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181.
A. K. Mitra M. Das Gupta R. K. Paliwal S. V. Singh 《Journal of Earth System Science》2003,112(2):223-232
A daily rainfall dataset and the corresponding rainfall maps have been produced by objective analysis of rainfall data. The
satellite estimate of rainfall and the raingauge values are merged to form the final analysis. Associated with epochs of monsoon
these rainfall maps are able to show the rainfall activities over India and the Bay of Bengal region during the BOBMEX period.
The intra-seasonal variations of rainfall during BOBMEX are also seen using these data. This dataset over the oceanic region
compares well with other available popular datasets like GPCP and CMAP. Over land this dataset brings out the features of
monsoon in more detail due to the availability of more local raingauge stations. 相似文献
182.
Separate lead isotope analyses of leachate and residue fractions are applied to a broad spectrum of rocks commonly investigated in metallogenic studies. Resulting data highlight a systematic behavior of leachate and residue fractions with respect to lead isotope compositions, which essentially depends on the mineralogical composition of the rock. Granitoid and high-grade metamorphic rocks have residue compositions virtually identical to common lead. In contrast, low-grade metasedimentary rocks may have residue compositions swamped by radiogenic lead of leach-resistant zircons. Mafic magmatic rocks have residues that are often more radiogenic than leachates, depending on the ratio of leach-refractory zircons to common lead in the residual fraction of these rocks. Separate leachate and residue analyses of source rocks provide two lead isotope end members whose mixture may represent lead with the appropriate ore fluid composition. Our leaching experiments indicate that hot acid solutions (and by inference hydrothermal fluids) preferentially leach radiogenic lead from medium- to high-grade metamorphic and granitoid rocks, whereas they preferentially leach common lead from low-grade metasedimentary and mafic magmatic rocks. The method presented in this study provides a reliable alternative to other methods (i.e., age-correction of bulk-rock compositions) for the determination of the common lead signature of felsic to intermediate magmatic rocks. This may be preferable to age-corrected bulk-rock analyses, where ages to apply for corrections of bulk-rock data are not known or where moderately to highly altered rocks must be used. Case studies of orogenic gold and MVT districts of Peru (Pataz and San Vicente, respectively) show that separate leachate and residue lead isotope analyses carried out systematically on whole rocks allow a more thorough evaluation of metal source reservoirs than does the standard method of age-corrected or uncorrected bulk-rock analyses. 相似文献
183.
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185.
Stanley N. Davis Stephen Moysey DeWayne L. Cecil Marek Zreda 《Hydrogeology Journal》2003,11(2):217-227
Natural production of the radionuclide chlorine-36 (36Cl) has provided a valuable tracer for groundwater studies. The nuclear industry, especially the testing of thermonuclear
weapons, has also produced large amounts of 36Cl that can be detected in many samples of groundwater. In order to be most useful in hydrologic studies, the natural production
prior to 1952 should be distinguished from more recent artificial sources. The object of this study was to reconstruct the
probable preanthropogenic levels of 36Cl in groundwater in the United States. Although significant local variations exist, they are superimposed on a broad regional
pattern of 36Cl/Cl ratios in the United States. Owing to the influence of atmospherically transported ocean salt, natural ratios of 36Cl/total Cl are lowest near the coast and increase to a maximum in the central Rocky Mountains of the United States.
Electronic Publication 相似文献
186.
Reena De S. G. Gaonkar B. V. Srirama Sagina Ram J. R. Kayal 《Journal of Earth System Science》2003,112(3):413-419
A 12-station temporary microearthquake network was established by the Geological Survey of India for aftershock monitoring
of the January 26th, 2001 Bhuj earthquake (M
w 7.6) in the Kutch district of Gujarat state, western India. The epicentres of the aftershocks show two major trends: one
in the NE direction and the other in the NW direction. Fault-plane solutions of the best-located and selected cluster of events
that occurred along the NE trend, at a depth of 15–38 km, show reverse faulting with a large left-lateral strike-slip motion,
which are comparable with the main-shock solution. The NW trending upper crustal aftershocks at depth <10 km, on the other
hand, show reverse faulting with right-lateral strike-slip motion, and the mid crustal and lower crustal aftershocks, at a
depth of 15–38 km, show pure reverse faulting as well as reverse faulting with right-lateral and left-lateral strike-slip
motions; these solutions are not comparable with the main-shock solution. It is inferred that the intersection of two faults
has been the source area for stress concentration to generate the main shock and the aftershocks. 相似文献
187.
