首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   142篇
  免费   5篇
  国内免费   27篇
  2023年   5篇
  2022年   6篇
  2021年   2篇
  2020年   5篇
  2019年   3篇
  2018年   5篇
  2017年   4篇
  2016年   11篇
  2015年   5篇
  2014年   10篇
  2013年   7篇
  2012年   7篇
  2011年   12篇
  2010年   3篇
  2009年   8篇
  2008年   7篇
  2007年   10篇
  2006年   15篇
  2005年   2篇
  2004年   1篇
  2003年   6篇
  2002年   4篇
  2001年   4篇
  2000年   3篇
  1999年   2篇
  1997年   5篇
  1996年   1篇
  1995年   1篇
  1994年   4篇
  1993年   2篇
  1991年   1篇
  1985年   2篇
  1984年   2篇
  1982年   2篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1976年   1篇
  1963年   2篇
排序方式: 共有174条查询结果,搜索用时 15 毫秒
41.
On the north coast of Papua New Guinea, the construction of the Pacific Marine Industrial Zone is catalysing movements of people, capital and things, as well as of the ideas and imaginings which accompany and make them meaningful. Drawn from literary and postcolonial studies, the concept of worlding offers a narrative framework through which to think through these movements and the ways in which they complicate prevailing narratives of globalisation. At the Pacific Marine Industrial Zone, the neoliberal worldings that inform the project do not simply catalyse movements, but also act to impose barriers to movement. Local communities assert connection to place, but also generate new circuits of mobility, and rearticulate ideas of kastom (custom) that have movement at their core. An emphasis on worlding—drawing particularly on Heidegger's distinction between world and earth—allows for a more complex reflection on the relationship between mobility and emplacement, one that more fully illuminates the complexity of the relationship itself, and the way it is experienced at the PMIZ site.  相似文献   
42.
周氏似日本睡鼠Gliruloides zhoui是发现于新疆准噶尔盆地北缘晚渐新世铁尔斯哈巴合哺乳动物组合I带的一个化石新属种。新属似日本睡鼠Gliruloides的属征为:中等大小;颊齿咀嚼面凹;上、下颊齿通常具9条主要横脊,有时具次级附脊;上颊齿的前边附脊和后边附脊以及下颊齿的下前边附脊和下后边附脊都很发育,几乎占据了其所在齿谷的整个长度。上颊齿的横脊唇端趋于游离。M1和M2具V形或窄U形三角座,内脊不完整或近于完整,前中央脊不与内脊相连。下颊齿的下内脊通常不连续;下臼齿的下前边脊在唇端稍向后弯,但不与原尖相连。p4,m1-m3,P4,M1-M3的齿根数分别为2,2,3,3。新属与Glirulus在形态上相似,但Glirulus的上颊齿的三角座均为宽U型,具有完整的内脊,前中央脊通常与内脊相交,横脊唇端通常不游离。新属与Vasseuromys属的最主要形态差异在于上颊齿具有很发育的前边附脊和后边附脊,而后者上颊齿的前边附脊和后边附脊通常缺失或很不发育。归入该属的种还有土耳其早中新世的Vasseuromys duplex和Vasseuromys aff.V.duplex。土耳其Thrace早渐新世的Glis guerbuezi很可能是Gliruloides和Glirulus的共同祖先类型。Gliruloides可能生活于温湿的生态环境。  相似文献   
43.
44.
