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941.
Similarity model of feed support system for FAST 总被引:1,自引:0,他引:1
A new design of feed support system for Five hundred meter Aperture Spherical Telescope (FAST) is proposed in this paper.
According to the similarity theory, a 1:15 scale model of feed support system has been built to make systemic research on
the feasibility of the system. Then the control system and hardware structure of the feed support system are illustrated.
A complete astronomical observation track is run by the scale model and the experiments results demonstrate that the new feed
support system can satisfy the observation accuracy requirement of FAST. 相似文献
942.
Klaus KEIL Timothy J. McCOY Lionel WILSON Jean‐Alix BARRAT Doug RUMBLE Matthias M. M. MEIER Rainer WIELER Gary R. HUSS 《Meteoritics & planetary science》2011,46(11):1719-1741
Abstract– We studied the mineralogy, petrology, and bulk, trace element, oxygen, and noble gas isotopic compositions of a composite clast approximately 20 mm in diameter discovered in the Larkman Nunatak (LAR) 04316 aubrite regolith breccia. The clast consists of two lithologies: One is a quench‐textured intergrowth of troilite with spottily zoned metallic Fe,Ni which forms a dendritic or cellular structure. The approximately 30 μm spacings between the Fe,Ni arms yield an estimated cooling rate of this lithology of approximately 25–30 °C s?1. The other is a quench‐textured enstatite‐forsterite‐diopside‐glass vitrophyre lithology. The composition of the clast suggests that it formed at an exceptionally high degree of partial melting, perhaps approaching complete melting, and that the melts from which the composite clast crystallized were quenched from a temperature of approximately 1380–1400 °C at a rate of approximately 25–30 °C s?1. The association of the two lithologies in a composite clast allows, for the first time, an estimation of the cooling rate of a silicate vitrophyre in an aubrite of approximately 25–30 °C s?1. While we cannot completely rule out an impact origin of the clast, we present what we consider is very strong evidence that this composite clast is one of the elusive pyroclasts produced during pyroclastic volcanism on the aubrite parent body ( Wilson and Keil 1991 ). We further suggest that this clast was not ejected into space but retained on the aubrite parent body by virtue of the relatively large size of the clast of approximately 20 mm. Our modeling, taking into account the size of the clast, suggests that the aubrite parent body must have been between approximately 40 and 100 km in diameter, and that the melt from which the clast crystallized must have contained an estimated maximum range of allowed volatile mass fractions between approximately 500 and approximately 4500 ppm. 相似文献
943.
Alberto G. FAIRÉN James M. DOHM Victor R. BAKER Shane D. THOMPSON William C. MAHANEY Kenneth E. HERKENHOFF J. Alexis P. RODRÍGUEZ Alfonso F. DAVILA Dirk SCHULZE‐MAKUCH M. Ramy EL MAARRY Esther R. UCEDA Ricardo AMILS Hirdy MIYAMOTO Kyeong J. KIM Robert C. ANDERSON Christopher P. McKAY 《Meteoritics & planetary science》2011,46(12):1832-1841
Abstract– Six large iron meteorites have been discovered in the Meridiani Planum region of Mars by the Mars Exploration Rover Opportunity in a nearly 25 km‐long traverse. Herein, we review and synthesize the available data to propose that the discovery and characteristics of the six meteorites could be explained as the result of their impact into a soft and wet surface, sometime during the Noachian or the Hesperian, subsequently to be exposed at the Martian surface through differential erosion. As recorded by its sediments and chemical deposits, Meridiani has been interpreted to have undergone a watery past, including a shallow sea, a playa, an environment of fluctuating ground water, and/or an icy landscape. Meteorites could have been encased upon impact and/or subsequently buried, and kept underground for a long time, shielded from the atmosphere. The meteorites apparently underwent significant chemical weathering due to aqueous alteration, as indicated by cavernous features that suggest differential acidic corrosion removing less resistant material and softer inclusions. During the Amazonian, the almost complete disappearance of surface water and desiccation of the landscape, followed by induration of the sediments and subsequent differential erosion and degradation of Meridiani sediments, including at least 10–80 m of deflation in the last 3–3.5 Gy, would have exposed the buried meteorites. We conclude that the iron meteorites support the hypothesis that Mars once had a denser atmosphere and considerable amounts of water and/or water ice at and/or near the surface. 相似文献
944.
Keiko NAKAMURA‐MESSENGER Lindsay P. KELLER Simon J. CLEMETT Scott MESSENGER Motoo ITO 《Meteoritics & planetary science》2011,46(7):1033-1051
Abstract– We have developed new sample preparation and analytical techniques tailored for entire aerogel tracks of Wild 2 sample analyses both on “carrot” and “bulbous” tracks. We have successfully ultramicrotomed an entire track along its axis while preserving its original shape. This innovation allowed us to examine the distribution of fragments along the entire track from the entrance hole all the way to the terminal particle. The crystalline silicates we measured have Mg‐rich compositions and O isotopic compositions in the range of meteoritic materials, implying that they originated in the inner solar system. The terminal particle of the carrot track is a 16O‐rich forsteritic grain that may have formed in a similar environment as Ca‐, Al‐rich inclusions and amoeboid olivine aggregates in primitive carbonaceous chondrites. The track also contains submicron‐sized diamond grains likely formed in the solar system. Complex aromatic hydrocarbons distributed along aerogel tracks and in terminal particles. These organics are likely cometary but affected by shock heating. 相似文献
945.
