全文获取类型
收费全文 | 219篇 |
免费 | 33篇 |
国内免费 | 52篇 |
专业分类
测绘学 | 22篇 |
大气科学 | 13篇 |
地球物理 | 25篇 |
地质学 | 65篇 |
海洋学 | 119篇 |
天文学 | 6篇 |
综合类 | 42篇 |
自然地理 | 12篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 12篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2018年 | 6篇 |
2017年 | 11篇 |
2016年 | 10篇 |
2015年 | 11篇 |
2014年 | 11篇 |
2013年 | 12篇 |
2012年 | 12篇 |
2011年 | 12篇 |
2010年 | 7篇 |
2009年 | 13篇 |
2008年 | 10篇 |
2007年 | 13篇 |
2006年 | 15篇 |
2005年 | 12篇 |
2004年 | 13篇 |
2003年 | 12篇 |
2002年 | 12篇 |
2001年 | 22篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1990年 | 4篇 |
1989年 | 1篇 |
排序方式: 共有304条查询结果,搜索用时 9 毫秒
81.
82.
分析了目前国内金刚石制品中金刚石在胎体中的存在形式,金刚石的焊接机机理和改善金刚石表面性质的方法,研究了采用金属添加剂使金刚石表面形成金属碳化物界面层的工艺方法。通过生产工艺试验,实现了在常规制造工艺条件焉,金刚石与胎体金属的焊接,从而提高了制品的性能,生产效率,使用寿命,降低了产品成本。 相似文献
83.
Qigen Lin Pedro Lima Stefan Steger Thomas Glade Tong Jiang Jiahui Zhang Tianxue Liu Ying Wang 《地学前缘(英文版)》2021,12(6):262-276
China is one of the countries where landslides caused the most fatalities in the last decades.The threat that landslide disasters pose to people might even be greater in the future,due to climate change and the increasing urbanization of mountainous areas.A reliable national-scale rainfall induced landslide suscep-tibility model is therefore of great relevance in order to identify regions more and less prone to landslid-ing as well as to develop suitable risk mitigating strategies.However,relying on imperfect landslide data is inevitable when modelling landslide susceptibility for such a large research area.The purpose of this study is to investigate the influence of incomplete landslide data on national scale statistical landslide susceptibility modeling for China.In this context,it is aimed to explore the benefit of mixed effects mod-elling to counterbalance associated bias propagations.Six influencing factors including lithology,slope,soil moisture index,mean annual precipitation,land use and geological environment regions were selected based on an initial exploratory data analysis.Three sets of influencing variables were designed to represent different solutions to deal with spatially incomplete landslide information:Set 1(disregards the presence of incomplete landslide information),Set 2(excludes factors related to the incompleteness of landslide data),Set 3(accounts for factors related to the incompleteness via random effects).The vari-able sets were then introduced in a generalized additive model(GAM:Set 1 and Set 2)and a generalized additive mixed effect model(GAMM:Set 3)to establish three national-scale statistical landslide suscep-tibility models:models 1,2 and 3.The models were evaluated using the area under the receiver operating characteristics curve(AUROC)given by spatially explicit and non-spatial cross-validation.The spatial pre-diction pattern produced by the models were also investigated.The results show that the landslide inven-tory incompleteness had a substantial impact on the outcomes of the statistical landslide susceptibility models.The cross-validation results provided evidence that the three established models performed well to predict model-independent landslide information with median AUROCs ranging from 0.8 to 0.9.However,although Model 1 reached the highest AUROCs within non-spatial cross-validation(median of 0.9),it was not associated with the most plausible representation of landslide susceptibility.The Model 1 modelling results were inconsistent with geomorphological process knowledge and reflected a large extent the underlying data bias.The Model 2 susceptibility maps provided a less biased picture of landslide susceptibility.However,a lower predicted likelihood of landslide occurrence still existed in areas known to be underrepresented in terms of landslide data(e.g.,the Kuenlun Mountains in the northern Tibetan Plateau).The non-linear mixed-effects model(Model 3)reduced the impact of these biases best by introducing bias-describing variables as random effects.Among the three models,Model 3 was selected as the best national-scale susceptibility model for China as it produced the most plausible portray of rainfall induced landslide susceptibility and the highest spatially explicit predictive perfor-mance(median AUROC of spatial cross validation 0.84)compared to the other two models(median AUROCs of 0.81 and 0.79,respectively).We conclude that ignoring landslide inventory-based incomplete-ness can entail misleading modelling results and that the application of non-linear mixed-effect models can reduce the propagation of such biases into the final results for very large areas. 相似文献
84.
