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151.
N. V. Emel’yanov 《Solar System Research》2017,51(1):20-37
The general approach to studying the dynamics of moons of planets and asteroids consists in developing more and more accurate models of motion based on observational data. Not only the necessary ephemerides, but also some physical parameters of planets and moons are obtained this way. It is demonstrated in the present study that progress in this field is driven not only by the increase in accuracy of observations. The accuracy of ephemerides may be increased by expanding the observation time interval. Several problems arise on the way toward this goal. Some of them become apparent only when the procedure of observational data processing and use is examined in detail. The method used to derive astrometric data by processing the results of photometric observations of mutual occultations and eclipses of planetary moons is explained below. The primary contribution to the error of astrometric results is produced by the unaccounted noise level in photometric readings and the inaccuracy of received values of the albedo of moons. It is demonstrated that the current methods do not allow one to eliminate the noise completely. Extensive additional photometric measurements should be performed at different angles of rotation of moons and in different spectral bands of the visible wavelength range in order to obtain correct values of the albedo of moons. Many new distant moons of the major planets have been discovered in the early 21st century. However, the observations of these moons are scarce and were performed over short time intervals; as a result, some of the moons were lost. The necessity of further observations of these Solar System bodies is pointed out in the present study. Insufficient knowledge of asteroid masses is an obstacle to improving the accuracy of the ephemerides of Mars. The basic method for determining the masses of large asteroids consists in analyzing their influence on the motion of Mars, the Earth, and spacecraft. The masses of more than 100 large asteroids were determined this way. One of the principal techniques for Earth-based measurement of the masses of asteroids involves astrometric observations of binary asteroids. The determination of relative coordinates is made rather difficult by the apparent proximity of components. The success of these efforts depends on the availability of instrumentation and the expertise of observers skilled in adaptive optics and speckle interferometry. Collaboration between different research teams and observers is absolutely necessary. 相似文献
152.
M.?A.?IvanovEmail author L.?V.?Zasova M.?V.?Gerasimov O.?I.?Korablev M.?Ya.?Marov L.?M.?Zelenyi N.?I.?Ignat’ev A.?G.?Tuchin 《Solar System Research》2017,51(1):1-19
We discuss a change in the resurfacing regimes of Venus and probable ways of forming the terrain types that make up the surface of the planet. The interpretation of the nature of the terrain types and their morphologic features allows us to characterize their scientific priority and the risk of landing on their surface to be estimated. From the scientific point of view, two terrain types are of special interest and represent easily achievable targets: the lower unit of regional plains and the smooth plains associated with impact craters. Regional plains are probably a melting from the upper fertile mantle. The material of smooth plains of impact origin is a well-mixed and representative sample of the Venusian crust. The lower unit of regional plains is the most widespread one on the surface of Venus, and it occurs within the boundaries of all of the precalculated approach trajectories of the lander. Smooth plains of impact origin are crossed by the approach trajectories precalculated for 2018 and 2026. 相似文献
153.
Simone Lotti Teresa Mineo Christian Jacquey Silvano Molendi Matteo D’Andrea Claudio Macculi Luigi Piro 《Experimental Astronomy》2017,44(3):371-385
In this paper we are going to review the latest estimates for the particle background expected on the X-IFU instrument onboard of the ATHENA mission. The particle background is induced by two different particle populations: the so called “soft protons” and the Cosmic rays. The first component is composed of low energy particles (< 100s keV) that get funnelled by the mirrors towards the focal plane, losing part of their energy inside the filters and inducing background counts inside the instrument sensitivity band. The latter component is induced by high energy particles (> 100 MeV) that possess enough energy to cross the spacecraft and reach the detector from any direction, depositing a small fraction of their energy inside the instrument. Both these components are estimated using Monte Carlo simulations and the latest results are presented here. 相似文献
154.
M. D’Andrea S. Lotti C. Macculi L. Piro A. Argan F. Gatti 《Experimental Astronomy》2017,44(3):359-370
ATHENA is a large X-ray observatory, planned to be launched by ESA in 2028 towards an L2 orbit. One of the two instruments of the payload is the X-IFU: a cryogenic spectrometer based on a large array of TES microcalorimeters, able to perform integral field spectrography in the 0.2–12 keV band (2.5 eV FWHM at 6 keV). The X-IFU sensitivity is highly degraded by the particle background expected in the L2 orbit, which is induced by primary protons of both galactic and solar origin, and mostly by secondary electrons. To reduce the particle background level and enable the mission science goals, the instrument incorporates a Cryogenic AntiCoincidence detector (CryoAC). It is a 4 pixel TES based detector, placed < 1 mm below the main array. In this paper we report a scientific assessment of the CryoAC observational capabilities in the hard X-ray band (E > 10 keV). The aim of the study has been to understand if the present detector design can be improved in order to enlarge the X-IFU scientific capability on an energy band wider than the TES array. This is beyond the CryoAC baseline, being this instrument aimed to operate as anticoincidence particle detector and not conceived to perform X-ray observations. 相似文献
155.
