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911.
912.
Peter Brown Robert J. Weryk Daniel K. Wong James Jones 《Earth, Moon, and Planets》2008,102(1-4):209-219
The Canadian Meteor Orbit Radar is a multi-frequency backscatter radar which has been in routine operation since 1999, with
an orbit measurement capability since 2002. In total, CMOR has measured over 2 million orbits of meteoroids with masses greater
than 10 μg, while recording more than 18 million meteor echoes in total. We have applied a two stage comparative technique
for identifying meteor streams in this dataset by making use of clustering in radiants and velocities without employing orbital
element comparisons directly. From the large dataset of single station echoes, combined radiant activity maps have been constructed
by binning and then stacking each years data per degree of solar longitude. Using the single-station mapping technique described
in Jones and Jones (Mon Not R Astron Soc 367:1050–1056, 2006) we have identified probable streams from these single station
observations. Additionally, using individual radiant and velocity data from the multi-station velocity determination routines,
we have utilized a wavelet search algorithm in radiant and velocity space to construct a list of probable streams. These two
lists were then compared and only streams detected by both techniques, on multiple frequencies and in multiple years were
assigned stream status. From this analysis we have identified 45 annual minor and major streams with high reliability. 相似文献
913.
Peter Jenniskens 《Earth, Moon, and Planets》2008,102(1-4):505-520
The history of associating meteor showers with asteroidal-looking objects is long, dating to before the 1983 discovery that
3200 Phaethon moves among the Geminids. Only since the more recent recognition that 2003 EH1 moves among the Quadrantids are
we certain that dormant comets are associated with meteoroid streams. Since that time, many orphan streams have found parent
bodies among the newly discovered Near Earth Objects. The seven established associations pertain mostly to showers in eccentric
or highly inclined orbits. At least 35 other objects are tentatively linked to streams in less inclined orbits that are more
difficult to distinguish from those of asteroids. There is mounting evidence that the streams originated from discrete breakup
events, rather than long episodes of gradual water vapor outgassing. If all these associations can be confirmed, they represent
a significant fraction of all dormant comets that are in near-Earth orbits, suggesting that dormant comets break at least
as frequently as the lifetime of the streams. I find that most pertain to NEOs that have not yet fully decoupled from Jupiter.
The picture that is emerging is one of rapid disintegration of comets after being captured by Jupiter, and consequently, that
objects such as 3200 Phaethon most likely originated from among the most primitive asteroids in the main belt, instead. They
too decay mostly by disintegration into comet fragments and meteoroid streams. The disintegration of dormant comets is likely
the main source of our meteor showers and the main supply of dust to the zodiacal cloud.
Editorial handling: Frans Rietmeijer. 相似文献
914.
Peter Jenniskens 《Earth, Moon, and Planets》2008,102(1-4):5-9
The International Astronomical Union at its 2006 General Assembly in Prague has adopted a set of rules for meteor shower nomenclature,
a working list with designated names (with IAU numbers and three-letter codes), and established a Task Group for Meteor Shower Nomenclature in Commission 22 (Meteors and Interplanetary Dust) to help define which meteor showers exist from well defined groups of
meteoroids from a single parent body. 相似文献
915.
The orbital evolution of the two meteorites Příbram and Neuschwanstein on almost identical orbits and also several thousand
clones were studied in the framework of the N-body problem for 5,000 years into the past. The meteorites moved on very similar
orbits during the whole investigated interval. We have also searched for photographic meteors and asteroids moving on similar
orbits. There were five meteors found in the IAU MDC database and six NEAs with currently similar orbits to Příbram and Neuschwanstein.
However, only one meteor 161E1 and one asteroid 2002 QG46 had a similar orbital evolution over the last 2,000 years. 相似文献
916.
Josep M. Trigo-Rodriguez José M. Madiedo Peter S. Gural Alberto J. Castro-Tirado Jordi Llorca Juan Fabregat Standa Vítek Pep Pujols 《Earth, Moon, and Planets》2008,102(1-4):231-240
By using high-resolution, low-scan-rate, all-sky CCD cameras, the SPanish Meteor Network (SPMN) is currently monitoring meteor
and fireball activity on a year round basis. Here are presented just a sampling of the accurate trajectory, radiant and orbital
data obtained for meteors imaged simultaneously from two SPMN stations during the continuous 2006–2007 coverage of meteor
and fireball monitoring. Typical astrometric uncertainty is 1–2 arc min, while velocity determination errors are of the order
of 0.1–0.5 km/s, which is dependent on the distance of each event to the station and its particular viewing geometry. The
cameras have demonstrated excellent performance for detecting meteor outbursts. The recent development of automatic detection
software is also providing real-time information on the global meteor activity. Finally, some examples of the all-sky CCD
cameras applications for detecting unexpected meteor activity are given. 相似文献
917.
