全文获取类型
收费全文 | 977篇 |
免费 | 55篇 |
国内免费 | 10篇 |
专业分类
1042篇 |
出版年
2023年 | 6篇 |
2022年 | 21篇 |
2021年 | 36篇 |
2020年 | 31篇 |
2019年 | 36篇 |
2018年 | 25篇 |
2017年 | 28篇 |
2016年 | 28篇 |
2015年 | 22篇 |
2014年 | 54篇 |
2013年 | 60篇 |
2012年 | 33篇 |
2011年 | 40篇 |
2010年 | 20篇 |
2009年 | 37篇 |
2008年 | 39篇 |
2007年 | 44篇 |
2006年 | 33篇 |
2005年 | 22篇 |
2004年 | 24篇 |
2003年 | 23篇 |
2002年 | 17篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 17篇 |
1998年 | 14篇 |
1997年 | 17篇 |
1996年 | 15篇 |
1995年 | 13篇 |
1994年 | 5篇 |
1993年 | 11篇 |
1992年 | 24篇 |
1991年 | 23篇 |
1990年 | 15篇 |
1989年 | 18篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 16篇 |
1983年 | 15篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 7篇 |
1974年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有1042条查询结果,搜索用时 0 毫秒
1.
Three local populations from Northeast Iceland are surveyed for the occurrence of the deflecting wrinkle of the metaconid on second deciduous and first permanent lower molars. The trait occurs more frequently on dm2 than on M1, and no sexual dimorphism is found, as expected. However, the frequencies are clearly within those predicted by the Mongoloid dental complex for Mongoloid populations. It is therefore suggested that the inclusion of the deflecting wrinkle in the Mongoloid dental complex be re-evaluated, and the racial diagnostic value of the trait taken with reservation. 相似文献
2.
Jutta Begerow 《Biomarkers》1999,4(1):27-36
The aim of this study was to investigate to which extent noble-metal dental alloys contribute to the total platinum (Pt), palladium (Pd), and gold (Au) body burden of the general population. The urinary Pt, Pd, and Au excretion was determined in three non-occupationally exposed volunteers before and up to 3 months after insertion of a highgold dentalalloy. The in-vitro release of Pt, Pd, and Au from four different types of dental alloys into either artificial saliva or 1% lactic acid solution was additionally investigated. The Pt, Pd, and Au concentrations were determined by sector field inductively coupled plasma mass spectrometry (SF-ICP-MS). Before insertion of the high-gold dental alloy, the Pt excretion of the patients ranged between 1.0 and 7.4 ng l-1 (0.6-3.3 ng g-1 creatinine). In the immediate post-insertion phase the Pt excretion rose to 10.5-59.6 ng l-1 (14.5-33.2 ng g-1 creatinine). This is a mean increase by a factor of 12 compared with the average Pt excretion before insertion. Three months after insertion, the Pt excretion was still elevated by a factor of 7. Contrary to Pt, the Au and Pd excretion in urine was not significantly increased after insertion of this type of high-gold dental alloy. Our in-vitro investigations confirm the assumption that Pt, Pd, and Au are released from noble metal containing dental alloys by corrosion. Under the applied conditions, the release was in the lower ng cm-2 range. It can be concluded that the Pt release from dental alloys can predominantly contribute to the Pt exposure of non-occupationally exposed persons. It can exceed the exposure from all other environmental sources including the Pt release from automobile exhaust catalysts. 相似文献
3.
4.
S M Duray 《American journal of physical anthropology》1990,81(1):27-34
Clinical studies of the relationship between developmental enamel defects and caries susceptibility have often produced conflicting results. This has been due in part to a failure to distinguish between different types of defects. Studies of this association in prehistoric populations have been rare. The complete deciduous dentitions of 57 subadults from the Libben site, a large Late Woodland cemetery in Ottawa County, Ohio, were selected for analysis. Defects were classified as either hypoplasias (deficiencies in matrix apposition) or hypocalcifications (deficiencies in mineralization) and were graded for severity. The presence or absence of carious lesions was recorded for each tooth. Results indicate a strong positive relationship between hypocalcifications and caries susceptibility. The elevated caries susceptibility of hypocalcified teeth may be related to high levels of magnesium or altered enamel microcrystallite orientation within these teeth. Variations in the frequency of hypocalcifications may partially explain differences in caries rates that have been observed in different prehistoric populations. 相似文献
5.
Shape variations in the dentition and the cranium were analyzed for sevenSaguinus forms of the hairy-face tamarin by applying the factor analysis method. The results obtained for the dental and cranial measurements
were almost consistent with each other.
The magnitude of the difference in shape factors between theS. nigricollis group and theS. midas group is appreciably larger than that between the former group and theS. mystax group. If the ancestral geographic centre of origin is postulated as being within the region which is inhabited by the livingS. nigricollis group, the morphological distances between any pairs of groups correlate well with the geographic distances between them.
Concerning the dental and cranial morphologies, the physical changes in the three species group probably took place in two
directions; that is, from theS. nigricollis group to theS. mystax group, and from theS. nigricollis group to theS. midas group.
The forms belonging to each species group are more closely related to each other, with the exception ofS. imperator in theS. mystax group. The uniqueness ofS. imperator was clearly demonstrated by factor analysis and distance analysis. In theS. mystax group, although still hypothetical,S. imperator may have been related only through the basic ancestral stock toS. labiatus andS. mystax. 相似文献
6.
