全文获取类型
收费全文 | 130677篇 |
免费 | 1910篇 |
国内免费 | 1053篇 |
专业分类
测绘学 | 3043篇 |
大气科学 | 8837篇 |
地球物理 | 25828篇 |
地质学 | 46604篇 |
海洋学 | 11831篇 |
天文学 | 29450篇 |
综合类 | 375篇 |
自然地理 | 7672篇 |
出版年
2022年 | 789篇 |
2021年 | 1408篇 |
2020年 | 1541篇 |
2019年 | 1666篇 |
2018年 | 3522篇 |
2017年 | 3298篇 |
2016年 | 4028篇 |
2015年 | 2195篇 |
2014年 | 3892篇 |
2013年 | 6926篇 |
2012年 | 4165篇 |
2011年 | 5544篇 |
2010年 | 4884篇 |
2009年 | 6296篇 |
2008年 | 5667篇 |
2007年 | 5632篇 |
2006年 | 5194篇 |
2005年 | 3957篇 |
2004年 | 3839篇 |
2003年 | 3615篇 |
2002年 | 3448篇 |
2001年 | 3123篇 |
2000年 | 3020篇 |
1999年 | 2433篇 |
1998年 | 2553篇 |
1997年 | 2353篇 |
1996年 | 2027篇 |
1995年 | 2024篇 |
1994年 | 1727篇 |
1993年 | 1613篇 |
1992年 | 1537篇 |
1991年 | 1484篇 |
1990年 | 1564篇 |
1989年 | 1349篇 |
1988年 | 1228篇 |
1987年 | 1479篇 |
1986年 | 1275篇 |
1985年 | 1573篇 |
1984年 | 1758篇 |
1983年 | 1682篇 |
1982年 | 1577篇 |
1981年 | 1418篇 |
1980年 | 1305篇 |
1979年 | 1238篇 |
1978年 | 1201篇 |
1977年 | 1051篇 |
1976年 | 1033篇 |
1975年 | 985篇 |
1974年 | 989篇 |
1973年 | 1030篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Specific hydrological and hydrochemical conditions in Kenozero Lake have led to changes in the morphology of fishes at a cellular level. The abnormalities in the function of the respiratory, digestive, and excretory systems were recorded. The degree of pathology depended on the ecological features of the fish. The pathological changes were most pronounced in the gills of the fish species (orfe, perch, and roach) characterized by active mode of life and sensible to oxygen deficiency. The changes in the epithelium of gill filaments had a compensatory significance and were aimed at increasing the area of the functional surface of the gills under the conditions of hypoxia. 相似文献
992.
Pierre?MasselotEmail author Fateh?Chebana Taha?B.M.J.?Ouarda 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(2):509-522
Regional frequency analysis is an important tool to properly estimate hydrological characteristics at ungauged or partially gauged sites in order to prevent hydrological disasters. The delineation of homogeneous groups of sites is an important first step in order to transfer information and obtain accurate quantile estimates at the target site. The Hosking–Wallis homogeneity test is usually used to test the homogeneity of the selected sites. Despite its usefulness and good power, it presents some drawbacks including the subjective choice of a parametric distribution for the data and a poorly justified rejection threshold. The present paper addresses these drawbacks by integrating nonparametric procedures in the L-moment homogeneity test. To assess the rejection threshold, three resampling methods (permutation, bootstrap and Pólya resampling) are considered. Results indicate that permutation and bootstrap methods perform better than the parametric Hosking–Wallis test in terms of power as well as in time and procedure simplicity. A real-world case study shows that the nonparametric tests agree with the HW test concerning the homogeneity of the volume and the bivariate case while they disagree for the peak case, but that the assumptions of the HW test are not well respected. 相似文献
993.
994.
G. Lanzo M. Tallini G. Milana G. Di Capua F. Del Monaco A. Pagliaroli S. Peppoloni 《Bulletin of Earthquake Engineering》2011,9(6):1855-1875
The paper focuses on the strong motion array deployed in the upper Aterno River Valley, in the immediate outskirts north-west
of the town of L’Aquila, which is part of the Italian Strong Motion Network operated by the Department of Civil Protection.
