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291.
Deconvolution with wavelets and vaguelettes 总被引:2,自引:0,他引:2
The use of wavelets for the solution of convolution equations is studied as a possible alternative to the well-established
Fast Fourier Transform (FFT) technique. Two possible solution strategies are investigated: (1) The use of wavelets for the
representation of both the given data and the unknown solution. This leads to an algorithm with good de-noising and data-compression
properties. In terms of computational efficiency this algorithm is inferior to FFT. (2) The use of wavelets for the representation
of the unknown solution and of so-called vaguelettes for the representations of the given data. This leads to an algorithm
which is even faster than FFT.
Received: 14 October 1998 / Accepted: 30 November 1999 相似文献
292.
Preliminary orbit determination is a multipoint boundary value problem which may be solved by the generalized Newton-Raphson iteration. When applied formally the method suffers from extensive computer storage requirements, fairly long execution times and in some cases, insufficient accuracy. In this work we seek to remove these practical difficulties via modification of the computational algorithm in such a way that solution storage is eliminated for the most part and computational speed and tolerance to imprecise integration algorithms is improved. The modified methods are applied to nine typical preliminary orbit determination problems to demonstrate fast convergence and short computation times, even with very poor starting values for the iteration. Excellent precision of the resulting solution is also demonstrated as well as the algorithm's ability to handle circular, elliptic, parabolic and hyperbolic orbits. 相似文献
293.
The Archean Shawmere Anorthosite Complex, at the southern end of the Kapuskasing Structural Zone, consists dominantly of anorthosite (An65 –85) with minor gabbroic and ultramafic units, which are completely enclosed and cut by tonalites. Both the anorthosites and the tonalites are themselves cut by narrow dikes of gabbroic anorthosite. All of the rocks have undergone high grade metamorphism and are recrystallized so that few igneous textures remain.The anorthosites, gabbros and ultramafic rocks of this complex are cumulates which contain calcic plagioclase (An65–95) and have atomic Mg/(Mg + Fe2+) ratios (Mg#) greater than 0.6; less than 3 ppm Rb; 150–210 ppm Sr; and less than 60 ppm Ba. REE abundanees range from 0.2 to 10 times chondritic and exhibit both light-enriched and light-depleted REE patterns. The lower Mg# for the samples having more enriched light REE indicates substantial fractions of ferromagnesian minerals crystallized in addition to plagioclase during fractional crystallization, suggesting that the parent magma was basaltic, and not anorthositic. The ranges in Sr, Ba and REE abundances required for the magmas are typical of those for tholeiitic basalts from Archean greenstone belts. Thus the Shawmere Anorthosite Complex may represent cumulates of a crustal-level magma chamber which could have been the immediate source of basic Archean volcanics.One gabbroic anorthositic dike sample has a steeply fractionalted REE pattern with heavy REE abundances less than chondrites and a large positive Eu anomaly. The proposed interpretations is that this rock formed by partial melting of mafic cumulates, perhaps those of the Shawmere Anorthosite Complex itself. 相似文献
294.
J. S. Gilbert M. V. Stasiuk S. J. Lane C. R. Adam M. D. Murphy R. S. J. Sparks J. A. Naranjo 《Bulletin of Volcanology》1996,58(1):67-83
A radar and gravity survey of the ice-filled caldera at Volcán Sollipulli, Chile, indicates that the intra-caldera ice has
a thickness of up to 650 m in its central part and that the caldera harbours a minimum of 6 km3 of ice. Reconnaissance geological observations show that the volcano has erupted compositions ranging from olivine basalt
to dacite and have identified five distinct volcanic units in the caldera walls. Pre- or syn-caldera collapse deposits (the
Sharkfin pyroclastic unit) comprise a sequence which evolved from subglacial to subaerial facies. Post-caldera collapse products,
which crop out along 17 of the 20 km length of the caldera wall, were erupted almost exclusively along the caldera margins
in the presence of a large body of intra-caldera ice. The Alpehué crater, formed by an explosive eruption between 2960 and
2780 a. BP, in the southwest part of the caldera is shown to post date formation of the caldera. Sollipulli lacks voluminous
silicic pyroclastic rocks associated with caldera formation and the collapse structure does not appear to be a consequence
of a large-magnitude explosive eruption. Instead, lateral magma movement at depth resulting in emptying of the magma chamber
may have generated the caldera. The radar and gravity data show that the central part of the caldera floor is flat but, within
a few hundred metres of the caldera walls, the floor has a stepped topography with relatively low-density rock bodies beneath
the ice in this region. This, coupled with the fact that most of the post-caldera eruptions have taken place along the caldera
walls, implies that the caldera has been substantially modified by subglacial marginal eruptions. Sollipulli caldera has evolved
from a collapse to a constructional feature with intra-caldera ice playing a major role. The post-caldera eruptions have resulted
in an increase in height of the walls and concomitant deepening of the caldera with time.
Received: 12 June 1995 / Accepted: 7 December 1995 相似文献
295.
Cees W. Passchier Gilbert Wiplinger Talip Güngör Paul Kessener Gül Sürmelihindi 《地学学报》2013,25(4):292-297
A 38‐km‐long ancient aqueduct channel that served Roman Ephesos, Turkey was dislocated vertically over 3 m by a single seismic event on a normal fault. A new channel was constructed downstream from the fault in Roman times, next to and partly on top of the original channel. Archaeological investigations and study of carbonate deposits suggest a causative seismic event in the second half of the second century CE, probably in 178 CE, after the original channel had functioned for <35 years. The ?çme Tepe fault was identified as responsible for the displacement and may still constitute a seismic and tsunami hazard for the Turkish west coast, specifically for the city of Ku?adas?. Ancient aqueducts, of which more than 1400 are presently known, are a promising and almost untapped archive for archaeoseismic studies, especially in the Mediterranean area. 相似文献
296.
Gilbert M. Grosvenor 《The Professional geographer》1984,36(4):413-418
297.
Long wavelength magnetic anomalies of crustal origin derived from the POGO and MAGSAT satellite data often display a strong continuity across the now-rifted continental margins when the continents are reassembled into Pangaea. These anomalies predate the breakup of the supercontinent and represent major blocks whose crustal properties are broadly similar even though those blocks are no longer contiguous. 相似文献
298.
M.A. Wilson R.P. Philp A.H. Gillam T.D. Gilbert K.R. Tate 《Geochimica et cosmochimica acta》1983,47(3):497-502
Four humic extracts isolated from terrestrial, mahne, plankton and freshwater sources have been investigated by pyrolysis-gas chromatography-mass spectrometry. The results show that substantial quantities of phenols (some not derived from lignin), pyrroles and nitrites (derived from proteins, nucleic acids or porphyrins) are decomposition products. Small amounts of furans (derived from carbohydrates) and unsaturated ketones (derived from polycarboxylic aliphatic acids) are also present. The results illustrate how parent material, transport factors and biological activity affect the composition of humic extracts. 相似文献
299.
300.