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451.
At Shiotani, SW Japan, rhyolitic welded tuff forms a steep-sided funnel-shaped body, confined by Paleogene granitic rocks
to an elliptical area 1–1.5 km across. The Shiotani welded tuff is pervasively welded and foliated concordantly with the contact
that dips inward at angles of 70–90°. In contrast, nearby contemporary volcaniclastic deposits are non-welded and gently inclined.
Near the contact with the granite, the tuff is plastically deformed and shows lineations that plunge inward at angles of 40–65°.
Lithic and crystal clasts in the rheomorphic outer part are rotated in a plane normal to the foliations and parallel to the
lineations indicating downward flow of the welded tuff. The geometry and internal structures suggest that the Shiotani welded
tuff was emplaced and welded in a funnel-shaped eruption conduit. Upon collapse of a plinian or phreatoplinian eruption column,
the majority of the conduit-filling pyroclasts probably fell back en masse into the conduit. Heat and steam from underlying
magma and diffusion of interstitial volatiles into the glass perhaps reduced the viscosity of juvenile pyroclasts and facilitated
welding in the conduit, especially at deep levels. The hot welded pyroclasts then flowed down the conduit wall during welding
compaction and retreat of the magma. These processes resulted in increased welding toward the contacts and welding foliations
concordant with the steep wall. Emplacement of nearby correlative volcaniclastic mass-flow deposits in a shelf to upper bathyal
environment suggests a possibility that, when active, the Shiotani conduit was under the sea. Welding compaction would occur
even under the sea provided that the steam generated in the upper part of the conduit fill prevented water access.
Received: 28 February 1996 / Accepted: 5 May 1997 相似文献
452.
To accurately measure the pH, Eh, EC and temperature of groundwater retrieved from boreholes, a deep groundwater sampling
apparatus was developed which provided sensory measurements both in situ and in a flow-through cell at ground level. Under
a pressure of 1×106 Pa the in situ accuracy of the apparatus sensor was within the following limits: pH ±0.2, temperature ±0.1°C, Eh ±10 mV,
and EC ±2.4%. The measuring and sampling of deep groundwater from a borehole of more than 1000 m in depth was performed continuously
for 30 days. Values of pH were the same for the in situ sensor, the flow-through cell sensor and the laboratory measurements
of the sampled water. At the beginning of the sampling period, Eh values of the in situ sensor indicated deep groundwater
conditions. The apparatus is particularly useful for Eh measurement. Chemical composition and stable isotope ratios indicated
that the groundwater sampled from more than 1000 m depth was a connate water with a chemical composition slightly different
from seawater of the present time, and the groundwater retrieved from 800 m depth was a meteoric water. Natural radioactive
elements are thought to be the origin of the tritium in the groundwater retrieved from the 1000 m depth.
Received: 6 August 1996 / Accepted: 22 October 1996 相似文献
453.
The Nojima fault on the northwestern coast of Awaji Island, south of Kobe, was reactivated during the January 17, 1995 Hyogoken-nanbu earthquake. This fault rupture was dominated by right-lateral offset (max. 1.7 m) along a high-angle reverse fault which has a maximum vertical displacement of 1.3 m on the southeastern side. We repeatedly measured seven profiles across the fault scarp in two areas (Hirabayashi to the northeast and Ogura to the southwest) for approximately 1 year following the earthquake. The original profile of the fault scarp was an overhanging scarp at Hirabayashi and Ogura, corresponding to the 70–80 ° dip of the fault plane. The fault scarp at Hirabayashi displaces Plio-Pleistocene siltstones of the Osaka Group and is overlain by a thin bed of unconsolidated gravel. The Ogura area is entirely underlain by the Osaka Group. Scarp degradation at Hirabayashi occurred by collapse of the gravel bed and proceeded more quickly than at Ogura, where fault scarp degradation proceeded mainly by exfoliation of the Osaka Group siltstones. The degradation occurred at a very fast rate until March at Hirabayashi, and until June or July at Ogura. Since then, the degradation has been very slow. Our data strongly indicate that the scarp profile was initially controlled mainly by the dip of the fault plane, and scarp degradation has been primarily controlled by lithological factors. The degradation of the Nojima earthquake fault scarp proceeded much more quickly than that of normal fault scarps in the western U.S.A., where many observations of the initial stages of scarp degradation have been carried out. The extremely rapid degradation of the Nojima fault scarp in weak late Neogene siltstones might, in combination with rapid cultural modification of the landscape, explain the paucity of geomorphic scarps along the numerous active faults in Japan. This observation may also have implications for tectonic geomorphology and paleoseismicity studies in other countries characterised by weak bedrock and moderate to high rainfall regimes. 相似文献
454.
