全文获取类型
| 收费全文 | 222篇 |
| 免费 | 27篇 |
| 国内免费 | 27篇 |
专业分类
| 测绘学 | 12篇 |
| 大气科学 | 7篇 |
| 地球物理 | 63篇 |
| 地质学 | 26篇 |
| 海洋学 | 85篇 |
| 综合类 | 13篇 |
| 自然地理 | 70篇 |
出版年
| 2024年 | 1篇 |
| 2022年 | 4篇 |
| 2021年 | 2篇 |
| 2020年 | 9篇 |
| 2019年 | 4篇 |
| 2018年 | 2篇 |
| 2017年 | 9篇 |
| 2016年 | 10篇 |
| 2015年 | 16篇 |
| 2014年 | 23篇 |
| 2013年 | 19篇 |
| 2012年 | 21篇 |
| 2011年 | 27篇 |
| 2010年 | 14篇 |
| 2009年 | 18篇 |
| 2008年 | 20篇 |
| 2007年 | 2篇 |
| 2006年 | 13篇 |
| 2005年 | 12篇 |
| 2004年 | 11篇 |
| 2003年 | 6篇 |
| 2002年 | 7篇 |
| 2001年 | 1篇 |
| 1999年 | 3篇 |
| 1998年 | 2篇 |
| 1997年 | 3篇 |
| 1996年 | 4篇 |
| 1995年 | 3篇 |
| 1994年 | 1篇 |
| 1993年 | 3篇 |
| 1992年 | 3篇 |
| 1986年 | 1篇 |
| 1981年 | 1篇 |
| 1980年 | 1篇 |
排序方式： 共有276条查询结果，搜索用时 15 毫秒
81.
We examined the soil microfungal community of the saline Arubotaim Cave, Israel. A total of 68 species from 28 genera were isolated. The most prominent features of the cave mycobiota were: the prevailing number of melanin-containing micromycetes; the abundant presence of the Aspergillus species; a comparatively large share of sexual ascomycetes; and the spatial and temporal variation of the mycobiota composition. Nine species were considered as a characteristic micromycete core for the cave. Many of the micromycetes isolated are distributed worldwide. This confirms the conclusion of many mycologists working in areas with saline and arid soils that there is no specific halophilous mycobiota characteristic for these soils. 相似文献
82.
83.
Cliff R. Hupp 《地球表面变化过程与地形》1986,11(5):545-555
Variation in fluvial landforms and associated vegetation in the headward (upstream) direction has received little study and the controlling factors are not well understood. The relations among channel gradient, basin area, stream order, and the headward extent of fluvial landforms and vegetation was studied in 18 small basins and larger nearby stream reaches in the Massanutten Mountain area, northern Shenandoah Valley, Virginia. Low-order streams were traversed to their basin heads. Notice was made of the point or region of the disappearance of fluvial landforms. Indicator species were used to confirm landform identification. The studied landforms include the channel bar, channel shelf, floodplain, and terraces. Basin geomorphic characteristics were determined from topographic and geologic maps and ground surveys. Results suggest that gradient is the most important factor controlling the development of fluvial landforms. Floodplains have not developed along stream reaches where average channel gradients exceed 0.15. Channel shelves and associated vegetation occur farther upstream than floodplains. 相似文献
84.
Animals respond to climatic change by adapting or by altering distributional patterns. How an animal responds is influenced by where it is positioned within its geographic range; the probability of extirpation is increased near range boundaries. Here, we examine the impact of Holocene climatic fluctuations on a small mammalian herbivore, the bushy-tailed woodrat (Neotoma cinerea), at five locations within south central Idaho and northwestern Utah. Previous work demonstrated that woodrats adapt to temperature shifts by altering body size. We focus here on the relationship between body mass, temperature, and location within the geographic range. Body mass is estimated by measuring fossil fecal pellets, a technique validated in earlier work. Overall, we find the predicted phenotypic response to climate change: animals were larger during cold periods, and smaller during warmer episodes. However, we also identify several time periods when changes in environmental temperature exceeded the adaptive flexibility of N. cinerea. A smaller-bodied species, the desert woodrat (N. lepida) apparently invaded lower elevation sites during the mid-Holocene, despite being behaviorally and physically subordinate to N. cinerea. Analysis of contemporary patterns of body size and thermal tolerances for both woodrat species suggests this was because of the greater heat tolerance of N. lepida. The robust spatial relationship between contemporary body size and ambient temperature is used as a proxy to reconstruct local climate during the Holocene. 相似文献
85.
