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991.
Influence of surface heterogeneity on scalar dissimilarity in the roughness sublayer 总被引:1,自引:8,他引:1
Christopher A. Williams Todd M. Scanlon John D. Albertson 《Boundary-Layer Meteorology》2007,122(1):149-165
While it is generally known that surface heterogeneity weakens the application of Monin–Obukhov similarity (MOS), few studies
have investigated how seasonal changes in the degree of surface heterogeneity at a particular site may influence the validity
of the similarity application. Exploiting seasonal changes in forest function associated with senescence, we conduct a unique
evaluation of the effects of surface heterogeneity on the validity of similarity theory at two sites through time. Using high
frequency (10 Hz) velocity and scalar time series collected within the roughness sublayer over mixed hardwood deciduous and
coniferous forests during both periods of peak leaf area and senescence of deciduous foliage, we examined conformity with
proposed universal flux-variance predictions and agreement amongst normalized standard deviations of different scalars (temperature,
water vapour and carbon dioxide concentrations). Normalized scalar standard deviations were elevated above MOS flux-variance
predictions, with more pronounced deviations observed during and following senescence, particularly in the case of CO2. Power-law scaling of normalized standard deviations as a function of stability was upheld and robust to seasonal changes
in surface heterogeneity. However, dissimilarity of normalized standard deviations for the scalars increased during senescence,
as heterogeneity in the source/sink field increased. Scalewise decomposition of scalar time series using wavelet analysis
indicated that correlations between scalars were conservative through much of the inertial cascade but decayed for eddies
< 10 m. Senescence lowered correlations between scalars over a wide range of eddy sizes. These results demonstrate how seasonal
changes in surface physiology can cause a temporal production of heterogeneity in the source/sink field, thus weakening similarity
applications in the roughness sublayer. 相似文献
992.
993.
This paper outlines exploratory research undertaken by the “A New Sense of Place?” Project in Bristol, UK, into the potential new, location sensitive, computing technologies may have for enhancing urban children's socio‐spatial practices. The paper describes a series of workshops held with children in which mapping activities and use of the technologies are supported by the use of a Geographic Information System (GIS). The paper suggests that sound‐enabled GIS could play a major role in the management of such technologies. 相似文献
994.
The Sensitivity of Australian Fire Danger to Climate Change 总被引:14,自引:2,他引:12
Global climate change, such as that due to the proposed enhanced greenhouseeffect, is likely tohave a significant effect on biosphere-atmosphere interactions, includingbushfire regimes. Thisstudy quantifies the possible impact of climate change on fire regimes byestimating changes infire weather and the McArthur Forest Fire Danger Index (FDI), an index thatis used throughoutAustralia to estimate fire danger. The CSIRO 9-level general circulation model(CSIRO9 GCM)is used to simulate daily and seasonal fire danger for the present Australianclimate and for adoubled-CO2 climate. The impact assessment includes validation ofthe GCMs daily controlsimulation and the derivation of correction factors which improve theaccuracy of the firedanger simulation. In summary, the general impact of doubled-CO2is to increase firedanger at all sites by increasing the number of days of very high and extremefire danger.Seasonal fire danger responds most to the large CO2-induced changesin maximumtemperature. 相似文献
995.
996.
Carol A. Williams 《Celestial Mechanics and Dynamical Astronomy》1984,34(1-4):395-410
Small divisors caused by certain linear combinations of frequencies appear in all analytical planetary theories. With the exception of the deep resonance between Neptune and Pluto, they can be removed at the expense of introducing secular and mixed secular terms, limiting the domain in which the solution is valid. Because of them classical solutions are known not to converge uniformly; Poincaré referred to them as asymptotic. The KAM theory shows that if one is far enough from exact commensurability and has small enough planetary masses, expansions exist which will converge to quasi-periodic orbits. Solutions showing very small divisors are excluded from this region of convergence. The question of whether they are intrinsic to the problem or are just manifestations of the method of solution is not settled. Problems with a single commensurabily that can be isolated from the rest of the Hamiltonian may have solutions with no small divisors. The problem of two or more commensurabilities remains unsolved. 相似文献
997.
Elizabeth P. Turtle Laszlo P. Keszthelyi Jani Radebaugh Damon P. Simonelli David A. Williams Windy L. Jaeger H.Herbert Breneman Cynthia B. Phillips the Galileo SSI Team 《Icarus》2004,169(1):3-28
We present the observations of Io acquired by the Solid State Imaging (SSI) experiment during the Galileo Millennium Mission (GMM) and the strategy we used to plan the exploration of Io. Despite Galileo's tight restrictions on data volume and downlink capability and several spacecraft and camera anomalies due to the intense radiation close to Jupiter, there were many successful SSI observations during GMM. Four giant, high-latitude plumes, including the largest plume ever observed on Io, were documented over a period of eight months; only faint evidence of such plumes had been seen since the Voyager 2 encounter, despite monitoring by Galileo during the previous five years. Moreover, the source of one of the plumes was Tvashtar Catena, demonstrating that a single site can exhibit remarkably diverse eruption styles—from a curtain of lava fountains, to extensive surface flows, and finally a ∼400 km high plume—over a relatively short period of time (∼13 months between orbits I25 and G29). Despite this substantial activity, no evidence of any truly new volcanic center was seen during the six years of Galileo observations. The recent observations also revealed details of mass wasting processes acting on Io. Slumping and landsliding dominate and occur in close proximity to each other, demonstrating spatial variation in material properties over distances of several kilometers. However, despite the ubiquitous evidence for mass wasting, the rate of volcanic resurfacing seems to dominate; the floors of paterae in proximity to mountains are generally free of debris. Finally, the highest resolution observations obtained during Galileo's final encounters with Io provided further evidence for a wide diversity of surface processes at work on Io. 相似文献
998.
Changes of the geometry of the open field line region (namely, the polar cap) caused by the passage of a tangential IMF discontinuity are simulated using the model constructed by Akasofu and Roederer (1983). A singly-bounded open field line region tends to split into two, forming a narrow closed field line region and thus allowing the formations of a plasma sheet and of an auroral arc across the highest latitude region of the Earth. The three-dimensional geometry of some of the closed field lines in the narrow closed region is examined. In this connection, an interesting observation of the formation of an auroral arc over Thule, Greenland, is reported. 相似文献
999.
Volume transport fluctuations of the Florida Current (Gulf Stream), generated within the Straits of Florida by local meridional
wind stress, is investigated. A simple coastal response model was applied to the Straits of Florida and forced by along-channel
winds only. The predicted volume transports were in good agreement with transport estimates derived from moored current meters
and cable voltages for winter winds. Surprisingly, good agreement was also found for the annual transport cycle for the two
years of available data, suggesting that the seasonal change in local along-channel wind forcing provides a significant contribution
to the annual transport cycle of the Gulf Stream. 相似文献
1000.
I. P. Williams 《Astrophysics and Space Science》1972,18(1):223-225
The accumulation of floccules into protoplanets is discussed, and it is pointed out that the simplifications which have been introduced into recent numerical models may result in the incorrect conclusion being reached. 相似文献