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   85404篇
  免费   1381篇
  国内免费   525篇
测绘学   1761篇
大气科学   5613篇
地球物理   16270篇
地质学   30879篇
海洋学   7896篇
天文学   19922篇
综合类   220篇
自然地理   4749篇
  2022年   619篇
  2021年   1039篇
  2020年   1119篇
  2019年   1248篇
  2018年   2555篇
  2017年   2362篇
  2016年   2720篇
  2015年   1358篇
  2014年   2622篇
  2013年   4497篇
  2012年   2866篇
  2011年   3701篇
  2010年   3377篇
  2009年   4281篇
  2008年   3725篇
  2007年   3835篇
  2006年   3558篇
  2005年   2529篇
  2004年   2455篇
  2003年   2292篇
  2002年   2279篇
  2001年   1978篇
  2000年   1966篇
  1999年   1537篇
  1998年   1598篇
  1997年   1469篇
  1996年   1245篇
  1995年   1240篇
  1994年   1043篇
  1993年   1010篇
  1992年   930篇
  1991年   972篇
  1990年   936篇
  1989年   822篇
  1988年   757篇
  1987年   887篇
  1986年   777篇
  1985年   944篇
  1984年   1076篇
  1983年   1031篇
  1982年   954篇
  1981年   892篇
  1980年   794篇
  1979年   751篇
  1978年   732篇
  1977年   621篇
  1976年   626篇
  1975年   613篇
  1974年   589篇
  1973年   656篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Free flexural-gravity waves unevenly compressed in an ice-covered basin have been studied using a linear formulation. The conditions were specified allowing determination of the bounds of the angular area of wave disturbances and of the oscillation frequency intervals due to compression. The paper considers the distribution of the wave characteristics over frequency depending on compressive stresses and the direction of wave propagation.Translated by Vladimir A. Puchkin.  相似文献   
972.
973.
974.
A series of eight tracer experiments were carried out over one year (1983) on a low energy, macro-tidal beach in South Wales, UK. Tracer movement was monitored and 30 pebbles adjacent to coloured tracer pebbles were measured. Measurements were of the A, B, and C axes, roundness, Maximum Projection Sphericity and Oblate-Prolate indices. Analysis shows that through time, the percentage rejection of these properties increased. It is theorised that the surface tracers are 'misfits' or 'rejects' which have not found their equilibrium position in the pebble facies.  相似文献   
975.
976.
This paper discusses the conclusion derived during a joint U.S—Turkey expedition on the R/VKrorr on the dramatic variations of the O2–H2S zone in the Black Sea observed over the last 20 years. This conclusion is shown to be invalid since it was based on a comparison of data obtained at two stations only (in 1969 and 1988) that was made in various regions and in different seasons. Examples are provided for the inter-seasonal and mesoscale variations of hydrophysical and hydrochemical characteristics in the O2–H2S zone which, as to their scales, are comparable to or even exceed the variations registered during the expedition ofKrorr.Translated by Mikhail M. Trufanov.  相似文献   
977.
Sea-surface microlayer samples were collected from six nearshore areas receiving different amounts of anthropogenic inputs. The samples were analyzed for selected trace metals, chlorinated hydrocarbons, and polycyclic aromatic hydrocarbons. The relative toxicities of the samples were determined with fish embryo bioassays.Contaminant concentrations generally increased from offshore to the inshore stations. Contaminant concentrations were several orders of magnitude higher in microlayer samples from the highly industrialized Los Angeles and Long Beach harbors compared to samples from a site 15km offshore. Microlayer samples from the inshore stations were significantly more toxic, and induced significantly more developmental abnormalities and chromosome aberrations, than samples from the offshore stations.  相似文献   
978.
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   
979.
Our intent has been to develop rapid and sensitive bioassay procedures for laboratory and field applications based on hemolymph factors in animals such as the bay mussel, Mytilus edulis. We found that mussel hemolymph could be easily and repeatedly sampled from individual animals in sufficient amounts to allow analyses for lysozyme, proteolytic activity, total protein and hemocyte counts. In static tests there seemed to be graded responses indicating release of increasing amounts of the above factors into the hemolymph in roughly direct proportion to Cu2+ concentration at lethal and sublethal levels. We interpreted this to be evidence for increased lysosomal and cellular disruption as cupric ion exposure was increased or prolonged. At the same time, Cu2+ concentrations in the mussel hemolymph increased up to an order of magnitude above ambient in the range of 26 to 267 ppb. We felt that this was evidence for the release of Cu-binding proteins into the mussel hemolymph. Simultaneously with the above events the serum granulocytes increased in numbers above control values by factors of 3 or 4 in response to copper challenge while macrophage (terminology of Moore & Lowe, 1977) counts, including controls, declined precipitously.  相似文献   
980.
This paper discusses the possibility of measurement of the current velocity vector characteristics averaged over the time of continuous regular down-up probings from a moving carrier. The measurements can be carried out either from a moving vessel or from a helicopter, floating on or hovering above the sea surface. As an illustration for the suggested technique,in situ observations compiled by a free-component (±XYZ) VEGA-3 probe in the Guiana current region in March 1990 are provided. Comparison of the results with buoy data shows good agreement within the accuracy limits of the instruments employed.Translated by Vladimir A. Puchkin.  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