全文获取类型
收费全文 | 27709篇 |
免费 | 612篇 |
国内免费 | 558篇 |
专业分类
测绘学 | 661篇 |
大气科学 | 2158篇 |
地球物理 | 5660篇 |
地质学 | 9915篇 |
海洋学 | 2366篇 |
天文学 | 6156篇 |
综合类 | 135篇 |
自然地理 | 1828篇 |
出版年
2022年 | 211篇 |
2021年 | 297篇 |
2020年 | 316篇 |
2019年 | 323篇 |
2018年 | 619篇 |
2017年 | 588篇 |
2016年 | 696篇 |
2015年 | 543篇 |
2014年 | 732篇 |
2013年 | 1319篇 |
2012年 | 854篇 |
2011年 | 1137篇 |
2010年 | 951篇 |
2009年 | 1325篇 |
2008年 | 1128篇 |
2007年 | 1114篇 |
2006年 | 1034篇 |
2005年 | 874篇 |
2004年 | 883篇 |
2003年 | 841篇 |
2002年 | 779篇 |
2001年 | 719篇 |
2000年 | 666篇 |
1999年 | 606篇 |
1998年 | 588篇 |
1997年 | 597篇 |
1996年 | 454篇 |
1995年 | 428篇 |
1994年 | 393篇 |
1993年 | 341篇 |
1992年 | 321篇 |
1991年 | 288篇 |
1990年 | 311篇 |
1989年 | 283篇 |
1988年 | 238篇 |
1987年 | 315篇 |
1986年 | 260篇 |
1985年 | 349篇 |
1984年 | 390篇 |
1983年 | 374篇 |
1982年 | 336篇 |
1981年 | 313篇 |
1980年 | 313篇 |
1979年 | 283篇 |
1978年 | 312篇 |
1977年 | 264篇 |
1976年 | 269篇 |
1975年 | 275篇 |
1974年 | 235篇 |
1973年 | 239篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Ground-based thermal emission measurements of the zenith sky have been made at Peterborough, Ontario since January 1993. In this paper, the measurement of the 6 band of atmospheric CFC-12, an important greenhouse gas, is presented for a cold, clear day in January 1994. A spectrum of the non-CFC-12 emission features has been simulated using the FASCD3P radiation code and measured radiosonde profiles of temperature, pressure and humidity. This has enabled a satisfactory subtraction of the interfering emission features from the CFC-12 emission spectrum. A comparison of the observed and simulated 6-bands of CFC-12 shows good agreement at all frequencies of emission. From these spectra the total downward greenhouse radiative flux from the CFC-12 6 emission based for a very cold day has been estimated to be 0.27 W m−2±10%. 相似文献
72.
73.
Christian Betzler Jörn Fürstenau Thomas Lüdmann Christian Hübscher Sebastian Lindhorst Andreas Paul John J. G. Reijmer André W. Droxler 《Basin Research》2013,25(2):172-196
Multichannel high‐resolution seismic and multibeam data were acquired from the Maldives‐isolated carbonate platform in the Indian Ocean for a detailed characterization of the Neogene bank architecture of this edifice. The goal of the research is to decipher the controlling factors of platform evolution, with a special emphasis on sea‐level changes and changes of the oceanic currents. The stacking pattern of Lower to Middle Miocene depositional sequences, with an evolution of a ramp geometry to a flat‐topped platform, reflects variations of accommodation, which here are proposed to be primarily governed by fluctuations of relative sea level. Easterly currents during this stage of bank growth controlled an asymmetric east‐directed progradation of the bank edge. During the late middle Miocene, this system was replaced by a twofold configuration of bank development. Bank growth continued synchronously with partial bank demise and associated sediment‐drift deposition. This turnover is attributed to the onset and/or intensification of the Indian monsoon and related upwelling and occurrence of currents, locally changing environmental conditions and impinging upon the carbonate system. Mega spill over lobes, shaped by reversing currents, formed as large‐scale prograding complexes, which have previously been interpreted as deposits formed during a forced regression. On a regional scale, a complex carbonate‐platform growth can occur, with a coexistence of bank‐margin progradation and aggradation, as well as partial drowning. It is further shown that a downward shift of clinoforms and offlapping geometries in carbonate platforms are not necessarily indicative for a sea‐level driven forced regression. Findings are expected to be applicable to other examples of Cenozoic platforms in the Indo‐Pacific region. 相似文献
74.
