全文获取类型
收费全文 | 51652篇 |
免费 | 929篇 |
国内免费 | 404篇 |
专业分类
测绘学 | 1198篇 |
大气科学 | 3913篇 |
地球物理 | 10302篇 |
地质学 | 18620篇 |
海洋学 | 4349篇 |
天文学 | 11210篇 |
综合类 | 110篇 |
自然地理 | 3283篇 |
出版年
2021年 | 406篇 |
2020年 | 471篇 |
2019年 | 483篇 |
2018年 | 1149篇 |
2017年 | 1120篇 |
2016年 | 1330篇 |
2015年 | 858篇 |
2014年 | 1329篇 |
2013年 | 2603篇 |
2012年 | 1548篇 |
2011年 | 2075篇 |
2010年 | 1786篇 |
2009年 | 2397篇 |
2008年 | 2084篇 |
2007年 | 2079篇 |
2006年 | 1992篇 |
2005年 | 1539篇 |
2004年 | 1555篇 |
2003年 | 1470篇 |
2002年 | 1399篇 |
2001年 | 1308篇 |
2000年 | 1236篇 |
1999年 | 1049篇 |
1998年 | 1024篇 |
1997年 | 1054篇 |
1996年 | 781篇 |
1995年 | 822篇 |
1994年 | 783篇 |
1993年 | 651篇 |
1992年 | 646篇 |
1991年 | 590篇 |
1990年 | 632篇 |
1989年 | 562篇 |
1988年 | 534篇 |
1987年 | 623篇 |
1986年 | 550篇 |
1985年 | 709篇 |
1984年 | 745篇 |
1983年 | 771篇 |
1982年 | 703篇 |
1981年 | 630篇 |
1980年 | 672篇 |
1979年 | 564篇 |
1978年 | 573篇 |
1977年 | 524篇 |
1976年 | 499篇 |
1975年 | 499篇 |
1974年 | 470篇 |
1973年 | 473篇 |
1971年 | 312篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
81.
82.
N. Ivanova K. Belczynski J. M. Fregeau F. A. Rasio 《Monthly notices of the Royal Astronomical Society》2005,358(2):572-584
We study the evolution of binary stars in globular clusters using a new Monte Carlo approach combining a population synthesis code ( startrack ) and a simple treatment of dynamical interactions in the dense cluster core using a new tool for computing three- and four-body interactions ( fewbody ). We find that the combination of stellar evolution and dynamical interactions (binary–single and binary–binary) leads to a rapid depletion of the binary population in the cluster core. The maximum binary fraction today in the core of a typical dense cluster such as 47 Tuc, assuming an initial binary fraction of 100 per cent, is only ∼ 5–10 per cent. We show that this is in good agreement with recent Hubble Space Telescope observations of close binaries in the core of 47 Tuc, provided that a realistic distribution of binary periods is used to interpret the results. Our findings also have important consequences for the dynamical modelling of globular clusters, suggesting that 'realistic models' should incorporate much larger initial binary fractions than has usually been the case in the past. 相似文献
83.
An investigation of 531 active regions was made to determine the correlation between energy released by flares and the available energy in magnetic fields of the regions. Regions with magnetic flux greater than 1021 maxwell during the years 1967–1969, which included sunspot maximum, were selected for the investigation. A linear regression analysis of flare production on magnetic flux showed that the flare energy is correlated with magnetic energy with a coeificient of correlation of 0.78. Magnetic classification and field configuration also significantly affect the production of flares.This work was supported by the Aerospace Sponsored Research Program. 相似文献
84.
We present new 1.45-1.75 μm spectra of Europa's dark non-ice material with a spectral resolution (λ/δλ) of 1200, obtained by using adaptive optics on the Keck telescope to spatially separate the spectrum of the non-ice material from that of the surrounding ice-rich regions. Despite the great increase in spectral resolution over the previous best spectra of the non-ice material, taken with Galileo's near-infrared mapping spectrometer (NIMS) with λ/δλ=66, no new fine-scale spectral structure is revealed. The smoothness of the spectra is inconsistent with available laboratory spectra of crystalline hydrated salts at Europa temperatures, but is more consistent with various combinations of non-crystalline hydrated salts and/or hydrated sulfuric acid, as have been matched to the lower-resolution NIMS spectra. 相似文献
85.
