全文获取类型
收费全文 | 284篇 |
免费 | 10篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 8篇 |
2019年 | 12篇 |
2018年 | 29篇 |
2017年 | 17篇 |
2016年 | 18篇 |
2015年 | 15篇 |
2014年 | 17篇 |
2013年 | 65篇 |
2012年 | 9篇 |
2011年 | 17篇 |
2010年 | 5篇 |
2009年 | 10篇 |
2008年 | 5篇 |
2007年 | 6篇 |
2006年 | 3篇 |
2005年 | 5篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1969年 | 2篇 |
排序方式: 共有294条查询结果,搜索用时 15 毫秒
21.
Paola Boscato Christian Carioni Andrea Brandolini Laura Sadori Mauro Rottoli 《Journal of archaeological science》2008
The persistent uncertainty on the classification of the “new” glume wheat found in Neolithic and Bronze Age sites from Greece and other European settlements might be resolved only through analysis of its ancient DNA. Tools able to discriminate among different Triticum species on the basis of scarce, very damaged DNA, are therefore essential. While current attempts concentrate on DNA fragments sequencing and comparison, in some instances PCR-based selective amplification techniques might offer a cheaper and quicker alternative. The purpose of this research was therefore the identification of species-specific primers, able to distinguish caryopses of Triticum timopheevii subsp. timopheevii from those of Triticum turgidum subsp. dicoccum. Primers and their working conditions were defined and optimized using DNA from modern accessions. The ribosomal primers ITS1 tim and ITS2 tim, and the nuclear primer acetyl-coenzyme A tim clearly discriminated the sequences of Triticum timopheevii from other species. Finally, Neolithic charred wheat grains found in the sites of Sammardenchia (Pozzuolo del Friuli, Udine) and La Marmotta (Lago di Bracciano, Roma), belonging to the “new” wheat type or to emmer, were tested with the three selected primers. However, the results were not conclusive, because the samples analysed were apparently too degraded to yield useful DNA. 相似文献
22.
Alfred J. Andrea 《The Historian; a journal of history》1992,55(1):183-190
23.
María Gabriela Musaubach Anabela Plos María Del Pilar Babot 《Journal of archaeological science》2013,40(2):1186-1193
This paper presents, for the first time, a detailed study, from an archaeological perspective, of the morphological characteristics of the starch grains within the kernels of selected native wild grasses found in the Central Pampas of Argentina. We compared native wild grasses to maize starch grains, which can be distinguished from each other based on their size, shape and other attributes. The majority of the studied grains did not share morphological characteristics with maize starch grains. Considering this, it can be said that, if irregular and polyhedral grains with transverse or radial fissures dominate the starch assemblage, maize identification may be done on the basis of both morphology and size. Additionally, this research contributes to the characterization of the starch grains of the Panicoideae subfamily, which includes maize. Several classes of simple and compound starch grains are described and defined for native species of Pooideae, Chloridoideae, Arundinoideae, and Panicoideae subfamilies. The results obtained may constitute a baseline for the future determination of maize and wild grass use in archaeological contexts belonging to Middle/Late Holocene hunter–gatherers in the Pampas of Argentina and neighboring areas. 相似文献
24.
25.
26.
27.
28.
Local innovation networks are considered to be important to innovation and technological change and to growth prospects of regions and cities in Germany. When analysing the local (or regional) innovation system, one should consequently not only investigate horizontal and vertical relations among firms but also the contacts with universities and other research institutions. Furthermore, the role of government agencies and interest groups that provide financial support as well as commercial and technical information should also be taken into account. However, the review of relevant theoretical and empirical investigations related to the German experience shows that such innovation and R&D cooperation networks appear to be less significant than expected. In general various regional technology policy measures adopted in German states (the provision of research infrastructure, establishment of technology centres, innovative small and medium sized enterprises support programmes, etc.) have been more successful in economically better-off large cities than in the rural areas. Apart from offering a critical review of relevant theoretical and empirical research, this study introduces the present regional technology and R&D promotion policies in German states and examines the local innovation systems, taking Landshut as an example. 相似文献
29.
30.
Domenico Miriello Donatella Barca Andrea Bloise Annamaria Ciarallo Gino M. Crisci Teresa De Rose Caterina Gattuso Flavia Gazineo Mauro F. La Russa 《Journal of archaeological science》2010
This work describes the compositional characterisation of coccciopesto and natural pozzolanic mortars sampled in the Regio VI area of the archaeological site of Pompeii, with particular reference to the Casa di Pansa in Insula 6 and Casa 17 in Insula 2. Samples were studied by optical microscopy and analysed by XRF, SEM-EDS, LA-ICP-MS and XRPD. The XRF and SEM-EDS data, subjected to multivariate analysis (cluster analysis), identified the three main construction phases involved in building the Casa di Pansa. In addition, mineralogical and petrographic characteristics of the aggregate were determined and found to be compatible with pyroclastic deposits from the volcano Vesuvius. Study revealed C–S–H phases in the binder, due to pozzolanic hydration phemomena of hydrated lime with cocciopesto and natural pozzalana. 相似文献