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281.
The canopy surface is an undulating surface that follows the irregular contours of the upper tree crowns and defines the inner and the outer limits of the forest volume. In French Guiana, the height of the canopy surface was surveyed in both a primary and a 20-years old clear-felled secondary forest plot. The topographic surface was displayed in a three-dimensional mesh, where X and Y are horizontal co-ordinates, and Z is the canopy height measured from the ground with an optical telemeter. The statistical dispersion of Z-data, and the spatial tree height variations, are interpreted at different levels of ecosystem organisation, from forest type (primary or secondary forest) to the trees themselves, following the folded forest model theory (Oldeman 1992, 1994). The vertical growth of trees creates a convex pattern in the relief of canopy surface, whereas gaps make concavities which delimit impact of perturbation on the forest structure. These events are either the result of the dynamic of single trees (emergent and decayed trees), or arise from the dynamic of a group of trees working together (group of emergent trees or complex gaps). At the plot scale, the elementary events, convexities and concavities, are gathered on similar topo-sequences, and form canopy units either higher or lower than the average canopy height. This study suggests that the topography of the canopy surface is defined by a complex nested system from trees, to groups of trees, to canopy units, within a delimited floristic and physical environment. 相似文献
282.
283.
Liriomyza mystica Boucher & Nishida, sp. n., and Liriomyza prompta Boucher & Nishida, sp. n. are described from Costa Rica. Both species were reared from leaves of Bocconia frutescens L. (Papaveraceae). The latter species was also reared from B. arborea S. Watson. Larvae of L. mystica mine primary veins of large, relatively old, mature leaves, and L. prompta mine blades of small to large, mature leaves. These represent the first record of agromyzids feeding on Bocconia. Biological information is also given and illustrated. 相似文献
284.
T.?D.?Byram J.?H.?MyszewskiEmail author D.?P.?Gwaze W.?J.?Lowe 《Tree Genetics & Genomes》2005,1(3):85-92
Currently, both industrial and private landowners in the Western Gulf Forest Tree Improvement Program (WGFTIP) area are compensated
for their timber primarily based on the weight or volume of green wood reaching the mill gate. This places an immediate economic
focus on adaptability and volume growth. However, selection for volume growth alone could result in decreased wood quality
over time. Wood quality characteristics including stem straightness, wood specific gravity, and microfibril angle have either
neutral or slightly unfavorable genetic correlations with volume growth in the WGFTIP loblolly pine (Pinus taeda L.) program. Since most WGFTIP members also consider wood quality an important selection criterion, the WGFTIP must define
the best possible set of selection criteria given that (1) no single set of breeding objectives can be considered optimal
for multiple products and (2) improvement in wood quality has no readily recognized economic importance in the existing market.
To meet this challenge, the WGFTIP has implemented different strategies for its mainline breeding and deployment populations.
In the mainline population, consistent breeding and selection criteria are used across members, while in the various deployment
populations, selections are tailored to meet the specific needs of each member. The WGFTIP is also developing an elite wood
quality population (WQEPop) based on backward selection. For the WQEPop to be successful, the economic importance of improved
wood quality must be recognized, and landowners must be compensated for growing higher quality timber, especially if this
results in reduced volume production. Improved methodology for within-family selection and for wood quality trait measurement
is also important. 相似文献
285.
Regeneration is known to be limited at many temperate tree lines, but very little data is available on the impacts of altitude
and anthropogenic disturbance on regeneration patterns along tropical tree lines. The study focused on the reproductive traits
of two Polylepis species in the Páramo de Papallacta in Ecuador along an altitudinal gradient, and involved different intensities of cattle
trampling within subsequent altitudinal ranges. We analyzed flowering, fruit set, seed viability, germination, and seedling
establishment as well as stand structure of Polylepis incana and P. pauta. The numbers of P. incana inflorescences and seedlings per m2 showed a marginally significant decrease with increasing altitude. Mean tree height was
significantly lower at higher altitudes, while stem number increased. The number of P. pauta inflorescences also decreased significantly upslope. In both forest types, trampling was found to have a positive impact
on seedling abundance, presumably due to the removal of the litter layer. Thus, there was no evidence of negative effects
of moderate cattle grazing on both tree line species. However, sapling establishment was minimal inside the forest stands
at all altitudes and grazing levels, and we consequently observed a low proportion of narrow stems within all investigated
forests. Our results show that, along with vegetative growth limitations of adult trees, important regeneration traits such
as seedling and inflorescence numbers are also influenced by altitude, which might contribute to the formation of the upper
tree line. Nevertheless, recruitment in the forest interior was low overall indicating that further factors, such as light
conditions, affect regeneration of the studied species. 相似文献
286.
