全文获取类型
收费全文 | 516篇 |
免费 | 46篇 |
专业分类
林业 | 31篇 |
农学 | 18篇 |
104篇 | |
综合类 | 15篇 |
农作物 | 30篇 |
水产渔业 | 75篇 |
畜牧兽医 | 232篇 |
园艺 | 9篇 |
植物保护 | 48篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 22篇 |
2021年 | 28篇 |
2020年 | 38篇 |
2019年 | 34篇 |
2018年 | 33篇 |
2017年 | 30篇 |
2016年 | 27篇 |
2015年 | 23篇 |
2014年 | 25篇 |
2013年 | 29篇 |
2012年 | 35篇 |
2011年 | 39篇 |
2010年 | 17篇 |
2009年 | 18篇 |
2008年 | 24篇 |
2007年 | 20篇 |
2006年 | 12篇 |
2005年 | 17篇 |
2004年 | 10篇 |
2003年 | 17篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1971年 | 3篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有562条查询结果,搜索用时 31 毫秒
501.
Rubens Ribeiro Silva Alvaro José Gomes Faria Adriana Augusta Neto Tayna Alves Pereira Jaci De Souza Dias Antônio Carlos Martins Santos 《Communications in Soil Science and Plant Analysis》2019,50(10):1267-1277
The aim of this work was to evaluate the effect of phosphorus (P) levels on nodulation and soybean production components in Cerrado soils. The experimental design was randomized in blocks, with five replicates, and four consecutive crop seasons (2013/2014, 2014/2015, 2015/2016, and 2016/2017), being cultivated in the same experimental field area. In the first three crop seasons phosphate fertilization were carried out establishing the treatments of increasing levels of P: 0, 43.6, 87.3, 131.0, and 174.6 kg ha?1, and an additional level (farm standard) of 42 kg ha?1. The results of this work refer to the crop season 2016/2017 without different P application, evaluating the influence of content of previous crop seasons. The dry weight of roots, plant population, thousand grains weight, grain yield, nitrogen (N) and P content in leaves, number and dry weight of nodules were evaluated in the reproductive stages (R2 and R8) of soybean. Increasing levels of P in soil provided significant effects on nodulation, morphological components and production of soybean plants. Levels above 40 mg dm?3 of P available in soil provided a reduction in the number and dry weight of the nodules that are highly correlated to reduction on grain yield. 相似文献
502.
Ana Patrícia Souza De Lima Andréa Carla Lira Dos Santos Hozana Leite Dantas Manoel Adrião Gomes Filho Rodrigo Maggioni Maria Raquel Moura Coimbra 《Aquaculture Research》2008,39(13):1461-1466
Loss of genetic variability can be detrimental to a population's survival traits and fitness. These effects are likely to be maximized in shrimp closed broodstock rearing systems where post‐larvae are often produced from crosses of breeders collected from an associated grow‐out farm after mass selection. Longtime broodstock management in closed systems is also expected to lead to reduction in or even complete eradication of genetic variability. The present work aimed at monitoring the genetic variability of a Litopenaeus vannamei hatchery in the state of Pernambuco (Brazil), during three successive replacements, using microsatellite markers. No significant genetic diversity losses have been observed through the values of mean heterozygosity (Ho=0.460 and He=0.660 in the first sample; Ho=0.420 and He=0.620 in the second sample; and Ho=0.600 and He=0.660 in the third sample). However, some alleles appear to have been lost after three replacements. The diversity level was considered to be high and is comparable to those reported for wild populations, suggesting that the original imported founder stock of Brazilian L. vannamei is likely to have had a high genetic diversity, possibly due to multiple origins. 相似文献
503.
Concentrations of RNA and DNA, determined in two rainbow trout strains, Cornec and Mirwart, over a period of 9 months, were used to assess and characterize growth potential. More rapid growth and higher muscle nucleic acid concentrations in the Cornac strain trout, suggest a more metabolically active strain with higher rates of protein synthesis. On the other hand, the higher concentration of muscle DNA, in the Cornec strain, suggests a smaller cell size and a larger number of cells per unit weight issue. The faster decrease of DNA concentration, with increasing body weight, in the Mirwart strain, reflected a lower percentage of hyperplasia and consequently a lower capacity for growth. 相似文献
504.
