全文获取类型
收费全文 | 561篇 |
免费 | 56篇 |
国内免费 | 1篇 |
专业分类
林业 | 38篇 |
农学 | 20篇 |
148篇 | |
综合类 | 27篇 |
农作物 | 33篇 |
水产渔业 | 83篇 |
畜牧兽医 | 176篇 |
园艺 | 8篇 |
植物保护 | 85篇 |
出版年
2023年 | 5篇 |
2022年 | 8篇 |
2021年 | 15篇 |
2020年 | 17篇 |
2019年 | 19篇 |
2018年 | 31篇 |
2017年 | 23篇 |
2016年 | 26篇 |
2015年 | 28篇 |
2014年 | 30篇 |
2013年 | 34篇 |
2012年 | 42篇 |
2011年 | 40篇 |
2010年 | 26篇 |
2009年 | 21篇 |
2008年 | 41篇 |
2007年 | 27篇 |
2006年 | 30篇 |
2005年 | 31篇 |
2004年 | 17篇 |
2003年 | 15篇 |
2002年 | 17篇 |
2001年 | 12篇 |
2000年 | 19篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 6篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1966年 | 1篇 |
1945年 | 1篇 |
1944年 | 1篇 |
排序方式: 共有618条查询结果,搜索用时 15 毫秒
91.
Effect of the addition of Chaetoceros calcitrans,Navicula sp. and Phaeodactylum tricornutum (diatoms) on phytoplankton composition and growth of Litopenaeus vannamei (Boone) postlarvae reared in a biofloc system 下载免费PDF全文
Yllana Ferreira Marinho Luis Otavio Brito Clarissa Vilela Figueiredo da Silva Campos William Severi Humber Agrelli Andrade Alfredo Olivera Galvez 《Aquaculture Research》2017,48(8):4155-4164
The aim of this study was to evaluate the effect of the addition of Chaetoceros calcitrans, Navicula sp. and Phaeodactylum tricornutum (diatoms) on phytoplankton composition and the growth of Litopenaeus vannamei postlarvae reared in a biofloc system . Four treatments were used: BFT (biofloc system without feed and no addition of diatoms); BFT‐F (biofloc system with feed and no addition of diatoms); BFT‐D (biofloc system with the addition of diatoms and no feed); and BFT‐FD (biofloc system with the addition of feed and diatoms), all in triplicate. The shrimp (16 ± 0.02 mg) were stocked at 2500 postlarvae m?3 and fed a commercial feed. Diatoms were added on the 1st, 5th, 10th and 15th day at a density of 5 × 104 cells mL?1 for each species. No significant differences (P > 0.05) between treatments were observed for gross primary production, net ecosystem production and water column respiration rate. However, significant differences (P < 0.05) were observed for nitrite, orthophosphate, alkalinity, final weight, weight gain, yield, feed conversion ratio (FCR), phytoplankton and cyanobacteria composition. The BFT‐FD treatment had better performance parameters for final weight (270 mg), weight gain (254 mg), yield (0.67 Kg m?3) and FCR (0.61), indicating the benefits of the diatoms C. calcitrans, Navicula sp. and P. tricornutum for decreasing cyanobacteria and improving growth of L. vannamei postlarvae reared in biofloc systems. 相似文献
92.
Prevalence,geographic distribution and phenotypic differences of Piscirickettsia salmonis EM‐90‐like isolates 下载免费PDF全文
J Saavedra N Hernandez A Osses A Castillo A Cancino H Grothusen E Navas P Henriquez H Bohle F Bustamante P Bustos M Mancilla 《Journal of fish diseases》2017,40(8):1055-1063
Early reports accounted for two main genotypes of Piscirickettsia salmonis, a fish pathogen and causative agent of piscirickettsiosis, placing the single isolate EM‐90 apart from the prototypic LF‐89 and related isolates. In this study, we provide evidence that, contrary to what has been supposed, the EM‐90‐like isolates are highly prevalent and disseminated across Chilean marine farms. Molecular analysis of 507 P. salmonis field isolates derived from main rearing areas, diverse hosts and collected over 6 years, revealed that nearly 50% of the entire collection were indeed typed as EM‐90‐like. Interestingly, these isolates showed a marked host preference, being recovered exclusively from Atlantic salmon (Salmo salar) samples. Although both strains produce undistinguishable pathological outcomes, differences regarding growth kinetics and susceptibility to the antibiotics and bactericidal action of serum could be identified. In sum, our results allow to conclude that the EM‐90‐like isolates represent an epidemiologically relevant group in the current situation of piscirickettsiosis. Based on the consistency between genotype and phenotype exhibited by this strain, we point out the need for genotypic studies that may be as important for the Chilean salmon industry as the continuous surveillance of antimicrobial susceptibility patterns. 相似文献
93.
