全文获取类型
收费全文 | 854篇 |
免费 | 145篇 |
国内免费 | 98篇 |
专业分类
测绘学 | 2篇 |
地球物理 | 150篇 |
地质学 | 706篇 |
海洋学 | 91篇 |
天文学 | 14篇 |
综合类 | 22篇 |
自然地理 | 112篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 16篇 |
2021年 | 29篇 |
2020年 | 18篇 |
2019年 | 34篇 |
2018年 | 26篇 |
2017年 | 14篇 |
2016年 | 34篇 |
2015年 | 32篇 |
2014年 | 37篇 |
2013年 | 47篇 |
2012年 | 24篇 |
2011年 | 54篇 |
2010年 | 39篇 |
2009年 | 63篇 |
2008年 | 67篇 |
2007年 | 61篇 |
2006年 | 69篇 |
2005年 | 51篇 |
2004年 | 49篇 |
2003年 | 39篇 |
2002年 | 29篇 |
2001年 | 28篇 |
2000年 | 34篇 |
1999年 | 20篇 |
1998年 | 24篇 |
1997年 | 18篇 |
1996年 | 13篇 |
1995年 | 24篇 |
1994年 | 17篇 |
1993年 | 20篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1097条查询结果,搜索用时 15 毫秒
81.
82.
湖北郧西黄龙洞古人类遗址自2004年发现以来已进行过3次系统发掘,出土了距今约10万年的晚期智人牙齿化石、哺乳动物化石和38件石制品。文章从类型、原料、剥片技术、加工技术等方法对石制品进行综合分析。结果表明,黄龙洞古人类选择围岩内部的石英质岩脉和洞外河流形成的河卵石进行剥片和加工石器,类型包括石锤、石核、石片、石器、断块和碎屑等,个体以中小型居多;锤击法为剥片基本方法,砸击法被少量使用;石器多为片状毛坯制作而成,刮削器是石器的主要类型,此外还有手镐、砍砸器、石锥和雕刻器等,石器为锤击法单向简单加工而成。另外,结合洞穴自然环境、动物化石埋藏及考古分析等证据,探讨了古人类于更新世晚期对黄龙洞的利用方式和生存行为。 相似文献
83.
TRACE ELEMENT DISTRIBUTION AND IMPLICATIONS IN SEDIMENTS ACROSS THE ALLERØD–YOUNGER DRYAS BOUNDARY IN THE NETHERLANDS AND BELGIUM 下载免费PDF全文
ALEXANDRE V. ANDRONIKOV ANNELIES VAN HOESEL IRINA E. ANDRONIKOVA WIM Z. HOEK 《Geografiska Annaler: Series A, Physical Geography》2016,98(4):325-345
In the Northern Hemisphere, the Younger Dryas cooling occurred between 12.8 and 11.7 ka bp . This cooling is thought to have been the result of an abrupt change in atmospheric and oceanic circulations. One of the hypotheses explaining such a change suggests that just before the onset of the Younger Dryas cooling, multiple airbursts/impacts occurred over the Northern Hemisphere. We studied the late Pleistocene sediments from the Netherlands and Belgium to check whether a sudden short event might have taken place just before the onset of the Younger Dryas cooling. The geochemical features revealed suggest that such events might have occurred. The presence of products of biomass burning is suggested on the basis of trace element features of sediments from the lower Younger Dryas boundary. The presence of a volcanic component and a component resulting from extensive biomass burning in the sediments of c. 12.9 ka bp are indicated on the basis of trace element features. The volcanic component may be related to the Laacher See volcano eruption, whereas the cause of the extensive biomass burning remains unclear. 相似文献
84.
In this paper, the currently accepted correlation of the Early Pleistocene Ludhamian stage of England with the Tiglian‐A sub‐stage of the Netherlands is challenged. Recent investigations of Early Pleistocene marine North Sea deposits from a borehole near Noordwijk (the Netherlands) yielded evidence from molluscs, dinoflagellate cysts and sporomorphs for an alternation of warm‐temperate and arctic intervals within the Praetiglian and Tiglian stages. Marine equivalents of the terrestrial‐based pollen sub‐stages Tiglian A and B have been recognised in the upper part of the sequence. A Praetiglian age can be assigned to the lower part of the sequence on the basis of mollusc analysis. Within the Praetiglian, an alternation of warm and cold phases has been recognised from both the dinoflagellate cyst and molluscan records. Three cold phases within the Praetiglian are tentatively correlated with marine isotope stages (MIS) 96–100. The molluscan assemblages provide evidence for climate forcing of the sea level: highest sea levels are reached in the warm‐temperate intervals. Within the Praetiglian, an interval with an acme zone of the dinoflagellate cyst Impagidinium multiplexum, is correlated with the Ludhamian and tentatively linked to MIS 97 and/or MIS 96. The cold molluscan assemblages from the Noordwijk borehole include an acme zone of Megayoldia thraciaeformis, the first and only occurrence of this North Pacific bivalve in the North Sea Basin. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
85.
This research paper analyses the grain-size characteristics of the Quaternary deposits at Xingshan near Siping, Jilin province in China by employing graphic measures to study the grain size distribution and its mode of transport and deposition. The Quaternary deposits at Xingshan lie unconformable on Cretaceous rocks made of siltstone, mudstone and sandstone. The average grain size is between 8.06 to 8.55Φ (0.002 6 ~0.003 7 mm). The Quaternary deposits at Xingshan mainly compose of very fine silt to clay. The compositions of the grade are clay 63% and silt 37%. The clay size components are weathered debris transported and deposited by flowing water from the SE highlands or hills to the low lying NW Xingshan plains whereas the silty components accumulated by aoelian process. The Quaternary deposits at Xingshan accumulated in the middle and late Pleistocene interglacial periods from (459.12~39.03) ka to (88.92~7.56) ka. The standard deviation ranged from 0.96 to 1.36Φ, indicating that the sediments are moderately to poorly sorted, Coefficient of skewness ranged from 0.16~0.31 with an average skewness of 0.218, (Positively skewed towards fine). Kurtosis values (0.84~1.05) from the grain size distribution and visual inspection of the frequency curves indicate platykurtic to mesokurtic curves and unimodal to bimodal grain-size distribution. The type of deposit formation is sand dune and the source is at a distal from its provenance. 相似文献
86.
