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531.
532.
A method for simulating future climate on regional space scales is developed and applied to northern Africa. Simulation with
a regional model allows for the horizontal resolution needed to resolve the region’s strong meridional gradients and the optimization
of parameterizations and land-surface model. The control simulation is constrained by reanalysis data, and realistically represents
the present day climate. Atmosphere–ocean general circulation model (AOGCM) output provides SST and lateral boundary condition
anomalies for 2081–2100 under a business-as-usual emissions scenario, and the atmospheric CO2 concentration is increased to 757 ppmv. A nine-member ensemble of future climate projections is generated by using output
from nine AOGCMs. The consistency of precipitation projections for the end of the twenty-first century is much greater for
the regional model ensemble than among the AOGCMs. More than 77% of ensemble members produce the same sign rainfall anomaly
over much of northern Africa. For West Africa, the regional model projects wetter conditions in spring, but a mid-summer drought
develops during June and July, and the heat stoke risk increases across the Sahel. Wetter conditions resume in late summer,
and the likelihood of flooding increases. The regional model generally projects wetter conditions over eastern Central Africa
in June and drying during August through September. Severe drought impacts parts of East Africa in late summer. Conditions
become wetter in October, but the enhanced rainfall does not compensate for the summertime deficit. The risk of heat stroke
increases over this region, although the threat is not projected to be as great as in the Sahel. 相似文献
533.
Geoffrey M. Morrison Sonia Yeh Anthony R. Eggert Christopher Yang James H. Nelson Jeffery B. Greenblatt Raphael Isaac Mark Z. Jacobson Josiah Johnston Daniel M. Kammen Ana Mileva Jack Moore David Roland-Holst Max Wei John P. Weyant James H. Williams Ray Williams Christina B. Zapata 《Climatic change》2015,131(4):545-557
534.
A. Hillaris O. Malandraki K.-L. Klein P. Preka-Papadema X. Moussas C. Bouratzis E. Mitsakou P. Tsitsipis A. Kontogeorgos 《Solar physics》2011,273(2):493-509
On 17 January 2005 two fast coronal mass ejections were recorded in close succession during two distinct episodes of a 3B/X3.8
flare. Both were accompanied by metre-to-kilometre type-III groups tracing energetic electrons that escape into the interplanetary
space and by decametre-to-hectometre type-II bursts attributed to CME-driven shock waves. A peculiar type-III burst group
was observed below 600 kHz 1.5 hours after the second type-III group. It occurred without any simultaneous activity at higher
frequencies, around the time when the two CMEs were expected to interact. We associate this emission with the interaction
of the CMEs at heliocentric distances of about 25 R
⊙. Near-relativistic electrons observed by the EPAM experiment onboard ACE near 1 AU revealed successive particle releases
that can be associated with the two flare/CME events and the low-frequency type-III burst at the time of CME interaction.
We compare the pros and cons of shock acceleration and acceleration in the course of magnetic reconnection for the escaping
electron beams revealed by the type-III bursts and for the electrons measured in situ. 相似文献
535.
Abstract– We have examined the relationship between natural thermoluminescence (TL) and 26Al in 120 Antarctic meteorites in order to explore the orbital history and terrestrial ages of these meteorites. Our results confirm the observations of Hasan et al. (1987) which were based on 23 meteorites. For most meteorites there was a positive correlation between natural TL and 26Al, reflecting their similarity in decay rate under Antarctic conditions and thus in terrestrial age. For a small group with low TL and high 26Al a small perihelion was proposed. Within this group, natural TL decreases with terrestrial age as determined by 36Cl measurements, although the rate of TL decay is faster (half‐life approximately 10 ka) and the ages that can be determined are smaller (<200 ka) than for most meteorites. The faster decay rate and lower natural TL levels are a reflection of recent exposure to higher radiation doses and higher temperatures, since this history would populate less stable TL traps with smaller electron densities. We sort the 120 meteorites by perihelion and terrestrial age. The normal perihelion group range up to approximately 1000 ka and the small perihelion group range up to approximately 200 ka. An intermediate perihelion group tends to have short terrestrial ages (20–60 ka). There is acceptable agreement between most (34 out of 43) of our present terrestrial age estimates and those determined by isotopic means, the exceptions reflecting complex irradiation histories, long burial times in the Antarctic, or other issues. 相似文献
536.
