in the water column change simultaneously and suggests that the normalization of 230Thex to 232Th makes (230Thex/232Th) a better chronometer. Our best-fit model suggests that crust 121DK experienced changes in growth rates at ∼122 and 312 ka and a growth with a constant 230Th initial flux. This chronology returns an age of 680 ka for the uppermost 1.5 mm. The (234U/238U) depth profile, however, was clearly affected by diffusion of 234U in the porous crust and can therefore not be used to derive a reliable chronology. One part of the crust seems isolated from pore water diffusion and can be physically recognized as a zone of very small porosity. On the basis of the (230Thex/232Th) chronology, major element chemistry is shown to be linked to climate change. Mn/Fe variations compare well with those in a Fe-Mn crust from the Pacific, showing systematic maxima during glacial stages 2 and 4. High Mn/Fe are tentatively interpreted to reflect expansion of the oxygen minimum zone during glacial periods, resulting from higher bioproductivity. In addition we note that the surface (230Th/232Th) activity ratio of crust 121DK is entirely consistent with advection of deep water from the western toward the eastern Atlantic basin. 相似文献
258.
Beached seabirds, mainly common guillemots Uria aalge, were collected on the Belgian coast during winter from 1990 to 1995. Concentrations of total and organic mercury, and of organochlorines (PCBs and pesticides) were determined in muscle, liver and kidney. They were high compared to summer data (up to one order of magnitude), and increased during winter. This increase is not due to changes of total body weight nor polar lipid content, and thus reflects an actual increase of the seabirds' contamination while wintering in the southern North Sea. The observed annual cycle can be understood by assuming differences in prey contamination: higher during winter in the southern North Sea ecosystem than during summer in the Atlantic water ecosystem. 相似文献
259.
Bernhard Schulz Claude Triboulet Claude Audren Hans-Rudolf Pfeifer Albert Gilg 《International Journal of Earth Sciences》2001,90(4):871-889
On Ile de Groix, Variscan metamorphic former tholeiitic and alkaline basalts occur as glaucophane-eclogites, blueschists and greenschists in isolated lenses and layers within metapelites. Whole-rock '18OSMOW values of the metabasites show limited variations (10.4-12.0) and no systematic differences among rock types and metamorphic grades. This provides no argument for large-scale blueschist-to-greenschist transformation driven by infiltration of externally derived fluids. Metamorphic mineralogical changes should have been triggered by internal fluids. Element variations in interlayered blue- and greenschists can be attributed to magmatic fractionation. Assemblages with garnet, clinopyroxene and glaucophane of a high-pressure/low-temperature (HP-LT) metamorphism M1, and NaCa-amphiboles (barroisite, magnesiohornblende, actinolite) of a medium-pressure/medium-temperature metamorphism M2 crystallized during deformation D1. Detailed core-rim zonation profiles display increasing and then decreasing AlIV in glaucophane of M1. NaCa-amphiboles of M2, mantling glaucophane and crystallized in porphyroblasts, show first increasing, then decreasing, AlIV and AlVI. Empirically calibrated thermobarometers allowed P-T path reconstructions. In glaucophane-eclogites of a metamorphic zone I, a prograde evolution to M1 peak conditions at 400-500°C/10-12 kbar was followed by a retrograde P-T path within the glaucophane stability field. The subsequent M2 evolution was again prograde up to >600°C at 8 kbar and then retrograde. Similarly, in metamorphic zones II and III, prograde and retrograde paths of M1 and M2 at lower maximal temperatures and pressures exist. The almost complete metamorphic cycle during M2 signalizes that the HP-LT rocks escaped from an early erosion by a moderate second burial event and explains the long-lasting slow uplift with low average cooling rates. 相似文献
260.