全文获取类型
收费全文 | 8019篇 |
免费 | 1594篇 |
国内免费 | 2296篇 |
专业分类
测绘学 | 724篇 |
大气科学 | 1674篇 |
地球物理 | 1855篇 |
地质学 | 4254篇 |
海洋学 | 1161篇 |
天文学 | 396篇 |
综合类 | 825篇 |
自然地理 | 1020篇 |
出版年
2024年 | 43篇 |
2023年 | 183篇 |
2022年 | 396篇 |
2021年 | 507篇 |
2020年 | 363篇 |
2019年 | 412篇 |
2018年 | 473篇 |
2017年 | 409篇 |
2016年 | 458篇 |
2015年 | 429篇 |
2014年 | 515篇 |
2013年 | 535篇 |
2012年 | 493篇 |
2011年 | 495篇 |
2010年 | 519篇 |
2009年 | 492篇 |
2008年 | 527篇 |
2007年 | 471篇 |
2006年 | 407篇 |
2005年 | 337篇 |
2004年 | 266篇 |
2003年 | 217篇 |
2002年 | 231篇 |
2001年 | 214篇 |
2000年 | 218篇 |
1999年 | 308篇 |
1998年 | 295篇 |
1997年 | 262篇 |
1996年 | 265篇 |
1995年 | 201篇 |
1994年 | 179篇 |
1993年 | 136篇 |
1992年 | 117篇 |
1991年 | 92篇 |
1990年 | 96篇 |
1989年 | 75篇 |
1988年 | 58篇 |
1987年 | 55篇 |
1986年 | 44篇 |
1985年 | 27篇 |
1984年 | 22篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 4篇 |
1976年 | 3篇 |
1954年 | 2篇 |
1938年 | 2篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
101.
湖子地区位于NNE向诸广-新兴铀成矿带与近EW向大东山-漳州大断裂复合部位,是华南早、晚两期铀成矿热液活动叠加区、放射性高场区,既有"硅化带大脉"型铀矿产出,又有"交点"型铀矿存在,找矿前景良好.文章在论述下庄矿田铀成矿地质环境、铀成矿特征及铀矿定位条件基础上,分析了湖子地区铀成矿条件与找矿前景,指出该区今后铀矿找矿方向是:① 6009号硅化断裂带,在其北段找硅化带大脉型铀矿,在其南段找"交点"型铀矿;②新桥-下庄硅化断裂带和6009号带之间成矿部位,寻找硅化带型和"交点"型铀矿;③NW向、近EW向辉绿岩脉与NNE向、NE向构造交汇部位(交点),寻找"交点"型铀矿. 相似文献
102.
103.
104.
105.
Cluster correspondence analysis examines the spatial autocorrelation of multi-location events at the local scale. This paper
argues that patterns of cluster correspondence are highly sensitive to the definition of operational neighborhoods that form
the spatial units of analysis. A subset of multi-location events is examined for cluster correspondence if they are associated
with the same operational neighborhood. This paper discusses the construction of operational neighborhoods for cluster correspondence
analysis based on the spatial properties of the underlying zoning system and the scales at which the zones are aggregated
into neighborhoods. Impacts of this construction on the degree of cluster correspondence are also analyzed. Empirical analyses
of cluster correspondence between paired vehicle theft and recovery locations are conducted on different zoning methods and
across a series of geographic scales and the dynamics of cluster correspondence patterns are discussed.
相似文献
106.
评价生物气生成量、生成期的元素平衡法及其应用 总被引:2,自引:0,他引:2
生物气的生成期对其成藏有至关重要的制约作用,但目前国内外尚缺少可信、有效方法来对此进行评价。针对这一难题,考虑到无论生物气的生成机理如何,都是一个有机元素之间的物质平衡过程,文章探索并建立了评价生物气生成量的元素平衡法,并利用松辽盆地大量的实际分析数据,对这一评价方法(模型)进行了标定和应用。结果表明,松辽盆地生物气的生成可能主要发生在800m以浅的埋深条件下;区内源岩生物气的生成量约为285.0×1012m3;生物气的主要生成期在嫩江组沉积末期之前。 相似文献
107.
Macrofaunal Spatial Patterns in Relationship to Environmental Variables in the Richibucto Estuary,New Brunswick,Canada 总被引:1,自引:0,他引:1
Estuarine macrobenthos respond to a variety of environmental gradients such as sediment type and salinity, and organic enrichment.
A relatively new influence, organic loading from suspended bivalve culture, has the potential to alter this response. A study
on soft-bottom macrobenthic communities was carried out in the Richibucto estuary (46°40′N, 64°50′W), New Brunswick, Canada,
with samples collected from 18 stations in late September and early October 2006. The site consisted of a large tidal channel
originating upstream in a small river. The channel was punctuated by bag culture of oysters along its length. A total of 88
species were recorded. The mean values of abundance, species richness, and diversity (H′) of macrofauna were 11,199 ind. m−2 (ranged from 4,371 to 19,930 ind. m−2), 23.4 species grab−1 and 3.29 grab−1, respectively. In general species richness and H′ increased from the upper estuary to the estuarine mouth. Multivariate analyses clearly exhibited the spatial distribution
in community structure, which coincided with the locations along the estuary (the upper, the lower and the mouth), as well
as inside and outside the channel. Species richness and diversity H′ showed strong positive correlations with salinity (21.2–25.2 ppt), and abundance was positively correlated with water depth
(1.0–4.5 m). Abundance and species richness were negatively correlated with both of silt–clay fraction (3.3–24.8%) and sorting
(σI). Species richness was also negatively correlated with organic content (1.9–12.7%). The BIO-ENV analyses identified silt–clay
fraction, σI and salinity as the major environmental variable combination influencing the macrofaunal patterns, and silt–clay fraction
as the single best-correlated variable. 相似文献
108.
109.
本文在分析GPS RTK定位工作模式的基础上,以苏州市为研究对象,讨论了"多对多"模式GPS台站网系统设计,研究了相应的操作规程,并进行了该模式下的定位试验,对定位结果的精度进行了分析,最后给出了结论。 相似文献
110.