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101.
Dauphiné twinning and texture memory in polycrystalline quartz. Part 3: texture memory during phase transformation 总被引:1,自引:0,他引:1
Hans-Rudolf?WenkEmail author N.?Barton M.?Bortolotti S.?C.?Vogel M.?Voltolini G.?E.?Lloyd G.?B.?Gonzalez 《Physics and Chemistry of Minerals》2009,36(10):567-583
Samples of quartz-bearing rocks were heated above the α (trigonal)–β (hexagonal) phase transformation of quartz (625–950°C)
to explore changes in preferred orientation patterns. Textures were measured both in situ and ex situ with neutron, synchrotron
X-ray and electron backscatter diffraction. The trigonal–hexagonal phase transformation does not change the orientation of
c- and a-axes, but positive and negative rhombs become equal in the hexagonal β-phase. In naturally deformed quartzites measured by
neutron diffraction a perfect texture memory was observed, i.e. crystals returned to the same trigonal orientation they started
from, with no evidence of twin boundaries. Samples measured by electron back-scattered diffraction on surfaces show considerable
twinning and memory loss after the phase transformation. In experimentally deformed quartz rocks, where twinning was induced
mechanically before heating, the orientation memory is lost. A mechanical model can explain the memory loss but so far it
does not account for the persistence of the memory in quartzites. Stresses imposed by neighboring grains remain a likely cause
of texture memory in this mineral with a very high elastic anisotropy. If stresses are imposed experimentally the internal
stresses are released during the phase transformation and the material returns to its original state prior to deformation.
Similarly, on surfaces there are no tractions and thus texture memory is partially lost. 相似文献
102.
L. Goddard A. Kumar A. Solomon D. Smith G. Boer P. Gonzalez V. Kharin W. Merryfield C. Deser S. J. Mason B. P. Kirtman R. Msadek R. Sutton E. Hawkins T. Fricker G. Hegerl C. A. T. Ferro D. B. Stephenson G. A. Meehl T. Stockdale R. Burgman A. M. Greene Y. Kushnir M. Newman J. Carton I. Fukumori T. Delworth 《Climate Dynamics》2013,40(1-2):245-272
Decadal predictions have a high profile in the climate science community and beyond, yet very little is known about their skill. Nor is there any agreed protocol for estimating their skill. This paper proposes a sound and coordinated framework for verification of decadal hindcast experiments. The framework is illustrated for decadal hindcasts tailored to meet the requirements and specifications of CMIP5 (Coupled Model Intercomparison Project phase 5). The chosen metrics address key questions about the information content in initialized decadal hindcasts. These questions are: (1) Do the initial conditions in the hindcasts lead to more accurate predictions of the climate, compared to un-initialized climate change projections? and (2) Is the prediction model’s ensemble spread an appropriate representation of forecast uncertainty on average? The first question is addressed through deterministic metrics that compare the initialized and uninitialized hindcasts. The second question is addressed through a probabilistic metric applied to the initialized hindcasts and comparing different ways to ascribe forecast uncertainty. Verification is advocated at smoothed regional scales that can illuminate broad areas of predictability, as well as at the grid scale, since many users of the decadal prediction experiments who feed the climate data into applications or decision models will use the data at grid scale, or downscale it to even higher resolution. An overall statement on skill of CMIP5 decadal hindcasts is not the aim of this paper. The results presented are only illustrative of the framework, which would enable such studies. However, broad conclusions that are beginning to emerge from the CMIP5 results include (1) Most predictability at the interannual-to-decadal scale, relative to climatological averages, comes from external forcing, particularly for temperature; (2) though moderate, additional skill is added by the initial conditions over what is imparted by external forcing alone; however, the impact of initialization may result in overall worse predictions in some regions than provided by uninitialized climate change projections; (3) limited hindcast records and the dearth of climate-quality observational data impede our ability to quantify expected skill as well as model biases; and (4) as is common to seasonal-to-interannual model predictions, the spread of the ensemble members is not necessarily a good representation of forecast uncertainty. The authors recommend that this framework be adopted to serve as a starting point to compare prediction quality across prediction systems. The framework can provide a baseline against which future improvements can be quantified. The framework also provides guidance on the use of these model predictions, which differ in fundamental ways from the climate change projections that much of the community has become familiar with, including adjustment of mean and conditional biases, and consideration of how to best approach forecast uncertainty. 相似文献
103.