胶州湾水母类生态研究Ⅰ.种类组成与群落特征 总被引：11，自引：5，他引：6
根据2003年5月-2004年9月胶州湾浮游生物浅水Ⅰ型网中水母的调查资料,分析了胶州湾水母类的种类组成和群落特征.共记录水母34种,其中水螅水母类31种,管母类2种,钵水母类1种,属胶州湾首次报道的有3种;订正并列出了到目前为止的胶州湾水母种属目录,累计共60种,其中水螅水母类52种,管水母3种,钵水母4种,栉水母1种.分析其群落特征结果表明,全年共有9种优势种,各月份水母的优势种类不尽相同,薮枝螅水母和半球美螅水母为春季和夏季的主要优势种,五角水母为秋季的主要优势种,八斑芮氏水母为冬季的主要优势种;水母的总丰度在调查时期内有3个高峰,分别为2003年6、9月份、2004年3月份,3月份作为最高峰丰度高达120.42ind/m^3;总种类数以2003年5、6月份为最多,共14种;1年中,5-11月份的群落多样性指数较12-4月份高;2003年12月到2004年3月各月优势种到下个月的更替基本是完全的（更替率为100%）,其它月份优势种的更替或者部分更替（0〈更替率〈100%）,或者没有更替（更替率为0）.本文中作者对80年代以来水母类的优势种、总种数及总丰度的变化进行了讨论,总种数比90年代有所增加,但未达到1984、1985年的水平;水母的总丰度水平也较80、90年代要高.本文中作者把胶州湾水母生态类群分为近岸低盐生态类型和大洋暖水性生态类型. 相似文献
86.
Xenophyophores are a group of exclusively deep-sea agglutinating rhizarian protozoans, at least some of which are foraminifera. They are an important constituent of the deep-sea megafauna that are sometimes found in sufficient abundance to act as a significant source of habitat structure for meiofaunal and macrofaunal organisms. This study utilised maximum entropy modelling (Maxent) and a high-resolution environmental database to explore the environmental factors controlling the presence of Xenophyophorea and two frequently sampled xenophyophore species that are taxonomically stable: Syringammina fragilissima and Stannophyllum zonarium. These factors were also used to predict the global distribution of each taxon. Areas of high habitat suitability for xenophyophores were highlighted throughout the world׳s oceans, including in a large number of areas yet to be suitably sampled, but the Northeast and Southeast Atlantic Ocean, Gulf of Mexico and Caribbean Sea, the Red Sea and deep-water regions of the Malay Archipelago represented particular hotspots. The two species investigated showed more specific habitat requirements when compared to the model encompassing all xenophyophore records, perhaps in part due to the smaller number and relatively more clustered nature of the presence records available for modelling at present. The environmental variables depth, oxygen parameters, nitrate concentration, carbon-chemistry parameters and temperature were of greatest importance in determining xenophyophore distributions, but, somewhat surprisingly, hydrodynamic parameters were consistently shown to have low importance, possibly due to the paucity of well-resolved global hydrodynamic datasets. The results of this study (and others of a similar type) have the potential to guide further sample collection, environmental policy, and spatial planning of marine protected areas and industrial activities that impact the seafloor, particularly those that overlap with aggregations of these conspicuously large single-celled eukaryotes. 相似文献
87.
88.
Dirk Böhme 《Limnologica》2011,41(2):80-89
Induced by a brine discharge study for a submerse gas storage cavern project, a suitable methodology for rapid impact assessment had to be found. In this paper a simple stochastic, stationary model is described for assessment of intensity and temporal variability of chloride pollution at the regional scale of the rivershed. Chloride concentration is used as a proxy of salinity. It is assumed to be the result of deterministic process (flow-dependent) and stochastic variation (estimated for boundary conditions and tributaries by an additive error term based on PERT distribution). This approach is suited to conduct Monte Carlo simulations in order to calculate long-time means and percentiles of the prospective in-stream chloride concentration (exposure model). The biocoenoses exposed to this pollution has to be evaluated in terms of chloride tolerance. Herefore Maximum Field Distributions (MFD) of relevant species (aquatic macrophytes, macroinvertebrates, fish) were compiled and merged to Species Sensitivity Distributions (SSDs). Critical aspects of MFD data quality are discussed. Chloride model simulations representing different discharge scenarios provide exposure parameters (e.g. 90th percentile) that can be compared with SSD-derived protection levels (e.g. maximum loss of 10% of taxa) to quantify and evaluate possible adverse effects as well as potential recolonisation in case of load removal. Crosslinks to conservation issues are relevant in the selection and position of rare or protected species in the SSD. As an analysis of the German legal framework and technical guidelines revealed lack of guidance and best practices for such assessment and impact evaluation, recent experience highlights serious needs in applied research. 相似文献
89.
90.
The Cook Inlet beluga whale, one of five Alaskan stocks, is genetically distinct and geographically isolated from other populations. Historically, Cook Inlet whales were hunted commercially, for sport, and for subsistence uses. The Marine Mammal Protection Act (MMPA) of 1972 ended commercial and sport hunting; in 1999, subsistence hunting voluntarily ended. In 2008, Cook Inlet beluga whales were listed as endangered under the Endangered Species Act after annual aerial surveys indicated the population was not recovering as expected. A combination of natural and anthropogenic factors may be affecting this population’s recovery. This study documented traditional and local ecological knowledge of Alaska Native subsistence hunters and fishers and commercial fishers through participatory research to explore ecological changes in Cook Inlet over time and to identify potential factors impacting this beluga whale population. Study results identified potential environmental and climate change factors including prey competition, health of beluga and their prey, and the presence of killer whales, the majority of which may indicate an ecosystem regime shift in the Cook Inlet region. Human-related factors included fisheries management and related prey reduction, water contamination, and anthropogenic-related noise. These results corroborate identified threats to beluga whales and also identify potential new areas of scientific investigation and management. As such this study demonstrates the value of incorporating traditional and local ecological knowledge into ongoing science and management. 相似文献