基于时间序列统计特性的森林变化监测 总被引:1,自引:0,他引:1
森林动态变化分析对揭示生态系统环境变化及植被恢复和布局重建等具有重要意义,时间序列的遥感数据为森林监测提供了基础数据。本文根据森林植被的统计学特性,在暗目标法的基础上,利用归一化植被指数NDVI实现森林样本自动选择;并融合NDVI构建了新的综合森林特征指数(Integrated Forest Z-Score,IFZ);以时间序列的IFZ分析森林动态信息,实现森林变化动态监测。以三峡大坝及周边区域森林为研究区,利用2001年至2012年每年生长季节(5月—10月)的Landsat TM影像检验本文算法。基于2002年、2006年和2010年三期7月—9月的Quick Bird影像的精度分析结果发现:研究区森林变化检测的总体精度可达96.53%,Kappa系数为0.9512。在添加NDVI指数后构建的IFZ提高了总体监测精度。其中,毁林类别的检测精度提高显著,漏检率和误检率分别为2.74%和3.64%;干扰后重建的森林类别的检测精度有一定提高,其漏检率和误检率分别为10.79%和10.51%。研究结果表明,改进暗目标法能提高森林样本的选样效率,添加NDVI的IFZ能提高森林动态变化的识别度。此外,本算法不仅能定性识别森林变化,而且能定量提供森林干扰发生时间和干扰强度。 相似文献
75.
建立基于Supernatural GIS的复杂三维模型,提出城市复杂三维模型建立的技术路线、关键技术及解决方案,并以实例验证该方法的可行性。 相似文献
76.
Significance of the remotely sensed thermal infrared measurements obtained over a citrus orchard 总被引:1,自引:0,他引:1
In this work we have developed a theoretical model that helps the interpretation of the remotely sensed thermal infrared measurements carried out over citrus orchards. A detailed analysis of the different factors which take part in the definition of the effective emissivity and temperature (observation height, viewing angle, type of soil, dimensions and separation between orange trees) is made. The model was validated under vertical observation in a citrus orchard during seven nights. In this situation we have determined that the model performs to an accuracy of about 1%. 相似文献
77.
78.
Two general approaches for compiling maps of components of the water-ice budget in regions of glacier nourishment are compared and the resulting maps are analyzed. The compilation of raw data is based on field measurements rather than remote sensing information. Translated by Edward Torrey, Alexandria, VA 22308 from: Materialy glyatsiologicheskikh issledovaniy, 1991, No. 72, pp. 94-102. 相似文献
79.
Another paper in a series of articles on ecological-geographic mapping (see for example, Mapping Sciences and Remote Sensing, Vol. 31, No. 3, July-September 1994, pp. 185-220) focuses on outlining a concise typology of such maps and providing a brief history of their emergence during the 1970s and 1980s. A subsequent section is devoted to methods and technology used in the compilation of ecological-geographic maps, particularly the multiple variants of data organization, processing, and cartographic representation that can be factored into research design. Translated by Edward Torrey, Alexandria, VA 22308 from: Geografiya i prirodnyye resursy, 1995, No. 4, pp. 10-18. 相似文献
80.
Within the confines of Earth Observation Scientific Knowledge and Technology Transfer in Hungary (EKAT) titled ESA PECS project we gained forum for utilization of our earth observation (EO) knowledge and possibility for further development of experiences. The project aims the horizontal preparation of Hungary for ESA membership – for a dynamically developing sphere in the common part of science, technology and business. For the efficient transfer and dissemination, we preconceived target groups and principles to reach main take-up points and to open new forums of information exchange. Nowadays, user-friendly service, complex supply and real-validation process all have great importance. Joining units of suitable data choice, entire ingestion–processing chains and ergonomic interfaces can only offer a timely and professional solution for the challenges of industry and business sectors. It has to be clearly seen, that information and communication technologies (ICT) and information control becomes a more and more significant part of EO services. 相似文献