全文获取类型
收费全文 | 459篇 |
免费 | 117篇 |
国内免费 | 105篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 69篇 |
地球物理 | 177篇 |
地质学 | 264篇 |
海洋学 | 75篇 |
天文学 | 1篇 |
综合类 | 40篇 |
自然地理 | 39篇 |
出版年
2024年 | 3篇 |
2023年 | 6篇 |
2022年 | 15篇 |
2021年 | 17篇 |
2020年 | 24篇 |
2019年 | 31篇 |
2018年 | 20篇 |
2017年 | 21篇 |
2016年 | 23篇 |
2015年 | 19篇 |
2014年 | 33篇 |
2013年 | 32篇 |
2012年 | 41篇 |
2011年 | 36篇 |
2010年 | 35篇 |
2009年 | 40篇 |
2008年 | 29篇 |
2007年 | 27篇 |
2006年 | 27篇 |
2005年 | 37篇 |
2004年 | 20篇 |
2003年 | 29篇 |
2002年 | 17篇 |
2001年 | 17篇 |
2000年 | 11篇 |
1999年 | 15篇 |
1998年 | 16篇 |
1997年 | 11篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1988年 | 1篇 |
排序方式: 共有681条查询结果,搜索用时 15 毫秒
651.
坡缕石/聚合物纳米复合材料的研究进展 总被引:14,自引:1,他引:13
坡缕石是一种层链状硅酸盐矿物。具有独特的纳米棒晶结构。是一种很有潜力的一维纳米增强材料。综述了坡缕石/聚合物纳米复合材料的研究进展,所涉及的聚合物包括丁苯橡胶、丁腈橡胶、聚乙烯、聚氯乙烯、聚苯乙烯、聚丙烯、环氧树脂、双马来酰亚胺树脂(BMI)和聚酰胺等。制备方法包括机械共混法、乳液共混共凝法、溶液共混法、熔融复合法和原位聚合法。研究表明。坡缕石纳米棒晶的分散在制备纳米复合材料的过程中非常重要,而超声波分散是目前最经济有效的方法。还简要论述了对甘肃某地坡缕石提纯并应用于丁腈橡胶制备纳米复合材料的研究。最后展望了坡缕石/聚合物纳米复合材料的应用前景。并对以后需要深入研究的方向进行了分析。 相似文献
652.
653.
654.
During extended winter(November–April),43% of the intraseasonal rainfall variability in China is explained by three spatial patterns of temporally coherent rainfall.These patterns were identified with empirical orthogonal teleconnection(EOT) analysis of observed 1982–2007 pentad rainfall anomalies and connected to midlatitude disturbances.However,examination of individual strong EOT events shows that there is substantial inter-event variability in their dynamical evolution,which implies that precursor patterns found in regressions cannot serve as useful predictors.To understand the physical nature and origins of the extratropical precursors,the EOT technique is applied to six simulations of the Met Office Unified Model at horizontal resolutions of 200–40 km,with and without air–sea coupling.All simulations reproduce the observed precursor patterns in regressions,indicating robust underlying dynamical processes.Further investigation into the dynamics associated with observed patterns shows that Rossby wave dynamics can explain the large inter-event variability.The results suggest that the apparently slowly evolving or quasi-stationary waves in regression analysis are a statistical amalgamation of more rapidly propagating waves with a variety of origins and properties. 相似文献
655.
《青岛海洋大学学报(英文版)》2014,(2):236-242
Molecularly imprinted polymers (MIPs) were prepared by the bulk polymerization using crystal violet as the template molecule, and the methacrylic acid and ethylene glycol dimetheacrylate as functional monomer and cross-linker, respectively. Sys- tematic investigations of synthetic conditions were conducted. The surface morphology and recognition mechanism of the obtained polymers were studied using scanning electron microscope and spectrophotometric analysis. MIPs showed high atTmity to template molecule and were successfully applied as special solid-phase extraction sorbent for selective extraction of crystal violet from natural seawater. An off-line molecularly imprinted solid-phase extraction (MISPE) method followed by high-performance liquid chroma- tography with diodearray detection for the analysis of crystal violet was also established. MISPE columns have good recoveries for crystal violet standard solutions and good linearity was obtained over the concentration range of 0-200 ~tg L-1 (R2 〉 0.99). Finally, two natural seawater samples were investigated. The recoveries of spiked seawater on the MISPE columns were from 44.47% to 62.34%, the relative standard deviation (n=3) being in the range of 2.89%-5.96%. 相似文献
656.
