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181.
H. Lammer A. Hanslmeier J. Schneider I. K. Stateva M. Barthelemy A. Belu D. Bisikalo M. Bonavita V. Eybl V. Coudé du Foresto M. Fridlund R. Dvorak S. Eggl J. -M. Grießmeier M. Güdel E. Günther W. Hausleitner M. Holmström E. Kallio M. L. Khodachenko A. A. Konovalenko S. Krauss L. V. Ksanfomality Yu. N. Kulikov K. Kyslyakova M. Leitzinger R. Liseau E. Lohinger P. Odert E. Palle A. Reiners I. Ribas H. O. Rucker N. Sarda J. Seckbach V. I. Shematovich A. Sozzetti A. Tavrov M. Xiang-Grüß 《Solar System Research》2010,44(4):290-310
After the discovery of more than 400 planets beyond our Solar System, the characterization of exoplanets as well as their host stars can be considered as one of the fastest growing fields in space science during the past decade. The characterization of exoplanets can only be carried out in a well coordinated interdisciplinary way which connects planetary science, solar/stellar physics and astrophysics. We present a status report on the characterization of exoplanets and their host stars by reviewing the relevant space- and ground-based projects. One finds that the previous strategy changed from space mission concepts which were designed to search, find and characterize Earth-like rocky exoplanets to: A statistical study of planetary objects in order to get information about their abundance, an identification of potential target and finally its analysis. Spectral analysis of exoplanets is mandatory, particularly to identify bio-signatures on Earth-like planets. Direct characterization of exoplanets should be done by spectroscopy, both in the visible and in the infrared spectral range. The way leading to the direct detection and characterization of exoplanets is then paved by several questions, either concerning the pre-required science or the associated observational strategy. 相似文献
182.
B. Funk E. Pilat-Lohinger R. Dvorak F. Freistetter B. Èrdi 《Celestial Mechanics and Dynamical Astronomy》2004,90(1-2):43-50
Since the first extrasolar planet was discovered about 10 years ago, a major point of dynamical investigations was the determination
of stable regions in extrasolar planetary systems where additional planets may exist. Using numerical methods, we investigate
the dynamical stability in known multiple planetary systems (HD74156, HD38529, HD168443, HD169830) with special interest on
the region between the two known planets and on the mean motion resonances inside this region. As a dynamical model we take
the restricted 4-body problem containing the host star, the two planets and massless test-planets. For our numerical integrations,
we used the Lie-integrator and additionally the Fast Lyapunov Indicators as a tool for detecting chaotic motion. We also investigated
the inner resonances with the outer planet and the outer resonances with the inner planet with test-planets located inside
the resonances. 相似文献
183.
The orbits of fictitious bodies around Jupiter’s stable equilibrium points L 4 and L 5 were integrated for a fine grid of initial conditions up to 100 million years. We checked the validity of three different dynamical models, namely the spatial, restricted three body problem, a model with Sun, Jupiter and Saturn and also the dynamical model with the Outer Solar System (Jupiter to Neptune). We determined the chaoticity of an orbit with the aid of the Lyapunov Characteristic Exponents (=LCE) and used also a method where the maximum eccentricity of an orbit achieved during the dynamical evolution was examined. The goal of this investigation was to determine the size of the regions of motion around the equilibrium points of Jupiter and to find out the dependance on the inclination of the Trojan’s orbit. Whereas for small inclinations (up to i=20°) the stable regions are almost equally large, for moderate inclinations the size shrinks quite rapidly and disappears completely for i>60°. Additionally, we found a difference in the dynamics of orbits around L 4 which – according to the LCE – seem to be more stable than the ones around L 5. 相似文献
184.
Soil is a dynamic natural body and fundamental resource. Human activities influence intensively the natural processes in soils.
They modify and accelerate the development of soils. In this investigation, the deposition of colluvial sediments (colluviation)
and soil formation are proposed as geoindicators for a better understanding of long-term environmental changes and environmental
impact assessment. Deposition of colluvial sediments during several time periods and subsequent soil formation under different
land-use systems reflect important aspects on the long-term human interference in the environment. In this study, we hypothesize
that intensive human activities and environmental changes during middle and late Holocene are responsible for a strong modification
of soils in an investigation area in Schleswig–Holstein (Germany). Soil age information together with geomorphological data,
physical, chemical and biological soil properties provide the database which is necessary to study the types and rates of
colluviation and soil formation. After the investigation with a high resolution in time and space, results show that middle
and late Holocene land-use changes and land management are responsible for soil formation in colluvial layers. Properties
of soils and sediments vary intensively from Mesolithic until Modern times. Intensive soil formation took place during periods
of geomorphodynamic stability in dense woodland. Evidence in our investigations shows that colluviation has a strong relation
with decision-making and environmental degradation in the past. This confirms, too, that a geoindicator concept is needed
to understand and to monitor long-term environmental changes and degradation. 相似文献
185.
