全文获取类型
收费全文 | 4762篇 |
免费 | 965篇 |
国内免费 | 1254篇 |
专业分类
测绘学 | 476篇 |
大气科学 | 787篇 |
地球物理 | 983篇 |
地质学 | 2825篇 |
海洋学 | 670篇 |
天文学 | 148篇 |
综合类 | 453篇 |
自然地理 | 639篇 |
出版年
2024年 | 48篇 |
2023年 | 145篇 |
2022年 | 329篇 |
2021年 | 347篇 |
2020年 | 284篇 |
2019年 | 291篇 |
2018年 | 325篇 |
2017年 | 290篇 |
2016年 | 307篇 |
2015年 | 280篇 |
2014年 | 292篇 |
2013年 | 281篇 |
2012年 | 231篇 |
2011年 | 257篇 |
2010年 | 268篇 |
2009年 | 237篇 |
2008年 | 219篇 |
2007年 | 211篇 |
2006年 | 150篇 |
2005年 | 160篇 |
2004年 | 155篇 |
2003年 | 179篇 |
2002年 | 310篇 |
2001年 | 241篇 |
2000年 | 209篇 |
1999年 | 206篇 |
1998年 | 119篇 |
1997年 | 87篇 |
1996年 | 79篇 |
1995年 | 81篇 |
1994年 | 75篇 |
1993年 | 59篇 |
1992年 | 57篇 |
1991年 | 28篇 |
1990年 | 32篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1958年 | 4篇 |
1957年 | 1篇 |
1954年 | 5篇 |
排序方式: 共有6981条查询结果,搜索用时 0 毫秒
191.
网络安全是信息管理人员最关心的问题,因为信息的泄露将造成不可估量的损失.本文从市气象局信息中心网络系统现状切题,分析了各个寸能存在的网络安全漏洞和风险,并归纳和提出了一些信息安全防护的策略和方法. 相似文献
192.
The research area is located in the western part of Sichuan basin as a Yangtze ecotope of Cathaysian Tethyan area. It is dominated by benthic fauna, including brachiopods, Fusulinids, corals, bivalves, foraminifers, ammonites, bryozoans,Crinoids and pleopods which are less common with traces of trilobites, stromatoporas, nautilus and sporopollens seen in one or two areas,which are obviously controlled by sedimentary environments and in accordance with sedimentary facies.Through the analysis of fossils and research on burial characteristics from middle Permian middleTriassic, based on the combination of the feature of fossils in time and space, seventeen communities are recognized, the coposition, construction and palaeoenvironment of each community are expounded. Study shows that different ecological type biocoenose are distributed in different locations, which are mainly represented by sessile benthic community in the main research area, composed of Mianzhu, Mianyang, Deyang and Santai and nektonic community in marginal areas in the research area subdivided into two parts: Areas around Guangyuan-Nanjiang-Tongjiang, located at the margins in the northeast of the research area, and areas around Wenchuan-Maoxian-Dayidafeishui situated at the western borders of the research area. According to the combination of communities with sedimentary characteristics,six kinds of biofacies have been recognized and described in the study area and biofacies pattern are established. Category,ecotype, typical community and sedimentary facies of each biofacies are elucidated in this paper. The subdivision and analysis of community are meaningful for the studies of paleoenvironment ,paleogeography and their evolutions,The research of biaofacies is important for the recovery of paleobiogeography and paleoplate tectonic characteristics. 相似文献
193.
地震预报意见以大量资料为基础,依靠专家经验和多学科知识并通过会商讨论形成。显著地震发生后,快速、准确、有效地研判震情可为后期应急指挥和地震现场工作奠定基础。本文以Datist软件为平台,基于四川及邻区的基础资料,设计研发符合四川震情的震后会商资料快速产出系统,当四川及邻区发生中强地震时,通过该系统可在收到地震短信5分钟内以请求触发的方式快速产出应急会商资料,并以微信、PowerPoint和Word的形式将基础资料发送给分析预报人员,为后期趋势分析奠定基础。 相似文献
194.
张晓 《气候变化研究进展》2006,2(2):89-92
介绍并评价有关国际非营利的人道救援组织提出的应对与全球气候变化相关的自然灾害的策略。首先,简要概述气候变化引发全球灾害的状况;然后,介绍国际红十字会的应对策略和减灾建议;最后是简要的评论。 相似文献
196.
197.
Journal of Geographical Sciences - Due to the atmospheric nuclear weapon tests carried out, terrestrial environments have been extensively contaminated by global fallout of plutonium (Pu)... 相似文献
198.
Natural Hazards - Land subsidence induced by groundwater exploitation is a typically multi-scale and multi-field coupling process. The adjustment process and action mechanism of soil mesostructure... 相似文献
199.
Experimental simulation of dolomite dissolution under burial diagenesis conditions and thermodynamic interpretation 总被引:3,自引:0,他引:3
Simulating experiments on dolomite dissolution by acetic acid were made under burial diagenesis conditions,at temperatures ranging from 75℃to 130℃ and pressures from 20 MPA to 30MPa,The results show that the dissolution rate of dolomite increased rapidly with increasing temperature and prssure,From 75℃/Mpa to 130℃/30 MPa,the total amount of released ca and Mg increased from 32.98mg/L to 337.9mg/L,over one order of magnitude in difference,Thermodynamic calculation indicates that the increment of Gibbs free energy (ΔG) of the chemical reaction decreases with increasing temperature and pressure.This thermodynamic result is consistent with the experimental result.Based on the Experimental results.it is suggested that secondary prosities formed by dolomite dissolution under conditions of deep burial diagenesis should be more common than those under epigenesis and shallow burial conditions,and therefore dolomite reservoires in the formations that have been deeply buried should be more abundant than in the formations that have only been shallowly buried. 相似文献
200.
Evolution of vegetation and climate since the last glacial maximum recorded at Dahu peat site, South China 总被引:7,自引:1,他引:7
Sporopollen analysis on a 346 cm peat record at Dahu, Jiangxi, chronologically constrained by 16 AMS 14C datings, provides an opportunity to reconstruct the vegetation evolution stages responding to cli-mate change in South China since the last glacial maximum. The result shows that during 18330-15630 cal a B.P., broad-leaved forest dominated the area, corresponding to mild, cool and fairly humid climate. At the interval of 15630-11600 cal a B.P., several evergreen broad-leaved species appeared within the broad-leaved forest, indicating moderate and humid condition. During early Holocene, broad-leaved evergreen forest community was constructed as Castanopsis/Lithorcarpus principally developed, suggesting a warm and humid scenario until 6000 cal a B. P. Since 6000 cal a B. P., abrupt forest deterioration happened with an contemporary increase of fern and herb communities, repre-senting a turnover to relatively cool and dry condition and as well, possible impact from human activi-ties. Meanwhile, several relatively cool and dry events can be identified in the sporopollen record, they can be correlated to the North Atlantic Heinrich event, YD and Holocene millennial-scale oscillations, implying that the low latitude climate was coupled with high latitude influences. Moreover, the varia-tions of temperature and humidity since LGM at Dahu were much smaller when compared with the re-cords in north monsoonal China. 相似文献