全文获取类型
收费全文 | 25440篇 |
免费 | 5116篇 |
国内免费 | 6689篇 |
专业分类
测绘学 | 1819篇 |
大气科学 | 4762篇 |
地球物理 | 6349篇 |
地质学 | 13711篇 |
海洋学 | 3427篇 |
天文学 | 990篇 |
综合类 | 2827篇 |
自然地理 | 3360篇 |
出版年
2024年 | 109篇 |
2023年 | 434篇 |
2022年 | 1220篇 |
2021年 | 1412篇 |
2020年 | 1179篇 |
2019年 | 1366篇 |
2018年 | 1486篇 |
2017年 | 1350篇 |
2016年 | 1586篇 |
2015年 | 1265篇 |
2014年 | 1548篇 |
2013年 | 1640篇 |
2012年 | 1637篇 |
2011年 | 1622篇 |
2010年 | 1596篇 |
2009年 | 1561篇 |
2008年 | 1479篇 |
2007年 | 1401篇 |
2006年 | 1149篇 |
2005年 | 1113篇 |
2004年 | 814篇 |
2003年 | 771篇 |
2002年 | 776篇 |
2001年 | 710篇 |
2000年 | 772篇 |
1999年 | 1059篇 |
1998年 | 826篇 |
1997年 | 886篇 |
1996年 | 813篇 |
1995年 | 687篇 |
1994年 | 564篇 |
1993年 | 512篇 |
1992年 | 399篇 |
1991年 | 287篇 |
1990年 | 236篇 |
1989年 | 177篇 |
1988年 | 175篇 |
1987年 | 128篇 |
1986年 | 106篇 |
1985年 | 71篇 |
1984年 | 53篇 |
1983年 | 45篇 |
1982年 | 36篇 |
1981年 | 28篇 |
1980年 | 36篇 |
1979年 | 32篇 |
1978年 | 15篇 |
1976年 | 11篇 |
1975年 | 15篇 |
1958年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
892.
893.
894.
895.
Q. H. Liu Y. Shu X. M. Zhu X. H. Yang M. Tan 《Australian Journal of Earth Sciences》2016,63(7):903-922
The effects of low- to high-angle (>30°) normal faults on sedimentary architectural units in the Eocene Wenchang Formation, Enping Sag, Pearl River Mouth Basin (PRMB), South China Sea were investigated utilising a high-quality 3D seismic data set and restored paleogeomorphology. It has been shown that sequence stratigraphic units and sedimentary architecture are significantly controlled by the low- to high-angle normal faults. The Wenchang Formation, a second-order sequence, can be subdivided into two para-second-sequences (the Lower and Upper Wenchang sequences, E2WL and E2WU) and seven third-order sequences (from base to top: SQ1~SQ7). The low-angle fault confined sequence architecture of the Wenchang Formation is mainly characterised by lateral stacking with the ratio of the vertical subsidence (V) to horizontal slip (H) being reduced from 1/2 for E2WL to 1/6 for E2WU. In contrast, the high-angle fault confined sequence is characterised by vertical stacking with the ratio of V/H close to 1 for sequences SQ1 to SQ7. In the 3D seismic area, the features of sediment-dispersal pattern were interpreted based on an integrated analysis of paleogeomorphology, seismic reflection characteristics, stratal thickness distribution and multiple attribute clustering. The results show that the large-scale fan delta, belt-shape lacustrine deposit and bird-foot braided delta systems mainly developed in the low-angle fault confined sequences, whereas small-scale fan delta, rhombus-shaped lacustrine deposit and lobe-shaped braided delta systems inherited tectono-sedimentary architectures in the high-angle fault confined sequences. 相似文献
896.
During the deposition of the Chang-7 (Ch-7) and Chang-6 (Ch-6) units in the Upper Triassic, gravity flows were developed widely in a deep lake in the southwestern Ordos Basin, China. Based on cores, outcrops, well-logs and well-testing data, this paper documents the sedimentary characteristics of the gravity-flow deposits and constructs a depositional model. Gravity-flow deposits in the study area comprise seven lithofacies types, which are categorised into four groups: slides and slumps, debris-flow-dominated lithofacies, turbidity-current-dominated lithofacies, and deep-water mudstone-dominated lithofacies. The seven lithofacies form two sedimentary entities: sub-lacustrine fan and the slump olistolith, made up of three and two lithofacies associations, respectively. Lithofacies association 1 is a channel–levee complex with fining-/thinning-upward sequences whose main part is characterised by sandy debris flow-dominated, thick-bedded massive sandstones. Lithofacies association 2 represents distributary channelised lobes of sub-lacustrine fans, which can be further subdivided into distributary channel, channel lateral margin and inter-channel. Lithofacies association 3 is marked by non-channelised lobes of sub-lacustrine fans, including sheet-like turbidites and deep-lake mudstones. Lithofacies association 4 is represented by proximal lobes of slump olistolith, consisting of slides and slumps. Lithofacies association 5 is marked by distal lobes of slump olistolith, comprising tongue-shaped debris flow lobes and turbidite lobes. It is characterised by sandy debris flow, muddy debris flow-dominated sandstone and sandstone with classic Bouma sequences. Several factors caused the generation of gravity flows in the Ordos Basin, including sediment supply, terrain slope and external triggers, such as volcanisms, earthquakes and seasonal floods. The sediment supply of sub-lacustrine fan was most likely from seasonal floods with a high net-to-gross and incised channels. Triggered by volcanisms and earthquakes, the slump olistolith is deposited by the slumping and secondary transport of unconsolidated sediments in the delta front or prodelta with a low net-to-gross and no incised channels. 相似文献
897.
898.
899.
900.
The northwestern Pacific(NWP) is a fog-prone area, especially the ocean east of the Kuril Islands. The present study analyzes how the Pacific–Japan(PJ) teleconnection pattern influences July sea fog in the fog-prone area using independent datasets. The covariation between the PJ index and sea fog frequency(SFF) index in July indicates a close correlation, with a coefficient of 0.62 exceeding the 99% confidence level. Composite analysis based on the PJ index, a case study, and model analysis based on GFDL-ESM2 M, show that in high PJ index years the convection over the east of the Philippines strengthens and then triggers a Rossby wave, which propagates northward to maintain an anticyclonic anomaly in the midlatitudes,indicating a northeastward shift of the NWP subtropical high. The anticyclonic anomaly facilitates the formation of relatively stable atmospheric stratification or even an inversion layer in the lower level of the troposphere, and strengthens the horizontal southerly moisture transportation from the tropical–subtropical oceans to the fog-prone area. On the other hand, a greater meridional SST gradient over the cold flank of the Kuroshio Extension, due to ocean downwelling, is produced by the anticyclonic wind stress anomaly. Both of these two aspects are favorable for the warm and humid air to cool, condense, and form fog droplets, when air masses cross the SST front. The opposite circumstances occur in low PJ index years, which are not conducive to the formation of sea fog. Finally, a multi-model ensemble mean projection reveals a prominent downward trend of the PJ index after the 2030 s, implying a possible decline of the SFF in this period. 相似文献