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321.
The KLY-4S Kappabridge and KLF-4A Magnetic Susceptibility Meter enable automated measurement of susceptibility variation with
field in the ranges of 2–450 A/m and 5–300 A/m (in effective values), respectively. Unfortunately, the measurement accuracy
decreases with decreasing field and it is not easy to decide whether the susceptibility variation at the lowest fields is
natural phenomenon or results from measuring errors. To overcome this problem, the accuracies of both the above instruments
were investigated experimentally using artificial specimens (mixture of pure magnetite and plaster of Paris) with variable
susceptibilities ranging from 1 × 10−5 to 5 × 10−2. The complete curve of the field variation of susceptibility of each specimen was measured 10 times and the relative error
was calculated for each field.
In the KLY-4S Kappabridge, in specimens with susceptibilities higher than 100 × 10−6, the relative errors are lower than 3% in all fields and lower than 1% in the fields stronger than 10 A/m. In the KLF-4A
Magnetic Susceptibility Meter, in relatively strongly magnetic specimens with susceptibilities 5 × 10−4 to 5 × 10−2, the relative error is less than 1.5% in the entire field range. While the former instrument is convenient for investigating
almost all rock types, the latter instrument is convenient for measuring moderately and strongly magnetic specimens.
To facilitate work with field variation of susceptibility curves, showing variable accuracies with field, the programme FieldVar
was written. One of its options is plotting the measured data with corresponding field-variable error bars. In this way, a
tool is offered for interpreting such susceptibility changes that are sound and reasonable from the point of view of measuring
accuracy. 相似文献
322.
Interaction of weak shock waves with a current sheet is investigated by a two-dimensional numerical magnetohydrodynamic model. In accordance with solar coronal conditions, a ratio of thermal to magnetic pressures of 0.1 and a shock Alfvén Mach number slightly above 1 are considered. It is found that even weak shock waves trigger magnetic field reconnection in current sheets. Based on this result, it is suggested that drifting chains of type I radio bursts are radio manifestations of the interactions of weakly super-Alfvénic shock waves with pre-existing current sheets distributed in an active region. This model of type I noise storms is then discussed in connection with the concept of nanoflares (localized reconnections) and the heating of the solar corona. 相似文献
323.
Modelling climate change impacts on maize growth and development in the Czech Republic 总被引:5,自引:0,他引:5
Summary The crop growth model CERES-Maize is used to estimate the direct (through enhanced fertilisation effect of ambient CO2) and indirect (through changed climate conditions) effects of increased concentration of atmospheric CO2 on maize yields. The analysis is based on multi-year crop model simulations run with daily weather series obtained alternatively
by a direct modification of observed weather series and by a stochastic weather generator. The crop model is run in two settings:
stressed yields are simulated in water and nutrient limited conditions, potential yields in water and nutrient unlimited conditions.
The climate change scenario was constructed using the output from the ECHAM3/T42 model (temperature), regression relationships
between temperature and solar radiation, and an expert judgement (precipitation).
Results: (i) After omitting the two most extreme misfits, the standard error between the observed and modelled yields is 11%.
(ii) The direct effect of doubled CO2: The stressed yields would increase by 36–41% in the present climate and by 61–66% in the 2 × CO2 climate. The potential yields would increase only by 9–10% as the improved water use efficiency does not apply. (iii) The
indirect effect of doubled CO2: The stressed yields would decrease by 27–29% (14–16%) at present (doubled) ambient CO2 concentration. The increased temperature shortens the phenological phases and does not allow for the optimal development
of the crop. The simultaneous decrease of precipitation and increase of temperature and solar radiation deepen the water stress,
thereby reducing the yields. The reduction of the potential yields is significantly smaller as the effect of the increased
water stress does not apply. (iv) If both direct and indirect effects of doubled CO2 are considered, the stressed yields should increase by 17–18%, and the potential yields by 5–14%. (v) The decrease of the
stressed yields due to the indirect effect may be reduced by applying earlier planting dates.
Received March 9, 2001 Revised September 25, 2001 相似文献
324.
Dr. J. Chaloupský 《International Journal of Earth Sciences》1978,67(1):72-90
The Cadomian and Variscan tectogeneses are two distinctive and easily distinguished cycles of a long-term geological process leading to the almost complete crustal consolidation of the Bohemian Massif. The internal parts of the massif are those of the main development of the Upper Proterozoic geosyncline and the intensive Cadomian metamorphism and plutonism.The Precambrian of the Bohemian Massif is divided into two principal regional chronostratigraphic units: the Moldanubian and the Brioverian; the age of the boundary between them is estimated at about 1000 Ma B. P. The Brioverian is subdivided into three units: the Lower, Middle and Upper. The Moldanubian is provisionally subdivided into two units: the Lower and the Upper.The maximum of the metamorphic activity of the Cadomian cycle falls approximately within the sedimentation interval of the Middle Brioverian, and that of the Variscan cycle in the Devonian. Compared with the Cadomian regional metamorphism which attained mostly amphibolite to granulite facies, the Variscan metamorphism generally did not exceed greenschist facies.The origin of the granitoid rocks of the massif is closely associated with the metamorphic processes of the two above-mentioned cycles. Cadomian granitoids are represented mostly by rocks of granodiorite-tonalite and durbachite types whereas the Variscan intrusives are dominated by rocks of granitic composition.
