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131.
Up to 400‐year‐old Rhododendron shrubs on the southeastern Tibetan Plateau: prospects for shrub‐based dendrochronology 下载免费PDF全文
Xiaoming Lu J. Julio Camarero Yafeng Wang Eryuan Liang Dieter Eckstein 《Boreas: An International Journal of Quaternary Research》2015,44(4):760-768
In harsh and treeless environments, shrubs constitute the dominant growth form of woody plants, thus offering the opportunity to extend dendrochronological networks beyond the uppermost and northernmost distribution limits of trees. However, shrub‐based dendrochronology has so far resulted in only a few long and climate‐responsive ring‐width chronologies at such stressful sites, particularly above the alpine tree line. A previous study on an alpine Rhododendron shrub species resulted in <80‐year‐long ring‐width chronologies. Here, we collected Rhododendron aganniphum var. schizopeplum stems from elevations between 4000 and 4500 m a.s.l. on the SE Tibetan Plateau and built six tree‐ring width chronologies. One of them is 401 years long and well replicated from AD 1670 to 2011 (EPS>0.85), thus representing the longest shrub chronology available to date. A principal component analysis (PCA) converted the total variability of all six site chronologies into PCs. Then, the six site chronologies and the PC1, accounting for 65.9% of the total variance of the tree‐ring width, were correlated with time series of monthly climate data. Based on this, the year‐to‐year variability of the ring‐width indices was positively correlated with July temperature, which thus turned out to be the dominant factor controlling growth. Accordingly, such long shrub‐ring chronologies may act as climatic and ecological proxies in treeless environments of the Tibetan Plateau. 相似文献
132.
Choon-Ki?Lee Shin-Chan?HanEmail author Dieter?Bilitza Jong-Kyun?Chung 《Journal of Geodesy》2011,85(12):921-929
The in situ measurements of electron contents from GRACE K-band (dual-frequency) ranging system and CHAMP planar Langmuir
probe were used to validate the international reference ionosphere (IRI) models. The comparison using measurements from year
2003 to 2007 shows a general agreement between data and the model outputs. The improvement in the newer IRI model (IRI-2007)
is evident with the measurements from the GRACE satellites orbiting at the higher altitude. We present the comparison between
the models and data comprehensively for various cases in solar activity, local time, season, and latitude. The IRI models
do not well predict the electron density in the years 2006 and later, when the solar activity is extremely low. The IRI models
generally overestimate the electron density during local winter while they underestimate during local summer. In the equatorial
region, the large difference at local sunrise lasts for all years and all seasons. The IRI models do not perform well in predicting
the anomaly in the polar region such as the Weddell Sea Anomaly. These discrepancies are likely due to smoothed (12-month
averaged) solar activity indices used in the IRI models and due to insufficient spherical harmonic representation not able
to capture small spatial scales. In near future, further improvement on the IRI models is expected by assimilating those in
situ satellite data by implementing higher resolution (spatial and temporal) parameterizations. 相似文献
133.
134.
Lutz Nasdala Dieter Grambole Jens Götze Ulf Kempe Tamás Váczi 《Contributions to Mineralogy and Petrology》2011,161(5):777-789
Synthetic ZrSiO4 and (mildly to strongly radiation-damaged) natural zircon samples were irradiated with 8.8 MeV 4He2+ ions (fluences in the range 1 × 1013–5 × 1016 ions/cm2). For comparison, an additional irradiation experiment was done with 30 MeV 16O6+ ions (fluence 1 × 1015 ions/cm2). The light-ion irradiation resulted in the generation of new (synthetic ZrSiO4) or additional (mildly to strongly metamict natural samples) damage. The maximum extent of the damage is observed in a shallow
depth range approximately 32–33 μm (8.8 MeV He) and ~12 μm (30 MeV O) below the sample surface, i.e. near the end of the ion
trajectories. These depth values, and the observed damage distribution, correspond well to defect distribution patterns as
predicted by Monte Carlo simulations. The irradiation damage is recognised from the notable broadening of Raman-active vibrational
modes, lowered interference colours (i.e. decreased birefringence), and changes in the optical activity (i.e. luminescence
emission). At very low damage levels, a broad-band yellow emission centre is generated whereas at elevated damage levels,
this centre is suppressed and samples experience a general decrease in their emission intensity. Most remarkably, there is
no indication of notable structural recovery in pre-damaged natural zircon as induced by the light-ion irradiation, which
questions the relevance of alpha-assisted annealing of radiation damage in natural zircon. 相似文献
135.
