全文获取类型
收费全文 | 2638篇 |
免费 | 336篇 |
国内免费 | 271篇 |
专业分类
测绘学 | 961篇 |
大气科学 | 230篇 |
地球物理 | 509篇 |
地质学 | 724篇 |
海洋学 | 230篇 |
天文学 | 47篇 |
综合类 | 213篇 |
自然地理 | 331篇 |
出版年
2024年 | 3篇 |
2023年 | 25篇 |
2022年 | 71篇 |
2021年 | 70篇 |
2020年 | 93篇 |
2019年 | 76篇 |
2018年 | 64篇 |
2017年 | 103篇 |
2016年 | 112篇 |
2015年 | 135篇 |
2014年 | 134篇 |
2013年 | 169篇 |
2012年 | 191篇 |
2011年 | 178篇 |
2010年 | 157篇 |
2009年 | 152篇 |
2008年 | 181篇 |
2007年 | 155篇 |
2006年 | 146篇 |
2005年 | 121篇 |
2004年 | 126篇 |
2003年 | 102篇 |
2002年 | 82篇 |
2001年 | 81篇 |
2000年 | 84篇 |
1999年 | 74篇 |
1998年 | 85篇 |
1997年 | 43篇 |
1996年 | 46篇 |
1995年 | 32篇 |
1994年 | 22篇 |
1993年 | 38篇 |
1992年 | 28篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3245条查询结果,搜索用时 31 毫秒
991.
小波分析在井水位的气压和潮汐改正中的应用 总被引:2,自引:0,他引:2
本文将小波分析方法应用于地下水位观测资料的气压和潮汐改正中。该方法利用小波将气压观测和理论重力固体潮资料分解为不同频段的时间序列,用最小二乘法求出气压和固体潮不同频段的响应系数,以消除气压和固体潮对水位的影响。用该方法计算的结果与一般线形回归分析方法得到的结果进行对比,发现该方法能更有效地分析和消除气压和固体潮对地下水位的影响。小波分解在井水位气压、潮汐改正中的应用以波动理论和振动理论为基础,它不仅考虑了观测资料的频率域特性,而且还能直接在时间域内计算出不同频率范围的气压系数和潮汐系数,具有明确的物理意义。 相似文献
992.
昆明人民胜利堂为钢筋混凝土、砖砌体及木结构混合而成的结构型式,其抗震改造设计较为复杂。简述了该结构抗震改造设计施工中的若干问题,以及解决这些问题所采取的相应措施。 相似文献
993.
The chemical oxygen demand (COD) parameter of a wastewater treatment plant is predicted based on wavelet decomposition, entropy, and neural networks (NN) for rapid COD analysis. This paper also describes the usage of wavelet and NNs for parameter prediction. Data from a wastewater treatment plant in Malatya, Turkey, were used. This dataset consists of daily values of influents and effluents for a year. To reduce the dimension of input parameters and to decrease the NN training time, wavelet decomposition and entropy were used. Test results were presented graphically. The test results of the trained model were found to be closer to the measured COD values. 相似文献
994.
995.
The objective of this study was to describe the proton promoted disproportion of synthetic manganite (γ-MnOOH) and to characterise
the resulting phase transformations. The solution and remaining solid phase after disproportionation was analysed by techniques
including atomic absorbance spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy
(SEM). In suspensions with pH between 5 and 7, −log[H+] was monitored for 17 months and equilibrium constants were determined at 9, 12 and 17 months of reaction time for the following
reaction (25 °C, 0.1 M (Na)NO3):
The formed MnO2 ages with time and the equilibrium constant for a metastable phase (ramsdellite or nsutite) as well as the most stable phase,
pyrolusite (β-MnO2), was determined. Furthermore, combined pH and pe (Eh) measurements were performed to study the equilibrium;
Real-time AFM measurements of the dissolution showed shrinkage of the length of the manganite needles with time (2 hours).
After 1 week SEM images showed that this decreased length also was followed by a reduced thickness of the manganite needles.
From the SEM images the morphology of the formed Mn(IV) oxides was studied. At pH 2.6, pyrolusite (β-MnO2) and MnCl2 were found in the XRD patterns. Throughout the pH range there were indications of ramsdellite (MnO1.97) in the XRD patterns, which coincided with the existence of a fraction of needle shaped crystals with smaller dimensions
(compared to manganite) in the SEM images. These observations together with the long term dissolution experiments suggest
that the dissolution of manganite initially forms a ramsdellite or nsutite phase that over time rearranges to form pyrolusite. 相似文献
996.
Driss Khattach Hamid Mraoui Driss Sbibih Touria Chennouf 《Comptes Rendus Geoscience》2006,338(8):521-526
The multiscale wavelet analysis has been applied to the gravity data from northeastern Morocco to map the major geological contacts, such us faults. Hence, the faults affecting the survey area were outlined with their importance level and dip direction. Seismic data confirm these results and testify the efficiency of this method, particularly in studying structure of plains. The structural map established is a very useful document in the planning of natural resources investigations (i.e. water, mines) to be undertaken in the area of study. To cite this article: D. Khattach et al., C. R. Geoscience 338 (2006). 相似文献
997.
E.?Terradellas M.?R.?SolerEmail author E.?Ferreres M.?Bravo 《Boundary-Layer Meteorology》2005,114(3):489-518
A wavelet method is used to estimate kinetic energy and fluxes from data collected under stable conditions during the CASES-99 field campaign. Results in the high frequency range are compared with those obtained by the traditional method used to estimate turbulent moments, which is based on the Reynolds decomposition of variables into a mean and a turbulent part. The fact that the wavelet transform performs much better as a filter than the averaging process accounts for most of the disagreements between results. Since the wavelet method can be applied at very different spectral ranges, it is also used to analyse two different coherent structures: a density current and a train of internal gravity waves. The strong burst of turbulence related to the density current reflects the complexity of the first event. The wavelet method discriminates the different scales of motion, which are present in the perturbation, and is therefore an ideal tool for assessing the interactions between them. A method based on the phase difference between wavelet-transformed time series is then applied to the analysis of the horizontal and vertical structure of the gravity waves, and a three-dimensional image of the oscillations is provided. 相似文献
998.
999.
1000.