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651.
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Paul Eccleston Bruce Swinyard Marcel Tessenyi Giovanna Tinetti Ingo Waldmann Marc Ferlet Ranah Irshad Tanya Lim Kevin Middleton Tom Bradshaw Martin Crook Tom Hunt Berend Winter Ian Bryson Naidu Bezawada William Taylor Neil Bowles Enzo Pascale Gianluca Morgante Emanuele Pace Alberto Adriani Jean-Michel Reess Marc Ollivier Roland Ottensamer Mirek Rataj Gonzalo Ramos Zapata Jan-Rutger Schrader Avri Selig Kate Isaak Martin Linder Ludovic Puig 《Experimental Astronomy》2015,40(2-3):427-447
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Klaus Keil Maria E. Zucolotto Alexander N. Krot Patricia M. Doyle Myriam Telus Tatiana V. Krot Richard C. Greenwood Ian A. Franchi John T. Wasson Kees C. Welten Marc W. Caffee Derek W. G. Sears My Riebe Rainer Wieler Edivaldo dos Santos Rosa B. Scorzelli Jerome Gattacceca France Lagroix Matthias Laubenstein Julio C. Mendes Philippe Schmitt‐Kopplin Mourad Harir Andre L. R. Moutinho 《Meteoritics & planetary science》2015,50(6):1089-1111
The Vicência meteorite, a stone of 1.547 kg, fell on September 21, 2013, at the village Borracha, near the city of Vicência, Pernambuco, Brazil. It was recovered immediately after the fall, and our consortium study showed it to be an unshocked (S1) LL3.2 ordinary chondrite. The LL group classification is based on the bulk density (3.13 g cm?3); the chondrule mean apparent diameter (0.9 mm); the bulk oxygen isotopic composition (δ17O = 3.768 ± 0.042‰, δ18O = 5.359 ± 0.042‰, Δ17O = 0.981 ± 0.020‰); the content of metallic Fe,Ni (1.8 vol%); the Co content of kamacite (1.73 wt%); the bulk contents of the siderophile elements Ir and Co versus Au; and the ratios of metallic Fe0/total iron (0.105) versus total Fe/Mg (1.164), and of Ni/Mg (0.057) versus total Fe/Mg. The petrologic type 3.2 classification is indicated by the beautifully developed chondritic texture, the standard deviation (~0.09) versus mean Cr2O3 content (~0.14 wt%) of ferroan olivine, the TL sensitivity and the peak temperature and peak width at half maximum, the cathodoluminescence properties of chondrules, the content of trapped 132Xetr (0.317 × 10?8cm3STP g?1), and the Raman spectra for organic material in the matrix. The cosmic ray exposure age is ~72 Ma, which is at the upper end of the age distribution of LL group chondrites. The meteorite is unusual in that it contains relatively large, up to nearly 100 μm in size, secondary fayalite grains, defined as olivine with Fa>75, large enough to allow in situ measurement of oxygen and Mn‐Cr isotope systematics with SIMS. Its oxygen isotopes plot along a mass‐dependent fractionation line with a slope of ~0.5 and Δ17O of 4.0 ± 0.3‰, and are similar to those of secondary fayalite and magnetite in the unequilibrated chondrites EET 90161, MET 96503, and Ngawi. These data suggest that secondary fayalite in Vicência was in equilibrium with a fluid with a Δ17O of ~4‰, consistent with the composition of the fluid in equilibrium with secondary magnetite and fayalite in other unequilibrated ordinary chondrites. Secondary fayalite and the chondrule olivine phenocrysts in Vicência are not in isotopic equilibrium, consistent with low‐temperature formation of fayalite during aqueous alteration on the LL parent body. That alteration, as dated by the 53Mn‐53Cr chronology age of secondary fayalite, took place Ma after formation of CV CAIs when anchored to the quenched angrite D'Orbigny. 相似文献
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Marc W. Pound Jave O. Kane Dmitri D. Ryutov Bruce A. Remington Akira Mizuta 《Astrophysics and Space Science》2007,307(1-3):187-190
Sometimes the most beautiful things are the hardest to understand. Pillars like those of the Eagle Nebula form at the boundary
between some of the hottest (10000~K) and coldest (10~K) gas in the Galaxy. Many physical processes come into play in the
birth and growth of such gaseous pillars: hydrodynamic instability, photoionization, ablation, recombination, molecular heating
and cooling, and probably magnetic fields. High-quality astronomical observations, quantitative numerical simulations, and
scaled laser experiments provide a powerful combination for understanding their formation and evolution.