H.M. Díaz-Mula P.J. Zapata F. Guillén D. Martínez-Romero S. Castillo M. Serrano D. Valero 《Postharvest Biology and Technology》2009,51(3):354-363
Eight plum cultivars (four dark-purple and four yellow) were harvested at the commercial ripening stage, and changes of fruit quality properties were evaluated during cold storage and subsequent shelf-life, with special emphasis on bioactive compounds (phenolics, anthocyanins and carotenoids) and antioxidant activity (TAA). From the eight plum cultivars, four showed the typical climacteric ripening pattern (‘Blackamber’, ‘Larry Ann’, ‘Golden Globe’ and ‘Songold’) while four behaved as suppressed-climacteric types (‘Golden Japan’ ‘Angeleno’, Black Diamond’ and ‘TC Sun’), the latter being described for the first time. At harvest, large variations in phytochemicals and antioxidant activity were found among cultivars in peel and pulp tissues, although phytochemical concentration and antioxidant activity were higher in the peel than in the flesh (2–40-fold depending on the bioactive compound). During storage, increases in total phenolics for all cultivars (peel and pulp), in total anthocyanin content in the peel of the dark-purple plums, and total carotenoids in the peel and pulp of the yellow cultivars were observed. This behaviour of the bioactive compounds was reflected in TAA changes, since hydrophilic-TAA (H-TAA) was correlated with both phenolics and anthocyanins, while lipophilic-TAA (L-TAA) was correlated with carotenoids. L-TAA comprised about 30–50% of the TAA in plum tissues. Carotenoids and phenolics (and among them the anthocyanins) could be the main lipophilic and hydrophilic compounds contributing to L-TAA and H-TAA, respectively. No significant loss of bioactive compounds and TAA occurred during prolonged plum storage. Moreover, for a better evaluation of the antioxidant potential of plums, the contribution to carotenoids should not be overlooked. 相似文献
94.
Alfredo Gallardo-Coll Carlos Ivn Prez-Rostro Martha Patricia Hernndez-Vergara 《International Aquatic Research》2019,11(1):43-55
During a growout period of 14 weeks, the productive performance, organosomatic indices and body composition of the Nile tilapia Oreochromis niloticus cultivated at high density reusing the water from systems with biofloc technology (BFT) were evaluated. Two treatments: tilapia cultured in biofloc (TB) and tilapia cultured in reused water biofloc (RW) were established. Mixed sex, juvenile Nile tilapia (average weight and length: 79.28 ± 14.44 g and 12.44 ± 0.70 cm) were stocked into 6 experimental units (0.2 m3) at a density of 100 fish/m3. Temperature, dissolved oxygen, total dissolved salts, pH, NH4–N, NH3–N and NO3–N were recorded daily, while NO2–N, general hardness, carbonate hardness and settleable solids were recorded weekly. The weight and length of the tilapias were recorded biweekly. Survival, productive performance, proximal composition and organosomatic indices of Nile tilapia were evaluated. The water parameters in RW treatment such as pH, total dissolved salts, NO2–N, NO3–N and carbonate hardness were significantly greater (p < 0.05), when compared to those obtained in TB treatment. Survival rate was > 98% under both treatments. The final weight (TB = 163.09 ± 42.34 g, RW = 159.23 ± 39.92 g), protein (19.1%) and lipid (2.2%) content of the tilapia were non-significantly different between treatments. In addition, no significant differences in the gonadosomatic and hepatosomatic indices were observed either between tilapia sex or between the treatments. The results suggest that the intensive cultivation of Nile tilapia in biofloc can be established using reuse water from BFT systems, without adverse effects on their survival, productive performance, proximal composition and gonadal development. 相似文献
95.
