全文获取类型
收费全文 | 22746篇 |
免费 | 266篇 |
国内免费 | 244篇 |
专业分类
测绘学 | 557篇 |
大气科学 | 1894篇 |
地球物理 | 4806篇 |
地质学 | 7778篇 |
海洋学 | 2129篇 |
天文学 | 4525篇 |
综合类 | 67篇 |
自然地理 | 1500篇 |
出版年
2020年 | 164篇 |
2019年 | 166篇 |
2018年 | 334篇 |
2017年 | 326篇 |
2016年 | 464篇 |
2015年 | 318篇 |
2014年 | 495篇 |
2013年 | 1139篇 |
2012年 | 492篇 |
2011年 | 764篇 |
2010年 | 648篇 |
2009年 | 868篇 |
2008年 | 786篇 |
2007年 | 748篇 |
2006年 | 740篇 |
2005年 | 658篇 |
2004年 | 678篇 |
2003年 | 651篇 |
2002年 | 614篇 |
2001年 | 519篇 |
2000年 | 511篇 |
1999年 | 497篇 |
1998年 | 471篇 |
1997年 | 460篇 |
1996年 | 396篇 |
1995年 | 393篇 |
1994年 | 349篇 |
1993年 | 339篇 |
1992年 | 313篇 |
1991年 | 272篇 |
1990年 | 315篇 |
1989年 | 245篇 |
1988年 | 277篇 |
1987年 | 322篇 |
1986年 | 278篇 |
1985年 | 404篇 |
1984年 | 427篇 |
1983年 | 430篇 |
1982年 | 354篇 |
1981年 | 334篇 |
1980年 | 355篇 |
1979年 | 318篇 |
1978年 | 325篇 |
1977年 | 279篇 |
1976年 | 302篇 |
1975年 | 284篇 |
1974年 | 294篇 |
1973年 | 298篇 |
1972年 | 193篇 |
1971年 | 151篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Late Glacial and Neoglacial (Little Ice Age) deposits on the Humboldt Massif were analyzed for relative-age dating parameters, including geomorphic and weathering characteristics, geochemical and soil properties. The soil chronosequence, formed in chemically uniform parent materials, provides an important database to study soil evolution in a tropical alpine environment. Extractable and total Fe and Al concentrations, examined to assess their use in relative-age determination, and as paleoenvironmental indicators, provide an important measure of the accumulation and downward profile movement over time of organically-bound Al, ferrihydrite and other crystalline forms (hematite and goethite) of extractable Fe. Ferrihydrite is particularly useful in determining former perched water levels in soils with relation to paleoclimate. The ratios of most Fe extracts are time dependent. The Fed/Fet ratio, within statistical limits, shows a slow increase from LIA (Little Ice Age) to Late Glacial soils, which closely correlates with other alpine soil studies in the middle latitudes and other tropical alpine locales. Values of Ald (dithionite) and Alo (oxalate extractable) generally do not correlate with time; however, Alp (pyrophosphate extractable) measured against Alt (total) provides insight on the downward translocation over time of organically-bound Al. Low leaching rates in this chronosequence are further supported by clay mineralogy trends and the geochemical data. 相似文献
72.
73.
74.
Empirical regression equations are presented for scaling Pseudo Relative Velocity Spectra, PSV(T), in terms of the Modified Mercalli Intensity M.M.I., local soil classification at the recording site (‘rock’, stiff or deep soil), and local geological condition (depth of sediments). It is shown that both the local soil classification and the local geological depth of sediments should be used simultaneously in the evaluation of site specific response spectra. 相似文献
75.
The Lower Cretaceous Fortress Mountain Formation occupies a spatial and temporal niche between syntectonic deposits at the Brooks Range orogenic front and post‐tectonic strata in the Colville foreland basin. The formation includes basin‐floor fan, marine‐slope and fan‐delta facies that define a clinoform depositional profile. Texture and composition of clasts in the formation suggest progressive burial of a tectonic wedge‐front that included older turbidites and mélange. These new interpretations, based entirely on outcrop study, suggest that the Fortress Mountain Formation spans the boundary between orogenic wedge and foredeep, with proximal strata onlapping the tectonic wedge‐front and distal strata downlapping the floor of the foreland basin. Our reconstruction suggests that clinoform amplitude reflects the structural relief generated by tectonic wedge development and load‐induced flexural subsidence of the foreland basin. 相似文献
76.
77.
78.
E. M. Gichangi M. Gatheru E. N. Njiru E. O. Mungube J. M. Wambua J. W. Wamuongo 《Climatic change》2015,130(2):287-297
79.
Sea ice in the western Antarctic Peninsula (WAP) region is both highly variable and rapidly changing. In the Palmer Station region, the ice season duration has decreased by 92 d since 1978. The sea-ice... 相似文献
80.