全文获取类型
收费全文 | 1042篇 |
免费 | 202篇 |
国内免费 | 306篇 |
专业分类
测绘学 | 46篇 |
大气科学 | 357篇 |
地球物理 | 257篇 |
地质学 | 516篇 |
海洋学 | 94篇 |
天文学 | 31篇 |
综合类 | 124篇 |
自然地理 | 125篇 |
出版年
2024年 | 9篇 |
2023年 | 16篇 |
2022年 | 59篇 |
2021年 | 55篇 |
2020年 | 64篇 |
2019年 | 78篇 |
2018年 | 68篇 |
2017年 | 76篇 |
2016年 | 85篇 |
2015年 | 59篇 |
2014年 | 81篇 |
2013年 | 48篇 |
2012年 | 62篇 |
2011年 | 63篇 |
2010年 | 54篇 |
2009年 | 59篇 |
2008年 | 35篇 |
2007年 | 52篇 |
2006年 | 45篇 |
2005年 | 49篇 |
2004年 | 35篇 |
2003年 | 26篇 |
2002年 | 27篇 |
2001年 | 21篇 |
2000年 | 30篇 |
1999年 | 68篇 |
1998年 | 43篇 |
1997年 | 31篇 |
1996年 | 31篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1993年 | 20篇 |
1992年 | 18篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有1550条查询结果,搜索用时 0 毫秒
21.
22.
23.
本文讨论了彗星中尘埃粒子的充电机制 ,带电特性和平衡电势的变化规律 ,分析了彗星尘埃的破碎特性和临界半径 ,得出了很有意义的结果 相似文献
24.
本文用1970-1995年的冕洞资料,分析了冕洞的分布规律,磁场极性的演化特征和冕洞的地磁效应,以及它们与太阳黑子周期的演化关系,得到了一些有意义的结论。特别指出赤道冕洞和极区冕洞具有相反的演化规律和不同的特征。 相似文献
25.
Zun-Lei Xu Kai-Kai Duan Zhao-Qiang Shen Shi-Jun Lei Tie-Kuang Dong Fabio Gargano Simone Garrappa Dong-Ya Guo Wei Jiang Xiang Li Yun-Feng Liang Mario Nicola Mazziotta Maria Fernanda Munoz Salinas Meng Su Valerio Vagelli Qiang Yuan Chuan Yue Jing-Jing Zang Ya-Peng Zhang Yun-Long Zhang Stephan Zimmer 《天文和天体物理学研究(英文版)》2018,(3)
The DArk Matter Particle Explorer(DAMPE),also known as Wukong in China,which was launched on 2015 December 17,is a new high energy cosmic ray and γ-ray satellite-borne observatory.One of the main scientific goals of DAMPE is to observe Ge V-Te V high energy γ-rays with accurate energy,angular and time resolution,to indirectly search for dark matter particles and for the study of high energy astrophysics. Due to the comparatively higher fluxes of charged cosmic rays with respect to γ-rays,it is challenging to identify γ-rays with sufficiently high efficiency,minimizing the amount of charged cosmic ray contamination. In this work we present a method to identify γ-rays in DAMPE data based on Monte Carlo simulations,using the powerful electromagnetic/hadronic shower discrimination provided by the calorimeter and the veto detection of charged particles provided by the plastic scintillation detector. Monte Carlo simulations show that after this selection the number of electrons and protons that contaminate the selected γ-ray events at~10 Ge V amounts to less than 1% of the selected sample.Finally,we use flight data to verify the effectiveness of the method by highlighting known γ-ray sources in the sky and by reconstructing preliminary light curves of the Geminga pulsar. 相似文献
26.
Surface soil moisture (SSM) is a critical variable for understanding water and energy flux between the atmosphere and the Earth's surface. An easy to apply algorithm for deriving SSM time series that primarily uses temporal parameters derived from simulated and in situ datasets has recently been reported. This algorithm must be assessed for different biophysical and atmospheric conditions by using actual geostationary satellite images. In this study, two currently available coarse‐scale SSM datasets (microwave and reanalysis product) and aggregated in situ SSM measurements were implemented to calibrate the time‐invariable coefficients of the SSM retrieval algorithm for conditions in which conventional observations are rare. These coefficients were subsequently used to obtain SSM time series directly from Meteosat Second Generation (MSG) images over the study area of a well‐organized soil moisture network named REMEDHUS in Spain. The results show a high degree of consistency between the estimated and actual SSM time series values when using the three SSM dataset‐calibrated time‐invariable coefficients to retrieve SSM, with coefficients of determination (R2) varying from 0.304 to 0.534 and root mean square errors ranging from 0.020 m3/m3 to 0.029 m3/m3. Further evaluation with different land use types results in acceptable debiased root mean square errors between 0.021 m3/m3 and 0.048 m3/m3 when comparing the estimated MSG pixel‐scale SSM with in situ measurements. These results indicate that the investigated method is practical for deriving time‐invariable coefficients when using publicly accessed coarse‐scale SSM datasets, which is beneficial for generating continuous SSM dataset at the MSG pixel scale. 相似文献
27.