Zusammenfassung Die assyntische und variszische Orogenese sind die wesentlichen strukturprägenden Ereignisse im Böhmischen Massiv. Die internen Teile des Massives sind aus der jung-proterozoischen Geosynklinale hervorgegangen und während der assyntischen Gebirgsbildung metamorphisiert und von Magmatiten durchdrungen worden. Das Präkambrium des Böhmischen Massives ist in zwei chronostratigraphische Einheiten zu gliedern: das Moldanubium und das Brioverian. Die Grenze liegt etwa bei 1000 Mill. Jahren. Das Brioverian läßt sich in drei Einheiten gliedern und das Moldanubium in zwei Einheiten.Das Maximum der metamorphen Überprägung während der assyntischen Orogenese fällt in die Sedimentationslücke im mittleren Brioverian; im variszischen Zyklus erfolgt die Metamorphose im Devon. Die assyntische Metamorphose erreicht Amphibolit- bis Granulitfazies, die variszische geht nicht über eine Grünschieferfazies hinaus.Die magmatischen Gesteine sind eng mit den beiden Orogenesen verbunden. Die assnytischen Magmatite sind vorwiegend Granodiorit-Tonalite und Durbachite, während die variszischen Magmatite aus Graniten bestehen.
Résumé Les tectogenèses cadomienne et varisque sont deux cycles différents, bien discernables, d'un processus géologique de longue durée, qui a conduit à la cosolidation presque complète du Massif de Bohème. La partie interne du Massif est celle du développement principal du géosynclinal protérozoïque supérieur et du métamorphisme et du plutonisme cadomiens.Le Précambrien du Massif de Bohème se divise en deux unités chronostratigraphiques régionales: le Moldanubien et le Briovérien. On estime l'âge de la limite entre elles à 1000 millions d'années environ. Le Briovérien est subdivisé en trois unités: inférieure, moyenne et supérieure. Le Moldanubien est divisé provisoirement en deux unités: inférieure et supérieure.La culmination de l'activité métamorphique du cycle cadomien tombe à peu près dans l'intervalle de sédimentation du Briovérien moyen, celle du cycle varisque dans le Dévonien. Comparé avec le métamorphisme régional cadomien qui le plus souvent a atteint le faciès amphibolite, le métamorphisme varisque, en général, n'a pas dépassé le faciès schistes verts.L'origine des roches granitoïdes du Massif et associée avec les processus métamorphiques des deux sus-dits cycles. Les granitoïdes cadomiens sont représentés pour la plupart par des roches du type des granodiorites-tonalites et durbachites, tandis que parmi les roches intrusives varisques prédominent des roches de composition granitique.
, , . - , , , . : Moldanubium Brioverian. 1 . Brioverian , a Moldanubium . Brioverian; . ; . . - , — qg.相似文献
325.
326.
The concept of seismicity of fast tensile fracturing is introduced and supported by the results of shear and of combined shear and tensile displacements along a loaded stress concentrator. The seismicity of tensile fracturing is demonstrated by means of acoustic (elastic) signals obtained during tensile fracturing in physical models under load; the basic physical relations between the parameters characterizing the loaded medium, load conditions, shear and tensile displacements, and release of acoustic energy are presented. For determining the tensile-source component in earthquakes a procedure based on the construction of radiation patterns is suggested and submitted for discussion. The criteria for selecting earthquakes with possible shear-tensile source mechanisms are listed and discussed. The existence of such a combined seismic source is sought in two shallow earthquakes which occurred in southern Iran in March 1977. In general, the paper should be regarded as a proposal to utilize the radiation characteristics of a seismic source—with all their insufficiencies—as a quick and simple tool for seeking combined shear and tensile mechanisms of seismic energy release. 相似文献
327.
Summary A method of spectral analysis based on the prediction of the signal by means of AR parameters is proposed. The essence of this method ranks it between the classical methods of spectral analysis and the method of maximum entropy. For sufficiently high SNR its resolution is higher than that of the classical methods. The new method enables power and phase spectra of the signal to be determined, and provides a better determination of the power spectrum amplitude. than the method of maximum entropy. A regularization procedure is presented which abolished the instability of the prediction filter, obtained by the least-squares method.
¶rt; n nma aaua, a a n¶rt;aauu uaa n amu naam. mm n m ¶rt;au aumu auu m¶rt; nma aaua nuu u¶rt; u m¶rt;a aua mnuu. n a¶rt;am n aa nm n au auuu m¶rt;au nu aau n ¶rt;mam u mu ua . nm mu ua n¶rt;m a¶rt;, m¶rt; aua mnuu. muu m m¶rt;a aua mnuu n¶rt; n nma aaua nm n¶rt;m m a nm ua. aam n¶rt;aa uma um m¶rt; auu a¶rt;am, m unaa uau ¶rt; ¶rt;u mu am u.相似文献
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