全文获取类型
收费全文 | 1153篇 |
免费 | 31篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 121篇 |
地球物理 | 238篇 |
地质学 | 417篇 |
海洋学 | 87篇 |
天文学 | 202篇 |
综合类 | 3篇 |
自然地理 | 108篇 |
出版年
2021年 | 10篇 |
2020年 | 12篇 |
2019年 | 10篇 |
2018年 | 15篇 |
2017年 | 24篇 |
2016年 | 19篇 |
2015年 | 19篇 |
2014年 | 28篇 |
2013年 | 60篇 |
2012年 | 25篇 |
2011年 | 47篇 |
2010年 | 35篇 |
2009年 | 64篇 |
2008年 | 34篇 |
2007年 | 28篇 |
2006年 | 44篇 |
2005年 | 33篇 |
2004年 | 49篇 |
2003年 | 48篇 |
2002年 | 33篇 |
2001年 | 30篇 |
2000年 | 27篇 |
1999年 | 34篇 |
1998年 | 29篇 |
1997年 | 18篇 |
1996年 | 19篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 18篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 25篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 18篇 |
1977年 | 13篇 |
1976年 | 12篇 |
1975年 | 19篇 |
1974年 | 13篇 |
1973年 | 10篇 |
1972年 | 11篇 |
排序方式: 共有1192条查询结果,搜索用时 516 毫秒
171.
Mineralium Deposita Referees 1992 相似文献
172.
173.
Three earthquakes of magnitude around 5 occurred offshore western Norway on 5th February, 1986, on 8th August, 1988, and on 23rd January, 1989. These earthquakes, representing the highest seismic activity level in this area for at least 30 years, were all felt by people over most of southern and central Norway. Focal-mechanism solutions for these earthquakes indicate thrust faulting along N-S to NNE-SSW striking fault planes, in response to NW-SE compressional stress, most probably of plate tectonic origin.
A number of high-quality digital recordings of the ground motions at various distances from these and other recent earthquakes in Norway have shown that source spectral as well as wave attenuation characteristics in this area are reasonably consistent with what has been derived from other intraplate areas. 相似文献
A number of high-quality digital recordings of the ground motions at various distances from these and other recent earthquakes in Norway have shown that source spectral as well as wave attenuation characteristics in this area are reasonably consistent with what has been derived from other intraplate areas. 相似文献
174.
The Meixner functions are utilized to relate the effective rainfall, the direct runoff and the unit hydrograph through linkage equations. The linkage equations are then employed to derive the unit hydrograph for given rainfall-runoff data on a small agricultural watershed. These functions are tested with regard to their ability to reproduce and predict the direct runoff hydrograph. The Meixner functions are found to be an effective analytical tool for hydrograph synthesis. Further, they compare well with the least squares and linear programming methods of the unit hydrograph derivation. 相似文献
175.
{We investigate the conversion of the 0.5–4 and 1–8 Å soft X-ray flux measurements made by detectors on the Geostationary Operational Environmental Satellites (GOES) into temperature and emission measures of coronal plasma using modern spectral models and modern understanding of coronal abundances. In particular, the original analysis by Thomas, Starr and Crannell (1985) is updated to take into account the realization that coronal abundances may be quite different from photospheric abundances. An important result of this analysis is that the derived temperatures and emission measures depend strongly on the assumed abundances even at high temperatures where continuum rather than spectral lines dominates the Sun’s X-ray spectrum. This occurs because the higher coronal abundances mean that most of the continuum is due to free–bound emission processes, not free–free emission, and thus is abundance-dependent. We find significant differences between modern calculations of the temperature response of the flux measurements and the versions currently in use: for a typical flare, emission measures may be up to a factor of 4 smaller than the current software suggests. Derived temperatures are similar for both photospheric and coronal abundances for cool flares (e.g., 15 MK), but for hot flares (e.g., 35 MK) coronal abundances can lead to significantly (~25%) lower temperatures being derived. 相似文献
176.
Roger K. Ulrich 《Astrophysics and Space Science》1970,7(2):183-200
The motion of convective cells in an environment which changes rapidly with depth is examined. In such an environment a cell may move through regions with different levels of ionization and with associated differences in heat capacity. The energy equation is cast in a manner which is independent of the history of these cells. The convective flux at a given level of the atmosphere is written as an average over an ensemble of cells originating at a range of other levels. A procedure for correcting the temperature gradient for these non-local effects is described and results for a model solar atmosphere are given. The principal results are: (1) The rms velocity varies smoothly and is non-zero well into the photosphere (e.g.,v
rsm=1.4 km/sec at =0.2); (2) Convective overshoot reduces the radiative flux to 60% and 90% of the total at =2.5 and 0.2 respectively; and (3) The interior adiabat of the convective envelope is less sensitive to the assumed value of the average cell size than in the usual treatment of convection.Supported in part by the National Science Foundation [GP-9433, GP-9114], the Office of Naval Research [Nonr-220(47)], and Air Force Grant AG-AFOSR-171-67. 相似文献
177.
Roger A. Kopp 《Solar physics》1972,27(2):373-393
The classical picture of the transition region is that of a thin spherically symmetric shell maintained in a steady average thermodynamical state by a balance between conductive heating from the hot overlying corona and radiative losses. The further analysis of existing extreme ultraviolet flux data casts doubt on the correctness of this simple model. It is shown that the downward heat flux between the chromosphere and corona cannot be nearly as large as the value 6 × 105 erg cm–)= 13.46 - 2.99 sin2 s–1 derived in previous studies by assuming a planar atmosphere, and in fact is insufficient to balance transition-region radiative losses. An alternative picture is developed, consisting of a transition region network covering only a small fraction of the solar disk. The dissipation of mechanical energy, previously neglected in many calculations of theoretical transition region models, appears to play a dominant role in the local energy balance of the network.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
178.
179.
180.
Peak fluxes of flare-associated 8–12 Å X-ray bursts occur at or near the time of the maximum energy content of the soft X-ray source volume. The amplitudes of flare-associated bursts may thus be used as a measure of the energy deposited in the source volume by non-thermal electrons and other processes. In the mean, the soft X-ray burst amplitude is apparently independent of the occurrence of a type III event. This is interpreted to indicate that electrons accelerated by the type III process do not directly participate in establishing the soft X-ray source volume. 相似文献