全文获取类型
收费全文 | 13523篇 |
免费 | 670篇 |
国内免费 | 988篇 |
专业分类
林业 | 3480篇 |
农学 | 957篇 |
基础科学 | 667篇 |
1352篇 | |
综合类 | 5614篇 |
农作物 | 1167篇 |
水产渔业 | 135篇 |
畜牧兽医 | 764篇 |
园艺 | 503篇 |
植物保护 | 542篇 |
出版年
2024年 | 55篇 |
2023年 | 156篇 |
2022年 | 329篇 |
2021年 | 399篇 |
2020年 | 355篇 |
2019年 | 463篇 |
2018年 | 316篇 |
2017年 | 500篇 |
2016年 | 672篇 |
2015年 | 530篇 |
2014年 | 768篇 |
2013年 | 764篇 |
2012年 | 1061篇 |
2011年 | 977篇 |
2010年 | 870篇 |
2009年 | 830篇 |
2008年 | 710篇 |
2007年 | 712篇 |
2006年 | 650篇 |
2005年 | 595篇 |
2004年 | 402篇 |
2003年 | 380篇 |
2002年 | 287篇 |
2001年 | 338篇 |
2000年 | 258篇 |
1999年 | 258篇 |
1998年 | 231篇 |
1997年 | 189篇 |
1996年 | 181篇 |
1995年 | 151篇 |
1994年 | 140篇 |
1993年 | 129篇 |
1992年 | 117篇 |
1991年 | 92篇 |
1990年 | 101篇 |
1989年 | 65篇 |
1988年 | 69篇 |
1987年 | 40篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 3篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1963年 | 2篇 |
1962年 | 1篇 |
1956年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
应用大叶相思、肯氏相思、毛娟相思、马占相思和厚荚相思等相思树种在东山县沿海沙地上营建防护林,并对其抗风、抗台风及抗连续干旱性能进行了测定。结果表明:厚荚相思抗风能力强,生长快,是较好的可在沿海沙地上适生的树种;相思树种抗台风能力较木麻黄弱,台风对相思树种的主要危害是断梢,但在以后的生长中能较快地得到恢复,对相思林分生长并不会产生大的影响;厚荚相思在沿海沙地上造林,不仅成活率高(95%以上),而且在遭受连续8个月的干旱后,旱死率为0,表现出很强的抗旱能力,而且在贫瘠的沙地土壤上生长表现良好,其生长量超过了木麻黄601无性系,是非常好的适合于沿海沙地条件的树种。 相似文献
902.
常江 《内蒙古林业调查设计》2001,24(2):11-12,42
文章根据西部地区的特点和生态建设的性质 ,提出创新产业机制 ,挖掘人才 ,以生物高科技为核心技术 ,充分应用现代农业技术 ,构建生态科技产业的途径。提高西部风蚀沙化地的利用水平 ,促进产业结构调整 ,加快区域特色经济的产业化进程 ,实现本地区可持续发展。 相似文献
903.
904.
In India, mangroves occupy 6740 km2 of which the Mahanadi delta andBhitarkanika mangrove forests of Orissa cover 191.44 km2, most of whichhas been severely overexploited. World wide concern to conserve mangrovesnecessitated propagation of mangroves to re-establish them on barren andswampy land along tidal creeks around Paradeep port of Orissa. Avicenniaofficinalis, Aegiceras corniculatum, Bruguiera parviflora, B. sexangula,Ceriops decandra, Excoecaria agallocha, Heritiera fomes, Kandelia candel,Rhizophora mucronata, Sonneratia apetala were vegetatively propagated andplanted over 10 ha of degraded salt-marshy wetlands of Mahanadi delta inpure and mixed stands depending on the intensity and the frequency of tidalinundation at the experimental site. Survival was significantly higher(80%) in S. apetala followed by A. officinalis, R. mucronata, K.candel and H. fomes (70–75%). S. apetala recorded the maximumgrowth in height (3.0 m after 2 years) whereas C. decandra showed theminimum growth (0.5 m). Growth performance was better with plants in mixedstands than the plantation with single species. This gives us hope topropagate and re-establish mangroves for conservation in scientificallymanaged plantations in a physiologically arid environment. 相似文献
905.
