全文获取类型
收费全文 | 249篇 |
免费 | 1篇 |
专业分类
250篇 |
出版年
2019年 | 2篇 |
2014年 | 5篇 |
2013年 | 15篇 |
2012年 | 4篇 |
2011年 | 10篇 |
2010年 | 16篇 |
2009年 | 10篇 |
2008年 | 11篇 |
2007年 | 12篇 |
2006年 | 9篇 |
2005年 | 18篇 |
2004年 | 7篇 |
2003年 | 2篇 |
2002年 | 4篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1966年 | 2篇 |
1963年 | 1篇 |
1959年 | 2篇 |
1958年 | 1篇 |
1957年 | 8篇 |
1956年 | 5篇 |
1955年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有250条查询结果,搜索用时 0 毫秒
1.
The Ordovician-Silurian boundary stratotype: consequences of its approval by the IUGS 总被引:4,自引:0,他引:4
PIERRE J. Lespérance CHRISTOPHER R. Barnes WILLIAM B. N. Berry ARTHUR J. Boucot MU Enzhi 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1987,20(3):217-222
Lespérance, Pierre J., Barnes, Christopher R., Berry, William B. N., Boucot, Arthur J. & Mu En-zhi 1987 07 15: The Ordovician-Silurian boundary stratotype: consequences of its approval by the IUGS.
The Ordovician-Silurian stratotype at Dob's Linn, Scotland is the second systemic boundary approved by the International Union of Geological Sciences (IUGS). A review of the internationally accepted criteria required of a stratotype shows that few of these are possessed by the Dob's Linn section. The strongest attribute of the section is the presence of zonal graptolites, although the boundary is recognized primarily on a single biological event (base of acuminatus Zone) for which the evolutionary relationships of the taxa are not established. In approving this boundary proposal in 1985, which received only simple majority support within the Ordovician-Silurian Boundary Working Group (OSBWG) and which fails to meet most of the accepted prerequisites for a stratotype, the International Commission on Stratigraphy (ICS) and the IUGS have established an unfortunate precedent. It follows that future systemic boundaries need not meet the accepted standards. It raises serious questions on the assessment and voting procedures of the International Commission on Stratigraphy and on the credence accorded the recommendations developed by the International Subcommission on Stratigraphic Classification of IUGS. 相似文献
The Ordovician-Silurian stratotype at Dob's Linn, Scotland is the second systemic boundary approved by the International Union of Geological Sciences (IUGS). A review of the internationally accepted criteria required of a stratotype shows that few of these are possessed by the Dob's Linn section. The strongest attribute of the section is the presence of zonal graptolites, although the boundary is recognized primarily on a single biological event (base of acuminatus Zone) for which the evolutionary relationships of the taxa are not established. In approving this boundary proposal in 1985, which received only simple majority support within the Ordovician-Silurian Boundary Working Group (OSBWG) and which fails to meet most of the accepted prerequisites for a stratotype, the International Commission on Stratigraphy (ICS) and the IUGS have established an unfortunate precedent. It follows that future systemic boundaries need not meet the accepted standards. It raises serious questions on the assessment and voting procedures of the International Commission on Stratigraphy and on the credence accorded the recommendations developed by the International Subcommission on Stratigraphic Classification of IUGS. 相似文献
2.
The pair, duo-trio and triangle tests were compared, using three levels of instructions with orange drink as medium and sucrose as stimulus. If the subjects know only the nature of the test, the pair test cannot be performed and the frequencies of correct responses above chance of the two other tests do not differ significantly, in this case the triangle test is the more efficient. If the subjects know the nature of the test and the nature of the stimulus, the frequency of correct responses above chance obtained for the pair test is significantly higher than those of the two other tests, in this case the pair test is more efficient. Finally, if the subjects know the nature of the test, the nature of the stimulus and whether or not the sample to be selected contains the stimulus, the conclusions are more difficult to achieve but the triangle test seems to be the more efficient. 相似文献
3.
ABSTRACT. Bloodstream forms of Trypanosoma musculi, cultured in Schneider's drosophila medium at room temperature, multiply and differentiate through a series of developmental stages into infective metacyclic trypomastigotes in 10 days. Oral inoculation with these culture forms into CBA mice produced a parasitemia similar to that produced by intraperitoneal infection with bloodstream forms except for a three-day longer prepatent period. Attempts to induce parasitemia with bloodstream forms given orally were unsuccessful. 相似文献
4.
AVRAM HERSHKO PIERRE MAMONT ROBERT SHIELDS GORDON M. TOMKINS 《Nature: New biology》1971,232(33):206-211
A hypothesis has been developed to relate stringent control in bacteria to a set of interactions involved in the regulation of growth of transformed and untransformed mammalian cells. 相似文献
5.
6.
7.
JANICE BRITTON-DAVIDIAN FABIENNE FEL-CLAIR JOËLLE LOPEZ PAUL ALIBERT PIERRE BOURSOT 《Biological journal of the Linnean Society. Linnean Society of London》2005,84(3):379-393
We assessed the fertility (reproductive success, litter size, testis weight, spermatocyte-to-spermatid ratio) of F1 s and backcrosses between different wild-derived outbred and inbred strains of two mouse subspecies, Mus musculus domesticus and M. m. musculus . A significant proportion of the F1 females between the outbred crosses did not reproduce, suggesting that female infertility was present. As the spermatocyte-to-spermatid ratio was correlated with testis weight, the latter was used to attribute a sterile vs. fertile phenotype to all males. Segregation proportions in the backcrosses of F1 females yielded 11 (inbred) to 17% (outbred) sterile males, suggesting the contribution of two to three major genetic factors to hybrid male sterility. Only one direction of cross between the inbred strains produced sterile F1 males, indicating that one factor was borne by the musculus X-chromosome. No such differences were observed between reciprocal crosses in the outbred strains. The involvement of the X chromosome in male sterility thus could not be assessed, but its contribution appears likely given the limited introgression of X-linked markers through the hybrid zone between the subspecies. However, we observed no sterile phenotypes in wild males from the hybrid zone, although testis weight tended to decrease in the centre of the transect. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 379–393. 相似文献
8.
9.
10.
Detecting and predicting how populations respond to environmental variability are eminent challenges in conservation research and management. This is particularly true for wildlife populations at high latitudes, many of which demonstrate changes in population dynamics associated with global warming. The Falkland Islands (Southwest Atlantic) hold one of the largest Gentoo Penguin Pygoscelis papua populations in the world, representing c. 34% of the global population. The numbers of breeding Gentoo Penguins at the Falkland Islands have shown a high degree of inter‐annual variability since monitoring commenced in 1990. However, proximate causes of annual variability in breeding numbers have not been explored. Here we examine 21 years of Gentoo Penguin breeding surveys from the Falkland Islands and assess whether inter‐annual variability in the number of breeding pairs were correlated with proxies of environmental variability. There was a positive correlation between the number of breeding pairs and a broad‐scale climatic variation index, the Southern Oscillation Index (SOI). In turn, the SOI was significantly correlated with spring sea surface temperature anomalies, indicating a more immediate atmospherically forced response to El Niño Southern Oscillation variability in the Southwest Atlantic than previously reported. However, we also describe a non‐linear response to environmental variability that may highlight foraging plasticity and/or the complexity of regional ecosystem interactions that operate across a range of different scales. 相似文献