全文获取类型
收费全文 | 271篇 |
免费 | 17篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 21篇 |
地球物理 | 71篇 |
地质学 | 73篇 |
海洋学 | 31篇 |
天文学 | 67篇 |
综合类 | 1篇 |
自然地理 | 19篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 19篇 |
2015年 | 9篇 |
2014年 | 8篇 |
2013年 | 17篇 |
2012年 | 15篇 |
2011年 | 18篇 |
2010年 | 17篇 |
2009年 | 17篇 |
2008年 | 12篇 |
2007年 | 21篇 |
2006年 | 10篇 |
2005年 | 13篇 |
2004年 | 4篇 |
2003年 | 11篇 |
2002年 | 5篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1984年 | 3篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有290条查询结果,搜索用时 15 毫秒
131.
We studied the problematic of uncertainties in the diffuse gamma radiation apparent in stacking analysis of EGRET data at low Galactic latitudes. Subsequently, we co-added maps of counts, exposure and diffuse background, and residuals, in varying numbers for different sub-categories of putatively and known source populations (like PSRs). Finally we tested for gamma-ray excess emission in those maps and attempt to quantify the systematic biases in such approach. Such kind of an analysis will help the classification processes of sources and source populations in the GLAST era. 相似文献
132.
133.
134.
Ocean and atmosphere changes in the Caribbean Sea during the twenty-first century using CMIP5 models
Ocean Dynamics - Coastal communities around the Caribbean Sea are vulnerable to global warming impacts, partly because of constraints on their adaptive capacity. We use three climate models... 相似文献
135.
Barth Alexander Troupin Charles Reyes Emma Alvera-Azcárate Aida Beckers Jean-Marie Tintoré Joaquín 《Ocean Dynamics》2021,71(3):293-308
Ocean Dynamics - DIVAnd (Data-Interpolating Variational Analysis, in n-dimensions) is a tool to interpolate observations on a regular grid using the variational inverse method. We have extended... 相似文献
136.
Rafael Maciel Peña Avto Goguitchaichvili Bernard Henry Leda Sánchez-Bettucci Juan Morales Bertha Aguilar Reyes Ana María Soler-Arechalde Manuel Calvo-Rathert 《Studia Geophysica et Geodaetica》2011,55(2):311-328
The paleosecular variation (PSV) and polarity transitions are two major features of the Earth’s magnetic field. Both PSV and
reversal studies are limited when age of studied units is poorly constrained. This is a case of Central and western Mexico
volcanics. Although many studies have been devoted to these crucial problems and more than 200 paleomagnetic directions are
available for the last 5 Ma, only few sites were dated directly. This paper presents new paleomagnetic results from seventeen
independent cooling units in the Michoacán-Guanajuato Volcanic Field (MGVF) in western Mexico. Twelve sites are directly dated
by 40Ar/39Ar or K-Ar methods and span from 2.78 to 0.56 Ma. The characteristic paleodirections are successfully isolated for 15 lava
flows. The mean paleodirection (inclination I and declination D) obtained in this study is I = 28.8°, D = 354.9°, and Fisherian
statistical parameters are k = 28, α95 = 7.3°, N=15, which corresponds to the mean paleomagnetic pole position Plat = 83.9°, Plong = 321.6°, K = 34, A95 = 6.6°. The paleodirections obtained in present study compiled with those, previously reported from the MGVF, are practically
undistinguishable from the expected Plio-Quaternary paleodirections. The paleosecular variation is estimated through the study
of the scatter of the virtual geomagnetic poles giving SF = 15.9 with SU =21.0 and SL = 12.7 (upper and lower limits respectively). These values agree reasonably well with the recent statistical Models. The
oldest sites analyzed (the Santa Teresa and Cerro Alto) yield normal polarity magnetizations as expected for the cooling units
belonging to the Gauss geomagnetic Chron. The interesting feature of the record comes from lava flows dated at about 2.35
Ma with clearly defined normal directions. This may point out the possible existence of a normal polarity magnetization in
the Matuyama reversed Chron older than the Reunion and may be correlated to Halawa event interpreted as the Cryptochron C2r.2r-1.