论一元立木材积模型的研建方法 总被引:5,自引:1,他引:5
对建立一元立木材积模型的两种常规方法进行了深入分析,提出了以树高—胸径模型为基础的二阶回归估计方法。利用该方法既可以提高模型切合性能,又能有效控制模型的拟合误差,并以西藏自治区的四旁树一元立木材积模型为例进行了说明。 相似文献
906.
Forage and wood yield of Acacia cyanophylla, also known as Acacia saligna, was studied in a 300–400 mm precipitation zone in Tunisia. Yields were measured during and after drought. This short (2–8
m) evergreen leguminous tree is used as a forage drought reserve in frost free regions where mean annual precipitation exceeds
250 mm. The standing crop of leafy forage builds up year after year for at least four years or until the tree is cut. It rapidly
regrows after cutting from coppice shoots. The leaves provide high protein forage for sheep and goats during the long dry
summer season typical of the Mediterranean climate as well as emergency forage during drought. The tree is used to stabilize
moving sand dunes, and as a windbreak to protect cropland. It also provides fuelwood and increasaes soil nitrogen by fixation.
The need for supplemental irrigation during establishment is a major constraint.
Research in the 350 mm precipitation zone of Tunisia found 3.2 year old trees to yield over 1400 kg of forage standing crop
per hectare after a severe drought. Trees harvested at 2.5 years of age in May, during the worst drought in over 30 years,
yielded a standing forage crop of 724 kg per hectare. Forage regrowth 8 months after cutting and 4 months after rains returned
was 700 kg/ha. The forage standing crop for trees harvested only once during the 3.2 year period was double the amount of
forage regrowth from trees harvested the previous year, but mean annual forage yield similar. This demonstrates that it is
possible for forage to be conserved as a living forage reserve for later use during drought. Total wood yield was only 1621
kg/ha for trees cut twice compared to 3683 kg/ha for trees cut only once.
Annual cutting will substantially reduce the amount of forage available during drought and reduce the production of fuelwood.
It may also reduce the vigor, productivity and life of the tree. Acacia cyanophylla alley cropped on cereal farmland can protect the soil from erosion, protect the associated crop from wind damage, fix nitrogen,
provide fuelwood and provide a reserve of high quality forage for use during drought.
This work was supported by the Government of Tunisia and the U.S.A.I.D. Tunisia Range Development and Management Project (664-0312.8). 相似文献
907.
908.
通过对多年来西双版纳高海拔山地逆温和橡胶树试种研究资料分析,论述了以坡向为主导因素的西双版纳高海拔山地小气候和精选橡胶树宜林地的问题,为制止盲目扩种橡胶树提供依据。 相似文献
909.
The conversion of anthropogenic into more natural, self-regenerating forests is one of the major objectives of forestry throughout
Europe. In this study, we present investigations on permanent plots with different silvicultural treatment in NE German pine
stands. Management of old-growth pine stands on acidic and nutrient-poor sandy sites differs in fencing, thinning, and planting
of certain tree species. The investigations were carried out on the community, population, and individual level of the pine
forest ecosystems. Thus, vegetation changes, size and height of tree populations, and height increment of tree individuals
were observed over a time span of 6 years. Special attention was paid to short-lived tree species such as, e.g., Frangula alnus and Sorbus aucuparia, as well as to Fagus sylvatica as one of the most typical forest tree species of Central Europe. Vegetation changes are interpreted as a consequence of
natural regeneration of formerly degraded forest sites, involving an increase in nutrient availability. High browsing pressure
can be considered as a key factor for the inhibition of tree seedlings and growth of saplings. Some Sorbus aucuparia individuals, however, succeeded in growing out of the browsing height also in unfenced stands. Few found specimens of Fagus sylvatica proved that this species is able to establish spontaneously on these relatively dry, acidic sites under continental climate
influence. Such natural regeneration processes, also including spontaneous rejuvenation of trees, can be integrated into silviculture
as passive forest conversion management. An active management like thinning of stands, planting of trees, and fencing can
accelerate forest conversion with regard to height growth and species number of trees. 相似文献
910.