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991.
A new algorithm is presented for the numerical integration of second-order ordinary differential equations with perturbations
that depend on the first derivative of the dependent variables with respect to the independent variable; it is especially
designed for few-body problems with velocity-dependent perturbations. The algorithm can be used within extrapolation methods
for enhanced accuracy, and it is fully explicit, which makes it a competitive alternative to standard discretization methods. 相似文献
992.
N. V. Chukanov I. V. Pekov S. Möckel A. A. Mukhanova D. I. Belakovsky L. A. Levitskaya G. K. Bekenova 《Geology of Ore Deposits》2010,52(7):599-605
Kamarizaite, a new mineral species, has been identified in the dump of the Kamariza Mine, Lavrion mining district, Attica Region, Greece, in association with goethite, scorodite, and jarosite. It was named after type locality. Kamarizaite occurs as fine-grained monomineralic aggregates (up to 3 cm across) composed of platy crystals up to 1 μm in size and submicron kidney-shaped segregations. The new mineral is yellow to beige, with light yellow streak. The Mohs hardness is about 3. No cleavage is observed. The density measured by hydrostatic weighing is 3.16(1) g/cm3, and the calculated density is 3.12 g/cm3. The wavenumbers of absorption bands in the IR spectrum of kamarizaite are (cm?1; s is strong band, w is weak band): 3552, 3315s, 3115, 1650w, 1620w, 1089, 911s, 888s, 870, 835s, 808s, 614w, 540, 500, 478, 429. According to TG and IR data, complete dehydration and dehydroxylation in vacuum (with a weight loss of 15.3(1)%) occurs in the temperature range 110–420°C. Mössbauer data indicate that all iron in kamarizaite is octahedrally coordinated Fe3+. Kamarizaite is optically biaxial, positive: n min = 1.825, n max = 1.835, n mean = 1.83(1) (for a fine-grained aggregate). The chemical composition of kamarizaite (electron microprobe, average of four point analyses) is as follows, wt %: 0.35 CaO, 41.78 Fe2O3, 39.89 As2O5, 1.49 SO3, 15.3 H2O (from TG data); the total is 98.81. The empirical formula calculated on the basis of (AsO4,SO4)2 is Ca0.03Fe 2.86 3+ (AsO4)1.90(SO4)0.10(OH)2.74 · 3.27H2O. The idealized formula is Fe 3 3+ (AsO4)2(OH)3 · 3H2O. Kamarizaite is an arsenate analogue of orthorhombic tinticite, space group Pccm, Pcc2, Pcmm, Pcm21, or Pc2m; a = 21.32(1), b = 13.666(6), c =15.80(1) Å, V= 4603.29(5) Å3, Z= 16. The strongest reflections of the X-ray powder diffraction pattern [\(\bar d\), Å (I, %) (hkl)] are: 6.61 (37) (112, 120), 5.85 (52) (311), 3.947 (100) (004, 032, 511), 3.396 (37) (133, 431), 3.332 (60) (314), 3.085 (58) (621, 414, 324). The type material of kamarizaite is deposited in the Mineralogical Collection of Technische Universität Bergakademie Freiberg, Germany, inventory number 82199. 相似文献
993.
A new method to reconstruct aquatic palaeoenvironments is presented. It is based on a non-metrical ‘fish environment reconstruction
index’ (FERI), calculated for the total fish community recorded at an archaeological site. As an example, a FERI is generated
for the Baltic Sea using the ecological requirements of northern European fish species. The present study evaluates the proposed
method by using fish bone assemblages from a region (the middle Holocene Baltic Sea coast) with well-studied hydrographic
history. The bones originate from consecutive human riparian and coastal settlements of hunter-gatherers. The results obtained
for the parameters salinity and sediment structure correlate well with geological knowledge. The new method shows a successive
change from freshwater to brackish and finally to nearly marine conditions before, during, and towards the end of the marine
transgression that created the present Baltic Sea. Additionally, a shift in the sediment structure from muddy to sandy/rocky
conditions is recognisable. 相似文献
994.
