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   1193篇
  免费   114篇
  国内免费   264篇
测绘学   82篇
大气科学   121篇
地球物理   482篇
地质学   580篇
海洋学   123篇
天文学   41篇
综合类   40篇
自然地理   102篇
  2022年   14篇
  2021年   11篇
  2020年   11篇
  2019年   11篇
  2018年   19篇
  2016年   15篇
  2015年   12篇
  2014年   23篇
  2013年   21篇
  2012年   55篇
  2011年   66篇
  2010年   18篇
  2009年   29篇
  2008年   51篇
  2007年   51篇
  2006年   71篇
  2005年   56篇
  2004年   54篇
  2003年   36篇
  2002年   56篇
  2001年   45篇
  2000年   60篇
  1999年   22篇
  1998年   26篇
  1997年   29篇
  1996年   20篇
  1995年   39篇
  1994年   47篇
  1993年   42篇
  1992年   33篇
  1991年   56篇
  1990年   50篇
  1989年   45篇
  1988年   43篇
  1987年   32篇
  1986年   29篇
  1985年   31篇
  1984年   22篇
  1983年   29篇
  1982年   13篇
  1981年   7篇
  1980年   18篇
  1965年   8篇
  1964年   8篇
  1959年   10篇
  1958年   21篇
  1957年   14篇
  1955年   7篇
  1954年   8篇
  1930年   6篇
排序方式: 共有1571条查询结果,搜索用时 0 毫秒
121.
海洋底质图     
根据第一个五年国民经济发展计划所拟定的关于扩大巴伦支海工业渔捞场的计划,在三十年代初期给苏维埃海洋地质学提供了编制底质图的任务。同时,为了支援我国的工业及保证航海的需要,也提出了控制苏联富饶的海洋资源的任务。 还在上古时代、在航海的早期,就萌发了对海底成分和特性的兴趣。我国在十八世纪、开始编制标有底质特性的原始航行图。以后,在所有国家的航行图上,通常注明底质的名称和它的颜色、或者其它特点的标记;这种底质标记的方法,目前还在采用,但它的缺  相似文献   
122.
IntroductionThe Late Triassic strata andflora developed andwell outcropped in southern Pri morye,Russia.Thestrata are marine and non-marine alternate for eachother and yield abundant mollusk and plant fossilsinwhich the Late Triassic Mongugai flora is well-known in the world.Kryshtofovich(1910,1921,1924)and Kryshtofovich&Prynada(1932)studiedthis florainthe earlier ti me,and consequently,Sre-brodolyskaja(1958,1961,1968),Schorokhova(1975,1977,1997,2004)and Krassilov&Schorokhova(1970,1975)ma…  相似文献   
123.
编写海岸水册是研究海岸水文和地貌的最终目的。海岸水册总括海的沿岸水文和地貌的全部费料(包括河口)。水册是修建商港、军港,规划商业航行和军事航行、鱼业、沿岸城市经济和设计海堤等工作所必需的。许多海洋国家最近才开始整理多年视察所得的零散的材料,编纂水册。苏联已编好了黑海水册,其他海岸水册也在编写中。  相似文献   
124.
Data of the hydrolysis of adenosine 5'-triphosphate have been re-evaluated using a computer program thatnumerically integrates the differential rate equations within a routine that optimizes rate coefficients givena suitable model and concentration versus time data. The model is tested by calculation of Hamilton R-values, the Fisher F-statistic, a sensitivity analysis,the standard errors on the rate coefficients and by constructing contour maps of the objective functionversus two rate coefficients. An optimization using only phosphate concentration data cannot distinguish between a model in whichadenosine 5'-monophosphate is formed predominantly directly with a molecule of pyrophosphate, andone in which it is formed via adenosine 5'-diphosphate. A more accurate set of rate coefficients iscalculated from existing data and the relative importance of the two paths determined.  相似文献   
125.
