全文获取类型
收费全文 | 42183篇 |
免费 | 739篇 |
国内免费 | 356篇 |
专业分类
测绘学 | 1316篇 |
大气科学 | 3097篇 |
地球物理 | 8619篇 |
地质学 | 13996篇 |
海洋学 | 3654篇 |
天文学 | 10296篇 |
综合类 | 114篇 |
自然地理 | 2186篇 |
出版年
2021年 | 329篇 |
2020年 | 365篇 |
2019年 | 453篇 |
2018年 | 979篇 |
2017年 | 907篇 |
2016年 | 1188篇 |
2015年 | 675篇 |
2014年 | 1125篇 |
2013年 | 2030篇 |
2012年 | 1227篇 |
2011年 | 1636篇 |
2010年 | 1497篇 |
2009年 | 2045篇 |
2008年 | 1790篇 |
2007年 | 1823篇 |
2006年 | 1709篇 |
2005年 | 1293篇 |
2004年 | 1312篇 |
2003年 | 1196篇 |
2002年 | 1247篇 |
2001年 | 1101篇 |
2000年 | 1021篇 |
1999年 | 907篇 |
1998年 | 887篇 |
1997年 | 894篇 |
1996年 | 712篇 |
1995年 | 673篇 |
1994年 | 632篇 |
1993年 | 551篇 |
1992年 | 476篇 |
1991年 | 501篇 |
1990年 | 472篇 |
1989年 | 493篇 |
1988年 | 437篇 |
1987年 | 509篇 |
1986年 | 461篇 |
1985年 | 541篇 |
1984年 | 661篇 |
1983年 | 575篇 |
1982年 | 558篇 |
1981年 | 511篇 |
1980年 | 449篇 |
1979年 | 438篇 |
1978年 | 449篇 |
1977年 | 389篇 |
1976年 | 348篇 |
1975年 | 354篇 |
1974年 | 328篇 |
1973年 | 363篇 |
1972年 | 264篇 |
排序方式: 共有10000条查询结果,搜索用时 422 毫秒
291.
P. von Ballmoos 《Experimental Astronomy》1995,6(4):85-96
Gamma-ray lines are the fingerprints of nuclear transitions, carrying the memory of high energy processes in the universe. Setting out from what is presently known about line emission in gamma-ray astronomy, requirements for future telescopes are outlined. The inventory of observed line features shows that sources with a wide range of angular and spectral extent have to be handled: the scientific objectives for gamma-ray spectroscopy are spanning from compact objects as broad class annihilators, over longlived galactic radioisotopes with hotspots in the degree-range to the extremely extended galactic disk and bulge emission of the narrow e– e+ line.The instrumental categories which can be identified in the energy range of nuclear astrophysics have their origins in the different concepts of light itself: geometrical optics is the base of modulating aperture systems-these methods will continue to yield adequate performances in the near future. Beyond this, focusing telescopes and Compton telescopes, based on wave- and quantum- optics respectively, may be capable to further push the limits of resolution and sensitivity. 相似文献
292.
293.
P. Persi M. Ferrari-Toniolo A. R. Marenzi M. Busso L. Corcione M. Marengo M. Tapia 《Astrophysics and Space Science》1995,224(1-2):535-536
We present the results of direct mid-IR images of the luminous young stellar objects GL 2591, S140-IRS1, and W51-IRS2. The sources show an extended mid-IR emission at the limit of our spatial resolution indicating the presence of dense circumstellar dust disks. 相似文献
294.
P. MAISONGRANDE A. RUIMY G. DEDIEU B. SAUGIER 《Tellus. Series B, Chemical and physical meteorology》1995,47(1-2):178-190
295.
