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981.
Unai López-de-Heredia Pilar Jiménez Pedro Díaz-Fernández Luis Gil 《Journal of Biogeography》2005,32(6):939-949
Aim To analyse the role of the Balearic Islands as a refuge area for evergreen Quercus (cork oak: Quercus suber L., holm oak: Q. ilex L., kermes oak: Q. coccifera L.), by using molecular, historical and palaeobotanical data. Location The Western Mediterranean Basin (Balearic Islands, eastern Iberia, Provence, Sardinia, Corsica, Sicily, Malta, Italy, Northern Africa). Methods We sampled 108 populations and used the PCR‐RFLP technique with five universal cpDNA primers to define haplotypes in the sampled populations. Diversity, differentiation parameters and spatial analysis of the populations, using a spatial version of amova , were linked to the geological history of the Western Mediterranean Basin in order to explain the present spatial pattern of the evergreen Quercus populations in the Balearics. Results Evergreen Quercus cpDNA shows a complex structure, with remnants of ancient diversity in the Balearics. Balearic populations of holm oak are related to Iberian populations, while for cork and kermes oaks, we found both Tyrrhenian and Iberian haplotypes. Main conclusions The complex spatial patterns of cpDNA in Balearic evergreen Quercus appears explicable in terms of a combination of physical (vicariance and long distance dispersal) and biological (introgressive hybridization) factors. The Balearics constitute a glacial refuge area and a reservoir of genetic variation with traces of ancient diversity from Messinian–Pliocene stages. 相似文献
982.
Gian Battista Bischetti Enrico A. Chiaradia Tommaso Simonato Barbara Speziali Barbara Vitali Paolo Vullo Antonio Zocco 《Plant and Soil》2005,278(1-2):11-22
Forest vegetation is known to increase hillslope stability by reinforcing soil shear resistance and by influencing hydrologic
conditions of soil. Although the importance of plant root systems for hillslope stability has received considerable attention
in recent years, the quantification of such an effect needs more investigation. In this paper, we present a synthesis of the
data gathered in the last 5 years for some species in different locations of the Alps and Prealps of Lombardy (Northern Italy)
with the aim to increase our knowledge on root tensile strength and on Root Area Ratio distribution within the soil. Concerning
root tensile strength we developed tensile strength–diameter relationships for eight species: green alder (Alnus viridis(Chaix) D.C.), beech (Fagus sylvatica L.), red willow (Salix purpurea L.), goat willow (Salix caprea L.), hazel (Corylus avellana L.), European ash (Fraxinus excelsior L.), Norway spruce (Picea abies (L.) Karst.) and European larch (Larix decidua Mill.). Results show a great variability among the different species and also for the same species. In general, however,
root strength (in terms of tension) tends to decrease with diameter according to a power law, as observed by other Authors.
Comparing the power law fitting curves for the considered species, it can be observed that they fall in a relatively narrow
band, with the exception of hazel, which appears the most resistant. Concerning the evaluation of root distribution within
the soil we estimated the Root Area Ratio (the ratio between the area occupied by roots in a unit area of soil) according
to its depth for five species (beech, Norway spruce, European larch, mixed hazel and ash) in three locations of Lombardy.
Results show that there is a great variability of root density for the same species well as for different points at the same
locality. The general behaviour of root density, in any case, is to decrease with depth according to a gamma function for
all the studied species. The results presented in this paper contribute to expanding the knowledge on root resistance behaviour
and on root density distribution within the soil. The studied location have allowed the implementation of soil–root reinforcement
models and the evaluation of the vegetation contribution to soil stability. 相似文献
983.
农田周围生态保留带中普通田鼠的种群生态学:种群数量动态及结构 总被引:2,自引:0,他引:2
于2003年5月~2004年11月,采用标志重捕法对栖息在生态保留带的普通田鼠种群结构和数量动态进行了跟踪研究。结果表明,两年中种群密度夏季最大分别达到410个体/hm2和641个体/hm2,春季最少分别达到166个体/hm2和153个体/hm2,种群数量从7月份开始增长,8月份种群密度减少并于11月份开始重新增长。种群中雌性个体数量比较多,雌性在种群中的居留时间较长,同时存活率比雄性高,这导致种群数量的季节变化。种群周转率比较高,在两个捕鼠期间种群中的80%个体被更新,这表明普通田鼠在生态保留带中的活动非常频繁,不断与周围的其他种群进行交流,提高了种群对环境的适应能力。种群中雌雄个体的巢区之间没有年间变化,活动巢区比较小,巢区长度2003年平均为11 m,最长为37.5 m,2004年平均为13 m,最长为52 m。Pearson相关指数表明种群数量和生态保留带年龄、覆盖率和高度之间没有相关性。 相似文献
984.
