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91.
本文通过对地形通视分析的基本设想的描述及其实践途径中有关问题的探讨,结合实例阐明了计算机自动进行通视分析的基本方法和处理技巧,并附有具体程序。 相似文献
92.
Jiankui?Shi?Email author Zhenxing?Liu Zhang?T.?L. Jianshan?Guo Manlian?Zhang Sheping?Shang Xigui?Luo 《中国科学D辑(英文版)》2003,46(10):986-993
Based on satellite observation data, using dynamics equation, the ionospheric O+ ion’s distribution in the synchronous altitude region for different geomagnetic activity indexK
p is studied by theoretical modeling and numerical analyzing, and semi-empirical models for the O+ ion’s density and flux versus longitude in the synchronous altitude region for differentK
p
are given. The main results show that in the synchronous altitude region: (i) The O+ ion’s density and flux in day-side are larger than those in nightside. (ii) With longitude changing, the higher the geomagnetic
activity indexK
p
is, the higher the O+ ion’s density and flux, and their variation amplitude will be. The O+ ion’s density and flux whenK
p ≥ 6 will be about ten times as great as that whenK
p
= 0. (iii) WhenK
p
= 0 orK
p ≥ 6, the O+ ion’s density reaches maximum at longitudes 120° and 240° respectively, and minimum in the magnetotail. WhenK
p
= 3−5, the O+ ion’s density gets to maximum at longitude 0°, and minimum in the magnetotail. However, the O+ ion’s flux reaches maximum at longitude 120° and 240° respectively, and minimum in the magnetotail for anyK
p
value. 相似文献
93.
Jean-Claude Andr Jean-Yves Caneill Michel Dqu Philippe Rogel Laurent Terray Yves Tourre 《Comptes Rendus Geoscience》2002,334(16):1115
The atmosphere and the ocean are subject to many dynamical instabilities, which limit the time during which their behaviour can be deterministically forecasted. At longer timescales, the atmosphere can be predicted at best using statistical methods, as a response to external forcing linked to sea- and land-surface anomalies. Climate being defined as the mean of atmospheric states, it appears that it can be predicted up to a few months in advance, which is the characteristic time of the so-called slow components of the climate system. Forecasting can sometimes be extended to longer time ranges, especially when the coupled ocean–atmosphere system exhibits internal variability modes, with characteristic times of a few years. Seasonal climate forecasting is most often based upon Monte-Carlo simulations, where the various realisations correspond to slightly different initial conditions. The present sate-of-the-art in Europe (ECMWF) and/or in the USA (IRI) allows to forecast such major phenomena, as El Niño, up to six months in advance. Finally, some parameters may exhibit predictability at still longer time-ranges (inter-annual to decadal), but only for certain regions. The example of electricity production is used to underline the potentially large economical benefit of seasonal climate forecasting. To cite this article: J.-C. André et al., C. R. Geoscience 334 (2002) 1115–1127.
Résumé
L'atmosphère et l'océan sont le siège d'instabilités dynamiques, qui limitent la durée pendant laquelle il est possible d'en prévoir l'évolution de façon déterministe. Au-delà, l'atmosphère n'est plus prévisible, au mieux, que de façon statistique, en fonction du forçage externe qu'exerce(nt) sur elle l'océan et/ou la surface des continents. Le climat (au sens d'une moyenne des états atmosphériques) se révèle ainsi prévisible jusqu'à des échéances temporelles de quelques mois, échelle de temps caractéristique des composantes dites « lentes » du système climatique. La prévision peut s'étendre à des échéances parfois plus longues, dans le cas où le système couplé océan–atmosphère posséderait des modes de variabilité temporelle de périodes caractéristiques de quelques années. La prévision climatique saisonnière est très souvent construite à partir de simulations de type Monte-Carlo, avec des ensembles de réalisations utilisant des conditions initiales légèrement différentes. Dans l'état actuel de ces prévisions, qu'elles soient réalisées en Europe (CEPMMT) ou aux États-Unis (IRI), il est possible de prévoir environ six mois à l'avance un certain nombre de phénomènes climatiques, en particulier ceux liés aux épisodes dits « El Niño », pour lesquels l'amplitude des variations est suffisamment importante. Il existe, par ailleurs, une prévisibilité à encore plus longue échéance (inter-annuelle à décennale), mais seulement pour certains paramètres et certaines régions. L'exemple de la production d'électricité montre l'importance économique potentielle très grande de la prévision climatique saisonnière. Pour citer cet article : J.-C. André et al., C. R. Geoscience 334 (2002) 1115–1127. 相似文献94.
Guillaume Favreau Christian Leduc Christelle Marlin Abdou Guéro 《Comptes Rendus Geoscience》2002,334(6):395-401
In southwest Niger, the Continental Terminal water table displays a natural hollow shape about 10 m in depth over an area of 4000 km2. A 10-year survey of this hollow aquifer has shown that current recharge is above . The water table has risen continuously since the 1950–1960s as a result of land clearance. This shows a disequilibrium in the aquifer balance. The long-term recharge rate is estimated by radioisotopes to be around . This figure fits with the only possible origin of the piezometric depression, i.e. evapotranspiration losses in its centre. To cite this article: G. Favreau et al., C. R. Geoscience 334 (2002) 395–401. 相似文献
95.
