全文获取类型
收费全文 | 56220篇 |
免费 | 6246篇 |
国内免费 | 8949篇 |
专业分类
测绘学 | 4126篇 |
大气科学 | 8777篇 |
地球物理 | 12259篇 |
地质学 | 27158篇 |
海洋学 | 5113篇 |
天文学 | 2984篇 |
综合类 | 5455篇 |
自然地理 | 5543篇 |
出版年
2024年 | 128篇 |
2023年 | 465篇 |
2022年 | 1525篇 |
2021年 | 1738篇 |
2020年 | 1417篇 |
2019年 | 1718篇 |
2018年 | 6143篇 |
2017年 | 5296篇 |
2016年 | 4220篇 |
2015年 | 1990篇 |
2014年 | 2167篇 |
2013年 | 2049篇 |
2012年 | 2916篇 |
2011年 | 4678篇 |
2010年 | 4025篇 |
2009年 | 4211篇 |
2008年 | 3614篇 |
2007年 | 3930篇 |
2006年 | 1455篇 |
2005年 | 1496篇 |
2004年 | 1345篇 |
2003年 | 1340篇 |
2002年 | 1171篇 |
2001年 | 1023篇 |
2000年 | 1159篇 |
1999年 | 1525篇 |
1998年 | 1229篇 |
1997年 | 1143篇 |
1996年 | 1052篇 |
1995年 | 918篇 |
1994年 | 789篇 |
1993年 | 718篇 |
1992年 | 579篇 |
1991年 | 456篇 |
1990年 | 332篇 |
1989年 | 309篇 |
1988年 | 277篇 |
1987年 | 153篇 |
1986年 | 147篇 |
1985年 | 90篇 |
1984年 | 99篇 |
1983年 | 73篇 |
1982年 | 64篇 |
1981年 | 76篇 |
1980年 | 52篇 |
1979年 | 32篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1958年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
871.
872.
北京地区3500a来的气候与环境变迁——兼论昆明湖的沧桑 总被引:3,自引:0,他引:3
通过对北京颐和园昆明湖中沉积物的沉积特征的研究,结合历史记载,对昆明湖水域的形成时间和发展过程有了深入的了解,据此对北京地区3500a以来的气候与环境变迁作出了科学的划分,为探讨北京地区未来的气候变化趋势将会有所启迪。 相似文献
873.
中国煤炭地质钻探技术发展五十年 总被引:1,自引:1,他引:1
概要介绍了煤田钻探技术五十年来的发展状况,提出了今后的设想。 相似文献
874.
贵州某机场的主要工程地质问题分析及其处理措施建议 总被引:1,自引:2,他引:1
贵州某机场为山区高填方机场,最大填方高度近60m,场址沟谷发育,基底为软硬交替的、顺倾向岩层的斜坡地区,笔者就该机场的主要工程地质问题一边坡稳定问题、沉降问题、地表水和地下水的排泄问题进行了不同程度的研究并提出了相应的处理措施。 相似文献
875.
Multi-parameter studies (stable isotopes in carbonate and organic matter, pigment,organic carbon and nitrogen contents) from a 660-yr continuous sediment core from Lake Cheng-hai, a closed, eutropic lake in southern China, provide information on lake historical eutrophi-cation. During the last 660 years, great changes have taken place in productivity and eutrophi-cation of Lake Chenghai in response to human activities. In 1690, the productivity of the lakebegan to increase as Lake Chenghai became closed from agriculture in the lake‘‘ s watershed. In 1942, Lake Chenghai evolved to eutrophic state, marked by an increase in organic carbon, ni-trogen, CaC03, pigment contents and obvious negative values of stable isotopes, which is more or less simultaneous with the large-scale population immigration during the period. In 1984, in-tensive human activities induced modern lacustrine productivity and eutrophic level. Human-in-duced trophic changes during the past few decades have affected the Lake Chenghai ecosystem tosuch an extent that it has never experienced before in the last 660 years. 相似文献
876.
本文简要介绍了台站财务管理的现状 ,针对目前台站管理中出现的一些问题 ,阐明加强台站财务管理与会计核算改革的必要性 ,并粗略提出地震台站财务管理工作的改革方向与对策。 相似文献
877.
The bulk composition of organic matter and saturated and aromatic hydrocarbons extracted from 16 samples collected from two Kuperschiefer profiles in the Rudna mine,Southwest Poland has been analyzed to study the role of organic matter during base metal enrichment in the Kupferschiefer shale.The results indicated that the extract yields and saturated hydrocarbon yields decreased with increasing base metal contents.GC and GC/MS analyses indicated that n -alkanes and alkylated aromatic compounds were depleted and may have served as hydrogen donators for thermochemical sulfate reduction.The enrichment of base metal is closely connected with the destruction of hydrocarbons. 相似文献
878.
From the studies of ore deposit geologic settings,sulfur isotopes,lead isotopes,carbon isotopes and oxygen isotopes,fluid inclusions and petrochemistry in this paper,the authors have drawn a conclusion that the ore-forming hydrothermal solutions are the high-temperature magmatic hydrothermal solutions for the gold ore deposit,and at the same time,the involvemety of crustal materials can not be ruled out .It is the first time that the authors have proposed that the Laozuoshan gold-ploymetallic ore deposit in Heilongjiang Province was formed in the calc-alkaline series environment at the margin of an active continent. 相似文献
879.
1IntroductionTheHongshijinggolddepositislocatedinthenorthofLuobupouLakeofRuoqiang ,about 30 0kmsouthwestofHamiCity ,Xinjiang .ItwasdiscoveredbytheSixthGeologicalTeamofXinjiangduringgeo chemicalexploration .TheHongshijinggolddeposit,whichoccursinthegold bearingformationcomposedofMiddleandLateCarboniferousvolcanicandpyroclasticrocks ,isabrittle ductileshearzonetypegolddepositcontrolledbyariftbelt.TheHongshijinggolddepositislocatedinthesouthwestoftheHongshi jing -Maotoushanmineralizationb… 相似文献
880.
朱义年 《中国地球化学学报》2003,22(4):302-312
Gneiss-distilled water interaction at room temperature was investigated with batch-reactors to study water-rock reaction and geochemical evolution of the aqueous phase with time. The ion concentrations in water were controlled not only by the dissolution of primary minerals, but also by the precipitation of secondary minerals. The decreasing fraction sizes of gneiss could favor dissolution and precipitation simultaneously. Ca^2 and K^ were the major cations, and HCO3^- was the major anion in water. All the ions except Ca^2 increased in concentration with time. The Ca^2 release from the rock to the aqueous phase was initially much faster than the release of K^ , Na^2 and Mg^2 . But after about 5 - 24 hours, the Ca^2 concentrations in water decreased very slowly with time and became relatively stable. During the experiment, the water varied from the Ca-( K)-HCO3-type water to the K-Ca-HCO3-type water, and then to the K-(Ca, Na)-HCO3-type water. The water-gneiss interaction was dominated by the dissolution of Kfeldspar in the solution. The remaining secondary minerals were mainly kaolinite, illite and K (Mg) -mica. 相似文献