全文获取类型
收费全文 | 12489篇 |
免费 | 767篇 |
国内免费 | 1301篇 |
专业分类
林业 | 1661篇 |
农学 | 893篇 |
基础科学 | 819篇 |
2653篇 | |
综合类 | 5055篇 |
农作物 | 538篇 |
水产渔业 | 956篇 |
畜牧兽医 | 682篇 |
园艺 | 204篇 |
植物保护 | 1096篇 |
出版年
2024年 | 81篇 |
2023年 | 276篇 |
2022年 | 429篇 |
2021年 | 464篇 |
2020年 | 468篇 |
2019年 | 573篇 |
2018年 | 393篇 |
2017年 | 563篇 |
2016年 | 677篇 |
2015年 | 555篇 |
2014年 | 689篇 |
2013年 | 806篇 |
2012年 | 922篇 |
2011年 | 921篇 |
2010年 | 735篇 |
2009年 | 752篇 |
2008年 | 653篇 |
2007年 | 688篇 |
2006年 | 581篇 |
2005年 | 395篇 |
2004年 | 393篇 |
2003年 | 302篇 |
2002年 | 277篇 |
2001年 | 225篇 |
2000年 | 203篇 |
1999年 | 185篇 |
1998年 | 167篇 |
1997年 | 150篇 |
1996年 | 131篇 |
1995年 | 160篇 |
1994年 | 111篇 |
1993年 | 119篇 |
1992年 | 111篇 |
1991年 | 91篇 |
1990年 | 90篇 |
1989年 | 92篇 |
1988年 | 61篇 |
1987年 | 36篇 |
1986年 | 12篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1963年 | 2篇 |
1962年 | 2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
951.
咸宁市红汁乳菇的分布和生态考察报告 总被引:2,自引:0,他引:2
经初步考察 ,咸宁市红汁乳菇分布广泛。发生时间为 4月下旬至 1 1月上旬。发生的迟早、发生量及持续时间的长短与海拔、土壤、植被、坡向、气候等因素有关 ,尤其是与发生时期内温度和降雨量的关系最大。 相似文献
952.
浙江分布新记录——白花映山红 总被引:1,自引:0,他引:1
报道了在浙江温岭大溪镇水坦村岩火尖发现的浙江分布新记录植物:白花映山红(Rhododendron simsii vat.albiflorum),并对其形态特征、生境及伴生植物作了介绍。 相似文献
953.
HU Yanjie LIN Fengming SHI Kunshan Research Institute of Forestry Policy Information Chinese Academy of Forestry Beijing P.R.China 《中国林业科技(英文版)》2007,6(2):62-73
The historical transition of timber distribution pattern in China was presented firstly with main parts of timber flows in China, which included timber markets, timber transport system and regulations of timber transport. Based on the overview on tropical timber flows in China, the trade flows of tropical timber from production and imports of tropical timber to export of tropical timber products were analyzed by vivid illustrations. At the same time, problems in timber trade flows in China were analysed in the end. 相似文献
954.
The plants of the genus Abies are dominant and key species in the dark coniferous forest in the Northern Hemisphere. There are 52 species, one subspecies
and 12 varieties in the genus Abies in the world. The history and modern distribution of Abies were discussed. The genus has three modern distribution centers: South Europe, North America and East Asia. These areas are
also rich in fossil records. The vertical distribution regions of Abies are from sea level to an elevation of 4,700 m, concentrated in 1,000–2,000 m (15 species). In China, the genus distributes
in 20 provinces, especially abundant in the Hengduan Mountains. Meanwhile, endemic and relic phenomena are obvious in this
genus. There are seven relic species with both limited individuals and limited distributed regions. Based on the fossil records
and the latest phylogenetic data, the following hypothesis was proposed: Abies originated from the middle and high altitudes of the Northern Hemisphere in the middle Cretaceous and it was dispersed southward
in the Eocene due to global climate cooling down. The distribution of Abies was deeply influenced by geological events such as the uplift of Himalaya, the Alps, the Rocky Mountains, the occurrence
of the Asian Monsoon as well as the Quaternary glaciers. Finally, the current distribution pattern appeared in the Quaternary.
The genus Abies has a fossil history and modern distribution pattern similar to that of Cathaya and Pseudolarix.
