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91.
Swept-frequency (1/10 MHz) ionosonde measurements were made at Helston, Cornwall (50°06N, 5°18W) during the total solar eclipse on August 11, 1999. Soundings were made every three minutes. We present a method for estimating the percentage of the ionising solar radiation which remains unobscured at any time during the eclipse by comparing the variation of the ionospheric E-layer with the behaviour of the layer during a control day. Application to the ionosonde date for 11 August, 1999, shows that the flux of solar ionising radiation fell to a minimum of 25±2% of the value before and after the eclipse. For comparison, the same technique was also applied to measurements made during the total solar eclipse of 9 July, 1945, at Sörmjöle (63°68N, 20°20E) and yielded a corresponding minimum of 16 ± 2%. Therefore the method can detect variations in the fraction of solar emissions that originate from the unobscured corona and chromosphere. We discuss the differences between these two eclipses in terms of the nature of the eclipse, short-term fluctuations, the sunspot cycle and the recently-discovered long-term change in the coronal magnetic field. 相似文献
92.
93.
Geologists may want to classify compositional data and express the classification as a map. Regionalized classification is a tool that can be used for this purpose, but it incorporates discriminant analysis, which requires the computation and inversion of a covariance matrix. Covariance matrices of compositional data always will be singular (noninvertible) because of the unit-sum constraint. Fortunately, discriminant analyses can be calculated using a pseudo-inverse of the singular covariance matrix; this is done automatically by some statistical packages such as SAS. Granulometric data from the Darss Sill region of the Baltic Sea is used to explore how the pseudo-inversion procedure influences discriminant analysis results, comparing the algorithm used by SAS to the more conventional Moore–Penrose algorithm. Logratio transforms have been recommended to overcome problems associated with analysis of compositional data, including singularity. A regionalized classification of the Darss Sill data after logratio transformation is different only slightly from one based on raw granulometric data, suggesting that closure problems do not influence severely regionalized classification of compositional data. 相似文献
94.
Relationships between gold concentration and structure in quartz veins from the Hodgkinson Province, northeastern Australia 总被引:1,自引:0,他引:1
The Hodgkinson Province is a tract of␣multiply deformed Silurian-Devonian rocks in north␣Queensland, Australia. Gold-bearing
quartz veins from the West Normanby Goldfield in the northern Hodgkinson Province were emplaced during the Permian D4 event, broadly coeval with regional granite emplacement. Taylors Fault, a major structure that formed during D2, hosts the veins which infill dilatational jogs opened during sinistral-normal reactivation of the fault in D4. Veins contain graphitic laminations that formed when fault planes segmented wallrocks adjacent to the veins, producing tabular
clasts that were tectonically sliced into the reefs. Laminations are the result of progressive shear strain, associated with
continued movement on the faults, which caused strain-enhanced dissolution of silicate minerals and residual graphite enrichment
in the clasts. This process produced graphite-coated shear planes that delimit zones of grain size reduction in the veins.
Laminations commonly contain stylolites, which nucleated on pronounced sinuosities of the shear planes due to progressive
shortening during D4. Gold particles have preferentially nucleated in zones of relatively coarser-grained quartz adjacent to the shear planes,
where shortening strain caused microfracturing and allowed fluid access. Gold may have been introduced with the quartz, but
was redistributed within the reefs and localized along the laminations by the effects of synchronous, progressive deformation.
Regionally, gold deposits show close spatial relationships with granite plutons of the Permian Whypalla Supersuite. Relationships
in the West Normanby Gold Field support a regional model of reef emplacement and gold mineralization during the Permian D4 event.
Received: 24 August 1997 / Accepted: 14 October 1997 相似文献
95.
Kristen E. K. Coppin Christopher J. Davis & Milena Micono 《Monthly notices of the Royal Astronomical Society》1998,301(1):L10-L14
We discuss the formation of spectral features in the decelerating ejecta of gamma-ray bursts, including the possible effect of inhomogeneities. These should lead to blueshifted and broadened absorption edges and resonant features, especially from H and He. An external neutral ISM could produce detectable H and He, as well as Fe X-ray absorption edges and lines. Hypernova scenarios may be diagnosed by Fe Kα and H Lyα emission lines. 相似文献
96.
Fly ash generated by coal-fired power plants is in part collected by filters in the emission stacks while a small portion
is vented into the atmosphere. Since many of the coalfired power plants in the western United States are located in the desnrt,
the ability to monitor fly ash emissions requires a chemical tracer that utilizes desert soil and plant interactions with
the fly ash deposited in the desert environment. This investigation presents the results of a controlled greenhouse experiment
in which a native desert plant, the brittlebush (Encelia farinosa), was grown on admixtures of desert soils and fly ash. The fly ash is strongly enriched in Sr and the brittlebush is a Sr
accumulator. The data demonstrate that (1) the brittlebush isotopically equilibrates with desert soils whose fly ash components
are as low as 0.25% by weight, (2) the fly ash Sr is apparently more available to the plant, than Sr derived from the soils,
and (3) the difference between the87Sr/86Sr ratio of the fly ash (0.70807) and soils (0.71097 to 0.71117) warrants further investigations in the natural environment
to determine the practicality of this method as a natural tracer of fly ash in the environment. 相似文献
97.
Mathematical Geosciences - In mineral deposit evaluation, the estimation of block values can involve the solution of as many as 100,000 systems of linear equations. To minimize computing costs it... 相似文献
98.
Two types of noise afflict strain and tilt measurement. They may be categorized as “active” noise, which is due to atmospheric pressure variations, temperature variations, water-table variations and so forth; and “passive” or signal-generated noise which is a consequence of the interaction of the strain field of interest with inhomogeneities of material properties local to the measurement site.The reason why both types of noise are normally reduced by the use of long base line instruments is explained and a simple, practical long base line tiltmeter is described. 相似文献
99.
P.M. Davis F.D. Stacey C.J. Zablocki J.V. Olson 《Physics of the Earth and Planetary Interiors》1979,19(4):331-336
Cancellation of extraterrestrial magnetic disturbances by taking simple differences between total field readings at spaced stations is imperfect. It is shown that improvement is possible when three component observatory data are available from a single station in the general, but not necessarily immediate, vicinity of an array of total field stations used in a tectonomagnetic study. The local effects of a magnetic disturbance field depend upon its orientation, so that local field differences are more effectively generated by certain orientations of the disturbance field. The orientation of the disturbance field which correlates best with a local difference field is determined by a least-squares method, so that the correlated vector signal can be routinely subtracted from the difference field record. Application of the technique to daily averages of records from three synchronised proton magnetometers on Kilauea volcano reveals a 1.5-nT change in the local field at the time of a flank eruption in May, 1973. This effect was obscured by noise in the raw difference field data. 相似文献
100.