全文获取类型
收费全文 | 85篇 |
免费 | 1篇 |
出版年
2018年 | 1篇 |
2014年 | 2篇 |
2013年 | 3篇 |
2012年 | 2篇 |
2011年 | 5篇 |
2010年 | 8篇 |
2009年 | 5篇 |
2008年 | 3篇 |
2007年 | 1篇 |
2006年 | 4篇 |
2005年 | 3篇 |
2004年 | 4篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 5篇 |
1971年 | 2篇 |
1968年 | 2篇 |
1966年 | 1篇 |
1957年 | 1篇 |
1956年 | 1篇 |
1949年 | 1篇 |
排序方式: 共有86条查询结果,搜索用时 80 毫秒
51.
MITCHELL A. LOCKWOOD DON B. FRELS JR. WILLIAM E. ARMSTRONG EUGENE FUCHS DONNIE E. HARMEL 《The Journal of wildlife management》2007,71(8):2732-2735
ABSTRACT We applied an 8-year selection process in an attempt to determine if yearling antler quality in subsequent cohorts could be improved by selecting for yearling male white-tailed deer (Odocoileus virginianus) exhibiting relatively superior antler potential under suboptimal nutritional conditions. In 41 single-sire (breeding M) breeding herds, 217 yearling males were produced on an 8% protein diet of limited quantity. All antler measurements increased significantly (P < 0.001) during the study: number of points (+3.2), inside spread (+96.5 mm), main beam length (+129.1 mm), basal circumference (+21.6 mm), and total antler weight (+231.3 g). Furthermore, mean gross Boone and Crockett (GBC) score increased (P < 0.001) linearly throughout the study, with the GBC of the 1999 cohort exceeding that of the 1993 cohort by 36.4 in (923.0 mm). These data provide insight to the effectiveness of a selection process (i.e., culling) in an overall deer-management program. 相似文献
52.
53.
Lignification and Xylogenesis in Lactuca Pith Explants Cultured In Vitro in the Presence of Auxin and Cytokinin: A Role for Endogenous Ethylene 总被引:2,自引:0,他引:2
MILLER A. RAYMOND; CRAWFORD DON L.; ROBERTS LORIN W. 《Journal of experimental botany》1985,36(1):110-118
Lignification and xylogenesis were studied in lettuce (Lactucasativa L. cv. Romaine) pith parenchyma explants cultured ona Murashige and Skoog basal medium supplemented with indole-3-aceticacid, kinetin, and glucose. Lignin formation was observed tooccur in two distinct phases, one preceding xylem differentiation(days 03 of culture) and another coincident with maximalxylogenesis (days 47). The rate of soluble phenolic productionby these explants increased concomitant with the first phaseof lignification, then decreased during the second phase. Addition of silver, an ethylene antagonist, to the culture mediuminhibited the second phase of lignification and markedly reducedwall-bound peroxidase activity. Exogenous L-methionine, an ethyleneprecursor, completely reversed the inhibitory effect of silveron ligm6cation and wall-bound peroxidase activity. Silver increasedphenylalanine ammonia-lyase activity, but had no effect on solublephenolic production or soluble pcroxidase activity. These resultssuggest that ethylene may play a role in controlling lignificationduring xylogenesis by inducing wall-bound peroxidase activity. Key words: Auxin, Cytokinin, Ethylene, Xylogenesis, Lignification, Phenylalanine ammonia-lyase, Peroxidase 相似文献
54.
55.
DON KALB 《American anthropologist》2004,106(2):413-414
The Anthropology of Globalization: Cultural Anthropology Enters the 21st Century. Ted C. Lewellen. Westport: Bergin and Garvey, 2002. 282 pp. 相似文献
56.
57.
DON A. DRISCOLL 《Austral ecology》1999,24(2):182-189
Populations that fluctuate in size may become small at particular times and therefore be at risk of extinction. I used skeletochronology to examine the potential for fluctuations in population size in the threatened frog species Geocrinia alba and Geocrinia vitellina from southwestern Australia. The change in number of lines of arrested growth (LAG) in toe bones of recaptured frogs indicated that most individuals probably gain one LAG annually. Therefore, skeletochronology can be used for age determination. From a combination of skeletochronology and a mark–recapture study, both species appear to live for a maximum of six years. However, the majority of adult males only bred in a single year, which gave rise to a consistently dominant three-year-old age class. A drop in the number of two-year-old frogs and a large increase in the number of three-year-olds (up to 85%) from 1993 to 1994 in both species highlighted the potential for substantial fluctuations in population size. Widespread changes in abundance of between 25 and 50% may therefore be expected over periods as short as one or two years, due to variation in recruitment success. 相似文献
58.
