全文获取类型
收费全文 | 1455篇 |
免费 | 368篇 |
国内免费 | 578篇 |
专业分类
测绘学 | 203篇 |
大气科学 | 132篇 |
地球物理 | 693篇 |
地质学 | 1030篇 |
海洋学 | 105篇 |
天文学 | 4篇 |
综合类 | 146篇 |
自然地理 | 88篇 |
出版年
2024年 | 4篇 |
2023年 | 15篇 |
2022年 | 36篇 |
2021年 | 61篇 |
2020年 | 84篇 |
2019年 | 96篇 |
2018年 | 75篇 |
2017年 | 77篇 |
2016年 | 103篇 |
2015年 | 93篇 |
2014年 | 100篇 |
2013年 | 113篇 |
2012年 | 116篇 |
2011年 | 121篇 |
2010年 | 106篇 |
2009年 | 122篇 |
2008年 | 130篇 |
2007年 | 137篇 |
2006年 | 101篇 |
2005年 | 100篇 |
2004年 | 94篇 |
2003年 | 79篇 |
2002年 | 74篇 |
2001年 | 49篇 |
2000年 | 54篇 |
1999年 | 42篇 |
1998年 | 37篇 |
1997年 | 39篇 |
1996年 | 33篇 |
1995年 | 29篇 |
1994年 | 19篇 |
1993年 | 14篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有2401条查询结果,搜索用时 15 毫秒
101.
1 Introduction Structural retro?t techniques (Roberts, 2005), such as restrainers, concrete shear keys, steel jackets, CFRPshells, base isolators, or dampers have been widely studied and implemented in actual structures based on the experiences learned from past earthquakes. In the Chi-Chi earthquake (EERI, 2001), the damage to simply-supported PCI girder bridges provided a different view from which to examine the function of a rubber bearing system for simply- supported bridges (NCREE,… 相似文献
102.
为了研究黄土山区地形对煤层群开采地表位移的影响,以榆林某矿为地质原型,利用数值软件模拟地表为近水平、正坡、负坡、凸面和凹面五种地形条件下煤层群开采。结果表明:黄土山区地形的变化,对煤层群开采顶板垂直应力影响不明显,对地表位移影响较大;单向坡开采,斜坡滑移引起的下沉量在坡顶与开采沉陷量形成“叠加”,在坡底形成“抵消”;在组合坡中,煤层群开采地表位移量相差很大,说明在变坡点附近地表位移较为复杂。 相似文献
103.
104.
在全球气候持续变暖背景下,北极地区冻土退化、冰川退缩、海冰减少等导致了一系列的生态环境问题,同时也使得资源勘探开发与国际新航道开通成为可能,北极地区的重要性日益凸显.依据2009—2019年6月期间有关北极研究的408篇ESI高影响论文,对发文量、主要作者、研究机构、国家、研究方向等字段进行分析,从自然科学角度,宏观而... 相似文献
105.
Nitin D. Rai Tor A. Benjaminsen Siddhartha Krishnan C. Madegowda 《Singapore journal of tropical geography》2019,40(1):124-139
Protected areas have had significant impacts on local communities primarily through the physical removal of people. In some instances, people continue to live within protected areas due to the inability of the state to evict them. The restrictions on livelihoods placed on people living inside protected areas lead to in situ displacement. We show how conservation enclosures in the Biligiri Rangaswamy Temple Tiger Reserve have produced a class of people that the state ‘lets die’ by banning customary practices such as fire use, hunting and harvesting of forest produce. Using longitudinal ethnographic, socio‐economic and ecological data, we demonstrate that conservation policy has alienated indigenous forest dwellers from their agricultural and forest‐land. The outcomes of conservation policy include dispossession through increased crop losses, reduced income from agriculture and forest produce, as well as a forest that is dominated by weeds due to fire suppression. The ban on hunting in particular has increased wildlife densities, which has enabled the state to accumulate revenues through the establishment of wildlife tourism facilities. All in all, centralized protected area governance has changed the relationships among people, forest and the state in a way that has produced adverse effects for both livelihoods and the ecosystem. 相似文献
106.
中尺度对流系统(MCS)是形成强对流天气的主要原因,云团在MCS生命周期中的分裂合并问题是临近预报的难点。为解决这一问题,本文提出了FCC方法,该方法使用质心位移和FY-2卫星数据预测多个对流单体的运动轨迹。多个案例分析证明,FCC算法在MCS的各个生命周期均能进行有效的预测,包括初生、成熟和消散阶段。此外,通过列联表方法验证了所提算法的有效性。 相似文献
107.
采用传统ELM算法进行滑坡位移预测时,其网络输出权值由最小二乘估计得出,导致ELM抗差能力较差,从而造成网络训练参数不准确。为此,将M估计与ELM相结合,提出一种基于M估计的RobustELM滑坡变形预测方法。该方法利用加权最小二乘方法来取代最小二乘法计算ELM输出权值,以减少滑坡监测数据中粗差对ELM预测的干扰。分别以链子崖、古树屋滑坡体为例,将Robust-ELM进行了单维、多维粗差的抵御性验证。结果表明,该方法能够有效降低粗差对预测的影响,具有良好的抗差能力。 相似文献
108.
On the basis of the previous studies, the simplest hyperbolic mild-slope equation has been gained and the linear time-dependent numerical model for the water wave propagation has been established combined with different boundary conditions. Through computing the effective surface displacement and transforming into the real transient wave motion, related wave factors will be calculated. Compared with Lin’s model, analysis shows that calculation stability of the present model is enhanced efficiently, because the truncation errors of this model are only contributed by the dissipation terms, but those of Lin’s model are induced by the convection terms, dissipation terms and source terms. The tests show that the present model succeeds the merit in Lin’s model and the computational program is simpler, the computational time is shorter, and the computational stability is enhanced efficiently. The present model has the capability of simulating transient wave motion by correctly predicting at the speed of wave propagation, which is important for the real-time forecast of the arrival time of surface waves generated in the deep sea. The model is validated against analytical solution for wave diffraction and experimental data for combined wave refraction and diffraction over a submerged elliptic shoal on a slope. Good agreements are obtained. The model can be applied to the theory research an d engineering applications about the wave propagation in a biggish area. 相似文献
109.
The proper identification and removal of outliers in the combination of rates of vertical displacements derived from GPS,
tide gauges/satellite altimetry, and GRACE observations is presented. Outlier detection is a necessary pre-screening procedure
in order to ensure reliable estimates of stochastic properties of the observations in the combined least-squares adjustment
(via rescaling of covariance matrices) and to ensure that the final vertical motion model is not corrupted and/or distorted
by erroneous data. Results from this study indicate that typical data snooping methods are inadequate in dealing with these
heterogeneous data sets and their stochastic properties. Using simulated vertical displacement rates, it is demonstrated that
a large variety of outliers (random scattered and adjacent, as well as jointly influential) can be dealt with if an iterative
re-weighting least-squares adjustment is combined with a robust median estimator. Moreover, robust estimators are efficient
in areas weakly constrained by the data, where even high quality observations may appear to be erroneous if their estimates
are largely influenced by outliers. Four combined models for the vertical motion in the region of the Great Lakes are presented.
The computed vertical displacements vary between − 2 mm/year (subsidence) along the southern shores and 3 mm/year (uplift)
along the northern shores. The derived models provide reliable empirical constraints and error bounds for postglacial rebound
models in the region. 相似文献
110.