全文获取类型
收费全文 | 9965篇 |
免费 | 1555篇 |
国内免费 | 2212篇 |
专业分类
测绘学 | 483篇 |
大气科学 | 1591篇 |
地球物理 | 2080篇 |
地质学 | 3999篇 |
海洋学 | 2640篇 |
天文学 | 137篇 |
综合类 | 624篇 |
自然地理 | 2178篇 |
出版年
2024年 | 48篇 |
2023年 | 156篇 |
2022年 | 352篇 |
2021年 | 404篇 |
2020年 | 425篇 |
2019年 | 521篇 |
2018年 | 407篇 |
2017年 | 457篇 |
2016年 | 492篇 |
2015年 | 532篇 |
2014年 | 629篇 |
2013年 | 736篇 |
2012年 | 647篇 |
2011年 | 629篇 |
2010年 | 558篇 |
2009年 | 610篇 |
2008年 | 604篇 |
2007年 | 668篇 |
2006年 | 585篇 |
2005年 | 511篇 |
2004年 | 452篇 |
2003年 | 395篇 |
2002年 | 363篇 |
2001年 | 308篇 |
2000年 | 319篇 |
1999年 | 274篇 |
1998年 | 216篇 |
1997年 | 252篇 |
1996年 | 197篇 |
1995年 | 161篇 |
1994年 | 144篇 |
1993年 | 118篇 |
1992年 | 132篇 |
1991年 | 89篇 |
1990年 | 67篇 |
1989年 | 51篇 |
1988年 | 44篇 |
1987年 | 23篇 |
1986年 | 29篇 |
1985年 | 30篇 |
1984年 | 16篇 |
1983年 | 26篇 |
1982年 | 15篇 |
1981年 | 15篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
Since 1979 the repeated observations and experiments of geomagnetic total intensity and vertical component have been carried
out for ten years in the geomagetic network which is located in Jiangsu Province, China. Three earthquakes aboveM
s 5.0 occurred during the decade, and some seismomagnetic effects were observed. The observation results show that the anomalies
of the vertical geomagnetic component can’t be observed untill some months before the earthquake (M
s>5.0) in this area.
In this paper it is suggested that a densely distributed network for continuous observation of geomagnetic vertical component
may catch seismomagnetic anomalies and thus improve earthquake prediction in the light of the geomagnetic measurements of
the mid — or — low latitude locations.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 80–87, 1991.
This study is sponsored by the Chinese Joint Seismological Science Foundation. 相似文献
992.
山东碳酸岩磷灰石的特征及其研究意义 总被引:6,自引:0,他引:6
鲁中隆起的北缘分布着100多个燕山期的碳酸岩体。本文详细研究了岩体中磷灰石的一些重要特征,包括晶体形态、物理性质、光学常数、晶胞参数、化学成分、包裹体及钕锶同位素组成等。并据所得资料对岩体的成因,成岩物质来源等问题进行探讨。 相似文献
993.
Judy Ehlen 《地球表面变化过程与地形》1992,17(1):53-67
The granite tors of Dartmoor are characterized by using the regional spatial patterns of 21 geomorphic, petrographic, and structural variables. The data were derived from topographic maps, field measurement, and laboratory analysis of rock samples collected in the field. Identification of spatial patterns and comparison of patterns between variables were made on contour maps generated from the data using ARC/INFO. Three tor types—summit tors, valleyside tors, and spur tors—are semiquantitatively characterized using these data and procedures. The three types of tors are distinguished with respect to variations in relative relief, joint spacing and joint type, rock texture, grain size, and composition. Summit tors have the highest relative relief (mean: 125·7 m), contain the most potassium feldspar (>30 per cent), and have the most widely-spaced primary vertical (>300 cm) and secondary horizontal joints (> 10 cm). The rocks are the most megacrystic (> 15 per cent) and the coarsest grained. Plagioclase is also abundant in summit tors. Valleyside tors have the lowest relative relief (mean: 72·9 m) and the most widely-spaced horizontal joints (primary, 60-200 cm; secondary, > 10 cm). Grain size, vertical joint spacing, and quartz and potassium feldspar abundances are intermediate. The shapes of valleyside tors are controlled by horizontal joints and the rocks are either very feebly magcrystic or equigranular in texture. Spur tors have intermediate relative relief (mean: 115·4 m), the narrowest joint spacing (vertical joints, < 200 cm, 50-75 cm; horizontal joints <60 cm, < 10 cm) and the finest grain. In addition, the rocks are feebly magacrystic. 相似文献
994.
Susan Marriott 《地球表面变化过程与地形》1992,17(7):687-697
Samples of sediment collected from the Severn floodplain between Worcester and Gloucester following the severe flooding in January and February 1990, were analysed for their grain size distribution. The results show that most sand was deposited within 20 m of the channel bank, but that fine sand may contribute to flood sediment across the width of the floodplain. James' (1985) numerical model of overbank sedimentation attempts to predict the transfer of sediment to the floodplain during flooding. Geometrical and hydraulic data relating to the Severn flood are used as input for a computer program of James' (1985) model. The pattern of sediment concentrations predicted by the model was compared with that obtained from statistical analysis of the flood sediment. The patterns were found to be similar, so James' (1985) model was considered to predict in a relative sense the distribution of flood sediment. 相似文献
995.
运用多项式回归分析和双随机样本检验,模拟日照时数和总辐射及其影响因子(可照时间、总云量和天文辐射、日照百分率)年值和1月值、7月值的三度空间分布场,取得了满意结果。这可应用在无测站地区,仅凭经纬度和海拔估算出上述气候要素值,估算的平均相对误差大多在5%以下(最好的达0.3‰)。 相似文献
996.
Considerations on the global seismic sequences: the second and the third largest aftershocks 总被引:1,自引:0,他引:1
Theodoros M. Tsapanos 《Geophysical Journal International》1992,111(3):630-636
998.
本文阐述了利用响应矩阵法建立地下水、地表水优化调度管理模型的约束条件、并用目标规划法进行管理模型计算的一个实例。这是一个位于黄河之滨的城市,市内有许多名泉。近年来大量开采地下水已使泉水干涸,而黄河水在某些月份含沙量很大,不宜全年开采。本计算求得了这个城市几个水源地与黄河水在一个枯水年(或丰水年)内各月份的优化开采量分配方案,使之既可保证泉水全年喷涌;叉可提供所需水量。 相似文献
999.
Chih-Hsiang Ho 《Mathematical Geology》1992,24(4):347-364
In this article, we model the volcanism near the proposed nuclear waste repository at Yucca Mountain, Nevada, U.S.A. by estimating the instantaneous recurrence rate using a nonhomogeneous Poisson process with Weibull intensity and by using a homogeneous Poisson process to predict future eruptions. We then quantify the probability that any single eruption is disruptive in terms of a (prior) probability distribution, since not every eruption would result in disruption of the repository. Bayesian analysis is performed to evaluate the volcanic risk. Based on the Quaternary data, a 90% confidence interval for the instantaneous recurrence rate near the Yucca Mountain site is (1.85×10–6/yr, 1.26×10–5/yr). Also, using-these confidence bounds, the corresponding 90% confidence interval for the risk (probability of at least one disruptive eruption) for an isolation time of 104 years is (1.0×10–3, 6.7×10–3), if it is assumed that the intensity remains constant during the projected time frame. 相似文献
1000.