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61.
The \(\mu _{O_2 } \) defined by the reaction 6 MnO+O2 =2 Mn3O4 has been determined from 917 to 1,433 K using electrochemical cells (with calcia-stabilized zirconta, CSZ) of the type: Steady emfs were achieved rapidly at all temperatures on both increasing and decreasing temperature, indicating that the MnO-Mn3O4 oxygen buffer equilibrates relatively easily. It therefore makes a useful alternative choice in experimental petrology to Fe2O3-Fe3O4 for buffering oxygen potentials at oxidized values. The results are (in J/mol, temperature in K, reference pressure 1 bar); \(\mu _{O_2 } \) (±200)=-563,241+1,761.758T-220.490T inT+0.101819T 2 with an uncertainty of ±200 J/mol. Third law analysis of these data, including a correction for the deviations in stoichiometry of MnO, impliesS 298.15 for Mn3O4 of 166.6 J/K · mol, which is 2.5 J/K · mol higher than the calorimetric determination of Robie and Hemingway (1985). The low value of the calorimetric entropy may be due to incomplete ordering of the magnetic spins. The third law value of Δ r H 298.15 0 is-450.09 kJ/mol, which is significantly different from the calorimetric value of-457.5±3.4 kJ/mol, calculated from Δ f H 298.15 0 of MnO and Mn3O4, implying a small error in one or both of these latter. 相似文献
62.
Donald G. Isaak Earl K. Graham Jay D. Bass Hong Wang 《Pure and Applied Geophysics》1993,141(2-4):393-414
We present new elasticity measurements on single-crystal fayalite and combine our results with other data from resonance, pulse superposition interferometry, and Brillouin scattering to provide a set of recommended values for the adiabatic elastic moduliC
ij and their temperature variations. We use a resonance method (RPR) with specimens that were previously investigated by pulse superposition experiments. The nineC
ij of fayalite are determined from three new sets of measurements. One set of our newC
ij data is over the range 300–500 K. We believe that the relatively large discrep ncies found in someC
ij are due in large part to specimen inhomogeneities (chemical and microstructural) coupled with differences in the way various techniques sample, rather than only systematic errors associated with experimental procedures or in the preparations of the specimens.Our recommendeaC
ij's (GPa) and (C
ij/T)
p
(GPa/K) are:
The resulting values for the isotropic bulk and shear moduli,K
s and , and their temperature derivatives are:K
s=134(4) GPa; =50.7(0.3) GPa; (K
s/T)
p
=–0.024(0.005) GPa/K; and (/T)
p
=–0.013(0.001) GPa/K. An important conclusion is thatK
s increases as the Fe/(Fe+Mg) ratio in olivine is increased. 相似文献
63.
A new estimate of Pluto's mass within the range of possible masses considered in an earlier work has enabled us to refine our model of Pluto's interior. 相似文献
64.
Graham Ryder Douglas B. Stoeser Ursula B. Marvin Janice F. Bower John A. Wood 《Earth, Moon, and Planets》1975,14(3-4):327-357
Boulder 1, Station 2, Apollo 17 is a stratified boulder containing dark clasts and dark-rimmed light clasts set in a light-gray friable matrix. The gray to black clasts (GCBx and BCBx) are multigenerational, competent, high-grade metamorphic, and partially melted breccias. They contain a diverse suite of lithic clasts which are mainly ANT varieties, but include granites, basaltic-textured olivine basalts, troctolitic and spinel troctolitic basalts, and unusual lithologies such as KREEP norite, ilmenite (KREEP) microgabbro, and the Civet Cat norite, which is believed to be a plutonic differentiate. The GCBxs and BCBxs are variable in composition, averaging a moderately KREEPy olivine norite. The matrix consists of mineral fragments derived from the observed lithologies plus variable amounts of a component, unobserved as a clast-type, that approximates a KREEP basalt in composition, as well as mineral fragments of unknown derivation. The high-temperature GCBxs cooled substantially before their incorporation into the friable matrix of Boulder 1. The light friable matrix (LFBx) is texturally distinct from the competent breccia clasts and, apart from the abundant ANT clasts, contains clasts of a KREEPy basalt that is not observed in the competent breccias. The LFBx lacks such lithologies as the granites and the Civet Cat norite observed in the competent breccias and in detail is a distinct chemical as well as textural entity. We interpret the LFBx matrix as Serenitatis ejecta deposited in the South Massif, and the GCBx clasts as remnants of an ejecta blanket produced by an earlier impact. The source terrain for the Serenitatis impact consisted of the competent breccias, crustal ANT lithologies, and the KREEPy basalts, attesting to substantial lunar activity prior to the impact. The age of the older breccias suggests that the Serenitatis event is younger than 4.01±0.03 b.y. 相似文献
65.