Chun-Wang Xiao Osbert J. Sun Guang-Sheng Zhou Jing-Zhu Zhao Gang Wu 《Trees - Structure and Function》2005,19(6):712-721
We studied the responses of leaf water potential (Ψw), morphology, biomass accumulation and allocation, and canopy productivity index (CPI) to the combined effects of elevated
CO2 and drought stress in Caragana intermedia seedlings. Seedlings were grown at two CO2 concentrations (350 and 700 μmol mol−1) interacted with three water regimes (60–70%, 45–55%, and 30–40% of field capacity of soil). Elevated CO2 significantly increased Ψw, decreased specific leaf area (SLA) and leaf area ratio (LAR) of drought-stressed seedlings, and increased tree height, basal
diameter, shoot biomass, root biomass as well as total biomass under the all the three water regimes. Growth responses to
elevated CO2 were greater in well-watered seedlings than in drought-stressed seedlings. CPI was significantly increased by elevated CO2, and the increase in CPI became stronger as the level of drought stress increased. There were significant interactions between
elevated CO2 and drought stress on leaf water potential, basal diameter, leaf area, and biomass accumulation. Our results suggest that
elevated CO2 may enhance drought avoidance and improved water relations, thus weakening the effect of drought stress on growth of C. intermedia seedings. 相似文献
985.
松辽盆地三肇地区泉头组三段上部介形类化石的指相意义 总被引:3,自引:0,他引:3
松辽盆地三肇地区白垩系下统泉头组三段上部(杨三组—杨一组)以大套的紫红、红色砂、泥岩沉积为主,在紫红色泥岩中含有较丰富、完整的介形类及其它门类化石。以往认为,这套以红色为基调的地层属河流相沉积。对其中介形类等化石的古生态、埋藏特征及丰度变化的研究表明,该地层的沉积环境应为浅水湖泊环境,而非河流等水上环境。湖相沉积自杨三组就已存在,向上分布范围不断扩大,反映了湖泊水域面积呈现逐渐扩大的趋势。 相似文献
986.
987.
Carter R. Newell C.H. Pilskaln B.A. MacDonald 《Journal of experimental marine biology and ecology》2005,321(2):109-124
In order to examine the importance of the settling of large particles to the food supply and feeding behavior of a benthic culture of the blue mussel, Mytilus edulis, we investigated the tidal dynamics of large (>0.5 mm diameter) marine aggregates, commonly known as marine snow, during three tidal cycles in July 1998 at a shallow, subtidal, low current flow regime site along the coast of Maine (Shorey Cove, Roque Island, Englishman's Bay, Maine).In situ, optically measured marine snow showed a distinct tidal signal displaying an increase in size and abundance through high tide with a peak on the early ebb tide as it settled to the bottom. Marine snow volume ranged an order of magnitude through the tidal cycle, from under 8 to over 80 mm3 l−1. An increase in the in situ marine snow volume corresponded with an increase in benthic mussel feeding activity (from 20% to 60% of maximum exhalant siphon area, which is an estimate of pumping rate) and maximum rates of pseudofeces production by the mussels during periods of low tidal current speeds. In contrast, mussels from the same population feeding on surface waters in shipboard chambers produced no pseudofeces and had high pumping rates (80-100% maximum exhalant siphon area) over the whole tidal period. A second peak in benthic mussel pumping rates also occurred during flood tide.Food quality was lower in the bottom waters due to significantly higher particulate inorganic matter (PIM, >2 mg l−1) when compared with the surface waters. PIM accounted for 95% of the total settled mass flux of 3.4 g m−2 day−1 measured in sediment traps deployed 1 m off the bottom, with organic carbon representing only 2.5% of the mass flux during the mid-summer conditions. At low-current sites such as Shorey Cove, Roque Island, Maine, the settling of marine snow provides an important additional source of food, albeit of low quality, to benthic populations of blue mussels. 相似文献
988.
