全文获取类型
收费全文 | 65784篇 |
免费 | 11605篇 |
国内免费 | 15891篇 |
专业分类
测绘学 | 7910篇 |
大气科学 | 9737篇 |
地球物理 | 14063篇 |
地质学 | 35908篇 |
海洋学 | 8048篇 |
天文学 | 2378篇 |
综合类 | 4939篇 |
自然地理 | 10297篇 |
出版年
2024年 | 212篇 |
2023年 | 673篇 |
2022年 | 1852篇 |
2021年 | 2189篇 |
2020年 | 2415篇 |
2019年 | 2893篇 |
2018年 | 2333篇 |
2017年 | 2701篇 |
2016年 | 2859篇 |
2015年 | 3194篇 |
2014年 | 3688篇 |
2013年 | 3944篇 |
2012年 | 4063篇 |
2011年 | 4364篇 |
2010年 | 3601篇 |
2009年 | 4279篇 |
2008年 | 4261篇 |
2007年 | 4706篇 |
2006年 | 4503篇 |
2005年 | 3994篇 |
2004年 | 3683篇 |
2003年 | 3429篇 |
2002年 | 3056篇 |
2001年 | 2661篇 |
2000年 | 2477篇 |
1999年 | 2279篇 |
1998年 | 1980篇 |
1997年 | 1810篇 |
1996年 | 1633篇 |
1995年 | 1407篇 |
1994年 | 1394篇 |
1993年 | 1176篇 |
1992年 | 867篇 |
1991年 | 640篇 |
1990年 | 527篇 |
1989年 | 421篇 |
1988年 | 333篇 |
1987年 | 211篇 |
1986年 | 142篇 |
1985年 | 104篇 |
1984年 | 47篇 |
1983年 | 30篇 |
1982年 | 38篇 |
1981年 | 27篇 |
1980年 | 32篇 |
1979年 | 37篇 |
1978年 | 43篇 |
1977年 | 27篇 |
1975年 | 4篇 |
1954年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 891 毫秒
181.
182.
尚永亮 《广东海洋大学学报》2003,23(2):27-29
古代荆湘之地域的特殊性使其成为朝廷贬官吏的首选之地和贬官的中转之地。在此 ,这些被贬官首创了大量关于贬谪的文学作品。其作品物色鲜明 ,楚地风情突出 ,具有近乎凝固化了的悲怨传统 ,早期逐臣、作品及谪地成为凝定的贬谪代码和符号 ,生成并积淀了深厚的人文精神。 相似文献
183.
184.
185.
The supraregional GIS-supported stochastical model, WEKU, for the determination of groundwater residence times in the upper
aquifers of large groundwater provinces is presented. Using a two-dimensional analytical model of groundwater flow, groundwater
residence times are determined within two extreme cases. In the first case, maximal groundwater residence times are calculated,
representing the part of groundwater, that is drained by the main surface water of a groundwater catchment area. In the second
case, minimal groundwater residence times for drainage into the nearest surface water are determined. Using explicit distribution
functions of the input parameters, mean values as well as potential ranges of variations of the groundwater residence times
are derived. The WEKU model has been used for the determination of groundwater residence times throughout Germany. The model
results – mean values and deviations of the groundwater velocity and the maximal and minimal groundwater residence times in
the upper aquifers – are presented by general maps and discussed in detail. It is shown that the groundwater residence times
in the upper aquifer vary regionally, differentiated between less than 1 year and more than 2000 years. Using this information,
the time scales can be specified, until measures to remediate polluted groundwater resources may lead to a substantial groundwater
quality improvement in the different groundwater provinces of Germany. With respect to its supraregional scale of application,
the WEKU model may serve as a useful tool for the supraregional groundwater management on a state, federal or international
level.
Received: 15 August 1995 · Accepted: 15 October 1995 相似文献
186.
山东省产业重心转移与可持续发展研究 总被引:22,自引:0,他引:22
孙希华 《地球信息科学学报》2001,3(1):27-31
本文利用经济空间结构的重心研究方法,分析了山东省近八年来产业重心的转移,提出了山东省产业可持续发展战略 相似文献
187.
A calculation formula on spherical pattern of Qinghai-Tibet plateau moving model is established. Tibet massif moves norward by east in speed of 28 mm/a, Ganshu-Qinghai massif moves to northeast in speed of 15 mm/a, Qomolangma Feng moves northward by a few east in speed of 35 ~42 mm/a. The low latitude perimeter is longer than the nigh latitude perimeter. When the Tibet massif moves northward, its latitude perimeter must be contracted and the Tibet massif must move eastward by Coriolis. Coriolis force is inertial in earth rotation. It makes the fall body turning to east and the rising block turning westward. In the Northern Hemisphere, it makes the northward body turning to east and the southward block turning to west.This is the reason why the tectonic zones of western Pacific are different from those of eastern Pacific. 相似文献
188.
Jean-Francois Guéguen Pho Hoang-Trong Hilaire Legros 《Geophysical Journal International》1987,89(3):839-855
Summary. A first-order form of the Euler's equations for rays in an ellipsoidal model of the Earth is obtained. The conditions affecting the velocity law for a monotonic increase, with respect to the arc length, in the angular distance to the epicentre, and in the angle of incidence, are the same in the ellipsoidal and spherical models. It is therefore possible to trace rays and to compute travel times directly in an ellipsoidal earth as in the spherical model. Thus comparison with the rays of the same coordinates in a spherical earth provides an estimate of the various deviations of these rays due to the Earth's flattening, and the corresponding travel-time differences, for mantle P -waves and for shallow earthquakes. All these deviations are functions both of the latitude and of the epicentral distance. The difference in the distance to the Earth's centre at points with the same geocentric latitude on rays in the ellipsoidal and in the spherical model may reach several kilometres. Directly related to the deformation of the isovelocity surfaces, this difference is the only cause of significant perturbation in travel times. Other differences, such as that corresponding to the ray torsion, are of the first order in ellipticity, and may exceed 1 km. They induce only small differences in travel time, less than 0.01s. Thus, we show that the ellipticity correction obtained by Jeffreys (1935) and Bullen (1937) by a perturbational method can be recovered by a direct evaluation of the travel times in an ellipsoidal model of the Earth. Moreover, as stated by Dziewonski & Gilbert (1976), we verify the non-dependence of this correction on the choice of the velocity law. 相似文献
189.
Variables related to urban park awareness are identified and methods for relaxing assumptions of perfect information in park use models are discussed. Park awareness is related to park characteristics (age and degree of development of the park), population characteristics (race, age, length of residence, recreation participation), and distance. Park attributes are stronger predictors of both park awareness and use than is distance. These findings parallel similar research on the cognitive aspects of shopping decisions. 相似文献
190.
《The Professional geographer》1987,39(1):85-94
Reviews of geographic software in this article: DEMO-GRAPHICS: WORLD POPULATIONS AND PROJECTIONS. ESP GAUSS. CEMODEL S. Damus LIMDEP. William H. Greene MICROSTAT 4.1 OTIS PCIPS. (Personal Computer Image Processing System) . H.J. Meyers and R. Bernstein. REGRESSION ANALYSIS OF TIME SERIES (RATS) SPSS/PC+ URBAN DATA MANAGEMENT SOFTWARE (UDMS) 相似文献