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排序方式: 共有196条查询结果,搜索用时 218 毫秒
91.
92.
Krzysztof T. Chyży Marek Urbanik Marian Soida Rainer Beck 《Astrophysics and Space Science》2002,281(1-2):409-410
Our VLA and Effelsberg radio polarization studies of the interacting and cluster galaxies (NGC 3627, NGC 4038/39, NGC 4254)
show that magnetic fields could help us in understanding galaxy peculiar gas motions and cluster environmental effects.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
93.
Kamil Tokár Paweł T. Jochym Przemysław Piekarz Jan Łażewski Małgorzata Sternik Krzysztof Parlinski 《Physics and Chemistry of Minerals》2013,40(3):251-257
The thermodynamical stability of a newly observed wadsleyite II phase in the Mg2SiO4 system is studied by the density functional theory. The wadsleyite II equation of state has been derived. The phase boundaries of Mg2SiO4 polymorphs: wadsleyite, wadsleyite II and ringwoodite are studied using the quasi-harmonic approximation at high external pressures. Clapeyron slopes determined for wadsleyite II–ringwoodite and wadsleyite–wadsleyite II boundaries are 0.0047 and 0.0058 GPa/K, respectively. It is shown that the wadsleyite II phase is not thermodynamically preferred in the pure Mg2SiO4 system and will probably not occur between wadsleyite and ringwoodite phases. 相似文献
94.
Magdalena Kądziałko-Hofmokl Jacek Szczepański Tomasz Werner Maria Jeleńska Krzysztof Nejbert 《Acta Geophysica》2013,61(3):535-568
The results of palaeomagnetic, rock magnetic, and microscopic study of Early Paleozoic metabasites and granulites from the Orlica?nie?nik Dome (OSD, Sudetes) have been combined with geochronological data. In the eastern part of the OSD (?nie?nik Massif, SM) ferrimagnetic pyrrhotite is prevalent, accompanied by various amounts of Fe-oxides. In the western part of the OSD (Orlica-Bystrzyca Massif, OBM) Fe-oxides dominate. All magnetic minerals originated during hydrothermal and weathering processes. The palaeomagnetic study revealed the presence of three secondary components of natural remanence: Late Carboniferous, Late Permian, and Mesozoic. Two Paleozoic components are related to volcanic activity in the Sudetes. They are carried by pyrrhotite and Fe-oxides and were isolated only in SM rocks. The Mesozoic component was determined in both parts of the OSD and is carried by Fe-oxides. It covers a time span, from ~160 to ~40 Ma, corresponding to a long period of alteration. 相似文献
95.
Rafael Fernandez-Carazo Elie Verleyen Dominic A. Hodgson Stephen J. Roberts Krzysztof Waleron Wim Vyverman Annick Wilmotte 《Journal of Paleolimnology》2013,50(1):15-31
Despite the dominance of cyanobacteria in polar freshwater aquatic ecosystems, little is known about their past biodiversity and response to climate and environmental changes. We explored the use of light microscopy of microfossils, high performance liquid chromatography of the fossil pigment composition and denaturing gradient gel electrophoresis of fossil 16S rRNA genes to study past and present-day differences in cyanobacterial community structure in response to climate changes in two adjacent maritime Antarctic lakes with contrasting depths (4 and 26 m) and light climates. Light microscopy was of limited use because of degradation of cell structures. Fossil cyanobacterial pigment concentrations were below the detection limits of our method in several sediment samples in the deep lake, but abundant and diverse in the sediment core from the shallow pond, probably as a consequence of increased light availability and/or a more diverse and abundant benthic cyanobacterial flora. Total carotenoid and chlorophyll concentrations were highest in both lakes between ca. 2,950 and 1,800 cal yr BP, which coincides with the late Holocene climate optimum recognised elsewhere in maritime Antarctica. Cyanobacterial molecular diversity was higher in the top few centimeters of the sediments in both lakes. In deeper sediments, the taxonomic turnover of cyanobacteria appeared to be relatively small in response to past climate anomalies in both lakes, underscoring the broad tolerance of cyanobacteria to environmental variability. This, however, may in part be explained by the low taxonomic resolution obtained with the relatively conserved 16S rRNA gene and/or the preferential preservation of particular taxa. Our results highlight the potential of fossil DNA in lake sediments to study colonization and succession dynamics of lacustrine cyanobacteria and warrant further investigation of the factors that affect preservation of cyanobacterial DNA. 相似文献
96.
