全文获取类型
收费全文 | 1334篇 |
免费 | 111篇 |
国内免费 | 128篇 |
专业分类
测绘学 | 162篇 |
大气科学 | 135篇 |
地球物理 | 243篇 |
地质学 | 395篇 |
海洋学 | 139篇 |
天文学 | 305篇 |
综合类 | 49篇 |
自然地理 | 145篇 |
出版年
2023年 | 13篇 |
2022年 | 18篇 |
2021年 | 23篇 |
2020年 | 24篇 |
2019年 | 42篇 |
2018年 | 34篇 |
2017年 | 37篇 |
2016年 | 38篇 |
2015年 | 37篇 |
2014年 | 60篇 |
2013年 | 65篇 |
2012年 | 53篇 |
2011年 | 59篇 |
2010年 | 34篇 |
2009年 | 83篇 |
2008年 | 71篇 |
2007年 | 92篇 |
2006年 | 79篇 |
2005年 | 78篇 |
2004年 | 77篇 |
2003年 | 72篇 |
2002年 | 49篇 |
2001年 | 52篇 |
2000年 | 57篇 |
1999年 | 40篇 |
1998年 | 44篇 |
1997年 | 29篇 |
1996年 | 27篇 |
1995年 | 22篇 |
1994年 | 11篇 |
1993年 | 16篇 |
1992年 | 19篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 5篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1972年 | 10篇 |
1971年 | 7篇 |
排序方式: 共有1573条查询结果,搜索用时 156 毫秒
21.
The trend of previous estimates of the world's ultimate recovery of oil suggests a figure of 1650 BBO, of which 1438 BBO have been discovered and 978 BBO remain to be produced. Some large reported reserve figures are questioned. Importance is attached to the mid-point of depletion when rising production tends to give way to decline. The share of the world's supply coming from six Middle East countries is set to continue to rise from its 1986 low of 16% to as much as 50% by 2010, with the likely consequence of higher oil prices and serious political implications. The world is rapidly approaching a turning point when it has to face the consequences of an irreversible decline in oil production. 相似文献
22.
23.
More and more researches show that neither the critical downward acceleration nor the critical slope of water waves is a universal constant. On the contrary, they vary with particular wave conditions. This fact moders the models either for the probability of wave breaking B or for the whitecap coverage W based on these criteria difficult to apply. In this paper and the one which follows we seek to develop models for the prediction of both B and W based on the kinematical criterion. First, several joint probabihstic distribution functions (PDFs) of wave characteristics are derived, based on which the breaking properties B and W are estimated. The estimation is made on the assumption that a wave breaks ff the horizontal velocity of water particles at its crest exceeds the local wave celerity, and whitecapping occurs in regions of fluid where water particles travel faster than the waves. The consequent B and W depend on wave spectral moments of orders 0 to 4.Then the JONSWAP spectrum is used to represent the fetch-limited sea waves in deep water, so as to relate the probahility of wave breaking and the whitecap coverage with wind parameters. To this end, the time-averaging technique proposed by Glazman (1986) is applied to the estimation of the spectral moments involved, and furthermore, the theoretical models are compared with available observations collected from published literature. From the comparison, the averaging time scale is determined. The final models show that the probability of wave breaking as well as the whitecap coverage depends on the dimensionless fetch. The agreement between these models and the database is reasonable. 相似文献
24.
25.
This paper is concerned with the models appropriate for the dynamic assessment of jack-ups, concentrating particularly on the long-term response due to random ocean waves and on work-hardening plasticity models used for spud-can response. A methodology for scaling of short-term statistics, calculated using a Constrained NewWave technique, is shown in a numerical experiment for an example jack-up and central North Sea location. The difference in long-term extreme response statistics due to various footing assumptions is emphasised. Results for two environmental load conditions are described (one excluding and one including wind and current effects) and the role of sea-state severity in the variation of short-term extreme response statistics is also highlighted. 相似文献
26.
立足样品测试数据,利用空间分析、空间插值、地质统计以及景观生态学方法,深入分析了深圳大鹏湾表层沉积物碎屑矿物的空间分布特征,并使用球状模型对相应半变异函数进行理论建模。结果表明,碎屑矿物分布的Hurst分维数为0.28~0.97,空间几何分维数为1.03~1.72;Moran Ⅰ型空间自相关系数-0.15~0.53。在此基础上,以等值线分布所包围范围作为划分尺度,以Shannon-Wiener信息指数作为度量,得到的矿物分布所反映出的信息量或者富集程度指数为0.88~1.85。 相似文献
27.
28.
运用德尔菲调查—灰色统计法确立水库鱼产力综合评价中的指标权重体系 总被引:1,自引:0,他引:1
本文运用德尔菲方法对水库鱼产力综合评价中指标权重的合理分配问题作了专家调查,并采用灰色统计法对调查结果进行归纳处理,从而确立了一个水库鱼产力影响因素诸层次各方面的评价指标权重体系,可供今后的评价工作参考使用。 相似文献
29.
Two commonly used methods of simulating random time series, given a target power spectrum, are discussed. Wave group statistics, such as the mean length of runs of high waves, produced by the different simulation schemes are compared. The target spectra used are obtained from ocean measurements, and cover a wide range of ocean conditions. For a sufficiently large number of spectral components, no significant differences are found in the wave group statistics produced by the two simulation techniques. 相似文献
30.