全文获取类型
收费全文 | 69873篇 |
免费 | 834篇 |
国内免费 | 660篇 |
专业分类
测绘学 | 1723篇 |
大气科学 | 4645篇 |
地球物理 | 13137篇 |
地质学 | 25432篇 |
海洋学 | 6470篇 |
天文学 | 16530篇 |
综合类 | 223篇 |
自然地理 | 3207篇 |
出版年
2022年 | 535篇 |
2021年 | 874篇 |
2020年 | 903篇 |
2019年 | 988篇 |
2018年 | 2157篇 |
2017年 | 2042篇 |
2016年 | 2421篇 |
2015年 | 1233篇 |
2014年 | 2283篇 |
2013年 | 3746篇 |
2012年 | 2480篇 |
2011年 | 3113篇 |
2010年 | 2789篇 |
2009年 | 3504篇 |
2008年 | 3020篇 |
2007年 | 3222篇 |
2006年 | 2923篇 |
2005年 | 2021篇 |
2004年 | 2012篇 |
2003年 | 1927篇 |
2002年 | 1897篇 |
2001年 | 1673篇 |
2000年 | 1517篇 |
1999年 | 1247篇 |
1998年 | 1265篇 |
1997年 | 1193篇 |
1996年 | 1018篇 |
1995年 | 985篇 |
1994年 | 869篇 |
1993年 | 756篇 |
1992年 | 761篇 |
1991年 | 736篇 |
1990年 | 775篇 |
1989年 | 641篇 |
1988年 | 633篇 |
1987年 | 676篇 |
1986年 | 624篇 |
1985年 | 778篇 |
1984年 | 836篇 |
1983年 | 747篇 |
1982年 | 711篇 |
1981年 | 641篇 |
1980年 | 604篇 |
1979年 | 614篇 |
1978年 | 584篇 |
1977年 | 486篇 |
1976年 | 461篇 |
1975年 | 471篇 |
1974年 | 421篇 |
1973年 | 473篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
A. S. Trew 《Astrophysics and Space Science》1982,82(1):223-228
The possible correlation noted between the intrinsic quasar luminosity and the absorption line expulsion velocity is re-examined using homogeneous data sets for metal and L only line systems. The method of analysis is chosen to enable any reasonable form of correlation to be found. No correlation is detected at a confidence level >10%. 相似文献
83.
The laboratory simulation experiments on volatilization from the melts formed due to micrometeoroid impacts on the lunar surface were carried out. The simulation was performed using modulated laser pulses incident on rocks and minerals in vacuum; in so doing microcraters on the targets, glass particles, condensates were formed and gases solved in the bulk of the rock and mineral grains were released. It is shown that volatilization from only the crater glass layers is negligible, which fully confirms the theoretical predictions of Nussinov and Chernyak.The volatilizations from the drops formed by the micrometeoric impacts can be noticeable. For micron-sized drops, predominant among the others after the impact, the volatilization of Na, K and other volatiles can be up to 10 to 20%. For larger-sized (d102 m) drops the volatilization should lead to the appearance of the significant gradients of the element concentrations over the particle cross-section and as a result of their normalization it leads to the surface enrichment by some elements (Si and others).The mechanism of dust formation due to the surface rocks attack by volatilizing alkaline metals (Naughtonet al.) on the Moon probably is not effective. It is the consequence of such a fact that the condensate of the target materials evaporated due to other simultaneous micrometeoric impacts and had the same (as the target has) elemental composition is the very strong background for volatilizing and condensating alkaline elements.Preliminary conclusions about a possible correlation between the composition and the sizes of dust particles in the Solar system and in the Universe (at similar initial composition) have been drawn. 相似文献
84.
The spreading angle of a number of light and dark Martian streaks is determined from selected Mariner 9 images. The resulting frequency distributions of spreading half-angles have maxima at ~5° for light, and ~7° for dark streaks; however the dark streaks have a secondary maximum spreading angle at ~14°. The smaller values, which include most streaks, are interpreted as crater-wake spreading phenomena. The larger value, found in only a few dark streaks or “tails,” may result from atmospheric diffusion and subsequent deposition of material from isolated sources such as vents or blowouts. An atmospheric diffusion-deposition analysis is presented, assuming this streak origin, from which it is possible to deduce the eddy diffusivity, K, in Mars' boudary layer. Calculated K values are found to agree with various theoretical estimates. They lie in the range 107 and 109 cm2 sec?1 and exhibit the proper scale dependence. Thus it appears that, in addition to streak-derived wind direction patterns and speed information, it is possible in a few cases to derive information on Mars' boundary-layer turbulence from streak-spreading measurements. 相似文献
85.
I. Lerche 《Astrophysics and Space Science》1976,43(1):91-96
We demonstrate that the so-called force balance point, due to either magnetic fields (then known more specifically as the Alfvén point) or to co-rotation (Roche point), together with the concepts of flux and mass conservation, allows one to place interesting limits on both the size and angular velocity of astrophysical objects emitting by mass accretion. We give three numerical examples, which would seem to be of some astrophysical interest. 相似文献
86.
87.
I. R. Plimer 《Mineralogy and Petrology》2006,88(3-4):443-478
Summary The Palaeoproterozoic Broken Hill Pb–Zn–Ag stratiform orebody is intimately associated with manganoan garnet-bearing rocks.
On stratigraphic and chemical grounds it is argued that garnet-rich metasediments below, equivalent to and above massive sulphide
were hydrothermal precipitates. Other manganoan garnet rocks formed during pre-metamorphic hydrothermal alteration, syn-metamorphic
dehydration and reaction of manganese with prograde pelitic rocks, reaction between cataclastic manganese-bearing sulphide
rocks injected along axial planes, shears and faults and pelitic wall rocks and reaction between dolerite dykes and sulphide
rocks. 相似文献
88.
89.
90.
The reservoir quality of Jurassic and Triassic fluvial and lacustrine-deltaic sandstones of the Yanchang Oil Field in the Ordos Basin is strongly influenced by the burial history and facies-related diagenetic events. The fluvial sandstones have a higher average porosity (14.8%) and a higher permeability (12.7×10?3 ?m2) than those of the deltaic sandstones (9.8% and 5.8 ×10?3 ?m2, respectively). The burial compaction, which resulted in 15% and 20% porosity loss for Jurassic and Triassic sandstones, respectively, is the main factor causing the loss of porosity both for the Jurassic and Triassic sandstones. Among the cements, carbonate is the main one that reduced the reservoir quality of the sandstones. The organic acidic fluid derived from organic matter in the source rocks, the inorganic fluid from rock-water reaction during the late diagenesis, and meteoric waters during the epidiagenesis resulted in the formation of dissolution porosity, which is the main reason for the enhancement of reservoir-quality. 相似文献