全文获取类型
收费全文 | 1170篇 |
免费 | 187篇 |
国内免费 | 97篇 |
专业分类
测绘学 | 99篇 |
大气科学 | 36篇 |
地球物理 | 675篇 |
地质学 | 305篇 |
海洋学 | 44篇 |
天文学 | 105篇 |
综合类 | 67篇 |
自然地理 | 123篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 23篇 |
2021年 | 38篇 |
2020年 | 33篇 |
2019年 | 45篇 |
2018年 | 50篇 |
2017年 | 36篇 |
2016年 | 33篇 |
2015年 | 43篇 |
2014年 | 57篇 |
2013年 | 63篇 |
2012年 | 60篇 |
2011年 | 55篇 |
2010年 | 34篇 |
2009年 | 61篇 |
2008年 | 55篇 |
2007年 | 56篇 |
2006年 | 55篇 |
2005年 | 54篇 |
2004年 | 68篇 |
2003年 | 54篇 |
2002年 | 44篇 |
2001年 | 33篇 |
2000年 | 46篇 |
1999年 | 40篇 |
1998年 | 46篇 |
1997年 | 33篇 |
1996年 | 26篇 |
1995年 | 22篇 |
1994年 | 29篇 |
1993年 | 47篇 |
1992年 | 26篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 14篇 |
1987年 | 11篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1454条查询结果,搜索用时 203 毫秒
11.
Ana Luisa Rosa Yutaka Isoda Kazuyuki Uehara Tomokazu Aiki 《Journal of Oceanography》2007,63(4):573-588
Hydrographic data and composite current velocity data (ADCP and GEK) were used to examine the seasonal variations of upper-ocean
flow in the southern sea area of Hokkaido, which includes the “off-Doto” and “Hidaka Bay” areas separated by Cape Erimo. During
the heating season (April–September), the outflow of the Tsugaru Warm Current (TWC) from the Tsugaru Strait first extends
north-eastward, and then one branch of TWC turns to the west along the shelf slope after it approaches the Hidaka Shelf. The
main flow of TWC evolves continuously, extending eastward as far as the area off Cape Erimo. In the late cooling season (January–March),
part of the Oyashio enters Hidaka Bay along the shallower part of the shelf slope through the area off Cape Erimo, replacing
almost all of the TWC water, and hence the TWC devolves. It is suggested that the bottom-controlled barotropic flow of the
Oyashio, which may be caused by the small density difference between the Oyashio and the TWC waters and the southward migration
of main front of TWC, permits the Oyashio water to intrude along the Hidaka shelf slope. 相似文献
12.
13.
讨论了Voronoi图的首最邻近递归收敛特性,即从任一伪最邻近对象开始,递归查找其首最邻近对象,最后必然收敛于最邻近对象.利用该特性,初步实现了移动目标直接邻近对象的连续查询. 相似文献
14.
Seismic hazard of Egypt 总被引:1,自引:0,他引:1
Earthquake hazard parameters such as maximum expected magnitude,M
max, annual activity rate,, andb value of the Gutenberg-Richter relation have been evaluated for two regions of Egypt. The applied maximum likelihood method permits the combination of both historical and instrumental data. The catalogue used covers earthquakes with magnitude 3 from the time interval 320–1987. The uncertainties in magnitude estimates and threshold of completeness were taken into account. The hazard parameter determination is performed for two study areas. The first area, Gulf of Suez, has higher seismicity level than the second, all other active zones in Egypt.b-values of 1.2 ± 0.1 and 1.0 ± 0.1 are obtained for the two areas, respectively. The number of annually expected earthquakes with magnitude 3 is much larger in the Gulf of Suez, 39 ± 2 than in the other areas, 6.1 ± 0.5. The maximum expected magnitude is calculated to be 6.5 ± 0.4 for a time span of 209 years for the Gulf of Suez and 6.1 ± 0.3 for a time span of 1667 years for the remaining active areas in Egypt. Respective periods of 10 and 20 years were reported for earthquakes of magnitude 5.0 for the two subareas. 相似文献
15.
葛焕称 《地震学报(英文版)》1995,8(1):57-63
OnsomeproblemsofseismiccrustalphaseHuan-ChengGE(葛焕称)(SeismologicalBureauofJiangsuProvince,Nanjing210014,China)Abstract:Inthis... 相似文献
16.
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
17.
Flood seasonality and generating conditions in the Tay catchment, Scotland from 1200 to present 总被引:1,自引:0,他引:1
Lindsey J McEwen 《Area》2006,38(1):47-64
The new maximum recorded river flows in Scotland since 1988 have triggered widespread interest in whether floods are becoming more frequent and in the conditions that generate floods of different magnitudes and frequencies. There are questions about the longer-term variability in flood-generating characteristics, and whether there are past analogues for present hydroclimatic variability. The present paper builds on previous work reconstructing a detailed historic flood chronology for the Tay, the largest catchment in Scotland, and its tributaries over the past 800 years, extending the gauged discharge record (1952 onwards). It categorizes flood-generating factors in the Tay catchment and analyses the hydro-meteorological conditions that have generated extreme and moderate floods over a historical period. This work is placed in a broader literature context of historical 'climaxes of storminess', periods of higher storm frequency, flood patterns observed in Scotland and Europe during the Little Ice Age and longer-term rainfall and temperature patterns. The paper concludes that the variability in flood-generating characteristics is highly dependent on the timescale of observation. Inevitably the relative dominance of winter and early spring flooding can vary from year to year and within specific time-periods, but so can the level of augmentation of the flood series with summer and autumn floods to produce notable 'flood years' and flood clusters. The Tay provides a good 'all-Scotland surrogate' for historical flood patterns, reflecting its gathering areas in eastern and western Scotland. The value of a historical approach to the assessment of flood seasonality and generating characteristics is clearly demonstrated. 相似文献
18.
An automated strategy for calculation of phase diagram sections and retrieval of rock properties as a function of physical conditions 总被引:9,自引:0,他引:9
We formulate an algorithm for the calculation of stable phase relations of a system with constrained bulk composition as a function of its environmental variables. The basis of this algorithm is the approximate representation of the free energy composition surfaces of solution phases by inscribed polyhedra. This representation leads to discretization of high variance phase fields into a continuous mesh of smaller polygonal fields within which the composition and physical properties of the phases are uniquely determined. The resulting phase diagram sections are useful for understanding the phase relations of complex metamorphic systems and for applications in which it is necessary to establish the variations in rock properties such as density, seismic velocities and volatile‐content through a metamorphic cycle. The algorithm has been implemented within a computer program that is general with respect to both the choice of variables and the number of components and phases possible in a system, and is independent of the structure of the equations of state used to describe the phases of the system. 相似文献
19.
20.
Two ordination techniques (Romaniszyn diagram, RD, and Canonical correspondence analysis, CCA) were applied to the same data set (fish assemblage composition along two Paraná river tributaries and associated environmental variables), to identify spatial community patterns and further to evaluate the performance of RD. The major patterns in these Brazilian streams were successfully revealed by both methods (i.e. clear separation of both tributaries on the basis of fish assemblage composition and environmental factors), but more complex situations may limit the application of RD in comparison with CCA. 相似文献