Sediment proxy records from a continuous, 1.5 million year long deep‐sea sediment core from a site in the western Norwegian Sea were used to obtain new insights into the nature of palaeoceanographic change in the northern North Atlantic (Nordic seas) during the climatic shift of the Mid‐Pleistocene Revolution (MPR). Red‐green sediment colour and magnetic susceptibility records both reveal significant differences in their mean values when comparing the intervals older than 700 000 yr (700 ka) with those from the past 500 kyr. The timing and duration of these changes indicates that the MPR in the Nordic seas is characterised by a gradual transition lasting about 200 kyr. Together with further sedimentological evidence this suggests that the mid‐Pleistocene climate shift was accompanied by a general change in ice‐drift pattern. It is further proposed that prior to the onset of the major late Pleistocene glaciations in the Northern Hemisphere a significant proportion of the ice in the eastern Nordic seas originated from a southern provenance, whereas later it dominantly came from the surrounding landmasses. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
87.
F. Marcolini G. Bigazzi F. P. Bonadonna E. Centamore R. Cioni G. Zanchetta 《第四纪科学杂志》2003,18(6):545-556
The stratigraphical context of two Middle Pleistocene fossiliferous palaeosols from Central Italy (Abruzzo and Tuscany) have been studied. Small mammals and molluscs occur in both palaeosols, which are covered by tephra layers that were analysed using an interdisciplinary approach. Application of fission‐track dating to apatites separated from the Case Picconetto tephra (Pescara, Abruzzo), yielded an age of 0.48 ± 0.04 Ma, indistinguishable from those previously determined for the Campani Quarry (Lower Valdarno, Tuscany) (0.46 ± 0.05 Ma and 0.48 ± 0.05 Ma). Geochemical and petrographic investigations indicate that these tephra originated from different volcanoes, the Alban Hills Volcanic Complex and the Vico Volcano (Latium) respectively. Small mammal and mollusc assemblages indicate different palaeoclimatic and palaeoenvironmental conditions for the Case Picconetto and Campani Quarry palaeosols. Warm and humid conditions can be inferred for the Campani Quarry site, whereas open and cold conditions can be inferred for Case Picconetto. On the basis of faunal data, fission‐track dates and attribution of tephra to specific volcanic eruptions, we suggest a correlation of these faunas with marine oxygen isotope stage 14 (Case Picconetto) and with marine oxygen isotope stage 11 (Campani Quarry), respectively. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
88.
F. W. Shotton D. H. Keen G. R. Coope A. P. Currant P. L. Gibbard M. Aalto S. M. Peglar J. E. Robinson 《第四纪科学杂志》1993,8(4):293-325
A complex of channels underlying the Baginton-Lillington Gravel (Baginton Formation) at Waverley Wood Quarry, Warwickshire is described. Fossil pollen and plant macrofossils, Coleoptera, Ostracoda, Mollusca and Mammalia are described from the channel-fill deposits. Consideration of all the evidence allows the identification of four separate stages of channel fill which largely occurred under a cool temperate climate. At the top of Channel 2 evidence for a cold, continental climatic episode can be recognised, suggesting that the whole complex was deposited under a fluctuating climate at the end of a temperate stage. At two levels in the channels human artefacts were recovered confirming the presence of Palaeolithic people in Warwickshire during the deposition of the sediments. Amino-acid geochronology suggests an age within the ‘Cromerian Complex’ Stage for the channels. The small vertebrate and molluscan faunas indicate that the deposits are no older than the latter part of the ‘Cromerian Complex’ Stage of East Anglia. The regional stratigraphic significance of the Waverley Wood succession is outlined. 相似文献
89.
在陕西省澄城县采集到一对保存相当完好的南方象第三上臼齿化石。我国关于南方象化石的报导不多,在陕西省则是首次发现。这一发现对了解更新世时期南方象在我国的分布提供了新资料。 相似文献
90.
Pollen and macrofossil analyses of two sequences of organic sediment in western Ireland have allowed the recognition of the latter parts of the Gortian Interglacial, a Middle Pleistocene temperate stage. The palaeobotanical information from the two sites identifies the preservation of partial sequences from the Gortian Interglacial (believed to be the equivalent of the Hoxnian Stage of Britain and the Holsteinian of Europe). The pollen and macrofossil data from one of the sites, Derrynadivva, span the middle and latter parts of the temperate stage. The results show that fire influenced the vegetation throughout the middle part of the temperate stage, and the termination of the organic depositional sequence appears to have been due to environmental deterioration. The former is identified through the abundant occurrence of charcoal in the sediments, whereas the latter is apparent in the sediment sequence and in the reworking of thermophilous pollen types into the upper part of the deposit. The second site, Burren Townland, records only part of the later zones of the interglacial, but the ericaceous assemblages of the latter part of the Gortian Interglacial are well developed and well preserved. Macrofossil analyses and scanning electron microscopy work on the pollen at the latter site has allowed the recognition of Rhododendron ponticum, adding to previous records of this species, which now has a very disjunct European distribution. 相似文献