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991.
V. P. Aleshin E. A. Grishin O. A. Ivlev D. D. Novgorodtsev V. D. Shargorodsky 《Kinematics and Physics of Celestial Bodies》2016,32(5):255-259
Telescopes with aperture higher than 3 m and with travel rate of optical axis of more than 4 angular degrees per second are examined. These telescopes are used for estimating the situation in near-Earth space. Up to now, there are three telescopes with such parameters: SOR, AMOS, SST (all in the United States). A telescope of the same class with aperture of 3.12 m (information telescope TI-3.12) is under completion at Altai Optical Laser Center. The main technical performances of the TI-3.12 telescope are described in the paper. Current problems are defined and ways for their solution are presented. 相似文献
992.
In understanding the nucleosynthesis of the elements in stars, one of the most important quantities is the reaction rate and
it must be evaluated in terms of the stellar temperature T, and its determination involves the knowledge of the excitation function σ(E) of the specific nuclear reaction leading to the final nucleus. In this paper, the effect of thermonuclear reaction rates
to the pre-main sequence evolution of low mass stars having masses 0.7, 0.8, 0.9 and 1M⊙ are studied by using our modified Stellar Evolutionary Program. 相似文献
993.
Lazarus E. Kopilovich 《Experimental Astronomy》2010,28(1):1-9
Estimates for the maximum number of elements of non-redundant configurations on integer square and hexagonal grids of given
sizes are derived (a “non-redundant” configuration implies that the vector differences between its elements are all distinct).
When projecting a large 2-D interferometer or a telescope, such an estimate can be used as a guide for evaluating the maximum
possible number of antennas in a non-redundant configuration that can be arranged within a given area. The suggested estimates
are empirical and based on the available data. They are obtained by reducing the problem to the linear case and by generalizing
the method applied therein. Examples of applying the method are presented. 相似文献
994.
The magneto-rotational evolution of a neutron star in the massive binary system 4U 2206+54 is discussed in light of the recent
discovery of its 5555 s rotational period and its average rate of spin-down. We show that this behavior of the neutron star
means that its magnetic field exceeds the quantum mechanical critical limit and it is an accretion magnetar. The system’s
evolution is explained by wind driven mass transfer without formation of an accretion disk. The constant character of the
x-ray source indicates a steady rate of accretion and raises anew the question of the stability of the boundary of the magnetosphere
of a star undergoing spherical accretion. A solution to this problem is also a key to determining the mechanism for the slowing
down of the star’s rotation. 相似文献
995.
Yu. A. Fadeyev 《Astronomy Letters》2010,36(5):362-369
Hydrodynamic calculations of nonlinear radial oscillations of LBV stars with effective temperatures 1.5 × 104 K ⩽ T
eff ⩽ 3 × 104 K and luminosities 1.2 × 106
L
⊙ ⩽ L ⩽ 1.9 × 106
L
⊙ have been performed. Models for the evolutionary sequences of Population I stars (X = 0.7, Z = 0.02) with initial masses 70M
⊙ ⩽ M
ZAMS ⩽ 90M
⊙ at the initial helium burning stage have been used as the initial conditions. The radial oscillations develop on a dynamical
time scale and are nonlinear traveling waves propagating from the core boundary to the stellar surface. The amplitude of the
velocity variations for the outer layers is several hundred km s−1, while the bolometric magnitude variations are within ΔM
bol ⩽ 0·
m
2. The onset of oscillations is not related to the κ-mechanism and is attributable to the instability of a self-gravitating envelope gas whose adiabatic index is close to its
critical value of Γ1 = 4/3 due to the dominant contribution of radiation in the internal energy and pressure. The interval of magnitude variation
periods (6 days ≤ II ≤ 31 days) encompasses all currently available estimates of the microvariability periods for LBV stars,
suggesting that this type of nonstationarity is pulsational in origin. 相似文献
996.
A. Papaioannou O. Malandraki A. Belov R. Skoug H. Mavromichalaki E. Eroshenko A. Abunin S. Lepri 《Solar physics》2010,266(1):181-193
In this work an analysis of a series of complex cosmic ray events that occurred between 17 January 2005 and 23 January 2005
using solar, interplanetary and ground based cosmic ray data is being performed. The investigated period was characterized
both by significant galactic cosmic ray (GCR) and solar cosmic ray (SCR) variations with highlighted cases such as the noticeable
series of Forbush effects (FEs) from 17 January 2005 to 20 January 2005, the Forbush decrease (FD) on 21 January 2005 and
the ground level enhancement (GLE) of the cosmic ray counter measurements on 20 January 2005. The analysis is focusing on
the aforementioned FE cases, with special attention drawn on the 21 January 2005, FD event, which demonstrated several exceptional
features testifying its uniqueness. Data from the ACE spacecraft, together with GOES X-ray recordings and LASCO CME coronagraph
images were used in conjunction to the ground based recordings of the Worldwide Neutron Monitor Network, the interplanetary
data of OMNI database and the geomagnetic activity manifestations denoted by K
p and D
st indices. More than that, cosmic ray characteristics as density, anisotropy and density gradients were also calculated. The
results illustrate the state of the interplanetary space that cosmic rays crossed and their corresponding modulation with
respect to the multiple extreme solar events of this period. In addition, the western location of the 21 January 2005 solar
source indicates a new cosmic ray feature, which connects the position of the solar source to the cosmic ray anisotropy variations.
