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931.
932.
933.
934.
We have attempted to reconstruct the orbit of the Farmington L5 chondrite which fell in Kansas in 1890. Because its radiation age is uniquely short (25 000 years), its orbit should still closely resemble that of its parent body. A search of 280 contemporary newspapers and other sources turned up more than 60 useable eyewitness reports from 32 localities, which led to the following estimate of the apparent radiant: height 60°, azimuth 20°, with an uncertainty of about 10°. Orbital elements were determined for this radiant for four plausible preatmospheric velocities: 13, 16, 19, and 22 km/sec. The results show quite definitely that Farmington had a small orbit of low inclination: semimajor axis 1–1.9 AU, perihelion ? 0.4 AU, aphelion ? 3.0 AU, inclination ? 16°. Because of the short radiation age, the parent body of Farmington must already have been in an Earth-crossing orbit when the meteorite was ejected from it by an impact. Of the 11 known Earth-crossing asteroids with encounter velocities below 22 km/sec, 1862 Apollo, Hermes, and 1865 Cerberus are passable matches, while 1620 Geographos and 1685 Toro are more marginal possibilities. Apparently Earth-crossing asteroids are the immediate parent bodies of at least some meteorites. Their ultimate source must be the ultimate source of most stony meteorites. 相似文献
935.
Toulon is an olivine-bronzite chondrite found near Toulon, Illinois in 1962. It contains abundant, well preserved chondrules, as well as glasses that are not well devitrified. Most of the metal has been weathered out. Olivine and pyroxene are well equilibrated. We have classified it as an H5 chondrite. 相似文献
936.
Comet P/Halley has been observed during its approach to perihelion at heliocentric distancesR = 11.0 AU and R = 8.2 AU. No extended coma is seen and limits can be placed on the fraction of the total light contributed by coma. The brightness of the comet varies on a short time scale. The variations may be due to transient activity or to rotation of the irregular nucleus. 相似文献
937.
Paul S. Sipiera Edward J. Olsen Dorothy L. Eatough Bruce D. Dod 《Meteoritics & planetary science》1983,18(1):63-75
Eleven recent chondrite finds from the Texas Panhandle have been examined and classified according to mineralogical and petrological criteria: five H's, five L's, and one LL chondrite. Five are distinct from nearby finds, while three remain ambiguous and three are related to previously reported chondrites. In addition, data are provided to classify the Muleshoe, Silverton, and Vigo Park chondrites, all of which were previously undescribed in the literature. 相似文献
938.
Edward J. Mannery Walter A. Siegmund Charles L. Hull 《Astrophysics and Space Science》1989,160(1-2):269-274
The Astrophysical Research Consortium 3.5 m telescope facility on Apache Point (2800 m above sea level) near the National Solar Observatory in southern New Mexico is nearing completion. The telescope mount has been installed and testing and fabrication of remaining subassemblies are underway. Thef/1.75 lightweight honeycomb primary mirror was cast April 1988 by the Steward Observatory Mirror Laboratory and is currently being figured.The 3.5 m optical telescope is an altitude over azimuth mechanical structure with Ritchey-Chrétien optics. The lightweight (1800 kg) mirror leads to a mount weighting only 41000 kg; readily available rolling element bearings are used to achieve the necessary performance at low cost and without the heat dissipation of externally pressurized types. Drive torques are applied by DC servo-driven capstans. These are coupled by friction to large diameter drive disks on each axis. No gears are used. Position feedback comes from low cost incremental encoders, also capstan coupled.We have recently completed a series of measurements of the telescope mount. These measurements show that the telescope is very stiff; the lowest natural frequencies are about 7.2 Hz. Initial tracking performance is good and the mount shows high resistance to wind-induced vibration. Our experience during acceptance testing suggests that routine power spectral analysis of drive motor torque and other parameters could be an important tool in the early detection of failures.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988. 相似文献
939.
The magnetic structure of arch filament systems 总被引:1,自引:0,他引:1
Edward N. Frazier 《Solar physics》1972,26(1):130-141
Photographic-type magnetograms are used in conjunction with H filtergrams to study the structure and evolution of magnetic fields associated with arch filament systems. The magnetograms show that the opposite ends of the arch filaments are indeed rooted in photospheric magnetic fields of opposite polarity. Furthermore, these magnetic field systems are in every case new magnetic flux appearing at the solar surface. Time lapse studies show the detailed process by which the flux tubes emerge through the surface. First, supergranules bring individual strands of magnetic flux to the surface and sweep the two feet of the flux tube to opposite sides of the supergranule. Then, the flux tube rises through the chromosphere, creating a visible arch filament. It is also shown that the observed rotation of the axis of an arch filament system in the plane of the solar surface is caused by the emergence of successive flux loops, each possessing different axial tilts. 相似文献
940.
Summary A high speed algorithm for computation of frequency-wavenumber (f-k) spectra is developed, and two real-time infrasonic data processing techniques that it makes possible, are described: (1) Signal detection by a search of f-k space. This process is compared to the N-4 correlator, a broad-band signal detector. The f-k search with a Fisher detector has a theoretical advantage, which we verify in practice. (2) An f-k filter technique for calculating 'best beam' estimates. This technique traces the beam containing maximum power, from frequency to frequency through f-k space, and thus allows for wandering of signal velocity and arrival azimuth. This maximum power function is taken as the frequency spectrum of the best beam. In our programs the Fisher statistic of the signal estimate, and the velocity and azimuth, are computed and displayed as functions of frequency. Examples from real data for both processing techniques are discussed. 相似文献