全文获取类型
收费全文 | 2674篇 |
免费 | 160篇 |
国内免费 | 27篇 |
专业分类
测绘学 | 65篇 |
大气科学 | 189篇 |
地球物理 | 843篇 |
地质学 | 928篇 |
海洋学 | 267篇 |
天文学 | 375篇 |
综合类 | 20篇 |
自然地理 | 174篇 |
出版年
2022年 | 11篇 |
2021年 | 46篇 |
2020年 | 44篇 |
2019年 | 40篇 |
2018年 | 120篇 |
2017年 | 113篇 |
2016年 | 185篇 |
2015年 | 123篇 |
2014年 | 144篇 |
2013年 | 199篇 |
2012年 | 154篇 |
2011年 | 143篇 |
2010年 | 136篇 |
2009年 | 160篇 |
2008年 | 129篇 |
2007年 | 132篇 |
2006年 | 84篇 |
2005年 | 84篇 |
2004年 | 91篇 |
2003年 | 68篇 |
2002年 | 38篇 |
2001年 | 41篇 |
2000年 | 45篇 |
1999年 | 37篇 |
1998年 | 37篇 |
1997年 | 34篇 |
1996年 | 31篇 |
1995年 | 20篇 |
1994年 | 28篇 |
1993年 | 21篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 15篇 |
1987年 | 11篇 |
1986年 | 17篇 |
1985年 | 11篇 |
1984年 | 20篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1975年 | 11篇 |
1974年 | 15篇 |
1973年 | 11篇 |
1972年 | 10篇 |
1971年 | 9篇 |
1970年 | 8篇 |
排序方式: 共有2861条查询结果,搜索用时 15 毫秒
191.
Quantification of salt weathering in porous stones using an experimental continuous partial immersion method 总被引:1,自引:0,他引:1
In this study, an experimental salt weathering simulation and porous stone durability classification are proposed. There are many laboratory tests that quantify durability against salt crystallisation weathering action. These are usually based on the total immersion of samples into a saline solution, which is not representative of the salt weathering mechanism. An experimental test based on partial immersion is suggested. This is a comparable study of weight loss and degradation of visual appearance due to salt crystallisation using, on the one hand, a standard durability test (UNE), and, on the other, the proposed durability test. The weight loss and visual appearance in our test is comparable to the degradation of building stone. The differences between weight loss data in both tests depend on the petrophysical properties: porous media and degree of coherence.
From this testing, a new durability classification as a function of dry weight loss in the partial immersion test is proposed. Four divisions of different types of materials can be made in this classification, which quantifies salt weathering action mainly in environments and mild climatic conditions. 相似文献
192.
Contamination by the pollutants SO2 and SO=4 was analyzed for the 1989–1992 period at four regional stations in Spain under the auspices of the EMEP-BAPMON program. The evolution of the time series of the daily pollution has also been assessed, and high mean concentrations at La Cartuja and Logroño observed, with values of 3.8 and 4.5 g m−3 for SO2, respectively. Maximum annual concentrations were recorded in 1989, when SO2 reached values of 6.24, 5.39, 5.71, and 9.30 g m−3 for the stations of La Cartuja, San Pablo de los Montes, Roquetas, and Logroño, respectively. This work attempts to establish a relationship between the concentrations of the pollutants - both SO2 gas and SO=4 aerosol - and the zones of emission or persistence of these long-range transported pollutants. In this way, those regions showing a greater impact on the air quality in each season have been determined. To achieve this, the trajectories of the air masses carrying away the pollution to each of the receiving stations were considered and followed by a sectorial analysis. Nonparametric statistical methods were implemented to contrast the chemical homogeneity among the different sectors. The criterion that several homogeneous sectors form a chemically homogeneous region was used. To improve this sectorial analysis, we have proposed a new technique based on the Potential-Source-Contribution Function (PSCF). Starting out from a set of specified regions, considered to be chemically homogeneous domains, it is possible to determine the likelihood that an air mass with particular characteristics (e.g., that a value of the daily concentration higher than the mean recorded at the station has been obtained) will arrive at a given station after having crossed one of the previously defined regions. Using this technique, it is possible to determine the source regions through which the air masses circulate and bring high pollution concentrations to the studied stations. Thanks to the PSCF, these statistical methods offer, through a sectorial analysis, the possibility to pass from a qualitative to a more quantitative view. 相似文献
193.
