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1.
A native nitrogen-fixing shrub facilitates weed invasion   总被引:33,自引:0,他引:33  
Invasions by exotic weedy plants frequently occur in highly disturbed or otherwise anthropogenically altered habitats. Here we present evidence that, within California coastal prairie, invasion also can be facilitated by a native nitrogen-fixing shrub, bush lupine (Lupinus arboreus). Bush lupines fix nitrogen and grow rapidly, fertilizing the sandy soil with nitrogen-rich litter. The dense lupine canopy blocks light, restricting vegetative growth under bushes. Heavy insect herbivory kills lupines, opening exposed nitrogen-rich sites within the plant community. Eventual re-establishment of lupine occurs because of an abundant and long-lived seed bank. Lupine germination, rapid growth, shading and fertilization of sites, and then death after only a few years, results in a mosaic of nutrient-rich sites that are available to invading species. To determine the role of bush lupine death and nitrogen enrichment in community composition, we examined nutrient dynamics and plant community characteristics within a site only recently colonized by lupine, comparing patches where lupines had recently died or were experimentally killed with adjacent areas lacking lupine. In experimentally killed patches, instantaneous pool sizes of exchangeable ammonium and nitrate nitrogen were higher than in adjacent sites free of lupine. Seedlings of the introduced grass Bromus diandrus accumulated 48% greater root biomass and 93% more shoot biomass when grown in a greenhouse in soil collected under experimentally killed lupines compared to B. diandrus seedlings grown in soil collected at least 1 m away from lupines. At the end of the spring growing season, total above-ground live plant biomass was more than twice as great in dead lupine patches as in the adjacent lupine-free grassland, but dead lupine patches contained 47% fewer plant species and 57% fewer native species. Sites where lupines have repeatedly died and reestablished during recent decades support an interstitial grassland community high in productivity but low in diversity, composed of mostly weedy introduced annual plants. In contrast, at a site only recently colonized by bush lupines, the interstitial grassland consists of a less productive but more diverse set of native and introduced species. We suggest that repeated bouts of lupine germination, establishment, and death can convert a rich native plant community into a less diverse collection of introduced weeds.  相似文献
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小麦/大豆间作中作物种间的竞争作用和促进作用   总被引:25,自引:3,他引:22  
春小麦/春大豆间作是西北一熟制灌区广泛采用的高产种植形式.本文采用田间小区和微区根系分隔试验研究了这种种植形式作物种间的竞争作用和促进作用.结果表明,小麦/大豆间作具有明显的间作优势.土地当量比为1.23~1.26.小麦为优势种,竞争力强于大豆,具有明显的间作边行优势.小麦边行优势的1/3贡献来自于地下部.小麦收获后,大豆生长具有恢复作用,认为这种恢复作用是间作优势的机制之一.间作相对于单作两种作物的收获指数均有显著提高.收获指数的种间促进作用是间作优势的另一机制.  相似文献
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根系间的相互作用——竞争与互利   总被引:21,自引:4,他引:17       下载免费PDF全文
陈伟  薛立 《生态学报》2004,24(6):1243-1251
植物根系间的相互作用分为竞争和互利两种形式 ,它是决定植物群落动态变化和群落结构的重要因素。根系间的竞争包括植株个体自身根系的竞争以及个体与个体根系间 (同种或异种 )的竞争两方面 ,前者的发生在农林系统中是不可避免的并且很难调控 ,后者可以分为种间植物根系的竞争和种内植物根系的竞争。还阐述了根系的竞争能力和与其密切相关的根系生长率、根组织的新陈代谢、植物的生长形式和根系的空间结构等植物特性 ,同时介绍了根系对水和养分的竞争机理、形式、影响以及竞争强度计算方法。接着具体分析包括根系错位在内的各种根系互利现象和相关机理。影响根系间相互作用的限制性因子有土壤营养的异质性、大气 CO2 浓度、地下草食生物、根系生产力和生物量、根系结构、形态和生理调节、土壤养分的扩散性以及植物间距等。随着科技的进步和各门学科的发展 ,未来根系的研究方向主要体现在结合实践优化农林系统中不同物种间的作用关系、预测根系竞争在全球气候变化下的发展规律、更新实验研究方法及手段研究作用机理等 3个方面。  相似文献
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The ubiquitous major intrinsic protein (MIP) family includes several transmembrane channel proteins known to exhibit specificity for water and/or neutral solutes. We have identified 84 fully or partially sequenced members of this family, have multiply aligned over 50 representative, divergent, fully sequenced members, have used the resultant multiple alignment to derive current MIP family-specific signature sequences, and have constructed a phylogenetic tree. The tree reveals novel features relevant to the evolutionary history of this protein family. These features plus an evaluation of functional studies lead to the postulates: (i) that all current MIP family proteins derived from two divergent bacterial paralogues, one a glycerol facilitator, the other an aquaporin, and (ii) that most or all current members of the family have retained these or closely related physiological functions. Received: 19 April 1996/Revised: 3 June 1996  相似文献
6.
