全文获取类型
收费全文 | 10915篇 |
免费 | 2524篇 |
国内免费 | 3624篇 |
专业分类
测绘学 | 1381篇 |
大气科学 | 2043篇 |
地球物理 | 2450篇 |
地质学 | 6764篇 |
海洋学 | 1474篇 |
天文学 | 325篇 |
综合类 | 1165篇 |
自然地理 | 1461篇 |
出版年
2024年 | 84篇 |
2023年 | 253篇 |
2022年 | 616篇 |
2021年 | 764篇 |
2020年 | 596篇 |
2019年 | 660篇 |
2018年 | 714篇 |
2017年 | 656篇 |
2016年 | 651篇 |
2015年 | 682篇 |
2014年 | 684篇 |
2013年 | 827篇 |
2012年 | 854篇 |
2011年 | 792篇 |
2010年 | 854篇 |
2009年 | 770篇 |
2008年 | 793篇 |
2007年 | 739篇 |
2006年 | 653篇 |
2005年 | 536篇 |
2004年 | 418篇 |
2003年 | 338篇 |
2002年 | 339篇 |
2001年 | 344篇 |
2000年 | 322篇 |
1999年 | 313篇 |
1998年 | 261篇 |
1997年 | 254篇 |
1996年 | 220篇 |
1995年 | 165篇 |
1994年 | 158篇 |
1993年 | 153篇 |
1992年 | 118篇 |
1991年 | 92篇 |
1990年 | 66篇 |
1989年 | 67篇 |
1988年 | 62篇 |
1987年 | 35篇 |
1986年 | 35篇 |
1985年 | 18篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 13篇 |
1975年 | 5篇 |
1960年 | 2篇 |
1958年 | 7篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
371.
Micro-communities are supposed to have more potential functions of biodegradation of polysaccharides than single strain; however, the intestinal micro-communities involved in the biodegradation of Enteromorpha polysaccharides (EP) were seldom reported. In order to obtain the EP-degrading micro-community, the intestines of Siganus oramin was obtained to isolate the micro-communities, which were enriched by 0.3% of EP as the sole carbon source. A stable micro-community with EP degradative capability was achieved after seven generations of subculture, named H1. Results showed that H1 was able to degrade 75% of EP within 24 hours, and the activity of EP lyases reached 500 U mL?1 in 32 hours. With denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene clone library analysis, ten bacteria closely related to Marinomonas pontica, Microbacterium sp., Leucobacter chironomi, Cyclobacterium sp., Algoriphagus winogradskyi, Pseudoalteromonas sp. and Vibrio sp. were determined. Furthermore, compared with the DGGE bands sequence and the clone library analysis, the dominant bacteria of the EP-biodegrading micro- community were Pseudoalteromonas sp. and Vibrio sp., with the respective proportion of 38% and 46%, and they should play an important role in EP degradation together with other degrading bacteria in the micro-community H1. 相似文献
372.
373.