Fault network of the Upper Silesian Coal Basin (USCB) is built of sets of strike-slip, oblique-slip and dip-slip faults. It is a typical product of force couple which acts evenly with the parallel of latitude, causing horizontal and anti-clockwise movement of rock-mass. Earlier research of focal mechanisms of mine tremors, using a standard fault plane solution, has shown that some events are related to tectonic directions in main structural units of the USCB. An attempt was undertaken to analyze the records of mine tremors from the period 1992–1994 in the selected coal fields. The digital records of about 200 mine tremors with energy larger than 1×104 J (M
L
>1.23) were analyzed with SMT software for seismic moment tensor inversion. The decomposition of seismic moment tensor of mine tremors was segmented into isotropic (I) part, compensated linear vector dipole (CLVD) part and double-couple (DC) part. The DC part is prevalent (up to 70%) in the majority of quakes from the central region of the USCB. A group of mine tremors with large I element (up to 50%) can also be observed. The spatial orientation of the fault and auxiliary planes were obtained from the computations for the seismic moment DC part. Study of the DC part of the seismic moment tensor made it possible for us to separate the group of events which might be acknowledged to have their origin in unstable energy release on surfaces of faults forming a regional structural pattern. The possible influence of the Cainozoic tectonic history of the USCB on the recent shape of stress field is discussed. 相似文献
194.
Mark S. T. Bukowinski Philip E. Wannamaker Manfred Koch Yukio Fujinawa Dr. Pradeep Talwani D. Möhlmann Andrew H. Knoll Lucia Lovison-Golob Krzysztof Haman Hanna Pawłowska Henryk Piwkowski Dr. Anthony Dore Nguyen Xuan Huy Edward R. Cook Jan Błecki Jacek Leliwa-Kopystynski Magdalena Sroczynska-Kozuchowska 《Pure and Applied Geophysics》1993,140(1):139-177
195.
Summary Four parameters defining the Earth's tri-axial ellipsoid (E) have been derived on the basis of the condition that the gravity potential on E be constant and equal to the actual geopotential value (W0) on the geoid. The geocentric gravitational constant, the angular velocity of the Earth's rotation, the actual 2nd degree geopotential Stokes parameters and W0 are taken to be the primary geodetic constants defining E and its (normal) gravity field. 相似文献
196.
Bulletin of Volcanology - Correlations on the eruptive behaviour of the volcano of Capelinhos (Fayal island) in 1957–58, with (a) solar activity, and (b) earth-tide amplitudes, by way of a... 相似文献
197.
Bulletin of Volcanology - In another paper of the author, a picture of the tectonics of the Azores was presented. The morphological analysis showed evidence of a folded and faulted structure and... 相似文献
198.
199.
200.
Milan Burša 《Studia Geophysica et Geodaetica》1970,14(1):1-9
Résumé De l'ensemble des coefficients harmoniques du développement du géopotentiel [3, 6, 7], calculé à partir des variations des
éléments orbitaux des satellites, on a calculé les paramètres de l'ellipso?de terrestre triaxial, représentant la surface
du géo?de. La solution fut effectuée par méthode analytique sous la condition du minimum de l'intégrale du carré de l'écart
du rayon vecteur du géo?de et de l'ellipso?de, de même que par calcul numérique à partir des valeurs discrètes 10°×10°.
Address: Politickych vězňů 12, Praha 1-Nové Město. 相似文献
Address: Politickych vězňů 12, Praha 1-Nové Město. 相似文献