全文获取类型
收费全文 | 139篇 |
免费 | 6篇 |
国内免费 | 1篇 |
出版年
2021年 | 2篇 |
2017年 | 3篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 7篇 |
2012年 | 6篇 |
2011年 | 2篇 |
2010年 | 7篇 |
2009年 | 4篇 |
2008年 | 6篇 |
2007年 | 3篇 |
2006年 | 3篇 |
2005年 | 4篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 10篇 |
1997年 | 8篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1967年 | 2篇 |
1963年 | 1篇 |
1959年 | 1篇 |
1954年 | 1篇 |
1950年 | 1篇 |
1933年 | 1篇 |
1924年 | 1篇 |
1923年 | 1篇 |
排序方式: 共有146条查询结果,搜索用时 31 毫秒
51.
Structure and organization of the bovine beta-globin genes 总被引:1,自引:0,他引:1
Genomic clones spanning the entire cow beta-globin gene locus have been
isolated and characterized. These clones demonstrate that the linkage of
embryonic-like (epsilon) genes and pseudogenes (psi) to the previously
described fetal (gamma) and adult (beta) genes is as follows: 5'-epsilon
3-epsilon 4-psi 3-beta-epsilon 1-epsilon 2-psi 1- psi 2-gamma-3'. Present
data indicate that, like that of the goat, the fetal and adult genes arose
via block duplication of an ancestral four- gene set:
epsilon-epsilon-psi-beta. This duplication event preceded the divergence of
cows and goats, which occurred greater than or equal to 18-20 Myr ago.
However, cows do not have the additional four-gene block containing a
preadult/stress globin gene (beta C). Furthermore, the cow fetal cluster
contains an extra beta-like pseudogene, which apparently arose by a
small-scale duplication. The fixation of this duplication may indicate a
possible evolutionary role for pseudogenes.
相似文献
52.
1. As part of a long-term study of the effects of elevated CO2 on biodiversity and ecosystem function in a calcareous grassland, we measured ecosystem carbon dioxide and water-vapour fluxes over 24-h periods during the 1994 and 1995 growing seasons. Data were used to derive CO2 and H2 O gas-exchange response functions to quantum flux density (QFD).
2. The relative increase in net ecosystem CO2 flux (NEC) owing to CO2 enrichment increased as QFD rose. Daytime NEC at high QFD under elevated CO2 increased by 25% to 60%, with the greatest increases in the spring and after mowing in June when above-ground biomass was lowest. There was much less stimulation of NEC in early June and again in October when the canopy was fully developed. Night-time NEC was not significantly altered under elevated CO2 .
3. Short-term reversal of CO2 concentrations between treatments after two seasons of CO2 exposure provided evidence for a 50% downward adjustment of NEC expressed per unit above-ground plant dry weight. However, when expressed on a land area basis, this difference disappeared because of a c. 20% increase in above-ground biomass under elevated CO2 .
4. Ecosystem evapotranspiration (ET) was not significantly altered by elevated CO2 when averaged over all measurement dates and positions. However, ET was reduced 3–18% at high QFD in plots at the top of the slope at our study site. In summary, CO2 enrichment resulted in a large stimulation of ecosystem CO2 capture, especially during periods of a large demand of carbon in relationship to its supply, and resulted in a relatively small and variable effect on ecosystem water consumption. 相似文献
2. The relative increase in net ecosystem CO
3. Short-term reversal of CO
4. Ecosystem evapotranspiration (ET) was not significantly altered by elevated CO
53.
Potato plants (Solanum tuberosum L.) were grown in water culturein a controlled environment. The growth rates of individualtubers were closely reflected by their 14C-content 20 h after14CO2 had been applied to the aerial parts of the shoot for4 h. The 14C-content of the tuber (sink strength) was significantlycorrelated to the 14C-concentration of the tuber tissue (14Cg1 fr. wt.=sink activity). The sink activity, which differedbetween individual tubers by up to a factor of 10, was alsoclosely related to the conversion rates of 14C into the starchand the remainder as well as to the 14C-content in the ethanolsoluble fraction. This indicates the simultaneous use of photosynthatefor growth and storage in the growing tubers. No preferenceof photosynthate utilization for either of these processes couldbe detected in relation to the sink activity of the tubers.Tubers with high sink activity imported 14C-labelled photosynthateat higher rates although their tissue contained higher concentrationsof reducing sugars and sucrose than the tissue of tubers withlow sink activity. Despite the close relationship between sinkactivity and the rate of starch synthesis (14C-conversion intostarch), no significant correlation was found between sink activityand the actual starch concentration of the tissue. The applicationof zeatin riboside directly onto individual tubers increasedtheir growth rates in comparison to non-treated tubers of thesame plant. The results indicate the importance of both growthand storage processes for the regulation of sink activity inyoung potato tubers. Key words: Potato tuber, 14C-photosynthate partitioning, zeatin riboside application 相似文献
54.
55.
Summary A novel nickel resistant, hyperaccumulatingN.crassa nir-2 mutant, isolated by us, sequestered 90% of Ni2+ from medium with 120 mg/l Ni2+. The parent wild strain showed comparable efficiency only at much lower concentrations (<10mg/l). The initial rapid rate and efficiency of Ni2+ removal could be maintained beyond 2 h by fresh addition of mycelial biomass. The results have been discussed from the stand point of the utility of metal resistant fungi in the control of environmental pollution. 相似文献
56.
57.
58.
Chuti Laowtammathron Eric CH Cheng Pei-Hsun Cheng Brooke R Snyder Shang-Hsun Yang Zach Johnson Chanchao Lorthongpanich Hung-Chih Kuo Rangsun Parnpai Anthony WS Chan 《BMC cell biology》2010,11(1):12
Background
Pluripotent stem cells that are capable of differentiating into different cell types and develop robust hallmark cellular features are useful tools for clarifying the impact of developmental events on neurodegenerative diseases such as Huntington's disease. Additionally, a Huntington's cell model that develops robust pathological features of Huntington's disease would be valuable for drug discovery research. 相似文献59.
Cynthia CH Khoo Joseph Piper Irma Sanchez-Vargas Ken E Olson Alexander WE Franz 《BMC microbiology》2010,10(1):130
Background
The RNA interference (RNAi) pathway acts as an innate antiviral immune response in Aedes aegypti, modulating arbovirus infection of mosquitoes. Sindbis virus (SINV; family: Togaviridae, genus: Alphavirus) is an arbovirus that infects Ae. aegypti in the laboratory. SINV strain TR339 encounters a midgut escape barrier (MEB) during infection of Ae. aegypti. The nature of this barrier is not well understood. To investigate the role of the midgut as the central organ determining vector competence for arboviruses, we generated transgenic mosquitoes in which the RNAi pathway was impaired in midgut tissue of bloodfed females. We used these mosquitoes to reveal effects of RNAi impairment in the midgut on SINV replication, midgut infection and dissemination efficiencies, and mosquito longevity. 相似文献60.
Nicoline BM Voet Gijs Bleijenberg George W Padberg Baziel GM van Engelen Alexander CH Geurts 《BMC neurology》2010,10(1):56