Jurassic studies in the Internal Zones of the Betic Cordillera are scarce since this zone is composed mainly of pre-Jurassic metamorphic rocks. Only the “Dorsal” and the Malaguide domains include fossiliferous Jurassic successions, as in Sierra Espuña (SE Spain), which is one of the bigger and well-exposed Jurassic outcrops of the Internal Zones. Collected Ammonite assemblages update and improve the precision of previous biostratigraphic data by the recognition of: the Domerian (= Upper Pliensbachian, in the Mediterranean Domain) Lavinianum (Cornacaldense Subzone), Algovianum (Ragazzoni, Bertrandi, Accuratum and Levidorsatum Subzones) and Emaciatum (Solare and Elisa Subzones) Zones; the Lower Toarcian Polymorphum and Serpentinum Zones; the Middle Toarcian, Bifrons and Gradata Zone; the Upper Toarcian Reynesi Zone; the Lower/Upper Bajocian, the Lower Callovian Bullatus and Gracilis Zones; the Middle/Upper Oxfordian Transversarium, Bifurcatus, Bimammatum and Planula Zones; and the Lower and Upper Kimmeridgian Platynota, Strombecki, Divisum and Beckeri Zones.The paleoenvironmental evolution of the Malaguide Jurassic at Sierra Espuña shows similarities with other Mediterranean Tethyan paleomargins. The biostratigraphic precision along with the litho- and biofacies analyses has enabled the interpretation that the Malaguide paleomargin evolved as a passive margin, developing shallow carbonate platforms, until the Domerian (Lavinianum Zone). Then, the platform broke up (Domerian, Lavinianum Zone-Upper Toarcian, Reynesi Zone) with the beginning of the rifting stage, beginning the development of horst-graben systems and the coeval drowning of the area. This stage ended in the upper Lower Callovian (Gracilis Zone) to the Middle Oxfordian (Transversarium Zone) interval, starting the drifting stage, which accentuated the horst-graben systems, leading to the deposition of condensed nodular limestones in the raised sea bottom.  相似文献   
45.
A quantitative method was developed to describe Lophodermium (Rhytismataceae, Ascomycetes) populations on Pinus thunbergii needle litter, and seasonal patterns of population variation were examined based on this method. We focused on the formation of black zone lines across needles and the production of Lophodermium ascocarps on needle portions delimitated by zone lines. The study was carried out at a soil erosion control site on a mountain slope and at a coastal sand dune site. Most Lophodermium spp. on needle litter were identified as L. pinastri according to morphological characteristics of ascocarps and ascospores and DNA analysis. Zone lines were produced on needles when isolates of L. pinastri were in contact with other isolates of L. pinastri or with isolates of other species in dual culture tests. This observation provided a rationale to consider that individual colonies with ascocarps and delimitated by zone lines were occupied by a single Lophodermium isolate. Frequency of occurrence of Lophodermium colonies, total colony length, and mean colony number per needle were higher at the coastal sand dune site than at the soil erosion control site. Total colony length and mean colony number also varied with season. Mean colony length and mean ascocarp number per colony were not different between sites or seasons.  相似文献   
46.
Aim  To determine if changes in the key bioclimatic parameters associated with rainfall seasonality can be quantified from fossil sequences and to distinguish them from changes in the total annual rainfall.
Location  Lake Masoko, southern Tanzania (9°20' S, 33°45' E, 840 m a.s.l.).
Methods  Fossil pollen was extracted from a long and well-dated sedimentary sequence spanning the period 45,000–4400 cal. yr bp . The modern habitat, geographical distribution and climatic range (mean annual rainfall and temperature, and length of the dry season) of selected East African plants were used to infer past rainfall attributes for the most characteristic fossil pollen taxa identified from the sediments of Lake Masoko.
Results  In the Masoko pollen sequence it has been possible to identify changes in the length/severity of the dry season during the last 45,000 cal. yr bp , which are interpreted to reflect shifts in the mean position of the Intertropical Convergence Zone (ITCZ) over the southern tropics. We suggest that this bioclimatic parameter has been the main driver of the vegetation dynamics in this area. The major inferred change occurred at the Younger Dryas–Holocene transition c . 11,800 cal. yr bp , when semi-deciduous forest disappeared, being replaced in the lake catchment by woodland, which persists to the present day in spite of locally high rainfall.
Main conclusions  In tropical regions under the influence of the ITCZ, the position and strength of which determine the distribution of rainfall through the year, more attention must be paid to the impact of the length and intensity of the dry season on the modern and past distribution and dynamics of the vegetation. This climatic parameter is as important as the total annual amount of rainfall, and probably one of the most relevant in lowland areas.  相似文献   
47.
