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71.
72.
Gan Lu Wang Yuanyuan Wang Yusheng Lev Benjamin Shen Wenjing Jiang Wen 《Natural Hazards》2021,107(3):2123-2153
Natural Hazards - Nowadays, frequent meteorological disasters that cause huge economic losses and ecological damages have swept the world. Thus, research investigates how to overcome the adverse... 相似文献
73.
74.
Lev Pirogov 《天文和天体物理学研究(英文版)》2018,(8)
In order to search for intensity fluctuations on the HCN(1–0) and HCO~+(1–0) line profiles, which could arise due to possible small-scale inhomogeneous structure, long-term observations of high-mass star-forming cores S140 and S199 were carried out. The data were processed by the Fourier filtering method. Line temperature fluctuations that exceed the noise level were detected. Assuming the cores consist of a large number of randomly moving small thermal fragments, the total number of fragments is ~ 4 × 10~6 for the region with linear size ~ 0.1 pc in S140 and ~ 10~6 for the region with linear size ~ 0.3 pc in S199. Physical parameters of fragments in S140 were obtained from detailed modeling of the HCN emission in the framework of the clumpy cloud model. 相似文献
75.
P. Reig I. Negueruela M. J. Coe J. Fabregat A. E. Tarasov R. K. Zamanov 《Monthly notices of the Royal Astronomical Society》2000,317(1):205-210
We report on the long-term variability of the Be/X-ray binary LS I +61° 235/RX J0146.9+6121. New optical spectroscopic and infrared photometric observations confirm the presence of global one-armed oscillations in the circumstellar disc of the Be star, and allow us to derive a V R band quasi-period of 1240±30 d. Pronounced shell events, reminiscent of the spectacular variations in Be stars, are also seen. We have found that the J , H and K infrared photometric bands vary in correlation with the spectroscopic V R variations, implying that the one-armed disc oscillations are prograde. The effect of the oscillations is not only seen in the H α line but is also seen in the He i λ 6678 and Paschen lines. As these lines are formed at different radii in the equatorial disc of the Be star, such effects confirm the global nature of the perturbation. The Keplerian disc has been found to be denser than the average for a sample of isolated Be stars, which may be indicative of some kind of interaction with the compact companion. Finally, from a Rossi X-ray Timing Explorer observation we derive a spin period of the neutron star of 1404.5±0.5 s. 相似文献
76.
D. Texier N. de Noblet S. P. Harrison A. Haxeltine D. Jolly S. Joussaume F. Laarif I. C. Prentice P. Tarasov 《Climate Dynamics》1997,13(12):865-881
The LMD AGCM was iteratively coupled to the global BIOME1 model in order to explore the role of vegetation-climate interactions
in response to mid-Holocene (6000 y BP) orbital forcing. The sea-surface temperature and sea-ice distribution used were present-day
and CO2 concentration was pre-industrial. The land surface was initially prescribed with present-day vegetation. Initial climate
“anomalies” (differences between AGCM results for 6000 y BP and control) were used to drive BIOME1; the simulated vegetation
was provided to a further AGCM run, and so on. Results after five iterations were compared to the initial results in order
to identify vegetation feedbacks. These were centred on regions showing strong initial responses. The orbitally induced high-latitude
summer warming, and the intensification and extension of Northern Hemisphere tropical monsoons, were both amplified by vegetation
feedbacks. Vegetation feedbacks were smaller than the initial orbital effects for most regions and seasons, but in West Africa
the summer precipitation increase more than doubled in response to changes in vegetation. In the last iteration, global tundra
area was reduced by 25% and the southern limit of the Sahara desert was shifted 2.5 °N north (to 18 °N) relative to today.
These results were compared with 6000 y BP observational data recording forest-tundra boundary changes in northern Eurasia
and savana-desert boundary changes in northern Africa. Although the inclusion of vegetation feedbacks improved the qualitative
agreement between the model results and the data, the simulated changes were still insufficient, perhaps due to the lack of
ocean-surface feedbacks.
Received: 5 December 1996 / Accepted: 16 June 1997 相似文献
77.