An Investigation of Digestion Methods for Trace Elements in Bauxite and Their Determination in Ten Bauxite Reference Materials Using Inductively Coupled Plasma‐Mass Spectrometry
下载免费PDF全文
![点击此处可从《Geostandards and Geoanalytical Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wen Zhang Liang Qi Zhaochu Hu Cunjiang Zheng Yongsheng Liu Haihong Chen Shan Gao Shenghong Hu 《Geostandards and Geoanalytical Research》2016,40(2):195-216
Trace elements from samples of bauxite deposits can provide useful information relevant to the exploration of the ore‐forming process. Sample digestion is a fundamental and critical stage in the process of geochemical analysis, which enables the acquisition of accurate trace element data by ICP‐MS. However, the conventional bomb digestion method with HF/HNO3 results in a significant loss of rare earth elements (REEs) due to the formation of insoluble AlF3 precipitates during the digestion of bauxite samples. In this study, the digestion capability of the following methods was investigated: (a) ‘Mg‐addition’ bomb digestion, (b) NH4HF2 open vessel digestion and (c) NH4F open vessel digestion. ‘Mg‐addition’ bomb digestion can effectively suppress the formation of AlF3 and simultaneously ensure the complete decomposition of resistant minerals in bauxite samples. The addition of MgO to the bauxite samples resulted in (Mg + Ca)/Al ratios ≥ 1. However, adding a large amount of MgO leads to significant blank contamination for some transition elements (V, Cr, Ni and Zn). The NH4HF2 or NH4F open vessel digestion methods can also completely digest resistant minerals in bauxite samples in a short period of time (5 hr). Unlike conventional bomb digestion with HF/HNO3, the white precipitates and the semi‐transparent gels present in the NH4HF2 and NH4F digestion methods could be efficiently dissolved by evaporation with HClO4. Based on these three optimised digestion methods, thirty‐seven trace elements including REEs in ten bauxite reference materials (RMs) were determined by ICP‐MS. The data obtained showed excellent inter‐method reproducibility (agreement within 5% for REEs). The relative standard deviation (% RSD) for most elements was < 6%. The concentrations of trace elements in the ten bauxite RMs showed agreement with the limited certified (Li, V, Cr, Cu, Zn, Ga, Sr, Zr and Pb) and information values (Co, Ba, Ce and Hf) available. New trace element data for the ten RMs are provided, some of which for the first time. 相似文献
374.
375.
对湖北大洪山地区一套紫红色砂-砾岩系沉积年代的再认识——碎屑锆石U-Pb年龄及其地质意义 总被引:1,自引:0,他引:1
湖北大洪山地区花山群六房咀组之上不整合覆盖了一套紫红色砂-砾岩。这套岩石的沉积时代存在争议,一种观点认为是南华纪早期;另一种观点认为是晚侏罗世。利用LA-ICP-MS分析技术,对这套碎屑沉积岩进行了碎屑锆石U-Pb测年,获得有效年龄数据125组,年龄值变化范围较大(3223~771Ma),主要集中于新太古代末—古元古代早期(约2500Ma)、古元古代(约2000Ma)和新元古代(约800Ma)3个时间段。对比鄂东南地区和三峡地区莲沱组岩石学特征和碎屑锆石年龄分布特征,认为其具有相似的物源,这套岩系沉积时代应该为南华纪早期而非晚侏罗世。综合分析扬子地块的前寒武纪年龄,认为扬子地块可能存在大量未岀露的新太古代末—古元古代早期(约2500Ma)基底,约2500Ma的岩石应该是扬子地块深部基底的重要组成部分。扬子地块存在广泛的古元古代(约2000Ma)岩浆活动,这期岩浆活动可能是Columbia超大陆聚合在扬子地块的响应。新元古代(约800Ma)扬子地块北缘存在Rodinia超大陆裂解同期裂谷,裂谷内基性岩可能为大洪山地区南华纪地层中基性岩砾石的物源。 相似文献
376.
西藏改则县多龙矿集区发现岩墙岭蛇绿岩残片 总被引:2,自引:0,他引:2
西藏班公湖-怒江缝合带北缘多龙矿集区是青藏高原新近发现的具有超大型远景的、典型的富金斑岩型铜矿集区,其成岩成矿地质背景是解决班公湖-怒江洋构造演化的关键问题之一。近年来的区域地质调查研究发现,多龙矿集区南侧出露岩墙岭蛇绿岩残片,应该是班公湖-怒江蛇绿岩带的重要组成部分。岩墙岭蛇绿岩主要由席状岩墙群、枕状玄武岩和硅质岩组成,整体呈棱形或透镜体状断续分布于侏罗系复理石沉积内,构成典型的网结状构造。糜棱岩普遍发育在岩墙岭蛇绿岩和围岩的接触部位。综合前人研究成果,初步认为多龙矿集区早白垩世成岩成矿作用应该形成于增生楔之上伸展拉张的构造环境。岩墙岭蛇绿岩的发现和确定进一步约束了多龙矿集区成岩成矿地质背景,同时为班公湖-怒江缝合带的延伸及其构造演化的研究提供了新的线索。 相似文献
377.
378.
379.
380.