__________
Translated from Acta Botanica Yunnanica, 2006, 28(5): 439–452 [译自: 云南植物研究] 相似文献
955.
毛竹蚧虫—蠕须盾蚧的观察研究 总被引:4,自引:0,他引:4
本文报导为害毛竹秆部的主要蚧虫——蠕须盾蚧。经多年来观察研究,在福建省尤溪、沙县、南平、建瓯、上杭等县市的毛竹林中常受该虫为害,严重者毛竹秆受害率达70%—90%。该虫一年发生2代,大量以成虫和少量以卵在雌介壳中越冬,5—6月和9—10月为为害的高峰期,而且世代重叠严重。其天敌发现有日本方头甲等多种;经药剂防治试验结果,以快灭磷、氧化乐果等农药,采用注射法或涂秆法效果显著。 相似文献
956.
Cynthia G. Locasio B. G. Lockaby Jon P. Caulfield M. Boyd Edwards M. Keith Causey 《New Forests》1990,4(4):261-269
Diversity of understory vegetation was compared among four intensities of site preparation and an adjacent 50-year-old pine-hardwood forest. The study site was a six-year-old loblolly pine (Pines taeda) plantation in the lower Piedmont of Georgia. Species richness and Shannon diversity indices were used to evaluate vine and woody (trees and shrubs) species diversity. Biomass distribution was compared among four plant categories: vines, forbs, grasses, and woody. Moderate intensity treatments (chainsaw and shear and chop) consistently ranked highest overall in diversity, with the mature pine-hardwood forest ranking lowest. Distribution of the four plant categories was not significantly affected by intensity of site preparation.Alabama Agricultural Experiment Station Series No. 9-892325P. 相似文献
957.
Bijan Payandeh 《New Forests》1988,2(3):145-160
Drainage and fertilization of an existing peatland black spruce (Picea mariana (Mill.) B.S.P.) stand and 24 possible methods of planting a clear-cut area near Cochrane, Ontario were evaluated by means of a recently developed forestry investment decision model, FIDME.Results indicate that, on the basis of the cost estimates used and assumptions made, drainage of the existing stand is the most economical treatment if it can reduce the rotation age by 30 years or more. Drainage combined with fertilization is the second best alternative if this treatment can reduce the rotation age by 40 years or more. Fertilization of the undrained site ranks a distant third, and then only if it reduces the rotation age by 10 years; otherwise, it will be uneconomical to apply.In the case of the clear-cut area, planting bare-root stock on a mechanically prepared but undrained site without weed control ranked first among the 24 alternatives considered; the same treatment, but with weed control included, ranked second. Planting containerized seedlings on a mechanically prepared but undrained site with weed control ranked third, followed by planting bare-root stock on a mechanically prepared and drained site with weed control. In contrast, planting containerized seedlings on an unprepared site and with no weed control ranked as the least cost-effective method considered. 相似文献
958.
959.
作者在编写《河北灌木志》绣线菊属时,对采于河北境内的本属植物标本进行了分类与分布研究。现知河北原产17种3变种,其中1新种,2河北新分布记录种,1河北新分布记录变种。编制了分种检索表;指出了相近种的区别点;简略记述了适生条件及分布区域。 相似文献
960.
云杉树叶象幼虫空间分布型及其抽样技术研究 总被引:3,自引:0,他引:3
为调查云杉树叶象幼虫在云杉S2-2、S2-3、S2-4苗龄型苗木上空间分布型及开展抽样技术调查研究,在云杉苗木中共设置了30块样地对该幼虫进行了调查。通过应用数理统计方法分析后得出:该幼虫有虫株率分布在云杉S2-2苗龄型苗木上呈对数函数分布趋势;在云杉S2-3、S2-4苗龄型苗木上呈指数函数分布趋势。应用聚集指标法分析得出:该幼虫空间分布型属聚集分布,并通过Iwao回归分析法和Toylor幂法则分析得出,云杉S2-2、S2-3苗龄型苗木上的幼虫个体间相互排斥;云杉S2-4苗龄型苗木上的幼虫个体间相互吸引。同时,应用Iwao的m*-m关系和序贯抽样方法,确定出了该幼虫的理论抽样数及抽样上限值和下限值。 相似文献