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   133篇
  免费   4篇
  国内免费   5篇
  142篇
  2023年   1篇
  2021年   4篇
  2020年   2篇
  2019年   5篇
  2018年   1篇
  2017年   3篇
  2016年   5篇
  2015年   9篇
  2014年   1篇
  2013年   8篇
  2012年   1篇
  2011年   9篇
  2010年   2篇
  2009年   3篇
  2008年   12篇
  2007年   6篇
  2006年   10篇
  2005年   4篇
  2004年   6篇
  2003年   3篇
  2002年   2篇
  2001年   1篇
  2000年   3篇
  1999年   1篇
  1998年   1篇
  1997年   2篇
  1996年   4篇
  1993年   1篇
  1992年   1篇
  1990年   2篇
  1988年   1篇
  1987年   2篇
  1986年   2篇
  1985年   4篇
  1984年   1篇
  1983年   1篇
  1982年   3篇
  1981年   3篇
  1978年   3篇
  1977年   1篇
  1976年   2篇
  1975年   3篇
  1974年   2篇
  1973年   1篇
排序方式: 共有142条查询结果,搜索用时 0 毫秒
1.
This paper addresses the question of the extent to which finger ridge-count data are useful features with which to study population variation in Subsaharan Africa. Each subject was represented by a vector of 20 ridge-counts, a radial and an ulnar count for each digit. Such data were available from 11 African groups, nine of which were indigenous Africans, and two, the South African Colored and South African Indians, contained a portion of non-African ancestory. The ridge-counts were first transformed to principal component scores and these were subjected to multivariate analysis of variance and distance analysis to elucidate intergroup variation. The primary findings were that ridgecounts provide a good reflection of variation on at least two levels, that of African versus non-African, and variation among Africans. Also, the principal components that reveal variation at these two levels are very different. We conclude that ridge-counts can only be useful in population studies if full account is taken of their multicomponent nature.  相似文献   
2.
3.
Volcanic ocean crust contains a global chemosynthetic microbial ecosystem that impacts ocean productivity, seawater chemistry and geochemical cycling. We examined the mineralogical effect on community structure in the aquifer ecosystem by using a four-year in situ colonization experiment with igneous minerals and glasses in Integrated Ocean Drilling Program Hole 1301A on the Juan de Fuca Ridge. Microbial community analysis and scanning electron microscopy revealed that olivine phases and iron-bearing minerals bore communities that were distinct from iron-poor phases. Communities were dominated by Archaeoglobaceae, Clostridia, Thermosipho, Desulforudis and OP1 lineages. Our results suggest that mineralogy determines microbial composition in the subseafloor aquifer ecosystem.  相似文献   
4.
The mechanism of inheritance of ridge count of plantar inter-digital areas has been studied among Brahmans of Sagar town of Central India. The correlation coefficient between ridge counts in various family relationships lend support to the concept of an additive genetic model.  相似文献   
5.
A new species of pycnogonid collected by the Chinese research vessel R/V Dayangyihao during cruises to the Southwest Indian Ridge in 2008 and 2009 is recorded. The new species, Austrodecus bamberi, is placed into the tristanense-section by the characters of 4-articled ovigers and present auxiliary claws and is distinguished from other species in this section by the number and length of tubercles on the first coxae.  相似文献   
6.
Abstract

A total of 89 species of elasmobranch and teleost fish was recorded from the West Norfolk Ridge in 1986. Between 50 and 60 of these have not previously been reported from the area. Fish species were caught in bottom trawls at depths between 100 m and 1100 m, principally on the Wanganella Bank. Depth distribution is discussed. Species composition is very similar to that of northern New Zealand.  相似文献   
7.
The use of sodium dithionite as the reducing agent to produce the radical cation of methyl viologen cofactor for the nitrate reductase-catalyzed reduction of nitrate to nitrite causes a negative interference in the diazonium salt azo dye determination of nitrite. The interference results from bisulfite, a reaction product of dithionite, reacting with the diazonium salt formed from nitrite and sulfanilamide. Addition of formaldehyde before the diazotization reaction masks this interference but at low acidity introduces a nonlinearity in the nitrite calibration curve. This nonlinearity is due to a competing reaction of formaldehyde with sulfanilamide to yield a Schiff base and can be eliminated by increasing the HCL content of the sulfanilamide reagent.  相似文献   
8.
Finger prints of the Bagathas, a dominant endogamous tribal population of Araku Valley in Andhra Pradesh (India) were analysed. They are distributed in Araku, Paderu and Chintapalli agency areas of Visakhapatnam district of A.P. Investigations on finger prints of 235 males and 235 females reveal that loops are higher in females (57.58%) than in males (49.19%). Sex differences in the distribution of the patterns are statistically significant (X2 = 27.8277; d.f. = 2; 0.001 > P). The index of pattern intensity shows a higher value in males (14.17) than the females (12.84). It is evident from the mean ridge counts that there is a clear sexual dimorphism, males showing higher mean ridge counts than females. Bagathas show greater affinity with the Valmikis in the frequency distribution of pattern types and in the pattern intensity index. However, a more detailed dermatoglyphic study of all the tribes of Andhra Pradesh yields information of great value in disclosing the pattern distributions among these Dravidian or proto-Australoid tribal populations.  相似文献   
9.
Functional ecosystems depend on biotic and abiotic connections among different environmental realms, including terrestrial, freshwater, and marine habitats. Accounting for such connections is increasingly recognized as critical for conservation of ecosystems, especially given growing understanding of the way in which anthropogenic landscape disturbances can degrade both freshwater and marine habitats. This need may be paramount in conservation planning for tropical island ecosystems, as habitats across realms are often in close proximity, and because endemic organisms utilize multiple habitats to complete life histories. In this study, we used Marxan analysis to develop conservation planning scenarios across the five largest islands of Hawaii, in one instance accounting for and in another excluding habitat connectivity between inland and coastal habitats. Native vegetation, perennial streams, and areas of biological significance along the coast were used as conservation targets in analysis. Cost, or the amount of effort required for conservation, was estimated using an index that integrated degree and intensity of anthropogenic landscape disturbances. Our results showed that when connectivity is accounted for among terrestrial, freshwater, and marine habitats, areas identified as having high conservation value are substantially different compared to results when connectivity across realms is not considered. We also showed that the trade-off of planning conservation across realms was minimal and that cross-realm planning had the unexpected benefit of selecting areas with less habitat degradation, suggesting less effort for conservation. Our cross-realm planning approach considers biophysical interactions and complexity within and across ecosystems, as well as anthropogenic factors that may influence habitats outside of their physical boundaries, and we recommend implementing similar approaches to achieve integrated conservation efforts.  相似文献   
10.
Habitat loss via human activity has fragmented populations of the golden snub-nosed monkey (Rhinopithecus roxellana), and thus affected patterns of gene flow. We investigated in-depth a single troop in the Qinling Mountains, central China, two major histocompatibility complex (MHC) class II loci, DQA1 and DQB1, and compared the resulting data with data from troops from the wider Qinling Mountains region. We found that a novel DQB1 allele was only present in the study troop and relatively few divergent alleles at the DQA1 and DQB1 loci were present compared with the wider population. The inbreeding coefficient (Fis) at the MHC region was lower than previous measurements, which may have reflected different sampling strategies. However, R. roxellana has relatively high diversity in MHC genes, even though it has probably experienced serious past population bottlenecks and reduced gene flow between populations. We also found that some alleles present in the wider population had been lost in the study troop, and suggest that conservation management strategies be implemented to increase gene flow between troops in order to increase genetic variation.  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