全文获取类型
收费全文 | 5253篇 |
免费 | 542篇 |
国内免费 | 157篇 |
专业分类
测绘学 | 237篇 |
大气科学 | 594篇 |
地球物理 | 1939篇 |
地质学 | 2120篇 |
海洋学 | 270篇 |
天文学 | 337篇 |
综合类 | 188篇 |
自然地理 | 267篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 23篇 |
2020年 | 5篇 |
2019年 | 14篇 |
2018年 | 433篇 |
2017年 | 374篇 |
2016年 | 249篇 |
2015年 | 151篇 |
2014年 | 118篇 |
2013年 | 115篇 |
2012年 | 648篇 |
2011年 | 426篇 |
2010年 | 118篇 |
2009年 | 136篇 |
2008年 | 118篇 |
2007年 | 114篇 |
2006年 | 129篇 |
2005年 | 832篇 |
2004年 | 872篇 |
2003年 | 654篇 |
2002年 | 175篇 |
2001年 | 69篇 |
2000年 | 44篇 |
1999年 | 16篇 |
1998年 | 6篇 |
1997年 | 17篇 |
1996年 | 11篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1987年 | 4篇 |
1985年 | 2篇 |
1980年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1965年 | 3篇 |
1963年 | 2篇 |
1961年 | 2篇 |
1959年 | 2篇 |
1955年 | 2篇 |
1954年 | 2篇 |
1951年 | 2篇 |
1948年 | 2篇 |
1925年 | 1篇 |
排序方式: 共有5952条查询结果,搜索用时 15 毫秒
971.
Shu?WuEmail author Zhengyu?Liu Rong?Zhang Thomas?L.?Delworth 《Journal of Oceanography》2011,67(1):27-35
We studied the relationship between the dominant patterns of sea surface temperature (SST) variability in the North Pacific
and the North Atlantic. The patterns are known as the Pacific Decadal Oscillation (PDO) and the Atlantic Multi-decadal Oscillation
(AMO). In the analysis we used two different observational data sets for SST. Due to the high degree of serial correlation
in the PDO and AMO time series, various tests were carried out to assess the significance of the correlations. The results
demonstrated that the correlations are significant when the PDO leads the AMO by 1 year and when the AMO leads the PDO by
11–12 years. The possible physical processes involved are discussed, along with their potential implication for decadal prediction. 相似文献
972.
In this paper, we examined the detailed morphology of two strains of Prorocentrum isolated from the coastal waters of Zhejiang (Wenling area), China, and Masan Bay of Korea. A taxonomic comparison was made among strains on the basis of morphological and molecular data. The cellular dimensions of the Chinese Wenling strain (LAMB090508) and Korean strain (PDKS0206) were similar and the cells of both strains were of asymmetric and elongated shape. The posterior end of most cells was rounded. Megacytic zones of aged cells were broader with dense tiny knobs. The roundish nucleus was located in the posterior part of the cell. A few irregular shaped chloroplasts were distributed within the cell. The nucleotide similarity of the two strains, determined from the 5.8S rDNA-ITS sequences, was 99.83%. The comparative results of morphology and molecular analysis suggest that both strains isolated from China and Korea were the identical species, Prorocentrum donghaiense Lu. 相似文献
973.
We studied the occurrence of missing rings (MR) around and along the stems of three Pinus halepensis and three Pinus pinea trees growing in a semiarid Mediterranean site in SE Spain. Tree-ring analyses were performed along 8 radii on stem discs taken at 1 m distances from the base to the top of the trees. The tree rings analysed showed that 19% were missing in P. halepensis and 10% in P. pinea. MR were recorded in 61% of P. halepensis and 24% of P. pinea in the years analysed. Dry conditions from January to May and high late winter to spring temperatures seem to be the main climatic elements promoting MR in both species. In our research into P. halepensis, the frequency of MR gradually decreased from the bottom upward, but no such pattern was observed in P. pinea. Most tree rings were missing only locally (LMR), indicating that wood formation occurred every year in at least some part of a tree, and the tree rings were often discontinuous around and along the stem. Since the frequency of LMR greatly varies around and along the stem, our results suggest that serial sectioning along the stem provides more information on wood formation and responses of trees to environment than studying the samples at breast height only. The disadvantage of the technique is that, as in our study case, research is based on a limited sample size, since it requires destructive sampling with tree felling, which is not usually possible or desirable on highly vulnerable semiarid forest ecosystems. 相似文献
974.