R. Krivonos A. Tkachenko R. Burenin E. Filippova I. Lapshov I. Mereminskiy S. Molkov M. Pavlinsky S. Sazonov M. Gubarev J. Kolodziejczak S. L. O’Dell D. Swartz Vyacheslav E. Zavlin B. D. Ramsey 《Experimental Astronomy》2017,44(1):147-164
The Astronomical Röntgen Telescope X-ray Concentrator (ART-XC) is a hard X-ray telescope with energy response up to 30 keV, to be launched on board the Spectrum Röntgen Gamma (SRG) spacecraft in 2018. ART-XC consists of seven identical co-aligned mirror modules. Each mirror assembly is coupled with a CdTe double-sided strip (DSS) focal-plane detector. Eight X-ray mirror modules (seven flight and one spare units) for ART-XC were developed and fabricated at the Marshall Space Flight Center (MSFC), NASA, USA. We present results of testing procedures performed with an X-ray beam facility at MSFC to calibrate the point spread function (PSF) of the mirror modules. The shape of the PSF was measured with a high-resolution CCD camera installed in the focal plane with defocusing of 7 mm, as required by the ART-XC design. For each module, we performed a parametrization of the PSF at various angular distances Θ. We used a King function to approximate the radial profile of the near on-axis PSF (Θ < 9 arcmin) and an ellipse fitting procedure to describe the morphology of the far off-axis angular response (9 < Θ < 24 arcmin). We found a good agreement between the seven ART-XC flight mirror modules at the level of 10%. The on-axis angular resolution of the ART-XC optics varies between 27 and 33 arcsec (half-power diameter), except for the spare module. 相似文献
156.
During the 50th cruise of R/V Akademik Mstislav Keldysh, on the south slope of the Atlantis massif (30°07′N; the Middle Atlantic Ridge), an inactive hydrothermal field named the
Lost Village was discovered. This new field was formed of light carbonate rock and was located near the active Lost City hydrothermal
field. The mineralogical associations of these fields were studied. A conclusion about the participation the ocean water in
the changing of the carbonate composition of the inactive hydrothermal field was reached. 相似文献
157.
An algorithm for considering time-correlated errors in a Kalman filter is presented. The algorithm differs from previous implementations
in that it does not suffer from numerical problems; does not contain inherent time latency or require reinterpretation of
Kalman filter parameters, and gives full consideration to additive white noise that is often still present but ignored in
previous implementations. Simulation results indicate that the application of the new algorithm yields more realistic and
therefore useful state and covariance information than the standard implementation. Results from a field test of the algorithm
applied to the problem of kinematic differential GPS demonstrate that the algorithm provides slightly pessimistic covariance
estimates whereas the standard Kalman filter provides optimistic covariance estimates. 相似文献
158.
1 STUDIEDREGIONANDANALYSISMETHODLocatedatnorthwesternmarginofTenggerDesertand70kmnortheastofMinqinCountyinGansuProvince,QingtuLakebelongstotheShiyangRiverDryDelta,andthealtitudeis1292-1310m.Theregionhasthecharacteroftemperatecontinentalariddesertcli… 相似文献
159.
160.
Two killifish common in east coast U.S.A. salt marshes,Cyprinodon variegatus Lacepede andFundulus heteroclitus Walbaum, differ in their ability to assimilate nitrogen from and grow on detritus.C. variegatus grew on a diet of detritus ofSpartina alterniflora Loisel, whileF. heteroclitus did not. In addition, when the fish were fed15N-labeledS. alterniflora detritus,15N:14N ratios inC. variegatus were higher than were ratios inF. heteroclitus. Therefore, even though both species ingest large amounts of detritus,C. variegatus makes more effective use of this portion of its diet. These dietary differences are corroborated by anatomical differences that suggest thatC. variegatus should make better use of detrital or plant tissues thanF. heteroclitus. In the label experiment, the degree of label in both fish was directly proportional to the degree of label in the food treatments. In previously published experiments designed to compare plant substrate with attached microbes as nitrogen sources for detritivores, %15N incorporated by a polychaete was also directly proportional to %15N in the detrital food. Therefore, it is difficult to distinguish between plant substrate and microbes as nitrogen sources for this detritivore. 相似文献