首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   665篇
  免费   7篇
  国内免费   1篇
  2023年   4篇
  2022年   4篇
  2021年   3篇
  2020年   7篇
  2019年   26篇
  2018年   34篇
  2017年   19篇
  2016年   17篇
  2015年   6篇
  2014年   34篇
  2013年   50篇
  2012年   22篇
  2011年   14篇
  2010年   10篇
  2009年   26篇
  2008年   19篇
  2007年   33篇
  2006年   17篇
  2005年   30篇
  2004年   16篇
  2003年   14篇
  2002年   16篇
  2001年   8篇
  2000年   4篇
  1999年   8篇
  1998年   4篇
  1997年   5篇
  1996年   8篇
  1995年   7篇
  1994年   5篇
  1993年   2篇
  1992年   8篇
  1991年   4篇
  1990年   4篇
  1989年   1篇
  1987年   6篇
  1986年   2篇
  1985年   26篇
  1984年   31篇
  1983年   20篇
  1982年   19篇
  1981年   16篇
  1980年   15篇
  1979年   8篇
  1978年   7篇
  1977年   12篇
  1976年   8篇
  1975年   8篇
  1974年   4篇
  1973年   2篇
排序方式: 共有673条查询结果,搜索用时 312 毫秒
101.
ABSTRACT

This article analyses network organizations founded by descendants of Turkish migrants in the Netherlands and France. By surveying members of two such organizations and interviewing several of their board members, we learn how these organizations function, their success in building and extending social networks, and their efficacy at improving labour market prospects for young second-generation professionals of Turkish descent. Our findings reveal a hybrid structure, whereby the organizations gear many of their activities towards mainstream society. In comparison to traditional immigrant organizations, their attitude is more open to other social groups, yet they still have a clear stronghold in the ethnic immigrant community. We conclude that ethnicity is not the main element in the successful second generation’s organizing process. Factors such as educational trajectories, professional ambitions, feelings of responsibility for other members and newly acquired socioeconomic status are the main reasons for this group to organize.  相似文献   
102.
Bone histology is an important tool for uncovering life history traits of extinct animals, particularly those that lack modern analogs, such as the non-avian dinosaurs. In most studies, histological analyses preferentially focus on long bones for understanding growth rates and determining age. Here we show, by analyzing ornithischians (a stegosaur and an ornithopod), saurischians (a sauropod and a theropod), and a crocodile, rib histology is a suitable alternative. The estimated age for all sampled taxa ranges between 14 to 17 years for Lourinhanosaurus antunesi and 27 to 31 years estimated for Draconyx loureiroi. The theropod Baryonyx was skeletally mature around 23–25 years of age but showed unfused neurocentral sutures, a paedomorphic feature possibly related to aquatic locomotion. Our results show that ribs can contain a nearly complete growth record, and reveal important information about individual age, point of sexual maturity, and, in some cases, sex. Because ribs are more available than long bones, this method opens new possibilities for studying rare and incomplete fossils, including holotypes.  相似文献   
103.
The taxonomic attribution of isolated hominin distal humeri has been a matter of uncertainty and disagreement notwithstanding their relative abundance in the fossil record. Four taxonomically-based morphotypes, respectively representing Pboisei, Probustus, non-erectus early Homo and Herectus, have been identified based on the cross-sectional outer shape variation of an assemblage of Plio-Pleistocene eastern and southern African specimens (Lague, 2015). However, the existence of possible differences between Paranthropus and Homo in the inner structural organisation at this skeletal site remains unexplored. We used noninvasive imaging techniques to tentatively characterize the endostructural organization of five early Pleistocene distal humeri from South Africa (TM 1517g, SK 24600, SKX 10924, SKX 34805) and Ethiopia (Gombore IB), which have been variably attributed to Paranthropus or Homo. While the investigated specimens reveal diverse degrees of inner preservation related to their taphonomic and diagenetic history, in all but SK 24600 from Swartkrans we could comparatively assess some geometric properties at the most distal cross-sectional level (%CA, Ix/Iy, Imax/Imin) and quantify cortical bone thickness topographic variation across the preserved shaft portions by means of a 2-3D Relative Cortical Thickness index. Whenever possible, we also provided details about the site-specific organization of the cancellous network and measured the same parameters in a comparative sample of twelve adult extant humans. For most features, our results indicate two main patterns: the first includes the specimens TM 1517g, SKX 10924 and SKX 34805, while the second endostructural morphotype sets apart the robust Homo aff. erectus Gombore IB specimen from Melka Kunture, which more closely resembles the condition displayed by our comparative human sample. Notably, marked differences in the amount and pattern of proximodistal cortical bone distribution have been detected between Gombore IB and SKX 34805 from Swartkrans. Given its discordant outer and inner signatures, we conclude that the taxonomic status of SKX 34805 deserves further investigations.  相似文献   
104.
