首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   70088篇
  免费   1503篇
  国内免费   1267篇
测绘学   1603篇
大气科学   5052篇
地球物理   14105篇
地质学   25811篇
海洋学   6314篇
天文学   15187篇
综合类   318篇
自然地理   4468篇
  2022年   505篇
  2021年   832篇
  2020年   886篇
  2019年   980篇
  2018年   1766篇
  2017年   1717篇
  2016年   1946篇
  2015年   1183篇
  2014年   1917篇
  2013年   3437篇
  2012年   2336篇
  2011年   3119篇
  2010年   2712篇
  2009年   3472篇
  2008年   3016篇
  2007年   3123篇
  2006年   2968篇
  2005年   2072篇
  2004年   2028篇
  2003年   1928篇
  2002年   1838篇
  2001年   1565篇
  2000年   1488篇
  1999年   1279篇
  1998年   1298篇
  1997年   1283篇
  1996年   1090篇
  1995年   1061篇
  1994年   913篇
  1993年   813篇
  1992年   780篇
  1991年   759篇
  1990年   833篇
  1989年   713篇
  1988年   672篇
  1987年   777篇
  1986年   717篇
  1985年   892篇
  1984年   1023篇
  1983年   934篇
  1982年   888篇
  1981年   800篇
  1980年   794篇
  1979年   711篇
  1978年   677篇
  1977年   695篇
  1976年   612篇
  1975年   610篇
  1974年   609篇
  1973年   667篇
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
81.
The authors describe the effect of copper pollution on the mitochondria from various areas of the Torpedo marmorata central nervous system. A high percentage of swollen mitochondria has been observed in neurons from animals experimentally exposed to high level of copper (4 ppm). The correlation with age pigment granules is discussed.  相似文献   
82.
In this paper the peculiarities of compiled oceanographic data sets, which consist primarily in the presence of some characteristic information as well as in the planned incomplete filling of the files with observations, are discussed. A number of special ways are suggested which essentially improve the packing density of computerized data without applying special archiving algorithms. The effectiveness of these methods has been tested by treating thein situ hydrological/chemical data file compiled in the Black Sea in 1988.Translated by Vladimir A. Puchkin.  相似文献   
83.
This study considers the influence of the effects of scattering due to Langmuir turbulent pulsations in the transfer of radiation in the spectral lines. The transfer equation of radiation in spectral lines, by taking into account scattering due to Langmuir turbulent pulsations, is written in a form convenient for application by numerical methods.The profile's intensity for a plane-parallel finite isothermal slab of a turbulent plasma in the case of complete redistribution of scattering by an atom are obtained. Numerical studies show that in this case with the broadening of spectral lines and the decreasing of self-reversal, the Langmuir frequency pe is of the same order as the electronic Doppler width De. Creation of the line satellites when pe is larger than the line width is shown with the aid of numerical methods.  相似文献   
84.
The equatorial photospheric rotation rate has been observed on 14 days in 1978–1980. The resulting rotation rate, = 14.14±0.04°/day, is 2% slower than the rate as observed for long-lived sunspots.Stationed at Kitt Peak National Observatory.Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.  相似文献   
85.
E. Irving  G. Pullaiah 《Earth》1976,12(1):35-64
The percentage of normal and reversed magnetization in land-based paleomagnetic studies of Phanerozoic rocks (0 to ? 570 m.y.) have been compiled in order to determine the long-term variation in polarity bias of the geomagnetic field. Where possible the results are compared with the record from marine magnetic anomalies. Only rarely is there an even balance between normal and reversed polarity. During the past 350 m.y. two quiet intervals can be recognized when few reversals occurred, the Cretaceous (KN about ? 81 to ? 110 m.y.) and Permo-Carboniferous (PCR about ? 227 to ? 313 m.y.). Less firmly established are two other quiet intervals, one in the Jurassic (JN about ? 145 to ? 165 m.y.), and one in the Triassic (TRN about ? 205 to ? 220 m.y.). Between these quiet intervals there are disturbed intervals when reversals were comparatively frequent. From ? 680 to ? 350 m.y. the paleomagnetic record is inadequate to delineate a succession of quiet and disturbed intervals although one is probably present. Maximum entropy spectral analysis reveals three periodicities, a dominant one at about 300 m.y. and others, less well-defined, at 113 and 57 m.y. The variations in polarity bias are compared with the paleosecular variation, and it is shown that the magnitude of the paleosecular variation is greater in disturbed than in quiet intervals. This indicates that the magnitude of paleosecular variation and polarity bias are governed by variations in the balance between non-dipole and dipole components of the field, and that these variations probably had their origin in processes near the core—mantle interface. The correspondence between the dominant periods of 300 m.y. and plate tectonics is noted and a causal relationship suggested.  相似文献   
86.
87.
88.
Lithology and Mineral Resources - The chemical composition and Nd isotope systematics were obtained for mudrocks (mudstones) from sections of the Siberian hypostratotype of the Riphean and Vendian...  相似文献   
89.
90.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号