Faizul Haq 《农业工程》2018,38(1):15-20
This paper communicates an analytical exploration of the vegetation above tree line in Nandiar valley western Himalayas with respect to climatic, edaphic and topographic factors. The alpine pasture stretches above the tree limits between elevations of 2850–3800 m. Thirteen stands were selected on the basis of physiognomy of vegetation in 2014–15. The leading life form and leaf spectra were therophytes and microphyll respectively. Four plant communities were identified through two ways indicator species analysis at cut level 2. Bray-Curtis ordination showed that maximum stands have common species. Detrended correspondence analysis grouped species having similar habitats in ordination space. Canonical correspondence analysis constrained species along different environmental variables. The significant result were contribution by phosphorous (P = 0.01) and wind speed (P = 0.08). Few plant species like Betula utilis and Podophyllum emodi are threatened due to its medicinal collection. The alpine pasture of Nandiar valley is under severe stress due to anthropogenic and grazing factors. Overall, this research article call for greater attention to the types of conservation actives occurring and the ways they are working together to protect and recover the global alpine biodiversity. 相似文献
287.
Summary The twolined chestnut borer, Agrilus bilineatus (Weber) (Coleoptera: Buprestidae), attacks oaks (Quercus spp.) and is associated with extensive mortality of trees in the eastern deciduous forests of North America. We tested the hypothesis that winter starch reserves of oak roots are an indicator of tree vigor and that only trees low in stored starch would be attacked by A. bilineatus. We measured the levels of stored starch in the roots of 200 non-infested healthy white oaks during the dormant season and determined their correlation with A. bilineatus attacks the following spring. There was a significant increase in A. bilineatus captures on sticky traps with a decrease in winter starch reserves. Trees low in stored starch that were also stressed by phloem-girdling attracted 3.7 times as many beetles as did non-girdled trees that were low in starch. However, non-girdled trees that had low winter starch reserves were also attacked. Only oaks that had had extremely low winter root starch reserves (<5mg/g dry weight of root sapwood tissue) were heavily attacked by A. bilineatus and subsequently died. One third of non-girdled low starch trees and 67% of phloem-girdled low starch trees died, whereas none of the trees with root starch >5 mg/g dry wt died. These results indicate that winter starch reserves are a good predictor of A. bilineatus attack.The investigation reported in this paper (No. 87-7-8-118) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director 相似文献
288.
289.
目的建立人工饲养健康树鼩血液学和血液生化指标的正常值参考范围,并探讨与不同物种的血液学和血液生化值的差异及相互关系。方法应用全自动血细胞仪和生化分析仪测定140只健康成年树鼩的血液学及血液生化指标。结果雌性与雄性比较,LYM%、PLT、RDW%、GLU、CREA的差异具有显著性(JP〈0.05),11P、CHOL、TG的差异具有极显著性(P〈0.01),其他指标的差异不具显著性,部分指标与恒河猴、大鼠及人的相应指标存在一定的差异。结论本文建立了健康树鼩的血液学及生化指标的正常值参考范围,可为应用该动物进行科学研究时提供参考。 相似文献
290.
运用响应函数、相关函数、单年分析等树木年轮气候学的方法 ,研究了锡林河流域草原沙地上白扦年轮生长指数的变异。结果表明 :白扦的生长对环境的变化相当敏感 ,当年 9月至上年 8月的月平均温度和月降雨量解释年轮宽度方差量的约 70 % ;白扦当年的生长量与上年 9月、当年 2月、5月的降雨量之间具明显的正相关性 ,而与当年 5月的大气温度具显著负相关关系。由于沙地具有渗透性较强和防止土壤深层水分蒸发的特点 ,特别是上年 8~10月的降雨可部分保存于沙地内 ,便于植物下年利用。由此认为 ,在沿锡林河流域中部的沙带上 ,建立以现有白扦为分布中心的人工白扦林将是完全可行的 相似文献