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排序方式: 共有454条查询结果,搜索用时 31 毫秒
101.
102.
Reconstruction of May—July precipitation in the north Helan Mountain, Inner Mongolia since A.D. 1726 from tree-ring late-wood widths 总被引:7,自引:0,他引:7
LIU Yu SHI Jiangfeng V. Shishov E. Vaganov YANG Yinke CAI Qiufang SUN Junyan WANG Lei & I. Djanseitov . State Key Laboratory of Loess Quaternary Geology Institute of Earth Environment Chinese Academy of Sciences Xi抋n China . Sukachev Institute of Forest Russian Academy of Sciences Kras-noyarsk Russia 《科学通报(英文版)》2004,49(4):405-409
Inrecentyears,greatprogressofdendroclimatologystudyhasbeenmadeinChina,andlotsofvaluabledatahavebeenobtained.Theclimaticfactors,suchastem-perature,precipitation,etc.,havebeenreconstructedonthebasisoftree-ringdataforthepastseveralcenturies[1—5].Thesedatahaveplayed(orwillplay)animportantroleinbothregionalandglobalchangeresearches[6].Sofar,however,tree-ringdatafromtheboundaryofthedeserttoloessareainnorthwestChinaaresparse[7].Thisstudywillusethetree-ringdataintermsofthestatisticalmethodtoreconstr… 相似文献
103.
Balbín M Fueyo A Tester AM Pendás AM Pitiot AS Astudillo A Overall CM Shapiro SD López-Otín C 《Nature genetics》2003,35(3):252-257
Matrix metalloproteinases (MMPs) have fundamental roles in tumor progression, but most clinical trials with MMP inhibitors have not shown improvements in individuals with cancer. This may be partly because broad-range inhibitors also reduce host-protective antitumor properties of individual MMPs. We generated mice deficient in collagenase-2 (Mmp8), an MMP mainly produced by neutrophils in inflammatory reactions and detected in some malignant tumors. Loss of Mmp8 did not cause abnormalities during embryonic development or in adult mice. Contrary to previous studies with MMP-deficient mice, however, the absence of Mmp8 strongly increased the incidence of skin tumors in male Mmp8(-/-)mice. Female Mmp8(-/-)mice whose ovaries were removed or were treated with tamoxifen were also more susceptible to tumors compared with wild-type mice. Bone marrow transplantation experiments confirmed that Mmp8 supplied by neutrophils was sufficient to restore the natural protection against tumor development mediated by this protease in male mice. Histopathological analysis showed that mutant mice had abnormalities in the inflammatory response induced by carcinogens. Our study identifies a paradoxical protective role for Mmp8 in cancer and provides a genetic model to evaluate the molecular basis of gender differences in cancer susceptibility. 相似文献
104.
105.
106.
The earliest-known ancestors of Recent Priapulomorpha from the Early Cambrian Chengjiang Lagersttte
HAN Jian SHU Degan ZHANG Zhifei & LIU Jianni .Department of Geology Key Laboratory for Continental Dynam- ics of the Education Ministry Northwest University Xi’an China .School of Earth Sciences Resources China University of Geo- sciences Beijing China 《科学通报(英文版)》2004,(17)
It was suggested and eventually has been profferedthat the representatives of all extant phyla, including someminor group, occurred during the Cambrian radia-tions[1—10]. Many priapulid-like fossil worms have beenreported from Cambrian Lagerst?tten, such as the EarlyCambrian Chengjiang Lagerst?tte[11—16], the Middle Cam-brian Burgess Shale[17], and the Middle Cambrian Kailifauna[18]. The palaeoscolecidan worms from these Lager-st?tten have been regarded as either a stem group of thepri… 相似文献
107.
Jiang Hui 《科学通报(英文版)》2007,52(6):789-796
Diatom data from core MD992271 on the North Icelandic shelf record a cooling trend through the last 3000 years. This is indicated by a general decrease in warm water species and an increase in cold water taxa. The relative abundance of these two diatom groups changed periodically, suggesting that the climate also fluctuated within this time period. The results of diatom-based transfer function calculation show that the summer sea-surface temperatures (SSTs) before 1400 cal. a BP were generally higher than the mean value for the last 3000 years and the summer SSTs fluctuated around the mean between 1400 and 700 cal. a BP, and dropped to the values below the mean after 700 cal. a BP. Four cooling events were distinguished, centered at around 2600, 1900, 1300 and 600 cal. a BP respectively. The results are not only consistent with the data from neighbouring cores HM107-03 and MD992275, but also comparable with those from the GISP2 ice core and from other marine sediment records in the North Atlantic. This suggests that changes in the summer SSTs reflect regional climate variations in the North Atlantic. On the North Icelandic shelf, the summer SST variation is a result of changes in the in-teraction between the cold and the warm currents in the area. 相似文献
108.
Miguel A. Gutiérrez-Naranjo Mario J. Pérez-Jiménez Agustín Riscos-Nú?ez Francisco J. Romero-Campero 《自然科学进展》2007,17(4):449-457
In this paper we discuss the potential usefulness of membrane systems as tools for modelling tumours. The approach is followed both from a macroscopic and a microscopic point of view. In the first case, one considers the tumour as a growing mass of cells, focusing on its external shape. In the second case, one descends to the microscopic level, studying molecular signalling pathways that are crucial to determine if a cell is cancerous or not. In each of these approaches we work with appropriate variants of membrane systems. 相似文献
109.
Insulin improves cardiac myocytes contractile function recovery in simulated ischemia-reperfusion: Key role of Akt 总被引:6,自引:0,他引:6
ZHANG Bo ZHANG Haifeng FAN Qian MA Xinliang & GAO Feng Department of Physiology The Fourth Military Medical University Xi抋n China Correspondence should be addressed to Gao Feng 《科学通报(英文版)》2003,48(13):1364-1369
There are abundant insulin receptors on the membrane of myocytes, which renders cardiomyocytes typical target cells of insulin. Accumulating evidence has indicated that abnormal insulin level is an important predisposing factor in diabetes-related cardiovascular disorders and may contribute to the development of cardiovascular diseases, such as coronary heart diseaseand heart failure. It has been shown that insulin couldreduce infarct size in experimental animals subjected to myocardial ischem… 相似文献
110.
Ricardo Mata-González Benjamín Figueroa-Sandoval Fernando Clemente Mario Manzano 《西北部美国博物学家》2011,67(1)
Vegetation cover and production were evaluated after nearly 7 years of livestock grazing exclusion and shrub control in an area with a long history of heavy livestock grazing in the southern Chihuahuan Desert, Mexico. An exclosure was established to prevent livestock grazing. In half of the excluded area, the main shrub, Larrea tridentata , was mechanically controlled. Outside the exclosure, heavy livestock grazing occurred as customary and shrubs were not controlled. Absence of grazing resulted in 50% higher grass cover and 35% higher total biomass. Larrea tridentata cover was twice as high on the grazed area as on the ungrazed area. Vegetation cover was dominated by grasses (42%) in the ungrazed area, whereas in the grazed area, cover was equally divided between grasses (28%) and shrubs (27%). Shrub control did not affect vegetation cover or herbage production. Multivariate analysis confirmed that inside the excluded area, shrub control had little impact on the plant community. The effect of grazing, however, clearly distinguished the community outside the exclosure from that inside the exclosure. 相似文献