Another important feature of the geomagnetic record obtained from the MGVF is the evidence of fully reversed geomagnetic field
within Bruhnes Chron, at about 0.56 Ma corresponding to the relative paleointensity minimum of global extent found in marine
sediments at about 590 ka. 相似文献
137.
The accuracy of the three‐dimensional modal pushover analysis (MPA) procedure in estimating seismic demands for unsymmetric‐plan buildings due to two horizontal components of ground motion, simultaneously, is evaluated. Eight low‐and medium‐rise structures were considered. Four intended to represent older buildings were designed according to the 1985 Uniform Building Code, whereas four other designs intended to represent newer buildings were based on the 2006 International Building Code. The median seismic demands for these buildings to 39 two‐component ground motions, scaled to two intensity levels, were computed by MPA and nonlinear response history analysis (RHA), and then compared. Even for these ground motions that deform the buildings significantly into the inelastic range, MPA offers sufficient degree of accuracy. It is demonstrated that PMPA, a variant of the MPA procedure, for nonlinear systems is almost as accurate as the well‐known standard response spectrum analysis procedure is for linear systems. Thus, for practical applications, the PMPA procedure offers an attractive alternative to nonlinear RHA, whereby seismic demands can be estimated directly from the (elastic) design spectrum. In contrast, the nonlinear static procedure specified in the ASCE/SEI 41‐06 Standard is demonstrated to grossly underestimate seismic demands for some of the unsymmetric‐plan buildings considered. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
138.
Lucas Fernandez Reyes 《地理信息系统科学与遥感》2013,50(1):68-73
Remote sensing inventories of the land and marine resources of Cuba, both from satellite and aerial platforms, are assessed in terms of their contributions to research on the country's physical and economic geography. Under the auspices of an international cooperative program “Interkosmos,” maps of many types have been upgraded, the costs of surveys have been reduced dramatically, and the potential for monitoring natural and human-induced change is being realized more fully. In addition, a study of weather and other conditions affecting image quality led to a determination of optimal times for conducting remote sensing surveys. Translated from: Vestnik Moskovskogo Universiteta, geografiya, 1988, No. 3, pp. 36-41, by Edward Torrey, Alexandria, VA 22308. 相似文献
139.
Bertha Aguilar Reyes Victoria Mejía Avto Goguitchaichvili Jaime Escobar Germán Bayona Francisco Bautista Juan C. Morales Thomas J. Ihl 《Studia Geophysica et Geodaetica》2013,57(4):741-754
Rock-magnetic investigations of environmental samples, such as soils, dust and leaves, can provide useful information on environmental stress. Aim of this paper is to report on the first magnetic survey carried out on environmental samples from Bogotá, Colombia, which is the fifth most populated city of Latin America. We studied three kinds of samples in order to evaluate their potential as pollution markers: soils, urban dust and leaves of the Sauco (Sambucus nigra) tree. Standard magnetic methods were used to analyze the three groups of samples, with special emphasis on leaves investigated here for the first time for environmental purposes. Samples were collected along two perpendicular transects in an area of the city presumably unpolluted, with two different systems of public transportation. Thermomagnetic curves obtained from soils and atmospheric dust show clearly defined ferrimagnetic phase (probably magnetite) as the main magnetic carrier. Curves of acquisition of isothermal remanent magnetization confirm the ferrimagnetic character of magnetic particles. Frequency-dependent magnetic susceptibility was found between 0 and 10%, suggesting less-important contribution of ultrafine super-paramagnetic magnetite. The apparent contradictory results between soils and the rest of samples may reflect different accumulation period for magnetic particles, being shorter for leaves and urban dust than for soils. 相似文献
140.