全文获取类型
收费全文 | 4296篇 |
免费 | 1273篇 |
国内免费 | 551篇 |
专业分类
测绘学 | 532篇 |
大气科学 | 310篇 |
地球物理 | 1987篇 |
地质学 | 1769篇 |
海洋学 | 273篇 |
天文学 | 55篇 |
综合类 | 341篇 |
自然地理 | 853篇 |
出版年
2024年 | 12篇 |
2023年 | 55篇 |
2022年 | 156篇 |
2021年 | 194篇 |
2020年 | 210篇 |
2019年 | 261篇 |
2018年 | 190篇 |
2017年 | 255篇 |
2016年 | 240篇 |
2015年 | 280篇 |
2014年 | 309篇 |
2013年 | 251篇 |
2012年 | 247篇 |
2011年 | 262篇 |
2010年 | 210篇 |
2009年 | 245篇 |
2008年 | 246篇 |
2007年 | 287篇 |
2006年 | 251篇 |
2005年 | 208篇 |
2004年 | 207篇 |
2003年 | 187篇 |
2002年 | 166篇 |
2001年 | 122篇 |
2000年 | 119篇 |
1999年 | 116篇 |
1998年 | 115篇 |
1997年 | 112篇 |
1996年 | 108篇 |
1995年 | 82篇 |
1994年 | 71篇 |
1993年 | 80篇 |
1992年 | 60篇 |
1991年 | 45篇 |
1990年 | 37篇 |
1989年 | 29篇 |
1988年 | 29篇 |
1987年 | 20篇 |
1986年 | 18篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1974年 | 1篇 |
1954年 | 14篇 |
排序方式: 共有6120条查询结果,搜索用时 15 毫秒
41.
Hydrogen isotope of individual n-alkanes from modern sediments and their application to environments
Zhongping LI Liwu LI Li DU 《中国地球化学学报》2006,25(B08):207-207
Hydrogen isotopes are commonly fractionated to a much greater extent and as a result display larger variations in δ values, In terms of the hydrogen isotope ratios of individual n-alkanes of 16 samples of modern sediments selected from four different locations in the southern part of Gansu, China, the δD values for most of the n-alkanes varied from -150‰-300‰, Variations in δD also occurred between different ranges of n-alkanes, effects of environmental changes on the hydrogen isotopic compositions of individual n-alkanes have been detected. Besides the δD values of n-alkanes, the δD values of lipids including pristane (Pr), phytane (Ph) were also examined, by the combination of D/H ratios with molecular fingerprinting, Our results further support the notion that hydrogen isotopes of n-alkanes from modern sediments can act as paleoclimatic and paleoenvironmental proxies and provide invaluable new sources of information in the research of paleoenvironment reconstruction. 相似文献
42.
43.
Michael Commer Stefan L. Helwig reas Hördt Carsten Scholl Bülent Tezkan 《Geophysical Journal International》2006,167(3):1172-1187
44.
David W. Kelley Stefanie A. Brachfeld Edward A. Nater Herbert E. Wright Jr. 《Journal of Paleolimnology》2006,35(1):193-206
Sediments from Lake Pepin on the Mississippi River, southeastern Minnesota, are used as provenance tracers to assess variations
in hydrology and sediment-transport during the middle Holocene. Three rivers contribute sediment to Lake Pepin, and each catchment
is characterized by a distinctly different geologic terrain. The geochemical fingerprint for each drainage basin was determined
from the elemental composition of heavy minerals in the silt-sized fraction of modern sediment samples. Down-core elemental
abundances were compared with these fingerprints by use of a chemical-mass-balance model that apportions sediment to the source
areas. We observed a decreased contribution from the Minnesota River during the interval ~6700–5500 14C yr BP, which we attribute to decreased discharge of the Minnesota River, likely controlled by a combination of precipitation,
snow melt, and groundwater input to the river. This hydrologic condition coincides with the mid-Holocene prairie period recorded
by fossil pollen data. The occurrence of this feature in a proxy record for hydrologic variations supports the hypothesis
that the mid-Holocene prairie period reflects drier conditions than before or after in midwestern North America. 相似文献
45.
46.
47.
48.
3D behaviour of contamination in landfill sites using 2D resistivity/IP imaging: case studies in Portugal 总被引:2,自引:0,他引:2
Aiming at defining a valid spatial contamination model, resistivity and induced polarization (IP) measurements were used to
investigate contamination plumes in the vicinity of two municipal landfills (Ovar and ílhavo). Previous geophysical surveys
and underground water samples confirmed the contamination. However 2D resistivity/IP surveys enabled in obtaining a more accurate
spatial model. The Ovar survey consisted of two profiles with nine Wenner soundings each; the ílhavo survey was carried out
along two individual lines using a Wenner standard pseudo-section. In both situations, negative IP values were found associated
with positive IP values, which can be explained mainly by 2D or 3D geometric effects caused by the presence of the conductive
plumes. The data were modelled using a 2D inversion program (RES2DINV) and the resulting resistivity and chargeability distributions
were displayed as pseudo-sections. The resistivity and chargeability pseudo-sections define the contamination plumes and the
sedimentary structure. These case studies illustrate the advantages of 2D resistivity/IP surveys for the mapping of shape
and dimension of contamination associated with landfills. 相似文献
49.
WU Yuan-yuan LIU Cai WANG Dian WANG Shi-yu College of GeoExploration Science Technology Jilin University Changchun China 《吉林大学学报(地球科学版)》2006,(Z2)
常见的几种地震子波有:零相位子波、最小相位子波、最大相位子波和混合相位子波。以不同类型的信号为激发子波,对不同地层模型合成地震道。仅用原始合成地震道记录的振幅谱来恢复原始记录,讨论不同方法下,由于激发子波的不同,对比分析原始记录与恢复记录的差异,及其恢复效果。 相似文献
50.
一种人机交互式的初至波反演方法是在反演过程中加入人为的干预,并利用人的经验控制反演的方向,使结果更加符合实际的地质情况。再将反演的结果与其它的短波长静校正方法相结合,就能够有效地提高静校正的精度。实例证明,这种方法是有效且可行的。 相似文献