Allison L. Steiner Jeremy S. Pal Sara A. Rauscher Jason L. Bell Noah S. Diffenbaugh Aaron Boone Lisa C. Sloan Filippo Giorgi 《Climate Dynamics》2009,33(6):869-892
Coupling of the Community Land Model (CLM3) to the ICTP Regional Climate Model (RegCM3) substantially improves the simulation
of mean climate over West Africa relative to an older version of RegCM3 coupled to the Biosphere Atmosphere Transfer Scheme
(BATS). Two 10-year simulations (1992–2001) show that the seasonal timing and magnitude of mean monsoon precipitation more
closely match observations when the new land surface scheme is implemented. Specifically, RegCM3–CLM3 improves the timing
of the monsoon advance and retreat across the Guinean Coast, and reduces a positive precipitation bias in the Sahel and Northern
Africa. As a result, simulated temperatures are higher, thereby reducing the negative temperature bias found in the Guinean
Coast and Sahel in RegCM3–BATS. In the RegCM3–BATS simulation, warmer temperatures in northern latitudes and wetter soils
near the coast create excessively strong temperature and moist static energy gradients, which shifts the African Easterly
Jet further north than observed. In the RegCM3–CLM3 simulation, the migration and position of the African Easterly Jet more
closely match reanalysis winds. This improvement is triggered by drier soil conditions in the RegCM3–CLM3 simulation and an
increase in evapotranspiration per unit precipitation. These results indicate that atmosphere–land surface coupling has the
ability to impact regional-scale circulation and precipitation in regions exhibiting strong hydroclimatic gradients. 相似文献
104.
A reanalysis of the relationship between strong westerlies and precipitation in the Great Plains and Midwest regions of North America 总被引:1,自引:0,他引:1
Robert K. Booth John E. Kutzbach Sara C. Hotchkiss Reid A. Bryson 《Climatic change》2006,76(3-4):427-441
A conceptual model relating expanded or strengthened mid-latitude summer westerlies with summer precipitation patterns has been used to explain past drought events in the Great Plains and Midwest of North America, including drought between 1200 and 1400 AD. However, this relationship was originally described using 20 years of instrumental data from the mid 20{th} century, and has not been verified with modern datasets. We reinvestigated the relationship between July westerlies and precipitation in the United States using instrumental records of the last 55 years. We also investigated whether changes in summer zonal flow patterns associated with precipitation anomalies represent a shift in the latitude of peak westerly winds or an increase in wind speed, or a combination of both.Finally, we briefly compare the pattern of precipitation anomalies to paleoclimatic records of drought between 1200 and 1400 AD. Results confirm that strong westerlies are associated with a band of decreased precipitation extending from the northern Rockies into the Midwest. Changes in summer westerlies associated with these patterns are characterized by a strengthening of mean westerly winds, with only a slight southward shift of peak winds over the Atlantic. Changes in the strength of the westerlies over both the Pacific and Atlantic appear to be important to precipitation deficits in the Midwest. Proxy-climate records from 1200 to 1400 AD indicate widespread drought in the Great Plains and Midwest, consistent with the hypothesis of stronger westerlies at this time. However, drought conditions also extended to other regions of North America, indicating a more detailed understanding of the potential causes and synoptic climatology is needed. 相似文献
105.
R. González Felipe H. J. Mosquera Cuesta A. Pérez Martínez H. Pérez Rojas 《中国天文和天体物理学报》2005,5(4):399-411
The equations of state for degenerate electron and neutron gases are studied in the presence of magnetic fields. After including quantum effects in the investigation of the structural properties of these systems, it is found that some hypermagnetized stars can be unstable according to the criterion of stability of pressures. Highly magnetized white dwarfs should collapse producing a supernova type Ia, while superstrong magnetized neutron stars cannot stand their own magnetic field and must implode, too. A comparison of our results with a set of the available observational data of some compact stars is also presented, and the agreement between this theory and observations is verified. 相似文献
106.
