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171.
Assessment of the vertical distribution on seismic ground motion 总被引:1,自引:0,他引:1
It is very important for the facilities such as nuclear power plants to infer seismic force loading on the earthquake stability assessment of the building foundation and the surrounding slope. The purpose of this paper was to propose a method to evaluate underground seismic coefficients, taking into account dynamic response along the depth in horizontally multi-layered ground. The dynamic property of the seismic coefficient was analyzed on the basis of earthquake records observed at hard and soft rock sites mostly found in Tertiary deposits and sedimentary ground sites of the Pleistocene and Holocene epoch. The evaluation methods of a vertical distribution on underground seismic coefficients were proposed for a few calculation methods on the classified layered ground. Extended evaluation for underground seismic coefficients was confirmed with respect to some multi-layered ground during strong motion. 相似文献
172.
Abstract Rb–Sr and Sm–Nd isochron ages were determined for whole rocks and mineral separates of hornblende‐gabbros and related metadiabases and quartz‐diorite from Shodoshima, Awashima and Kajishima islands in the Ryoke plutono‐metamorphic belt of the Setouchi area, Southwest Japan. The Rb–Sr and Sm–Nd whole‐rock‐mineral isochron ages for six samples range from 75 to 110 Ma and 200–220 Ma, respectively. The former ages are comparable with the Rb–Sr whole‐rock isochron ages reported from neighboring Ryoke granitic rocks and are thus due to thermal metamorphism caused by the granitic intrusions. On the contrary, the older ages suggest the time of formation of the gabbroic and related rocks. The initial 87Sr/86Sr and 143Nd/144Nd ratios of the gabbroic rocks (0.7070–0.7078 and 0.51217–0.51231 at 210 Ma, respectively) are comparable with those of neighboring late Cretaceous granites and lower crustal granulite xenoliths from Cenozoic andesites in this region. Because the gabbroic rocks are considered to be fragments of the lower crustal materials interlayered in the granulitic lower crust, their isotopic signature has been inherited from an enriched mantle source or, less likely, acquired through interaction with the lower crustal materials. The Sr and Nd isotopic and petrologic evidence leads to a plausible conclusion that the gabbroic rocks have formed as cumulates from hydrous mafic magmas of light rare earth element‐rich (Sm/Nd < 0.233) and enriched isotopic (?Sr > 0 and ?Nd < 0) signature, which possibly generated around 220–200 Ma by partial melting of an upper mantle. We further conclude that they are fragments of refractory material from the lower crust caught up as xenoblocks by granitic magmas, the latter having been generated by partial melting of granulitic lower crustal material around 100 Ma. 相似文献
173.
Gravelly spit deposits in a transgressive systems tract: the Pleistocene Higashikanbe Gravel, central Japan 总被引:1,自引:0,他引:1
The Pleistocene Higashikanbe Gravel, which crops out along the Pacific coast of the Atsumi Peninsula, central Japan, consists of well‐sorted, pebble‐ to cobble‐size gravel beds with minor sand beds. The gravel includes large‐scale foreset beds (5–10 m high) and overlying subhorizontal beds (0·5–3 m thick), showing foreset and topset structure, from which the gravel has previously been interpreted as deposits of a Gilbert‐type delta. However, (1) the gravel beds lack evidence of fluvial activity, such as channels in the subhorizontal beds; (2) the foresets incline palaeolandwards; (3) the gravels fill a fluvially incised valley; and (4) the gravels overlie low‐energy deposits of a restricted environment, such as a bay or an estuary. The foresets generally dip towards the inferred palaeoshoreline, indicating landward accretion of gravel. Reconstruction of the palaeogeography of the peninsula indicates that the Higashikanbe Gravel was deposited as a spit similar to that developed at the western tip of the present Atsumi Peninsula, rather than as a delta. According to the new interpretation, the large‐scale foreset beds are deposits on the slopes of spit platforms and accreted in part to the sides of small islets that are fragments of the submerging spit during relative sea‐level rise. The subhorizontal beds include nearshore deposits on the spit platform topsets and deposits of gravel shoals or bars, which are reworked sediments of the spit beach gravels during a transgression. The lack of spit beach facies in the subhorizontal beds results from truncation by shoreface erosion. Dome structure, which is a cross‐sectional profile of a recurved gravel spit at its extreme point, and sandy tidal channel deposits deposited between the small islets were also identified in the Higashikanbe Gravel. The Higashikanbe Gravel fills a fluvially incised valley and occupies a significant part of a transgressive systems tract, suggesting that gravelly spits are likely to be well developed during transgressions. The large‐scale foreset beds and subhorizontal beds of gravelly spits in transgressive systems tracts contrast with the foreset and topset beds of deltas, characteristic of highstand, lowstand and shelf‐margin systems tracts. 相似文献
174.
