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排序方式: 共有213条查询结果,搜索用时 93 毫秒
91.
The goal of this work is to derive the physical properties of dust envelopes around post-AGB stars by means of radiative transfer calculations. The model spectral energy distributions (SEDs) have been compared with observational data of the post-AGB stars IRAS 10215-5916, 16342-3814, 17150-3224, and 19500-1709 in the wavelength range from 0.4 to 1300µm. The match between our model SEDs and the observational data is very satisfactory. As a result, we have obtained estimates of the inner and outer radii, the density, the temperature, and the mass of the envelopes of the four objects. 相似文献
92.
We report the preliminary result of studying the nature of objects with a 21µm feature. New candidates are presented and possible carriers of the 21µm feature are discussed. 相似文献
93.
Here we present the results of 1.3 millimetre continuum measurements for intermediatemass stars in the Chamaeleon system of dark clouds. The detected millimetre radiation is most probably thermal emission from cold circumstellar dust grains. The measured millimetre fluxes are combined with infrared observations to model the broad-band spectral energy distribution (SED). In this way the parameters of the emission regions are determined.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A. 相似文献
94.
Dr. D. Henning 《Meteorology and Atmospheric Physics》1967,16(2-3):126-136
Zusammenfassung Ein vonPhillips formuliertes und vonSmagorinsky umgeschriebenes Kriterium, das vor allem Aussagen über die Bedingungen gestattet, unter denen sich Störungen vom Typ der Rossby-Wellen entwickeln können, wird näher untersucht. Die Parameter, die in verschiedener Weise voneinander abhängen, sind die Zahl dieser Wellen, meriodionaler und vertikaler Gradient der potentiellen Temperatur und geographische Breite. Die Lage der planetarischen Hochdruckgürtel ist, worauf zuerstFlohn hingewiesen aht, bestimmbar in Abhängigkeit von den genannten Gradienten (Abb. 1). Ein funktionaler Zusammenhang zwischen Wellenzahl und Baroklinität besteht dann, wenn bei labilster Kombination von Wellenzahl, thermischer Schichtung und Breite gerade Indifferenz erreicht wird: beide Größen ändern sich dann entgegengesetzt (Abb. 2). Für thermische Schichtung und Wellenzahl kann ein solcher Zusammenhang bei fester Breite für beliebige Zustände exisitieren — bei Labilisierung der Schichtung vergrößert sich die Wellenzahl.
Mit 2 Textabbildungen 相似文献
Summary A baroclinic instability criterion is analysed in some detail which has been derived byPhillips, and has been rewritten bySmagorinsky. This criterion essentially permkits to make statements about the conditions by which disturbances of the Rossby-typemay develop. The parameters depending on one another in different ways are the wave number, the meridional and vertical gradients of potential temperature, and the latitude. The position of the planetary high pressure belts can be determined as a function of these gradients (Fig. 1), as has been demonstrated byFlohn. The wave number represents a function of the meridional temperature gradient by the condition that the most unstable combination of wave number, static stability, and latitude just leads to indifiference (in the sense of the criterion): both quantities are then varying in opposite directions (Fig. 2). At constant latitude and arbitary conditions otherwise the wave number is a function of static stability, or vice versa — the wave number increases if static, stability decreases.
Résumé On examkine ici de plus près un critère formulé parPhillips et midifié parSmagorinsky, cirtère qui permet de déterminer les conditions initiales en partant desquelles des perturbations du type des ondes de Rossby peuvent se former. Les paramètres — dont l'interdépendance est complexe —sont: le nombre de ces ondes, les gradients méditional et vertical de la température potentielle et la latitude. La position des ceintures planétaires de haute pression, dont l'importance a àté signalée parFlohn — peutêtre déterminée à l'aide de ces gradients (Fig. 1). Un rapport fonctionnel entre le nombre d'ondullations et la baroclinité s'établit lorsque — par suite de la combinaison la moins stable du nombre d'ondulations, de l'étagement thermique et de la latitude —on obtient juste un état indifférent: ces deux grandeurs se modifient alors en sens inverse (Fig. 2). A une latitude donnée, un tel rapport entre l'étagement thermique et le nombre d'ondulations peut exister dans n'importe quelles conditions: si l'étagement devient moins stable, le nombre des ondulatiosn augmente.
Mit 2 Textabbildungen 相似文献
95.
Unplanned ore dilution has a direct and large influence on the cost of a stope, and ultimately on the profitability of a mining
operation. This paper presents the results of an examination of factors influencing ore dilution in a blasthole stoping environment.
For the study, a comprehensive database was established, incorporating information related to the design, construction, excavation
and cavity surveys of 172 sequentially mined long hole stope case histories from two orezones. Through a review of the case
studies, it was demonstrated that, in addition to stope dimension, the amount of unplanned dilution differed according to
stope type. Five stope types were identified, based on their position within a tabular blasthole mining sequence. Measured
overbreak varies with stope type, with secondary stopes generating a greater volume of hanging-wall dilution than do primary
stopes. Furthermore, a case study is presented to demonstrate the role cablebolts installed in the stope hanging-wall play
to control ore dilution. The study illustrates relationships between measured hanging-wall overbreak, cablebolt orientation
and stope type. 相似文献
96.
