全文获取类型
收费全文 | 29355篇 |
免费 | 7417篇 |
国内免费 | 11363篇 |
专业分类
测绘学 | 5125篇 |
大气科学 | 4545篇 |
地球物理 | 5689篇 |
地质学 | 19297篇 |
海洋学 | 6049篇 |
天文学 | 450篇 |
综合类 | 2436篇 |
自然地理 | 4544篇 |
出版年
2024年 | 270篇 |
2023年 | 685篇 |
2022年 | 1724篇 |
2021年 | 2159篇 |
2020年 | 1704篇 |
2019年 | 2092篇 |
2018年 | 1821篇 |
2017年 | 1612篇 |
2016年 | 1685篇 |
2015年 | 1957篇 |
2014年 | 1916篇 |
2013年 | 2480篇 |
2012年 | 2589篇 |
2011年 | 2787篇 |
2010年 | 2772篇 |
2009年 | 2647篇 |
2008年 | 2657篇 |
2007年 | 2465篇 |
2006年 | 2517篇 |
2005年 | 2098篇 |
2004年 | 1452篇 |
2003年 | 1168篇 |
2002年 | 1090篇 |
2001年 | 1011篇 |
2000年 | 871篇 |
1999年 | 485篇 |
1998年 | 220篇 |
1997年 | 181篇 |
1996年 | 166篇 |
1995年 | 110篇 |
1994年 | 101篇 |
1993年 | 80篇 |
1992年 | 93篇 |
1991年 | 47篇 |
1990年 | 67篇 |
1989年 | 28篇 |
1988年 | 18篇 |
1987年 | 33篇 |
1986年 | 31篇 |
1985年 | 26篇 |
1984年 | 24篇 |
1983年 | 20篇 |
1982年 | 22篇 |
1979年 | 17篇 |
1974年 | 9篇 |
1965年 | 11篇 |
1964年 | 13篇 |
1963年 | 13篇 |
1957年 | 14篇 |
1954年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
271.
272.
随着遥感应用技术飞速发展,及近年来高分辨率传感器的不断出现,人们对遥感影像的数字化处理也有了长足进步.但在遥感地质方面,由于"同物异谱"和"同谱异物"现象广泛存在,使计算机自动提取遥感影像上的岩性信息出现较大误差.完全人工解译虽准确率较高,但速度慢,如何将计算机自动提取与人工解译有效结合起来是本次研究的重点.文章以康恩纳德斑岩铜矿床地区ETM 遥感影像为数据源,以计算机自动提取与人工解译相结合,根据已有地质资料,对该区ETM 遥感影像进行岩性信息提取.通过在包古图地区对提取模型进行验证,结果表明两者相互结合可以大大提高识别精度,为进一步地质工作提供良好的遥感信息. 相似文献
273.
以中亚环巴尔喀什成矿带为典型研究区域,结合地质矿产、地球物理、地球化学和信息科学等信息数据及野外调查成果,以斑岩铜矿为主要矿床类型,以中比例尺对新疆及邻区的跨境巴尔喀什.准噶尔成矿带的含矿潜力进行整体研究.分析中亚大型矿集区成矿地质条件,总结研究区斑岩铜矿成矿规律,建立多元信息综合识别标志及矿床模型.结合空间数据分析技术,以ArcGIS为平台,建立中亚跨境成矿带主、客观模型整合的大型矿集区预测系统,得出中亚成矿带矿集区预测分布图,通过理论研究到技术方法的实现,为境内寻找大型矿集区奠定基础. 相似文献
274.
275.
276.
277.
278.
279.
Based on the theory of thermal conductivity, in this paper we derived a formula to estimate the prolongation period (AtL) of cooling-crystallization process of a granitic melt caused by latent heat of crystallization as follows:△tL=QL×△tcol/(TM-TC)×CP where TM is initial temperature of the granite melt, Tc crystallization temperature of the granite melt, Cp specific heat, △tcol cooling period of a granite melt from its initial temperature (TM) to its crystallization temperature (Tc), QL latent heat of the granite melt.
The cooling period of the melt for the Fanshan granodiorite from its initial temperature (900℃) to crystallization temperature (600℃) could be estimated -210,000 years if latent heat was not considered. Calculation for the Fanshan melt using the above formula yields a AtL value of -190,000 years, which implies that the actual cooling period within the temperature range of 900°-600℃ should be 400,000 years. This demonstrates that the latent heat produced from crystallization of the granitic melt is a key factor influencing the cooling-crystallization process of a granitic melt, prolongating the period of crystallization and resulting in the large emplacement-crystallization time difference (ECTD) in granite batholith. 相似文献
The cooling period of the melt for the Fanshan granodiorite from its initial temperature (900℃) to crystallization temperature (600℃) could be estimated -210,000 years if latent heat was not considered. Calculation for the Fanshan melt using the above formula yields a AtL value of -190,000 years, which implies that the actual cooling period within the temperature range of 900°-600℃ should be 400,000 years. This demonstrates that the latent heat produced from crystallization of the granitic melt is a key factor influencing the cooling-crystallization process of a granitic melt, prolongating the period of crystallization and resulting in the large emplacement-crystallization time difference (ECTD) in granite batholith. 相似文献
280.
Research Advances and Exploration Significance of Large-area Accumulation of Low and Medium Abundance Lithologic Reservoirs 总被引:1,自引:1,他引:0
In recent years, a series of large low and medium abundance oil and gas fields are discovered through exploration activities onshore China, which are commonly characterized by low porosity-permeability reservoirs, low oil/gas column height, multiple thin hydrocarbon layers, and distribution in overlapping and connection, and so on. The advantageous conditions for large-area accumulation of low-medium abundance hydrocarbon reservoirs include: (1) large (fan) delta sandbodies are developed in the hinterland of large flow-uncontrolled lake basins and they are alternated with source rocks extensively in a structure like "sandwiches"; (2) effective hydrocarbon source kitchens are extensively distributed, offering maximum contact chances with various sandbodies and hydrocarbon source rocks; (3) oil and gas columns are low in height, hydrocarbon layers are mainly of normal-low pressure, and requirements for seal rock are low; (4) reservoirs have strong inheterogeneity and gas reservoirs are badly connected; (5) the hydrocarbon desorption and expulsion under uplifting and unloading environments cause widely distributed hydrocarbon source rocks of coal measures to form large-area reservoirs; (6) deep basin areas and synclinal areas possess reservoir-forming dynamics. The areas with great exploration potential include the Paleozoic and Mesozoic in the Ordos Basin, the Xujiahe Formation in Dachuanzhong in the Sichuan basin, deep basin areas in the Songliao basin etc. The core techniques of improving exploration efficiency consist of the sweetspot prediction technique that focuses on fine characterization of reservoirs, the hydrocarbon layer protecting and high-speed drilling technique, and the rework technique for enhancing productivity. 相似文献