A hydrological–lithostratigraphical model was developed for assessment of transmission losses and groundwater recharge from runoff events in arid water courses where hydrological and meteorological records are incomplete. Water balance equations were established for reaches between hydrometric stations. Because rainfall and tributary flow data are scarce, lateral inflow, which is an essential component of the water balance equation, could not be estimated directly. The solution was obtained by developing a method which includes a hydrological–lithostratigraphical analogy. This is based on the following assumptions: (a) runoff resulting from a given rainfall event is related to the watershed surface lithology; (b) for a given event, the spatial distribution of runoff reflects the distribution of rainfall: and (c) transmission losses are uniquely related to the total inflow to the reach. The latter relationship, called the loss function, and the water balance equation comprise a model which simultaneously assesses lateral inflow and transmission losses for runoff events recorded at the terminal stations. The model was applied to three reaches of the arid Nahal Tsin in Israel. In this case study, the transmission losses were of the same order of magnitude as the flow at the major hydrometric stations. The losses were subdivided into channel moistening, which subsequently evaporates, and deep percolation, which recharges groundwater. For large runoff events, evaporation was substantially smaller than the losses. The mean annual recharge of groundwater from runoff events in the Tsin watershed was 4·1×106 m3, while the mean annual flow volume at the major stations ranged from 0·6 to 1·5×106 m3. Once in 100 years, the annual recharge may be seven times higher than the mean annual value, but the recharge during most years is very small. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
78.
Subduction zones with deep seismicity are believed to be associated with the descending branches of convective flows in the mantle and are subordinated to them. Therefore, the position of subduction zones can be considered as relatively fixed with respect to the steady-state system of convective flows. The lithospheric plate overhanging a subduction zone (as a rule of continental type) may:
- 1. (1) either move away from the subduction zone; or
- 2. (2) move onto it. In the first case extensional conditions originate behind the subduction zone and the new oceanic crust of back-arc basins forms. In the second case active Andean-type continental margins with thickening of the crust and lithosphere are observed.
79.
Pavel E. Tarasov Rachid Cheddadi Joel Guiot Sytze Bottema Odile Peyron Jordina Belmonte Vittoria Ruiz-Sanchez Fatima Saadi Simon Brewer 《第四纪科学杂志》1998,13(4):335-344
An objective method for the assignment of pollen spectra to appropriate biomes has been published recently. The aim of this paper is to improve the distinction between warm and cool steppes, thus refining vegetation and climate reconstruction, particularly during the Last Glacial Maximum. A set of modern pollen spectra from the Mediterranean and Kazakhstan regions, dominated today by open vegetation types, has been analysed statistically in order to relate pollen taxa abundances to warm and cool grass/shrub plant functional types (PFTs). A statistical test using modern pollen data shows that the method is able to distinguish between cool and warm steppe biomes with a high degree of confidence. The method has been applied to two fossil pollen records. The results of this exercise showed that cool steppe dominated in central Greece between 18 000 and 13 000 yr BP, while in western Iran the vegetation was at the boundary between cool and warm steppes. These vegetation types were replaced by warm mixed forest in Greece and warm steppe in Iran after that time span. © 1998 John Wiley & Sons, Ltd. 相似文献
80.
High dispersion CCD spectra are used to study the profiles of the Hα and Hβ lines of 48 stars in early spectral classes in
the young diffuse binary cluster h/χ Per. In addition, moderate resolution spectra of 15 B and Be stars were taken over the
interval 4400–4960 Å. One or, possibly, two new Be stars are discovered. The major parameters of the Hα line are measured
for the observed B and Be stars. The spectra over 4400–4960 Å are used to estimate Teff, logg, and υsin i. No traces of emission are detected in the Hα line profiles for 28 of the stars and emission is observed in the Hα line
for 20. During our observations an absorption profile of the Hα line was observed for some of the stars, such as Oo146, Oo566,
Oo922, and Oo1268, although they have previously been identified as Be stars. A significant long-term variability of the Hα
line is discovered for the Be stars Oo1161 and Oo2242. Oo2371 manifests a variability in its faint emission spectrum which
is typical of close binary systems that include a Be star.
__________
Translated from Astrofizika, Vol. 51, No. 2, pp. 305–319 (May 2008). 相似文献