Amongst the most frequently made assumptions in simple population models are that individuals interact equally with every other individual and that dispersal occurs with equal likelihood to any location. This is especially true for models of a single population (as opposed to a patchy population or metapopulation). For many species of animals and probably for all plant species these assumptions are unlikely to hold true. Here one much-studied population model—the Ricker model—is reformulated such that interactions occur only between individuals located within a certain distance of each other and dispersal distance is finite. Two alternative reformulations are presented. Results demonstrate that both limiting the interaction neighbourhood and reducing dispersal distance tend to stabilise the global population dynamics, although the extent to which this occurs depends upon the reformulation used. Spatial pattern formation is a feature of the simulated population. At lower intrinsic rates of growth (r) these patterns tend to be static, while for higher r, they are dynamic. Both the stabilisation of global dynamics and spatial pattern formation are well-described features of metapopulation models. Here, similar effects are shown to occur on a single contiguous patch of habitat.  相似文献   
48.
A total of 1280 (670 females and 610 males) Squatina guggenheim , an angel shark endemic to the south-west Atlantic, was caught during five research cruises (1995, 1997 and 1998) carried out in the Argentine-Uruguayan Common Fishing Zone (AUCFZ) at depths of 3·5–266 m. All angel sharks captured were sexed and measured. Of the 947 examined for stomach contents, 556 (58·7%) contained food and 391 (41·3%) were empty. Numerically, bony fishes were the principal dietary component (89·7%), followed by crustaceans (4·8%) and molluscs (4·4%). The most important prey species were Engraulis anchoita (58·3%), shrimps (4·4%) and Ilex argentinus (2·3%). Male and female diets were not found to differ significantly ( P  > 0·01), however, the diets of different size classes showed significant differences ( P  ≤ 0·01) (group 1, 23–44, group 2, 45–74 and group 3, 75–91 cm L T). Low rates of cannibalism were observed. The spatial and seasonal variability in the trophodynamics of S. guggenheim is discussed.  相似文献   
49.
基于土地利用景观格局对城市热岛效应的影响研究较多,但准确识别对城市热岛效应具有重要影响的关键斑块和节点方面的研究亟待开展。以新型中小城市株洲云龙示范区为例,以城市热岛网络构建为切入点,应用形态学空间格局分析(Morphological Spatial Pattern Analysis, MSPA)与景观连通性模型识别城市发展进程中核心热景观斑块和关键节点,并分析其时空演变特征。研究结果表明:(1)2007—2018年云龙示范区热岛斑块趋于集中,热岛面积较研究初期有明显增加,从地表温度空间分布上体现为城区与周边农村的温度对比更加鲜明,表明城市化进程中建设用地呈聚集扩散趋势。(2)研究期间热岛核心区占热景观面积比最大,且比例有明显上升趋势。而边缘、支线、孤岛、桥接、环线以及孔隙形态类型面积占比均呈现出不同程度的下降趋势,表明热岛斑块之间聚集程度不断提高。(3)识别出景观连通度重要性值较高的前20热景观斑块,其中前3斑块的重要性值和面积占比较大,属于极重要与重要两个热岛核心斑块重要性等级,值得重点关注与优化。(4)对重要性值高的热岛核心区域可优先采取降温措施,可以打断节点之间连接减缓整个区域...  相似文献   
50.
The present study investigates the chemical composition, antioxidant and antimicrobial bioactivities of essential oil and hexane extract from Citrus limon leaves. The isolation of essential oil was carried out using the Clevenger apparatus. The percentage yield of essential oil and hexane extract from Citrus limon leaves was 0.59 and 0.50 %, respectively. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) scavenging assay highlighted that Citrus limon leaves essential oil (CLEO) and hexane extract exhibited the significant antioxidant potential of 69.64 and 67.55 %, respectively, compared to the BHT standard. Similarly, a significant inhibition in linoleic acid peroxidation was recorded in both CLEO (81.93 %) and hexane extract (50.34 %). Characterization of chemical constituents in CLEO and extract was executed using GC/MS, where Limonene was detected as a major compound in CLEO (60.52 %) and hexane extract (73.62 %). The haemolytic activity ranged from 2.46 to 5.75 % revealing negligible cytotoxicity of CLEO and hexane extract. In silico studies agree with the in vitro antimicrobial studies, where vinimalol, taraxasterol, and moretenol present in CLEO showed strong interactions/inhibition against dihydroorotase and DNA gyrase from E. coli, and the tyrosyl-tRNA synthetase and DNA gyrase from S. aureus. Based on the current data, it may be concluded that both CLEO and hexane extract possessed significant bioactivities, such as antimicrobial and antioxidant activity, with minimal cytotoxicity.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号