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991.
The preflare phase of the flare SOL2011-08-09T03:52 is unique in its long duration, in that it was covered by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Nobeyama Radioheliograph, and because it showed three well-developed soft X-ray (SXR) peaks. No hard X-rays (HXR) are observed in the preflare phase. Here we report that no associated radio emission at 17 GHz was found either, despite the higher sensitivity of the radio instrument. The ratio between the SXR peaks and the upper limit of the radio peaks is higher by more than one order of magnitude than the ratio in regular flares. The result suggests that the ratio between acceleration and heating in the preflare phase was different than in regular flares. Acceleration to relativistic energies, if any, occurred with lower efficiency. 相似文献
992.
Diego G. Lloveras Alberto M. Vásquez Federico A. Nuevo Richard A. Frazin 《Solar physics》2017,292(10):153
Using differential emission measure tomography (DEMT) based on time series of EUV images, we carry out a quantitative comparative analysis of the three-dimensional (3D) structure of the electron density and temperature of the inner corona (\(r<1.25\,\mathrm{R}_{\odot}\)) between two specific rotations selected from the last two solar minima, namely Carrington Rotations (CR)1915 and CR-2081. The analysis places error bars on the results because of the systematic uncertainty of the sources. While the results for CR-2081 are characterized by a remarkable north–south symmetry, the southern hemisphere for CR-1915 exhibits higher densities and temperatures than the northern hemisphere. The core region of the streamer belt in both rotations is found to be populated by structures whose temperature decreases with height (called “down loops” in our previous articles). They are characterized by plasma \(\beta\gtrsim1\), and may be the result of the efficient dissipation of Alfvén waves at low coronal heights. The comparative analysis reveals that the low latitudes of the equatorial streamer belt of CR-1915 exhibit higher densities than for CR-2081. This cannot be explained by the systematic uncertainties. In addition, the southern hemisphere of the streamer belt of CR-1915 is characterized by higher temperatures and density scale heights than for CR-2081. On the other hand, the coronal hole region of CR-1915 shows lower temperatures than for CR-2081. The reported differences are in the range \({\approx}\,10\,\mbox{--}\,25\%\), depending on the specific physical quantity and region that is compared, as fully detailed in the analysis. For other regions and/or physical quantities, the uncertainties do not allow assessing the thermodynamical differences between the two rotations. Future investigation will involve a DEMT analysis of other Carrington rotations selected from both epochs, and also a comparison of their tomographic reconstructions with magnetohydrodynamical simulations of the inner corona. 相似文献
993.
S. G. Sichevskij 《Astrophysical Bulletin》2017,72(1):51-57
Based on the spectral observations of the LAMOST (DR2) survey, the radii, masses, and luminosities of 700 481 stars were estimated. These stars belong to spectral types A, F, G, and K, and have metallicities between ?0.845 and 0.0. To determine the properties of the stars, we used up-to-date models of the stellar interior structure, computed with account for the stellar evolution rate and the initial mass function. The use of evolutionary estimates for two types of stars—with and without rotation—allowed us to account for the uncertainty associated with the lack of data on the rotation velocity of the stars under consideration. The obtained stellar radii, together with the photometric estimates of interstellar extinction and angular diameters can be used to study the dependence of interstellar extinction on distance as well as to estimate the stellar distances. 相似文献
994.
J. Zverko I. Romanyuk I. Iliev D. Kudryavtsev I. Stateva E. Semenko 《Astrophysical Bulletin》2017,72(1):16-23
We analyzed the spectra of a well known SB1 binary HD199892 for which the projected rotational velocity v sin i, introduced in the literature, significantly differs when determined from the lines of Ca II at 3933 Å and ofMg II at 4481 Å. Contrary to the former findings, we discovered the signs of spectral lines of a companion star in the profile of Hβ as well as weak metallic lines in the high resolution high S/N spectra covering the most of the visual region. We estimated the secondary star to be a main sequence A4V star with a mass of 2.2M ⊙ and derived its radial velocity which resulted in the mass of the primary M = 4.6M ⊙. Short sections of the spectra in the Mg II 4481 Å and Ca II 3933 Å regions are analyzed as well. 相似文献
995.
A. N. Sarkisyan A. S. Vinokurov Yu. N. Solovieva O. N. Sholukhova A. E. Kostenkov S. N. Fabrika 《Astrophysical Bulletin》2017,72(4):486-501
We present a code for the optimal extraction of long-slit 2D spectra in crowded stellar fields. Its main advantage and difference from the existing spectrum extraction codes is the presence of a graphical user interface (GUI) and a convenient visualization system of data and extraction parameters. On the whole, the package is designed to study stars in crowded fields of nearby galaxies and star clusters in galaxies. Apart from the spectrum extraction for several stars which are closely located or superimposed, it allows the spectra of objects to be extracted with subtraction of superimposed nebulae of different shapes and different degrees of ionization. The package can also be used to study single stars in the case of a strong background. In the current version, the optimal extraction of 2D spectra with an aperture and the Gaussian function as PSF (point spread function) is proposed. In the future, the package will be supplemented with the possibility to build a PSF based on a Moffat function. We present the details of GUI, illustrate main features of the package, and show results of extraction of the several interesting spectra of objects from different telescopes. 相似文献
996.
