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排序方式: 共有388条查询结果,搜索用时 31 毫秒
241.
Jordi Figuerola Iris Charalambidou Luis Santamaria Andy J. Green 《Die Naturwissenschaften》2010,97(6):555-565
Long distance dispersal may have important consequences for gene flow and community structure. The dispersal of many plants
depends on transport by vertebrate seed dispersers. The shapes of seed shadows produced by vertebrates depend both on movement
patterns of the dispersers and on the dynamics and effects of passage through the disperser’s gut (i.e. the retention time,
survival and germination of ingested seeds). A combination of experiments with captive waterbirds and aquatic plant seeds
was used to analyse the following: (a) the effects of inter- and intra-specific variation in seed size and duck species on
seed retention time in the gut and (b) the relationship between retention time and the percent germination and germination
rates of seeds. Among the three Scirpus species used, those with smaller seeds showed higher survival after ingestion by birds and longer retention times inside
their guts than those with larger seeds. For Potamogeton pectinatus, only seeds from the smaller size class (<8 mg) survived ingestion. Retention time affected the percent germination and germination
rate of Scirpus seeds but in a manner that varied for the different plant and bird species studied. We recorded both linear and non-linear
effects of retention time on percent germination. In addition, germination rate was positively correlated with retention time
in Scirpus litoralis but negatively correlated in Scirpus lacustris. Small seed size can favour dispersal over larger distances. However, the effects of retention time on percent germination
can modify the seed shadows produced by birds due to higher percent germination of seeds retained for short or intermediate
periods. The changes in dispersal quality associated with dispersal distance (which is expected to be positively related to
retention time) will affect the probability of seedling establishment over longer distances and, thus, the spatial characteristics
of the effective seed shadow. 相似文献
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Mark T. Cullen MD Sandro Gabrielli Jacqueline J. Green Nicola Rizzo Maurice J. Mahoney Carolyn Salafia Luciano Bovicelli John C. Hobbins 《黑龙江环境通报》1990,10(10):643-651
Thirty cases of cervical cystic hygroma were diagnosed in the first trimester of pregnancy. Karyotype analysis was available in 29 (97 per cent). Fifteen (52 per cent) had a chromosomal abnormality. The ultrasound appearance was described as posterior cervical, lateral cervical, or cervical hygroma with hydrops. Of the 14 euploid embryos, six were electively aborted, two are undelivered, and six have been delivered as phenotypically normal infants. In cases in which the chromosomes were normal and the pregnancy continued, all lesions resolved by 18 weeks. 相似文献
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247.
Energy transduction in membrane systems 总被引:3,自引:0,他引:3
248.
The recent Green Paper ‘War on Waste’ urges local authorities to organize the recovery and re-use of waste materials in their areas. It is ambiguous, however, on the question of whether recovery should be regarded primarily as a commercial venture or a social service. In this article some of the factors to be considered before embarking on a recovery programme are discussed, and the authors identify some of the arguments for and against the view that recovery is properly a local authority service. Questions considered include the costs and savings associated with a recovery scheme, the impact of the activities of opportunists and the role of the private contractor and voluntary organizations. 相似文献
249.
V. L. Maggio L. R. Alexander V. E. Green J. B. Gill D. G. Patterson Jr. B. N. Green 《毒物与环境化学》2013,95(2-3):143-154
We present the salient characteristics of tuning procedures that have evolved from our 3 years of experience while producing large amounts of data of the highest quality. Our laboratory routinely analyzes 2,3,7,8‐substituted dioxins and furans at parts per quadrillion levels in 50–100 g of human serum samples using the VG 70S/SE stand‐alone gas chromatography/mass spectrometry (GC/MS) system at 10000 resolution (defined by 5% overlap) in the selected ion recording mode. Trace measurement of dioxins and furans in human biological matrices—for example, whole blood, serum, or adipose tissue‐requires reproducible instrument tuning within day as well as among days for quality results. Additionally, instument‐tuning procedures among operators must be reproducible to minimize operator bias because periodically different operators are used. Instrument tuning is highly subjective and argumentive; therefore, to minimize the ambiguity within our laboratory, we have standardized our technique to reproducibly tune the GC/MS system. 相似文献
250.
Florian Winkler Nicole Schoedel Hans-Jörg Zander Roland Ritter 《International Journal of Greenhouse Gas Control》2011
Flue gas purification is a necessary method to avoid emission of sour gases like SOx and NOx into the environment. Another important aspect is the zero CO2 emission from coal-fired power plants. Oxyfuel technology is one of the processes to reach this goal. LINDE KCA Dresden in cooperation with Vattenfall Europe is operating a pilot plant producing liquefied CO2. Product specification and material requirements make flue gas purification for the removal of SOx and NOx unavoidable. The new oxyfuel technologies offer new process conditions for flue gas purification which are not available at atmospheric conditions.At Linde laboratories, catalytic and non-catalytic DeNOx and DeSOx processes have been screened for oxyfuel application. After first feasibility studies, laboratory experiments and economic evaluations, it was decided to develop a process based on wet scrubber systems to remove NOx from flue gas, simultaneously producing ammonia nitrites which can be thermally decomposed into nitrogen in a second step. After demonstration of the single process steps on laboratory scale, a pilot scrubber was erected and commissioned in 2010 at Schwarze Pumpe Oxyfuel Pilot Plant. In September 2010, the successful completion of the pilot tests demonstrated the NOx removal efficiency of this technology. The data from the pilot plant tests have been used to finalise a kinetic model describing the NOx absorption behaviour regarding NOx removal rate and nitrite selectivity for demonstration of plant scale up. This DeNOx-process is now marketed under the name “LICONOX”. 相似文献