Mark E. Hodson 《Geochimica et cosmochimica acta》2006,70(7):1655-1667
Laboratory determined mineral weathering rates need to be normalised to allow their extrapolation to natural systems. The principle normalisation terms used in the literature are mass, and geometric- and BET specific surface area (SSA). The purpose of this study was to determine how dissolution rates normalised to these terms vary with grain size. Different size fractions of anorthite and biotite ranging from 180-150 to 20-10 μm were dissolved in pH 3, HCl at 25 °C in flow through reactors under far from equilibrium conditions. Steady state dissolution rates after 5376 h (anorthite) and 4992 h (biotite) were calculated from Si concentrations and were normalised to initial- and final- mass and geometric-, geometric edge- (biotite), and BET SSA. For anorthite, rates normalised to initial- and final-BET SSA ranged from 0.33 to 2.77 × 10−10 molfeldspar m−2 s−1, rates normalised to initial- and final-geometric SSA ranged from 5.74 to 8.88 × 10−10 molfeldspar m−2 s−1 and rates normalised to initial- and final-mass ranged from 0.11 to 1.65 molfeldspar g−1 s−1. For biotite, rates normalised to initial- and final-BET SSA ranged from 1.02 to 2.03 × 10−12 molbiotite m−2 s−1, rates normalised to initial- and final-geometric SSA ranged from 3.26 to 16.21 × 10−12 molbiotite m−2 s−1, rates normalised to initial- and final-geometric edge SSA ranged from 59.46 to 111.32 × 10−12 molbiotite m−2 s−1 and rates normalised to initial- and final-mass ranged from 0.81 to 6.93 × 10−12 molbiotite g−1 s−1. For all normalising terms rates varied significantly (p ? 0.05) with grain size. The normalising terms which gave least variation in dissolution rate between grain sizes for anorthite were initial BET SSA and initial- and final-geometric SSA. This is consistent with: (1) dissolution being dominated by the slower dissolving but area dominant non-etched surfaces of the grains and, (2) the walls of etch pits and other dissolution features being relatively unreactive. These steady state normalised dissolution rates are likely to be constant with time. Normalisation to final BET SSA did not give constant ratios across grain size due to a non-uniform distribution of dissolution features. After dissolution coarser grains had a greater density of dissolution features with BET-measurable but unreactive wall surface area than the finer grains. The normalising term which gave the least variation in dissolution rates between grain sizes for biotite was initial BET SSA. Initial- and final-geometric edge SSA and final BET SSA gave the next least varied rates. The basal surfaces dissolved sufficiently rapidly to influence bulk dissolution rate and prevent geometric edge SSA normalised dissolution rates showing the least variation. Simple modelling indicated that biotite grain edges dissolved 71-132 times faster than basal surfaces. In this experiment, initial BET SSA best integrated the different areas and reactivities of the edge and basal surfaces of biotite. Steady state dissolution rates are likely to vary with time as dissolution alters the ratio of edge to basal surface area. Therefore they would be more properly termed pseudo-steady state rates, only appearing constant because the time period over which they were measured (1512 h) was less than the time period over which they would change significantly. 相似文献
66.
Manuela A. Fehr Mark Rehkämper Alex N. Halliday Maria Schönbächler Bodo Hattendorf 《Geochimica et cosmochimica acta》2006,70(13):3436-3448
Tellurium isotope data acquired by multiple-collector inductively coupled plasma-mass spectrometry (MC-ICPMS) are presented for sequential acid leachates of the carbonaceous chondrites Orgueil, Murchison, and Allende. Tellurium isotopes are produced by a broad range of nucleosynthetic pathways and they are therefore of particular interest given the isotopic anomalies previously identified for other elements in these meteorites. In addition, the data provide new constraints on the initial solar system abundance of the r-process nuclide 126Sn, which decays to 126Te with a half-life of 234,500 years. The 126Te/128Te ratios of all leachates were found to be identical, within uncertainty, despite variations in 124Sn/128Te of between about 0.002 and 1.4. The data define a 126Sn/124Sn ratio of <7.7 × 10−5 at the time of last isotopic closure, consistent with the value of <18 × 10−5 previously reported for bulk carbonaceous chondrites. How close this is to the initial 126Sn/124Sn ratio of the solar system depends on when the investigated samples last experienced redistribution of Sn and Te. No clear evidence is found for nucleosynthetic anomalies in the abundances of p-, s-, and r-process nuclides. The largest effect detected in this study is a small excess of the r-process nuclide 130Te in a nitric acid leachate of Murchison. This fraction displays an anomalous ε130Te of +3.5 ± 2.5. Although barely resolvable given the analytical uncertainties, this is consistent with the presence of a small excess r-process component or an s-process deficit. The general absence of anomalies contrasts with previous results obtained for K, Cr, Zr, Mo, and Ba isotopes in similar leachates, which display nucleosynthetic anomalies of up to 3.8%. The reason for this discrepancy is unclear but it may reflect volatility and more efficient mixing of Te in the solar nebula. 相似文献
67.