F.M. Boyce 《大气与海洋》2013,51(3):195-206
Abstract The paper discusses the possibility of extracting electrical energy from the thermal energy stored in stratified lakes. Three situations are examined, an open lake or pond acting as a solar collector, a combination of waste heat and solar energy, and selective withdrawal of warm and cold streams from a stratified hydroelectric reservoir. Approximate calculations of the energy returns are made for typical conditions. The returns are limited by environmental factors as well as a short operating season. By using the deep stratified Great Lakes (Superior, Huron, Michigan and Ontario) as solar collectors, a few thousand megawatts of electrical power could be produced in the Great Lakes Basin during the summer months. This power could be produced on a year‐round basis by a single large nuclear generating station. 相似文献
657.
为了研究刘桥一矿含水层水化学特征,在分析矿区水文地质条件的基础上,对各个含水层投产前后水质动态变化进行详细研究,并将各含水层中的矿化度、总硬度以及阴阳离子所占的比例进行对比。结果表明,随着出水时间的增加,出水点水样中Na++K+和SO42-平均含量在逐渐减少,Mg2+有所增加,Ca2+和HCO3-变化不大;总硬度和总矿化度表现出不同程度的降低。最后,从突水点水样分析结果和附近的太灰、八含长观孔的水位变化情况,推测出太灰水和八含水联系紧密,也是6煤层底板的主要突水水源。 相似文献
658.
为掌握黄土高原土壤干燥化程度的空间分布特征,定量评价雨季前、后土壤干燥化程度,于2013年在黄土高原南北方向布设一条样带(N=86),获取雨季前、后0~5 m剖面土壤含水量。采用地统计学方法分析了土壤干燥化指数的空间分布规律及变异特征。结果表明:在黄土高原地区,土壤干燥化程度存在明显的纬度地带性,且雨季前土壤干燥化指数的空间变异程度高于雨季后;经过雨季降水的补给,土壤干层在一定程度上得到修复,且中部地区的修复效果明显优于南部及北部地区;土壤干燥化指数剖面分布特征在雨季前、后的差异主要表现在浅层0~2.3 m土层,这主要归因于降水对浅层土壤水分的补给。 相似文献
659.
本文以辽河油田某断块油藏为研究对象,基于室内实验,结合正交设计试验,以提高原油采收率程度为评价指标,开展了稠油油藏注超临界CO_2驱影响因素研究,并分析了不同变量对注超临界CO_2驱油效率的影响权重。结果表明:CO_2驱油效率随渗透率、气体注入量、油藏温度的增加而增加,随原油粘度的增加而降低,其中:渗透率对原油采收率的影响程度最大,其次是原油粘度、气体注入量、油藏温度、压力。最后,本文总结并分析了我国注CO_2驱油提高原油采收率技术存在的主要问题,并提出拟解决措施。 相似文献
660.
Dogan Cetin Tayfun Sengul Shobha K. Bhatia Mahmoud M. Khachan 《Marine Georesources & Geotechnology》2017,35(5):678-687
Coal ash producing is an increasing trend because of its high energy demand worldwide. For transportation, disposal, and reuse of the industrial waste materials, geotextile tube’s dewatering technology has been widely used over the last three decades, which helps to decrease the volume of the dewatered slurry. In this study, effect of usage of polymer and fibers on dewatering characteristic of fly ash slurries was investigated. For the experimental investigation, an anionic polymer and short nylon fibers were used. As a new concept, centrifuge test is introduced as an alternative for the widely used pressure filtration test (PFT). Centrifuge test was used to evaluate final solid content of the retained sediments and change in slurry volume of fly ash. Tests were conducted on unconditioned and anionic polyacrylamide and/or fiber conditioned fly ash slurries. Centrifuge test results were compared with PFT results with respect to final solid content. It was found that fiber and/or polymer usage has remarkable effect on the dewatering rate of fly ash slurry. It was also found that final solid content of fly ash slurries was decreased by inclusion of fibers and polymer, which indicates that fiber and/or polymer usage can create more permeable soil body. 相似文献