Gleb S Pokrovski Jacques Schott Jean-Louis Hazemann 《Geochimica et cosmochimica acta》2003,67(19):3559-3573
The influence of aqueous silica on the hydrolysis of iron(III) nitrate and chloride salts in dilute aqueous solutions (mFe ∼ 0.01 mol/kg) was studied at ambient temperature using X-ray absorption fine structure (XAFS) spectroscopy at the Fe K-edge. Results show that in Si-free iron nitrate and chloride solutions at acid pH (pH < 2.5), Fe is hexa-coordinated with 6 oxygens of H2O- and/or OH-groups in the first coordination sphere of the metal, at an Fe-O distance of 2.00 ± 0.01 Å. With increasing pH (2.7 < pH < 13), these groups are rapidly replaced by bridging hydroxyls (-OH-) or oxygens (-O-), and polymerized Fe hydroxide complexes form via Fe-(O/OH)-Fe bonds. In these polymers, the first atomic shell of iron represents a distorted octahedron with six O/OH groups and Fe-O distances ranging from 1.92 to 2.07 Å. The Fe octahedra are linked together by their edges (Fe-Fe distance 2.92-3.12 Å) and corners (Fe-Fe distance ∼3.47 ± 0.03 Å). The Fe-Fe coordination numbers (Nedge = 1-2; Ncorner = 0.5-0.7) are consistent with the dominant presence of iron dimers, trimers and tetramers at pH 2.5 to 2.9, and of higher-polymerized species at pH > 3.At pH > 2.5 in the presence of aqueous silica, important changes in Fe(III) hydrolysis are detected. In 0.05-m Si solutions (pH ∼ 2.7-3.0), the corner linkages between Fe octahedra in the polymeric complexes disappear, and the Fe-Fe distances corresponding to the edge linkages slightly increase (Fe-Feedge ∼ 3.12-3.14 Å). The presence of 1 to 2 silicons at 3.18 ± 0.03 Å is detected in the second atomic shell around iron. At basic pH (∼12.7), similar structural changes are observed for the iron second shell. The Fe-Si and Fe-Fe distances and coordination numbers derived in this study are consistent with (1) Fe-Si complex stoichiometries Fe2Si1-2 and Fe3Si2-3 at pH < 3; (2) structures composed of Fe-Fe dimers and trimers sharing one or two edges of FeO6-octahedra; and (3) silicon tetrahedra linked to two neighboring Fe octahedra via corners. At higher Si concentration (0.16 m, polymerized silica solution) and pH ∼ 3, the signal of the Fe second shell vanishes indicating the destruction of the Fe-Fe bonds and the formation of different Fe-Si linkages. Moreover, ∼20 mol.% of Fe is found to be tetrahedrally coordinated with oxygens in the first coordination shell (RFe-O = 1.84 Å). This new finding implies that Fe may partially substitute for Si in the tetrahedral network of the silica polymers in Si-rich solutions.The results of this study demonstrate that aqueous silica can significantly inhibit iron polymerization and solid-phase formation, and thus increase the stability and mobility of Fe(III) in natural waters. The silica “poisoning” of the free corner sites of iron-hydroxide colloids should reduce the adsorption and incorporation of trace elements by these colloids in Si-rich natural waters. 相似文献
188.
189.
Kirt E. Moody 《Estuaries and Coasts》2003,26(3):759-764
Blue crabsCallinectes sapidus in lower Chesapeake Bay are subject to high rates of predation during the late summer of their first year of growth as they
migrate out of vegetated nursery habitats. Predators, potentially contributing to this pattern, were identified in video-recorded
field observations of tethered juvenile crabs (20–25 mm carapace width). Predators were also tested in large laboratory tanks
containing similarly-sized untethered crabs as prey. Seven different predators attacked tethered crabs in the field. Only
two predators, larger blue crabs and northern puffers,Sphoeroides maculatus, consistently succeeded in preying on crabs in both field and laboratory settings. These results confirm the importance of
cannibalism on juvenile blue crabs and identify puffers as a potentially overlooked source of predation pressure. 相似文献
190.