86.
87.
88.
B. Ahmed G. J. Alner H. Araujo J. C. Barton A. Bewick M. J. Carson D. Davidge J. V. Dawson T. Gamble S. P. Hart R. Hollingworth A. S. Howard W. G. Jones M. K. Joshi V. A. Kudryavtsev T. B. Lawson V. Lebedenko M. J. Lehner J. D. Lewin P. K. Lightfoot I. Liubarsky R. Lüscher J. E. McMillan B. Morgan G. Nicklin S. M. Paling R. M. Preece J. J. Quenby J. W. Roberts M. Robinson N. J. T. Smith P. F. Smith N. J. C. Spooner T. J. Sumner D. R. Tovey 《Astroparticle Physics》2003,19(6):691-702
The NAIAD experiment (NaI Advanced Detector) for weakly interacting massive particle (WIMP) dark matter searches at Boulby mine (UK) is described. The detector consists of an array of encapsulated and unencapsulated NaI(Tl) crystals with high light yield. Six crystals are collecting data at present. Data accumulated by four of them (10.6 kg × year exposure) have been used to set upper limits on the WIMP–nucleon spin-independent and WIMP–proton spin-dependent cross-sections. Pulse shape analysis has been applied to discriminate between nuclear recoils, as may be caused by WIMP interactions, and electron recoils due to gamma background. Various calibrations of crystals are presented. 相似文献
89.
Dirk Pandel France A. Córdova Steve B. Howell 《Monthly notices of the Royal Astronomical Society》2003,346(4):1231-1241
We present an analysis of X-ray and ultraviolet (UV) data of the dwarf nova VW Hyi that were obtained with XMM–Newton during the quiescent state. The X-ray spectrum indicates the presence of an optically thin plasma in the boundary layer that cools as it settles on to the white dwarf. The plasma has a continuous temperature distribution that is well described by a power law or a cooling flow model with a maximum temperature of 6–8 keV. We estimate from the X-ray spectrum a boundary layer luminosity of 8 × 1030 erg s-1 , which is only 20 per cent of the disc luminosity. The rate of accretion on to the white dwarf is 5 × 10−12 M⊙ yr−1 , about half of the rate in the disc. From the high-resolution X-ray spectra, we estimate that the X-ray emitting part of the boundary layer is rotating with a velocity of 540 km s−1 , which is close to the rotation velocity of the white dwarf but is significantly smaller than the Keplerian velocity. We detect a 60-s quasi-periodic oscillation of the X-ray flux, which is likely to be due to the rotation of the boundary layer. The X-ray and the UV flux show strong variability on a time-scale of ∼1500 s. We find that the variability in the two bands is correlated and that the X-ray fluctuations are delayed by ∼100 s. The correlation indicates that the variable UV flux is emitted near the transition region between the disc and the boundary layer and that accretion rate fluctuations in this region are propagated to the X-ray emitting part of the boundary layer within ∼100 s. An orbital modulation of the X-ray flux suggests that the inner accretion disc is tilted with respect to the orbital plane. The elemental abundances in the boundary layer are close to their solar values. 相似文献
90.
Summary ?The rare earth, major and trace element geochemistry of Jurassic deep marine manganese shales allow insight into their environment
of deposition. We present data of 24 samples from the Northern Calcareous Alps (Eastern Alps), collected from Late Jurassic
strata of the Tennengebirge and from Early Jurassic strata of the Karwendel Mts. Whereas major and trace element geochemistry
is controlled by the detrital input, rare earth element data and the relationship between total organic carbon and (pyritic)
sulfur can be used to constrain the origin of the manganese accumulation. The data of this study are compatible with a hydrogenous
precipitation of manganese by strongly varying redox-conditions at the sediment–water interface of a slope basin.
Received December 21, 2001; revised version accepted February 18, 2002 相似文献