CAI Zhiwu ZHAO Dongming CHEN Jinping JIAO Wenhai 《地球空间信息科学学报》2006,9(1):18-23
Introduction Thepotentialvulnerabilityofsatellitenaviga tionsystemthatreliesongroundstationsisthat thesystemwouldbreakdownifgroundstations weredestroyed,whichcannotmeettherequire mentofnavigationwarfare[1].Withthedevelop mentofsuchspace basedsystemsasgrou… 相似文献
96.
Vyacheslav M. Zobin Carlos J. Navarro-Ochoa Gabriel A. Reyes-Dávila 《Bulletin of Volcanology》2006,69(2):141-147
In July–August 2003, the andesitic lava dome at Volcán de Colima, México, was destroyed by a sequence of explosions that replaced the 2×106 m3 dome with a crater 200 m across and 30 m deep. The two strongest explosions occurred on July 17 and August 28. The initial low-frequency impulses that they produced, which were recorded on broadband seismic records, allowed an estimation of the counter forces of the initiating process as being equal to 0.3×1011 N and 1×1011 N for the July and August events, respectively. The seismic characteristics follow the Nishimura-Hamaguchi scaling law for volcanic explosions, reflecting self-similarity in the processes initiating explosive events. The results also show that counter forces can discriminate between the sizes of explosive eruptions that are assigned the same magnitude by conventional methods of classification such as the Volcanic Explosivity Index. The increasing use of broadband seismometers may therefore provide the basis for using counter forces to determine the magnitude of explosive eruptions. 相似文献
97.
Expeditions to Muztagata (in the eastern Pamirs) during the summer seasons of 2002 and 2003 collected precipitation samples
and measured their oxygen isotopes. The δ
18O in precipitation displays a wide range, varying from −17.40‰ to +1.33‰ in June-September 2002 and from −22.31‰ to +4.59‰
in May-August 2003. The δ
18O in precipitation correlates with the initial temperature of precipitation during the observing periods. The positive correlation
between δ
18O and temperature suggests that δ
18O can be used as an indicator of temperature in this region. The δ
18O values in fresh-snow samples collected from two snow events at different elevations on the Muztagata Glacier show a strong
“altitude effect”, with a ratio of nearly −0.40% per 100 m from 5500 m to 7450 m. 相似文献
98.
Adam Carter Benjamin van Wyk de Vries Karim Kelfoun Patrick Bachèlery Pierre Briole 《Bulletin of Volcanology》2007,69(7):741-756
A clear model of structures and associated stress fields of a volcano can provide a framework in which to study and monitor
activity. We propose a volcano-tectonic model for the dynamics of the summit of Piton de la Fournaise (La Reunion Island,
Indian Ocean). The summit contains two main pit crater structures (Dolomieu and Bory), two active rift zones, and a slumping
eastern sector, all of which contribute to the actual fracture system. Dolomieu has developed over 100 years by sudden large
collapse events and subsequent smaller drops that include terrace formation. Small intra-pit collapse scars and eruptive fissures
are located along the southern floor of Dolomieu. The western pit wall of Dolomieu has a superficial inward dipping normal
fault boundary connected to a deeper ring fault system. Outside Dolomieu, an oval extension zone containing sub-parallel pit-related
fractures extends to a maximum distance of 225 m from the pit. At the summit the main trend for eruptive fissures is N80°,
normal to the north–south rift zone. The terraced structure of Dolomieu has been reproduced by analogue models with a roof
to width ratio of approximately 1, suggesting an original magma chamber depth of about 1 km. Such a chamber may continue to
act as a storage location today. The east flank has a convex–concave profile and is bounded by strike-slip fractures that
define a gravity slump. This zone is bound to the north by strike-slip fractures that may delineate a shear zone. The southern
reciprocal shear zone is probably marked by an alignment of large scoria cones and is hidden by recent aa lavas. The slump
head intersects Dolomieu pit and may slide on a hydrothermally altered layer known to be located at a depth of around 300 m.
Our model has the summit activity controlled by the pit crater collapse structure, not the rifts. The rifts become important
on the mid-flanks of the cone, away from pit-related fractures. On the east flank the superficial structures are controlled
by the slump. We suggest that during pit subsidence intra-pit eruptions may occur. During tumescence, however, the pit system
may become blocked and a flank eruption is more likely. Intrusions along the rift may cause deformation that subsequently
increases the slump’s potential to deform. Conversely, slumping may influence the east flank stress distribution and locally
control intrusion direction. These predictions can be tested with monitoring data to validate the model and, eventually, improve
monitoring. 相似文献
99.
Serge H. Zbaz Togouet Thomas Njine Norbert Kemka Moise Nola Samuel Foto Menbohan Walter Koste Claude Boutin Rick Hochberg 《Limnologica》2007,37(4):311-322
Studies on the biodiversity and population dynamics of freshwater planktonic Gastrotricha have been carried out in conjunction with a physical–chemical analysis of the water in the Yaounde Municipal Lake (Cameroon, Central Africa) over a 14 months period (November 1996–December 1997). The results obtained allow to consider the Yaounde Municipal Lake as an eutrophic lake. It harbours eight species of Gastrotricha belonging to four genera (Chaetonotus, Dasydytes, Neogossea and Polymerurus) of the order Chaetonotida. This community was characterized by high abundances of populations, and was dominated by the genus Neogossea and Chaetonotusreaching up to 2000 ind. L−1. Polymerurus was mostly abundant at the almost anoxic bottom layers. The highest abundances were found mostly during the rainy season, when there is an important sedimentation process of organic matter, and were influenced by several different environmental factors such as dissolved oxygen, temperature and pH of the water.
Finally this community which may play an important role in the water bodies, is a potential water quality indicator. 相似文献