SONIA WOLFE-COOTE JOHAN LOUW COLIN WOODROOF DON F. DU TOIT 《Cell biology international》1996,20(2):95-101
An investigation into the development of the Vervet monkey endocrine pancreas revealed a sequence of occurrence of pancreatic peptides that differed from previous reports in mice, dog and human with PP and somatostatin occurring before glucagon and insulin. All four pancreatic peptides were identified, immunohistochemically, in only one of the pancreatic primordial buds, before fusion of the two buds to form the pancreas. This questions the hypothesis that the heterogeneous endocrine cell distribution seen in the adult pancreas is due to the contribution of only PP cells by the ventral bud and non-PP cells by the dorsal bud. Co-localization of glucagon and PP was observed extensively in the developing pancreas and the predominant expression of one over the other in an apparently organized non-random manner accounted for the glucagon- and PP-rich areas seen in the developing pancreas. A small number of cells immunoreactive to glucagon and PP were also observed in the adult. Reports of plasticity of differentiation of other pancreatic cells led us to investigate regeneration potential of the adult monkey pancreas. Partial obstruction of the Vervet monkey main pancreatic duct, by cellophane wrapping, resulted in duct cell proliferation and differentiation to form new endocrine tissue in a way that mimics normal organogenesis. Focal areas of hepatocytes were found in the regenerated pancreas of one monkey, illustrating further the latent developmental capabilities of adult pancreas cells. These findings could lead to interesting new therapies for pancreas and liver disease. 相似文献
59.
In the absence of hormone stimulation, prophase-blocked oocytes of Marthasterias glacialis have been induced to undergo meiosis reinitiation up to female pronucleus formation by pulse incubation in isoosmotic urea-sea water solutions. Even when this procedure was not effective all along the breeding season, it could trigger full maturation when applied to so-called "incompetent oocytes" that did not complete maturation following microinjection-induced mixing of their nucleoplasm and cytoplasm.
32 P phosphate incorporation into proteins and cell fusion experiments demonstrate that this treatment produces an increased protein phosphorylation which appears tightly associated with the production of M-phase promoting factor (MPF). Instead, when oocytes are maintained in the inducing medium, dephosphorylation soon occurs and MPF is no longer present to support meiosis. Under these conditions, the GV-disrupted oocytes present a permanent nucleolus and do not form a meiotic spindle. The same cytological aspect was also obtained when the oocytes were treated in the presence of 90 μM emetine or 150 μM of the intracellular chelator Quin 2-AM.
These data suggest that urea-induced maturation may involve an intracellular Ca2+ shift which would be required to activate both MPF precursor molecules and the resting female centers which stand in the animal cortex outside the nucleus and give rise to the poles of the first maturation spindle. They also show that nuclear disruption alone, without protein phosphorylation, cannot trigger meiosis reinitiation of incompetent oocytes. 相似文献
These data suggest that urea-induced maturation may involve an intracellular Ca
60.
Genetic diversity in the Eurasian otter, Lutra lutra, in Scotland. Evidence from microsatellite polymorphism 总被引:1,自引:0,他引:1
JOHN F. DALLAS PHILIP J. BACON DAVID N. CARSS JAMES W. H. CONROY ROSIE GREEN DON J. JEFFERIES HANS KRUUK FREDA MARSHALL STUART B. PIERTNEY PAUL A. RACEY 《Biological journal of the Linnean Society. Linnean Society of London》1999,68(1-2):73-86
The relationship between microsatellite diversity and geographical fragmentation and isolation was studied in Scottish populations of the Eurasian otter, Lutra lutra. The geographic range of the study encompassed isolated archipelagos, islands adjacent to the Scottish mainland and both fragmented and continuous mainland populations. Tissue samples of 496 individuals from across Scotland were assayed for polymorphism at ten microsatellites. The isolation of populations on Shetland, and to a lesser degree on Orkney, was associated with reduced levels of microsatellite diversity. Most of the remaining island and fragmented mainland populations contained levels of microsatellite diversity similar to the high levels observed in die continuous mainland populations. Unexpectedly, both island and continuous mainland populations showed similar rates of departures from mutation-drift equilibrium. Such departures could have arisen from a variety of local demographic processes besides population bottlenecks. Gene flow appeared to be a major factor maintaining microsatellite diversity in all of these populations except the one on Shedand. 相似文献