全文获取类型
收费全文 | 99714篇 |
免费 | 1929篇 |
国内免费 | 747篇 |
专业分类
测绘学 | 2689篇 |
大气科学 | 7782篇 |
地球物理 | 20251篇 |
地质学 | 32984篇 |
海洋学 | 8579篇 |
天文学 | 22857篇 |
综合类 | 225篇 |
自然地理 | 7023篇 |
出版年
2020年 | 714篇 |
2019年 | 762篇 |
2018年 | 1558篇 |
2017年 | 1542篇 |
2016年 | 2131篇 |
2015年 | 1499篇 |
2014年 | 2275篇 |
2013年 | 4962篇 |
2012年 | 2303篇 |
2011年 | 3332篇 |
2010年 | 2940篇 |
2009年 | 4174篇 |
2008年 | 3783篇 |
2007年 | 3554篇 |
2006年 | 3502篇 |
2005年 | 3128篇 |
2004年 | 3147篇 |
2003年 | 2934篇 |
2002年 | 2811篇 |
2001年 | 2536篇 |
2000年 | 2443篇 |
1999年 | 2242篇 |
1998年 | 2188篇 |
1997年 | 2146篇 |
1996年 | 1845篇 |
1995年 | 1761篇 |
1994年 | 1630篇 |
1993年 | 1492篇 |
1992年 | 1430篇 |
1991年 | 1312篇 |
1990年 | 1510篇 |
1989年 | 1346篇 |
1988年 | 1221篇 |
1987年 | 1471篇 |
1986年 | 1258篇 |
1985年 | 1601篇 |
1984年 | 1880篇 |
1983年 | 1740篇 |
1982年 | 1649篇 |
1981年 | 1567篇 |
1980年 | 1345篇 |
1979年 | 1332篇 |
1978年 | 1334篇 |
1977年 | 1246篇 |
1976年 | 1161篇 |
1975年 | 1067篇 |
1974年 | 1115篇 |
1973年 | 1144篇 |
1972年 | 712篇 |
1971年 | 657篇 |
排序方式: 共有10000条查询结果,搜索用时 33 毫秒
141.
A family of related Pc1-2 (0.2–10 s) discrete daytime geomagnetic pulsations is presented using pulsation data obtained at Davis, Antarctica, a typical polar-cap station. The morphological properties of IPRP and Pclb pulsation regimes, which maximize in amplitude and frequency of occurrence under the projection of the polar cusp, are examined. Furthermore, two other variations of discrete pulsation bursts yet to be named are also presented, viz IPFP (Intervals of Pulsations with Falling Period) and IPAP (Intervals of Pulsations with Alternating Period) which are observed on rare occasions. It is also suggested that the Pc1b (0.2–5 s) should be extended to incorporate Pc2b (5–10 s) which from the results in this paper are physically the same phenomenon and could be collectively classified as IPCP (Intervals of Pulsations with Constant Period). 相似文献
142.
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
143.
144.
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
145.
H. L. Xu S. Svanberg R. D. Cowan P.-H. Lefèbvre P. Quinet E. Biémont 《Monthly notices of the Royal Astronomical Society》2003,346(2):433-440
Radiative lifetime measurements were performed with time-resolved laser-induced fluorescence techniques for 24 levels of Nd ii in the energy range 20 500–32 500 cm−1 . For 17 levels, no previous experimental data exist. These results have allowed the testing of new theoretical calculations with the relativistic Hartree–Fock method taking configuration interactions and core-polarization effects into account, and a satisfying agreement has been found for this complex ion. A new set of calculated oscillator strengths, accurate within a few per cent for the strongest transitions, is presented for 107 lines of astrophysical interest appearing in the wavelength range 358.0–1100.0 nm. These results will be useful to evaluate abundance values of neodymium in chemically peculiar stars in relation with cosmochronology. 相似文献
146.
We present four epochs of observations of the Galactic X-ray binarySS433 using the Australian Telescope Compact Array (ATCA). These observations, taken on 4 February, 29 February, 23 March and 27 June 2000, at four frequencies ranging from 1–9 Ghz, are used to monitor the circular polarised emission from the source. We obtain circular polarisation spectra for the first three epochs with spectralindices α, (m c ∝ν α), equal to 0.07±0.10, –1.07±0.09 and –0.18±0.05 and also observe a sign change in Stokes V. This change of handedness may indicate along-term restructuring of the magnetic field. 相似文献
147.
J. Dommanget 《Journal of Astrophysics and Astronomy》2003,24(3-4):99-109
A research that we conducted in 1963 on the evolution of the binaries based on the available orbital data to obtain a philosophical
degree, led to the establishment of an interesting and new diagram between the logarithm of the total mass and a particular
parameterX, bound to the areal constant. This appeared to have a real physical significance but the basic observational material was
insufficiently extended to assure its undeniable existence. In 1981, a new research based on a more extended orbital material,
has confirmed this diagram. Presently, another important increase in the orbital material and the availability of highly accurate
trigonometric parallaxes produced by the Hipparcos satellite, gave us the opportunity to confirm once more the stability of
this diagram. This last research is here described. 相似文献
148.
Jean-Pierre Macquart Kinwah Wu Diana C. Hannikainen Robert J. Sault David L. Jauncey 《Astrophysics and Space Science》2003,288(1-2):105-119
We compare the observational properties of the circular polarization in Galactic jet sources with that observed in AGN, and outline the constraints they place on the mechanism responsible for the circular polarization. We also discuss the implications of the time scale of polarization variations on the mechanism responsible for the circular polarization. 相似文献
149.
150.