May Christine Modenesi-Gauttieri Silvio Takashi Hiruma Claudio Riccomini 《Geomorphology》2002,43(3-4)
Integration of landform and structural analysis allowed the identification of Late Pleistocene–Holocene pulses of tectonic activity in the Campos do Jordão Plateau with ages and regimes similar to the ones from the continental rift. Fault reactivation along Precambrian shear zones give rise to a series of conspicuous morphotectonic features, determine the formation of stream piracy phenomena, and divide the plateau into smaller blocks. Recognition of these tectonic pulses as well as of their effects in landform development—particularly clear on the Campos de São Francisco at the highest area of the SE edge of the plateau—show that besides the climate-related Quaternary environmental changes significant neotectonic instability should be considered in the geomorphic evolution of the Campos do Jordão Plateau. 相似文献
455.
Takashi Nishiyama 《Natural Resources Research》1996,5(3):155-168
In recent years, the rate of consumption of minerals and energy has been increasing. Herein, a few fundamental components of mineral consumption including population growth, rising standard of living, advances in technology, and economic growth are analyzed. Copper is one of the best resources for illustrating the growth of metal consumption and components of that growth because statistical data for copper are quite comprehensive. Among the various factors examined, an index of rising standards of living is the most significant factors explaining growth of copper consumption. 相似文献
456.
457.
458.
Kazunori Arita Takashi Ikawa Tanio Ito Akihiko Yamamoto Matsuhiko Saito Yasunori Nishida Hideyuki Satoh Gaku Kimura Teruo Watanabe Takeshi Ikawa Toru Kuroda 《Tectonophysics》1998,290(3-4):197-210
This study is the first integrated geological and geophysical investigation of the Hidaka Collision Zone in southern Central Hokkaido, Japan, which shows complex collision tectonics with a westward vergence. The Hidaka Collision Zone consists of the Idon'nappu Belt (IB), the Poroshiri Ophiolite Belt (POB) and the Hidaka Metamorphic Belt (HMB) with the Hidaka Belt from west to east. The POB (metamorphosed ophiolites) is overthrust by the HMB (steeply eastward-dipping palaeo-arc crust) along the Hidaka Main Thrust (HMT), and in turn, thrusts over the Idon'nappu Belt (melanges) along the Hidaka Western Thrust (HWT). Seismic reflection and gravity surveys along a 20-km-long traverse across the southern Hidaka Mountains revealed hitherto unknown crustal structures of the collision zone such as listric thrusts, back thrusts, frontal thrust-and-fold structures, and duplex structures. The main findings are as follows. (1) The HMT, which dips steeply at the surface, is a listric fault dipping gently at a depth of 7 km beneath the eastern end of the HMB, and cutting across the lithological boundaries and schistosity of the Hidaka metamorphic rocks. (2) A second reflector is detected 1 km below the HMT reflector. The intervening part between these two reflectors is inferred to be the POB, which is only little exposed at the surface. This inference is supported by the high positive Bouguer anomalies along the Hidaka Mountains. (3) The shallow portion of the IB at the front of the collision zone has a number of NNE-dipping reflectors, indicative of imbricated fold-and-thrust structures. (4) Subhorizontal reflectors at a depth of 14 km are recognized intermittently at both sides of the seismic profile. These reflectors may correspond to the velocity boundary (5.9–6.6 km/s) previously obtained from seismic refraction profiling in the northern Hidaka Mountains. (5) These crustal structures as well as the back thrust found in the eastern end of the traverse represent characteristics of collisional tectonics resulting from the two collisional events since the Early Tertiary. 相似文献
459.
Tetsuo Yanagi Takahide Hagita Toshiro Saino Takashi Ishimaru Sinchiro Noriki 《Journal of Oceanography》1995,51(4):459-470
Transport mechanism of suspended matter above the shelf slope is investigated with the use of the moorings of time-series sediment trap, current meter and nephelometer at three stations at the mouth of Tokyo Bay, Japan during 21 to 25 August 1993. Tidal pump mechanism is effective for the transport of suspended matter at the shelf edge, but the boring-like flood tidal current resuspends the settled suspended matter, on the bottom of shelf slope and the resuspended matter is resulted to be moved upslope in one tidal cycle at 10 m above the bottom of shelf slope. 相似文献
460.