Joachim T. Haug Carolin Haug Dieter Waloszek Günter Schweigert 《Swiss Journal of Geoscience》2011,104(1):85-98
Developmental biology has become a major issue for understanding the evolution of Arthropoda. While usually only the ontogenies of extant species are studied, developmental information of fossil arthropods may exhibit developmental patterns not present in living ones. Crustacea possess, basically, a more gradual development than, for example, pterygote insects and would, therefore, be appropriate candidates for the study of fossil ontogenies. Remarkably, famous fossil deposits like the Devonian Rhynie Chert or the Early Palaeozoic ‘Orsten’-type deposits do not comprise the generally macroscopic malacostracan Crustacea (although most probably adult malacostracan fossils have already been found in the Cambrian). By contrast, the Late Jurassic Solnhofen Lithographic Limestones of southern Germany provide thousands of specimens (although only few morphotypes) that can be identified as malacostracan larvae, together with juvenile specimens differing in certain morphological aspects from their conspecific adults. More recent investigations with up-to-date imaging methodology on additional malacostracan crustacean larvae yielded also reconstructible developmental sequences of species from the Solnhofen deposits. The very similar fossil deposits of the Cretaceous lithographic limestones of Lebanon have also yielded malacostracan larvae and juvenile specimens. We present a summary of the occurrences of crustacean fossils providing developmental information and a demonstration of the potential of the lithographic limestones in this context. The importance of developmental data for understanding crustacean evolution is also highlighted. 相似文献
136.
Continental slope terraces at the southern Argentine margin are part of a significant contourite depositional system composed of a variety of drifts, channels, and sediment waves. Here, a refined seismostratigraphic model for the sedimentary development of the Valentin Feilberg Terrace located in ~4.1?km water depth is presented. Analyzing multichannel seismic profiles across and along this terrace, significant changes in terrace morphology and seismic reflection character are identified and interpreted to reflect variations in deep water hydrography from Late Miocene to recent times, involving variable flow of Antarctic Bottom Water and Circumpolar Deep Water. A prominent basin-wide aggradational seismic unit is interpreted to represent the Mid-Miocene climatic optimum (~17?C14?Ma). A major current reorganization can be inferred for the time ~14?C12?Ma when the Valentin Feilberg Terrace started growing due to the deposition of sheeted and mounded drifts. After ~12?Ma, bottom water flow remained vigorous at both margins of the terrace. Another intensification of bottom flow occurred at ~5?C6?Ma when a mounded drift, moats, and sediment waves developed on the terrace. This may have been caused by a general change in deep water mass organization following the closure of the Panamanian gateway, and a subsequent stronger southward flow of North Atlantic Deep Water. 相似文献
137.
Philipp R. Heck Frank J. Stadermann Dieter Isheim Orlando Auciello Tyrone L. Daulton Andrew M. Davis Jeffrey W. Elam Christine Floss Jon Hiller David J. Larson Josiah B. Lewis Anil Mane Michael J. Pellin Michael R. Savina David N. Seidman Thomas Stephan 《Meteoritics & planetary science》2014,49(3):453-467
Atom‐probe tomography (APT) is currently the only analytical technique that, due to its spatial resolution and detection efficiency, has the potential to measure the carbon isotope ratios of individual nanodiamonds. We describe three different sample preparation protocols that we developed for the APT analysis of meteoritic nanodiamonds at sub‐nm resolution and present carbon isotope peak ratios of meteoritic and synthetic nanodiamonds. The results demonstrate an instrumental bias associated with APT that needs to be quantified and corrected to obtain accurate isotope ratios. After this correction is applied, this technique should allow determination of the distribution of 12C/13C ratios in individual diamond grains, solving the decades‐old question of the origin of meteoritic nanodiamonds: what fraction, if any, formed in the solar system and in presolar environments? Furthermore, APT could help us identify the stellar sources of any presolar nanodiamonds that are detected. 相似文献
138.
Dieter Lorenz-Petzold 《Astrophysics and Space Science》1985,113(2):419-422
We derive some new perfect solutions in five dimensions. The solutions given are the generalizations of theL(4, 7) vacuum solution given recently by Demaret and Hanquin (1985) in an incorrect form only. 相似文献
139.
140.
Maxima of calculated topographical line-of-sight (LOS) gravity attractions caused by Ishtar Terra are shifted to the north with respect to the measured LOS free air gravity maxima south of the highland. This implies a tendency to isostatic compensation of central Ishtar and mass surpluses at the continental border and the southern forelands.The following scenario is compatible with the interpretation of the gravity anomalies and morphological features. Relative motions of the lowland Sedna Planitia against continental Ishtar Terra have caused buckling and flat subduction of the lowland lithospheric material. (Deep subduction can be ruled out by thermal reasons). The free air gravity high is modelled by surplus masses of the buckling and of the high density subducting plate. Evidence for this is given by several compressional features like Ut and Vesta Rupes at the southern continental border and ridges at the SW-flanks of Maxwell Montes. It is further supported by several possible volcanic-tectonic depressions located in the southern part of Ishtar. This local interpretation does not necessarily imply the existence of global plate tectonics on Venus like on Earth, but at least limited horizontal movements of the Venusian lithosphere seem to be likely. This result shows that plate recycling must be considered for heat transfer through the lithosphere beside conduction and hot spot volcanism.Contribution No. 273, Institut für Geophysik der Universität Kiel, F.R.G. 相似文献