Bj?rn Sandstr?m Hans Annersten Eva-Lena Tullborg 《International Journal of Earth Sciences》2010,99(1):1-25
Red-staining of rocks due to fluid–rock interaction during hydrothermal circulation in fractures is a common feature in crystalline
sequences. In this study, red-stained metagranitic rock adjacent to fractures in Forsmark, central Sweden, has been studied
with emphasis on the mineral reactions and associated element mobility occurring during the alteration. The main mineral reactions
associated with the hydrothermal alteration are an almost complete saussuritization of plagioclase accompanied by total chloritization
of biotite. Magnetite has been partly replaced by hematite whereas quartz and K-feldspar were relatively unaffected by the
hydrothermal alteration. We show that redistribution of elements on the whole rock scale was very limited and is mainly manifested
by enrichment of Na2O and volatiles and depletion of CaO, FeO and SiO2 in the red-stained rock. However, on the microscale, element redistribution was more extensive, with both intragranular and
intergranular migration of e.g. Ca, K, Na, Al, Si, Fe, Ba, Cs, Rb, Sr, Ti and REEs. The altered rock shows a shift towards
higher total oxidation factors, but the change is smaller than 1σ and the red-staining of the rock is due to hematite dissemination
rather than a significant oxidation of the rock. An increase in the connected porosity is also observed in the altered rock. 相似文献
995.
A literature review of the impacts of anticipated climate change on unconfined aquifers is presented, along with a conceptual framework for evaluating the complex responses of surface and subsurface hydrology to climate variables in cold regions. The framework offers a way to conceptualize how changes in one component of the system may impact another by delineating the relationships among climate drivers, hydrological responses, and groundwater responses in a straight-forward manner. The model is elaborated in the context of shallow unconfined aquifers in the boreal environment of Finland. In cold conditions, climate change is expected to reduce snow cover and soil frost and increase winter floods. The annual surface water level maximum will occur earlier in spring, and water levels will decrease in summer due to higher evapotranspiration rates. The maximum recharge and groundwater level are expected to occur earlier in the year. Lower groundwater levels are expected in summer due to higher evapotranspiration rates. The flow regimes between shallow unconfined aquifers and surface water may change, affecting water quantity and quality in the surface and groundwater systems. 相似文献
996.
Yeşim İslamoğlu Mathias Harzhauser Martin Gross Gonzalo Jiménez-Moreno Stjepan Coric Andreas Kroh Fred Rögl Jan van der Made 《International Journal of Earth Sciences》2010,99(1):183-200
The Oligocene depositional history of the Thrace Basin documents a unique paleogeographic position at a junction between the
Western Tethys and the Eastern Paratethys. As part of the Tethys, shallow marine carbonate platforms prevailed during the
Eocene. Subsequently, a three-staged process of isolation started with the Oligocene. During the Early Rupelian, the Thrace
Basin was still part of the Western Tethys, indicated by typical Western Tethyan marine assemblages. The isolation from the
Tethys during the Early Oligocene is reflected by oolite formation and endemic Eastern Paratethyan faunas of the Solenovian
stage. The third phase reflects an increasing continentalisation of the Thrace Basin with widespread coastal swamps during
the Late Solenovian. The mollusc assemblages are predominated by mangrove dwelling taxa and the mangrove plant Avicennia is recorded in the pollen spectra. The final continentalisation is indicated by the replacement of the coastal swamps by
pure freshwater swamps and fluvial plains during the Late Oligocene (mammal zone MP 26). This paleogeographic affiliation
of the Thrace Basin with the Eastern Paratethys after ~32 Ma contrasts all currently used reconstructions which treat the
basin as embayment of the Eastern Mediterranean basin. 相似文献
997.
