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851.
852.
We performed high-pressure experiments on the crystallization of water ice I and III in the ammonia-water (NH3)x(H2O)(1−x) system, and apply the results to the interiors of icy bodies in the Solar System. Phase equilibrium lines between an entirely liquid solution and a liquid solution in which water ice forms (liquidus lines) were determined for ammonia concentration by mass X equal to 0.034, 0.0472, 0.111, 0.176, and 0.229. Growth-melting of ice I as well as ice III crystals were observed. Application of the results to icy satellites that are potential bearers of ammonia shows that ammonia admixture decreases the depth of the liquidus surface. A shift of the liquidus temperature within a satellite depends on three parameters: the ammonia concentration, X; the temperature gradient, α; and the product of density and gravity, ρg. 相似文献
853.
Krystyna Szeroczyńska Andrzej Tatur Jan Weckström Michał Gąsiorowski Agnieszka M. Noryśkiewicz Elwira Sienkiewicz 《Journal of Paleolimnology》2007,38(1):25-47
A 2.5-m-long sediment core was retrieved from Lake Somaslampi, a small lake located in a kame field on the north slope of
the Scandes Mountains in Finnish Lapland. Holocene environmental changes were inferred from the lithological, geochemical,
pollen, diatom and Cladocera records stored in the lake sediment. The chronology was based on six radiocarbon AMS dates supported
by a palynological control chronology. The sediment profile consists of a glacial sedimentary sequence truncated by a lacustrine
one. A hiatus, tentatively correlated with climate cooling and advances of glaciers during the 8.2 ka yrs BP “Finse cooling
Event”, occurs between these sequences. The glacial sequence was composed of fluvioglacial clastics, smoothly changing into
glacio-lacustrine diatomaceous ooze deposited in a meromictic proglacial lake that covered the kame field. The meromixis was
probably caused by the greater depth of the lake, the extended ice-cover, and the microbial mats covering large areas of the
lake bottom. A distinct change in the biota of the glacio-lacustrine sediments indicates higher trophic conditions than during
deposition of the fluvioglacial clastics. The late-Pleistocene vegetation was characterised by subarctic birch tundra vegetation
(Betula–Salix–Ericaceae) with low biodiversity gradually changing to Betula–Pinus dominance in the early Holocene. The lake was deep and had a diatom inferred pH ~ 7 indicated also by the dominance of planktonic
Cladocera.
The base of the lacustrine sediment sequence (6,650–6,300 cal. BP) consisted of loess-rich sediment indicating an increase
in eolian activity. This is also supported by the pollen record, which is dominated by more long-distant taxa such as Alnus and Pinus, and by the increased C/N ratio of the sediment. After the initial meromictic phase of the lake, an abrupt lowering of the
water level occurred. Lake Somaslampi was isolated from the larger Pre-Lake Somas basin and became holomictic, shallow, much
warmer and more productive, until the deterioration of climate around 3,000 yr BP and the increased input of clastics from
the tundra soils. The vegetation followed the general climatic trend by gradually changing from the dominance of Betula and Pinus to the dominance of more tundra-related vegetation like Poaceae and Cyperaceae. However, the higher frequencies of planktonic
Cladocera and centric diatoms in the most recent sediments indicates higher trophic conditions, increased turbulence and a
prolonged ice-free period, which can possibly be linked to the recent climate warming especially in areas of higher altitude
and latitude. 相似文献
854.
855.
An explosive eruption occurred at the summit of Bezymianny volcano (Kamchatka Peninsula, Russia) on 11 January 2005 which
was initially detected from seismic observations by the Kamchatka Volcanic Eruption Response Team (KVERT). This prompted the
acquisition of 17 Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite images of the volcano over
the following 10 months. Visible and infrared data from ASTER revealed significant changes to the morphology of the summit
lava dome, later seen with field based thermal infrared (TIR) camera surveys in August 2005. The morphology of the summit
lava dome was observed to have changed from previous year’s observations and historical accounts. In August 2005 the dome
contained a new crater and two small lava lobes. Stepped scarps within the new summit crater suggest a partial collapse mechanism
of formation, rather than a purely explosive origin. Hot pyroclastic deposits were also observed to have pooled in the moat
between the current lava dome and the 1956 crater wall. The visual and thermal data revealed a complex eruption sequence of
explosion(s), viscous lava extrusion, and finally the formation of the collapse crater. Based on this sequence, the conduit
could have become blocked/pressurized, which could signify the start of a new behavioural phase for the volcano and lead to
the potential of larger eruptions in the future. 相似文献
856.
Aleksander Brzeziński 《Journal of Geodesy》2007,81(6-8):543-551
A simple digital filter is derived for application to studies concerning geophysical excitation of nutation. Attention is
focused on the inverse solution, i.e., inferring the excitation function from the time-series of the celestial pole offsets
observed by very long baseline interferometry (VLBI). Filter properties are discussed by comparing its transfer function with
that of the original differential equation of nutation. An excellent agreement in both the amplitude and phase response is
shown at frequencies between −5 and + 5 cycles per year, which is the frequency band with expected geophysical signals. The
difference appears at higher frequencies, leading to a spurious oscillation produced by the filter. This undesired effect
is considered and the algorithm enabling its removal is described. 相似文献
857.