175.
Hikaru Sawada Ernest Tafumanei Mugandani Tomohiko Sato Yusuke Sawaki Shuhei Sakata Yukio Isozaki Shigenori Maruyama 《地学学报》2019,31(5):438-444
The ca. 2.2–2.1 Ga Magondi Supergroup on the Zimbabwe Craton in Southern Africa is mainly composed of sedimentary rocks deposited in a rift basin/passive continental margin, which record a unique episode in carbon isotope perturbation called the Lomagundi–Jatuli Event (LJE). This study reports new U–Pb ages of detrital zircons from the Deweras and Lomagundi groups of the Magondi Supergroup, and of igneous zircons from underlying granitoids, to constrain the timing of the LJE and to identify the provenance of the Magondi Supergroup. Most analysed detrital zircon grains range in ages between ca. 2.9 and 2.6 Ga. Three ca. 2.3–2.2 Ga detrital zircons from sandstone of the Deweras Group, with the youngest 207Pb‐206Pb age of 2,216 ± 22 Ma, indicate the onset of LJE in the Zimbabwe Craton was almost simultaneous to that in Fennoscandia and the Superior Craton, supporting the global synchronicity of the LJE. 相似文献
176.
Hiroki Iwata Yoshiko Kosugi Keisuke Ono Masayoshi Mano Ayaka Sakabe Akira Miyata Kenshi Takahashi 《Boundary-Layer Meteorology》2014,151(1):95-118
Methane ( ${\mathrm {CH}}_{4}$ ) fluxes observed with the eddy-covariance technique using an open-path ${\mathrm {CH}}_{4}$ analyzer and a closed-path ${\mathrm {CH}}_{4}$ analyzer in a rice paddy field were evaluated with an emphasis on the flux correction methodology. A comparison of the fluxes obtained by the analyzers revealed that both the open-path and closed-path techniques were reliable, provided that appropriate corrections were applied. For the open-path approach, the influence of fluctuations in air density and the line shape variation in laser absorption spectroscopy (hereafter, spectroscopic effect) was significant, and the relative importance of these corrections would increase when observing small ${\mathrm {CH}}_{4}$ fluxes. A new procedure proposed by Li-Cor Inc. enabled us to accurately adjust for these effects. The high-frequency loss of the open-path ${\mathrm {CH}}_{4}$ analyzer was relatively large (11 % of the uncorrected covariance) at an observation height of 2.5 m above the canopy owing to its longer physical path length, and this correction should be carefully applied before correcting for the influence of fluctuations in air density and the spectroscopic effect. Uncorrected ${\mathrm {CH}}_{4}$ fluxes observed with the closed-path analyzer were substantially underestimated (37 %) due to high-frequency loss because an undersized pump was used in the observation. Both the bandpass and transfer function approaches successfully corrected this flux loss. Careful determination of the bandpass frequency range or the transfer function and the cospectral model is required for the accurate calculation of ${\mathrm {CH}}_{4}$ fluxes with the closed-path technique. 相似文献
177.