A thick layer of carbonised seeds was encountered in an 11th century a.d. room situated in the seigneurial part of the village of La Gravette. This paper presents the first results of charcoal and seed analyses which give information on the food products stored in the granary and on their arrangement there. Triticum aestivum/durum/turgidum was by far the most important stored crop, while Avena sp., then Hordeum vulgare, Secale cereale, Triticum monococcum and Vitis vinifera were secondary. Weeds were poorly represented. Charcoals were dominated by deciduous Quercus sp., and 11 additional wood taxa were recorded, including especially Fagus sylvatica, Fraxinus sp., Rosaceae, Corylus avellana, Acer campestre and Ulmus sp. According to the charcoal distribution, Quercus and Fagus were probably building materials while most of other taxa would have been used for basketry, wattling or joinery work. In the western part of the granary, naked wheat was stored in bulk. In the eastern part, various crops (at least naked wheat, barley, rye, oat and grape) were stored in small amounts, most of which were probably separated by light wooden structures. The cereal crops had largely been processed and cleaned. The stored products probably represent taxes paid to the lord who owned the granary.  相似文献   
105.
Fabien Knoll 《Geobios》2009,42(6):755
The remains of an ornithopod dinosaur from the Upper Barremian (Lower Cretaceous) of Auxerre (Burgundy, France) are described. They consist of several vertebrae and a fragmentary scapula. Despite obvious morphological and dimensional affinities with the species Iguanodon bernissartensis, the state of the specimen does not allow any identification more precise than Iguanodontia indet. Reappraisal of the French Upper Barremian record of medium and large-sized ornithopods reveals that no specimen can be definitely determined to the specific level.  相似文献   
106.
Although France is less affected by the rise in obesity than neighboring countries, the prevalence of obesity has increased, changing the distribution of this pathology in the population. We analyze this evolution by social status, education, income and gender, region of residence, using the three French national Health Surveys conducted in 1981, 1992 and 2003. The average body weight of both women and men has increased in France since 1981 and accelerated since the 1990s. This trend is obtained among all age groups. Nevertheless, this process did not affect all socioeconomic groups similarly. Geographical differences increased between north-east, where the prevalence of obesity is higher, and the Mediterranean region, where it is lower. Likewise, the gap between social and occupational categories has greatly widened: obesity has increased much faster among farmers and blue-collar workers than among managers and professionals. In contrast to women, poorer men are not more likely to be more obese than others. Our findings suggest that differences in BMI values increased substantially among social groups in France, in particular among women.  相似文献   
107.
108.
