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961.
H. Varvoglis 《Earth, Moon, and Planets》1991,54(3):257-267
Many trajectories of the third body are integrated numerically in a modified elliptical restricted three body problem (ERTBP), in which the eccentricity, e, of the orbit of the second primary varies sinusoidally with time. It is found that, in the case of the 2:1 resonance, the introduction of the time variability of e modifies significantly the behaviour of the trajectories of the third body. In particular their osculating eccentricity e, present the following two notable features: (a) In all cases it shows a definite chaotic variation, which appears at significantly shorter time-scales than the one found by Wisdom in the e = constant case. (b) In many cases it shows a significant increase, up and beyond the (critical) value e
crit = 0.52. As a result the third body approaches the first primary at distances smaller than 0.29 (where by we denote the semi-major axis of the trajectory of the second primary around the first), which in the actual Sun-Jupiter-asteroid problem corresponds to the semi-major axis of Mars. Our result might be of interest in the context of explaining the Kirkwood gaps at the resonances where the osculating eccentricity of asteroid trajectories calculated in the classical (e = constant) ERTBP does not reach Mars crosser values. 相似文献
962.
Ideal and resistive ballooning modes are investigated for different ratios of a two-layer stratified density region representing a model for the photospheric/coronal boundary. Construction of the ballooning equations using a WKB approach is justified by comparison between the values of the growth rate obtained using Hain-Lüst and ballooning equations together with a WKB integral relation. Different values of the density ratio, radius, and resistivity are considered. Sausage-type and kink-type instabilities are found. One of these, depending on the value of r remained unstable for large density ratios. The other instability tended to marginal stability as the density ratio was increased, and allowed parallel and perpendicular flows across the boundary. This is contrary to the predictions of both the rigid-wall and flow-through conditions. 相似文献
963.
We investigate, via a two-dimensional (nonplanar) MHD simulation, a situation wherein a bipolar magnetic field embedded in a stratified solar atmosphere (i.e., arch-filament-like structure) undergoes symmetrical shear motion at the footpoints. It was found that the vertical plasma flow velocities grow exponentially leading to a new type of global MHD-instability that could be characterized as a Dynamic Shearing Instability, with a growth rate of about 8{ovV}
A
a, where {ovV}
A is the average Alfvén speed and a
–1 is the characteristic length scale. The growth rate grows almost linearly until it reaches the same order of magnitude as the Alfvén speed. Then a nonlinear MHD instability occurs beyond this point. This simulation indicates the following physical consequences: the central loops are pinched by opposing Lorentz forces, and the outer closed loops stretch upward with the vertically-rising mass flow. This instability may apply to arch filament eruptions (AFE) and coronal mass ejections (CMEs).To illustrate the nonlinear dynamical shearing instability, a numerical example is given for three different values of the plasma beta that span several orders of magnitude. The numerical results were analyzed using a linearized asymptotic approach in which an analytical approximate solution for velocity growth is presented. Finally, this theoretical model is applied to describe the arch filament eruption as well as CMEs. 相似文献
964.
The new procedure of earthquake hazard evaluation developed by Kijko and Sellevoll is tested and applied for the border region of Czechoslovakia and Poland. The new method differs from the conventional approach. It incorporates the uncertainty of earthquake magnitudes, and accepts mixed data containing only large historical events and recent, complete catalogues. Seismic hazard has been calculated for nine regions determined in the border area. In the investigated area, data of historical catalogues are uncertain or, in many cases, the epicentral intensities are unknown. Thus, a number of assumptions have to be adopted in data preparation of catalogues since the year 1200. The calculated values of parameters b in the Gutenberg-Richter frequency-intensity relation as well as the return periods, seem to be reasonable and are generally confirmed by the results obtained from catalogues for the last 80–130 years. 相似文献
965.
By modifying the online software of the Westerbork Synthesis Radio Telescope it is possible to sample the radio emission from a field containing a pulsar synchronously with the pulsed signal. Recording the emission from eight separate temporal windows, we can simultaneously observe both the on-pulse and off-pulse signals. We are using this technique for three different kinds of pulsar investigation: (a) to check and improve the positions of some pulsars; (b) to look for unpulsed components; and (c) to search for weak extended emission around pulsars. Observations have been carried out at 6, 21, 49, and 92 cm. Examples of results from all three types of investigation are given.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain. 相似文献
966.
