全文获取类型
收费全文 | 6513篇 |
免费 | 282篇 |
国内免费 | 81篇 |
专业分类
测绘学 | 236篇 |
大气科学 | 514篇 |
地球物理 | 1541篇 |
地质学 | 2191篇 |
海洋学 | 531篇 |
天文学 | 1185篇 |
综合类 | 28篇 |
自然地理 | 650篇 |
出版年
2022年 | 30篇 |
2021年 | 76篇 |
2020年 | 87篇 |
2019年 | 124篇 |
2018年 | 181篇 |
2017年 | 163篇 |
2016年 | 234篇 |
2015年 | 176篇 |
2014年 | 200篇 |
2013年 | 408篇 |
2012年 | 258篇 |
2011年 | 345篇 |
2010年 | 291篇 |
2009年 | 384篇 |
2008年 | 340篇 |
2007年 | 293篇 |
2006年 | 272篇 |
2005年 | 261篇 |
2004年 | 266篇 |
2003年 | 207篇 |
2002年 | 215篇 |
2001年 | 118篇 |
2000年 | 144篇 |
1999年 | 102篇 |
1998年 | 115篇 |
1997年 | 81篇 |
1996年 | 86篇 |
1995年 | 83篇 |
1994年 | 90篇 |
1993年 | 76篇 |
1992年 | 88篇 |
1991年 | 69篇 |
1990年 | 55篇 |
1989年 | 51篇 |
1988年 | 58篇 |
1987年 | 53篇 |
1986年 | 57篇 |
1985年 | 69篇 |
1984年 | 65篇 |
1983年 | 79篇 |
1982年 | 57篇 |
1981年 | 65篇 |
1980年 | 58篇 |
1979年 | 66篇 |
1978年 | 51篇 |
1977年 | 35篇 |
1976年 | 29篇 |
1975年 | 26篇 |
1974年 | 29篇 |
1973年 | 30篇 |
排序方式: 共有6876条查询结果,搜索用时 109 毫秒
611.
Christine Lane Michael Haslam Michael Petraglia Peter Ditchfield Victoria Smith Ravi Korisettar 《Quaternary Science Reviews》2011,30(15-16):1819-1824
The ~74 ka BP Youngest Toba Tuff (YTT), from the largest known Quaternary volcanic eruption, has been found for the first time as a non-visible (crypto-) tephra layer within the Billa Surgam caves, southern India. The occurrence of the YTT layer in Charnel House Cave provides the first calendrical age estimate for this much debated Pleistocene faunal sequence and demonstrates the first successful application of cryptotephrochronology within a cave sequence. The YTT layer lies ~50 cm below a major sedimentological change, which is related to global cooling around the MIS 5 to MIS 4 transition. Using this isochronous event layer the Billa Surgam Cave record can be directly correlated with other archaeological sites in peninsular India and palaeoenvironmental archives across southern Asia. 相似文献
612.
613.
Soil moisture influences many hydrologic applications including agriculture, land management and flood prediction. Most remote‐sensing methods that estimate soil moisture produce coarse resolution patterns, so methods are required to downscale such patterns to the resolutions required by these applications (e.g. 10‐ to 30‐m grid cells). At such resolutions, topography is known to affect soil moisture patterns. Although methods have been proposed to downscale soil moisture based on topography, they usually require the availability of past high‐resolution soil moisture patterns from the application region. The objective of this article is to determine whether a single topographic‐based downscaling method can be used at multiple locations without relying on detailed local observations. The evaluated downscaling method is developed on the basis of empirical orthogonal function (EOF) analysis of space–time soil moisture data at a reference catchment. The most important EOFs are then estimated from topographic attributes, and the associated expansion coefficients are estimated on the basis of the spatial‐average soil moisture. To test the portability of this EOF‐based method, it is developed separately using four data sets (Tarrawarra, Tarrawarra 2, Cache la Poudre and Satellite Station), and the relationships that are derived from these data sets to estimate the EOFs and expansion coefficients are compared. In addition, each of these downscaling methods is applied not only for the catchment where it was developed but also to the other three catchments. The results suggest that the EOF downscaling method performs well for the location where it is developed, but its performance degrades when applied to other catchments. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
614.
615.
Elizabeth A. V. Mackie Jeremy M. Lloyd Melanie J. Leng Michael J. Bentley Carol Arrowsmith 《第四纪科学杂志》2007,22(6):579-591
Carbon isotopes (δ13C) and C/N ratios from bulk organic matter have recently been used as alternative proxies for relative sea‐level (RSL) reconstruction where there are problems associated with conventional biological indictors. A previous study on a single isolation basin (Upper Loch nan Eala) in northwest Scotland has shown a clear relationship between δ13C, C/N ratios and palaeosalinity from Younger Dryas and Holocene aged sediments. In this paper we present results of δ13C and C/N ratio analyses from other isolation basins in northwest Scotland over the Holocene and the Lateglacial period in order to validate this technique. The results from the Holocene sequences support the earlier findings that this technique can be used to identify RSL change from isolation basins over the Holocene in this region. The relationship between δ13C, C/N ratios and RSL change is not apparent in sediments of Lateglacial age. Other environmental variables such as atmospheric CO2 concentration, poor vegetation development and temperature influence δ13C values during this period. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
616.
617.
We presented a finite‐element‐based algorithm to simulate plane‐strain, straight hydraulic fractures in an impermeable elastic medium. The algorithm accounts for the nonlinear coupling between the fluid pressure and the crack opening and separately tracks the evolution of the crack tip and the fluid front. It therefore allows the existence of a fluid lag. The fluid front is advanced explicitly in time, but an implicit strategy is needed for the crack tip to guarantee the satisfaction of Griffith's criterion at each time step. We enforced the coupling between the fluid and the rock by simultaneously solving for the pressure field in the fluid and the crack opening at each time step. We provided verification of our algorithm by performing sample simulations and comparing them with two known similarity solutions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
618.
619.
620.