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61.
S.?PetitEmail author A.?Decarreau F.?Martin R.?Buchet 《Physics and Chemistry of Minerals》2004,31(9):585-592
The aim of this paper is to determine a relationship between the wavenumbers of the first OH-stretching overtones (W2OH) and the wavenumbers of the OH-stretching fundamentals (WOH) to help to interpret the near-infrared (NIR) spectra. The first overtone (2OH) bands appear at wavenumbers less than twice those of the fundamental bands (OH), due to the anharmonic character of vibrations, X = W2OH/2 - WOH, with X being the anharmonicity constant. Talc samples with various crystal chemistries are used to solve the equation and the experimental data are well fitted with X = –85.6 cm–1. As far as the authors are aware, it is the first time that the anharmonicity constant for the OH-stretching vibrations is determined for phyllosilicates. The anharmonicity constant remains almost unchanged for several types of clay samples. Therefore the relation, established from talc samples because their absorption bands are narrow and their wavenumber range of OH vibrations is wide, can be used for any other clay minerals. 相似文献
62.
Although the field of view of the Normal Incidence Spectrometer (NIS) of the Coronal Diagnostic Spectrometer (CDS) is 4×4 arc min, it is possible to observe the full solar disk by forming a mosaic of images taken in succession. This paper describes just such a study which has been used to collect images of the Sun simultaneously in six wavelengths between 304 Ú and 630 Ú, and with a temperature coverage between 5×104 K and 2.5×106 K. A representative sample of the resulting images is presented. These data can be used to explore the origin of solar EUV variability, and examine large-scale solar features. Another use of these data is to calibrate the pointing of the CDS Offset Pointing System (OPS), by comparing them against the SOHO Extreme ultraviolet Imaging Telescope (EIT) full-disk images taken at the same time. Many joint observations are made with CDS and other SOHO instruments, and calibration of the pointing is crucial to the co-pointing of the instruments, and to the analyses of these data. Coalignment is done by fitting to a cross-correlation function, using an IDL procedure which can be applied to any CDS/NIS data set. The accuracy of an individual coalignment can be demonstrated to be in the range 1–2 arc sec. The overall accuracy of the OPS calibration is ±5 arc sec, mainly attributable to measurement error in the actuator positions. An onboard Spartan Intermediate Sun Sensor of the Lockheed design, which was intended to provide greater pointing accuracy, exhibits a time-varying calibration, possibly due to a gradual loss of sensitivity. 相似文献
63.
Sara F. Martin 《Solar physics》1979,64(1):165-176
Bright and dark curvilinear structures observed between the two major chromospheric ribbons during the flare of 29 July 1973 on films from the Big Bear Solar Observatory are interpreted as a typical system of coronal loops joining the inner boundaries of the separating flare ribbons. These observations, made through a 0.25 Å H filter, only show small segments of the loops having Doppler shifts within approximately ± 22 km s–1 relative to the filter passband centered at H, H -0.5 Å or H +0.5 Å. However, from our knowledge of the typical behavior of such loop systems observed at the limb in H and at 5303 Å, it has been possible to reconstruct an appoximate model of the probable development of the loops of the 29 July flare as they would have been viewed at the limb relative to the position of a prominence which began to erupt a few minutes before the start of the flare. It is seen that the loops ascended through the space previously occupied by the filament. On the assumption that H fine structures parallel the magnetic field, we can conclude that a dramatic reorientation of the direction of the magnetic field in the corona occurred early in the flare, subsequent to the start of the eruption of the filament and prior to the time that the H loops ascended through the space previously occupied by the filament. 相似文献
64.
Ethane (C2H6), methylacetylene (CH3C2H or C3H4) and diacetylene (C4H2) have been discovered in Spitzer 10-20 μm spectra of Uranus, with 0.1-mbar volume mixing ratios of (1.0±0.1)×10−8, (2.5±0.3)×10−10, and (1.6±0.2)×10−10, respectively. These hydrocarbons complement previously detected methane (CH4) and acetylene (C2H2). Carbon dioxide (CO2) was also detected at the 7-σ level with a 0.1-mbar volume mixing ratio of (4±0.5)×10−11. Although the reactions producing hydrocarbons in the atmospheres of giant planets start from radicals, the methyl radical (CH3) was not found in the spectra, implying much lower abundances than in the atmospheres of Saturn or Neptune where it has been detected. This finding underlines the fact that Uranus' atmosphere occupies a special position among the giant planets, and our results shed light on the chemical reactions happening in the absence of a substantial internal energy source. 相似文献
65.
Martin Hassellv 《Marine Chemistry》2005,94(1-4):111
A new method for the characterization of chromophoric colloidal organic matter in seawater has been applied to samples from the Baltic Sea, Kattegatt and Skagerrak seas. Size fractionation of the sample by Flow Field-Flow Fractionation and measurement of the fluorescent and UV absorbing properties of the individual size fractions result in a relative molar mass distribution (RMM) of the optical properties. The RMM distributions have been used to estimate number and weight average relative molar masses, and polydispersity indices. At least two sources of coloured organic matter were identified from the ratio of fluorescence to UV: the Baltic surface water and the Skagerrak deep water. The dominating processes were mixing and dilution, but processes such as photo bleaching of fluorescence are also believed to be important. The RMM distribution derived from UV detection (1150–1300 Dalton) increased with increasing salinity while that derived for fluorescence (1500–1250 Dalton) decreased with increasing salinity. The specific UV absorbance taken as a proxy of the aromaticity of the chromophoric organic material showed decreasing trend with both increasing salinity and increasing UV derived weight average relative molar mass. Increasing polydispersity of the colloidal material was also observed as a function of salinity. 相似文献
66.