We describe typical features of the chemical composition of proto-planetary disks around brown dwarfs. We model the chemical evolution in the disks around a low-mass T Tauri star and a cooler brown dwarf over a time span of 1 Myr using a model for the physical structure of an accretion disk with a vertical temperature gradient and an extensive set of gas-phase chemical reactions. We find that the disks of T Tauri stars are, in general, hotter and denser than the disks of lower-luminosity substellar objects. In addition, they have more pronounced vertical temperature gradients. The atmospheres of the disks around low-mass stars are more strongly ionized by UV and X-ray radiation, while less dense brown-dwarf disks have higher fractional ionizations in their midplanes. Nevertheless, in both cases, most molecules are concentrated in the so-called warm molecular layer between the ionized atmosphere and cold midplane, where grains with ice mantles are abundant. 相似文献
97.
Henning Knutsen 《Astrophysics and Space Science》1989,162(2):315-336
An exact solution of Einstein's equations for a static isentropic perfect fluid sphere is examined in detail. The analysis yields a strong indication that the model isstable with respect to infinitesimal radial pulsations. This means that the temperature is decreasing outwards. We prove that the adiabatic speed of sound is everywhere less than the speed of light if and only if the radius of the sphere is larger than 1.61 times its Schwarzschild radius. We further show that the strong energy condition is fulfilled everywhere if and only if the radius is larger than 1.76 times the Schwarzschild radius. The necessary and sufficient condition for the speed of sound to be decreasing outwards is given, and we find that this criterion is fulfilled if the fluid is causal. Taking the values of the pressure and the density to be somewhere given by the maximum values from Baymet al.'s equation of state, i.e., 0=5.1×1014 g cm–3 andp
0=7.4×1033 dyne cm–2, we find the maximum mass of the fluid sphere to be 2.5 solar masses.Dedicated to the memory of the late George Cunliffe McVittie (1904–1988). 相似文献
98.
Carlos Descourvières Niels Hartog Bradley M. Patterson Carolyn Oldham Henning Prommer 《Applied Geochemistry》2010
The injection and recovery of oxic water into deep anoxic aquifers may help to alleviate short- and long-term imbalance between freshwater supply and demand. The extent and structure of physical and geochemical heterogeneity of the aquifer will impact the water quality evolution during injection, storage and recovery. Water–sediment interactions within the most permeable parts of the aquifer, where the bulk of the injectant will penetrate, may dominate, however, water quality may also be impacted by interactions within the finer-grained, less permeable but potentially highly reactive media. In this study, the heterogeneity of the reductive capacity of an aquifer selected for water reuse projects was characterised, the amount, type and reactivity of the sedimentary reductants present determined, and the relationship between reductive capacity and sedimentary lithologies quantified. The average potential reductive capacities (PRCTOT), based on total organic C and pyrite concentrations of the sediment, were quantified for sands (382 μmol O2 g−1), clays (1522 μmol O2 g−1), and silts (1957 μmol O2 g−1). Twenty-seven samples, spanning the three different lithologies, were then incubated for 50 days and the measured reductive capacities (MRC) determined for the sands (29.2 μmol O2 g−1), silts (136 μmol O2 g−1), and clays (143 μmol O2 g−1). On average, the MRC were 10% of the PRCTOT. The main consumers of O2 were pyrite (20–100%), sedimentary organic matter (SOM; 3–56%), siderite (3–28%) and Fe(II)-aluminosilicates (8–55%). The incubation data plus hydrogeochemical modelling, indicated that pH-buffering was controlled firstly by dissolution of trace level carbonates, followed by dissolution of feldspars. Zinc, Co, Ni, Cd and Pb were readily mobilized during incubation. 相似文献
99.
Sam Boggs David H. Krinsley Gordon G. Goles Abbas Seyedolali Henning Dypvik 《Meteoritics & planetary science》2001,36(6):783-791
Abstract— Quartz grains subjected to high‐strain‐rate shock waves owing to meteorite or cometary impact on Earth's surface commonly display shock lamellae. These lamellae appear as remarkably straight, thin, planar features (microstructures) in sets within which lamellae are essentially parallel to each other and spaced ≤ 20 μm apart. Two or more intersecting sets are typically present. Shock lamellae are commonly recognized and identified by optical methods, by use of the transmission electron microscope (TEM), and by etching polished sections and subsequent examination with a scanning electron microscope (SEM) operated in the secondary electron mode. We present here a method for observing planar microstructures in shocked quartz by using a cathodoluminescence (CL) detector attached to a SEM. The method relies on the fact that planar microstructures in quartz arising as a result of shock display no CL whatever; thus, they show up as distinct, thin, black lines on otherwise luminescent quartz grains. We used scanning CL imaging to study shocked quartz from the Ries Crater, Germany, a well‐known impact crater of Miocene age. We demonstrate that shock‐produced planar microstructures are clearly displayed in SEM‐CL images and can be distinguished from microfractures generated by tectonism, and subsequently filled with quartz, and other similar features not related to impact events. The SEM‐CL method provides a powerful supplement to other methods of identifying shocked quartz. It commonly provides better spatial resolution than does standard optical methods, and does not require etching of quartz grains. Further, it is easier and faster to use than are TEM methods, although it is not capable of the fine‐scale defect analysis possible with TEM. 相似文献
100.