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191.
O. V. Ilyina N. S. Tychkov A. M. Agashev A. V. Golovin A. E. Izokh O. A. Kozmenko N. P. Pokhilenko 《Doklady Earth Sciences》2016,467(2):408-411
The results of the first study of the PGE distribution in deformed lherzolites of the Udachnaya kimberlite pipe (Yakutia) are presented here. The complex character of evolution of the PGE composition in the Deformed lherzolites is assumed to be the result of silicate metasomatism. At the first stage, growth in the amount of clinopyroxene and garnet in the rock is accompanied by a decrease in the concentration of the compatible PGE (Os, Ir). During the final stage, the rock is enriched with incompatible PGE (Pt, Pd) and Re possible due to precipitation of submicron-sized particles of sulfides in the interstitial space of these mantle rocks. 相似文献
192.
Study of the material composition of Fe-Mn crusts from submarine rises in the central part of the Sea of Japan, with modern
precision methods applied, has yielded a high (up to 854 g/t) concentration of gallium contained in sorbed form. The new data
obtained have allowed a new genetic type of gallium deposits—hydrothermal-sedimentary—to be distinguished. 相似文献
193.
194.
Abstract— An oxide layer adjacent to the surface of the Hoba Ni-Fe meteorite was analyzed chemically and mineralogically. Maghemite, magnetite, goethite and lepidocrocite were the main Fe minerals found in the oxide layer surrounding Hoba. Most of the Ni from the unweathered original meteorite was distributed among the above minerals with spinel-type oxides (maghemite and magnetite) having the largest Ni fraction. Some Ni migrated to the limestone in which the meteorite is embedded. No evidence for zaratite or akaganeite was found in the oxide layer. Sulfate derived from the oxidation of troilite precipitated as gypsum. Phosphate accumulation in limestone in contact with the meteorite is probably due to phosphate adsorbed on Fe-oxides. Maghemite with some magnetite was the oxidation product immediately next to the meteorite metal surface, which accommodated most of the Ni and Fe from the meteorite into its structure. Upon oxidation, some of the Ni, which was incorporated into calcite, was released. Cobalt associated with the oxides stayed within the oxide structure regardless of the oxidation state and did not migrate to the limestone. This suggests that Co may be a good tracer for oxides of meteoritic origin. 相似文献
195.
The OSIRIS‐REx target asteroid (101955) Bennu: Constraints on its physical,geological, and dynamical nature from astronomical observations 下载免费PDF全文
D. S. Lauretta A. E. Bartels M. A. Barucci E. B. Bierhaus R. P. Binzel W. F. Bottke H. Campins S. R. Chesley B. C. Clark B. E. Clark E. A. Cloutis H. C. Connolly M. K. Crombie M. Delbó J. P. Dworkin J. P. Emery D. P. Glavin V. E. Hamilton C. W. Hergenrother C. L. Johnson L. P. Keller P. Michel M. C. Nolan S. A. Sandford D. J. Scheeres A. A. Simon B. M. Sutter D. Vokrouhlický K. J. Walsh 《Meteoritics & planetary science》2015,50(4):834-849
We review the results of an extensive campaign to determine the physical, geological, and dynamical properties of asteroid (101955) Bennu. This investigation provides information on the orbit, shape, mass, rotation state, radar response, photometric, spectroscopic, thermal, regolith, and environmental properties of Bennu. We combine these data with cosmochemical and dynamical models to develop a hypothetical timeline for Bennu's formation and evolution. We infer that Bennu is an ancient object that has witnessed over 4.5 Gyr of solar system history. Its chemistry and mineralogy were established within the first 10 Myr of the solar system. It likely originated as a discrete asteroid in the inner Main Belt approximately 0.7–2 Gyr ago as a fragment from the catastrophic disruption of a large (approximately 100‐km), carbonaceous asteroid. It was delivered to near‐Earth space via a combination of Yarkovsky‐induced drift and interaction with giant‐planet resonances. During its journey, YORP processes and planetary close encounters modified Bennu's spin state, potentially reshaping and resurfacing the asteroid. We also review work on Bennu's future dynamical evolution and constrain its ultimate fate. It is one of the most Potentially Hazardous Asteroids with an approximately 1‐in‐2700 chance of impacting the Earth in the late 22nd century. It will most likely end its dynamical life by falling into the Sun. The highest probability for a planetary impact is with Venus, followed by the Earth. There is a chance that Bennu will be ejected from the inner solar system after a close encounter with Jupiter. OSIRIS‐REx will return samples from the surface of this intriguing asteroid in September 2023. 相似文献
196.
K. W. Helen Lau Keith E. Louden Sharon Deemer Jeremy Hall John R. Hopper Brian E. Tucholke W. Steven Holbrook Hans Christian Larsen † 《Geophysical Journal International》2006,167(1):157-170
New multichannel seismic reflection data were collected over a 565 km transect covering the non-volcanic rifted margin of the central eastern Grand Banks and the Newfoundland Basin in the northwestern Atlantic. Three major crustal zones are interpreted from west to east over the seaward 350 km of the profile: (1) continental crust; (2) transitional basement and (3) oceanic crust. Continental crust thins over a wide zone (∼160 km) by forming a large rift basin (Carson Basin) and seaward fault block, together with a series of smaller fault blocks eastwards beneath the Salar and Newfoundland basins. Analysis of selected previous reflection profiles (Lithoprobe 85-4, 85-2 and Conrad NB-1) indicates that prominent landward-dipping reflections observed under the continental slope are a regional phenomenon. They define the landward edge of a deep serpentinized mantle layer, which underlies both extended continental crust and transitional basement. The 80-km-wide transitional basement is defined landwards by a basement high that may consist of serpentinized peridotite and seawards by a pair of basement highs of unknown crustal origin. Flat and unreflective transitional basement most likely is exhumed, serpentinized mantle, although our results do not exclude the possibility of anomalously thinned oceanic crust. A Moho reflection below interpreted oceanic crust is first observed landwards of magnetic anomaly M4, 230 km from the shelf break. Extrapolation of ages from chron M0 to the edge of interpreted oceanic crust suggests that the onset of seafloor spreading was ∼138 Ma (Valanginian) in the south (southern Newfoundland Basin) to ∼125 Ma (Barremian–Aptian boundary) in the north (Flemish Cap), comparable to those proposed for the conjugate margins. 相似文献
197.