67.
Paula Lindgren Lydia Hallis Fredrik S. Hage Martin R. Lee John Parnell Anders Plan Alistair Doye Ian MacLaren 《Meteoritics & planetary science》2019,54(11):2698-2709
A carbon‐rich melt fragment from the Gardnos impact structure has been studied for a better understanding of the preservation and structural form(s) of carbon that have been processed by impact melting. The carbon was analyzed in situ in its original petrographic context within the melt fragment, using high‐resolution techniques including focused ion beam‐transmission electron microscopy and electron energy loss spectroscopy. Results show that the carbon is largely uniform and has a nanocrystalline grain size. The Gardnos carbon has a graphitic structure but with a large c/a ratio indicating disorder. The disorder could be a result of rapid heating to high temperatures during impact, followed by rapid cooling, with not enough time to crystallize into highly ordered graphite. However, temperature distribution during impact is extremely heterogenous, and the disordered Gardnos carbon could also represent material that avoided extreme temperatures, and thus, it was preserved. Understanding the structure of carbon during terrestrial impacts is important to help determine if the history of carbon within extraterrestrial samples is impact related. Furthermore, the degree of preservation of carbon during impact is key for locating and detecting organic compounds in extraterrestrial samples. This example from Gardnos, together with previous studies, shows that not all carbon is lost to oxidation during impact but that impact melting can encapsulate and preserve carbon where it is available. 相似文献
68.
Matthew J. Genge Luke Alesbrook Natasha V. Almeida Helena C. Bates Phil A. Bland Mark R. Boyd Mark J. Burchell Gareth S. Collins Luke T. Cornwell Luke Daly Hadrien A. R. Devillepoix Matthias van Ginneken Ansgar Greshake Daniel Hallatt Christopher Hamann Lutz Hecht Laura E. Jenkins Diane Johnson Rosie Jones Ashley J. King Haithem Mansour Sarah McMullan Jennifer T. Mitchell Gavyn Rollinson Sara S. Russell Christian Schröder Natasha R. Stephen Martin D. Suttle Jon D. Tandy Patrick Trimby Eleanor K. Sansom Vassilia Spathis Francesca M. Willcocks Penelope J. Wozniakiewicz 《Meteoritics & planetary science》2024,59(5):948-972
Fusion crusts form during the atmospheric entry heating of meteorites and preserve a record of the conditions that occurred during deceleration in the atmosphere. The fusion crust of the Winchcombe meteorite closely resembles that of other stony meteorites, and in particular CM2 chondrites, since it is dominated by olivine phenocrysts set in a glassy mesostasis with magnetite, and is highly vesicular. Dehydration cracks are unusually abundant in Winchcombe. Failure of this weak layer is an additional ablation mechanism to produce large numbers of particles during deceleration, consistent with the observation of pulses of plasma in videos of the Winchcombe fireball. Calving events might provide an observable phenomenon related to meteorites that are particularly susceptible to dehydration. Oscillatory zoning is observed within olivine phenocrysts in the fusion crust, in contrast to other meteorites, perhaps owing to temperature fluctuations resulting from calving events. Magnetite monolayers are found in the crust, and have also not been previously reported, and form discontinuous strata. These features grade into magnetite rims formed on the external surface of the crust and suggest the trapping of surface magnetite by collapse of melt. Magnetite monolayers may be a feature of meteorites that undergo significant degassing. Silicate warts with dendritic textures were observed and are suggested to be droplets ablated from another stone in the shower. They, therefore, represent the first evidence for intershower transfer of ablation materials and are consistent with the other evidence in the Winchcombe meteorite for unusually intense gas loss and ablation, despite its low entry velocity. 相似文献
69.
The Kazhdumi Formation of the Bangestan Group is a well-known source rock that has produced abundant oil in most petroleum fields in the Zagros Basin, which stretches from northwest to southwest Iran over hundreds of kilometres. The formation reaches a thickness of 230 m at the type section in northwest Zagros but thins out to 40–50 m in wells studied from the South Pars giant petroleum field, where it comprises mainly grey shales with occasional intercalations of marls and sandstones. South Pars, best known as the Iranian part of the world's largest non-associated gas field, contains small quantities of oil above and below the Kazhdumi Formation. 相似文献
70.
High-resolution topographic mapping of Norwegian deep-water Lophelia coral reefs and their immediate surrounding seafloor has disclosed striking associations with small (<5?m diameter) ‘unit’ pockmarks. A total of four study areas with Lophelia reefs and unit pockmarks are here described and discussed. At the large Fauna reef, which spans 500?m in length and 100?m in width (25?m in height), there is a field of 184 unit pockmarks occurring on its suspected upstream side. Three other, intermediate-sized Morvin reefs are associated with small fields of unit pockmarks situated upstream of live Lophelia colonies. For two of the latter locations, published data exist for geochemical and microbial analyses of sediment and water samples. Results indicate that these unit pockmarks are sources of light dissolved hydrocarbons for the local water mass, together with nutrient-rich pore waters. It is suggested that the ‘fertilized’ seawater flows with the prevailing bottom current and feeds directly into the live portion of the Lophelia reefs. With an estimated growth rate of ~1?cm per year for the Morvin Lophelia corals, it would take between 1,000 and 2,000?years for the reefs to colonize the closest unit pockmarks, currently occurring 10–20?m from their leading (live) edges. 相似文献