In order to simulate a possible natural administration route of xenoestrogens male flounder Platichthys flesus were exposed via the diet to the alkylphenol 4-tert-octylphenol. Treatment with 4-tert-octylphenol (10, 50 and 100 mg OP kg(-1) BW) or 17beta-estradiol (0.05 mg kg(-1) BW) every second day during a period of 11 days resulted in a significant increase in plasma vitellogenin (Vtg) concentrations. The induction of Vtg was greatest in the fish receiving 50 mg OP kg-' BW. A significant accumulation of 4-tert-octylphenol was found in liver and muscle tissue of the OP treated groups. The tissue concentrations of 4-tert-octylphenol and the plasma vitellogenin concentration were positively correlated. The results show that 4-tert-octylphenol accumulates in liver and muscles of flounder P. flesus, and exerts estrogenic effects such as vitellogenin induction.  相似文献   
126.
Recently, detection of discrete features in the X-ray afterglow spectra of GRB 970508 and GRB 970828 was reported. The most natural interpretation of these features is that they are redshifted Fe K emission complexes. The identification of the line emission mechanism has drastic implications for the inferred mass of radiating material and hence the nature of the burst site. X-ray spectroscopy provides a direct observational constraint on these properties of gamma-ray bursters. We briefly discuss how these constraints arise in the context of an application to the spectrum of GRB 970508.  相似文献   
127.
The grazing pressure of the macrofaunal invertebrates associated with the biomass of Ulva rigida in the Venice lagoon, their species composition and relationship with environmental variables have been studied. Fifteen sampling campaigns were carried out during different seasons both in the central basin of the lagoon, dominated by macroalgae (especially U. rigida C. Ag.) and in the southern basin, prevalently populated by seagrasses (especially Zostera marina L.). Replicate experiments were conducted in the field by exposing Ulva fronds in net cages of 10 and 1 mm (control) mesh-sizes to allow or prevent grazer entrance. The grazing pressure was determined as Ulva growth rate difference in the cages. In the absence of invertebrate herbivores, Ulva exhibited per cent relative growth rates (%RGRs) ranging from 1.5 to 9.5% day(-1), whereas in their presence the %RGRs were significantly lower (from -2.5 to 3.4% day(-1)) and frequently negative, especially in the station dominated by macroalgae. In this area, peak grazing rates and macrofauna biomasses of up to 8.6% day(-1) and 1,480 g m(-2) fwt (84.4 ash-free dry weight), respectively, were found. On the whole, during in field experiments in the Ulva-dominated station, herbivores removed an amount of biomass whose percentage ranged from 59 to 165% (mean: 103%) of the biomass yield (grazers excluded) found in the cages. These results suggest the possibility that grazers could act as an important factor affecting Ulva production in the Venice lagoon. Macrofauna populations were analysed by means of multivaliate techniques applied to biological variables only and biological and environmental variables together. Data of individual abundance, after a log(x + 1) transformation and the calculation of the Bray-Curtis matrix, were classified using the Cluster Analysis and ordinated by means of the Non-Metric Multidimensional Scaling (MDS) technique, in accordance with the strategies used in the study of multispecies distributions. Finally, biological and environmental variables were analysed together by means of correlation matrices and the Principal Component Analysis.  相似文献   
128.
129.
<正> 本书论及了近年来近景摄影测量重大发展的状况。近景摄影测量并不仅仅涉及地形测图,而是有着广泛应用领域的测量技术。本书在向从事测量和数据获取的专业人员讲述近景摄影测量原理及用途。第一章概述近景摄影测量的起源,早期模拟方法的应用和近期解析技术的发展。当读者将注意力转向实用领域时便知,过去在近景摄影测量精度方面的研究限多,而对时间和费用两个“参数”的考虑则不足。为此,作者强调指出,要使近景摄影测量普遍用于生产过程,则应把研究重点转到时间和  相似文献   
130.
本文把为变形分析设计的一个数学模型用于大地测量控制网平差。估计一等控制点的相对速度被认为是其数据内容可靠性的有效度量,控制网是根据逐次分批测量的参与点划分,一个动力网固有排列缺陷问题作了详细的讨论,包括所提出解法的说明。  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