全文获取类型
收费全文 | 78篇 |
免费 | 7篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 12篇 |
地球物理 | 13篇 |
地质学 | 36篇 |
海洋学 | 5篇 |
天文学 | 21篇 |
综合类 | 1篇 |
自然地理 | 3篇 |
出版年
2023年 | 1篇 |
2019年 | 1篇 |
2017年 | 1篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 2篇 |
2012年 | 2篇 |
2011年 | 4篇 |
2010年 | 2篇 |
2009年 | 9篇 |
2007年 | 6篇 |
2006年 | 9篇 |
2005年 | 2篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1983年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1947年 | 1篇 |
1943年 | 1篇 |
排序方式: 共有93条查询结果,搜索用时 0 毫秒
91.
Seth W. Bigelow Michael J. Papaik Caroline Caum Malcolm P. North 《Climatic change》2014,123(2):215-224
Large trees (>76 cm breast-height diameter) are vital components of Sierra Nevada/Cascades mixed-conifer ecosystems because of their fire resistance, ability to sequester large amounts of carbon, and role as preferred habitat for sensitive species such as the California spotted owl. To investigate the likely performance of large trees in a rapidly changing climate, we analyzed growth rings of five conifer species against 20th century climate trends from local weather stations. Over the local station period of record, there were no temporal trends in precipitation, but maximum temperatures increased by 0.10 to 0.13 °C/decade (summer and autumn), and minimum temperatures increased by 0.11 to 0.19 °C/decade in all seasons. All species responded positively to precipitation, but more variation was explained by a significant positive response to minimum winter temperatures. High maximum summer temperature adversely affected growth of two species, and maximum spring temperatures in the year prior to ring formation were negatively associated with growth of one species. The strong coherent response to increasing minimum temperatures bodes well for growth of large trees in Sierra/Cascades region mixed conifer forest under continued climatic warming, but these trees will still be under threat by the increased fire intensity that is a indirect effect of warming. 相似文献
92.
Chris Pearson Tanya Lim Chris North George Bendo Luca Conversi Darren Dowell Matt Griffin Terry Jin Nicolas Laporte Andreas Papageorgiou Bernhard Schulz Dave Shupe Anthony J. Smith Kevin Xu 《Experimental Astronomy》2014,37(2):175-194
The different algorithms appropriate for point source photometry on data from the SPIRE instrument on-board the Herschel Space Observatory, within the Herschel Interactive Processing Environment (HIPE) are compared. Point source photometry of a large ensemble of standard calibration stars and dark sky observations is carried out using the 4 major methods within HIPE: SUSSEXtractor, DAOphot, the SPIRE Timeline Fitter and simple Aperture Photometry. Colour corrections and effective beam areas as a function of the assumed source spectral index are also included to produce a large number of photometric measurements per individual target, in each of the 3 SPIRE bands (250, 350, 500μm), to examine both the accuracy and repeatability of each of the 4 algorithms. It is concluded that for flux densities down to the level of 30mJy that the SPIRE Timeline Fitter is the method of choice. However, at least in the 250 and 350μm bands, all 4 methods provide photometric repeatability better than a few percent down to at approximately 100mJy. The DAOphot method appears in many cases to have a systematic offset of ~8 % in all SPIRE bands which may be indicative of a sub-optimal aperture correction. In general, aperture photometry is the least reliable method, i.e. largest scatter between observations, especially in the longest wavelength band. At the faintest fluxes, <30mJy, SUSSEXtractor or DAOphot provide a better alternative to the Timeline Fitter. 相似文献
93.
Ryan North Lloyd T. White Mitchell Nancarrow Anthony Dosseto Dominique Tanner 《Geostandards and Geoanalytical Research》2023,47(1):125-142
Zircon geochemistry can vary over micrometre scales; therefore, natural reference materials need to be well characterised before being used to calculate trace element mass fractions in unmeasured samples. Moreover, reference material homogeneity needs to be ensured with the accelerating rate of geoanalytical developments to map mineral chemistry at increasingly finer scales. Here, we investigate trace element zoning in four widely used zircon reference materials: 91500, Mud Tank, Temora and Plešovice, as well as zircon crystals from the Mount Dromedary/Gulaga Igneous Complex, Australia. Sub-micrometre resolution focused ion beam scanning electron microscope (FIB-SEM) based time-of-flight secondary ion mass spectrometry (ToF-SIMS) and 5 μm resolution LA-ICP-MS mapping show that trace elements are zoned in all reference materials, though 91500 exhibited the least zonation. We demonstrate that FIB-SEM-based ToF-SIMS can rapidly resolve variations in trace elements (e.g., U, Th, Sc, Y, Gd, Dy, Yb and Li) at sensitivities down to the μg g-1 level with a spatial resolution of 195 nm for areas 100 × 85 μm to 959 × 828 μm. Zircon 91500 is recommended for future quantitative analyses provided that (1) the spatial distribution of elements is imaged before analysis of unknown samples and (2) it is used in conjunction with a doped glass as the primary reference material. 相似文献