Rudolf Musil 《Central European Journal of Geosciences》2011,3(2):147-154
The area defined as the N — S transect of Central Europe encompasses Slovenia, Croatia, Hungary, southern Slovakia, northern Austria, Moravia and southern Poland. Physical and biological environmental analysis have been undertaken for the Gravettian period of the last glacial, between 31 and 22 ka cal BP. Mammal faunas have been recorded from different provinces, which have climatic differences. These climatic differences are reflected in the sediments, the plant cover and the fauna. Over the course of several warm and cold events from 31–22 ka the biodiversity of the individual provinces has remained roughly the same, but important quantitative changes have occurred in the individual faunas. 相似文献
186.
187.
Safe operation and performance of dams is one of the key issues in permafrost regions. At present, the existing dams are 40–45 years old and they are reaching their design life limit. Intensive geocryological processes(thermokarst, thermal erosion, frost heaving, suffosion, concentrated seepage along the voids left by melt ice and others) begin to develop at the early stages of construction. These processes are even more intensive under severe climatic conditions of the permafrost zone due to the large thermal and moisture gradients and the resulting complex thermal stress-strain state in the structures. Determining safety criteria is a critical and difficult task in dam safety management. The existing procedures need to be continuously refined and improved depending on dam importance class. Some researchers recommend introducing process development criteria(stability, destabilization, and extremality) for more objective assessment of dam safety, in addition to the existing two condition criteria. In other words, they call for a multi-factor dam – environment interaction system. A case study of safety declaration for an existing dam is presented. 相似文献
188.
Ulf B��ntgen Rudolf Br��zdil Petr Dobrovolny Mirek Trnka Tom��? Kyncl 《Theoretical and Applied Climatology》2011,105(1-2):167-180
Past, present, and projected fluctuations of the hydrological cycle, associated to anthropogenic climate change, describe a pending challenge for natural ecosystems and human civilizations. Here, we compile and analyze long meteorological records from Brno, Czech Republic and nearby tree-ring measurements of living and historic firs from Southern Moravia. This unique paleoclimatic compilation together with innovative reconstruction methods and error estimates allows regional-scale May?CJune drought variability to be estimated back to ad 1500. Driest and wettest conditions occurred in 1653 and 1713, respectively. The ten wettest decades are evenly distributed throughout time, whereas the driest episodes occurred in the seventeenth century and from the 1840s onward. Discussion emphasizes agreement between the new reconstruction and documentary evidence, and stresses possible sources of reconstruction uncertainty including station inhomogeneity, limited frequency preservation, reduced climate sensitivity, and large-scale constraints. 相似文献
189.
190.
Christoph Janssen Richard Wirth Andreas Reinicke Erik Rybacki Rudolf Naumann Hans-Rudolf Wenk Georg Dresen 《Earth and Planetary Science Letters》2011,301(1-2):179-189
With transmission electron microscopy (TEM) we observed nanometer-sized pores in four ultracataclastic and fractured core samples recovered from different depths of the main bore hole of the San Andreas Fault Observatory at Depth (SAFOD). Cutting of foils with a focused ion beam technique (FIB) allowed identifying porosity down to the nm scale. Between 40 and 50% of all pores could be identified as in-situ pores without any damage related to sample preparation. The total porosity estimated from TEM micrographs (1–5%) is comparable to the connected fault rock porosity (2.8–6.7%) estimated by pressure-induced injection of mercury. Permeability estimates for cataclastic fault rocks are 10? 21–10? 19 m2 and 10? 17 m2 for the fractured fault rock. Porosity and permeability are independent of sample depth. TEM images reveal that the porosity is intimately linked to fault rock composition and associated with deformation. The TEM-estimated porosity of the samples increases with increasing clay content. The highest porosity was estimated in the vicinity of an active fault trace. The largest pores with an equivalent radius > 200 nm occur around large quartz and feldspar grains or grain-fragments while the smallest pores (equivalent radius < 50 nm) are typically observed in the extremely fine-grained matrix (grain size < 1 μm). Based on pore morphology we distinguish different pore types varying with fault rock fabric and alteration. The pores were probably filled with formation water and/or hydrothermal fluids at elevated pore fluid pressure, preventing pore collapse. The pore geometry derived from TEM observations and BET (Brunauer, Emmett and Teller) gas adsorption/desorption hysteresis curves indicates pore blocking effects in the fine-grained matrix. Observations of isolated pores in TEM micrographs and high pore body to pore throat ratios inferred from mercury injection suggest elevated pore fluid pressure in the low permeability cataclasites, reducing shear strength of the fault. 相似文献