Mafalda M. R. S. Catarino Mnica R. S. Gomes Susana M. F. Ferreira Sílvia C. Gonalves 《Aquaculture Research》2019,50(3):876-881
Garra rufa has a high commercial value, but their rearing methods are still unknown. Aspects like an adequate daily dose and feeding frequency need to be investigated. This work aimed to establish the optimal feed dose per day to obtain satiation and the optimal frequency of feeding to rear a specific size class of G. rufa. A total of 60 fish were distributed by six aquaria containing 10 fish. First, the fish were fed twice per day, by providing a feed dose correspondent to 1% of their body weight and increasing 0.1 g/fish on the following days, until finding feed leftovers on the next morning. Afterwards, the fish went through a 1 month experimental trial to evaluate the optimal feeding frequency. Fish growth was compared between feeding the optimal daily dose distributed in two or three feeding moments per day. The optimal dose that ensured satiation was 0.042 g fish?1 day?1 (3.2% of fish’ body weight). Feeding the fish three times per day promoted higher growth rates, since the fish’ total length was statistically different between feeding frequencies. Statistically significant differences between feeding frequencies were not observed for growth performance parameters. These results contribute to the aquaculture of this target species, allowing fish industry to more efficiently respond to the high demand for G. rufa and, simultaneously, for its preservation in the wild. 相似文献
505.
Otvio Mesquita de Sousa Nayara Yoshimini de Oliveira Vanessa Villanova Kuhnen Eduardo Gomes Sanches 《Aquaculture Research》2019,50(10):3009-3016
Salt‐water recirculation systems using automatic feeders are a new frontier for marine aquaculture. The definition of the feed frequency is fundamental for the correct use of automatic feeders. Different feeding frequencies (1, 3, 6, 12 and 18 times a day) using automatic feeders were evaluated in two experiments on the performance of the dusky grouper (Epinephelus marginatus) in salt‐water recirculation system. In the first experiment, three feeding frequencies were evaluated: feeding once a day; three times a day and six times a day. In the second experiment, three feeding frequencies were evaluated: feeding six times a day; 12 times a day and 18 times a day. Waters parameters (temperature, salinity, oxygen level, total ammonia, pH and oxidation‐reduction potential) were maintained at specific ranges for the species. Among all the evaluated frequencies, 12 times a day provided the best productive performance, obtaining superior results for final weight, final biomass, specific growth rate and daily weight gain. For juveniles of the dusky grouper, the ideal feeding frequency is regular feedings every 2 hours, which is impractical to run without the use of automatic feeders. 相似文献
506.
The influence of the soil mineral phase on organic matter storage was studied in loess derived surface soils of Central Germany. The seven soils were developed to different genetic stages. The carbon content of the bulk soils ranged from 8.7 to 19.7 g kg—1. Clay mineralogy was confirmed to be constant, with illite contents > 80 %. Both, specific surface area (SSA, BET‐N2‐method) and cation exchange capacity (CEC) of bulk soils after carbon removal were better predictors of carbon content than clay content or dithionite‐extractable iron. SSA explained 55 % and CEC 54 % of the variation in carbon content. The carbon loadings of the soils were between 0.57 and 1.06 mg C m—2, and therefore in the ”︁monolayer equivalent” (ME) level. The increase in SSA after carbon removal (ΔSSA) was significantly and positively related to carbon content (r2 = 0.77). Together with CEC of carbon‐free samples, ΔSSA explained 90 % of the variation in carbon content. Clay (< 2 μm) and fine silt fractions (2—6.3 μm) contained 68—82 % of the bulk soil organic carbon. A significantly positive relationship between carbon content in the clay fraction and in the bulk soil was observed (r2 = 0.95). The carbon pools of the clay and fine silt fractions were characterized by differences in C/N ratio, δ13C ratio, and enrichment factors for carbon and nitrogen. Organic matter in clay fractions seems to be more altered by microbes than organic matter in fine silt fractions. The results imply that organic matter accumulates in the fractions of smallest size and highest surface area, apparently intimately associated with the mineral phase. The amount of cations adhering to the mineral surface and the size of a certain and specific part of the surface area (ΔSSA) are the mineral phase properties which affect the content of the organic carbon in loess derived arable surface soils in Central Germany most. There is no monolayer of organic matter on the soil surfaces even if carbon loadings are in the ME level. 相似文献
507.
Osnan Lennon Lameira Silva Antnia Rafaela Gonalves Macedo Emília do Socorro Conceio de Lima Nunes Keila Diniz Campos Leiliane Cristina Cardoso Araújo Xenna Tiburo Anne Suellen Oliveira Pinto Maria Regina Sarkis Peixoto Joele Micheli da Silva Ferreira Ana Carolina Ramos da Silva Renata Santana Lorenzo Raices Adriano Gomes da Cruz Leandro Juen Rossineide Martins da Rocha 《Aquaculture Research》2020,51(6):2336-2348
The objective of this study was to evaluate the effect of environmental factors on the fatty acid profiles and physicochemical composition of Crassostrea gasar cultured in two locations with differences in salinity and precipitation gradients. The study period was divided into four seasonal divisions—the rainy–dry transition period, the dry season, dry–rainy transition and the rainy season. The salinity, pH and temperature were measured at each site during specimen collection. A total of 712 oyster samples were used for fatty acid profiling and physicochemical analysis. Salinity and precipitation were the environmental parameters that influenced the fatty acid profile and physicochemical characteristics of oysters. C. gasar exhibited excellent values of n3 polyunsaturated fatty acids (DHA, EPA and eicosatrienoic), with a predominance of these acids during periods of higher precipitation. Variations in precipitation and salinity resulted in significant differences in oyster nutritional characteristics. Oysters grown in Amazonian estuaries can be considered nutritious throughout the year, with better conditions during the rainy season. 相似文献
508.