537.
Christina Neal Olga Girina Sergey Senyukov Alexander Rybin Jeffrey Osiensky Pavel Izbekov Gail Ferguson 《Natural Hazards》2009,51(2):245-262
More than 65 potentially active volcanoes on the Kamchatka Peninsula and the Kurile Islands pose a substantial threat to aircraft on the Northern Pacific (NOPAC), Russian Trans-East (RTE), and Pacific Organized Track System (PACOTS) air routes. The Kamchatka Volcanic Eruption Response Team (KVERT) monitors and reports on volcanic hazards to aviation for Kamchatka and the north Kuriles. KVERT scientists utilize real-time seismic data, daily satellite views of the region, real-time video, and pilot and field reports of activity to track and alert the aviation industry of hazardous activity. Most Kurile Island volcanoes are monitored by the Sakhalin Volcanic Eruption Response Team (SVERT) based in Yuzhno-Sakhalinsk. SVERT uses daily moderate resolution imaging spectroradiometer (MODIS) satellite images to look for volcanic activity along this 1,250-km chain of islands. Neither operation is staffed 24 h per day. In addition, the vast majority of Russian volcanoes are not monitored seismically in real-time. Other challenges include multiple time-zones and language differences that hamper communication among volcanologists and meteorologists in the US, Japan, and Russia who share the responsibility to issue official warnings. Rapid, consistent verification of explosive eruptions and determination of cloud heights remain significant technical challenges. Despite these difficulties, in more than a decade of frequent eruptive activity in Kamchatka and the northern Kuriles, no damaging encounters with volcanic ash from Russian eruptions have been recorded. 相似文献
538.
Radio noise storms show that suprathermal electrons (a few tens of keV) are present in the vicinity of active regions during several hours or even a few days. Where and how these electrons are energized is not yet well known. A flare-like sudden energy release in the active region is in general observed at the onset of noise storms, either as a fully developed flare or, more often, as a soft X-ray brightening without conspicuous H signature. In order to investigate to what extent electrons energized in the active region contribute to the noise-storm emission in the overlying coronal structures, we combine radio imaging (Nançay radioheliograph) with X-ray spectral observations at photon energies of a few keV (GOES) and - for the first time - around 10 keV (WATCH/GRANAT). In two of four studied events the WATCH data show a significant excess of the deka-keV count rate above the expectation from an isothermal fit to the GOES fluxes. Although the electron population producing the deka-keV X-ray emission would be energetic enough to power the simultaneous radio noise storm, the much longer duration of the radio emission requires time-extended particle acceleration. The acceleration probably occurs in the corona overlying the X-ray emitting region, triggered by the processes which give rise to the X-ray brightenings. 相似文献
539.
Slope streaks are a form of gravity-driven mass-movements that frequently occur on Mars today. The cause of slope streak formation remains unclear; both, dry and wet processes have been suggested. Here, we observationally constrain the time of the year during which slope streaks form. Imagery from four Mars-orbiting cameras is mined to identify locations that have been imaged repeatedly, and the overlapping images are surveyed for streak activity. A search algorithm automatically finds the locations on the surface that have been imaged most often based on a graph representation. Dark slope streaks are found to form sporadically throughout the Mars year. At one study site in the Olympus Mons Aureole, observations constrain slope streak formation to at least five distinct time intervals within a single Mars year. New slope streaks form spatially isolated or in small groups within a few kilometers of one another. The observations suggest that slope streak triggering is unrelated to season and not caused by any large regional events. Most slope streaks are caused by sporadic events of small spatial extent. 相似文献
540.
Biological interest in the exploration of Mars is briefly described as is the biological experiments package to be flown as part of the Viking 1975 lander payload. 相似文献