The array is composed of six accelerometric stations located along a cross section of the valley. The importance of this array
relies on the fact that a large amount of high-quality records were obtained during the 2009 L’Aquila seismic sequence, from
both the mainshock and several aftershocks. These data are especially important to investigate site effects in sediment-filled
valleys during moderate earthquakes in epicentral area because well-documented observational studies are very limited in the
literature. However, the main drawback for the study of site effects in the Aterno valley is the lack of a detailed knowledge
of the geometry of the valley, soil layering and dynamic properties of materials. The main motivation for this study stems
from the need to provide a reliable subsoil model of the valley coupled with high-quality strong motion data. Based on the
above, in the framework of S4 project, a major effort was undertaken to get a trustworthy cross section of the valley by an
ad hoc investigation, comprising geological and geotechnical surveys as well as an extensive geophysical campaign, characterized
by both active and passive measurements. These results were complemented by additional geological and geotechnical data available
in the literature. By merging all the information acquired, a 2D subsoil model of the transversal section of the upper Aterno
valley has been produced. The valley is characterised by an asymmetric shape with a shallower rock basement at the western
edge of the valley that deepens at the valley centre. Moreover, based on the results of geophysical tests, representative
Vs values were assigned to the different lithologic units forming the alluvial deposits filling the valley. Shear wave velocity
is a fundamental parameter for ground response studies and it is also effective in classifying the accelerometric station
from a seismic point of view. The 2D model may be therefore, considered a benchmark model for future studies of site effects.
It will offer the possibility to examine site effects with a complex underlying geology and to validate the results of numerical
simulations of site response analyses with the numerous observations from earthquake recordings, both for weak and strong
ground motion conditions. 相似文献
995.
Determining the location of buried plastic water pipes from measurements of ground surface vibration
J.M. MuggletonY. Gao 《Journal of Applied Geophysics》2011,75(1):54-61
‘Mapping the Underworld’ is a UK-based project, which aims to create a multi-sensor device that combines complementary technologies for remote buried utility service detection and location. One of the technologies to be incorporated in the device is low-frequency vibro-acoustics, and techniques for detecting buried infrastructure, in particular plastic water pipes, are being investigated. One of the proposed techniques involves excitation of the pipe at some known location with concurrent vibrational mapping of the ground surface in order to infer the location of the remainder of the pipe. In this paper, measurements made on a dedicated pipe rig are reported. Frequency response measurements relating vibrational velocity on the ground to the input excitation were acquired. Contour plots of the unwrapped phase revealed the location of the pipe to within 0.1-0.2 m. Magnitude contour plots revealed the excitation point and also the location of the pipe end. By examining the unwrapped phase gradients along a line above the pipe, it was possible to identify the wave-type within the pipe responsible for the ground surface vibration. Furthermore, changes in the ground surface phase speed computed using this method enabled the location of the end of the pipe to be confirmed. 相似文献
996.
997.
Digitization of the daily prominence sketches based on data from the global observational network of visual solar spectroscopes was performed for 1922–1934. More than 55000 prominences were distinguished. The results of analysis of distributions by area, height, and prominence location are presented. In addition, the prominence characteristics were compared to those obtained from more recent observations at the Kislovodsk Mountain Astronomical Station of Pulkovo Observatory. The distributions of prominence areas and heights are close to lognormal. The maximal height distribution corresponds to ~25–40 arcsecs. A second maximum also exists for prominence heights of ~70–90 arcsecs. 相似文献
998.
The upper crustal location of the foci of the Spitak earthquake of December 7, 1988, and its aftershocks is proved. It is demonstrated that the seismological network in Armenia and Georgia allowed unequivocal focal depth identification based on the kinematic data. The waveforms of all the Spitak earthquakes are typical of sources in the upper crust. It is noted that up to now, mantle earthquakes in the Caucasus have only been revealed in the Terek–Sunzha depression. 相似文献
999.
1000.