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   93468篇
  免费   1575篇
  国内免费   1569篇
测绘学   3040篇
大气科学   6896篇
地球物理   18490篇
地质学   35609篇
海洋学   7156篇
天文学   17785篇
综合类   2342篇
自然地理   5294篇
  2022年   398篇
  2021年   699篇
  2020年   780篇
  2019年   829篇
  2018年   6287篇
  2017年   5476篇
  2016年   4629篇
  2015年   1544篇
  2014年   2262篇
  2013年   3790篇
  2012年   3169篇
  2011年   5603篇
  2010年   4465篇
  2009年   5638篇
  2008年   4983篇
  2007年   5206篇
  2006年   2941篇
  2005年   2551篇
  2004年   2648篇
  2003年   2496篇
  2002年   2166篇
  2001年   1857篇
  2000年   1773篇
  1999年   1391篇
  1998年   1490篇
  1997年   1394篇
  1996年   1099篇
  1995年   1144篇
  1994年   961篇
  1993年   872篇
  1992年   850篇
  1991年   759篇
  1990年   856篇
  1989年   717篇
  1988年   650篇
  1987年   814篇
  1986年   663篇
  1985年   855篇
  1984年   921篇
  1983年   863篇
  1982年   831篇
  1981年   727篇
  1980年   679篇
  1979年   611篇
  1978年   606篇
  1977年   552篇
  1976年   545篇
  1975年   500篇
  1974年   507篇
  1973年   471篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
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   
983.
Sea surface temperature and zooplankton, North Sea, 1948 to 1983   总被引:2,自引:0,他引:2  
  相似文献   
984.
985.
A 15-cm-thick carbonate substrate encrusted with ferromanganese oxides from the Vityaz Fracture Zone, Central Indian Ridge was analyzed to reconstruct the paleoceanography of the region. Based on the calcareous nannoplankton assemblage, an early Pliocene age has been assigned to the calcareous substrate. Among the nannoplankton, discoasters outnumber coccoliths and show signs of dissolution. The presence of certain species of benthic Foraminifera such as Uvigerina, Lenticulina, Bulimina and Bolivina, indicates the infringement of the oxygen minimum zone during the deposition of the carbonates. The occurrence of a Reticulofenestra pseudoumbilica zone of early Pliocene age suggests a change in depositional conditions coinciding with the time of formation of the large depositional hiatuses documented in sediment cores from adjacent basins of the western Indian Ocean. These hiatuses resulted from the prevalence of intermediate subsurface currents such as the Somali Current or the Western Boundary Current.  相似文献   
986.
High-resolution seismic profiles and petrographic data from surface and subsurface sediment samples from Mersin Bay, together with lithologic data from boreholes, were used to determine the origin and distribution of the pre- or early-Holocene unconformities in Mersin Bay (eastern Mediterranean). Reflectors corresponding to unconformities separate the younger, unconsolidated, marine transgressive sediments (Holocene) from the underlying, relatively coarser, consolidated sediments (Plio-Pleistocene). These unconformities correspond mainly to the erosional and subaerially deposited or later subaerially weathered land surfaces. These unconformities are probably related to the latest Pleistocene or earliest Holocene sea-level low stands.  相似文献   
987.
988.
Equations recently developed by Pitzer are applied to a seawater model on the assumption that only interactions between ions of opposite charge sign are significant. This model is shown to give good agreement with available experimental data for the osmotic coefficient and for the mean-ion activity coefficients of the major electrolyte components. The results are compared with the predictions of the ion-association model and with a number of models using the concept of specific ionic interaction. The relative merits of the various models are discussed. Pitzer's original equations are modified to enable the calculation of conventional single-ion activity coefficients. These values are compared with those obtained on the basis of alternative conventions and an encouraging measure of agreement is observed. It is concluded that the new model introduces a fluency into the specific interaction approach that should greatly facilitate the incorporation of trace components into future models.  相似文献   
989.
An acoustic locator—a sodar—is a unique instrument for getting the objective characteristics of the current state of the atmospheric boundary layer (ABL) owing to a combination of such properties as remoteness, mobility, resolution, and information content. This study demonstrates the capabilities of a sodar to obtain data on the second moments of the field of wind-velocity fluctuations, in particular, the profiles of momentum flux in the lower ABL, which are very important in practical applications. A corresponding method is described, and the results of its experimental verification and some examples of its application under the conditions of different ABL stratification are presented.  相似文献   
990.
Visualization of a collapsing vertical packet of patches in a laboratory experiment and the results of acoustical sounding under field conditions allowed us to discriminate the stage of its evolution which was previously unknown. It is defined by the variations of the horizontal dimensions of patches and their effective scattering surface with a period ofT=150–250/N, whereN is the Brunt-Väisälä frequency. The horizontal dimensions of patches can reach 40% of their final dimensions at the evolution stage discriminated.Translated by Mikhail M. Trufanov.  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