S. G. Sichevskij 《Astrophysical Bulletin》2017,72(2):141-149
We describe Bayesian probabilistic approach to estimating the properties of stars and the interstellar extinction law based on photometric observations and using prior data about the parameters of the stars. The accuracy of the resulting estimates is analyzed in the case of SDSS and 2MASS surveys. We found that our estimates have no systematic deviations in the case of photometric accuracy typical of the surveys considered and errors of prior data of ΔT eff = ±150 K and Δlog g = ±0.5. Note that the error of the estimated interstellar extinction A 0 is of about 0. m 3, and the error of the R 0 estimate depends on extinction and is close 0.2 for moderate A0 values. The fractional error of the estimated stellar angular diameters is close to 10%. A possible application of our approach is to determine the dependence of interstellar extinction on distance using stars closely located in the same sky area. 相似文献
997.
B. A. Kagan E. V. Sofina A. A. Timofeev 《Izvestiya Atmospheric and Oceanic Physics》2010,46(2):224-231
In order to reproduce the diapycnal mixing induced by internal tidal waves (ITWs) in the Arctic Ocean, we use a modified version
of the three-dimensional finite-element hydrothermodynamic model QUODDY-4. We found that the average (over the tidal cycle)
and integral (by depth) baroclinic tidal energy dissipation rate in individual areas of the Siberian continental shelf and
in the straits between the Canadian Arctic archipelago are much higher than in the open ocean and its values on ridges and
troughs are qualitatively similar to one another. Moreover, in the area of open-ocean ridges, the baroclinic tidal energy
dissipation rate increases as it approaches the bottom, but only in the bottom boundary layer; on the Mid-Atlantic and Hawaii
ridges, such an increase is observed within a few hundreds of meters away from the bottom. The average (in area and depth
of the open ocean) coefficient of diapycnal mixing defined by the baroclinic tidal energy dissipation rate is higher than
the coefficient of molecular kinematic viscosity and only a few times lower than the canonical value of the coefficient of
vertical turbulent viscosity, which is used in models of global oceanic circulation. Coupled with the reasoning on the localization
of baroclinic tidal energy dissipation, this fact leads to the conclusion that disregarding the contribution that ITW-induced
diapycnal mixing makes to the ocean-climate formation is hardly justified. 相似文献
998.
B. I. Nazarov S. F. Abdullaev V. A. Maslov 《Izvestiya Atmospheric and Oceanic Physics》2010,46(4):475-481
We studied the temperature variations of the lower air layer caused by dust content using a dust storm in Dushanbe in November
2007 as an example. Quantitative estimates of air cooling and a decrease in the diurnal temperature difference due to a diminishing
horizontal visibility range are given. Observations of air temperature variations due to the dust content of the atmosphere
in an arid zone are presented. The critical value of aerosol concentration for toggling between the greenhouse and antigreenhouse
effects is determined. The long-term effect of dust aerosol on climate is analyzed. 相似文献
999.
Kh. M. Saidova 《Oceanology》2010,50(4):542-548
The compositional changes and frequency variations in the foraminiferal communities through the sediment section across Dvina
Bay allow us to identify 14 ecological-stratigraphic zones. Based on the 14C dates for the foraminiferal tests, the distinguished ecozones correspond to the appropriate Holocene stages and substages.
Because most of the foraminiferal species identified in the Holocene sediments are abundant and diverse in the modern oceans,
they provide a powerful tool for the reconstruction of the paleoenvironmental changes during the Holocene. 相似文献
1000.
This paper is a short review of publications on the influence that solar activity and geomagnetic disturbances (cosmic weather)
have on physical-chemical systems. The effects of cosmic weather may some-times be detected by the presence of an uncontrolled
factor in these experiments. Direct reactions to cosmic weather are reliably identified in quantitative observations over
various test systems, mainly water solutions. The effects of cosmic weather are also found from the data obtained by monitoring
some simple physical systems, including semiconductors. All these effects are either cosmic physical rhythms or they are easily
registered sporadic heliogeophysical events (e.g., magnetic storms). There are convincing data that demonstrate the influence
that cosmic weather has on the accident rate in various engineering and physical systems. Researchers are at odds on the physical
nature of the main physical agent, but the contribution of electromagnetic fields to these processes is considered important. 相似文献