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971.
George C. Lee 《地震工程与工程振动(英文版)》2008,7(3):I0001-I0001
During the past several months, we have been considering "Special Issues" on a variety of topics for the journal of Earthquake Engineering and Engineering Vibration. We are pleased to announce that the December 2008 issue will be 相似文献
972.
This study presents ductility demand spectra for single degree of freedom (SDOF) systems under multiple near- and far-fault seismic ground motions. The main innovation has to do with the quantification of the seismic sequence effect directly into ductility demands, a phenomenon which has not been studied in the past. Due to lack of real seismic sequences records, this paper examines only artificial sequences, where they have been generated by a rational and random combination of real single events. A statistical investigation of more than 120 millions dynamic inelastic analyses is conducted to obtain expressions for the ductility demands, in terms of the period of vibration, the viscous damping, the post-yield stiffness and the force reduction factor. It is found that due to the seismic sequence effect, it is certainly insufficient to consider only the ‘design earthquake’, since this traditional hypothesis leads to underestimated ductility demands and therefore to underestimated structural damage. 相似文献
973.
Orissa is an important area for gem variety of corundum deposits in India. Spectroscopic studies, such as ESR, OAS on samples from Sardapur, Orissa, were carried out to ascertain the colour cause of corundum. Electron spin resonance (ESR) spectroscopic study was carried out on the samples to detect the presence of paramagnetic ions i.e. Fe2+, Fe3+, Ti4+, Cr3+ and V3+ etc. The variable temperature experiment carried out to observe the effect of heating on peak valence state change in paramagnetic ions. Samples were cut and polished to obtain the optical absorption spectrum (OAS) to detect the colour causing transition ions/defect centres. The samples of gem variety were step heated up to 300°C for colour enhancement studies. EPMA analysis has revealed the low chromium concentration in the rubies. The varying hues of red in the corundum are due to the presence of bivalent and trivalent iron and charge transfer process along with Cr3+ absorption in the 550 nm region. 相似文献
974.
George Miliaresis 《Earth Science Informatics》2012,5(1):1-12
A new method for elevation and latitude decorrelation stretch of multi-temporal land surface temperature (LST) in the East
Africa Rift System (EARS) from MODIS 2008 monthly average night imagery and Globe digital elevation model (DEM) is presented.
Multiple linear regression analysis of principal components images (PCAs) quantifies the variance explained by elevation and
latitude. Selective variance reduction (SVR) reconstructs the multi-temporal LST imagery from the residual images and selected
PCAs by taking into account the portion of variance not related to elevation and latitude. Clustering of the reconstructed
imagery identifies two major thermal anomalies a) in the Afar Triangle, and b) a new one in between the Ethiopia and Kenya.
These regions present LST values higher than the elevation and latitude predicted ones through out the year. It is assumed
that the new thermal anomaly corresponds to a triple junction formed in between the Ethiopian Rift and the Eastern and the
Western branches of the EARS, in an area where active volcanoes and mantle plume activity concentrate. SVR is expected to
assist tectonic and volcanic zones characterization on the basis of their thermal response. 相似文献
975.
Jim M. Raines James A. Slavin Thomas H. Zurbuchen George Gloeckler Brian J. Anderson Daniel N. Baker Haje Korth Stamatios M. Krimigis Ralph L. McNutt Jr 《Planetary and Space Science》2011,59(15):2004-2015
The MESSENGER Fast Imaging Plasma Spectrometer (FIPS) measured the bulk plasma characteristics of Mercury's magnetosphere and solar wind environment during the spacecraft's first two flybys of the planet on 14 January 2008 (M1) and 6 October 2008 (M2), producing the first measurements of thermal ions in Mercury's magnetosphere. In this work, we identify major features of the Mercury magnetosphere in the FIPS proton data and describe the data analysis process used for recovery of proton density (np) and temperature (Tp) with a forward modeling technique, required because of limitations in measurement geometry. We focus on three regions where the magnetospheric flow speed is likely to be low and meets our criteria for the recovery process: the M1 plasma sheet and the M1 and M2 dayside and nightside boundary-layer regions. Interplanetary magnetic field (IMF) conditions were substantially different between the two flybys, with intense reconnection signatures observed by the Magnetometer during M2 versus a relatively quiet magnetosphere during M1. The recovered ion density and temperature values for the M1 quiet-time plasma sheet yielded np∼1–10 cm−3, Tp∼2×106 K, and plasma β∼2. The nightside boundary-layer proton densities during M1 and M2 were similar, at np∼4–5 cm−3, but the temperature during M1 (Tp∼4–8×106 K) was 50% less than during M2 (Tp∼8×106 K), presumably due to reconnection in the tail. The dayside boundary layer observed during M1 had a density of ∼16 cm−3 and temperature of 2×106 K, whereas during M2 this region was less dense and hotter (np∼8 cm−3 and Tp∼10×106 K), again, most likely due to magnetopause reconnection. Overall, the southward interplanetary magnetic field during M2 clearly produced higher Tp in the dayside and nightside magnetosphere, as well as higher plasma β in the nightside boundary, ∼20 during M2 compared with ∼2 during M1. The proton plasma pressure accounts for only a fraction (24% for M1 and 64% for M2) of the drop in magnetic pressure upon entry into the dayside boundary layer. This result suggests that heavy ions of planetary origin, not considered in this analysis, may provide the “missing” pressure. If these planetary ions were hot due to “pickup” in the magnetosheath, the required density for pressure balance would be an ion density of ∼1 cm−3 for an ion temperature of ∼108 K. 相似文献
976.