Crustal thinning beneath the Rwenzori region, Albertine rift, Uganda, from receiver-function analysis 总被引:1,自引:1,他引:0
Ingo Wölbern G. Rümpker A. Schumann A. Muwanga 《International Journal of Earth Sciences》2010,99(7):1545-1557
The Rwenzori mountains in western Uganda, with a maximum elevation of more than 5,000 m, are located within the Albertine
rift valley. We have deployed a temporary seismic network on the Ugandan side of the mountain range to study the seismic velocity
structure of the crust and upper mantle beneath this section of the rift. We present results from a receiver-function study
revealing a simple crustal structure along the eastern rift flank with a more or less uniform crustal thickness of about 30 km.
The complexity of inner-crustal structures increases drastically within the Rwenzori block. We apply different inversion techniques
to obtain reliable results for the thickness of the crust. The observations expose a significantly thinner crust beneath the
Rwenzori range with thickness values ranging from about 20–28 km beneath northern and central parts of the mountains. Our
study therefore indicates the absence of a crustal root beneath the Rwenzori block. Beneath the Lake Edward and Lake George
basins we detect the top of a layer of significantly reduced S-wave velocity at 15 km depth. This low-velocity layer may be
attributed to the presence of partial melt beneath a region of recent volcanic activity. 相似文献
998.
Nuray Tokgöz 《Environmental Earth Sciences》2010,59(7):1559-1567
The concept of sustainable development has gained wide acceptance in the fields of mining and environmental studies. Mining
is a temporary activity, but its impact on the environment persists long after mine closure. The aim of this research is to
investigate the effect of land-use change on the stability of the Agacli landslide, northern coastal part of the Istanbul
(Turkey), spanning periods of mining, reclamation, and afforestation. Geological and geophysical surveys were performed to
determine the effects of erosion on the landslide. To assess the possibility of water responsible for triggering a landslide–gully
complex, the dynamic elastic parameters of the field are calculated. Field observations indicate that surface erosion and
gully development have ceased in the afforested area; however, gullies in non-forested areas continue to increase in size
and depth. Uncontrolled surface water and water from stock watering ponds have trigger erosion and rapid sedimentation of
the landslide–gully complex, resulting in over-steepening and enhanced landslide activity on the flanks of the main slide. 相似文献
999.
1000.
Soil-precipitation feedbacks during the South American Monsoon as simulated by a regional climate model 总被引:1,自引:0,他引:1
Anna A. Sörensson Claudio G. Menéndez Patrick Samuelsson Ulrika Willén Ulf Hansson 《Climatic change》2010,98(3-4):429-447
We summarize the recent progress in regional climate modeling in South America with the Rossby Centre regional atmospheric climate model (RCA3-E), with emphasis on soil moisture processes. A series of climatological integrations using a continental scale domain nested in reanalysis data were carried out for the initial and mature stages of the South American Monsoon System (SAMS) of 1993–92 and were analyzed on seasonal and monthly timescales. The role of including a spatially varying soil depth, which extends to 8 m in tropical forest, was evaluated against the standard constant soil depth of the model of about 2 m, through two five member ensemble simulations. The influence of the soil depth was relatively weak, with both beneficial and detrimental effects on the simulation of the seasonal mean rainfall. Secondly, two ensembles that differ in their initial state of soil moisture were prepared to study the influence of anomalously dry and wet soil moisture initial conditions on the intraseasonal development of the SAMS. In these simulations the austral winter soil moisture initial condition has a strong influence on wet season rainfall over feed back upon the monsoon, not only over the Amazon region but in subtropical South America as well. Finally, we calculated the soil moisture–precipitation coupling strength through comparing a ten member ensemble forced by the same space–time series of soil moisture fields with an ensemble with interactive soil moisture. Coupling strength is defined as the degree to which the prescribed boundary conditions affect some atmospheric quantity in a climate model, in this context a quantification of the fraction of atmospheric variability that can be ascribed to soil moisture anomalies. La Plata Basin appears as a region where the precipitation is partly controlled by soil moisture, especially in November and January. The continental convective monsoon regions and subtropical South America appears as a region with relatively high coupling strength during the mature phase of monsoon development. 相似文献