A diatom dataset and diatom-salinity inference model for southeast Australian estuaries and coastal lakes 总被引:1,自引:1,他引:0
To quantify the relationship between diatom species assemblages and the water chemistry of southeast Australian estuaries
and coastal lakes, a new dataset of 81 modern diatom samples and water chemistry data was created. Three hundred and ninety-nine
species from 53 genera were identified in 36 samples from 32 coastal water bodies in eastern Tasmania and 45 samples from
13 coastal water bodies in southern Victoria. Multivariate statistical analyses revealed that the sampling sites were primarily
distributed along salinity and nutrient gradients, and that salinity, nitrate + nitrite, phosphate and turbidity explained
independent portions of variance in the diatom data. Species salinity optima and tolerances were determined and a diatom-salinity
inference model (WAinv r
2 = 0.72, r
2jack = 0.58, RMSEP = 0.09 log ppt) was developed. This new information on diatom species’ salinity preferences provides a
useful tool for quantitatively reconstructing salinity changes over time from diatom microfossils preserved in the sediments
of a range of estuaries and coastal lakes in southeast Australia. This is valuable for studies investigating long-term human
impacts and climate change in the region. 相似文献
975.
Ryan?D.?MillsEmail author Allen?F.?Glazner 《Contributions to Mineralogy and Petrology》2013,166(1):97-111
We conducted experiments on an alkali basalt at 1-atmosphere in order to investigate the effects of temperature cycling on crystal coarsening. Experiments at 1,150 °C near the Ni–NiO buffer indicate that coarsening of plagioclase and olivine crystals is greatly accentuated by temperature cycling. For a given experiment duration, crystal number density decreases with temperature cycle amplitude and average crystal size increases with increasing amplitude. We observed little correlation between cycle period and crystal number density or average crystal size. We suggest that dissolution and size-proportional crystal growth during repeated heating and cooling decrease crystal number density and increase average crystal size. These experiments indicate that the texture of silicate minerals can be modified by temperature cycling and that phenocrysts may develop quicker in silicate magmas when the magma temperature is cycled. 相似文献
976.
Effect of the addition of granitic powder to an acidic soil from Galicia (NW Spain) in comparison with lime 总被引:1,自引:1,他引:0
Benita?Silva Remigio?ParadeloEmail author Nuria?Vázquez Eduardo?García-Rodeja María?Teresa?Barral 《Environmental Earth Sciences》2013,69(2):429-441
The impact of diffuse pollution, agricultural land use and climate change on the long-term response of subsurface–surface water quality is not well understood, but is a prerequisite for evaluation of water management options. The goal of this study is to model geochemical evolution of water chemistry from the infiltration through soil into the unsaturated zone, transport through bedrocks and granular aquifers to a river in order to identify zones of steep concentration gradients and high dynamics under transient flow conditions. A numerical model was constructed comprising a 2-D 1,500 m × 150 m vertical cross-section of typical sedimentary rock formations, a glacio-fluvial quaternary gravel aquifer in the valley and soil layers. The model coupled saturated/un-saturated flow and reactive transport under steady state and transient conditions. Geochemical interactions, include intra-aqueous kinetic reactions of oxygen with dissolved organic matter, as well as kinetics of carbonate dissolution/precipitation. This model section was chosen to provide insight in to the principal processes and time scales affecting water chemistry along different flow paths. The numerical simulator MIN3P was used, a finite volume program for variably saturated subsurface flow and multi-component reactive transport. The results show that subsurface water residence times range from approximately 2 to 2,000 years. Different zones are to be expected with respect to the development of mineral equilibria; namely, purely atmospherically influenced, as well as open and closed system carbonate dissolution. Short-term responses to daily averaged changes in precipitation, however, are only visible to some extent in the shallower and near-river parts of flow system and solute loads. This can most likely be explained by directional changes in flow paths, indicating that equilibrium geochemical condition predominate at the hillslope scale, i.e. water quality depends on transport pathways rather than on kinetic effects. The extent of reducing conditions is controlled by the presence of organic-rich layers (i.e. peat deposits), the dissolution kinetics of aquifer organic matter and the subsequent mixing with oxygenated water by hydrodynamic dispersion. 相似文献
977.
Discovery of Paleogene marine stratum along the southern side of Yarlung-Zangbo suture zone and its implications in tectonics 总被引:5,自引:0,他引:5
Hyesu Yun 《中国科学D辑(英文版)》2005,48(5):647-661
The final withering of Tibetan Tethys predicated the absolute retreat of seawater from Tibet, one of the most direct and valid marks of which is the age of the latest marine deposits in the area. Therefore, the dis-cussion on the closing age of Tibetan Tethys actuallyis the dating of the latest marine sediment in the area. In the study of late evolution of Tethys, the study on the latest marine sediments in southern Tibet is the major object of geologists. In this field, a lot of works have… 相似文献
978.
城镇土地集约利用研究 总被引:47,自引:1,他引:47
小城镇发展战略地位的确立,加速了城镇化进程,城镇化过程中的用地粗放与人均耕地锐减之间的矛盾,是提出城镇土地集约利用的依据。从城镇土地集约利用内涵界定入手,分析了城镇土地集约利用的必要性,探讨了城镇土地集约利用定量评价的原则,从城镇存量土地产出率、土地利用强度、土地投入强度和土地可持续度4个方面建立了城镇土地集约利用评价指标总系统。指出城镇发展与土地集约利用的途径。 相似文献
979.
980.