R Macchiarelli 《American journal of physical anthropology》1989,78(4):575-594
The Ra's al-Hamra prehistoric fishermen lived in isolation on the Qurum rocky promontorium in Oman during the 5th-4th millennia BC. To date, they represent the most ancient and numerous human fossil group excavated from the Arabian peninsula. Like other contemporaneous archaeologically documented small communities along the desert Arabian coasts, they intensively exploited ocean resources and collected molluscs from nearby mangrove swamps. The present study analyzes aspects of dental anthropology (including crown variation, morphology, dental wear, and oral health), in 600 permanent teeth from 49 individuals of both sexes excavated at the Mesolithic RH5-site by the Italian Archaeological Mission in Oman from 1981 to 1985. In association with a general low degree of morphometric variation, the Ra's al-Hamra dental crowns show low sexual dimorphism and are consistently reduced in size. These features are unexpected in a preagricultural population, especially when these data are compared to other eastern African and near Middle Eastern prehistoric populations. These data are discussed within the general context of human dental structural reduction occurring during the post-Pleistocene and are interpreted according to the "increasing population density effect" model. There are other significant differences that characterize the Ra's al-Hamra dentitions with respect to both eastern and western prehistoric human groups. The frequency of numerous nonmetric crown traits supports the hypothesis that a microdifferentiation phenomenon occurred in this marginal area. The preliminary skeletal analysis and the palaeodemographic profile show that the Omani prehistoric fishermen were affected by genetic isolation and inbreeding as well as strong environmental stress. Because of the grit assimilated with dried fish and the high shellfish consumption, dental wear was extreme in all age groups at Ra's al-Hamra and occasionally was responsible for serious hematogenously spread infections. In spite of the great anthropological importance of ancient Arabian populations, very few studies on skeletal and dental samples have been completed. The present paper offers an odontological data set for future comparative research in the area. 相似文献
7.
Mehmet Yaar can 《American journal of physical anthropology》1989,78(1):3-8
This study analyzes and compares the dental size variation and sexual dimorphism of the Highland Beach Mound people, a late southeastern prehistoric aboriginal Florida population (ca. 800-1200 AD) with a somewhat earlier midwestern group (ca. 200-800 AD) and an Archaic sample (ca. 4160-2558 BC). The lengths and breadths of maxillary and mandibular permanent teeth of 99 individuals were measured, and crown surface areas were calculated for the molars. Results indicated that there was little sexual dimorphism. Only the mesiodistal dimensions of the upper P2 and lower C were significantly different at the P less than 0.05 level. In terms of dental size, what appears to be a chronologically based reduction in most points of comparison was seen in all three groups, with the exception of the molars, which were larger in the Highland Beach sample than in the earlier Schultz Mound. 相似文献
8.
Masahito Natori 《Primates; journal of primatology》1988,29(2):263-276
The dental and cranial morphologies of all species ofSaguinus, S. oedipus, S. geoffroyi, S. leucopus, S. nigricollis, S. fuscicollis, S. labiatus, S. mystax, S. imperator, S.
bicolor, andS. midas are examined. The following hypotheses are developed by cladistic methodology, using only synapomorphic characters to assess
the interspecific relationships ofSaguinus.Saguinus are divided into two main groups; one consists ofS. oedipus, S. geoffroyi, andS. leucopus, and the other includesS. inustus, S. nigricollis, S. fuscicollis, S. labiatus, S. mystax, S. imperator, S. bicolor, andS. midas. In the former group,S. oedipus is more closely related toS. geoffroyi than either is toS. leucopus. In the latter group,S. labiatus, S. mystax, andS. imperator are classified into one group, andS. bicolor andS. midas form one monophyletic group. 相似文献
9.
Culture and characterization of dental follicle cells from rat molars 总被引:12,自引:0,他引:12
Summary Because the dental follicle is necessary for the eruption of teeth of limited eruption, it was the objective of this study to determine if the cells of the follicle could be cultured in vitro. To achieve this, dental follicles and associated enamel organs were dissected from the first and second mandibular molars of 6–7-day-old rats (secretory stage of amelogenesis), and then cultured in a medium that promotes fibroblast growth — the predominant cell type of the dental follicle. The cultured cells grew to confluency and were kept through 3 passages before experimentation. The cultured cells were fibroblastic in shape, elongate with processes, and transmission electron microscopy revealed that they contained an abundant rough endoplasmic reticulum, but did not form desmosomes. Immunofluorescent staining for anti-vimentin showed that all the cells stained and electron-microscopic immunogold labeling indicated that the antibody was associated with intermediate filaments. As revealed by SDS-polyacrylamide gel electrophoresis and Western blotting, the cultured cells synthesized and secreted the extracellular matrix molecules fibronectin and procollagens. Subsequent immunofluorescence staining of permeabilized and non-permeabilized cells confirmed the presence of fibronectin and type I collagen both intra- and extracellularly. Thus, based on all the above characteristics, the cultured cells appeared to be fibroblasts derived from the dental follicle, although a few of the fibroblasts may be derived from undifferentiated mesenchymal cells interposed between the alveolar bone and follicle. Experiments now can be conducted to determine how these cultured cells respond directly to growth factors that alter the rates of tooth eruption. 相似文献
10.
David W. Cameron 《Primates; journal of primatology》1991,32(3):329-343
This paper examines the pattern(s) of sexual dimorphism within the upper dentition ofProconsul specimens from the early Miocene of east Africa. These fossils are compared against the corresponding dentition ofPan troglodytes andGorilla gorilla using principal components and cluster analyses. This paper demonstrates that both sexes ofPan andGorilla are characterized by their own distinctive shape patterns. It is also demonstrated that someProconsul specimens examined here display a pattern that is dissimilar from otherProconsul specimens also examined. This suggests that at least two species ofProconsul may have to be recognized as having lived in this region during the early Miocene. The identification of distinct patterns
withinProconsul also suggests that their overall shape and size range are more similar toPan than toGorilla. 相似文献