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91.
两次春季强风暴天气环境场对比分析 总被引:2,自引:2,他引:0
利用NCAR/NCEP再分析资料和常规气象观测资料,对发生在长江中下游的两次春季强风暴天气影响系统、不稳定条件、触发机制进行对比分析。结果表明:(1)两次强风暴天气,都是在东北冷涡大背景、高空槽、低层切变线和偏西气流的有利形势下产生的;(2)两次强风暴过程的近地面比湿不足12 g/kg,相对湿度在600 hPa附近呈现低—高—低的变化,近地面的水汽通量在强对流发生地附近辐合;(3)流场分布表征:低层辐合、高层辐散;强风暴发生前后垂直速度是下沉—上升—上升运动减弱的变化;(4)风暴发生前近地层温度梯度明显加强;K指数30℃、SWEAT指数100;(5)上层干冷空气下传侵入引发的对流不稳定层结、较强垂直风切变、能量锋区的存在、高低空急流耦合所造成的抽吸作用均有利于触发强对流天气的产生;(6)两次强风暴过程的不同点有:近地面第1次过程的湿度比第2次过程的湿度低;第1次过程的能量锋区自下而上北抬,第2次过程南撤。 相似文献
92.
对重要干扰过程导致森林植被向大气中的碳排放量进行评估,对于合理评估森林碳汇功能及其在应对全球气候变化中的作用是有重要意义的。本文基于有关森林干扰发生情况的林业统计资料和有关干扰引起生物量C转移过程与比例的假设条件,估算了近20年来采伐、火灾与病虫鼠害三种主要干扰每年从森林植被直接排放到大气中的C量。结果表明,近20年来,中国森林遭受了比较强烈的采伐、火灾与病虫鼠害干扰,并且这三种干扰在进入21世纪后有着比较明显的增加趋势。相应地,在1990-2009年间,采伐、火灾与病虫鼠害的C排放量年均分别为3425.16万tC、161.29万tC、428.80万tC,合计为4015.24万t。三种干扰的总C排放量在1990-1999年间年均为3079.40万t,在2000-2009年间年均为4951.09万t。从不同森林类型分布区的排放来看,中国森林主要干扰的年均C排放量及其年代际变化呈现比较明显的区域特征。干扰对中国森林碳平衡有着重大影响,针对干扰的森林管理可能具有较大的增汇潜力,并且在未来有关森林与陆地生态系统碳收支的模型研究中需考虑主要干扰的影响。 相似文献
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97.
A Holocene climatic record denoted by geochemical indicators from Barkol Lake in the northeastern Xinjiang,NW China 总被引:1,自引:0,他引:1
The Barkol Lake, as a closed inland lake, is located at the northeast Xinjiang in northwest China. A combination of geochemical
indicators including δ18O and δ13C of carbonate, TOC, carbonate contents, as well as grain size proxies and magnetic susceptibility of sediments obtained from
a newly recovered section at this lake, provides a high-resolution history of climatic change in the past 9400 years. Multi-indicators
reflect that Holocene climatic change in the study region generally follows the Westerly Wind pattern of Holocene, and three
climatic periods can be identified. Between 9400 and 7500 cal a B.P., climate was characterized by relatively drier and colder
condition. From 7500 to 5800 cal a B.P., a relatively warmer and moister climate prevailed, but between 5800 and 3500 cal
a B.P., climate shifted towards warmer and drier conditions. A relatively colder and wetter climate prevailed during 3500∼1000
cal a B.P., then it changed towards cold and dry between 1000 and 500 cal a B.P.; after 500 cal a B.P., climate changed towards
warm and dry conditions again. This study reflects that during the Middle Holocene (from ca 7000 to 3500 cal a B.P.), variations
of carbonate δ18O of sediments from several lakes in the northern Xinjiang were synchronous with that of Qinghai Lake, where was strongly
influenced by the South Asian monsoon; however, after 3500 cal a B.P. this consistency was interrupted, possibly resulting
from a re-domination of the Westerly Wind and the retreat of South Asian monsoon in the northern Xinjiang. 相似文献
98.
LI Zhengguo TANG Huajun YANG Peng WU Wenbin CHEN Zhongxin ZHOU Qingbo ZHANG Li ZOU Jinqiu 《地理学报》2012,22(1):29-45
We investigated the responses of cropland phenophases to changes of agricultural thermal conditions in Northeast China using the SPOT-VGT Normalized Difference Vegetation Index (NDVI) ten-day-composed time-series data, observed crop phenophases and the climate data collected from 1990 to 2010. First, the phenological parameters, such as the dates of onset-of-growth, peak-of-growth and end-of-growth as well as the length of the growing season, were extracted from the smoothed NVDI time-series dataset and showed an obvious correlation with the observed crop phenophases, including the stages of seedling, heading, maturity and the length of the growth period. Secondly, the spatio-temporal trends of the major thermal conditions (the first date of ≥10℃, the first frost date, the length of the temperature-allowing growth period and the accumulated temperature (AT) of ≥10℃) in Northeast China were illustrated and analyzed over the past 20 years. Thirdly, we focused on the responses of cropland phenophases to the thermal conditions changes. The results showed that the onset-of-growth date had an obvious positive correlation with the first date of ≥10℃ (P < 0.01), especially in the northern part of the Songnen Plain, the eastern part of the Sanjiang Plain and the middle and eastern parts of Jilin Province. For the extracted length of growing season and the observed growth period, notable correlations were found in almost same regions (P < 0.05). However, there was no obvious correlation between the end-of-growth date and the first frost date in the study area. Opposite correlations were observed between the length of the growing season and the AT of ≥10℃. In the northern part of the Songnen Plain, the eastern part of the Sanjiang Plain and the middle part of Jilin and Liaoning Provinces, the positive correlation coefficients were higher than the critical value of 0.05, whereas the negative correlation coefficients reached a level of 0.55 (P < 0.05) in the middle and southern parts of Heilongjiang Province and some parts of the Sanjiang Plain. This finding indicated that the crop growth periods were shortened because of the elevated temperature; in contrast, the extended growth period usually meant a crop transformation from early- or middle-maturing varieties into middle or late ones. 相似文献
99.
滇黔桂三角地区锑矿床流体包裹体研究 总被引:7,自引:1,他引:7
通过对滇黔桂三角地区四个代表性锑矿床中矿物流体包裹体特征、相变行为的系统观察和测定,以及对包裹体气液相成分的分析,获得了本区两种类型锑矿床成矿过程中成矿流体的温度、盐度、密度、流体成分、成矿压力、矿化深度及pH、fo2、还原参数等成矿的物理化学参数。结果表明:本区锑矿床成矿流体以NaCl-H2O体系为主,中—弱碱性,中—低盐度,主成矿期成矿温度峰值为150~200℃。 相似文献
100.
本文主要探讨在高密度的楼群中,如何测量倾斜楼房的倾斜量,计算纠偏所需的相对沉降量,为纠偏工程的设计提供精度可靠的数据;在纠偏过程中,利用观测的沉降值监控纠偏速度,使其均匀沉降,安全生产。 相似文献