In the future, this feature could serve as an indicator of the solar source and can prove to be a valuable asset, especially
when satellite data are unavailable. 相似文献
997.
During studies of spectra of the star Θ1 Ori C with high photometric and spectral resolution we have discovered a system of spectral lines indicating a large negative
radial velocity (RV). We designate this star as Θ1 Ori C3. 相似文献
998.
The evolution of the 27-day recurrence in the series of two solar indices (Wolf number WN and 10.7 cm radio flux F) and two geomagnetic indices (Dst and ζ, variance of the geomagnetic field recorded at a magnetic observatory) have been studied over the 1957 – 2007 time
span. Spectral energies contained in two period domains (25 – 27.3 and 27.3 – 31 days), designated as E
1 and E
2, have been computed. Whereas the evolution of E
1 is the same for the four indices, that of E
2 is essentially different for WN and F on the one hand, Dst and ζ on the other hand. Some general conclusions on the dynamics of the solar outer layers are inferred from these results.
First the solar activity, as measured by WN, and when averaged over a few years, evolves in the same way whatever the latitude.
Second, two families of coronal holes (CHs) are identified; the rapidly and the slowly rotating CHs evolve quite differently. 相似文献
999.
G. A. Gontcharov 《Astronomy Letters》2010,36(8):584-595
The first results of the construction of a three-dimensional reddening map for stars within 1600 pc of the Sun are presented.
Analysis of the distribution of 70 million stars from the 2MASS catalog with the most accurate photometry on the (J-Ks)-Ks diagram supplemented with Monte Carlo simulations has shown that one of the maxima of this distribution corresponds to F-type
dwarfs and subgiants with a mean absolute magnitude M
Ks
= 2⊙
m
5. The shift of this maximum toward large J-Ks with increasing Ks reflects the reddening of these stars with increasing heliocentric distance. The distribution of the sample of stars over
Ks, l, and b cells with a statistically significant number of stars in each cell corresponds to their distribution over three-dimensional
spatial cells. As a result, the reddening E(J-Ks) has been determined with an accuracy of 0·
m
03 for spatial cells with a side of 100 pc. All of the known large absorbing clouds within 1600 pc of the Sun have manifested
themselves in the results obtained. The distances to the near and far edges of the clouds have been determined with a relative
accuracy of 15%. The cases where unknown clouds are hidden behind known ones on the same line of sight have been found. The
distance dependence of reddening is considered for various Galactic latitudes and longitudes. The absorbing matter of the
Gould Belt is shown to manifest itself at latitudes up to 40° and within 600 pc of the Sun. The size and influence of the
Gould Belt may have been underestimated thus far. The absorbing matter at latitudes up to 60° and within 1600 pc of the Sun
has been found to be distributed predominantly in the first and second quadrants in the southern hemisphere and in the third
and fourth quadrants in the northern hemisphere. The warping of the absorbing layer in the near Galaxy apparently manifests
itself in this way. A nonrandom orientation of the clouds relative to the Sun is possible. The mass of the baryonic dark matter
in solar neighborhoods can then be considerably larger than is generally believed. 相似文献
1000.
Jayanta Roy Yashwant Gupta Ue-Li Pen Jeffrey B. Peterson Sanjay Kudale Jitendra Kodilkar 《Experimental Astronomy》2010,28(1):25-60
The new era of software signal processing has a large impact on radio astronomy instrumentation. Our design and implementation
of a 32 antennae, 33 MHz, dual polarization, fully real-time software backend for the GMRT, using only off-the-shelf components,
is an example of this. We have built a correlator and a beamformer, using PCI-based ADC cards and a Linux cluster of 48 nodes
with dual gigabit inter-node connectivity for real-time data transfer requirements. The highly optimized compute pipeline
uses cache efficient, multi-threaded parallel code, with the aid of vectorized processing. This backend allows flexibility
in final time and frequency resolutions, and the ability to implement algorithms for radio frequency interference rejection.
Our approach has allowed relatively rapid development of a fairly sophisticated and flexible backend receiver system for the
GMRT, which will greatly enhance the productivity of the telescope. In this paper we describe some of the first lights using
this software processing pipeline. We believe this is the first instance of such a real-time observatory backend for an intermediate
sized array like the GMRT. 相似文献