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191.
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348-YEAR PRECIPITATION RECONSTRUCTION FROM TREE-RINGS FOR THE NORTH SLOPE OF THE MIDDLE TIANSHAN MOUNTAINS*
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Correlation census shows that the correlation between the tree-ring chronologies in the Urumqi River Basin and precipitation during July in the last year to February in the concurrent year is significant,and the best single correlation coefficient is 0.74,with significance level of 0.0001.Using two residual chronologies collected from west Baiyanggou and Boerqingou,precipitation for 348 years can be reconstructed in the North Slope of middle Tianshan Mountains,its explained variance is 62%.According to much verification from independent precipitation data,historical climate records,glacier and other data.it shows that the reconstructed precipitation series of 348 years is reliable.Analysis of precipitation features indicates that there were three wet periods occurring during 1671-1692,1716-1794 and 1825-1866 and three dry periods during 1693-1715,1795-1824 and 1867-1969.Two wet periods,during 1716-1794 and 1825-1866,correspond to the times of the second and the third glacial terminal moraine formation,which is infront of No.1 glacier in Urumqi River source.According to computation,corresponding annual precipitation amounts are 59mm and 30mm more than now.The reconstructed precipitation series has a significant drying trend from 1716 to 1969.and has better representativeness to the precipitation of Urumqi and Changji Prefecture on the North Slope of Tianshan Mountains. 相似文献
194.
U. Schreiber M. Schneider C.H. Rowe G.E. Stedman W. Schlüter 《Surveys in Geophysics》2001,22(5-6):603-611
Ring laser rotation sensors are best known from inertial navigation, wherethey have many advantages over mechanical gyroscopes. They have recentlybeen greatly improved, and show potential as fully independent length-of-daysensors. We discuss some important aspects of current limitations in theirperformance. In particular we demonstrate a novel scheme for thestabilisation of a large ring laser against frequency pulling effectsinduced by backscatter. 相似文献
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196.
Radon anomalies on three kinds of faults in California 总被引:1,自引:0,他引:1
Radon emanation is known to be anomalously high along active faults in many parts of the world. We tested this relationship in California during July and early August 1992, using a portable radonmeter to conduct soil-air radon surveys at 5 sites across three kinds of faults: Creeping, locked, and freshly broken.Along a 350-m long survey line across a creeping segment of the San Andreas fault at Nyland Ranch in San Juan Bautista, we found anomalous radon concentrations not in the creep zone itself as determined by a creepmeter, but on the adjacent sides, 10 and 30 meters from the center line of the fault. The anomalous values were 5 times higher than the background values measured farther away from the fault. A similar radon anomaly was observed along a 420-m long survey line across a creeping segment of the Calaveras fault near 7th Street in Hollister. There, the anomalous values were about 6 to 11 times the background values and about 40 and 50 m from the center line of the fault. The double-peaked featire of the anomalies may be indicative of a relatively low gas permeability of the fault-gouge materials in the creeping zones and high permeability of fractured rocks in the adjacent shear zones.Along a 144-m survey line across the currently locked segment of the San Andreas fault at the Earthquake Trail near Olema, the radon concentration was indeed anomalously high in the fault zone, by a factor of two above background values. However, the maximum values (3 to 6 times background) again were recorded about 10 meters from the center line.Three weeks after the magnitude 7.5 Landers earthquake of 28 June 1992, we conducted a survey along a 300-m line across the earthquake fault alongside Encantado Road in the epicenter area. The radon values measured at the two main fault breaks were an order of magnitude higher than the background values. A similar result was found along a 420-m line alongside Reche Road about 1.7 km south of Encantado Road. 相似文献
197.
G. Mastrolorenzo 《Bulletin of Volcanology》1994,56(6-7):561-572
The tuff ring of Averno (3700 years BP) is a wide maar-type, lake-filled volcano which formed during one of the most recent explosive eruptions inside the Campi Flegrei caldera.The eruptive products consist of (a) a basal coarse unit, intercalated ballistic fallout breccia, subplinian pumice deposits and pyroclastic surge bedsets and (b) an upper fine-grained, stratified, pyroclastic surge sequence.During the deposition of the lower unit both purely magmatic (lapilli breccia) and hydromagmatic episodes (wavy and planar bedded, fine ash pyroclastic surge bedsets) coexisted. The hydromagmatic deposits exhibit both erosive and depositional features. The upper unit mostly comprises fine grained, wet pyroclastic surge deposits. The pyroclastic surges were controlled by a highly irregular pre-existing topography, produced by volcano-tectonic dislocation of older tuff rings and cones.Both the upper and lower units show decreasing depletion of fines with increasing distance from the vent. The ballistic fallout layers, however, exhibit only a weak increase in fines with distance from the vent, in spite of marked fining of the lapilli and blocks. The deposits consist dominantly of moderately to highly vesicular juvenile material, generated by primary magmatic volatile driven fragmentation followed by episodes of near-surface magma-water interaction.The evolution of the eruption toward increased fragmentation and a more hydromagmatic character may reflect that the progressive depletion in magmatic volatiles and a decrease in conduit pressure during the last stage of the eruption, possibly associated with a widening of the vent at sea level. 相似文献
198.
可可西里地区错达日玛陨坑湖成因初探 总被引:2,自引:1,他引:2
本文根据可可西里地区综合调查资料和地球资源卫星遥感信息的研究,分析了错达日玛环形构造体系网络及湖泊地貌构型特征的动力条件,从而确定了错达日玛陨坑湖的成因类型,并建立了陨坑湖形成过程的演化模式. 相似文献
199.
The drift loss cone instability, propagating nearly transverse to the ambient magnetic field, is studied in the ring current
plasma taking into account the relative driftU between electrons and protons due to density gradients. The growth rates attain maxima and then decrease as the wave number
parallel to the magnetic fieldk
II increases. The peak values of the growth rates, maximised with respect tok
II, are enhanced by the increase in number density, electron temperature and loss cone index, and by the decrease in βt, the ratio of the proton thermal pressure to magnetic field pressure. The unstable frequencies fall in the range of 5 to
30Ωp with the growth rate γ ≥Ωp. In the ring current region betweenL=4 and 5, the instability will generate a strong turbulence in the frequency range between 5–500 Hz which can produce fluctuating
electric fields 0. 5–5 mV/m and magnetic field 0.8–80mγ. This instability can also occur on the auroral field lines, which
connect to the region of intense earthward plasma flow in the distant magnetotail and produce a broad band electrostatic noise. 相似文献
200.