We describe the decay phase of one of the largest active regions of solar cycle 22 that developed by the end of June 1987. The center of both polarities of the magnetic fields of the region systematically shifted north and poleward throughout the decay phase. In addition, a substantial fraction of the trailing magnetic fields migrated equatorward and south of the leading, negative fields. The result of this migration was the apparent rotation of the magnetic axis of the region such that a majority of the leading polarity advanced poleward at a faster rate than the trailing polarity. As a consequence, this region could not contribute to the anticipated reversal of the polar field.The relative motions of the sunspots in this active region were also noteworthy. The largest, leading, negative polarity sunspot at N24 exhibited a slightly slower-than-average solar rotation rate equivalent to the mean differential rotation rate at N25. In contrast, the westernmost, leading, negative polarity sunspot at N21 consistently advanced further westward at a mean rate of 0.13 km s–1 with respect to the mean differential rotation rate at its latitude. These sunspot motions and the pattern of evolution of the magnetic fields of the whole region constitute evidence of the existence of a large-scale velocity field within the active region.Solar Cycle Workshop Paper. 相似文献
107.
The Babcock solar dynamo model and known interactions of the interplanetary magnetic field with the earth's magnetosphere are used to explain the relations found between geomagnetic indices at solar minimum and the sunspot number at the following solar maximum. We augment the work of Kane (1987) by updating his method of analysis, including recent smoothed aa and AP indices. We predict a smoothed maximum sunspot number of 163±40 to peak in October 1990±9 months for solar cycle 22. This value is close to the Schatten and Sofia (1987) predicted value of 170±25, using more direct solar indicators.Now at Dept. of Astronomy, Univ. of Washington 相似文献
108.
Julie C. Libarkin Anne U. Gold Sara E. Harris Karen S. McNeal Ryan P. Bowles 《Climatic change》2018,150(3-4):403-416
The relationship between climate change understanding and other variables, including risk perception, beliefs, and worldviews, is an important consideration as we work to increase public attention to climate change. Despite significant effort to develop rigorous mechanisms for measuring affective variables, measurement of climate change understanding is often relegated to unvalidated questions or question sets. To remedy this situation, we constructed and analyzed a climate change concept inventory using a suite of validity and reliability steps, including Rasch analysis. The resultant 21-item test has a high degree of validity and reliability for measuring understanding about basic climate change processes. Inventory scores along with other variables were included in a model of climate change risk perception, providing both concurrent validity for the test and new insight into the importance of understanding, worldview, and values on risk perception. We find that environmental beliefs and cultural cognition worldview play a larger role in predicting an individual’s risk perception than knowledge. Implications for addressing climate change are considered. 相似文献
109.
Real-time storm detection and weather forecast activation through data mining and events processing 总被引:1,自引:0,他引:1
Xiang Li Beth Plale Nithya Vijayakumar Rahul Ramachandran Sara Graves Helen Conover 《Earth Science Informatics》2008,1(2):49-57
Each year across the USA, destructive weather events disrupt transportation and commerce, resulting in both loss of lives
and property. Mitigating the impacts of such severe events requires innovative new software tools and cyberinfrastructure
through which scientists can monitor data for specific severe weather events such as thunderstorms and launch focused modeling
computations for prediction and forecasts of these evolving weather events. Bringing about a paradigm shift in meteorology
research and education through advances in cyberinfrastructure is one of the key research objectives of the Linked Environments
for Atmospheric Discovery (LEAD) project, a large-scale, interdisciplinary NSF funded project spanning ten institutions. In
this paper we address the challenges of making cyberinfrastructure frameworks responsive to real-time conditions in the physical
environment driven by the use cases in mesoscale meteorology. The contribution of the research is two-fold: on the cyberinfrastructure
side, we propose a model for bridging between the physical environment and e-Science1 workflow systems, specifically through events processing systems, and provide a proof of concept implementation of that model
in the context of the LEAD cyberinfrastructure. On the algorithmic side, we propose efficient stream mining algorithms that
can be carried out on a continuous basis in real time over large volumes of observational data.
1 e-Science is used to describe computationally intensive science that is typically carried out in highly distributed network 相似文献
110.
The Eocene Trihueco Formation is one of the best exposed successions of the Arauco Basin in Chile. It represents a period of marine regression and transgression of second-order duration, during which barrier island complexes developed on a muddy shelf. The strata are arranged in classical shoaling-upward parasequences of shoreface and beach facies capped by coal-bearing, back-barrier lagoon deposits. These fourth-order cycles are superimposed upon third-order cycles which caused landward and seaward shifts of the coastal facies belts. The final, punctuated rise in sea level is represented by shelf mudrocks with transgressive incised shoreface sandstones. Relative sea-level oscillations as revealed in the stratigraphy of the Trihueco Formation show a reasonable correlation with published Eocene eustatic curves. 相似文献