Effects of the dietary protein : lipid ratio on growth and nutrient utilization in gilthead seabream (Sparus aurata L.) 总被引:1,自引:0,他引:1
Gilthead seabream Sparus aurata L. (initial mean body weight: 42.5 g) were fed four experimental diets containing either 47 or 51% of dry matter (DM) as protein and either 15 or 21% as lipid for 12 weeks. Each diet was hand-distributed to triplicate groups of 60 fish, three times a day until satiation. The digestibility coefficients of the dietary components were determined using chromic oxide as a marker. The levels of protein or lipid in the diets did not affect the digestibility. Fish regulated their feed intake and attained the same weight at the end of the experiment. However, feed efficiency varied between diets, with best values obtained with both diets containing 21% lipid. When diets contained only 15% lipid, feed efficiency increased with dietary protein level. Nitrogen retention was significantly higher with high fat diets regardless of dietary protein level. Neutral lipid deposition was significantly higher in liver for diets rich in lipids. It was elevated in muscle only in fish fed the diet containing 47% protein and 21% lipid and this deposition in muscle contributed to a significant increase in body fat content. Phosphorus load to the environment, measured as percentage retention of ingested or digestible phosphorus, was significantly lower with both diets higher in lipids. 相似文献
509.
The wild tomato accession Lycopersicon hirsutum f. glabratum ‘PI 134417’ is a promising source of resistance to arthropods
in tomato. It is self compatible and intercrosses easily with the cultivated species Lycopersicon esculentum. It is resistant
to several arthropods, including spider mites, and these resistances have been related to the presence of high contents of
2-tridecanone (2-TD) and other methyl ketones in the leaves. The objective of this study was to evaluate the contribution
of 2-TD concentration in the leaflets of Lycopersicon for resistance to the spider mites Tetranychus urticae (Koch, 1836)
and T. ludeni Zacher, 1913. Plants of two segregating generations (F2) were evaluated through the thumbtack bioassay (Weston & Snyder, 1990) in two different assays. Both experiments included
as checks L. esculentum ‘TSWV-547’ (mite susceptible), L. hirsutum f. glabratum ‘PI 134417’ (resistant) and the interspecific
hybrid F1 (TSWV-547 × PI 134417). In the first experiment, 10 genotypes selected from F2 (TSWV-547 × PI 134417), with contrasting 2-TD concentrations in the leaflets, were tested for resistance to T. urticae. In
a second experiment, seven genotypes of the F2 (TSWV-547 × BPX-318p1#230), also with contrasting 2-TD concentrations, were used to evaluate the resistance to T. ludeni.
BPX-318p1#230 is a single plant selected from the segregating population F2 (TSWV-547 × PI 134417) for its high 2-TD content. In both experiments, high negative correlations (r = − 0.88; − 0.91 and
− 0.93 in the first experiment, and r = − 0.78, − 0.99 and − 0.96 in the second experiment) were found between the 2-TD content
and average distance travelled by the spider mites after 60, 90 and 120 minutes, respectively. The level of resistance (repellency)
to spider mites T. urticae and T. ludeni in the genus Lycopersicon appears to be mediated by the 2-TD levels present in the
tomato leaflets. The similar results of both experiments showed that selection for high 2-TD content in leaflets can lead
to genetic improvement in the direction of increased levels of spider mite resistance in tomato.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
510.
Marcio Costa Rebecca Di Pietro Jos Antonio Bessegatto Priscilla Fajardo Valente Pereira Fernanda C. Stievani Roberta Gaberlini Gomes Júlio A. N. Lisba J. Scott Weese 《The Canadian veterinary journal. La revue veterinaire canadienne》2021,62(10):1123
The purpose of this study was to characterize the fecal microbiota of horses with acute and chronic diarrhea before and after fecal microbiota transplantation (FMT). Six client-owned horses with acute and chronic diarrhea received FMT from 2 healthy donor horses. Microbiota analysis using next-generation sequencing was performed on fecal samples collected before and 2 and 7 d after FMT. Signs of diarrhea improved in 4 horses, whereas the remaining 2 horses did not survive. There was a significant difference in the number of bacterial species between donors and recipients (P < 0.05). The Order Lactobacillales and the genera Lactobacillus, Intestinimonas, and Streptococcus were increased in the microbiota of diarrheic horses, and Saccharofermentans genus increased in healthy donors. The results suggest that FMT from the healthy donors was not effective over a 7-day period as it did not change the fecal microbiota of the diarrheic horses. Further research to improve the efficacy of FMT in horses is needed. 相似文献