全文获取类型
收费全文 | 86249篇 |
免费 | 980篇 |
国内免费 | 550篇 |
专业分类
测绘学 | 2144篇 |
大气科学 | 5431篇 |
地球物理 | 16169篇 |
地质学 | 33324篇 |
海洋学 | 7402篇 |
天文学 | 19070篇 |
综合类 | 291篇 |
自然地理 | 3948篇 |
出版年
2022年 | 573篇 |
2021年 | 929篇 |
2020年 | 978篇 |
2019年 | 1112篇 |
2018年 | 4258篇 |
2017年 | 3813篇 |
2016年 | 3461篇 |
2015年 | 1225篇 |
2014年 | 2167篇 |
2013年 | 3756篇 |
2012年 | 3105篇 |
2011年 | 4931篇 |
2010年 | 4419篇 |
2009年 | 5196篇 |
2008年 | 4375篇 |
2007年 | 4979篇 |
2006年 | 3057篇 |
2005年 | 2276篇 |
2004年 | 2166篇 |
2003年 | 2176篇 |
2002年 | 2007篇 |
2001年 | 1715篇 |
2000年 | 1548篇 |
1999年 | 1150篇 |
1998年 | 1179篇 |
1997年 | 1220篇 |
1996年 | 954篇 |
1995年 | 959篇 |
1994年 | 905篇 |
1993年 | 808篇 |
1992年 | 775篇 |
1991年 | 760篇 |
1990年 | 798篇 |
1989年 | 740篇 |
1988年 | 704篇 |
1987年 | 780篇 |
1986年 | 657篇 |
1985年 | 871篇 |
1984年 | 926篇 |
1983年 | 848篇 |
1982年 | 768篇 |
1981年 | 803篇 |
1980年 | 718篇 |
1979年 | 624篇 |
1978年 | 656篇 |
1977年 | 619篇 |
1976年 | 554篇 |
1975年 | 542篇 |
1974年 | 535篇 |
1973年 | 571篇 |
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
381.
Analyses of primary and early diagenetic fluid inclusions in the halite from the Late Ordovician Mallowa Salt, Canning Basin, Western Australia indicate a Ca‐rich composition and high concentration of parent brines in the basin which were close to sylvite and carnallite precipitation. The salt‐bearing series in the sampled interval was overheated up to 62 °C. The recorded differences in gas compositions result from the input of several gas sources including dispersed organic matter in the salt series and hydrocarbon deposits in the underlying rocks. The high concentration of the brines in fluid inclusions does not allow quantitative reconstruction of the chemical composition of Late Ordovician parent seawater. Using the information from Early Cambrian and Late Silurian basins as a proxy, however, the new data indicate that Late Ordovician seawater was undoubtedly Ca‐rich and, in comparison with modern seawater, had a similar K content, considerably lower Mg content (c. 30%), approximately three times the Ca content and one‐third the SO4 content. 相似文献
382.
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
383.
384.
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
385.
386.
387.
We present a 2D general circulation model of Titan's atmosphere, coupling axisymmetric dynamics with haze microphysics, a simplified photochemistry and eddy mixing. We develop a parameterization of latitudinal eddy mixing by barotropic waves based on a shallow-water, longitude-latitude model. The parameterization acts locally and in real time both on passive tracers and momentum. The mixing coefficient varies exponentially with a measure of the barotropic instability of the mean zonal flow. The coupled GCM approximately reproduces the Voyager temperature measurements and the latitudinal contrasts in the distributions of HCN and C2H2, as well as the main features of the zonal wind retrieved from the 1989 stellar occultation. Wind velocities are consistent with the observed reversal time of the North-South albedo asymmetry of 5 terrestrial years. Model results support the hypothesis of a non-uniform distribution of infrared opacity as the cause of the Voyager temperature asymmetry. Transport by the mean meridional circulation, combined with polar vortex isolation may be at the origin of the latitudinal contrasts of trace species, with eddy mixing remaining restricted to low latitudes most of the Titan year. We interpret the contrasts as a signature of non-axisymmetric motions. 相似文献
388.
389.
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
390.
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