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991.
地理信息系统中自然语言查询的分词处理与应用 总被引:4,自引:3,他引:1
随着地理信息系统应用的不断发展,本文提出了在地理信息系统中对基于受限自然语言的查询语句进行分词处理的方法--首字扩词分词法。该分词方法在汲取正向最大匹配分词方法的核心思想--长词优先原则。为了缩小匹配范围,提高匹配效率,该方法首先根据查询自然语言的首字对词汇库的记录进行筛选,得到以该首字开头的词汇库子集;然后再按照长词优先原则把原查询语句与词汇库子集进行匹配,切分查询语句。通过比较,该方法比正向最大匹配方法具有较小的时间复杂度。同时,采用DELPHI编程语言在计算机上得到了实现。 相似文献
992.
用RT-PCR方法从1个H5N1亚型禽流感病毒分离株A/Chicken/Guangdong/DH/1997扩增NA基因cDNA片段,将其克隆至pMD18-T载体,获得重组质粒pMD-NA,并对其核苷酸序列进行测定和分析。结果表明,该毒株的NA基因长度为1350bp,编码449个氨基酸,与其它H5N1亚型AIV分离株的核苷酸序列同源性为97.0%~99.4%,氨基酸序列同源性为97.7%~99.1%,提示禽流感病毒NA基因保守性较高。NA基因氨基酸序列的聚类分析表明该毒株与来自香港的A/Pheasant/HK/FY155/01和A/Ch/HK/FY150/01两个分离株处于同一进化枝,亲缘关系较近。 相似文献
993.
994.
The aim of the study was 1)to determine the relation between the Kuroshio meander and the intensity of the subtropic high
pressure over the Pacific Ocean, and then to obtain statistical validity for the observational conclusion that the occurrence
time of the Kuroshio meander leads the time of strengthened C-circulation of Europe by one or more years; 2) to develop a
method to predict the occurrence time of flood or drought periods in the Changjiang River Valley from the occurrence time
of the Kuroshio meander, since there is a close relation between the occurrence time of the drought or flood periods in the
Changjiang River Valley and the occurrence time of the strong or weak periods of C-circulation of Europe; and 3) to develop
a logical explanation verifiable by remote sensing technique and other means that the warm species phytoplanktons collected
recently in the Jiaozhou Bay of Shandong Peninsula in China were carried there by a new warm current branch of the Kuroshio
in the East China Sea.
This paper was presented at the Conference on Western Pacific Circulation Influence on the China Seas in Qingdao, 1987, and
approved for publishing as a monograph. 相似文献
995.
In a search for infrared excess objects near the galactic plane, a star field of 28.5 square degrees in Vela has been measured on UK Schmidt plates R4272 and 14183 with the Cosmos machine at Royal Observatory, Edinburgh. The magnitude limit is around 20 in R and around 19 in I. 131 infrared excess objects with colour index R-I > 2.5 are discovered in the field, and 3 red stellar objects have been identified as the optical counterparts of IRAS point sources. 相似文献
996.
997.
本文通过太阳活动区光球和色球速度场和磁场观测资料,讨论了黑子活动区附近流场的精细结构,论述了太阳大气中物质的流动呈纤维结构,以及速度场纤维与磁场,色球纤维和网络结构之间的关系。 相似文献
998.
In this paper, observation data in 25 GPS reference stations of China have been analyzed by calculating GPS position coordinate time-series with GIPSY. Result shows there is an obvious trend variation in such time-series. The trend variations of time series along the longitude and latitude coordinate reflect the motion of each position in the global-plate, in which the trend variation in the vertical direction reveals some large-scale construction information or reflects the local movement around the positions. The analysis also shows that such time-series have a variation cycle of nearly 1.02 a, but the reason still remains to be further studied. At the end of this paper, response of the time-series of M S=8.1 Kunlunshan earthquake was analyzed, and the seismogenic process of M S=8.1 Kunlunshan earthquake, according to the time proceeding and the feature of anomaly, was divided into 3 phases—changes in blocks with forces, strain accumulation, quick accumulation and slow release of energy. At the initial stage of seismogenic process of M S=8.1 earthquake and at the imminent earthquake, coseismic process as well as during the post earthquake recovery, anomaly in vertical direction is always in a majority. The anomalous movement in vertical direction at the initial stage resulted in a blocking between faults, while at the middle stage of seismogenic process, the differential movement between blocks are in a majority, which is the major reason causing energy accumulating at the blocking stage of faults. 相似文献
999.
Guojiang?WanEmail author Jing’an?Chen Siqin?Xu Fengchang?Wu P.?H.?Santschi 《中国科学D辑(英文版)》2005,48(4):484-496
The fundamental assumption of 210Pb sediment dating is the stable flux of 210Pbex, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively
constant, the 210Pbex activity in sediments will be exponentially reduced with sedimentation age. 210Pbex in lake water is incorporated into sediments mainly via organic particulates. If the sedimentation flux of organic matter
in lake water is suddenly increased, 210Pbex will be significantly deposited and then transferred into sediments. On the one hand such sudden purification effect is obviously
unfit for the fundamental assumption of 210Pb dating; on the other hand, the sudden enhancement of 210Pbex flux would be indicative of the conspicuous variation of primary productivity of lake water. This problem will be discussed
in accordance with the variation trend of 210Pbex in the vertical profile of recent sediments of Lake Chenghai, Yunnan Province. The sediment core was collected from the deep-water
area of Lake Chenghai in June 1997. The vertical profile of 137Cs activity is characterized by a tree-peak pattern. This profile gave reliable ages, and also showed the stability of sediment
accumulation in the recent ten years. The vertical profile of 210Pbex activity displays a specific distribution of peaks, and is similar to the vertical profile of Corg. This phenomenon seems to be related to the mechanism of constraining the transfer of 210Pbex into lake sediments. The average atomic ratios of Horg/Corg and Corg/Norg in Lake Chenghai sediments are 5.51 and 7.04, respectively, indicating that the organic matter was predominantly derived
from the remains of endogenic algae. In terms of the three-stage evolutionary characteristics of organic matter in sediments,
i.e., “deposition-de-composition-accumulation”, the sedimentation fluxes (F(Corg)) of organic carbon (Corg) since 1970 were calculated by modeling. The sedimentation fluxes of 210Pbex (F(210Pbex)) in different years display good synchronous relations with the sedimentation flux of organic carbon (F(Corg)), especially in the years of 1972–1974 and 1986–1989. The variation of F(Corg) led to the variation of F(210Pbex); the variation of F(210Pbex) reflects, to some extent, the historical variation of lake productivity. 相似文献