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   551篇
  免费   13篇
  国内免费   2篇
测绘学   20篇
大气科学   20篇
地球物理   144篇
地质学   154篇
海洋学   73篇
天文学   82篇
综合类   1篇
自然地理   72篇
  2021年   4篇
  2020年   7篇
  2019年   6篇
  2018年   6篇
  2017年   7篇
  2016年   9篇
  2015年   9篇
  2014年   12篇
  2013年   32篇
  2012年   12篇
  2011年   29篇
  2010年   16篇
  2009年   15篇
  2008年   19篇
  2007年   16篇
  2006年   18篇
  2005年   13篇
  2004年   14篇
  2003年   24篇
  2002年   14篇
  2001年   11篇
  2000年   18篇
  1999年   8篇
  1998年   11篇
  1997年   13篇
  1996年   14篇
  1995年   7篇
  1994年   7篇
  1993年   6篇
  1992年   3篇
  1991年   8篇
  1990年   8篇
  1988年   4篇
  1987年   10篇
  1986年   14篇
  1985年   14篇
  1984年   5篇
  1983年   8篇
  1982年   8篇
  1981年   13篇
  1980年   15篇
  1979年   9篇
  1978年   7篇
  1977年   3篇
  1976年   4篇
  1974年   10篇
  1973年   6篇
  1972年   3篇
  1968年   5篇
  1948年   3篇
排序方式: 共有566条查询结果,搜索用时 250 毫秒
81.
We present a geometric study of the radio and γ-ray pulsar B1055−52 based on recent observations at the Parkes radio telescope. We conclude that the pulsar's magnetic axis is inclined at an angle of 75° to its rotation axis and that both its radio main pulse and interpulse are emitted at the same height above their respective poles. This height is unlikely to be higher or much lower than 700 km, a typical value for radio pulsars.
It is argued that the radio interpulse arises from emission formed on open fieldlines close to the magnetic axis which do not pass through the magnetosphere's null (zero-charge) surface. However, the main pulse emission must originate from fieldlines lying well outside the polar cap boundary beyond the null surface, and farther away from the magnetic axis than those of the outer gap region where the single γ-ray peak is generated. This casts doubt on the common assumption that all pulsars have closed, quiescent, corotating regions stretching to the light cylinder.  相似文献   
82.
MIRI is the Mid InfraRed Instrument for the James Webb Space Telescope (JWST) and will provide imaging, coronography and integral field spectroscopy in the range between 4.9 and 28.6  $\upmu \hbox{m}.$ We summarise solar system observations which may be possible with this instrument, drawing on examples of observations made with previous space missions such as IRAS, ISO and Spitzer.  相似文献   
83.
Corwin J. Wright 《Icarus》2012,219(1):274-282
Temperature measurements from the Mars Climate Sounder on NASA’s Mars Reconnaissance Orbiter are examined for gravity wave signals using the Stockwell transform, a technique previously applied to terrestrial temperature profiles. An analysis is presented for internal-gravity waves throughout the martian atmosphere for the period July 2007–May 2009, representing a full martian year of data, divided by season. Momentum fluxes observed in the altitude range 200–20 Pa are measured as ~10?5–10?3 Pa, significantly higher than at equivalent altitudes on Earth, and are primarily peaked around the tropics. Observed orographic effects are minimal; the primary observed effects are seasonal. Waves are shown to vary significantly in wavelength with latitude, but are generally approximately zonally symmetric. Horizontal wavelengths are consistently much shorter in the northern hemisphere than the southern.  相似文献   
84.
Integration of extensive fieldwork, remote sensing mapping and 3D models from high-quality drone photographs relates tectonics and sedimentation to define the Jurassic–early Albian diapiric evolution of the N–S Miravete anticline, the NW-SE Castel de Cabra anticline and the NW-SE Cañada Vellida ridge in the Maestrat Basin (Iberian Ranges, Spain). The pre shortening diapiric structures are defined by well-exposed and unambiguous halokinetic geometries such as hooks and flaps, salt walls and collapse normal faults. These were developed on Triassic salt-bearing deposits, previously misinterpreted because they were hidden and overprinted by the Alpine shortening. The Miravete anticline grew during the Jurassic and Early Cretaceous and was rejuvenated during Cenozoic shortening. Its evolution is separated into four halokinetic stages, including the latest Alpine compression. Regionally, the well-exposed Castel de Cabra salt anticline and Cañada Vellida salt wall confirm the widespread Jurassic and Early Cretaceous diapiric evolution of the Maestrat Basin. The NE flank of the Cañada Vellida salt wall is characterized by hook patterns and by a 500-m-long thin Upper Jurassic carbonates defining an upturned flap, inferred as the roof of the salt wall before NE-directed salt extrusion. A regional E-W cross section through the Ababuj, Miravete and Cañada-Benatanduz anticlines shows typical geometries of salt-related rift basins, partly decoupled from basement faults. These structures could form a broader diapiric region still to be investigated. In this section, the Camarillas and Fortanete minibasins displayed well-developed bowl geometries at the onset of shortening. The most active period of diapiric growth in the Maestrat Basin occurred during the Early Cretaceous, which is also recorded in the Eastern Betics, Asturias and Basque-Cantabrian basins. This period coincides with the peak of eastward drift of the Iberian microplate, with speeds of 20 mm/year. The transtensional regime is interpreted to have played a role in diapiric development.  相似文献   
85.
This article is a discussion and critique of public intellectualism in the present. Rather than reify a self-aggrandized form of public intellectualism within academia that centers individualized intellectual development and that encourages a greater flow of findings outward to communities, I highlight black women public intellectuals who have used their skills, talents, and station within the university and society in novel ways. Moreover, I suggest that scholars take seriously the questions, research methods, and analyses emerging from the general public, particularly from within communal and political organizations. These encouragements are illustrated by highlighting three political education workshops that have been developed across the United States.  相似文献   
86.
M. Zeilik  E.L. Wright 《Icarus》1974,23(4):577-579
Before perihelion, the 8.8–21 μm luminosity of Comet Kahoutek (1973f) was on the order of 1021 ergsec?1 and dropped to 1020 ergsec?1 after perihelion.  相似文献   
87.
88.
89.
90.
Wilbur Zelinsky's 1971 paper in Geographical Review entitled the “Hypothesis of the Mobility Transition” was both forward‐looking and offered innovative ideas regarding human geographic mobility. One of the most interesting aspects of the paper was a set of predictions for mobility in a “future superadvanced society”. Many of these predictions have now come to pass, including a general decline in international and internal migration and residential change, the increasing regulation of migration ‐ especially internally, and the possibility that the widespread adoption of information and communication technologies has impacted human geographic mobility. Hence, this essay looks at the mobility transition not as an obsolete frame of reference but as a prescient, pliable, and adaptable framework which not only informs the study of human geographic mobility today but also, perhaps, even into the future.  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