Peter S. Gural 《Earth, Moon, and Planets》2008,102(1-4):269-275
An ever increasing variety of electronic instrumentation is being brought to bear in meteor studies and analysis, with unique
meteor detection challenges arising from the attempt to do automated and near real-time processing of the imagery. Recent
algorithm developments in the literature have been applied and implemented in software to provide reliable meteor detection
in all-sky imagers, wide-field intensified video, and narrow field-of-view telescopic systems. The algorithms that have been
employed for meteor streak detection include Hough transforms with phase coded disk, localized Hough transforms with matched
filtering, and fast moving cluster detection. They have found application in identifying meteor tracks in the Spanish Fireball
Network all-sky images, detailed analysis of video recordings during the recent Leonid meteor storms, and development of a
detection/cueing technology system for rapid slew and tracking of meteors. 相似文献
918.
Douglas O. ReVelle Elizabeth A. Sukara Wayne N. Edwards Peter G. Brown 《Earth, Moon, and Planets》2008,102(1-4):337-344
We have recently digitized and partially reanalyzed the historic bolide infrasonic database. These 10 events were originally
detected by the U.S. Air Force Technical Applications Center (AFTAC) from ∼1960 to 1974. In this paper we present the first
preliminary reanalysis results for two of the 10 bolide events, namely the Revelstoke bolide of 3/31/1965 as well as the Prince
Edward Islands (P.E.I). S. African bolide of 8/03/1963, which were among the largest bolides detected during this time period.
These bolides have been investigated initially since they are most likely to have had a significant effect on the computed
global influx rate of ReVelle (Global Infrasonic Monitoring of Large Bolides, pp 483–490, 2001) as indicated in Brown et al. (Nature, 420:314–316, 2002). We are in the process of recomputing all relevant infrasonic propagation quantities such as plane wave back azimuth, signal
velocities, power spectra, spectrograms, as well as energy estimates using multiple techniques. In a future paper we will
present a complete digital reanalysis of the AFTAC bolide infrasonic data and its final resulting global bolide influx implications. 相似文献
919.
Flux-transport type solar dynamos have achieved considerable success in correctly simulating many solar cycle features, and are now being used for prediction of solar cycle timing and amplitude. We first define flux-transport dynamos and demonstrate how they work. The essential added ingredient in this class of models is meridional circulation, which governs the dynamo period and also plays a crucial role in determining the Sun’s memory about its past magnetic fields. We show that flux-transport dynamo models can explain many key features of solar cycles. Then we show that a predictive tool can be built from this class of dynamo that can be used to predict mean solar cycle features by assimilating magnetic field data from previous cycles. 相似文献
920.
Laurence A. J. GARVIE Grant BAUMGARDNER Peter R. BUSECK 《Meteoritics & planetary science》2008,43(5):899-903
Abstract— Carbonaceous nanoglobules are ubiquitous in carbonaceous chondrite (CC) meteorites. The Tagish Lake (C2) meteorite is particularly intriguing in containing an abundance of nanoglobules, with a wider range of forms and sizes than encountered in other CC meteorites. Previous studies by transmission electron microscopy (TEM) have provided a wealth of information on chemistry and structure. In this study low voltage scanning electron microscopy (SEM) was used to characterize the globule forms and external structures. The internal structure of the globules was investigated after sectioning by focused ion beam (FIB) milling. The FIB‐SEM analysis shows that the globules range from solid to hollow. Some hollow globules show a central open core, with adjoining smaller cores. The FIB with an SEM is a valuable tool for the analysis of extraterrestrial materials, even of sub‐micron‐sized “soft” carbonaceous particles. The rapid site‐specific cross‐sectioning capabilities of the FIB allow the preservation of the internal morphology of the nanoglobules, with minimal damage or alteration of the unsectioned areas. 相似文献