全文获取类型
收费全文 | 4467篇 |
免费 | 570篇 |
国内免费 | 386篇 |
专业分类
测绘学 | 146篇 |
大气科学 | 232篇 |
地球物理 | 906篇 |
地质学 | 1496篇 |
海洋学 | 279篇 |
天文学 | 1866篇 |
综合类 | 139篇 |
自然地理 | 359篇 |
出版年
2024年 | 20篇 |
2023年 | 54篇 |
2022年 | 66篇 |
2021年 | 103篇 |
2020年 | 90篇 |
2019年 | 117篇 |
2018年 | 90篇 |
2017年 | 106篇 |
2016年 | 127篇 |
2015年 | 126篇 |
2014年 | 213篇 |
2013年 | 222篇 |
2012年 | 203篇 |
2011年 | 176篇 |
2010年 | 167篇 |
2009年 | 321篇 |
2008年 | 291篇 |
2007年 | 380篇 |
2006年 | 295篇 |
2005年 | 267篇 |
2004年 | 222篇 |
2003年 | 217篇 |
2002年 | 191篇 |
2001年 | 172篇 |
2000年 | 188篇 |
1999年 | 172篇 |
1998年 | 181篇 |
1997年 | 94篇 |
1996年 | 105篇 |
1995年 | 74篇 |
1994年 | 72篇 |
1993年 | 41篇 |
1992年 | 48篇 |
1991年 | 22篇 |
1990年 | 51篇 |
1989年 | 38篇 |
1988年 | 36篇 |
1987年 | 19篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 8篇 |
1978年 | 6篇 |
1954年 | 3篇 |
排序方式: 共有5423条查询结果,搜索用时 0 毫秒
111.
根据1900~2000年中国大陆、台湾及全球地层记录及前人的研究,论证了地层周期存在的可能性及形成机制。作者认为,是太阳活动、月球运动轨道及各行星运动轨道的周期性变化,通过磁力及万有引力改变地球内部物质的分布,从而引起地球自转速度的周期性变化,最终致使地展出现周期性的活跃期及平静期。 相似文献
112.
对宝鸡市2011年1月~2013年12月连续3 a按月收集的大气降尘样品进行详细系统环境磁学实验分析。结果表明:宝鸡市大气降尘中磁性矿物含量相对较高,主要的磁性矿物为多畴和假单畴的低矫顽力亚铁磁性矿物,并伴有少量的赤铁矿等高矫顽力的硬磁性矿物,磁畴主要由粗颗粒的MD(多畴)和PSD(准单畴)组成。大气降尘的磁性矿物种类和粒径大小随季节并没有明显的变化,但是磁性矿物含量表现出明显的随年际和季节变化的特征。磁性矿物浓度呈现逐年降低的趋势,指示宝鸡市空气污染程度在逐年减轻,这可能与宝鸡市各种污染措施的实施有关,大气环境质量得到很好的控制和稳定。宝鸡市每年从10月份到次年3月份为磁性矿物浓度最大时期,这与冬季采暖期燃煤释放的污染物有关,另外宝鸡市特殊的地形和气象因素对大气粉尘的扩散产生重要的影响。因此,依据污染来源、地形等因素进行合理的交通和产业布局则是宝鸡市大气污染防治的重要措施之一。 相似文献
113.
A. I. Efimov L. N. Samoznaev V. E. Andreev I. V. Chashei M. K. Bird 《Astronomy Letters》2000,26(8):544-552
A statistical analysis of the Faraday-rotation fluctuations (FRFs) of linearly polarized radio signals from the Helios 1 and Helios 2 spacecraft shows that the FRF time power spectra can be of three types. Spectra of the first type are well fitted by a single power law in the range of fluctuation frequencies 1–10 mHz. Spectra of the second type are a superposition of a power law and two quasi-harmonic components with fluctuation frequencies of about v1=4 mHz (fundamental frequency) and v2=8 mHz (second harmonic). Spectra of the third type exhibit only one of the two quasi-harmonic components against the background of a power law. The spectral density of the quasi-harmonic components can be represented by a resonance curve with a fairly broad [Δυ ≈ (0.5–1.3)υ1,2] distribution relative to the v=v1, 2 peak. The intensity of the quasi-harmonic FRF has a radial dependence that roughly matches the radial dependence for the background FRF, while their period at the fundamental frequency is approximately equal to the period of the wellknown 5-min oscillations observed in the lower solar atmosphere. The fluctuations with 5-min periods in FRF records can be explained by the presence in the outer corona of isolated trains of Alfvén waves generated at the base of the chromosphere-corona transition layer and by acoustic waves coming from deeper layers. 相似文献
114.