Andrew W. BECK David W. MITTLEFEHLDT Harry Y. McSWEEN Jr Douglas RUMBLE III Cin‐Ty A. LEE Robert J. BODNAR 《Meteoritics & planetary science》2011,46(8):1133-1151
Abstract– The absence of dunite (>90 vol% olivine) in the howardite, eucrite, and diogenite (HED) meteorite suite, when viewed with respect to spectroscopic and petrologic evidence for olivine on Vesta, is problematic. Herein, we present petrologic, geochemical, and isotopic evidence confirming that Miller Range (MIL) 03443, containing 91 vol% olivine, should be classified with the HED clan rather than with mesosiderites. Similarities in olivine and pyroxene FeO/MnO ratios, mineral compositions, and unusual mineral inclusions between MIL 03443 and the diogenites support their formation on a common parent body. This hypothesis is bolstered by oxygen isotopic and bulk geochemical data. Beyond evidence for its reclassification, we present observations and interpretations that MIL 03443 is probably a crustal cumulate rock like the diogenites, rather than a sample of the Vestan mantle. 相似文献
946.
G. F. HERZOG David FINK Jeffrey KLEIN Donald D. BOGARD L. E. NYQUIST C.‐Y. SHIH D. H. GARRISON Young REESE J. MASARIK R. C. REEDY G. RUGEL T. FAESTERMANN G. KORSCHINEK 《Meteoritics & planetary science》2011,46(2):284-310
Abstract– We report measurements of cosmogenic nuclides in up to 11 bulk samples from various depths in Norton County. The activities of 36Cl, 41Ca, 26Al, and 10Be were measured by accelerator mass spectrometry; the concentrations of the stable isotopes of He, Ne, Ar, and Sm were measured by electron and thermal ionization mass spectrometry, respectively. Production rates for the nuclides were modeled using the LAHET and the Monte Carlo N‐Particle codes. Assuming a one‐stage irradiation of a meteoroid with a pre‐atmospheric radius of approximately 50 cm, the model satisfactorily reproduces the depth profiles of 10Be, 26Al, and 53Mn (<6%) but overestimates the 41Ca concentrations by about 20%. 3He, 21Ne, and 26Al data give a one‐stage cosmic‐ray exposure (CRE) age of 115 Ma. Argon‐36 released at intermediate temperatures, 36Arn, is attributed to production by thermal neutrons. From the values of 36Arn, an assumed average Cl concentration of 4 ppm, and a CRE age of 115 Ma, we estimate thermal neutron fluences of 1–4 × 1016 neutrons cm?2. We infer comparable values from ε149Sm and ε150Sm. Values calculated from 41Ca and a CRE age of 115 Ma, 0.2–1.4 × 1016 neutrons cm?2, are lower by a factor of approximately 2.5, indicating that nearly half of the 149Sm captures occurred earlier. One possible irradiation history places the center of proto‐Norton County at a depth of 88 cm in a large body for 140 Ma prior to its liberation as a meteoroid with a radius of 50 cm and further CRE for 100 Ma. 相似文献
947.
948.
Shear‐type buildings with Maxwell model‐based brace–damper systems are studied in this paper with a primary emphasis on the effects of brace stiffness. A single‐story building with a viscous damper installed on top of a Chevron‐brace is first investigated. Closed‐form solutions are derived for the simple structure, relating the brace stiffness and damper coefficient to the targeted reduction in response displacement or acceleration. For a given brace stiffness, the solution is minimized to give a set of formulae that will allow the optimal damper coefficient to be determined, assuring the desired performance. The model is subsequently extended to multistory buildings with viscous dampers installed on top of Chevron‐braces. For a targeted reduction in the mean square of the interstory drift, floor acceleration or base shear force, the minimum brace stiffness and optimal damper coefficients are obtained through an iterative procedure. The response reduction, which signifies the improved performance, is achieved by a combination of brace stiffness and viscous damper coefficients, unlike conventional approaches where damper coefficients are typically optimized independent of brace stiffnesses. Characteristics of multi‐degree‐of‐freedom systems are studied using a 2‐story and a 10‐story buildings where the effects of brace stiffness on the overall performance of the building can be quantified. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
949.
950.
作为大气中最重要的含氮有机化合物,有机胺易与硫酸、硝酸气体生成胺盐,促进新颗粒的形成,同时也可与臭氧、OH自由基、NO3自由基发生氧化反应,是二次气溶胶的前体物.综述了国内外关于大气有机胺检测技术的研究进展,对常规的离线检测技术和在线质谱技术进行了介绍和对比,重点介绍了质谱法工作原理以及测定大气有机胺的优越性,并对其未来发展进行了展望. 相似文献