We consider dynamically consistent mean-field dynamos in a spherical shell of incompressible fluid. The generation of magnetic field and differential rotation is parameterized by the - and -effects, respectively. Extending previous investigations, we include now the cases of moderate and rapid rotation in the sense that the inverse Rossby number can approach or exceed unity: This can lead to disk-shaped
-contours, which are in better accordance with recent results of helioseismology than cylindrical
-contours. On the other hand, in order to obtain -dynamo cycles the Taylor number has to be so large, that eventually cylindrical -contours become unavoidable (cf. Taylor-Proudman theorem). We discuss the different possibilities in a state diagram, where the inverse Rossby number and the relative correlation length are taken as the elementary parameters for mean-field dynamos. 相似文献
967.
Crustal structure of the Rhenish Massif: results of deep seismic reflection lines Dekorp 2-North and 2-North-Q 总被引:1,自引:1,他引:0
Prof. Dr. W. Franke Prof. Dr. R. K. Bortfeld Dr. M. Brix Dr. G. Drozdzewski Prof. Dr. H. J. Dürbaum Prof. Dr. P. Giese Dr. W. Janoth Dr. H. Jödicke Chr Reichert Dipl.-Geophys. Dr. A. Scherp J. Schmoll Dipl.-Geophys. R. Thomas Dipl.-Geophys. Dr. M. Thünker Prof. Dr. K. Weber Dr. M. G. Wiesner Prof. Dr. H. K. Wong 《International Journal of Earth Sciences》1990,79(3):523-566
The reflection seismic line DEKORP 2-N reveals an almost complete cross section through the Rhenohercynian Zone, the most external part of the Variscan orogen in Europe.The northern part of DEKORP 2-N and a NE-directed branch (2-N-Q) reveal the Cretaceous of the Münsterland basin and the underlying folded Palaeozoic rocks. The northward decreasing intensity of folding is depicted in great detail by the highly reflective Late Carboniferous coal-measures and deeper reflections down to the level of the Givetian/Frasnian shallow-water carbonates.In the Devonian and older rocks of the Rhenish Massif, bedding is only represented by relatively weak, short and irregular reflections. These are truncated by stronger, southward dipping reflections, which exhibit the listric curvature and flat/ramp geometry characteristic of faults. In the northern part of the section, the thrusts appear to be blind. From the Ebbe Anticline southwards, prominent reflections can be correlated with important thrust faults known from the surface, such as the Ebbe-, Siegen-, Müsen- and Sackpfeife- Thrusts, as well as further important thrust faults in the Lahn- and Dill Synclines. The basal thrust of the extremely thin-skinned Giessen Nappe is only recognizable for a very short distance.At depth, the thrusts flatten out in a relatively transparent zone between 3–5 s TWT, with strongly reflective bands at its bottom and top. The transparent zone might correlate with a high-conductivity layer detected in a magnetotelluric survey; it represents either graphitic metapelites or a zone with an interconnected, brine-filled pore space. The seismic record relates either to lithological differences, or to rheological boundaries.The lower crust in the north is characterized by a relatively transparent zone, which wedges out towards south under the northern margin of the Siegen Anticline. Comparisons with a similar feature in the ECORS profile »Nord de la France« suggest that the transparent zones in both sections correspond to a pre-Palaeozoic basement, such as it underlies the Brabant Massif. Further south, the lower crust is increasingly reflective.The curvilinear, thrust-related reflections are cut by a conjugate set of much weaker, N- and S-dipping reflectors indicating a later deformation with pure shear. Displacement of some marker reflections suggests late- or post-Variscan compression.In an alternative interpretation, these straight and weak reflections represent the only thrust faults, while the curvilinear elements might relate to bedding.A southward rise of the Moho from approx. 11 to 8.5 s TWT is probably due to Tertiary rifting.