We put our most recent hydrodynamic model to the test, by creating simulated observations from it and comparing them directly
to the actual radioastronomical observations. Successfully reproducing major characteristics of the observations in this manner
is an important step in designing appropriate laser experiments. 相似文献
659.
Marie‐Jeanne Teil Martine Blanchard Cendrine Dargnat Karen Larcher‐Tiphagne Marc Chevreuil 《水文研究》2007,21(18):2515-2525
The occurrence and fate of six phthalate esters were investigated in the River Seine and two tributaries in the Paris area, at six sites from upstream to downstream, throughout different seasons, with special attention given to a flood episode. At all sites, except the River Marne, whatever the period, diethylhexyl phthalate (DEHP) displayed the highest concentration (0·323–0·779 µg l?1 as mean values), followed by di‐n‐butyl phthalate (DnBP; 0·211–0·526 µg l?1 as mean values), which is consistent with the production pattern. High phthalate concentrations appeared to be related to population density and industrial distribution. The strongest values were located downstream from wastewater treatment plant effluent inputs. Seasonal variations were closely related to river flow and air and water temperature. The annual evolution of phthalates was linked to the hydrological conditions. During the flood episode at Paris, the DEHP concentration displayed a sharp increase (260 to 1123 ng l?1) occurring 9 days before the flood peak. The simultaneous fluctuations of NH4, typical of domestic origin, and of DEHP suggests a similar origin from combined sewer overflows for both compounds. Other elevated values corresponded to the highest precipitation amounts, and demonstrated the contribution of non‐point‐source runoff and wastewater overflow to DEHP inputs. The DEHP concentration relationship with river flow displayed a clockwise hysteresis loop, corresponding to a ‘first‐flush’ effect in which the finite supplies are swept along in the early stage of the flood. Annual fluxes for 2004 at Paris were 2257 kg of DEHP and 1613 kg of DnBP. The flood period seemed to have a minor impact on annual phthalate transport (29·5% and 41% of the total for DEHP and for DnBP, respectively), which is contrary to annual suspended solids transport (69%). Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
660.
Carolus J. Schrijver Marc L. Derosa Thomas R. Metcalf Yang Liu Jim Mctiernan Stéphane Régnier Gherardo Valori Michael S. Wheatland Thomas Wiegelmann 《Solar physics》2006,235(1-2):161-190
We compare six algorithms for the computation of nonlinear force-free (NLFF) magnetic fields (including optimization, magnetofrictional,
Grad–Rubin based, and Green's function-based methods) by evaluating their performance in blind tests on analytical force-free-field
models for which boundary conditions are specified either for the entire surface area of a cubic volume or for an extended
lower boundary only. Figures of merit are used to compare the input vector field to the resulting model fields. Based on these
merit functions, we argue that all algorithms yield NLFF fields that agree best with the input field in the lower central
region of the volume, where the field and electrical currents are strongest and the effects of boundary conditions weakest.
The NLFF vector fields in the outer domains of the volume depend sensitively on the details of the specified boundary conditions;
best agreement is found if the field outside of the model volume is incorporated as part of the model boundary, either as
potential field boundaries on the side and top surfaces, or as a potential field in a skirt around the main volume of interest.
For input field (B) and modeled field (b), the best method included in our study yields an average relative vector error En = 〈 |B−b|〉/〈 |B|〉 of only 0.02 when all sides are specified and 0.14 for the case where only the lower boundary is specified, while the total
energy in the magnetic field is approximated to within 2%. The models converge towards the central, strong input field at
speeds that differ by a factor of one million per iteration step. The fastest-converging, best-performing model for these
analytical test cases is the Wheatland, Sturrock, and Roumeliotis (2000) optimization algorithm as implemented by Wiegelmann
(2004). 相似文献