全文获取类型
收费全文 | 3190篇 |
免费 | 1781篇 |
国内免费 | 835篇 |
专业分类
测绘学 | 195篇 |
大气科学 | 68篇 |
地球物理 | 215篇 |
地质学 | 3719篇 |
海洋学 | 793篇 |
天文学 | 156篇 |
综合类 | 240篇 |
自然地理 | 420篇 |
出版年
2024年 | 43篇 |
2023年 | 108篇 |
2022年 | 207篇 |
2021年 | 197篇 |
2020年 | 198篇 |
2019年 | 264篇 |
2018年 | 263篇 |
2017年 | 91篇 |
2016年 | 118篇 |
2015年 | 145篇 |
2014年 | 169篇 |
2013年 | 197篇 |
2012年 | 212篇 |
2011年 | 205篇 |
2010年 | 164篇 |
2009年 | 246篇 |
2008年 | 212篇 |
2007年 | 191篇 |
2006年 | 98篇 |
2005年 | 127篇 |
2004年 | 151篇 |
2003年 | 157篇 |
2002年 | 131篇 |
2001年 | 122篇 |
2000年 | 123篇 |
1999年 | 116篇 |
1998年 | 148篇 |
1997年 | 140篇 |
1996年 | 160篇 |
1995年 | 162篇 |
1994年 | 157篇 |
1993年 | 167篇 |
1992年 | 163篇 |
1991年 | 145篇 |
1990年 | 110篇 |
1989年 | 114篇 |
1988年 | 28篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1972年 | 2篇 |
1960年 | 2篇 |
1958年 | 1篇 |
1945年 | 1篇 |
1941年 | 1篇 |
排序方式: 共有5806条查询结果,搜索用时 187 毫秒
53.
54.
本文建立了国土资源评价的指标系统,应用“三角形法”进行了综合评价,高度概括了区域国土资源的宏观特征。 相似文献
55.
Brian Gulson Karen Mizon Michael Korsch Honway Louie Michael Wu Jenny Stauber J. Michael Davis Alan Taylor 《中国地球化学学报》2006,25(B08):62-62
This is a 4-year longitudinal study to evaluate changes to the environment and exposure of young children associated with the introduction of methylcyclopentadienyl manganese tricarbonyl (MMT) into Australia in 2000. The cohort includes 57 females and 56 males; age range of 0.29 to 3.9 years. Samples are collected every 6 months from children in residences located at varying distances from major traffic thoroughfares in Sydney. Environmental samples: air, house and day care dustfall, soil, dust sweepings and gasoline. Samples from children: blood, urine, handwipes prior to and after playing outdoors, and a 6-day duplicate diet. All samples are analyzed for a suite of 20 elements using ICP-MS. Results are presented for the first three 6-month sampling periods for Pb and Mn. For dustfall accumulation, there was no significant change over the 3 sampling periods (time) for Pb or Mn, and a positive relationship between ‘traffic exposure' (traffic volume and proximity to the road) and Pb but not Mn. For handwipes, Pb and Mn in wipes taken from children after playing outdoors were usually significantly greater than for wipes taken prior to playing. There was no significant association between Pb or Mn in handwipes with traffic exposure. Dustfall accumulation was a significant predictor for Pb in the handwipes, and dust sweepings were a significant predictor of Mn in handwipes. 相似文献
56.
Yoko Fujikawa Daisuke Yoneda Atushi Minami Hiroshi Yashima Toshio Tonokai Sotoji Tani Masami Fukui Tatuhide Hamasaki Masataka Sugahara 《中国地球化学学报》2006,25(B08):113-113
Biological iron and manganese removal utilizing indigenous iron and manganese oxidizing bacteria (IRB hereafter) in groundwater can also be applied to arsenic removal according to our pilot-scale test. The arsenic removal probably occurred through sorption and complexation of arsenic to iron and manganese oxides formed by enzymic action of IRB. We investigated the chemical properties of iron and manganese oxides in IRB floc and the valence state of arsenic sorbed to the floc to clarify the mechanisms of the arsenic [especially As (Ⅲ)] removal. The floc samples were collected from two drinking water plants using IRB (Jyoyo and Yamatokoriyama, Japan), and our pilot - scale test site where arsenic and iron removal using IRB is under way (Mukoh, Japan). The Jyoyo and Yamatokoriyama IRB floc samples were subjected to As (Ⅲ) and As(Ⅴ) sorption experiments. The elemental composition of the floc samples was measured. XANES spectra were collected on As, Fe and Mn K-edges at synchrotron radiation facility Spring 8 (Hyogo, Japan). FT-IR and the X-ray diffraction spectra of the samples were also obtained. The IRB floc contained ca. 35 % Fe, 0.3%-3.5% Mn and 2%-6% P. The samples were highly amorphous and contained ferrihidrites and hydrated iron phosphate. According to XANES analyses of IRB, As associated with IRB was in +5 valence state when As (Ⅲ) (or As (Ⅴ)) was added in laboratory sorption test, Fe in +3 valence state, and Mn a mixture of+3 and +4 valence states. Small shift was observed in the XANES spectra of IRB on As K-edge as the equilibration time of the sorption experiment was increased. Gradual oxidation of a small amount of As (Ⅲ) associated with IRB or change in arsenic binding with sorption site were the probable mechanism. 相似文献
57.
58.
对PDC钻头冠部形状及不同的布齿密度和切削齿在不同的磨损状态下对PDC钻头切削齿受力的影响进行了分析;用相邻的3个切削齿之间的关系(不同的切削齿与切削齿之间的径向距离和切削齿之间的高度差)来分析PDC钻头冠部形状和切削齿布齿密度对切削齿受力的影响,以及将切削齿的磨损状态简化成与切削齿在钻头上装配方向垂直的平面来分析切削齿磨损状态对切削齿受力的影响。 相似文献
59.
介绍了一种新型齿形的复合片钻头,在硬致密泥岩中钻进,与常规复合片钻头相比,具有很高的钻进效率和高的钻头寿命,解决了泥岩钻进效率低的难题。 相似文献
60.
本文对影响南极细菌S-15-13生长和胞外多糖产量的主要环境因子进行了研究,同时采用16S rDNA序列分析及系统发育分析方法对其进行了分子鉴定。结果表明:菌株S-15-13最佳产糖条件为:培养时间,56h;培养温度,8℃;碳源,1.0%葡萄糖;NaCl浓度,3.0%;pH,6.0-7.0。16S rDNA序列分析和系统发育分析表明,菌株S-15-13属于假交替单胞菌属(Pseudoaltero- monas)。 相似文献