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131.
以福建省沙县15年生(13年生时间伐)和17年生(10年生时间伐)的乳源木莲-杉木中龄混交林(杉莲比为7:3)为研究对象,通过应用Ruark异速生长模型,对间伐后混交林中乳源木莲的树冠结构进行研究。结果表明,在混交条件下,不同间伐期对树冠形状有显著影响:13年生时间伐,乳源木莲树冠生长受到限制不能充分扩展,树冠形状近似抛物线形,枝长分布方式对下部层次造成遮荫,不利于乳源木莲树木的光合作用;而10年生时间伐,乳源木莲具有圆锥形树冠、较大的枝倾角和较高的叶面积指数,因此有利于树冠对光的截获,从而增加单株生物产量,有利于培育乳源木莲大径材。杉莲混交林中乳源木莲累积叶面积指数可以分别用以下模型进行估测:y(10年生时间伐)=2.6211Z^0.1318 e^0.0417z(R^2=0.9418)和y(13年生时间伐)=1.7546Z^0.6122e^-0.1411z(R^2=0.9923)。通过残差百分比检验和后验检验表明,模型拟合度较高,预测效果良好。 相似文献
132.
为了改良白花泡桐的干形,对树冠结构、生长性状与干形的遗传相关进行了剖析和通径分析,计算出主要树冠性状、生长性状对干形的63个选择指数方程。结果表明,胸径、小枝数、分枝总长、冠表面积和树高对形数、圆满度的决定系数在0.405~0.940和0.426~1.064之间。由以上5性状和形数或圆满度组成的综合选择指数方程效果最好。对形数选择的遗传进度、相对效率分别为0.155和159.0157%。对圆满度选择的遗传进度、相对效率分别为0.174和128.3679%。 相似文献
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135.
Johannes?EichhornEmail author Regina?Icke Ansgar?Isenberg Uwe?Paar Egbert?Sch?nfelder 《European Journal of Forest Research》2005,124(4):335-347
The evaluation uses the longest available time series for beech and oak defoliation in Germany. The data from Hesse, starting
from 1984, show a typical pattern: for the first 12 years, a continuous increase in defoliation was observed ranging from
an average value of 14% in 1984 to a peak value of 30%. This was followed by a subsequent decrease in the loss of foliage
accompanied by a high variability, until the last monitoring in 2003, where an average value of 25% defoliation was observed.
For both tree species, the years of trend reversal were identical. The same pattern was observed in the German federal states:
Rhineland-Palatinate, North Rhine-Westphalia, and Bavaria. The year of trend reversal was identical in Hesse and Rhineland-Palatinate.
In North Rhine-Westphalia, it occurred 1 year earlier and in Bavaria 3 years earlier. Whereas defoliation trends were clearly
demonstrated, tree mortality did not appear on a large scale. The sample trees were grouped into four discrete clusters according
to their annual defoliation values from 1984 to 2003. In 1996, the clusters represent 15, 25, 35, and 50% defoliation values.
Regarding beech in Hesse, there was no overlap in the defoliation curves observed among the different clusters. These four
clusters having different degrees of defoliation over the whole time span of 20 years were used for a further detailed statistical
analysis. For discrete variables like crown spacing and—in the case of beech—fruit bearing, mosaic plots were applied in order
to visualize relations of low dimensional contingency tables, with defoliation trends being used as the response variable.
The data show for beech a very clear relation between defoliation and age, relative crown spacing, stand composition, and
fruit bearing. Regarding oak, besides age and relative crown spacing, the years with significant appearance of biotic stress
factors—leaf eating insects—show a clear relation to trends of defoliation. The statistical model used in this study—logistic
regression—allows applying a multinomial response variable and a number of continuous or categorical explanatory variables.
With this approach, an iterative optimized selection of effect variables was used to test the relevance of different variables
on the defoliation pattern of the same four clusters mentioned above. For this, the variables were grouped in an iterative
process with five steps, starting with a few basic variables of tree and site information, and ending with a total of more
than 20 variables in the fifth step. The process selects first the variables which are of significance on the defoliation,
and calculates the possible errors in the grouping of the different trees to the four clusters. In this analysis of beech,
the basic tree and stand variables: age, relative crown spacing, stand composition and fruit bearing proved to be the most
relevant group of parameters, with the other variables explaining the variation of defoliation only to a minor extent. More
complex model levels do not change any basic selected variables; however, Cation Exchange Capacity (CEC), C/N-ratio, Al- and
Ca-proportion of CEC are additionally selected and give a hint of the relevance of soil conditions. Regarding beech, the errors
of the statistical model are lower compared to oak. 相似文献
136.
137.
Fodder grass productivity and soil fertility changes under four grass+tree associations in Kerala, India 总被引:1,自引:0,他引:1
Adapted tree+grass combinations make a valuable contribution to forage production in the Indian peninsula, but knowledge of
the interactive effects between trees and grasses on their production is limited. We, therefore, conducted a field experiment
involving combinations of four trees and grasses, besides monospecific grass controls, for seven years, to investigate grass
productivity in association with leguminous and non-leguminous multipurpose trees (MPT) having disparate canopy architecture,
and to assess the end-of-rotation soil fertility changes. Post rotation changes in herbage productivity were evaluated by
growing teosinte (Zea mexicana) for three years. The four MPTs were Acacia auriculiformis, Ailanthus triphysa, Casuarina equisetifolia and Leucaena leucocephala. Grasses included Pennisetum purpureum (hybrid napier), Brachiaria ruziziensis (congo signal), Panicum maximum (guinea grass) and teosinte. Lower tree branches were pruned from fifth year. Understorey herbage production increased until
three years in all tree+grass combinations, but declined subsequently, as tree crowns expanded. Overall, casuarina among MPTs,
and hybrid napier and guinea grass among forage crops, were more productive than others. Pruning MPTs generally favoured greater
herbage production. Understorey light levels for acacia, ailanthus, casuarina and leucaena were 17, 60, 55 and 55% of that
in the open at five years. During the post-rotation phase, MPT plots were characterised by higher soil nutrient capital and
consequently teosinte yields were higher than in the treeless control treatment. All previous tree-grass combinations showed
an increasing trend till two years after MPT felling. Yield levels declined subsequently, despite at variable rates. Careful
selection of the tree and grass components is, therefore, crucial for optimising herbage productivity in silvopastoral systems.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
138.
本文用统计分析方法对江西分宜县山下林场杉木、马尾松人工林的林内降雨、林冠截留和树干茎流进行了研究。结果表明:在该林分中林内降雨量和树干茎流量随降雨量的增加而以直线形式增加;林冠截留量随降雨量的增加呈幂函数关系上升。在杉木林内,随郁闭度的增大,林内降雨率和树干茎流率减少,而林冠截留率增大,马尾松林和杉木林相比,林内降雨率和树干茎流率较大,而林冠截留率较小。 相似文献
139.
以红松种子园中的生长形状相对一致的嫁接母树为试验材料,研究不同树冠修剪和切根方法对母树雌雄球花分化数量的影响。结果表明,不同处理均对母树雌雄球花分化数量有显著的促进作用,其中:剪去树冠第一层轮枝和顶梢部分,在第二层轮枝中选留3个生长健壮且分布均匀的侧枝,其余侧枝全部剪除的处理方法,对雌球花分化数量的增加作用最为明显,差异达到极显著水平;切断试验母树3/4环形沟中的根系和试验母树环形沟中全部根系的处理方法,对雌雄球花分化数量的增加作用最为明显,差异达到极显著水平。 相似文献
140.