S. P. Plunkett G. E. Brueckner K. P. Dere R. A. Howard M. J. Koomen C. M. Korendyke D. J. Michels J. D. Moses N. E. Moulton S. E. Paswaters O. C. St. Cyr D. G. Socker D. Wang G. M. Simnett D. K. Bedford D. A. Biesecker C. J. Eyles S. J. Tappin R. Schwenn P. L. Lamy A. Llebaria 《Solar physics》1997,175(2):699-718
We report observations by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft of three coronal green-line
transients that could be clearly associated with coronal mass ejections (CMEs) detected in Thomson-scattered white light.
Two of these events, with speeds >25 km s-1, may be classified as ‘whip-like’ transients. They are associated with the core of the white-light CMEs, identified with
erupting prominence material, rather than with the leading edge of the CMEs. The third green-line transient has a markedly
different appearance and is more gradual than the other two, with a projected outward speed <10 km s-1. This event corresponds to the leading edge of a ‘streamer blowout’ type of CME. A dark void is left behind in the emission-line
corona following each of the fast eruptions. Both fast emission-line transients start off as a loop structure rising up from
close to the solar surface. We suggest that the driving mechanism for these events may be the emergence of new bipolar magnetic
regions on the surface of the Sun, which destabilize the ambient corona and cause an eruption. The possible relationship of
these events to recent X-ray observations of CMEs is briefly discussed.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004981125702 相似文献
296.
We suggest that the dynamical regime(s) underlying quasi-periodic oscillations observed in the spectra of bright galactic-bulge
X-ray sources are nonlinear with a mixed phase space. The important feature of such regimes is that they are generic among
nonlinear Hamiltonian and nearly Hamiltonian systems of more than two degrees of freedom. We give a simple example of such
chaotic (deterministic) systems whose spectra share a number of features with those observed for quasiperiodic oscillations
of such sources. 相似文献
297.
A. W. Shafter J. A. Hill E. L. Robinson P. Szkody J. R. Thorstensen M. A. Wood 《Astrophysics and Space Science》1987,130(1-2):125-126
SW UMa is an unusual dwarf nova in several respects. Recent observations by Robinsonet al. (1986) have established that SW UMa is an SU UMa system, while Shafter, Szkody, and Thorstensen (1986) have presented evidence suggesting that SW UMa may be a DQ Her system as well. If the DQ Her classification is confirmed then SW UMa will be the only system to have this dual classification. Finally, time resolved spectroscopy of SW UMa has revealed the presence of an S-wave component in the H emission which has an unexpected phasing relative to the line wings.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986. 相似文献
298.
Using the leaky-box model the upper limit of the antiproton-proton flux ratio at the top of the atmosphere has been estimated from the latest primary nucleon spectrum and accelerator data on
inclusive reactions. The estimated value of
flux ratio comes out to be (3.6±0.3)×10–4 is in accord with the previous results but still far from the measurements. 相似文献
299.
During the type IV burst on 24 April, 1985 we observed at 234 MHz an untypical, strong, nearly six hours lasting continuum emission incorporating several groups of broadband pulsations, zebra patterns, fiber bursts, and a new fine structure phenomenon. The power spectra of the groups of broadband pulsations reveal no simple structure. There is only one common periodic component between 0.3 s and 0.4 s. Slowly drifting chains of narrowband fiber bursts are described as a new fine structure by spectrograms and simultaneously recorded single frequency intensity profiles. A qualitative model of this new fine structure is suggested. 相似文献
300.
The paper presents the results obtained from the UV-spectrometer of the Solar Spectrum Experiment during the Spacelab 1 mission in December 1983. The irradiance data concern 492 passbands, which are located between 200 and 358 nm at almost equidistant wavelengths separated by about 0.3 nm. The passbands have a well-defined, bell-shaped profile with a full width at half maximum of about 1.3 nm. The data, which have an error budget between 4 and 5%, agree closely with the spectral distributions observed by Heath (1980) and Mentall et al. (1981) and confirm that the solar irradiance and the fluxes of Sun-like stars show about the same spectral distribution down to at least 240 nm. 相似文献