S. K. Paul 《Atmospheric Research》2000,52(4)
Measurements on drop size were made in cumulus clouds over Pune (inland region) during the summer monsoon seasons. In this paper, the measurements of the cloud drop spectra made in non-raining clouds at different levels and for different thickness have been studied. Also, those on the days with rain and with no rain (the rain being observed within the clouds) have been compared. The average spectra broadened with height. The concentration of drops >50 μm (NL), liquid water content (LWC), mean volume diameter (MVD) and dispersion increased with height. The concentration of drops <20 μm (NS) and total concentration (NT) decreased with height. The spectra were broader, while NS and NT are smaller and the other parameters are greater for thicker clouds as compared to those for thinner. The spectra were broader, while NS and NT are smaller and the other parameters are greater on the days with rain with respect to those on the days with no rain. The distributions were bimodal at higher levels, for thicker clouds and on the days with rain, while they were unimodal at lower levels, for thinner clouds and on the days with no rain. The variations of the cloud drop spectra, preceding rain, at initial stage of rain and following rain are discussed. 相似文献
115.
姜效典 《中国海洋大学学报(自然科学版)》1992,(2)
由磁异常Z_α和重力异常g,利用样条函数的微、积分性质,从泊松方程出发,直接解得磁性体的磁化方向。该方法适用于任意形状磁性体的磁异常。 相似文献
116.
末次冰盛期后黄河三角洲沉积物的磁性特征及其沉积环境 总被引:1,自引:0,他引:1
On the basis of measuring the magnetic parameters of sediment in Core YDZ1, combined with a grain size analysis and Carbon-14 dating, the magnetic properties of sediment and sedimentary environment in the Huanghe(Yellow River) Delta area after the last glacial maximum have been studied. The results show that the ferrimagnetic minerals of a pseudo single domain and multi domain particles dominate the magnetic properties of sediment in Core YDZ1. The imperfect anti ferrimagnetic minerals have more contribution on sediment in a depth of 24.0–22.1 m, and more stable-single domain and pseudo single domain particles exist. The susceptibility of anhysteretic remanent magnetization and the ratio of the susceptibility of anhysteretic remanent magnetization to saturation isothermal remanent magnetization show a decrease trend below depth of 24 m, a marked increase trend in a depth of 24.0–13.5 m, and a rapid decrease at depth of 13.5 m, then a fluctuation trend upward. The above two magnetic parameters and the ratio of the susceptibility of anhysteretic remanent magnetization to the mass susceptibility can be regarded as the proxy indicators for the content of clay(4 μm)and the fine-grained size(32 μm). The sedimentary environment after the last glacial maximum in the Huanghe Delta area has experienced the fluvial facies, the tidal flat facies, the neritic facies, the pro delta facies, the delta front facies and the floodplain facies. Thickness of the Holocene transgression layer is 10.5 m and the depth of substrate is about 24 m according to the YDZ1 core. The sedimentary dynamic has a variation trend with strongweak-strong, which has been proved by the Flemming triangular schema. 相似文献
117.
118.
本文给出了基于L0模求解该问题的非凸模型,借助于稀疏正则化方法来克服问题的不适定性。该模型利用紧小波框架对信号进行稀疏逼近,并利用L0模度量稀疏性。提出了求解该模型的投影迭代硬阈值算法,并证明了算法的全局收敛性。该算法每一步都有闭式解,计算过程简洁高效。数值实验表明,方法在重建信号的视觉质量和量化指标方面均优于所对比的pFISTA方法。 相似文献
119.
120.