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981.
982.
Matthias Beilicke 《Astrophysics and Space Science》2007,309(1-4):139-145
The HESS experiment (High Energy Stereoscopic System), consisting of four imaging atmospheric Cherenkov telescopes (IACTs)
in Namibia, has observed many extragalactic objects in the search for very high energy (VHE) γ-ray emission. These objects include active galactic nuclei (AGN), notably Blazars, Seyferts, radio galaxies, starburst galaxies
and others. Beyond the established sources, γ-ray emission has been detected for the first time from several of these objects by HESS, and their energy spectra and variability
characteristics have been measured. Multi-wavelength campaigns, including X-ray satellites, radio telescopes, and optical
observations, have been carried out for AGNs, in particular for PKS 2155-304, H 2356-309 and 1ES 1101-232, for which the implications
concerning emission models are presented. Also results from the investigations of VHE flux variability from the giant radio
galaxy M 87 are shown.
For the HESS Collaboration. 相似文献
983.
984.
We report results from a multi-wavelength study of the 3B/X1.2 two-ribbon disk flare (S15E44), which was well observed by both ground-based and space-borne instruments. Two pairs of conjugate kernels - K1 and K4, and K2 and K3 - in the Ha images are identified. These kernels are linked by two different systems of EUV loops. Kl and K4 correspond to the two 17 GHz and 34 GHz microwave sources observed by the Nobeyama Radioheliograph (NoRH), while K2 and K3 have no corresponding microwave sources. Optical spectroscopic observations suggest that all the four kernels are possible precipitating sites of non-thermal electrons. Thus the energy of electron deposited in K2 and K3 should be less than 100 keV. Two-dimensional distributions of the full widths at half maximum (FWHM) of the Ha profiles and the line-of-sight (LOS) velocities derived from the Ca Ⅱ 8542 (?) profiles indicate that the largest FWHM and LOS velocity tends to be located near the outer edges of Ha kernels, which is consistent with the scenario of current two-ribbon flare models and previous results. When non-thermal electron bombardment is present, the observed Ha and Ca Ⅱ 8542 (?) profiles are similar to previous observational and theoretical results, while the He I 10830 A profiles are different from the theoretical ones. This puts some constraints on future theoretical calculation of the He I 10830 (?) line. 相似文献
985.
Jarken Esimbek 《中国天文和天体物理学报》2005,5(5):557-562
A maser spectral line system is newly implemented on the Urumqi 25m Radio Telescope. The system consists mainly of a cooling receiver and a 4096 channels digital correlation spectrometer. The frequency resolution of the spectrometer at the maximum signal bandwidth of 80MHz is 19.5kHz. After careful calibrations observation at the 1665 MHz OH maser emission was made towards a number of sources, including W49N and W75N. The observed results demonstrate that the digital correlation spectrometer is suitable for astronomical spectral line observations. 相似文献
986.
Pei-Sheng Chen Yi-Fei Gao Hong-Guang Shan 《中国天文和天体物理学报》2007,7(5):657-668
All galaxies with extragalactic H_2O maser sources observed so far are collected. With the 2MASS and the IRAS photometric data an infrared study is performed on those galaxies.By a comparison between the H_2O maser detected sources and non-detected sources in the infrared it is indicated that infrared properties in the IRAS 12-25μm and 60-100μm are important for producing H_2O masers in galaxies.It is also found that the H_2O maser galaxies with different nuclear activity types have rather different infrared properties mainly in the IRAS 12-60μm region. 相似文献
987.
