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   40860篇
  免费   5753篇
  国内免费   7928篇
测绘学   8473篇
大气科学   7514篇
地球物理   8739篇
地质学   14196篇
海洋学   4761篇
天文学   2023篇
综合类   3217篇
自然地理   5618篇
  2024年   172篇
  2023年   462篇
  2022年   1182篇
  2021年   1544篇
  2020年   1695篇
  2019年   2079篇
  2018年   1449篇
  2017年   2022篇
  2016年   1932篇
  2015年   2047篇
  2014年   2488篇
  2013年   3008篇
  2012年   2600篇
  2011年   2706篇
  2010年   2117篇
  2009年   2597篇
  2008年   2621篇
  2007年   2908篇
  2006年   2732篇
  2005年   2208篇
  2004年   2084篇
  2003年   1720篇
  2002年   1369篇
  2001年   1199篇
  2000年   1078篇
  1999年   997篇
  1998年   933篇
  1997年   772篇
  1996年   658篇
  1995年   574篇
  1994年   506篇
  1993年   466篇
  1992年   313篇
  1991年   258篇
  1990年   177篇
  1989年   185篇
  1988年   145篇
  1987年   85篇
  1986年   76篇
  1985年   69篇
  1984年   40篇
  1983年   17篇
  1982年   36篇
  1981年   28篇
  1980年   28篇
  1979年   17篇
  1977年   23篇
  1976年   27篇
  1973年   20篇
  1971年   17篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
61.
The investigation of mineral, granulometric and chemical composition of sediments of the River Krka estuary (Yugoslavia) were performed in order to elucidate the origin of the sediments and the pattern of sedimentation. Estuarine surface sediments were found to be fine-grained with a bimodal distribution. Environmental conditions in estuarine sediments favour conservation of the organic matter (anoxic conditions). The carbohydrates in the sediments were investigated to determine whether they are of terrigenous or authigenous origin. Glucose, galactose, mannose, xylose, rhamnose, glucosamine and glucuronic acid were detected in the sediments. Their mutual relationship indicates a preferentially terrigenous source of sedimented organic material in estuarine sediments.  相似文献   
62.
63.
Measurements of salinity perturbations in a partially mixed estuary have been used to evaluate the usefulness of an inductive salinometer and to determine some of the characteristics of the salinity perturbations. The salinometer performed satisfactorily under most conditions. Although internal wave like effects were present, the turbulence fluctuations were dominant. The salinity fluctuations and the turbulent fluxes sw and su were found to behave in a manner similar to the density fluctuations in a thermally stratified atmospheric boundary layer and a laboratory open channel flow. A quadrant analysis suggested that the contribution of each quadrant to the turbulent flux changed with Ri. The turbulence parameters ν and cγ were found to decrease and increase respectively as Ri increases.  相似文献   
64.
1 INTRODUCTIONThe South China Sea (SCS) is a semi-enclosedmarginal sea in western North Pacific Ocean withvery complex topography and is the important pas-sage connecting the Pacific and Indian Oceans. Ithas great impact to the global climate and a greatinterest of many oceanography researchers. Twodominant surface hydrographic and circulation fea-tures in the northern SCS are a strong fresh waterexpansion and a warm and high-salinity seawaterintrusion such as the SCS Diluted Water…  相似文献   
65.
66.
Motivated by recent high-resolution observations of the solar surface, we investigate the problem of non-linear magnetoconvection in a three-dimensional compressible layer. We present results from a set of numerical simulations which model the situation in which there is a weak imposed magnetic field. This weak-field regime is characterized by vigorous granular convection and spatially intermittent magnetic field structures. When the imposed field is very weak, magnetic flux tends to accumulate at the edges of the convective cells, where it forms compact, almost 'point-like' structures which are reminiscent of those observed in the quiet Sun. If the imposed field is slightly stronger, there is a tendency for magnetic flux to become concentrated into 'ribbon-like' structures which are comparable to those observed in solar plages. The dependence of these simulations upon the strength of the imposed magnetic field is analysed in detail, and the concept of the fractal dimension is used to make a further, more quantitative comparison between these simulations and photospheric observations.  相似文献   
67.
青藏块体东北缘地壳水平运动状态   总被引:10,自引:6,他引:4  
应用青藏块体东北缘1999~2003年多期GPS观测资料,计算了不同时段GPS点水平运动速率。通过分析发现:甘青块体可分为东部块体和西部块体,东、西部块体的运动状态存在明显的差异;受2001年11月14日昆仑Ms8.1地震的影响,震后地壳运动状态发生了明显的改变。  相似文献   
68.
A number of different lahars have been recognized from a systematic survey of a mapping project. The high setting temporamre feature of the deposits indicates a relationship between the lahar and the Millennium eruption event of Tianchi Volcano. The lahars caused a dramatic disaster. Recognize of the huge avalanche scars and deposits around Tianchi Volcano imply another highly destructive hazard. Three types of different texture of the avalanche deposits have been recognized. There was often magma mixing processes during the Millennium eruption of Tianchi Volcano, indicating a mixing and co-eruption regime of the eruption.  相似文献   
69.
The UV spectra of mixture solutions consisting of tyrosine,tryptophane,phenylalanine,cystine,histidineand 3,4-dihydroxyl phenylalanine have been measured.The numbers,identities and concentrations of theamino acids in the mixtures have been determined successfully using target factor analysis.The effectsof the wavelength range and the selected sampling interval on the results are discussed.Twenty-fivesynthetic mixture samples have been analysed successfully.The average recoveries are 98·9 for Tyr,96·5for Trp,105·6 for Phe,98·1 for Cys,98·9 for His and 106·4 for Di-phe.The results obtained are ingood agreement with those obtained by the Kalman filter method.  相似文献   
70.
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