全文获取类型
收费全文 | 5864篇 |
免费 | 191篇 |
国内免费 | 91篇 |
专业分类
测绘学 | 169篇 |
大气科学 | 553篇 |
地球物理 | 1447篇 |
地质学 | 2024篇 |
海洋学 | 552篇 |
天文学 | 768篇 |
综合类 | 22篇 |
自然地理 | 611篇 |
出版年
2021年 | 61篇 |
2020年 | 65篇 |
2019年 | 90篇 |
2018年 | 124篇 |
2017年 | 117篇 |
2016年 | 158篇 |
2015年 | 147篇 |
2014年 | 204篇 |
2013年 | 326篇 |
2012年 | 246篇 |
2011年 | 269篇 |
2010年 | 196篇 |
2009年 | 304篇 |
2008年 | 289篇 |
2007年 | 263篇 |
2006年 | 222篇 |
2005年 | 189篇 |
2004年 | 199篇 |
2003年 | 189篇 |
2002年 | 192篇 |
2001年 | 133篇 |
2000年 | 138篇 |
1999年 | 114篇 |
1998年 | 107篇 |
1997年 | 93篇 |
1996年 | 86篇 |
1995年 | 87篇 |
1994年 | 79篇 |
1993年 | 65篇 |
1992年 | 65篇 |
1991年 | 69篇 |
1990年 | 67篇 |
1989年 | 59篇 |
1988年 | 58篇 |
1987年 | 65篇 |
1986年 | 43篇 |
1985年 | 73篇 |
1984年 | 80篇 |
1983年 | 72篇 |
1982年 | 65篇 |
1981年 | 76篇 |
1980年 | 63篇 |
1979年 | 57篇 |
1978年 | 38篇 |
1977年 | 55篇 |
1976年 | 63篇 |
1975年 | 46篇 |
1974年 | 57篇 |
1973年 | 48篇 |
1972年 | 25篇 |
排序方式: 共有6146条查询结果,搜索用时 0 毫秒
31.
Peter Bond 《Astronomy& Geophysics》2003,44(2):2.30-2.32
Peter Bond reports on reappraisal for NASA in the aftermath of the loss of the shuttle Columbia, refinement of an extrasolar planet's mass and rethinking of ideas about water on Mars. 相似文献
32.
Feature Environmental geophysics: a site characterization tool for urban regeneration in the post-mining era 总被引:1,自引:0,他引:1
Peter Styles 《Geology Today》2003,19(5):173-178
The closure and decay of industrial activity involving mining, chemical or light industrial operations has scarred the landscape of urban areas. The Government has major initiatives in urban regeneration to remediate these 'brown-field sites'. 相似文献
33.
34.
35.
36.
Distribution and morphology of sinkholes triggered by flooding following Tropical Storm Alberto at Albany, Georgia, USA 总被引:1,自引:0,他引:1
Flooding of the Flint River in July 1994 triggered the collapse of at least 312 sinkholes in the karstic Dougherty Plain at Albany, Georgia. We examined the distribution and morphology of these new sinkholes to evaluate the mode of formation, to characterize early stages of the evolution of sinkhole form, and to estimate the lowering of the surface associated with the development of new sinkholes.Eighty-eight percent of sinkholes occur inside the limits of flooding, especially in areas of sandy overburden, and they often follow joint-controlled linear trends. Sinkhole dimensions are log-normally distributed with median values of circumference = 5.7 m, length = 1.8 m, width = 1.6 m, and depth = 0.7 m; asymmetry (L:W) = 1.2. Cross-sectional forms range from narrow cylinders to large bowls, with many sinkholes having undercut sides.Flooding triggered the formation of sinkholes by saturating and liquefying overburden, which caused soil arches to collapse and flow into cavities in bedrock. The prevalence of sinkholes near the periphery of flooding suggests that drainage and loss of buoyant support as flood waters subsided may also have contributed to failure. A volume ratio index is used to quantify the three dimensional geometric form of sinkholes. Initially, small cylindrical shafts open over a bedrock joint, followed by progressive slumping that leads to widening and increases in volume to a final bowl form. Estimates of the aggregate volume of overburden transported underground in flooded areas range from 7,990 to 11,130 m3. Averaged over flooded areas, this accounts for 0.26 to 0.37 mm/km2 lowering of the surface. Based on a 500 year recurrence interval for the flood event, values for lowering of the surface range from 0.52 to 0.74 mm per 1,000 years. These values are an order of magnitude less than estimates of carbonate dissolution and suggest that transport of overburden underground is limited by triggering events. 相似文献
37.
Antenna field 2 of the Tromsø Heating facility consists of six rows of six horizontal crossed full wave dipoles aligned with the rows running geographic east-west. In previous experiments on ELF/VLF wave generation it has been the practice to feed the rows in parallel, with HF radiation amplitude modulated at the ELF/VLF frequency it was desired to radiate (AM configuration). Here we describe how the antenna array was also configured so that it could be fed with a continuous wave (CW) input power but still carry information at an ELF/VLF frequency. To effect this the three southern most rows of the antenna array were driven with a CW signal at 4.04 MHz and the three northernmost rows with a CW signal at frequency greater than 4.04 MHz by the ELF/VLF frequency it was desired to radiate (CW configuration). Experiments were performed with modulation/difference frequencies of 565 and 2005 Hz and the signals were received at the Lycksele Geophysical Observatory, 500 km south of the heating facility. The signals were typically 11 dB greater in the AM than the CW configuration, despite the fact that the average power delivered to the ionosphere in the CW configuration was four times that in the AM configuration. Significant harmonic radiation (both odd and even) was produced in the AM configuration but no harmonic radiation was detected in the CW configuration. A simple theory has been developed to model the fields produced by HF heating using the two techniques (AM,CW). A good agreement has been obtained between the experimental observations and model computations. The model has been extended to show how the relative efficiency of generation, AM/CW, varies with the frequency of the ELF/VLF radiation and HF antenna element spacing. Radiation patterns for the ‘ionospheric ELF/VLF antenna’ have also been derived for the two generation techniques. 相似文献
38.
39.
Zhengtong Xie Peter R. Voke Paul Hayden Alan G. Robins 《Boundary-Layer Meteorology》2004,111(3):417-440
A family of wall models is proposed that exhibits moresatisfactory performance than previousmodels for the large-eddy simulation (LES) of the turbulentboundary layer over a rough surface.The time and horizontally averaged statistics such asmean vertical profiles of windvelocity, Reynolds stress, turbulent intensities, turbulentkinetic energy and alsospectra are compared with wind-tunnel experimental data.The purpose of the present study is to obtain simulatedturbulent flows that are comparable with wind-tunnelmeasurements for use as the wind environment for thenumerical prediction by LES of source dispersion in theneutral atmospheric boundary layer. 相似文献
40.