Bryan M. Gaensler Maura McLaughlin Stephen Reynolds Kazik Borkowski Nanda Rea Andrea Possenti Gianluca Israel Marta Burgay Fernando Camilo Shami Chatterjee Michael Kramer Andrew Lyne Ingrid Stairs 《Astrophysics and Space Science》2007,308(1-4):95-99
“Rotating RAdio Transients” (RRATs) are a newly discovered astronomical phenomenon, characterised by occasional brief radio
bursts, with average intervals between bursts ranging from minutes to hours. The burst spacings allow identification of periodicities,
which fall in the range 0.4 to 7 seconds. The RRATs thus seem to be rotating neutron stars, albeit with properties very different
from the rest of the population. We here present the serendipitous detection with the Chandra X-ray Observatory of a bright point-like X-ray source coincident with one of the RRATs. We discuss the temporal and spectral properties of
this X-ray emission, consider counterparts in other wavebands, and interpret these results in the context of possible explanations
for the RRAT population.
B.M.G. acknowledges the support of NASA through LTSA grant NAG5-13023 and of an Alfred P. Sloan Fellowship. 相似文献
988.
11 samples of lava and pumice from the cone of Changbaishan Tianchi Volcano, Jiling, China, were dated by using high precision U - series TIMS method. We conclude that the bottom of the cone formed before 350 ka, the middle part in 70~80 ka, the upper during 20~ 1ka, and the top less than 1ka, and the age based periods of the volcano eruption since Late Pleistocene is given as follows: > 350ka, 70ka, 18 ~ 25ka, 10ka, 4C5ka, 1~0.75ka, which may offer the basis for the study of volcanic disaster in future. In addition, the principle of dating young volcanic rocks by using U - series TIMS method is introduced briefly. Differentiation characteristics of U and Th in different minerals of the volcanic rocks are discussed, and the ability producing isochrons, based on U and Th differentiation, are discussed. In the last part of the paper,the closure of samples to the elements U and Th, which is important for age results, is discussed by using (234U/238U)radioactivity ratio which can be used to monitor if the samples have been weathered or eroded or leached since the time they formed. In this study, all samples have (234U/238U) activity ratios within 1% of secular equilibrium ((234U/238U) radioactivity ratios are unity), indicating no disturbance of the 234U- 238U system. All of these discussions show that the TIMS method is good to date Tianchi volcanics and the results are reliable. 相似文献
989.
The three-dimensional P-wave velocity structure of Mount Spurr is determined to depths of 10 km by tomographic inversion
of 3,754 first-arriving P-wave times from local earthquakes recorded by a permanent network of 11 seismographs. Results show
a prominent low-velocity zone extending from the surface to 3–4 km below sea level beneath the southeastern flank of Crater
Peak, spatially coincident with a geothermal system. P-wave velocities in this low-velocity zone are approximately 20% slower
than those in the shallow crystalline basement rocks. Beneath Crater Peak an approximately 3-km-wide zone of relative low
velocities correlates with a near-vertical band of seismicity, suggestive of a magmatic conduit. No large low-velocity zone
indicative of a magma chamber occurs within the upper 10 km of the crust. These observations are consistent with petrologic
and geochemical studies suggesting that Crater Peak magmas originate in the lower crust or upper mantle and have a short residence
time in the shallow crust. Earthquakes relocated using the three-dimensional velocity structure correlate well with surface
geology and other geophysical observations; thus, they provide additional constraints on the kinematics of the Mount Spurr
magmatic system.
Received: 4 December 1997 / Accepted: 27 February 1998 相似文献
990.
Yu Yu Yong-Feng Huang 《中国天文和天体物理学报》2007,7(5):669-674
With the successful launch of Swift satellite,more and more data of early X-ray afterglows from short gamma-ray bursts have been collected.Some interesting features such as unusual afterglow light curves and unexpected X-ray flares are revealed.Especially,in some cases,there is a fiat segment in the X-ray afterglow light curve.Here we present a simplified model in which we believe that the flattening part is due to energy injection from the central engine.We assume that this energy injection arises from the magnetic dipole radiation of a millisecond pulsar formed after the merger of two neutron stars.We check this model with the short GRB 060313.Our numerical results suggest that energy injection from a millisecond magnetar could make part of the X-ray afterglow light curve flat. 相似文献