武汉市汤逊湖沉积物重金属垂向变化的磁响应特征及环境意义 总被引:3,自引:1,他引:3
对武汉汤逊湖湖泊沉积物T06-1样芯进行了磁性测量、重金属分析和粒度分析,探讨了利用磁参数追踪、指示城市湖泊重金属污染的可行性。结果表明,低矫顽力的亚铁磁矿物主导了沉积物的磁性特征。磁参数,SIRM和ARM与重金属Cr,Zn,Cu和Pb呈现较为一致的垂向变化特征:55cm之下,磁参数值和重金属的含量均较低且稳定;在50~10cm之间,两者基本呈现随深度的减小而增加的趋势,其中在20~10cm区间,出现小范围内波动;而10cm至表层,元素含量和磁参数值随深度减小而急剧增加。选取粘土((4μm)对沉积物中Cr,Zn,Cu和Pb进行粒度校正的结果显示:校正后元素的变化趋向于平稳,但在表层的10cm处Cr,Pb,Zn和Cu的含量仍然较高,表明了表层沉积物中金属元素的含量主要受人类活动的影响。相关分析也表明了磁参数X1,SIRM和ARM与重金属Cr,Pb,Zn和Cu之间均呈显著相关关系(0.62≤R≤0.86),表明磁参数可以用于追踪和指示汤逊湖湖泊沉积物重金属污染。 相似文献
28.
Effect of chemical fertilizers on the fractionation of Cu,Cr and Ni in contaminated soil 总被引:1,自引:0,他引:1
Jie Liu Chang-Qun Duan Yi-Nian Zhu Xue-Hong Zhang Cheng-Xian Wang 《Environmental Geology》2007,52(8):1601-1606
Effect of chemical fertilizers (urea, NH4Cl, Ca(NO3)2, KCl and KH2PO4) on the fractionation of Cu, Cr and Ni was studied by a 4-month incubation experiment. Using sequential extraction procedure,
it was found that the application of fertilizers could change the distribution of Cu, Cr and Ni in the fractions of soil.
Applying urea (CO(NH2)2) significantly decreased the concentrations of Cu, Cr and Ni in water soluble plus exchangeable (WE) fraction, but increased
those in Fe–Mn oxides bound (FM) fraction (p < 0.01). However, application of NH4Cl caused an increase in the WE fraction by 27.7% for Cu, 111.5% for Cr and 20.4% for Ni. The CO(NH2)2 raised the soil pH from 4.51 to 4.96, whereas NH4Cl lowered the pH of soil by 0.44 units. The WE fraction of the three heavy metals was significantly increased, while the
FM fraction was significantly decreased by adding KCl (p < 0.01). Moreover, the supply of KH2PO4 reduced the WE and carbonate bound (CB) fractions of Cu, Cr and Ni in the soil, however, it raised Cu and Ni in the residual
(RS) fraction and Cr in the FM fraction. In addition, the mobility index indicated that KCl and NH4Cl increased the mobility of Cu, Cr and Ni in the soil, whereas urea and KH2PO4 decreased the mobility of the three metals in the soil. These results suggest that applying chemical fertilizers does not
only provide plant nutrients, but may also change the speciation and mobility of heavy metals in the soil. 相似文献
29.
Conditional nonlinear optimal perturbation: Applications to stability,sensitivity, and predictability 总被引:4,自引:0,他引:4
Conditional nonlinear optimal perturbation (CNOP) is a nonlinear generalization of linear singular vector (LSV) and features
the largest nonlinear evolution at prediction time for the initial perturbations in a given constraint. It was proposed initially
for predicting the limitation of predictability of weather or climate. Then CNOP has been applied to the studies of the problems
related to predictability for weather and climate. In this paper, we focus on reviewing the recent advances of CNOP’s applications,
which involves the ones of CNOP in problems of ENSO amplitude asymmetry, block onset, and the sensitivity analysis of ecosystem
and ocean’s circulations, etc. Especially, CNOP has been primarily used to construct the initial perturbation fields of ensemble
forecasting, and to determine the sensitive area of target observation for precipitations. These works extend CNOP’s applications
to investigating the nonlinear dynamical behaviors of atmospheric or oceanic systems, even a coupled system, and studying
the problem of the transition between the equilibrium states. These contributions not only attack the particular physical
problems, but also show the superiority of CNOP to LSV in revealing the effect of nonlinear physical processes. Consequently,
CNOP represents the optimal precursors for a weather or climate event; in predictability studies, CNOP stands for the initial
error that has the largest negative effect on prediction; and in sensitivity analysis, CNOP is the most unstable (sensitive)
mode. In multi-equilibrium state regime, CNOP is the initial perturbation that induces the transition between equilibriums
most probably. Furthermore, CNOP has been used to construct ensemble perturbation fields in ensemble forecast studies and
to identify sensitive area of target observation. CNOP theory has become more and more substantial. It is expected that CNOP
also serves to improve the predictability of the realistic predictions for weather and climate events plays an increasingly
important role in exploring the nonlinear dynamics of atmospheric, oceanic and coupled atmosphere-ocean system.
Supported by National Basic Research Program of China (Grant Nos. 2006CB403606, 2007CB411800), National Natural Science Foundation
of China (Grant Nos. 40830955, 40675030, 40505013), Institute of Atmospheric Physics, Chinese Academy of Sciences (Grant No.
IAP07202), and LASG State Key Laboratory Special Fund 相似文献
30.