The locality Valbro (Quercy, France) has yielded a rich fossil vertebrate fauna. Here are presented the geological context, a preliminary faunal list and the systematics of the Rodentia and carnivores, the most abundant taxa of the fauna. The Rodentia are known from 11 taxa: the Theridomyidae Blainvillimys gregarius Schlosser, 1884, Blainvillimys ?gemellus Vianey-Liaud, 1989, Issiodoromys medius (Vianey-Liaud, 1976) and S. cayluxi Schlosser, 1884, the Aplodontidae Plesispermophilus angustidens Filhol, 1882, the Gliridae Butseloglis tenuis (Bahlo, 1975), Butseloglis micio (Misonne, 1957) and Bransatoglis planus (Bahlo, 1975), the Sciuridae Palaeosciurus goti Vianey-Liaud, 1974 and cf. Oligopetes sp., and the Cricetidae Atavocricetodon sp. aff. A. nanus (Pelaez-Campomanes, 1995). Thirteen taxa of carnivores are present at Valbro; among the Hyaenodontida: Hyaenodon leptorhynchus Laizer et Parieu, 1838 and cf. Apterodon sp.; among the Carnivora: a Feliformia gen. et sp. indet., the Nimravidae Nimravus intermedius (Filhol, 1872), Dinailurictis bonali Helbing, 1922 and Nimravidae gen. et sp. indet. (Certainly belonging to one the two already identified species), the Ursida Pachycynodon crassirostris Schlosser, 1888, Pachycynodon sp., Amphicynodon sp. 1 cf. A. typicus (Schlosser, 1888), Amphicynodon ? sp. 2 and Ursida gen. et sp. indet. cf. Pachycynodon boriei (Filhol, 1876), the Mustelida M. olivieri Bonis, 1997, the Carnivora incertae sedis Palaeogale sectoria (Gervais, 1848–1852), the Arctoidea gen. et sp. indet. and Carnivora gen. et sp. indet. (probably representing taxa already identified at lower taxonomic levels). The evolutionary grade of B. gregarius of Valbro compares to that of the species from Mas de Got, La Plante 2 and Cavalé, which supports an MP22 age for Valbro. This datation is further supported by the association of Theridomyinae yielded by the locality (B. gregarius, B. gemellus, I. medius and S. cayluxi), and by the presence of a N. intermedius that well compares the material of the species from Villebramar, La Plante et Mas de Got, of D. bonali, P. sectoria, M. olivieri (species known only from Mas de Got), and by additional evidence from the remaining vertebrates from Valbro, especially the squamates. Despite a limited amount of specimens (341 specimens have been studied), the faunas of rodents and carnivores from Valbro are the most speciose and diverse known for the MP22 level and, for the Carnivora fauna in particular, for the Oligocene of the Old World.  相似文献   
109.
Amniotes are rare in Late Carboniferous strata, especially in Europe, and despite a global diversification. They are generally more common in Lower Permian deposits. The French record around the Pennsylvanian-Cisuralian boundary is therefore re-examined. Each basin which yielded amniote remains is provided with general data on its sedimentology, stratigraphy, dating, and palaeontological content. Seven specimens are reported, of which five are synapsids and two are reptiles, each of them being a holotype. Their respective age is reassessed. The use of the regional Stephanian and Autunian stages is discussed, but their traditional sense is retained. There is currently no amniote in the Stephanian sensu stricto (= Early Gzhelian) of France. The Stephanian-Autunian Transitional Zone (= Late Gzhelian) contains the unique amniote Stereorachis blanziacensis. The Autunian sensu stricto (= Asselian) contains five, Stereorachis dominans, Haptodus baylei, Callibrachion gaudryi, Belebey augustodunensis, and Aphelosaurus lutevensis. Finally, Neosaurus cynodus can be assigned either to the Transitional Zone or to the Autunian sensu stricto. The amniote diversity increases through the Pennsylvanian-Cisuralian boundary. Despite the low number of specimens, the French record is representative of the global evolution of amniotes.  相似文献   
110.
《Comptes Rendus Palevol》2014,13(6):483-488
The Chalonnes-sur-Loire outcrop is the most complete Llandovery section in the Ligerian domain (Armorican Massif, NW France); it displays a ca. 10 m-thick sequence of organic-rich black bedded cherts alternating with black graptolitic shales, which were deposited above glaciomarine diamictites of the Hirnantian glaciation. It is likely the black cherts accumulated under eutrophic waters, on the outer shelf part (distal offshore) of a Gondwanan margin, situated at intermediate to high latitudes of the Southern hemisphere. Hydrofluoric acid processing allowed the extraction of radiolarians; seven species are identified in the best preserved sample discovered so far. All seven are common species in tropical assemblages known from Alaska and Nevada, which are characteristic of the Orbiculopylorum assemblage, of Aeronian to early Telychian age. This age is in good agreement with independent age control from graptolites in the Chalonnes section, suggestive of an Aeronian age for the radiolarian-yielding level.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号