全文获取类型
收费全文 | 1506篇 |
免费 | 153篇 |
国内免费 | 1篇 |
专业分类
林业 | 124篇 |
农学 | 85篇 |
基础科学 | 2篇 |
269篇 | |
综合类 | 34篇 |
农作物 | 103篇 |
水产渔业 | 153篇 |
畜牧兽医 | 726篇 |
园艺 | 22篇 |
植物保护 | 142篇 |
出版年
2024年 | 1篇 |
2023年 | 26篇 |
2022年 | 51篇 |
2021年 | 93篇 |
2020年 | 95篇 |
2019年 | 95篇 |
2018年 | 101篇 |
2017年 | 96篇 |
2016年 | 91篇 |
2015年 | 67篇 |
2014年 | 82篇 |
2013年 | 97篇 |
2012年 | 111篇 |
2011年 | 125篇 |
2010年 | 56篇 |
2009年 | 50篇 |
2008年 | 62篇 |
2007年 | 73篇 |
2006年 | 62篇 |
2005年 | 32篇 |
2004年 | 37篇 |
2003年 | 25篇 |
2002年 | 30篇 |
2001年 | 21篇 |
2000年 | 11篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1966年 | 1篇 |
1962年 | 1篇 |
1937年 | 1篇 |
排序方式: 共有1660条查询结果,搜索用时 31 毫秒
31.
32.
Morlin Carneiro Franciele Angeli Furlani Carlos Eduardo Zerbato Cristiano Candida de Menezes Patricia da Silva Gírio Lucas Augusto Freire de Oliveira Mailson 《Precision Agriculture》2020,21(5):979-1007
Precision Agriculture - Crop monitoring through remote sensing techniques enable greater knowledge of average variability in crop growth. Canopy sensors help provide information on the variability... 相似文献
33.
da Silva Isadora Gonçalves Castoldi Renata de Oliveira Charlo Hamilton César de Souza Miranda Mateus Nunes Thaíssa Dias Cardoso Costa Luciene Lacerda Lemes Ernane Miranda 《Journal of Crop Science and Biotechnology》2020,23(2):191-196
Journal of Crop Science and Biotechnology - The cultivation of sweet corn is expanding in Brazil, but there are serious constraints about the availability of commercial cultivars. The selection of... 相似文献
34.
Fabrício Alves Oliveira Derly José Henriques da Silva Germano Leão Demolin Leite Gulab Newandram Jham Marcelo Picanço 《Scientia Horticulturae》2009
The aim of this study was to evaluate resistance to Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) by antixenosis on 57 Lycopersicon esculentum Mill. accessions from the Horticultural Germplasm Bank (HGB) of Universidade Federal de Viçosa and by the three commercial cultivars (Santa Clara, Moneymaker and TOM-601) under greenhouse conditions. A randomized complete block design was used with three replications. Infestations with T. absoluta adults were performed weekly and the following characteristics were evaluated: number of small, large and total mines/leaf and % of leaves mined at days 60, 75 and 90 after planting. Low infestation occurred at days 60 and 75 but at day 90, infestation was sufficient to evaluate insect damage. Based on these data it was concluded that only accessions HGB-674 and HGB-1497 appeared to be the most promising. In addition, to determine possible chemical causes of resistance, hexane extracts were analyzed at day 90 by gas chromatography/mass spectrometry and the major peaks identified by a mass spectral database using similarity index. Nine hydrocarbons, viz., hexadecane, heptadecane, eicosane, tricosane, 2-methyltricosane, tetracosane, hexacosane, octacosane and triacontane were identified in the hexane extracts in many samples. Tricosane, tetracosane and hexacosane presented significant correlations with the leaves mined. Only tricosane presented a negative correlation with the number of small mines (r = −0.28), total number of mines (r = −0.27) and % of leaves mined (r = −0.22). However, tetracosane and hexacosane presented significant positive correlations (r = 0.25 and 0.24, respectively) with the % of leaves mined. 相似文献
35.
36.