This study estimated the trends in the number of days that fall within the near-zero (0?°C) range of the temperature continuum. This narrow range has importance for potential transportation hazards and freeze-thaw cycles. While the tails of the air-temperature distribution and their trends often are closely examined under the climate change context, the frequency and trend of other portions of the air-temperature distribution can be equally important, as many societal impacts are caused by events in the non-tail region, such as near-zero °C temperatures (NZT). Examining the trend of the number of NZT days over the conterminous USA for the period of 1948–1949 through 2010–2011, we found three distinct spatial clusters. The most distinctive spatial clusters are found along the West Coast (positive temperature trends leading to a decrease in NZT days), the High Plains and Northern Rockies (positive temperature trends leading to an increase in NZT days), and the southeastern USA (negative temperature trends leading to an increase in NZT days). While trends in the number of NZT days are linked to changes in mean minimum air temperature, increasing minimum temperature leads to a positive trend at NZT days only at some locations. 相似文献
178.
Shigenao Maruyama Takashi YabukiTetsuya Sato Koutaro TsubakiAtsuki Komiya Mikihito WatanabeHiroshi Kawamura Katsumi Tsukamoto 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(5):567-574
The American physical oceanographer Henry Stommel and co-workers proposed “the perpetual salt fountain” and suggested the possibility of upwelling deep seawater without an energy source. In the open ocean, deep seawater containing rich nutrients becomes a source of primary production. Previously, we have tested Stommel's hypothesis by numerical simulations and in ocean experiments, and confirmed the upwelling of a perpetual salt fountain. In the present study, we conducted an open-ocean experiment in the Philippines Sea, and succeeded to demonstrate an increase in chlorophyll concentration. The chlorophyll concentration at the pipe outlet was much greater than that in the surrounding seawater. Satellite ocean-color image around the pipe was analyzed, and the signal of artificial upwelling is investigated. Composite analysis of satellite chlorophyll image indicates an increased surface chlorophyll distribution in the vicinity of pipe position, in which the increasing signal is much larger than the expected production based on nutrient supply. Although the problem must be further discussed, this increased signal is shown to be statistically significant. This mechanism may contribute to effective utilization of fishery resources in subtropical oligotrophic region. 相似文献
179.
Hurford G.J. Schmahl E.J. Schwartz R.A. Conway A.J. Aschwanden M.J. Csillaghy A. Dennis B.R. Johns-Krull C. Krucker S. Lin R.P. McTiernan J. Metcalf T.R. Sato J. Smith D.M. 《Solar physics》2002,210(1-2):61-86
The Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) observes solar hard X-rays and gamma-rays from 3 keV to
17 MeV with spatial resolution as high as 2.3 arc sec. Instead of focusing optics, imaging is based on nine rotating modulation
collimators that time-modulate the incident flux as the spacecraft rotates. Starting from the arrival time of individual photons,
ground-based software then uses the modulated signals to reconstruct images of the source. The purpose of this paper is to
convey both an intuitive feel and the mathematical basis for this imaging process. Following a review of the relevant hardware,
the imaging principles and the basic back-projection method are described, along with their relation to Fourier transforms.
Several specific algorithms (Clean, MEM, Pixons and Forward-Fitting) applicable to RHESSI imaging are briefly described. The
characteristic strengths and weaknesses of this type of imaging are summarized. 相似文献
180.
Jiangtao Su Yu Liu Hiroki Kurokawa Xinjie Mao Shangbin Yang Hongqi Zhang Haimin Wang 《Solar physics》2007,242(1-2):53-63
We present new observations of the interactions of two close, but distinct, Hα filaments and their successive eruptions on
5 November 1998. The magnetic fields of the filaments are both of the sinistral type. The interactions between the two filaments
were initiated mainly by an active filament of one of them. Before the filament eruptions, two dark plasma ejections and chromospheric
brightenings were observed. They indicate that possible magnetic reconnection had occurred between the two filaments. During
the first filament eruption, salient dark mass motions transferring from the left erupting filament into the right one were
observed. The right filament erupted 40 minutes later. This second filament eruption may have been the result of a loss of
stability owing to the sudden mass injection from the left filament. Based on the Hα observations, we have created a sketch
for understanding the interactions between two filaments and accompanying activities. The traditional theory of filament merger
requires that the filaments share the same filament channel and that the reconnection occurs between the two heads, as simulated
by DeVore, Antiochos, and Aulanier (Astrophys. J.
629, 1122, 2005; 646, 1349, 2006). Our interpretation is that the external bodily magnetic reconnection between flux ropes of the same chirality is another
possible way for two filament bodies to coalesce.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献