全文获取类型
收费全文 | 7208篇 |
免费 | 1118篇 |
国内免费 | 1952篇 |
专业分类
测绘学 | 975篇 |
大气科学 | 1053篇 |
地球物理 | 1398篇 |
地质学 | 4163篇 |
海洋学 | 827篇 |
天文学 | 339篇 |
综合类 | 604篇 |
自然地理 | 919篇 |
出版年
2024年 | 24篇 |
2023年 | 76篇 |
2022年 | 154篇 |
2021年 | 225篇 |
2020年 | 205篇 |
2019年 | 299篇 |
2018年 | 219篇 |
2017年 | 298篇 |
2016年 | 325篇 |
2015年 | 352篇 |
2014年 | 402篇 |
2013年 | 483篇 |
2012年 | 422篇 |
2011年 | 444篇 |
2010年 | 367篇 |
2009年 | 496篇 |
2008年 | 561篇 |
2007年 | 560篇 |
2006年 | 536篇 |
2005年 | 457篇 |
2004年 | 470篇 |
2003年 | 399篇 |
2002年 | 341篇 |
2001年 | 280篇 |
2000年 | 300篇 |
1999年 | 258篇 |
1998年 | 230篇 |
1997年 | 223篇 |
1996年 | 160篇 |
1995年 | 158篇 |
1994年 | 135篇 |
1993年 | 107篇 |
1992年 | 67篇 |
1991年 | 51篇 |
1990年 | 52篇 |
1989年 | 30篇 |
1988年 | 30篇 |
1987年 | 17篇 |
1986年 | 16篇 |
1985年 | 18篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
81.
82.
83.
84.
85.
86.
87.
地理信息服务中数据传输性能分析 总被引:2,自引:0,他引:2
地理信息服务系统具有数据密集型和计算密集型的特点,对网络环境的设置有着特殊的需求。本文从地理信息服务系统中对数据传输应用的角度出发,从网络数据传输协议的传输层和应用层两个层次分析地理信息服务系统应用的特殊性,并根据系统应用的特殊需求提出相应的解决方案,提高整个应用系统中各类数据传输的效率、性能和系统运行的稳定性,提高地理信息服务系统为多用户提供地图服务、位置服务以及各种应用服务的综合能力。提高系统适应多用户并发访问海量数据的地图服务作业和频繁访问实效性很强的位置服务作业的能力。 相似文献
88.
The 40Ar/39Ar method using a laser probe opened the door to microscale measurements and diffusion profiles frozen in samples. In the first decade since the initial application of a laser for 40Ar/39Ar dating in 1973, practical applications have been few. This is due not only to the fact that the laser and vacuum technologies were immature but that mass spectrometry was also in its infancy. In those days, the sensitivity of a mass spectrometer was generally insufficient to measure the small amount of argon degassed from a geological sample by a laser. These problems have subsequently been solved by new technologies. To understand their current status, a brief history of their development is outlined. This outline focuses on the required detection limit in micro scale measurement, practical approaches for accurate measurement are explained through examples in our laboratory specifically relating to the technical aspects of 40Ar/39Ar dating. 相似文献
89.
Takeshi Ohno Tsuyoshi Komiya Yuichiro Ueno Takafumi Hirata Shigenori Maruyama 《Gondwana Research》2008,14(1-2):126
We measured both mass-dependent isotope fractionation of δ88Sr (88Sr/86Sr) and radiogenic isotopic variation of Sr (87Sr/86Sr) for the Neoproterozoic Doushantuo Formation that deposited as a cap carbonate immediately above the Marinoan-related Nantuo Tillite. The δ88Sr and 87Sr/86Sr compositions showed three remarkable characteristics: (1) high radiogenic 87Sr/86Sr values and gradual decrease in the 87Sr/86Sr ratios, (2) anomalously low δ88Sr values at the lower part cap carbonate, and (3) a clear correlation between 87Sr/86Sr and δ88Sr values. These isotopic signatures can be explained by assuming an extreme greenhouse condition after the Marinoan glaciation. Surface seawater, mixed with a large amount of freshwater from continental crusts with high 87Sr/86Sr and lighter δ88Sr ratios, was formed during the extreme global warming after the glacial event. High atmospheric CO2 content caused sudden precipitation of cap carbonate from the surface seawater with high 87Sr/86Sr and lighter δ88Sr ratios. Subsequently, the mixing of the underlying seawater, with unradiogenic Sr isotope compositions and normal δ88Sr ratios, probably caused gradual decrease of the 87Sr/86Sr ratios of the seawater and deposition of carbonate with normal δ88Sr ratios. The combination of 87Sr/86Sr and δ88Sr isotope systematics gives us new insights on the surface evolution after the Snowball Earth. 相似文献
90.
The Anzishan ophiolite, a typical ophiolitic block of early Carboniferous age in the Mian-Lue suture zone of the Qinling Mountains, central China, consists of amphibolites/metabasalts, gabbros and gabbroic cumulates. All of these rocks, as well as those in the Hunshuiguan-Zhuangke (HZ) block, have compositions similar to normal MORB and back-arc basin basalts (BABB) with high εNd(t) values, indicating that they were derived from a depleted mantle source. The Mian-Lue suture zone also contains blocks of other lithologies, e.g., rift volcanic rocks in the Heigouxia block and arc volcanic rocks in the Sanchazi block. Although they are in fault contact with each other, the presence of these different blocks in the Mian-Lue suture zone may represent a complete Wilson cycle, from initial rifting to open ocean basin to final subduction and continent-continent collision, during the late Paleozoic-early Triassic. In this region, the North and South China Cratons were separated by Paleo-Tethys at least until the early Carboniferous, and final amalgamation of both cratons along the Qinling orogenic belt took place in the Triassic. 相似文献