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91.
Stable isotopes of nitrogen are potentially a valuable tool for regional assessments of nitrogen saturation because they provide an integrated measure of the past nitrogen cycling history of a site. We measured δ15N of soil and litter, as well as net nitrification potential, at three sites across a nitrate-loss gradient in the White Mountains, New Hampshire to test the hypotheses: (1) that δ15N in soil and litter increase across a spatial gradient of nitrate loss; and (2) that δ15N in soil and litter is elevated when nitrification is elevated. δ15N was found not to vary significantly among the three sites. Patterns of leaf litter and forest floor δ15N, however, were strongly influenced by species composition in individual plots. Beech litter had significantly higher δ15N than yellow birch, sugar maple, and red maple. The conifer-dominated plots had significantly lower δ15N in both the organic soil horizons and in litter than did the hardwood-dominated plots. When we adjusted for spatial heterogeneity in mineral soil δ15N values by using an enrichment factor, δ15Nfoliar − δ15NBs, in place of absolute soil δ15N values, a positive relationship was found with net nitrification for hardwoods. δ15N may also be a useful tool for evaluating species differences in nitrogen cycling and nitrogen uptake. The distinct pattern we observed of decreasing δ15N across the continuum from hardwood-dominated to conifer-dominated sites may suggest that local drivers (for example, nitrification rate) regulate the absolute value of foliar δ15N, while species-driven factors (e.g., timing and type of uptake) control the foliar δ15N value of one species relative to another in the same plot. 相似文献
92.
In order to infer successional changes in structure, species composition and diversity of warm-temperate forest, we compared secondary stands regenerating after clear-felling (41–64-years old) with old-growth stands at altitudes between 300 and 800 m on Yakushima Island, southern Japan. Stem density and maximum stem diameter differed between secondary and old-growth stands, but basal area and aboveground biomass did not. At lower altitudes, the dominant species in old-growth stands with a strong sprouting capacity (Castanopsis cuspidata) also dominated secondary stands, and species composition of secondary and old-growth stands was similar. At higher altitudes, by contrast, the dominant species in old-growth stands (Distylium racemosum) had little sprouting capacity and was poorly represented in diverse secondary stands, which were dominated by Castanopsis or other less abundant species. Secondary stands had greater species diversity (Shannon–Wiener index) than old-growth stands, particularly at higher altitudes. This was due to greater species richness resulting from higher stem density per area, but not to greater evenness. We grouped the component species that share ecologically similar traits into four guilds (fagaceous, primary evergreen, secondary evergreen and deciduous species). Secondary stands were characterized by greater numbers of deciduous and secondary evergreen species. We concluded that different sprouting capacities of dominant species and different regeneration traits among guilds are responsible for the change in species composition and diversity during succession. 相似文献
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96.
华中神农架箭竹(Fargesia spathacea)群落之海拔多样性(英文) 总被引:5,自引:0,他引:5
通过对华中神农架海拔1500米至2600米之间11个箭竹样方的研究,阐述了箭竹群落物种丰富度,物种多样性,物种均匀性,生活型谱及群落类型的海拔变化。从最低样方(1680米)到最高样地(2570米),微管束植物从30种降为7种,服从线性模型:Y=55.991.83X(R2=0.84,P<0.001);物种多样性从3.18降为1.78,服从线性模型:Y=4.670.10X (R2=0.72,P=0.001;物种均匀度在0.83至0.99之间变化,但与海拔并不相关。在生活型谱中,一年生植物,地下芽植物和大高位芽树木的百分比随海拔升高而升高;灌木和中高位芽树木随海拔升高而降低;多年生草本和半灌木与海拔关系不大。箭竹群落可分为5种类型:常绿阔叶林下,落叶阔叶林下,温性针叶林下,寒温性针叶林与混交林下,纯箭竹林。图4表2参19。 相似文献
97.
XIAO Jian-hua 《河南林业科技》2015,35(1)
在信阳市城市园林植物种类与生长状况实地调查的基础上,结合2002年至2012年连续3次信阳市园林植物普查资料,澄清了信阳市城市园林绿化植物种类及分布情况。调查结果表明,信阳市城市应用园林绿化植物物种较为丰富,共276种,同时新筛选出适生乡土园林绿化植物35种。分析了信阳市园林植物应用配置中存在的问题,提出了信阳市园林植物应用发展对策,对指导信阳市城市园林绿化工作有积极作用。 相似文献
98.
对太原市河流生态廊道和道路生态廊道的草本植被进行调查,分析其植物种类构成和分布格局,探讨城市生态廊道植物多样性及景观效益。结果表明,太原城市生态廊道草本植物有 174 种,隶属于 41 科 20 属,其中乡土植物 107 种,所占比例 61.49%;外来植物 48 种,所占比例 27.59%;入侵植物 19 种,所占比例 10.92%。相关分析表明,距离城市中心越远,调查样点草本植物多样性越高,可见城市化进程降低了城市生态廊道的植物丰富度。总体来看,道路生态廊道草本植被多样性高于河流生态廊道。不同廊道中入侵种占比的分布规律并不一致,河流生态廊道入侵种比例随着城市中心距离的增加而增加;而道路生态廊道恰恰相反,距城市中心越近,入侵种占比反而越大。 相似文献
99.
由于蝴蝶对环境变化反应比较灵敏,常被作为检测环境质量变化的指示生物。对宁夏云雾山国家级自然保护区蝶类群落的结构组成与多样性做了初步调查。结果表明:云雾山蝴蝶共有29种,隶属于6科26属。其中,眼蝶科的属和物种数量最多,为8属8种;凤蝶科最少,仅1属1种。通过Margalef物种丰富度指数、Shannon-Wiener多样性指数、Pielou均匀度指数和Berger-Parker优势度指数对蝶类的多样性进行分析,眼蝶科的多样性指数最高,但均匀度指数和优势度指数均最低,分别为1.57、0.76和0.28;弄蝶科的丰富度指数最高,达到1.31;蛱蝶科的优势度指数最高,达到0.44;灰蝶科的均匀度指数最高,但多样性指数最低,分别为0.96和1.34;粉蝶科的丰富度指数最低,为0.82。眼蝶科在云雾山保护区是优势科,物种丰富,但物种相对集中,群落结构不稳定,而凤蝶科物种较为贫乏,需要对其加以保护。 相似文献
100.
The annual dynamics of fish assemblage in a pond-connecting canal of a South Moravian pond aquaculture facility was studied
to reveal potential assemblage effects on pond stocks and vice versa. The species richness of fish assemblage and seasonal
dynamics of its development were predominantly dependent upon the fish stock of the interconnected ponds (particularly due
to escapees during the period of pond harvesting), which contributed to a considerable increase of commercial fish species
occurrence. Using a seasonal parameter, the season proved to have a major impact on fish assemblage dynamics (r = −0.71, P < 0.001). Spring samples were dominated by commercial fishes of aquaculture origin (mainly Cyprinus carpio). Occurrence of several fish species originating from the wild (bleak, Alburnus alburnus, chub, Leuciscus cephalus and roach, Rutilus rutilus) was also reported.
The pond canal was found to be an important reservoir site of persistent survival and potential subsequent spreading of some
undesirable alien fishes such as topmouth gudgeon (Pseudorasbora parva) and gibel carp (Carrasius auratus). Moreover, more attention should be paid to the potential negative impacts of all fishes of aquaculture origin upon the
natural ecosystem and to the adverse effects due to the immigration of wild fish into aquaculture pond farming units. 相似文献