全文获取类型
收费全文 | 95534篇 |
免费 | 1050篇 |
国内免费 | 556篇 |
专业分类
测绘学 | 2395篇 |
大气科学 | 6349篇 |
地球物理 | 17682篇 |
地质学 | 36187篇 |
海洋学 | 8008篇 |
天文学 | 21586篇 |
综合类 | 324篇 |
自然地理 | 4609篇 |
出版年
2022年 | 587篇 |
2021年 | 915篇 |
2020年 | 1030篇 |
2019年 | 1090篇 |
2018年 | 4268篇 |
2017年 | 3878篇 |
2016年 | 3541篇 |
2015年 | 1307篇 |
2014年 | 2395篇 |
2013年 | 4231篇 |
2012年 | 3205篇 |
2011年 | 4983篇 |
2010年 | 4501篇 |
2009年 | 5265篇 |
2008年 | 4557篇 |
2007年 | 5127篇 |
2006年 | 3261篇 |
2005年 | 2508篇 |
2004年 | 2394篇 |
2003年 | 2372篇 |
2002年 | 2162篇 |
2001年 | 1900篇 |
2000年 | 1726篇 |
1999年 | 1445篇 |
1998年 | 1399篇 |
1997年 | 1455篇 |
1996年 | 1137篇 |
1995年 | 1129篇 |
1994年 | 1070篇 |
1993年 | 968篇 |
1992年 | 947篇 |
1991年 | 930篇 |
1990年 | 1057篇 |
1989年 | 898篇 |
1988年 | 871篇 |
1987年 | 960篇 |
1986年 | 783篇 |
1985年 | 1074篇 |
1984年 | 1209篇 |
1983年 | 1146篇 |
1982年 | 1077篇 |
1981年 | 1033篇 |
1980年 | 953篇 |
1979年 | 871篇 |
1978年 | 896篇 |
1977年 | 800篇 |
1976年 | 754篇 |
1975年 | 674篇 |
1974年 | 744篇 |
1973年 | 760篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
451.
A flare of OH maser emission was discovered in W75N in 2000. Its location was determined with the Very Long Baseline Array (VLBA) to be within 110 au from one of the ultracompact H ii regions, Very Large Array 2 (VLA2). The flare consisted of several maser spots. Four of the spots were found to form Zeeman pairs, all of them with a magnetic field strength of about 40 mG. This is the highest ever magnetic field strength found in OH masers, an order of magnitude higher than in typical OH masers. Three possible sources for the enhanced magnetic field are discussed: (i) the magnetic field of the exciting star dragged out by the stellar wind; (ii) the general interstellar field in the gas compressed by the magnetohydrodynamic shock; and (iii) the magnetic field of planets which orbit the exciting star and produce maser emission in gaseous envelopes. 相似文献
452.
453.
Alexei V. Tsygvintsev 《Celestial Mechanics and Dynamical Astronomy》2003,86(3):237-247
We consider the planar three-body problem and prove that, apart from some exceptional cases, there is no additional first integral meromorphic with respect to positions, mutual distances and momenta. 相似文献
454.
455.
Near the inner edge of the Edgeworth-Kuiper Belt (EKB) are Pluto and Charon, which are known to have N2- and H2O-dominated surface ices, respectively. Such non-polar and polar ices, and perhaps mixtures of them, also may be present on other trans-Neptunian objects. Pluto, Charon, and all EKB objects reside in a weak, but constant UV-photon and energetic ion radiation environment that drives chemical reactions in their surface ices. Effects of photon and ion processing include changes in ice composition, volatility, spectra, and albedo, and these have been studied in a number of laboratories. This paper focuses on ice processing by ion irradiation and is aimed at understanding the volatiles, ions, and residues that may exist on outer solar system objects. We summarize radiation chemical products of N2-rich and H2O-rich ices containing CO or CH4, including possible volatiles such as alcohols, acids, and bases. Less-volatile products that could accumulate on EKB objects are observed to form in the laboratory from acid-base reactions, reactions promoted by warming, or reactions due to radiation processing of a relatively pure ice (e.g., CO → C3O2). New IR spectra are reported for the 1–5 mu;m region, along with band strengths for the stronger features of carbon suboxide, carbonic acid, the ammonium and cyanate ions, polyoxymethylene, and ethylene glycol. These six materials are possible contributors to EKB surfaces, and will be of interest to observers and future missions. 相似文献
456.
Churyumov K. I. Klesachonok V. V. Mussaev F. A. Bikmaev I. F. Galazutdinov G. H. 《Earth, Moon, and Planets》1997,78(1-3):105-110
We present the results of the preliminary study of the comet Hale-Bopp spectrum obtained April 17, 1997 by K. Churyumov and F. Mussayev with the help of the 1-meter Zeiss reflector and the echelle spectrometer (spectral resolutionλ/Δ λ ≈ 50000), CCD and the long slit, oriented along the radius-vector(“Sun-comet direction”). Energy distributions for three selected regions including the C3, C2 (0-0) and CN(Δ ν = 0) molecules emissions of the comet Hale-Bopp spectrum were built. The rotational lines of the CN(Δ ν = 0) band were identified. The nature of the high emission peak near λ 4020 Å in the C3 band is discussed. The presence of the cometary continuum of the nonsolar origin is assumed. 相似文献
457.
The supraregional GIS-supported stochastical model, WEKU, for the determination of groundwater residence times in the upper
aquifers of large groundwater provinces is presented. Using a two-dimensional analytical model of groundwater flow, groundwater
residence times are determined within two extreme cases. In the first case, maximal groundwater residence times are calculated,
representing the part of groundwater, that is drained by the main surface water of a groundwater catchment area. In the second
case, minimal groundwater residence times for drainage into the nearest surface water are determined. Using explicit distribution
functions of the input parameters, mean values as well as potential ranges of variations of the groundwater residence times
are derived. The WEKU model has been used for the determination of groundwater residence times throughout Germany. The model
results – mean values and deviations of the groundwater velocity and the maximal and minimal groundwater residence times in
the upper aquifers – are presented by general maps and discussed in detail. It is shown that the groundwater residence times
in the upper aquifer vary regionally, differentiated between less than 1 year and more than 2000 years. Using this information,
the time scales can be specified, until measures to remediate polluted groundwater resources may lead to a substantial groundwater
quality improvement in the different groundwater provinces of Germany. With respect to its supraregional scale of application,
the WEKU model may serve as a useful tool for the supraregional groundwater management on a state, federal or international
level.
Received: 15 August 1995 · Accepted: 15 October 1995 相似文献
458.
E. Tóth F. Deak C. S. Gyurkócza Z. S. Kasztovszky R. Kuczi G. Marx B. Nagy S. Oberstedt L. Sajó-Bohus C. S. Sükösd G. Toth N. Vajda 《Environmental Geology》1997,31(1-2):123-127
A steady radon exhalation is assumed in most publications. In a village of North-East Hungary, however, high radon concentrations
have been measured, differing strongly in neighbouring houses and varying in time, due to the interplay of geochemical phenomena.
Received: 20 November 1995 · Accepted: 18 June 1996 相似文献
459.
The equivalent width calculations for the fundamental vibration rotation band lines of HeH+ have been carried out for a non-DA white dwarf model with an effective temperature of 12 000 K. BothP andR branch lines with rotational quantum numbersJ=3 to 18 were included in the calculations. A search for these lines in helium rich white dwarfs is suggested. 相似文献
460.