Question: Is it possible to model the germinative and resprouting behaviour of plant species in Atlantic shrublands and woodlands in relation to fire intensity? Is it possible to recognise different functional regenerative types in these plant species? Location: Galicia, NW Iberian Peninsula. Methods: We explored the patterns of germination and resprouting plant responses in relation to different intensities of fire using data from 37 trees, shrubs and herbaceous species growing in Atlantic shrublands and woodlands. Results: Synthesizing their germinative and resprouting behaviour, we created two graphical models: the Functional Germinative Model (FGM) and the Functional Sprouting Model (FSM). Integrating the germinative and resprouting responses, and taking into account fire intensity, we created the Functional Regenerative Model (FRM), which predicts the post‐fire recuperation of the populations of each species. The FRM has been validated with data from four Atlantic communities. We identified four plant functional regenerative types (PFRT) for Atlantic forest vegetation and we propose three intensities of response. Conclusions: The extracted models (FGM, FSM and FRM) and the grouping of species in four PFRTs could be applicable to more Atlantic species, to disturbance ecology in general and to population, community and landscape management. 相似文献
989.
LUCAS C. R. SILVA † LEONEL STERNBERG‡ MUNDAYATAN HARIDASAN§ WILLIAM A. HOFFMANN¶ FERNANDO MIRALLES-WILHELM AUGUSTO C. FRANCO 《Global Change Biology》2008,14(9):2108-2118
Upland tropical forests have expanded and contracted in response to past climates, but it is not clear whether similar dynamics were exhibited by gallery (riparian) forests within savanna biomes. Because such forests generally have access to ample water, their extent may be buffered against changing climates. We tested the long‐term stability of gallery forest boundaries by characterizing the border between gallery forests and savannas and tracing the presence of gallery forest through isotopic analysis of organic carbon in the soil profile. We measured leaf area index, grass vs. shrub or tree coverage, the organic carbon, phosphorus, nitrogen and calcium concentrations in soils and the carbon isotope ratios of soil organic matter in two transitions spanning gallery forests and savanna in a Cerrado ecosystem. Gallery forests without grasses typically show a greater leaf area index in contrast to savannas, which show dense grass coverage. Soils of gallery forests have significantly greater concentrations of organic carbon, phosphorus, nitrogen and calcium than those of savannas. Soil organic carbon of savannas is significantly more enriched in 13C compared with that of gallery forests. This difference in enrichment is in part caused by the presence of C4 grasses in savanna ecosystem and its absence in gallery forests. Using the 13C abundance as a signature for savanna and gallery forest ecosystems in 1 m soil cores, we show that the borders of gallery forests have expanded into the savanna and that this process initiated at least 3000–4000 bp based on 14C analysis. Gallery forests, however, may be still expanding as we found more recent transitions according to 14C activity measurements. We discuss the possible mechanisms of gallery forest expansion and the means by which nutrients required for the expansion of gallery forest might accumulate. 相似文献
990.
Biodiversity enhances individual performance but does not affect survivorship in tropical trees 总被引:1,自引:0,他引:1
We developed an analytical method that quantifies the relative contributions of mortality and individual growth to ecosystem function and analysed the results from the first biodiversity experiment conducted in a tropical tree plantation. In Sardinilla, central Panama, over 5000 tree seedlings were planted in monoculture and mixed-species plots. After 5 years of growth, mixed-species plots yielded, on average, 30–58% higher summed tree basal area than did monocultures. Simulation models revealed that the increased yield of mixed-species plots was due mostly to enhancement of individual tree growth. Although c . 1500 trees died during the experiment, mortality was highly species-specific and did not differ consistently between biodiversity treatments. Our results show that the effects of biodiversity on growth and mortality are uncoupled and that biodiversity affects total biomass and potentially self-thinning. The Sardinilla experiment suggests that mixed-species plantings may be a viable strategy for increasing timber yields and preserving biodiversity in tropical tree plantations. 相似文献