全文获取类型
收费全文 | 9273篇 |
免费 | 689篇 |
国内免费 | 3篇 |
专业分类
林业 | 829篇 |
农学 | 369篇 |
基础科学 | 60篇 |
2549篇 | |
综合类 | 240篇 |
农作物 | 449篇 |
水产渔业 | 944篇 |
畜牧兽医 | 3564篇 |
园艺 | 142篇 |
植物保护 | 819篇 |
出版年
2023年 | 79篇 |
2022年 | 112篇 |
2021年 | 228篇 |
2020年 | 213篇 |
2019年 | 151篇 |
2018年 | 467篇 |
2017年 | 464篇 |
2016年 | 463篇 |
2015年 | 363篇 |
2014年 | 412篇 |
2013年 | 614篇 |
2012年 | 729篇 |
2011年 | 655篇 |
2010年 | 382篇 |
2009年 | 302篇 |
2008年 | 527篇 |
2007年 | 535篇 |
2006年 | 430篇 |
2005年 | 431篇 |
2004年 | 369篇 |
2003年 | 325篇 |
2002年 | 263篇 |
2001年 | 197篇 |
2000年 | 203篇 |
1999年 | 171篇 |
1998年 | 29篇 |
1997年 | 35篇 |
1996年 | 28篇 |
1995年 | 20篇 |
1994年 | 13篇 |
1993年 | 17篇 |
1992年 | 56篇 |
1991年 | 40篇 |
1990年 | 40篇 |
1989年 | 46篇 |
1988年 | 36篇 |
1987年 | 39篇 |
1986年 | 45篇 |
1985年 | 47篇 |
1984年 | 35篇 |
1983年 | 34篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1979年 | 31篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1974年 | 26篇 |
1973年 | 45篇 |
1972年 | 30篇 |
1971年 | 25篇 |
排序方式: 共有9965条查询结果,搜索用时 15 毫秒
101.
Jaime Puértolas Marta Pardos María Dolores Jiménez Ismael Aranda José Alberto Pardos 《Annals of Forest Science》2008,65(6):611-611
102.
103.
Bioactive plants from Argentina and Bolivia 总被引:4,自引:0,他引:4
Antibacterial and molluscicidal activities of methanol and chloroform extracts of 16 plant species belonging to the families Compositae and Melastomataceae were evaluated. The chloroform extract of Vernonanthura tweediana and the methanol extract of Senecio santelisis resulted to be very toxic to brine shrimp nauplii (LC(50)=1 microg/ml). Chloroform extracts of S. santelisis and Senecio leucostachys as well as the methanol extract of Wedelia subvaginata displayed molluscicidal effects on Biomphalaria peregrina showing LC(100)<100 microg/ml. Moderate antibacterial action was produced by the chloroform extracts of Flaveria bidentis, Grindelia scorzonerifolia and Vernonia incana against two strains of Staphylococcus aureus. 相似文献
104.
Jorge Durán Alexandra Rodríguez José María Fernández-Palacios Antonio Gallardo 《Annals of Forest Science》2010,67(2):207-207
105.
David Sánchez-Gómez Juan Majada Ricardo Alía Isabel Feito Ismael Aranda 《Annals of Forest Science》2010,67(5):505-504
106.
Insecticidal activity of Vitex mollis 总被引:3,自引:0,他引:3
Organic extracts from the leaves of Vitex mollis were assessed for their toxic effect on fall armyworm neonate larvae (Spodoptera frugiperda), an important insect pest of corn. The extracts showed insecticidal and insect growth regulatory activity, being CHCl(3)-MeOH (1:1) extract the most active, also found to be toxic in the Artemia salina test. 相似文献
107.
We present an approach to generate and evaluate different silvicultural development paths and to optimize the development of a Norway spruce stand, using a long-term planning horizon. To generate a silvicultural path, the maximum stand density was applied. At each thinning event, three possible thinning intensities (10, 20, 30% of the stem number per ha) were randomly chosen. A search algorithm known as modified Accelerated Simulated Annealing (mASA) was used to estimate the optimum combination of stand paths for a given forest as a whole. Production and economic management objectives were considered and then compared. The economic criterion was the Expected Stand Value (ESV) with a 4% discount rate. The generated data set of 38 Norway spruce stands (comprising a total of 123.8 ha) was used in the case study. The result with the best combination of paths was presented in a digitized forest map. Forest management simulation was performed using a specially developed computer program, for a planning horizon of 20 years. The mASA proved to be an effective search method for identifying optimum paths. 相似文献
108.
J. Heuveldop H. W. Fassbender L. Alpízar G. Enríquez H. Fölster 《Agroforestry Systems》1988,6(1-3):37-48
During 7 years (1979–1985) cacao harvests (beans and husks) have been recorded for the agroforestry systems ofTheobroma cacao underCordia alliodora andErythrina poeppigiana shade trees. The mean oven dry cacao yields were 626 and 712 kg.ha−1.a−1 cocoa beans underC. alliodora andE. poeppigiana respectively. Harvests have gradually increased over the years and the plantation has now reached maturity.
Annual extraction of N, P, K, Ca and Mg in fruits, which is relatively small, was calculated on the basis of chemical analyses.
The following average values were found (kg.ha−1.a−1):
At the age of 8 years, theC. alliodora trees have reached 26.7 cm diameter (DBH) and 14.0 m in height. Mean annual growth (from age 5 to 7) is 14.6 m3.ha−1.a−1.
Natural plant residue production has been measured for 4 years (Nov. 1981–Oct. 1985). UnderE. poeppigiana it has reached a value of 8.91 t.ha−1.a−1 and underC. alliodora 7.07 t.ha−1.a−1. The shade trees have contributed 57 and 47% respectively. Transference and decomposition rates are high and important in
the nutrient cycles.
The nutrient content of the litter was analysed and corresponding average yearly transfers were (kg.ha−1.a−1):
For part I see Vol. 4, No. 3, 1986.
Agroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesselschaft für Technische Zusammenarbeit),
Turrialba, Costa Rica 相似文献
109.
FlordeFátima Rosas-Cárdenas Noé Durán-Figueroa Jean-Philippe Vielle-Calzada Andrés Cruz-Hernández Nayelli Marsch-Martínez Stefan de Folter 《Plant methods》2011,7(1):4
Background
Small RNAs emerged over the last decade as key regulators in diverse biological processes in eukaryotic organisms. To identify and study small RNAs, good and efficient protocols are necessary to isolate them, which sometimes may be challenging due to the composition of specific tissues of certain plant species. Here we describe a simple and efficient method to isolate small RNAs from different plant species. 相似文献110.
In late 2003, a new disease appeared in protected bean crops in southeastern Spain, causing a decrease of over 50% in production.
Several samples of affected plants were collected and analyzed and the agent of this disease was identified as the bacterium
Erwinia aphidicola, which had never been described as a pathogen previously. We attempted to determine the possible bacterium transmission through
seeds, using 120 commercial bean seeds from the same batch as that used in an affected farm, and 120 seeds from the fruiting
plants of the same farm. Seed coats, cotyledons and leaves of plants originating from them, were taken and analyzed. Several
of the developed symptoms on plants from commercial and fruiting plant seeds were internervial chlorosis, necrotic pits and
rough roots and they coincided with those observed on affected crops. Bacteria present in commercial seed cotyledons were
isolated and analyzed by biochemical and molecular tests. Results confirmed the presence of Erwinia aphidicola in four analyzed seeds; moreover, Bacillus simplex/Bacillus muralis, Pseudomonas mendocina, Pseudomonas putida and Paenibacillus polymyxa were also identified. 相似文献