Jorge Dresdner Carlos Chávez Miguel Quiroga Daniel Jiménez Paulina Artacho Alfredo Tello 《Aquaculture Economics & Management (Blackwell Science)》2019,23(1):1-27
We measure the impact that sanitary treatments that control ectoparasite Caligus rogercresseyi abundance have on unit production costs of Salmo salar farms in Chile. We follow complete production cycles for a sample of farms between 2009 and 2015. We estimate a simultaneous salmon biomass growth and Caligus abundance model. The statistical analysis determines the effect of antiparasitic treatments, location of farms, environmental conditions and Caligus abundance on the salmon growth profile. Using outside cost information, we simulate how unit production costs vary by treatment and farm characteristics. Our results suggest that unit production costs increase on average by $1.4?US/kg with Caligus and treatments. Treatment costs are compensated by higher harvesting levels, and unit production costs are invariant to the situation without treatment. All estimated effects differ depending on farm’s environmental and spatial conditions, suggesting that the design of cost-effective intervention calls for discriminatory regulation under heterogeneous conditions. 相似文献
96.
Baker AL Baker LR Beshore E Blenman C Castillo ND Chen YP Doose LR Elston JP Fountain JW Gehrels T Kendall JH Kenknight CE Norden RA Swindell W Tomasko MG Coffeen DL 《Science (New York, N.Y.)》1975,188(4187):468-472
For 2 weeks continuous imaging, photometry, and polarimetry observations were made of Jupiter and the Galilean satellites in red and blue light from Pioneer 11. Measurements of Jupiter's north and south polar regions were possible because the spacecraft trajectory was highly inclined to the planet's equatorial plane. One of the highest resolution images obtained is presented here along with a comparison of a sample of our photometric and polarimetric data with a simple model. The data seem consistent with increased molecular scattering at high latitudes. 相似文献
97.
Performance of a photo‐heterotrophic,hypersaline system for intensive cultivation of white leg shrimp (Litopenaeus vannamei) with minimal water replacement in lined ponds using a stochastic approach 下载免费PDF全文
Luis Daniel Moreno‐Figueroa José Naranjo‐Páramo Alfredo Hernández‐Llamas Mayra Vargas‐Mendieta José Andrés Hernández‐Gurrola Humberto Villarreal‐Colmenares 《Aquaculture Research》2018,49(1):57-67
The aim of the study was to evaluate the performance of Litopenaeus vannamei in an intensive photo‐heterotrophic hypersaline system with minimal seawater replacement, and establish relationships between parameters of a stochastic production model and relevant water quality variables. Six experimental 1000 m2 lined ponds were stocked at a density of 120 shrimp m?2 for a 105‐day trial. Salinity increased from 37 to 45 ± 2 g/L, and the water level was maintained with the weekly addition of filtered seawater, equivalent to 1.6% per day. The stochastic model predicted that, at harvest, there is 95% confidence that the system produces between 12.1 and 14.7 t/ha with a mean final individual weight of 13.1 g and a mean survival of 84.2%. Sensitivity analyses showed that dissolved oxygen and individual final weight of shrimp were the main variables influencing yield variance. Nitrogenous compounds were maintained between optimal cultivation levels (NH3–NH4+ = 0.73 ± 0.43 mg/L, N–NO2? = 0.09 ± 0.05 mg/L, N–NO3? = 3.22 ± 0.11 mg/L). Heterotrophic bacteria (6.6 ± 3.4 × 105 CFU/ml) and chlorophyll‐α concentration (108.5 ± 80.2 μg/L) showed a similar development pattern, indicating a strong relationship between bacteria and microalgae during cultivation. Vibrio spp. concentrations were low (1.24 ± 1.42 × 103 CFU/ml). It was shown that the photo‐heterotrophic system could be used in hypersaline conditions, typical of semi‐arid regions, to consistently produce between 12.1 and 14.7 t/ha in 15 weeks. 相似文献
98.