Lene L. Delsett Patrick S. Druckenmiller
yvind Hammer Krzysztof Hryniewicz Espen M. Knutsen Maayke J. Koevoets Hans A. Nakrem Aubrey J. Roberts Jrn H. Hurum 《Geology Today》2019,35(1):20-25
In the Mesozoic seas, the apex predators were reptiles. From the Arctic archipelago of Svalbard, the Spitsbergen Mesozoic Research Group has excavated numerous well preserved marine reptile skeletons in order to understand the biology of these animals and the environment they lived in. The work of eleven field seasons has made this one of the largest and most productive palaeontological research projects in the high Arctic world‐wide. The initial eight seasons focused on one of the richest occurrences of Late Jurassic—earliest Cretaceous (c. 150–139 Ma) marine reptiles in the world, and nearly sixty specimens have been collected, together with a diverse assemblage of invertebrates, some of which are associated with methane seeps. The last three seasons were spent investigating events further back in time, as Spitsbergen preserves the remains from some of the first marine reptile radiations in the wake of the most devastating extinction in the history of the Earth, at the Permian–Triassic boundary (c. 252 Ma). 相似文献
97.
The soil biological activity of mountain meadows is a significant factor that determines the health and utility of these regions. The climax stage of this area is forest, but to maintain semi-natural grassland, which is characterised by high biodiversity,low-intensity land use(mowing or grazing) is necessarily required. To understand the effect of various mowing regimes on the soil biological activity and plants, the soil microbial activity(microbial biomass carbon, dehydrogenase activity and number of the cultivable fraction of soil microbial community),annelids community(density and species composition earthworms and enchytraeids) and plant species composition were investigated. The study area was located in the Pieniny National Park in the Carpathian Mountains, in a meadow belonging to the association Dactylis glomerata-Poa trivialis. The investigated variants were divided according to mowing regime:traditional scything – hand mowing(HM), mechanical mowing(MM), or the abandonment of mowing – nonmowing(NM). The microbial activities(expressed by,e.g. microbial biomass carbon and the number of phosphorus bacteria) were affected by the mowing regime. The density of earthworms was higher in the HM and MM than in the NM variants. The largest changes in plant species composition were caused by the abandonment of mowing(NM). The mean number of plant species was positively correlated with soil moisture, earthworm density, and microbial activity(expressed indirectly by dehydrogenases activity). The soil microbial community, such as vegetative bacteria forms and ammonifying bacteria,were positively associated with pH value, and the microbial and total organic carbon content. The results presented here indicate that there is no single form of optimal management for all living organisms.Decisions about mowing regimes, or abandonment of use, should be preceded by multi-aspect studies,including plants and soil biota. 相似文献
98.
Variations of geomagnetic components X, Y, and Z recorded in 19 Intermagnet European observatories in 2004 were analysed. The original data from all observatories were preliminarily
processed. In the first step, periods longer than three hours were filtered out. In the second step, variations of vertical
geomagnetic component Z were separated into external and internal parts. We introduced a non-dimensional index η defined as the square root of a ratio of the energy of the external part of the vertical component to that of the horizontal
components. Maps of the surface distribution of a new magnetic index η for the area of Europe at selected time periods were created, and their time changes are presented. The time changes of η for selected observatories are also shown. Moreover, we discuss a very interesting phenomenon we discovered, that has never
been described in geophysical literature. Namely, in the recordings of all the observatories we noticed the presence of very
regular variations, observed almost exclusively in the vertical component Z, which is quite unusual. These regular variations occur in the form of sinusoidal “wave packets”. The amplitudes of these
variations do not depend on the geomagnetic latitude and appear in the records of all the observatories we analyzed. They
occur in quiet days, which suggests that their source is in the ionosphere. 相似文献
99.
100.
Results of the application of tropospheric corrections from different troposphere models for precise GPS rapid static positioning 总被引:1,自引:0,他引:1
Paweł Wielgosz Jacek Paziewski Andrzej Krankowski Krzysztof Kroszczyński Mariusz Figurski 《Acta Geophysica》2012,60(4):1236-1257
In many surveying applications, determination of accurate heights is of significant interest. The delay caused by the neutral
atmosphere is one of the main factors limiting the accuracy of GPS positioning and affecting mainly the height coordinate
component rather than horizontal ones. Estimation of the zenith total delay is a commonly used technique for accounting for
the tropospheric delay in static positioning. However, in the rapid static positioning mode the estimation of the zenith total
delay may fail, since for its reliable estimation longer observing sessions are required. In this paper, several troposphere
modeling techniques were applied and tested with three processing scenarios: a single baseline solution with various height
differences and a multi-baseline solution. In specific, we introduced external zenith total delays obtained from Modified
Hopfield troposphere model with standard atmosphere parameters, UNB3m model, COAMPS numerical weather prediction model and
zenith total delays interpolated from a reference network solution. The best results were obtained when tropospheric delays
derived from the reference network were applied. 相似文献