全文获取类型
收费全文 | 2464篇 |
免费 | 224篇 |
国内免费 | 487篇 |
专业分类
测绘学 | 1030篇 |
大气科学 | 66篇 |
地球物理 | 266篇 |
地质学 | 1072篇 |
海洋学 | 319篇 |
天文学 | 5篇 |
综合类 | 264篇 |
自然地理 | 153篇 |
出版年
2024年 | 21篇 |
2023年 | 44篇 |
2022年 | 110篇 |
2021年 | 143篇 |
2020年 | 125篇 |
2019年 | 131篇 |
2018年 | 75篇 |
2017年 | 158篇 |
2016年 | 162篇 |
2015年 | 157篇 |
2014年 | 172篇 |
2013年 | 148篇 |
2012年 | 158篇 |
2011年 | 187篇 |
2010年 | 151篇 |
2009年 | 139篇 |
2008年 | 109篇 |
2007年 | 142篇 |
2006年 | 134篇 |
2005年 | 117篇 |
2004年 | 81篇 |
2003年 | 82篇 |
2002年 | 43篇 |
2001年 | 57篇 |
2000年 | 55篇 |
1999年 | 30篇 |
1998年 | 42篇 |
1997年 | 28篇 |
1996年 | 35篇 |
1995年 | 22篇 |
1994年 | 17篇 |
1993年 | 16篇 |
1992年 | 17篇 |
1991年 | 11篇 |
1990年 | 18篇 |
1989年 | 6篇 |
1988年 | 12篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1978年 | 1篇 |
排序方式: 共有3175条查询结果,搜索用时 15 毫秒
151.
ZHANG ZuxunHU XiangyunZHANG Jianqing 《地球空间信息科学学报》2001,4(4):49-55
1 IntroductionAtpresent,manycommercialdigitalphotogram metricworkstations (DPW )havebeendevelopedandappliedintopracticalproduction .Mostofthemcanautomatically generatedigitalterrainmodel(DTM)anddigitalortho_image (DOM ) ,buttherearenotanysystemswhichcanautoma… 相似文献
152.
153.
154.
155.
156.
Partitioning of heavy metals on soil samples from column tests 总被引:3,自引:0,他引:3
R. N. Yong W. Z. W. Yaacob S. P. Bentley C. Harris B. K. Tan 《Engineering Geology》2001,60(1-4):307-322
In this study, column tests were used to determine the retention capability of three types of estuarine alluvia collected adjacent to landfill sites in South Wales. Selective sequential extraction (SSE) was used to study the retention mechanisms of heavy metals in the soil columns obtained from leaching experiments. Acid digestion was later used to check the validity of the SSE results. Breakthrough curves show good retention of heavy metal ions (Pb, Cu, and Zn) by all soils, where almost 99% of heavy metals were retained with the Ce/Co values in the order of 10−3. The retention strength of these soils was observed to be constant up to five pore volumes (PV). This corresponds with the pH of the effluents and pore water of soil slices, which also show good buffering capacity against very acidic leachate up to 5PV. The heavy metal extraction profiles from SSE show very similar trends with the retention profiles from the leaching experiments, where heavy metals were retained mainly at the top part where the leachate entered the column. SSE indicates qualitatively that heavy metals precipitated with carbonates and amorphous materials (oxides/hydroxides) are higher than heavy metal retention via exchangeable mechanisms. The mass balance calculation gives range of deviation of 1–16% of the total soil extraction. The distribution of the heavy metals with various soil constituents are ranked in the following order: Carbonates>Amorphous oxides hydroxides>Organic matter>Exchangeable phases. 相似文献
157.
158.
Sediments of eight groyne fields along the middle course of the River Elbe (river km 287?390) were geochemically studied. The 78 sediment samples were analysed for pH and grain size distribution. The grain size fraction < 2 μm was used for mineralogical and chemical analysis: semiquantitative clay mineral analysis; total element content (Al, Ca, Fe, K, Mn, Cd, Cr, Cu, Ni, Pb, Zn), total inorganic and organic C, and bonding form fractionation with a six‐step sequential chemical extraction. The latter was performed on selected samples (n = 32). The sediments along the Elbe's course are still contaminated with heavy metals far above the local geogenic background level. An enrichment factor of more than 15 was calculated for zinc. Cr and Ni are the elements with the lowest enrichment. The bonding form analysis of selected heavy metals shows a dominance of relatively immobile bonding forms, e. g. the moderately reducible and the residual fraction, which implies a relative low mobility potential. Only Zn poses a higher potential threat to the environment, since it has a higher percentage of the first three extracted phases: adsorbed, carbonate, and easily reducible fraction. 相似文献
159.
采用马弗炉将样品与NaOH混合进行熔融煅烧,热去离子水提取、离心、稀释后过OnGuard Ⅱ H柱和过滤膜进行前处理,抑制型电导离子色谱法检测,测定了Ta2O5和Nb2O5的氟离子、氯离子和硫酸根离子。该方法对三种被测阴离子的检测限(s/N=3)在0.15~0.70μg/g(以固体样品实际浓度计)或0.136~0.623μg/L(以溶液浓度计),标准曲线线性范围均在两个数量级以上,方法的精密度(RSD,n=7)小于5.46%,回收率为88%~106%,具有灵敏度高、选择性好、重现性佳、对环境友好等特点,用于实际样品的检测,结果令人满意。 相似文献
160.
1∶10 000地形图植被要素的采集和更新较为复杂,考虑国土部门现有的现势性较强的土地利用现状数据可以用来补充1∶10 000地形图中的植被信息,积极开展试验.本文作者利用广东省现有的土地利用现状数据,结合航空(卫星)正射影像图、1∶10 000矢量数据进行了充分试验,走出了一条植被更新的新路子,为省级基础地理信息数据库的完善和更新提供了一种新方法. 相似文献