Alfredo Hernández-Llamas Javier M.J. Ruiz-Velazco Victor M. Gomez-Muñoz 《Aquacultural Engineering》2011,45(2):66-73
We investigated the variability of shrimp Litopenaeus vannamei production by incorporating stochastic elements into deterministic stock models and determined the contribution that white spot disease, zootechnical parameters, water quality, and alternative management strategies have on variability. The model was calibrated for intensive shrimp cultivation in the State of Nayarit, Mexico. Mean annual production increased as a consequence of improved management from 8000 kg ha−1 to 22,000 kg ha−1 when cultivation was not affected by the disease and from 3200 kg ha−1 to 10,400 kg ha−1 when the disease affected production. When simultaneously considering both cases, mean annual production increased from 6300 kg ha−1 to 16,800 kg ha−1. White spot disease was a major factor determining variability of production. Shrimp production was particularly sensitive to levels of dissolved oxygen when management was inadequate, while final weight and mortality rate of shrimp were more sensitive when management improved. Water temperature and salinity had intermediate importance, and mortality caused by the disease and the time when mortality occurred had intermediate or low relevance. Improving management increased shrimp production and diminished variability. The duration of cultivation and stocking density were the most important management variables controlling variability of production when cultivation was affected by the white spot disease. When the disease was not present, pond size and duration of cultivation were the main factors affecting production. Starting time of aeration had relatively lower importance in determining variability, while the stochastic values of dissolved oxygen, in contrast, became most important. These results call for studies on improving aeration management to reduce variability of dissolved oxygen in ponds. 相似文献
99.
J. Albaladejo Montoro J. Alvarez Rogel J. Querejeta E. Díaz V. Castillo 《Land Degradation \u0026amp; Development》2000,11(4):315-325
Erosion control at low–medium radioactive waste disposal sites is an important concern. A study was carried out in El Cabril (Córdoba, Spain) on two 40 per cent anthropic steep slopes in order to test the effectiveness of hydro‐seeding techniques for controlling soil erosion. Two groups of 10 m × 3 m plots were established. The treatments tested were: hydro‐seeding with the application of vegetal mulch (VM); hydro‐seeding with added humic acids (HA); hydro‐seeding with vegetal mulch and humic acids added (VM + HA); and a control without hydro‐seeding or soil amendment (C). Fifteen run‐off producing rainfall events were recorded during the study period, with intensities ranging between 2 mm h−1 and 33·6 mm h−1. All treatments significantly reduced runoff and soil loss (p < 0·05). The VM+HA treatment was the most effective, reducing 98·5 per cent of total soil loss. The HA treatment (97·1 per cent reduction) was also more effective than the VM treatment (94·8 per cent reduction). A great reduction in runoff and sediment yield was observed in the treated plots during the first stages after hydro‐seeding. This result may be attributed to the combined effect of: (a) the protection against raindrop impact due to the application of straw and mulch to the soil surface, and (b) a general improvement in the soil's structure brought by the organic amendments. Seven months after hydro‐seeding, an increase in the density of the plant cover could be added to the beneficial effects mentioned above. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
100.
López-López A Montaño A Cortés-Delgado A Garrido-Fernández A 《Plant foods for human nutrition (Dordrecht, Netherlands)》2008,63(2):87-91
For nutritional purposes, a survey of the vitamin B6 levels from a variety of commercial presentations of table olives was carried out, taking into account the three main processing types (Spanish-style, directly brined, and ripe olives). The analysis was performed by HPLC, following the official French method for vitamin B6 determination in foodstuffs. In-house validation data for two commercial table olives showed that the method precision was good (coefficient of variation <6%) and recovery was quantitative (104% on average). There was a wide range of values for vitamin B6 in table olives (0–69.3 μg/100 g edible portion). The highest mean content was found in directly brined olives (33.9 μg/100 g edible portion) followed by Spanish-style (14.4 μg/100 g) and ripe olives (4.3 μg/100 g). On average, samples of the Gordal and Carrasqueña cultivars showed the highest vitamin B6 content in the case of Spanish-style olives, but in directly brined olives as well as in ripe olives the effect of cultivar was not statistically significant (p?0.05). 相似文献