全文获取类型
收费全文 | 26073篇 |
免费 | 3834篇 |
国内免费 | 5715篇 |
专业分类
测绘学 | 2234篇 |
大气科学 | 3879篇 |
地球物理 | 5383篇 |
地质学 | 13472篇 |
海洋学 | 4099篇 |
天文学 | 2198篇 |
综合类 | 1738篇 |
自然地理 | 2619篇 |
出版年
2024年 | 178篇 |
2023年 | 530篇 |
2022年 | 1205篇 |
2021年 | 1501篇 |
2020年 | 1303篇 |
2019年 | 1402篇 |
2018年 | 1614篇 |
2017年 | 1551篇 |
2016年 | 1575篇 |
2015年 | 1355篇 |
2014年 | 1547篇 |
2013年 | 1729篇 |
2012年 | 1760篇 |
2011年 | 1843篇 |
2010年 | 1744篇 |
2009年 | 1625篇 |
2008年 | 1626篇 |
2007年 | 1537篇 |
2006年 | 1393篇 |
2005年 | 933篇 |
2004年 | 745篇 |
2003年 | 756篇 |
2002年 | 853篇 |
2001年 | 781篇 |
2000年 | 637篇 |
1999年 | 555篇 |
1998年 | 418篇 |
1997年 | 419篇 |
1996年 | 343篇 |
1995年 | 335篇 |
1994年 | 285篇 |
1993年 | 244篇 |
1992年 | 201篇 |
1991年 | 145篇 |
1990年 | 121篇 |
1989年 | 130篇 |
1988年 | 97篇 |
1987年 | 68篇 |
1986年 | 67篇 |
1985年 | 52篇 |
1984年 | 46篇 |
1983年 | 41篇 |
1982年 | 42篇 |
1981年 | 32篇 |
1980年 | 28篇 |
1979年 | 35篇 |
1978年 | 20篇 |
1976年 | 17篇 |
1975年 | 22篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
251.
介绍了GIS在城市轨道交通建设中的应用,分析了轨道交通建设的评价要素和对GIS系统的建设要求提出了系统设计的总体思路和框架及应用前景。 相似文献
252.
253.
The West Kunlun orogenic belt is located at the conjunction of the paleo-Asian tectonic system and the Tethys tectonic system.
Petrological and mineralogical studies of the Early Cambrian metamorphic surface crust in this region have shown that in case
the metamorphism reached low-temperature granulate facies, the typical mineral assemblage is biotite-garnet-silimanite-K feldspar-plagioclase-quartz.
The peak metamorphic temperatures are within the range of 720–740°C and the pressure is 0.6 GPa ±. Three types of metamorphic
zircon have been detected in the metamorphic rocks: the complex inclusion-bearing type ; the early relic zircon inclusion-bearing
type; and the inclusion-free type. SHRIMP age determination of these three types of metamorphic zircon have revealed that
these zircons were formed principally during 400–460 Ma, indicating that pre-Cambrian metamorphic surface crust rocks underwent
low-temperature granulite facies metamorphism during the Caledonian. In combination with the geological characteristics of
this region, it is considered that when the oceanic basin was closed, there occurred intense intracontinental subduction (type
A), bringing part of the Early Cambrian metamorphic basement in this region downwards to the lower crust. Meanwhile, there
were accompanied with tectonic deformation at deep levels and medium- to high-grade metamorphism. This study provided important
chronological and mineralogical evidence for the exploration of the evolutionary mechanism and process of the West Kunlun
Early Paleozoic.
Part of the results from the research project “ Research on the West Kunlun pre-Cambrian tectonic events” under the program
“ Research on the important geological problems of China’ s pre-Cambrian” (No. 200113900070) sponsored by the China National
Geological Surveying Bureau. 相似文献
254.
Comprehensive lithogenetic analysis of the Nyurol paleobasin revealed a large shoal area surrounded by basins. The shoal area is composed of organogenic buildups covered by sediments of isolated and inner lagoons. The organogenic buildups are divided into two types: Stromatopora bioherms and mud-mounds. Regularities of the distribution of organogenic buildups are considered. 相似文献
255.
The Rainbow hydrothermal field (36° N Mid-Atlantic Ridge) is one of the three presently known fields related to serpentinization of ultramafic rocks accompanied by the formation of hydrogen- and methane-rich solutions. Gas chromatographic (GC) and molecular gas chromatographic–mass spectrometric (GC-MS) investigations of sulfide ores and sediments from this field confirmed a predominantly biological nature of bitumoids related to the high-temperature transformation of biomass of the hydrothermal biological community. At the same time, ores of the Rainbow field contain significant amounts of compounds that are not directly related to biogenic synthesis. This fact suggests the possibility of an abiogenic synthesis of methane and even complex hydrocarbons during the serpentinization of ultramafic rocks. 相似文献
256.
Thirty four-frequency line profiles of Class II methanol masers have been analyzed to investigate carefully the coincidences of various spectral features. Data at 6.7, 12.2, 107, and 156.6 GHz have been analyzed. Two clusters of Class II methanol maser lines at 6.7 and 12.2 GHz are observed in the spectra of many sources. These maser-line clusters are located on either side of the thermal methanol lines at 107 and 156.6 GHz. To avoid the effect of amplification in these thermal methanol lines, a similar analysis was performed for 80 sources having both maser emission at 6.7 GHz and thermal CS emission. The relative distributions of the methanol maser lines and the thermal CS line confirm on the basis of richer statistics that the maser lines are located in two clusters on either side of the thermal feature. It is proposed that the two maser-line clusters correspond to two edges of a Keplerian disk. The thermal methanol and CS emission is formed in dense molecular cores, whose centers are coincident with the disk centers. 相似文献
257.
A. P. Geptner Yu. I. Pikovskii L. T. Protasevich T. A. Alekseeva M. E. Ramenskaya 《Lithology and Mineral Resources》2003,38(6):509-521
Relationships of mineralized microbiota with the content of polycyclic aromatic hydrocarbons in hydrothermal systems are considered. It has been established that the mineralized microbiota can serve as an indicator of hydrothermal hydrocarbon flows in present-day and ancient deposits. 相似文献
258.
为了解决工程CAD系统中数据处理效率低及方便工程CAD软件的开发维护,介绍了基于Windows平台开发的冷冲模CAD系统的面向对象工程数据库系统,讨论了工程数据库系统的数据模型、逻辑设计、系统的体系结构和功能实现。 相似文献
259.
中国西南低空急流活动的统计分析 总被引:11,自引:0,他引:11
参照北美研究低空急流气候特征的方法,对中国低空急流进行重新定义,实现了低空急流定义的统一,并在此基础上对低空急流活动特征进行了分析。结果表明:中国低空急流主要有两个活动中心,分别位于江南地区和东北地区;江南地区的低空急流活动主要有两个活跃期,分别为1-4月和6-7月;东北地区的低空急流活动主要表现为2月、8-9月两个活动较弱期;江南地区的低空急流主要在6-8月表现出独立的急流轴,东北地区则主要在8月份;汛期低空急流活动与长江流域区域性暴雨有伴随性,多雨年急流次数很多,少雨年则很少;长江中下游及两湖盆地附近急流活动有明显的日变化。 相似文献
260.