Abbreviations MORB Mid-Ocean Ridge Basalt - TWT two-way travel time, seconds (s) - CMP common mid-point - VP vibration point - SNR signal to noise ratio 相似文献
Zusammenfassung Das reflexionsseismische Profil DEKORP 2-N stellt einen fast vollständigen Querschnitt durch das Rhenohercynikum dar.Der nördliche Teil des Profiles 2-N sowie ein SW/NE-verlaufender Abzweig (2-N-Q) zeigen die Transgression der Münsterländer Kreide und das unterlagernde gefaltete Paläozoikum. Schichtgebundene Reflektoren (flözführendes Karbon, devonischer Massenkalk) bilden das Ausklingen der variscischen Faltung nach NW detailliert ab.In den devonischen und vordevonischen Sedimenten des rechtsrheinischen Schiefergebirges erzeugt die Schichtung nur relativ schwache, kurze und unregelmäßige Reflexionen. Diese werden von stärkeren, südfallenden Reflektoren abgeschnitten, die aufgrund ihrer listrischen Krümmung und flat/ramp-Geometrie wahrscheinlich als Überschiebungen zu interpretieren sind. Im Nordteil des Schiefergebirges sind diese Überschiebungen offenbar blind, werden also nahe der Oberfläche durch Faltung kompensiert. Im Ebbe-Sattel und weiter südlich lassen sich die meisten der starken, südfallenden Reflektoren zweifelsfrei mit bekannten Großüberschiebungen korrelieren (Ebbe-, Siegen-, Müsen-, Sackpfeife-Ü, sowie weitere Überschiebungen in der Lahn- u. Dill-Mulde). Die Basisüberschiebung der Giessen-Decke wird nur teilweise abgebildet.Zur Tiefe hin zeigen die Überschiebungen ein zunehmend flacheres Einfallen, und verschwinden in einer relativ transparenten Zone zwischen 3 und 5 s TWT, die im Hangenden und Liegenden durch dünne, stark reflektive Zonen begrenzt ist. Diese transparente Zone entspricht möglicherweise einer Zone hoher integrierter Leitfähigkeit, die in einem begleitenden magnetotellurischen Experiment nachgewiesen worden ist; es handelt sich entweder um einen Graphit-führenden Phyllit-Horizont oder eine mächtigere permeable Zone mit Elektrolyt-gefülltem Porenraum. Die hochreflektiven Bänder über und unter der transparenten Zone entsprechen entweder lithologischen Kontrasten oder rheologischen Grenzen, die vermutlich von einer scherenden Verformung überprägt worden sind.Die Unterkruste im N-Teil des Profiles enthält einen relativ transparenten Bereich, der nach Süden hin unter dem Nordteil des Siegener Sattels keilförmig ausläuft. Ein ähnliches Bild zeigt der Nordteil des ECORS-Profiles »Nord de la France«. Die transparenten Bereiche beider Profile entsprechen wahrscheinlich einem prä-paläozoischen kristallinen Basement, das das Brabanter Massif unterlagert und sich rechtsrheinisch fortsetzt. Südlich des transparenten Keiles wird die Unterkruste zunehmend reflexionsreicher. Die listrisch gekrümmten, an Überschiebungen gebundenen Reflektoren werden von einem konjugierten System schwächerer, N- u. S-fallender Reflektoren abgeschnitten, die auf eine jüngere, bruchhafte Verformung durch reine Scherung hindeuten. Der Versatz einiger älterer Reflektoren deutet auf spät- oder postvariscische Kompression hin.In einer alternativen Interpretation werden nur diese jüngeren Reflektoren als Überschiebungen gedeutet; die älteren, gekrümmten Elemente müßten dann primären lithologischen Grenzen entsprechen.Die Moho steigt von ca. 11 s TWT im N auf 8.5 s TWT unter dem Taunus an. Die Krustenverdünnung im Süden geht wahrscheinlich auf Dehnung im Tertiär zurück.
Résumé Le profil sismique par réflexion DEKORP-2-N représente une transversale quasiment complète à travers la zone rhénohercynienne. La partie septentrionale du DEKORP-2-N ainsi qu'une branche de direction SW-NE (2-N-Q) mettent en évidence la transgression du Crétacé du Münsterland sur le Paléozoïque sous-jacent plissé. Des réflecteurs liés à la stratification (à savoir: le Houiller et les calcaires de plate-forme dévoniens) illustrent de façon détaillée la diminution vers le nord de l'intensité du plissement varisque.Dans les sédiments dévoniens et pré-dévoniens du Massif Rhénan à l'est du Rhin, la stratification ne fournit que que des réflexions relativement faibles, courtes et irrégulières. Elles sont tronquées par des réflecteurs plus intenses, à pendage sud qui, en raison de leur courbure listrique et de leur géométrie en «flat/ramp», doivent être interprétés comme des chevauchements. Dans la partie septentrionale du Massif, ces chevauchements sont apparemment aveugles, c'est-à-dire qu'ils sont compensés, près de la surface, par le plissement. Dans l'anticlinal d'Ebbe, ainsi que plus au sud, la plupart des réflecteurs intenses à plongement sud peuvent être corrélés avec des chevauchements majeurs connus, tels ceux de Ebbe, Siegen, Müsen, Sackpfeife et d'autres encore dans les synclinaux de la Lahn et de la Dill. Le chevauchement basai de la nappe de Giessen n'est que partiellement représenté.Les chevauchements deviennent de plus en plus plats en profondeur pour disparaître dans une zone relativement transparente qui se situe entre 3–5 sec