R.D. Oudmaijer M.E. van den Ancker D. Baines P. Caselli J.E. Drew M.G. Hoare S.L. Lumsden B. Montesinos S. Sim J.S. Vink H.E. Wheelwright W.J. de Wit 《Astronomische Nachrichten》2011,332(3):238-241
The Herbig Ae/Be stars are intermediate mass pre‐main sequence stars that bridge the gap between the low mass T Tauri stars and the Massive Young Stellar Objects. In this mass range, the acting star forming mechanism switches from magnetically controlled accretion to an as yet unknown mechanism, but which is likely to be direct disk accretion onto the star. We observed a large sample of Herbig Ae/Be stars with X‐shooter to address this issue from a multi‐wavelength perspective. It is the largest such study to date, not only because of the number of objects involved, but also because of the large wavelength coverage from the blue to the near‐infrared. This allows many accretion diagnostics to be studied simultaneously. By correlating the various properties with mass, temperature and age, we aim to determine where and whether the magnetically controlled mass accretion mechanism halts and the proposed direct disk accretion takes over. Here, we will give an overview of the background, present some observations and discuss our initial results. We will introduce a new accretion diagnostic for the research of Herbig Ae/Be stars, the HeI 1.083 μm line (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
198.
Europa's surface is chemically altered by radiolysis from energetic charged particle bombardment. It has been suggested that hydrated sulfuric acid (H2SO4·nH2O) is a major surface species and is part of a radiolytic sulfur cycle, where a dynamic equilibrium exists between continuous production and destruction of sulfur polymers Sx, sulfur dioxide SO2, hydrogen sulfide H2S, and H2SO4·nH2O. We measured the rate of sulfate anion production for cyclo-octal sulfur grains in frozen water at temperatures, energies, and dose rates appropriate for Europa using energetic electrons. The measured rate is GMixture(SO42−)=fSulfur (r0/r)βG1 molecules (100 eV)−1, where fSulfur is the sulfur weight fraction, r is the grain radius, r0=50 μm, β≈1.9, and G1=0.4±0.1. Equilibrium column densities N are derived for Europa's surface and follow the ordering N(H2SO4) » N(S)>N(SO2)>N(H2S). The lifetime of a sulfur atom on Europa's surface for radiolysis to H2SO4 is τ(−S)=120(r/r0)β years. Rapid radiolytic processing hides the identity of the original source of the sulfurous material, but Iogenic plasma ion implantation and an acidic or salty ocean are candidate sources. Sulfate salts, if present, would be decomposed in <3800 years and be rapidly assimilated into the sulfur cycle. 相似文献
199.
Andrew J. Westphal Christopher Snead Janet Borg Eric Quirico Pierre‐Ivan Raynal Michael E. Zolensky Gianluca Ferrini Luigi Colangeli Pasquale Palumbo 《Meteoritics & planetary science》2002,37(6):855-865
Abstract— It has now been about a decade since the first demonstrations that hypervelocity particles could be captured, partially intact, in aerogel collectors. But the initial promise of a bonanza of partially‐intact extraterrestrial particles, collected in space, has yet to materialize. One of the difficulties that investigators have encountered is that the location, extraction, handling and analysis of very small (10 μm and less) grains, which constitute the vast majority of the captured particles, is challenging and burdensome. Furthermore, current extraction techniques tend to be destructive over large areas of the collectors. Here we describe our efforts to alleviate some of these difficulties. We have learned how to rapidly and efficiently locate captured particles in aerogel collectors, using an automated microscopic scanning system originally developed for experimental nuclear astrophysics. We have learned how to precisely excavate small access tunnels and trenches using an automated micromanipulator and glass microneedles as tools. These excavations are only destructive to the collector in a very small area—this feature may be particularly important for excavations in the precious Stardust collectors. Using actuatable silicon microtweezers, we have learned how to extract and store “naked” particles—essentially free of aerogel—as small as 3 μm in size. We have also developed a technique for extracting particles, along with their terminal tracks, still embedded in small cubical aerogel blocks. We have developed a novel method for storing very small particles in etched nuclear tracks. We have applied these techniques to the extraction and storage of grains captured in aerogel collectors (Particle Impact Experiment, Orbital Debris Collector Experiment, Comet‐99) in low Earth orbit. 相似文献
200.
The UCSD solar X-ray instrument on the OSO-7 satellite observes X-ray bursts in the 2–300 keV range with 10.24 s time resolution. Spectra obtained from the proportional counter and scintillation counter are analyzed for the event of November 16, 1971, at 0519 UT in terms of thermal (exponential spectrum) and non-thermal (power law) components. The energy content of the approximately 20 × 106K thermal plasma increased with the 60 s duration hard X-ray burst which entirely preceded the 5 keV soft X-ray maximum. If the hard X-rays arise by thick target bremsstrahlung, the nonthermal electrons above 10 keV have sufficient energy to heat the thermally emitting plasma. In the thin target case the collisional energy transfer from non-thermal electrons suffices if the power law electron spectrum is extrapolated below 10 keV, or if the ambient plasma density exceeds 4 × 1010 cm–3.Formerly at UCSD. 相似文献