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   55821篇
  免费   344篇
  国内免费   320篇
测绘学   1412篇
大气科学   3303篇
地球物理   9995篇
地质学   23593篇
海洋学   4437篇
天文学   11740篇
综合类   255篇
自然地理   1750篇
  2022年   493篇
  2021年   715篇
  2020年   765篇
  2019年   841篇
  2018年   3994篇
  2017年   3539篇
  2016年   2870篇
  2015年   756篇
  2014年   1500篇
  2013年   2124篇
  2012年   2426篇
  2011年   4002篇
  2010年   3536篇
  2009年   3911篇
  2008年   3286篇
  2007年   3941篇
  2006年   1861篇
  2005年   1256篇
  2004年   1169篇
  2003年   1190篇
  2002年   1047篇
  2001年   863篇
  2000年   738篇
  1999年   496篇
  1998年   517篇
  1997年   536篇
  1996年   404篇
  1995年   423篇
  1994年   382篇
  1993年   329篇
  1992年   328篇
  1991年   341篇
  1990年   372篇
  1989年   313篇
  1988年   278篇
  1987年   291篇
  1986年   225篇
  1985年   330篇
  1984年   351篇
  1983年   325篇
  1982年   309篇
  1981年   298篇
  1980年   314篇
  1979年   227篇
  1978年   272篇
  1977年   219篇
  1976年   198篇
  1975年   196篇
  1974年   200篇
  1973年   221篇
排序方式: 共有10000条查询结果,搜索用时 937 毫秒
31.
Leningrad State University. Translated from Astrofizika, Vol. 32, No. 2, pp. 267–275, March–April, 1990.  相似文献   
32.
Photographic spectra of SN1987A in the LMC have been obtained from 1987 February 25 to 1988 June 30. Microdensitometer tracings of these have been reduced to intensity and corrections for instrumental response have been applied to the spectra. This paper presents these data in an atlas format, discusses the reduction procedures in detail, and presents radial velocity measurements of selected lines in the spectra  相似文献   
33.
In this paper we analyse error-removing techniques used without sufficient theoretical support in a previous paper, where Chandrasekhar's higher-order perturbation theories were developed for either uniformly or differentially-rotating polytropic stars.  相似文献   
34.
Solutions of field equations of the generalized theory of gravitation for neutral and charged point masses are found. The problem is formulated so that the solution may be expressed in harmonic, isotropic, Schwarzschild and, if necessary, any other coordinates. A method for the solution of the static axisymmetric problem (an analogue of a well-known Weyl's solution) is also proposed.  相似文献   
35.
36.
37.
Observations of the brightness, color, and polarization of the fuor V1057 Cyg over more than 30 years are presented and briefly discussed. Variability of the linear polarization was found.  相似文献   
38.
Today one of the main questions standing before geology of Venus is comprehension of tectonic style on surface of this planet. The observed ridge belts on the images of the radar surveyors of Venera-15 and -16 are related to one aspect of a solution of this problem. In general there are two views on the origin of the ridge belts on the planet. Some of the investigators consider them as a result of compression while others as extension. These discrepancies are connected with uncertainties of interpretations of the major structures of these belts, i.e., the ridges. This paper represents a review of evidence in favor of extension and compression observed within the ridge belts. Moreover it discusses the major speculative ideas and models of the ridge belts origin. The supporters of a ridge formation by extension suggest that these linear features are results of crust cracking and intruding of magma along these cracks so they propose that the ridge belts on the plains of Venus can represent analogies of the spreading zones on Earth. Other investigators assume that the ridge of belts represent structures of folding and or thrust faulting due to the tectonic compression environment so the ridge belts can be analogies of the orogenic belts and subduction zones on Earth. So the question of the ridge belts' origin remains controversial and for a solution, set one's hope on the Magellan mission.'Geology and Tectonics of Venus', special issue edited by Alexander T. Basilevsky (USSR Acad. of Sci., Moscow), James W. Head (Brown University, Providence), Gordon H. Pettengill (MIT. Cambridge, Massachusetts) and R. S. Saunders (J.P.L., Pasadena).  相似文献   
39.
The coherent plasma process such as parametric decay instability (PDI) has been applied to a homogeneous and unmagnetized plasma. These instabilities cause anomalous absorption of strong electromagnetic radiation under specific conditions of energy and momentum conservation and thus cause anomalous heating of the plasma. The maximum plasma temperatures reached are functions of luminosity of the radio radiation and plasma parameters. We believe that these processes may be taking place in many astrophysical objects. Here, the conditions in the sources 3C 273, 3C 48 and Crab Nebula are shown to be conducive to the excitation of PDI. These processes also contribute towards the absorption of 21cm radiation  相似文献   
40.
A new procedure to separate the instrumental and atmospheric components of stray light is presented. It is based on the dependence of the aureole's atmospheric component on the air mass and is applied to measurements taken with the Vacuum Newton Telescope (VNT) at the Observatorio del Teide (Tenerife). The resulting instrumental part is independent of the air mass.The variation of both components with wavelength is also studied. The instrumental component shows no dependence on wavelength, in contrast to the atmospheric one which is greater in the blue than in the red.It is concluded that observations with air masses larger than two will probably be strongly affected by stray light.  相似文献   
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