TWT. Celle-ci est prise en sandwich par des zones minces à forte réflectivité. La zone transparente correspond probablement à une zone de conductivité intégrée élevée dont l'existence a par ailleurs été démontrée dans un essai magnétotellurique mené parallèlement. Il s'agit soit d'un horizon phyllitique graphiteux, soit d'une zone perméable plus épaisse dont les pores sont remplis d'électrolyte. Les bandes à haute réflectivité au-dessus et en-dessous de la zone transparente correspondent soit à des contrastes lithologiques, soit à des limites rhéologiques probablement accentuées par la déformation cisaillante.La croûte inférieure dans la partie septentrionale du profil comporte un domaine relativement transparent qui s'amincit vers le S et se termine, en dessous de la partie nord de l'anticlinal de Siegen, en forme de coin. La partie nord du profil ECORS «Nord de la France» montre une image semblable.Les domaines transparents des deux profils correspondent vraisemblablement à un soubassement cristallin pré-paléozoïque qui est sousjacent au Paléozoïque du Massif du Brabant et se prolonge vers l'est au-delà du Rhin. Au sud du coin transparent, la réflectivité de la croûte inférieure va en augmentant. Les réflecteurs listriques liés à des chevauchements sont recoupés par un système conjugué de réflecteurs plus faibles à plongement nord et sud qui indiquent des failles plus récentes. Le déplacement de quelques réflecteurs plus anciens suggère l'effet d'une compression tardiou post-varisque.Dans une interprétation alternative, seuls ces réflecteurs plus récents sont considérés comme correspondant à des chevauchements. Dans ce cas, les éléments courbes plus anciens devraient représenter des limites lithologiques primaires.Le Moho s'élève à partir de 11 sec TWT environ au nord jusqu'à 8.5 sec TWT en-dessous du Taunus. L'amincissement crustal au sud résulterait du régime de distension survenu au Tertiaire.
DEKORP 2 Nord. x-t- ray-tracing'a. 6,0 6,6 /, — 7,0 8,2 /. 6,25 /. 28 30 . , .
Abbreviations MORB Mid-Ocean Ridge Basalt - TWT two-way travel time, seconds (s) - CMP common mid-point - VP vibration point - SNR signal to noise ratio 相似文献
968.
Dust particles (glass, tungsten, and nickel) with sizes ranging from 0.25 to 3m were levitated in a Paul-trap and charged by ions or electrons. For ions the particle potential is limited at field strength of about 1×109 V m–1 by a temperature-dependent discharge mechanism. The particles interaction with 2 to 20 keV electrons always leads to positive surface potentials which can be explained in terms of a decreased absorption of electrons by small particles. Micrometer sized agglomerates were used for the investigation of the electrostatic fragmentation. Fragmentation takes place in a twofold manner: small surface flufl can be removed or the parent particle can be disrupted into smaller agglomerates.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain. 相似文献
969.
The quality and capabilities of the ROSAT survey (0.1–2.0 keV) for the study of the diffuse X-ray background and the interstellar medium are discussed. All-sky maps created from data collected during the survey phase of ROSAT operations will greatly exceed previous surveys in spatial resolution (5 arc min pixels) and statistical significance (better than 25% for unbinned pixels). The spectral information of the survey will, in general, be greater as well. Finally, because of the survey geometry, very accurate contamination identification and background subtraction will be possible ensuring the reliability of the data.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain. 相似文献
970.
J. Zahradník M. Antonini G. Grünthal J. Janský D. Procházková E. Schmedes A. Špičak J. Zedník 《Pure and Applied Geophysics》1990,133(1):53-71
The main shock of the West-Bohemian earthquake swarm, Czechoslovakia, (magnitudem=4.5, depthh=10 km) exhibits an irregular areal distribution of macroseismic intensities 6° to 7° MSK-64. Four lobes of the 6° isoseismal are found and the maximum observed intensity is located at a distance of 8 km from the instrumentally determined epicentre. This distribution can be explained by the energy flux of the directS wave generated by a circular source, the hypocentral location and focal mechanism of which are taken from independent instrumental studies. The theoretical intensity, which is assumed to be logarithmically proportional to the integrated squared ground-motion velocity (i.e.,I=const+log v
2
(t)dt), fits the observed intensity with an overall root-mean-square error less than 0.5°. It is important that the present intensity data can also be equally well explained by the isotropic source. The fit was attained by means of a horizontally layered model though large fault zones and an extended sedimentary basin suggest a significant lateral heterogeneity of the epicentral region. The results encourage a broader application of the simple modelling technique used. 相似文献