Kathryn E. Davis Rodney L. Anderson Daniel J. Scheeres George H. Born 《Celestial Mechanics and Dynamical Astronomy》2011,109(3):241-264
This paper presents a method to construct optimal transfers between unstable periodic orbits of differing energies using invariant
manifolds. The transfers constructed in this method asymptotically depart the initial orbit on a trajectory contained within
the unstable manifold of the initial orbit and later, asymptotically arrive at the final orbit on a trajectory contained within
the stable manifold of the final orbit. Primer vector theory is applied to a transfer to determine the optimal maneuvers required
to create the bridging trajectory that connects the unstable and stable manifold trajectories. Transfers are constructed between
unstable periodic orbits in the Sun–Earth, Earth–Moon, and Jupiter-Europa three-body systems. Multiple solutions are found
between the same initial and final orbits, where certain solutions retrace interior portions of the trajectory. All transfers
created satisfy the conditions for optimality. The costs of transfers constructed using manifolds are compared to the costs
of transfers constructed without the use of manifolds. In all cases, the total cost of the transfer is significantly lower
when invariant manifolds are used in the transfer construction. In many cases, the transfers that employ invariant manifolds
are three times more efficient, in terms of fuel expenditure, than the transfer that do not. The decrease in transfer cost
is accompanied by an increase in transfer time of flight. 相似文献
977.
Daniel D. DURDA Clark R. CHAPMAN Mark J. CINTALA George J. FLYNN Melissa M. STRAIT Anderson MINNICK 《Meteoritics & planetary science》2011,46(1):149-155
Abstract– We present results of a set of impact experiments designed to examine the effects of impacts onto rocky blocks resting on and embedded within regoliths. The targets were approximately 500 g granodiorite blocks, struck with one‐eighth inch aluminum spheres at nominal speeds of approximately 5 km s?1. The granodiorite blocks were emplaced in 20–30 grade silica sand to simulate an asteroidal or lunar regolith; block burial depths ranged from resting flush on the surface to submerged completely below the surface. We observe a trend for largest remnant mass to increase with block burial depth. Documentary still image and high‐speed video of the resulting block fragments and surrounding regolith reveal new insights into the morphologies of blocks and secondary craters observed on asteroids like 433 Eros. 相似文献
978.
Muhammad Akbar Khan Muhammad Akhtar George Iliopoulos 《Journal of the Geological Society of India》2014,84(3):352-360
The late Miocene-early Pliocene fossil deposits of Hasnot in northern Pakistan have yielded a very rich vertebrate fauna. In this paper we describe the remains of Cervidae from six of these localities. By dental remains, at least four species of cervids are documented. These remains significantly widen the time distribution of the cervids and draw back the first appearance of cervids in the Dhok Pathan Formation of the Siwaliks. The data indicate a diverse set of coexisting ungulates in the area, subsisting within a mosaic of habitats. 相似文献
979.
Shao-Yi Huang Yue-Gau Chen George S. Burr Manoj K. Jaiswal Yunung Nina Lin Gongming Yin Jingwei Liu Shujun Zhao Zhongquan Cao 《Quaternary Research》2014
We present a reconstructed lithologic column compiled from a series of lacustrine outcrops along a tributary of the Nyang River, a major tributary of the Yarlung-Tsangpo in southeast Tibet. The deposits were preserved between terraces at altitudes of 2950–3100 m asl. The stratigraphic record features at least two sets of coarsening-upward sequences depicting episodic aggradation and progradation of a glacially dammed lake related delta. Recognized facies changes illustrate the evolution cycles of depositional environments from pro-delta, delta front, to delta plain. Radiocarbon and optically stimulated luminescence dates reveal an aging-downward trend in stratigraphic order and provide an approximate timeline for the formation of glacially dammed lakes in late Pleistocene. This result reflects that the Zelunglung Glacier had progressively advanced to block the Yarlung-Tsangpo river and the dam materials had stepwise stacked up to an altitude of 3095 m asl during Marine Oxygen Isotope Stages 4 to 2. 相似文献
980.
Recognition of cyclic steps in sandy and gravelly turbidite sequences,and consequences for the Bouma facies model 总被引:2,自引:0,他引:2
Preservation of cyclic steps contrasts markedly with that of subcritical‐flow bedforms, because cyclic steps migrate upslope eroding their lee face and preserving their stoss side. Such bedforms have not been described from turbidite outcrops and cores as yet. A conceptual block diagram for recognition of cyclic steps in outcrop has been constructed and is tested by outcrop studies of deep water submarine fan deposits of the Tabernas Basin in south‐eastern Spain. Experimental data indicate that depositional processes on the stoss side of a cyclic step are controlled by a hydraulic jump, which decelerates the flow and by subsequent waxing of the flow up to supercritical conditions once more. The hydraulic jump produces a large scour with soft‐sediment deformation (flames) preserved in coarse‐tail normal‐graded structureless deposits (Bouma Ta), while near‐horizontal, massive to stratified top‐cut‐out turbidite beds are found further down the stoss side of the bedform. The architecture of cyclic steps can best be described as large, up to hundreds of metres, lens‐shaped bodies that are truncated by erosive surfaces representing the set boundaries and that consist of nearly horizontal lying stacks of top‐cut‐out turbidite beds. The facies that characterize these bedforms have traditionally been described as turbidite units in idealized vertical sequences of high‐density turbidity currents, but have not yet been interpreted to represent bedforms produced by supercritical flow. Their large size, which is in the order of 20 m for gravelly and up to hundreds of metres for sandy steps, is likely to have hindered their recognition in outcrop so far. 相似文献