Beach seines are widely used to estimate the density and species richness of fishes in estuaries. We evaluated the causes
and extent of bias in estimates from seines using a series of field experiments in small estuaries in southern California,
USA. Seining in spatially paired areas that were either enclosed by block nets or not, revealed that seines used without block
nets und erestimated density by more than 4-fold and species richness by more than 2-fold relative to blocked areas. Seining
in paired blocked areas with seines of two lengths revealed that net length affected estimates of density, but not species
richness; a 7.6-m long seine produced 1.6-fold higher estimates of total density than did a 15.2-m long seine due to increased
catches of demersal fishes, but not midwater species. Paired sampling in blocked areas also revealed that many fishes initially
evaded capture by the seine. Estimates of density but not species richness were significantly higher in areas through which
a seine was swept 5 times compared to once. This was due to higher catches of demersal fishes but not midwater fishes in areas
seined 5 times. Repeated seining through blocked areas revealed that the vast majority (90% or more) of species and individuals
of midwater fishes were captured within the first 5 sweeps, compared to only about 50% of the individuals of demersal species.
A mark-recapture study in blocked areas revealed lower probabilities of capture for demersal species relative to midwater
species. 相似文献
68.
We evaluated the sampling characteristics of enclosure traps in estuaries in southern California, USA. Using enclosure traps
that sampled 0.25, 0.5, and 1-m2 footprints, we found that enclosure trap size significantly affected estimates of fish density and the precision of these
estimates. The highest estimates were produced by the 0.5-m2 trap and the lowest by the 0.25-m2 trap. Precision of the density estimates improved with increasing trap size, while the proportion of zero values in the data
sets decreased and estimates of species richness increased. The largest trap was difficult to use in the field and often did
not function properly; thus we concluded that intermediate enclosure trap sizes offered the best compromise between statistical
and logistical considerations. By examination of burrows in sediment cores taken in fished out enclosure traps, we found no
evidence to support the widely held view that burrow-dwelling fishes evaded capture by hiding in burrows. We also used mark-recapture
techniques to estimate recovery efficiency in 0.43-m2 enclosure traps. Recovery efficiency averaged 91% and did not differ significantly among estuaries or sampling stations within
estuaries. Based on extensive netting within enclosure traps, we determined that in areas with dense fish populations (>90
fish 0.43-m−2), netting could be ceased after the first sweep that captured no fish with only a trivial effect on the estimate of density.
In more sparsely populated areas, netting had to continue until 2–3 sweeps had captured no fish in order to obtain estimates
of density that were within 90% of the actual values present. Overall, we found enclosure traps to be effective tools for
sampling small, abundant fishes in shallow estuaries in southern California, but we recommend that care be taken when choosing
trap size and sampling (netting) effort within traps in order to optimize their sampling characteristics. 相似文献
69.
The effects of advection, dispersion, and biological processes on nitrogen and phytoplankton dynamics after a storm event
in December 2002 are investigated in an estuary located on the northern New South Wales coast, Australia. Salinity observations
for 16 d after the storm are used to estimate hydrodynamic transports for a one-dimensional box model. A biological model
with nitrogen limited phytoplankton growth, mussel grazing, and a phytoplankton mortality term is forced by the calculated
transports. The model captured important aspects of the temporal and spatial dynamics of the bloom. A quantitative analysis
of hydrodynamic and biological processes shows that increased phytoplankton biomass due to elevated nitrogen loads after the
storm was not primarily regulated by advection or dispersion in spite of an increase in river flow from <1 to 928×103 m3 d−1. Of the dissolved nitrogen that entered the surface layer of the estuary in the 16 d following the storm event, the model
estimated that 28% was lost through exchange with the ocean or bottom layers, while 15% was removed by the grazing of just
one mussel species,Xenostrobus securis, on phytoplankton, and 50% was lost through other biological phytoplankton loss processes.X. securis grazing remained an important loss process even when the estimated biological parameters in the model were varied by factors
of ± 2. The intertidal mangrove pneumatophore habitat ofX. securis allows filtering of the upper water column from the lateral boundaries when the water column is vertically stratified, exerting
top-down control on phytoplankton biomass. 相似文献
70.
Darren F. Mark John Parnell Simon P. Kelley Sarah C. Sherlock 《Journal of Geochemical Exploration》2006,89(1-3):259
Integration of fluid inclusion analysis with high spatial resolution Ar–Ar dating of K-feldspar cements has been used to resolve and reconstruct palaeo-fluid flow. Fluid inclusion analysis allows discrimination of distinct cement phases, thereby identifying discrete episodes of fluid flow. Ar–Ar dating of the same cements via high spatial resolution laserprobe establishes absolute age constraints on the framework previously constructed. Integration of these two datasets yields temperature–composition–time data. 相似文献