Bogusław M. Domański 《Acta Geophysica》2007,55(3):267-287
An analysis of source parameters of the two unexpected earthquakes from the Kaliningrad (Russia) area is presented. The earthquakes
occurred on 21 September 2004 at 11:05:01 and 13:32:31 UT, respectively. The first event was located at the latitude φ = 54.924°N and the longitude λ = 20.120°E, with a depth h = 16 km, and the second event at φ = 54.876°N, λ = 20.120°E and h = 20 km.
Magnitudes Mw of the two events were very similar: 5.1 and 5.2. The magnitude values reported by various international data centers have
been meaningfully different. The reason is the presence of high-frequency components in Z velocity component of the S wavefield.
They were observed along the direction defined by two stations, BLEU in Sweden and SUW in Poland, located in opposite sides
of the source. Along the direction perpendicular to it, the effects are relatively very small. The high-frequency waves are
understood to mean components in the 6–8 Hz band for event 1 and 2-4 Hz for event 2. The effects in question are also clearly
visible on displacement spectrograms. The magnitude values calculated at such stations from S-wave amplitudes or from seismic
spectra are clearly overestimated and are close to 6. Therefore, we made a careful selection of channels in order to determine
the spectral parameters and, on this basis, the source parameters.
The size of the source is relatively small, of about 2 km. The closest seismic station is at 100 source radii from the source.
One can clearly see the effect of the TT zone which markedly reduces the seismic moment value for seismic stations laying
on the opposite sides of the source. Both events have very similar spatial distributions of the source parameters: magnitude,
seismic moment and radius. 相似文献
858.
Lindsay R. Kendall John W. Ewart Paul N. Ulrich Adam G. Marsh 《Estuaries and Coasts》2007,30(1):154-162
Delaware's Inland Bays comprise a large estuarine system with a restricted access to the Atlantic Ocean (Indian River Inlet).
As part of a local oyster stock enhancement and restoration effort, we conducted a survey for the protozoan pathogenPerkinsus marinus (Dermo) in oysters from a newly established reef. Using standardized methods for the polymerase chain reaction (PCR) amplification
of the non-transcribed spacer (NTS) region, we were surprised to find no detectable titers of this pathogen in the 30 oysters
sampled in the first year of the project. The detection threshold of the PCR coupled with chemiluminescent detection was 30
fgP. marinus NTS DNA. We were able to detect a trace presence of this pathogen in a few hard clams (Mercenaria mercenaria) from the same locale, indicating that aPerkinsus sp. was present in the Inland Bay system. Subsequent monitoring of the reef system using a fluid thioglycollate assay over
3 yr revealed no epizootic outbreaks of this pathogen within the planted oyster population. Two large mortality episodes that
did appear in the oyster population were attributable to abiotic conditions and not pathogen exposure. This study emphasizes
that all potential sources of mortality in the environment are important to consider when designing oyster seeding projects.
In the Delaware Inland Bays,P. marinus does not appear to have a large enough oyster host population to become a significant disease threat at present. Because
of the low parasite incidence levels in the Inland Bay system in 2000, the James Farm oyster reef restoration project presents
an ideal model system to follow the population dynamics between an oyster-host population and a latent or reservoir pathogen
population. 相似文献
859.
M. Malinowski M. Grad A. Guterch E. Takcs Z.
liwiski L. Antonowicz E. Iwanowska G.R. Keller E. Hegeds 《Tectonophysics》2007,439(1-4):89-106
The extent of the Variscan deformation front is one of the key problems of the regional geology of the Central European Permian Basin system, particularly in its Polish part. Conventional reflection seismics usually fails to produce a satisfactory image of the pre-Permian strata due to the shielding effect of Zechstein (Upper Permian) evaporites. Thus we used a novel seismic acquisition technique to study the base of the Permian complex and its Variscan basement. In the GRUNDY 2003 experiment we combined wide-angle reflection–refraction measurements with the near-vertical reflection seismics by the use of the constant geophone array with dense (100 m) receiver spacing occupying 50-km long profile. 3D design of the experiment, covering 50 × 10 km area, helped in eliminating the effect of out-of-plane propagations and local inhomogeneities. An effective integration of traveltime tomography, CDP reflection processing and prestack depth migration of wide-angle reflections applied to our data, allowed us to present the model in which we deduced the contact zone of the Variscan overthrust structure (Variscan front) with its molasse-filled foredeep. The latter might be a gas-generation zone, which is of a great importance for hydrocarbons prospecting in this area. 相似文献
860.
Results of centimeter-wavelength RATAN-600 observations of several hundred NVSS objects with a wide range of flux densities are presented. Changes in spectral-index distributions from strong-to faint-object populations are estimated. In the transition from strong to faint radio sources, the number of steep-and ultrasteep-spectrum objects decreases and the minimum between steep-and flat-spectrum objects, which was first discovered in the 1970s, becomes less distinct. A less certain increase in the fraction of inverted-spectrum objects is also found. Comparison with theoretical models of radio-source evolution suggests that the decrease in the number of steep-and ultrasteep-spectrum objects can be naturally explained by a sharp decrease in the fraction of classical FRII radio galaxies. The decrease in the sharpness of the minimum may be due to the growing contribution from the population with spectral indices 0.7–0.5, which is usually identified with starbust galaxies. The small increase in the fraction of inverted-spectrum radio sources can be attributed to the growing number of objects with active nuclei. Our spectrum-based conclusions are confirmed by the morphology of the FIRST Catalog images. The number of radio sources associated with supermassive black holes in the Early Universe is estimated using data from the SDSS Catalog. 相似文献