全文获取类型
收费全文 | 1765篇 |
免费 | 252篇 |
国内免费 | 335篇 |
专业分类
测绘学 | 261篇 |
大气科学 | 330篇 |
地球物理 | 403篇 |
地质学 | 596篇 |
海洋学 | 285篇 |
天文学 | 33篇 |
综合类 | 147篇 |
自然地理 | 297篇 |
出版年
2024年 | 10篇 |
2023年 | 21篇 |
2022年 | 45篇 |
2021年 | 63篇 |
2020年 | 69篇 |
2019年 | 87篇 |
2018年 | 67篇 |
2017年 | 84篇 |
2016年 | 84篇 |
2015年 | 95篇 |
2014年 | 104篇 |
2013年 | 112篇 |
2012年 | 104篇 |
2011年 | 111篇 |
2010年 | 94篇 |
2009年 | 112篇 |
2008年 | 103篇 |
2007年 | 112篇 |
2006年 | 98篇 |
2005年 | 70篇 |
2004年 | 92篇 |
2003年 | 67篇 |
2002年 | 52篇 |
2001年 | 41篇 |
2000年 | 43篇 |
1999年 | 50篇 |
1998年 | 50篇 |
1997年 | 35篇 |
1996年 | 36篇 |
1995年 | 35篇 |
1994年 | 46篇 |
1993年 | 35篇 |
1992年 | 24篇 |
1991年 | 16篇 |
1990年 | 25篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1976年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有2352条查询结果,搜索用时 15 毫秒
21.
A new earthquake catalogue for central, northern and northwestern Europe with unified Mw magnitudes, in part derived from chi-square maximum likelihood regressions, forms the basis for seismic hazard calculations
for the Lower Rhine Embayment. Uncertainties in the various input parameters are introduced, a detailed seismic zonation is
performed and a recently developed technique for maximum expected magnitude estimation is adopted and quantified. Applying
the logic tree algorithm, resulting hazard values with error estimates are obtained as fractile curves (median, 16% and 84%
fractiles and mean) plotted for pga (peak ground acceleration; median values for Cologne 0.7 and 1.2 m/s2 for probabilities of exceedence of 10% and 2%, respectively, in 50 years), 0.4 s (0.8 and 1.5 m/s2) and 1.0 s (0.3 and 0.5 m/s2) pseudoacclerations, and intensity (I0 = 6.5 and 7.2). For the ground motion parameters, rock foundation is assumed. For the area near Cologne and Aachen, maps
show the median and 84% fractile hazard for 2% probability of exceedence in 50 years based on pga (maximum median value about
1.5 m/s2), and 0.4 s (>2 m/s2) and 1.0 s (about 0.8 m/s2) pseudoaccelerations, all for rock. The pga 84% fractile map also has a maximum value above 2 m/s2 and shows similarities with the median map for 0.4 s. In all maps, the maximum values fall within the area 6.2–6.3° E and
50.8–50.9° N, i.e., east of Aachen. 相似文献
22.
A gravity core collected from the upper slope of southwest of Quilon at a water depth of 776 m (Lat: 8°12′263″N, Long: 76°28′281″E)
was analysed for texture (carbonate free), calcium carbonate and organic carbon. Variation in silicic fraction seems to be
controlled by silt, i.e., enrichment from 15 ka BP to 10 ka BP and then constant in Holocene. Below 15 ka BP, the silicic
fraction gets depleted compared to the Holocene section with a minimum around 21 ka BP. Clay content remains nearly constant
except in the Holocene where it shows an enrichment. Carbonate content of less than 63 micron when computed by subtracting
coarse fraction content from the total carbonate suggests that the total carbonates are mainly concentrated in the finer fraction.
All these carbonate phases show an inverse relationship with silicic fraction except in Holocene. Below 15 ka BP, CaCO3 dominates in sediments comprising more than 65%, such an increase is also seen in the coarse fraction. Coarse fraction from
these sections contains abundant nodular type aggregates encrusting small forams. This period is marked by a high sedimentation
rate comparable to Holocene. These parameters suggest that the productivity and precipitation have increased in the Holocene
due to the intensification of the southwest monsoon. During the last glacial maximum and early deglacial period the high sedimentation
rate indicates redeposition of the carbonates from the existing carbonate lithofacies situated between Quilon and Cape Comorin
probably due to the slope instability. 相似文献
23.
GIS叠置图层方差分量的极大似然估计 总被引:1,自引:0,他引:1
针对GIS叠置中的同名点,以维希特分布密度为似然函数,提出了各图层方差分量的极大似然估计方法。该方法不依赖残差,不需要迭代就能估计未知参数和方差分量。 相似文献
24.
25.
Dynamic damaging potential of ground motions must be evaluated by the response behaviour of structures, and it is necessary to indicate what properties of ground motions are most appropriate for evaluation. For that purpose, the behaviour of energy input process and hysteretic energy dissipation are investigated in this study. It is found that the momentary input energy that is an index for the intensity of input energy is related to the characteristics of earthquakes such as cyclic or impulsive, and to the response displacement of structures immediately. On the basis of these results, a procedure is proposed to predict inelastic response displacement of structures by corresponding earthquake input energy to structural dissipated damping and hysteretic energy. In this procedure the earthquake response of structures is recognized as an input and dissipation process of energy, and therefore structural properties and damaging properties of ground motions can be taken into account more generally. Lastly, the studies of the pseudodynamic loading test of reinforced concrete structure specimens subjected to ground motions with different time duration are shown. The purpose of this test is to estimate the damaging properties of ground motions and the accuracy of the proposed prediction procedure. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
26.
非常规综合物化探方法油气预测研究中存在的主要问题为:缺乏系统与综合的基础性理论研究,异常形成的机理还不十分清楚,在参数的优化组合及异常的求取上尚有诸多不足。针对后一种情况,选择松辽盆地东岭构造作为实验区进行了有益的探索。选取低能吸附烃、放射性测氡及土壤热释光三类参数进行了优化组合,分别计算了综合指标MAE与MAC及组合熵,然后对各值采用泛克里格法求取异常,取得了良好的效果。下一步研究应从异常形成的机理入手,建立三维非常规综合物化探油气预测模式,以提高油气预测成功率。 相似文献
27.
A total of four times of rhabdosome complication events, i.e., the lateral branching of graptolite stipes during the Late Middle Ordovician, the secondary branching of graptolite stipes at the earliest Upper Ordovician, the early Qiantangjiangian of Upper Ordovician and the middle Qiantangjiangian, respectively, is discussed in this paper. These events and other adaptation events demonstrate close relationships between a diverse graptolite fauna and sea level changes, and consequently can be employed to study sea level fluctuations. It is safe to conclude that the complication of rhabdosome started at the maximum flooding surface (MFS) and terminated at the beginning of regression. 相似文献
28.
Yan Y. Kagan 《Geophysical Journal International》2002,149(3):731-754
29.
30.
根据统计分布与信息熵理论,定义了震级信息熵Hm和地震间隔时间信息熵Ht,并推导了它们的计算公式。通过时空扫描和计算,发现强震前1~3年Hm和Ht出现低值异常,与地震有较好的对应关系,可以作为一组中期或中短期预测指标。 相似文献