全文获取类型
收费全文 | 6683篇 |
免费 | 168篇 |
专业分类
6851篇 |
出版年
2020年 | 63篇 |
2019年 | 75篇 |
2018年 | 406篇 |
2017年 | 316篇 |
2016年 | 362篇 |
2015年 | 116篇 |
2014年 | 104篇 |
2013年 | 1591篇 |
2012年 | 150篇 |
2011年 | 307篇 |
2010年 | 303篇 |
2009年 | 146篇 |
2008年 | 197篇 |
2007年 | 210篇 |
2006年 | 87篇 |
2005年 | 116篇 |
2004年 | 90篇 |
2003年 | 45篇 |
2002年 | 62篇 |
2001年 | 81篇 |
2000年 | 69篇 |
1999年 | 70篇 |
1998年 | 58篇 |
1997年 | 59篇 |
1996年 | 53篇 |
1995年 | 46篇 |
1994年 | 55篇 |
1993年 | 60篇 |
1992年 | 62篇 |
1991年 | 45篇 |
1990年 | 42篇 |
1989年 | 47篇 |
1988年 | 53篇 |
1987年 | 58篇 |
1986年 | 45篇 |
1985年 | 76篇 |
1984年 | 62篇 |
1983年 | 86篇 |
1982年 | 76篇 |
1981年 | 70篇 |
1980年 | 75篇 |
1979年 | 62篇 |
1978年 | 59篇 |
1977年 | 84篇 |
1976年 | 50篇 |
1975年 | 66篇 |
1974年 | 51篇 |
1973年 | 40篇 |
1971年 | 38篇 |
1969年 | 36篇 |
排序方式: 共有6851条查询结果,搜索用时 0 毫秒
991.
992.
993.
Stable carbon- and nitrogen-isotope ratios were measured for segments along the shafts of hair from eight individuals from the site of Pacatnamu, located in the Jequetepeque Valley on the north coast of Peru. All are from known grave contexts dating from Moche (ca. 450–750 A.D.) to Lambayeque periods (ca. 900–1100 A.D.). The mean δ13C and δ15N values of hair segments from individuals are comparable to those of bone, and demonstrate increased consumption of marine resources in the Lambayeque times relative to the Moche period. 相似文献
994.
We report palaeogenetic analysis of domesticated dog (Canis familiaris) remains excavated from three archaeological sites from southeast France and dating from Middle Neolithic. Ancient DNA analysis was attempted on teeth and bone samples taken from 11 dogs. Three 266-base-pair fragments of the mitochondrial genome Hypervariable Region I (HVR-I) could be retrieved and revealed two haplotypes belonging to HVR-I lineage C. These three sequences were compared to the sequences of Swedish and Italian Neolithic dogs and permitted to confirm that clade C was largely represented all over Western Europe during this period. One haplotype defined in Neolithic French dog was observed for the first time in Canis mtDNA, underlining the loss of mitochondrial diversity in Europe since the Neolithic. Finally, these results point out mitochondrial lineage replacement in Europe, since lineage C represents only 5% of extant European dogs. Altogether, these results support the proposition that palaeogenetic studies are essential for the reconstruction of the past demographic history and the domestication process of dogs. 相似文献
995.
Gloria Cuenca-Bescós Lawrence G. Straus Manuel R. González Morales Juan C. García Pimienta 《Journal of archaeological science》2009
El Mirón is a large cave in the Cantabrian Cordillera of northern Spain that presents a long archaeostratigraphic sequence radiocarbon-dated by over 60 assays to between 41,000 and 2000 BP. The sediments, collected from four areas within the cave and sieved-washed with fine wire meshes, contain microvertebrate remains of fish, frogs, lizards, birds and mammals, of which the latter are most abundant. Preliminary taphonomic analysis suggests that the microvertebrates were naturally collected by owls and (less) small carnivores. Small mammal assemblages are useful for palaeoenvironmental reconstruction because they are linked to particular habitats and are sensitive to environmental changes. The small mammals from El Mirón are ideal for this because sample sizes are large, bone preservation is good, and the stratigraphic sequence is long. In this paper we reconstruct the late Quaternary environments in the Cantabrian region of Spain using small-mammal assemblages from El Mirón Cave. On the basis of the ecologic adaptations of this suite of fauna, the majority still extant, we have identified seven habitat types, which are plotted through time. The evolution of the small mammal assemblages at El Mirón reveals seven major climatic shifts that correspond closely to the climatic changes recognized in the Iberian Peninsula during the last 41 kyr. 相似文献
996.
Brian S. Robinson George L. Jacobson Martin G. Yates Arthur E. Spiess Ellen R. Cowie 《Journal of archaeological science》2009,36(10):2184-2191
A paucity of archaeological remains of Atlantic salmon in Northeast North America has been cited as evidence that the species may have been present in the region only during and after the Little Ice Age (ca. 1450–1850 AD), one of coldest periods of the Holocene. However, significant problems of preservation, recovery and identification remain. Here, improved methods of identification use vertebra structure to distinguish salmon from trout, and strontium/calcium ratios to differentiate sea-run from landlocked salmon. In addition to the Little Ice Age, Atlantic salmon is identified in tightly dated contexts at 7000–6500 and 3500–3000 calendar years BP, during climate periods that were comparatively warm and wet. 相似文献
997.
998.
Rodolfo Fattovich 《African Archaeological Review》2009,26(4):275-290
Yeha, in Tigray, is the most impressive site with evidence for South Arabian influence dating to the first millennium BC in
the northern Horn of Africa (Eritrea and northern Ethiopia). The evidence from this site was used to identify a ‘Pre-Aksumite’
or ‘Ethiopian-Sabean’ Period (mid-first millennium BC) when an early Afro-Arabian state apparently arose in the region. A
‘Pre-Aksumite Culture’, characterised by South Arabian elements, was also suggested as a distinctive archaeological culture
in northern Ethiopia and Eritrea. However, recent fieldwork in these countries suggests that a Pre-Aksumite culture actually
did not exist and South Arabian features were restricted to a few sites, which were scattered in a mosaic of different archaeological
cultures in the first millennium BC. This hypothesis is tested through a comparison between the ceramics from Yeha and those
from Matara and other sites of the first millennium BC in Tigray and Eritrea. 相似文献
999.
1000.