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   625篇
  免费   68篇
  国内免费   133篇
测绘学   8篇
大气科学   16篇
地球物理   81篇
地质学   297篇
海洋学   257篇
天文学   2篇
综合类   38篇
自然地理   127篇
  2024年   5篇
  2023年   11篇
  2022年   20篇
  2021年   21篇
  2020年   29篇
  2019年   25篇
  2018年   17篇
  2017年   29篇
  2016年   19篇
  2015年   20篇
  2014年   27篇
  2013年   31篇
  2012年   45篇
  2011年   35篇
  2010年   33篇
  2009年   37篇
  2008年   41篇
  2007年   41篇
  2006年   57篇
  2005年   35篇
  2004年   38篇
  2003年   33篇
  2002年   26篇
  2001年   18篇
  2000年   19篇
  1999年   15篇
  1998年   15篇
  1997年   18篇
  1996年   8篇
  1995年   14篇
  1994年   5篇
  1993年   12篇
  1992年   4篇
  1991年   2篇
  1990年   3篇
  1988年   1篇
  1987年   6篇
  1986年   7篇
  1985年   1篇
  1984年   2篇
  1982年   1篇
排序方式: 共有826条查询结果,搜索用时 804 毫秒
181.
陈军雄  张宏泽柏 《山地学报》2006,24(B10):282-287
高寒草甸氮素循环过程中的物理过程、化学过程和生物过程与土壤、植物的发生、发育紧密联系,因此对物理、化学、生物三个不同过程高寒草甸氮素循环的研究现状进行了分析。  相似文献   
182.
The effects of oxidation potential (Eh) and zinc sulphate on the separation of chalcopyrite from pyrite were investigated at pH 9.0. The flotation recovery of these minerals is Eh dependent with maximum separation obtained at 275 mV SHE. Zinc sulphate addition improved this mineral separation at an Eh value of 275 mV by selectively depressing pyrite flotation. A different result was obtained at lower Eh values where zinc sulphate addition improved chalcopyrite flotation but had no or little effect on pyrite flotation. These opposite effects of zinc sulphate on mineral flotation were reconciled by examining the surface species of these minerals. The selective depression of pyrite flotation by zinc sulphate was also confirmed in the flotation of two copper ores.  相似文献   
183.
Industrial processes involving multi-phase flows such as flotation require understanding of the relationships between bubbles, solid particles and the flow. Modern experimental tools are employed in this effort to measure with great accuracy the basic features of the motion of all three phases in turbulent flow. We employed a unique Digital Particle Image Velocimeter (DPIV) that can record with great accuracy and kHz temporal resolution, velocity vectors of all three phases, namely the fluid, the solid particles and the air bubbles. The interaction of these three phases was studied in homogeneous isotropic turbulence generated by cylindrical grids. Particles and bubbles were released into the turbulence and the motions of the three phases were monitored. The experimental results obtained in the present work were compared with the predictions of the models published in the literature.  相似文献   
184.
研究了氯化钠存在下氯化亚锡-十六烷基三甲基氯化铵体系对Os(Ⅳ)-三氯锡酸络阴离子的浮选行为。实验表明,在盐酸介质中,体系可以浮选分离Os(Ⅳ),其浮选率为95.2%。98.0%。方法加标回收率为94.0%-98.5%,精密度为2.1%-7.7%(RSD,n=5)。方法可用于从大量基体金属中分离Os(Ⅳ),对实际样品分离的分析结果与其他方法推荐值相符。  相似文献   
185.
包气带中原油的迁移和降解研究   总被引:16,自引:0,他引:16  
在石油的开采和集输过程中,常常有大量的原油抛洒和泄漏,这对土壤和植物地造成严重污染,本文通过大量野外和室内的原油渗透试验,含油地层的淋滤试验和石油的生物降解试验,来研究石油污染物在包气带中迁移,转化和降解规律,从而地下水石油污染的潜在性作出科学的评价。  相似文献   
186.
内蒙古大地构造分区及其特征   总被引:17,自引:0,他引:17  
依据内蒙古全区的地层资料,采用板块构造观点,依据建造类型、生物群特征、构造环境对内蒙古大地构造进行了分区。共划分了华北板块、西伯利亚板块、塔里木板块三个一级构造单元。华北地块、华北北部大陆边缘、华北西部大陆边缘、塔里木北东大陆边缘和西伯利亚东南大陆边缘五个二级构造单元。并进一步划分了火山型和非火山型被动陆缘等十个三级构造单元。对各单元特征进行了较为系统的介绍和论述,特别是融入了大量新的1/5万区调成果资料,在诸多方面有了新的认识。  相似文献   
187.
The distribution of ring-C monoaromatic and triaromatic steroid hydrocarbons of about fifty crude oils and sediments of various origins and ages were studied in order to test their validity as geochemical source and maturity parameters. Three ratios appeared to be useful maturity parameters, i.e. A/B cis to trans isomers in non-rearranged monoaromatics, mono/triaromatics and shortvs long-chain homologues. Four other variations may be considered as source parameters depending upon lithology or other palaeo-environmental conditions, i.e. rearranged vs non-rearranged monoaromatics, 5β/5α -methyl rearranged monoaromatics, carbon number distribution and occurrence of a yet unknown series of methylated triaromatic steroids. 5α-Methyl rearranged monoaromatics seem to be particularly important in anhydrites from sabkha environments. Recent identification of most aromatic steroid constituents occurring in geological samples confers on this class of compounds an increasing value as correlation parameters in geochemical studies.  相似文献   
188.
Immunological and biochemical techniques were used to investigate organic matter in microbial mats from Solar Lake (Sinai, Egypt). Antibodies, elicited in rabbits against samples taken at different depths from a core of these mats, were used for the detection of immunological determinants preserved in these samples. Special attention was given to an antiserum directed against a top mat fraction (3–10 mm depth) and an antiserum against a fraction from a lower section of the core (380–390 mm depth). Both antisera, tested in a dot-blot immunobinding assay, were found to give positive reactions with organic matter from different depths of the sediment. An immunohistochemical experiment with the antisera points to antigenic determinants on Recent and subfossil sheaths of Microcoleus. In addition, extracts of sediment samples were submitted to electrophoresis in polyacrylamide gels in order to characterize the separated macromolecules by immunological means. The results showed a rapid decrease in the number of antigenic determinants from Recent to subfossil samples. However, even in the deepest layers of the sediment (690–700 mm depth) intact biopolymers were detected.  相似文献   
189.
本文应用色谱-质谱和气相色谱等技术分析鉴定了辽河断陷盆地西部凹陷下第三系原油和生油岩饱和烃中的甾、萜烷等生物标记化合物。并利用甾、萜烷等生物标记化合物和其它地质、地球化学资料,讨论了油、岩的生物先体性质,将其做了分类对比,确定了沙河街组、东营组和前中生界潜山原油的原生性和次生性。  相似文献   
190.
姜波  李俊锋  张渊 《世界地质》2004,23(3):309-312
经对尾矿中绢云母试验研究,确定尾矿中回收绢云母的工艺采用先粗选后浮选的方法,同时加入捕收剂BK,抑制剂B—1和B—2,使绢云母的纯度达到98%,尾矿中绢云母产出率为6%。  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