2008~2009年,在浙江省海洋水产养殖研究所永兴基地研究了底质、饵料、温度和盐度对平均壳长为32.28±3.98mm的尖刀蛏(Cultelles scalprum)幼贝存活率和生长率的影响.结果表明:尖刀蛏幼贝以软泥底质最佳,实验条件下存活率达到76.7%,其次为沙底质,存活率为71.7%,最差为硬泥底质,存活率仅为60.0%;几种易于大规模培养的微藻中,最适宜的饵料为牟氏角毛藻,实验条件下存活率达到90.0%,生长率达到25.9%,其次为球等鞭金藻和亚心形扁藻;尖刀蛏幼贝存活的适宜温度为10~30℃,最适生长温度为26~30℃;存活的适宜盐度为18~26,最适生长盐度为22.尖刀蛏与其他大多数沿岸贝类一样属于广温广盐性品种,其幼贝更适宜于在盐度较低的环境中生存. 相似文献
85.
海水利用是解决沿海地区淡水资源短缺的重要途径,但其排放的废水可能对海洋生态环境造成不利影响。文中分析了海水的盐度、温度以及携带的化学物质对海洋生态环境的潜在威胁,结果表明:浓海水、温排水排海可能会破坏排放海域的生态环境,影响海洋生物的繁殖、生长和发育,从而导致生物的种类数量、生物量和分布范围等发生变化,需要引起关注和重视。建议海水利用工程建设合理选址、优化设计,鼓励采用循环经济产业模式,延伸海水利用产业链条,以降低对海洋环境的不利影响;并加强排海废水对海洋生态环境影响的研究和监测工作,为改扩建或新建海水利用工程提供环境影响评价依据。 相似文献
86.
测绘行业近几年发生了巨大的变化 ,传统的测量方法大多被数字化手段所代替 ,然而部分测绘仪检部门在处理测距仪器检定数据时有的采用自行编制的功能不甚完备的程序进行计算。针对这种情况 ,作者开发了长度计量仪器测距指标处理系统 (KRA) ,该系统能较为全面地满足光电测量仪器检测数据的后期处理。本文就该系统的开发和运用作了详细阐述。 相似文献
87.
Spatial dependence can obscure relationships between response and explanatory variables because of structuring within the residuals reducing variance and biasing coefficient estimates. Here, we highlight the influence of the spatial component, in the presence of spatial dependence, on abundance trends. This is illustrated using abundance data for a Critically Endangered reef fish, dageraad Chrysoblephus cristiceps, which were obtained from a long-term monitoring programme in the Tsitsikamma National Park marine protected area, South Africa. Correlograms illustrate distinct spatial structuring in the abundance data, and spatial variables were determined as more important than temporal variables when ranked according to predictive power using a random forest analysis. A generalised additive model (GAM) that did not account for spatial dependencies was compared to a generalised additive mixed model (GAMM) that incorporated a spatial residual correlation structure. Results derived from the spatially explicit GAMM differed considerably from the GAM lacking a spatial component, with the latter deemed to produce over-precise and partially biased abundance trends. The study emphasises the importance of space in accurately modelling abundance estimates, particularly temporal trends, and provides an introduction to the minimal statistical requirements necessary to address the violations associated with spatial autocorrelation. 相似文献
88.
Habitat suitability index(HSI) models have been widely used to analyze the relationship between species abundance and environmental factors, and ultimately inform management of marine species. The response of species abundance to each environmental variable is different and habitat requirements may change over life history stages and seasons. Therefore, it is necessary to determine the optimal combination of environmental variables in HSI modelling. In this study, generalized additive models(GAMs) were used to determine which environmental variables to be included in the HSI models. Significant variables were retained and weighted in the HSI model according to their relative contribution(%) to the total deviation explained by the boosted regression tree(BRT). The HSI models were applied to evaluate the habitat suitability of mantis shrimp Oratosquilla oratoria in the Haizhou Bay and adjacent areas in 2011 and 2013–2017. Ontogenetic and seasonal variations in HSI models of mantis shrimp were also examined. Among the four models(non-optimized model, BRT informed HSI model,GAM informed HSI model, and both BRT and GAM informed HSI model), both BRT and GAM informed HSI model showed the best performance. Four environmental variables(bottom temperature, depth, distance offshore and sediment type) were selected in the HSI models for four groups(spring-juvenile, spring-adult, falljuvenile and fall-adult) of mantis shrimp. The distribution of habitat suitability showed similar patterns between juveniles and adults, but obvious seasonal variations were observed. This study suggests that the process of optimizing environmental variables in HSI models improves the performance of HSI models, and this optimization strategy could be extended to other marine organisms to enhance the understanding of the habitat suitability of target species. 相似文献
89.
师郡 《测绘与空间地理信息》2000,23(2):38-39
文章提出的方法近似于平台法,但又有不同,不需要设置专用平台、检测可在室内进行,因此一般的测绘单位都可自己定期对测距仪进行检定,并且由于消除了外界因素的影响,使得检定结果更为可靠。 相似文献
90.