Fusuo Zhang  Long Li 《Plant and Soil》2003,248(1-2):305-312
This paper reviews recent research on the processes involved in the yield advantage in wheat (Triticum aestivum L.)/maize (Zea mays L.), wheat/soybean [Glycine max (L.) Merr.], faba bean (Vicia faba L.)/maize, peanut (Arachis hypogaea L.)/maize and water convolvulus (Ipomoea aquatica Forsk.)/maize intercropping. In wheat/maize and wheat/soybean intercropping systems, a significant yield increase of intercropped wheat over sole wheat was observed, which resulted from positive effects of the border row and inner rows of intercropped wheat. The border row effect was due to interspecific competition for nutrients as wheat had a higher competitive ability than either maize or soybean had. There was also compensatory growth, or a recovery process, of subordinate species such as maize and soybean, offsetting the impairment of early growth of the subordinate species. Finally, both dominant and subordinate species in intercropping obtain higher yields than that in corresponding sole wheat, maize or soybean. We summarized these processes as the `competition-recovery production principle'. We observed interspecific facilitation, where maize improves iron nutrition in intercropped peanut, faba bean enhances nitrogen and phosphorus uptake by intercropped maize, and chickpea facilitates P uptake by associated wheat from phytate-P. Furthermore, intercropping reduced the nitrate content in the soil profile as intercropping uses soil nutrients more efficiently than sole cropping.  相似文献
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小麦-大豆间作中小麦对大豆磷吸收的促进作用   总被引:16,自引:1,他引:15       下载免费PDF全文
李隆  李晓林  张福锁 《生态学报》2000,20(4):629-633
采用塑料膜,20μm尼龙网分司以及不分隔两种俄根系的盆栽装置研究了小麦,大豆间作种间磷吸收的促进作用。结果表明,两种作物根系用尼龙网分隔后,即种间磷竞争作用基本消除后,小麦对大豆磷吸收具有明显的促进和,表现为大豆生物学产量明显提高,是塑料膜分隔的2.5倍,是无分隔4.6倍,尼龙网分隔,大豆分隔,大豆的根系活力高于塑料膜分隔45.2%,达显著水平,此外,尼龙网分隔形成小麦根面,大豆的根系呈偏向小麦根  相似文献
9.
Interspecific complementary and competitive interactions between maize (Zea mays L. cv. Zhongdan No. 2) and faba bean (Vicia faba L. cv. Linxia Dacaidou) in maize/faba bean intercropping systems were assessed in two field experiments in Gansu province, northwestern China, plus a microplot experiment in one treatment of one of the field experiments in which root system partitions were used to determine interspecific root interactions. Intercropping effects were detected, with land equivalent ratio values of 1.21–1.23 based on total (grain+straw) yield and 1.13–1.34 based on grain yield. When two rows of maize were intercropped with two rows of faba bean, both total yield and grain yield of both crop species were significantly higher than those of sole maize and faba bean on an equivalent area basis. When two rows of pea (Pisum sativum L. cv. Beijing No. 5) were intercropped with two rows of faba bean, neither total yield nor grain yield of faba bean was higher than of sole faba bean on an equivalent area basis. Interspecific competition between maize and faba bean was relatively weak, with mean relative crowding coefficients of 0.99–1.02 for maize and 1.55–1.59 for faba bean. The microplot experiment in which partitions were placed between root systems showed a significant positive yield effect on maize when the root systems intermingled freely (no partition) or partly (400 mesh nylon net partition) compared with no interspecific root interaction (plastic sheet partition). This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献
10.
Ectomycorrhizal fungal communities at forest edges   总被引:14,自引:2,他引:12  
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