Effects of density on growth and survival of juvenile Red Swamp Crayfish, Procambarus clarkii (Girard), reared under laboratory conditions 总被引:2,自引:0,他引:2
Ricardo Oliveira Ramalho Alexandra Marçal Correia & Pedro Manuel Anastácio 《Aquaculture Research》2008,39(6):577-586
The aim of this study was to quantify the importance of population density on the growth and survival of juvenile red swamp crayfish, Procambarus clarkii (Girard), and to understand the effects of density on both the period between moults and the increment per moult at high densities without food limitation. A laboratory experiment was performed to determine growth and survival of juvenile crayfish at five densities (20, 40, 60, 80 and 100 crayfish m?2). Density clearly affected crayfish growth. The impact of density on final weight was higher than on total length increase, growth rate and final length (FL) (by decreasing order of effect). When comparing minimum and maximum densities, we observed that FL suffered a 34% reduction. Number of moults, mean intermoult period (IP) and survival were not significantly affected by density. Our results indicated that the IP and the percentage of increment per moult are affected by the size of crayfish before moult and we provide equations for these relations. Our findings are relevant both for crayfish aquaculture management and for the management of wild or harvested rice‐field crayfish populations. 相似文献
37.
Leila Hayashi Nair S. Yokoya Srgio Ostini Ricardo T.L. Pereira Elisabete S. Braga Eurico C. Oliveira 《Aquaculture (Amsterdam, Netherlands)》2008,277(3-4):185-191
The potential of the red alga Kappaphycus alvarezii to remove nutrients was tested to treat effluents of Trachinotus carolinus fish cultivation, and the production of carrageenan in this condition was analyzed. Experiments were conducted in four tanks of 8000 L with approximately 1200 fishes of 30 g each integrated with three tanks of 100 L with 700 g of K. alvarezii, as initial biomass per tank. Seawater was re-circulated between tanks with seaweed and with fish. As a control, three tanks with seawater circulating in an open system were utilized. Seawater samples were collected daily for 10 days and concentrations of nitrate, nitrite, ammonium and phosphate were determined in the inflow and outflow water of the tanks. Significant differences between both collecting points were considered as nutrient removal by the seaweed. Growth rates and carrageenan yields were also analyzed in seaweed cultivated in seawater and in effluents. Growth rates of seaweed cultivated in tanks were lower than those obtained in open sea and in laboratory cultivation. Effluents had concentrations of nitrate and nitrite ca. 100 times higher than in the control. Maximum values of nutrient removal on effluents were: nitrate = 18.2%; nitrite = 50.8%; ammonium = 70.5% and phosphate = 26.8%. All plants survived throughout the experimental period, but some developed “ice–ice”, a disease associated with physiological stress. After the experimental period, some plants selected and cultivated in open sea presented higher growth rates in 40 days, indicating nutrient storage. No significant differences between carrageenan yields of K. alvarezii cultivated in seawater and in the effluents were observed. Our results show that K. alvarezii can be utilized as a biofilter for fish cultivation effluents, reducing the eutrophication process and can also be processed for carrageenan production, which provides an additional benefit to the fisheries. 相似文献
38.
The Neotropical freshwater fish fauna is very rich—according to the most recent catalogue 71 families and 4,475 species have
been described. However, only a small amount of general information is available on the composition of Neotropical marine
fishes. In Brazil, 1,298 marine species have been recorded. General analysis of available cytogenetic and population genetic
data clearly indicates research has been mainly concentrated on freshwater fishes. Thus, today, cytogenetic information is
available for 475 species of Characiformes, 318 species of Siluriformes, 48 species of Gymnotiformes, 199 freshwater species
that do not belong to the superorder Ostariophysi, and only 109 species of marine fishes. For the species studied, only about
6% have sex chromosomes and about 5% have supernumerary or B chromosomes. A review of the cytogenetic studies shows that these
data have provided valuable information about the relationships between fish groups, the occurrence of cryptic species and
species complexes, the mechanism of sex determination and sex chromosome evolution, the distribution of nucleolus organizer
regions, the existence supernumerary chromosomes, and the relationship between polyploidy and evolution. In relation to populations
in Neotropical marine waters, the studies have shown the presence of cryptic species, which has important implications for
fishery management. Different levels of genetic structuring can be found among Neotropical freshwater migratory fish species.
This raises important implications for fish population genetic diversity and consequently its sustainable utilization in inland
fisheries and aquaculture, specifically for conservation of ichthyo-diversity and survival. 相似文献
39.
40.