全文获取类型
收费全文 | 1610篇 |
免费 | 139篇 |
专业分类
林业 | 116篇 |
农学 | 35篇 |
基础科学 | 12篇 |
512篇 | |
综合类 | 51篇 |
农作物 | 69篇 |
水产渔业 | 206篇 |
畜牧兽医 | 595篇 |
园艺 | 30篇 |
植物保护 | 123篇 |
出版年
2024年 | 2篇 |
2023年 | 12篇 |
2022年 | 20篇 |
2021年 | 30篇 |
2020年 | 25篇 |
2019年 | 43篇 |
2018年 | 81篇 |
2017年 | 71篇 |
2016年 | 66篇 |
2015年 | 52篇 |
2014年 | 71篇 |
2013年 | 114篇 |
2012年 | 134篇 |
2011年 | 128篇 |
2010年 | 76篇 |
2009年 | 65篇 |
2008年 | 80篇 |
2007年 | 100篇 |
2006年 | 83篇 |
2005年 | 81篇 |
2004年 | 70篇 |
2003年 | 72篇 |
2002年 | 60篇 |
2001年 | 51篇 |
2000年 | 51篇 |
1999年 | 40篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1945年 | 1篇 |
排序方式: 共有1749条查询结果,搜索用时 15 毫秒
81.
I. Abdel E. Abellán O. López-Albors P. Valdés M.J. Nortes A. García-Alcázar 《Aquaculture International》2004,12(6):523-538
Osteological malformations are always considered an important problem in intensive aquaculture. This work studies the effect of rearing temperature on malformations in sea bass, Dicentrarchus labrax. To this end, two batches of the species were subjected to the following incubation/cultivation temperatures: 15 °C/natural and 19/19 °C, from fertilization until 190 days after hatching. The different malformations were studied in 1643 juveniles at 190 days and classified by categories. The Chi-square statistic was calculated to verify the relationship between the presence of anomalies and the application of different temperatures. The percentage of anomalies observed in individuals reared at a high temperature (19/19 °C) was 66.44%. In both temperature systems, opercular malformations were those which caused a greater delay in growth. The results found indicated that temperature played a very important role in the development of deformations, which may be of interest from the viewpoint of aquaculture. 相似文献
82.
- Amphibian populations worldwide are in decline. Proactive conservation techniques such as translocations into created and restored wetlands have gained popularity in recent years but may fail owing to high predation and low environmental adaptability.
- The Mexican axolotl (Ambystoma mexicanum), affected by rapid urbanization, is now possibly extinct in the wild despite millions living in captivity throughout the world.
- The aim of this study was to explore whether ponds from an artificial wetland can function as temporary shelters for a viable population of axolotls that could be re-introduced into their native ecosystem in Xochimilco once it is restored.
- Egg-laying and hatching of 11 unique axolotl pairs placed into reproductive enclosures and larval survival to 7 weeks and up to 12 months were examined. Physicochemical and biological parameters were estimated and compared among ponds.
- The results from this study are encouraging as they suggest that two ponds have adequate conditions for axolotls to reproduce and for larvae and juveniles to survive.
83.
The first attempts at applying aquacultural techniques to sharpsnoutseabream (Diplodus puntazzo) have proved very promising.One of the factors to keep in mind when analysing the viability of a speciesforindustrial farming is that of consumer acceptance of the product, a variablethat can be measured by sensory evaluation tests. To that end, 107 participantsfrom a number of work centres were assessed with hedonic sensory tests usingsharpsnout seabream samples. For reference purposes, the tasting also includedgilthead seabream samples. Participants were asked to fill out a questionnairethat included questions concerning their preferences for any one fish. Weanalysed the sensory attributes of both fish species using a hedonic scale, andalso their acceptability (disposition to purchase) to consumers. The resultsproved fairly encouraging with a view to sharpsnout seabream large-scaleproduction. All attributes tested in the sensory profile analysis werepositively rated. About 60% of the surveyed population would consider buyingsharpsnout seabream at a price similar to that of gilthead seabream (10∈),and 85% found it to be pleasing to the eye. Aside from flavour, its texture,juiciness and fat level are the most important appraisal attributes. Efforts toimprove the organoleptic characteristics of the species should focus mainly onthese attributes. 相似文献
84.
Sponges corresponding to the Jaspidae family have proved to be a prolific source of bioactive natural products. Among these, the bengamides and the bengazoles stand out by virtue of their unprecedented molecular architectures and impressive biological profiles, including antitumor, antibiotic and anthelmintic properties. As a consequence, intense research activity has been devoted to these compounds from both chemical and biological standpoints. This review describes in detail the research into these classes of natural products and the benefits they offer in chemistry and biology. 相似文献
85.
Becerril-Campos Adriana Araceli Ocampo-Anguiano Perla Viridiana Mondragón-Jacobo Candelario Escobar-García Konisgmar Camacho-Barrón Mariela Anaya-Loyola Miriam Aracely Feregrino-Perez Ana Angélica García-Gasca Teresa Ahumada-Solórzano Santiaga Marisela 《Plant foods for human nutrition (Dordrecht, Netherlands)》2022,77(3):421-426
Plant Foods for Human Nutrition - High-fat/high-fructose diets promote early metabolic disorders in weight and lipid and glucose metabolism. Bioactive compounds such as polyphenols and fiber... 相似文献
86.
García-Gamboa Ricardo Domínguez-Simi Miguel Ángel Gradilla-Hernández Misael Sebastián Bravo-Madrigal Jorge Moya Andrés González-Avila Marisela 《Plant foods for human nutrition (Dordrecht, Netherlands)》2022,77(2):212-219
Plant Foods for Human Nutrition - There is great interest in the search for new alternatives to antimicrobial drugs, and the use of prebiotics and probiotics is a promising approach to this... 相似文献
87.
Aitor Gastón Juan I. García-Viñas Alfredo J. Bravo-Fernández César López-Leiva Juan A. Oliet Sonia Roig Rafael Serrada 《New Forests》2014,45(5):641-653
An expert on local flora usually is the best option for plant species selection in most ecological restoration projects; although species selection often needs to be dealt with swiftly as well as on a limited budget, and obtaining the opinion of a local expert may not always be an economically viable alternative. In such cases, species distribution models (SDM) may offer a faster and more cost effective alternative. We asked six experts to rank native tree species according to their suitability at 24 forest sites. The predictive performance of the suitability rankings was evaluated by assessing their ability to discriminate present from absent species in the observed tree assemblages at each evaluation site. We used the area under the receiver operating characteristic curve to calculate the probability that the estimated suitability for a species present at a particular evaluation site is greater than the estimate for an absent species (both picked at random). Suitability rankings were also obtained from the predictions of SDM and the same procedure was used to estimate the predictive performance of the set of models at each site. The experts offered concordant suitability rankings at almost every evaluation site. There were no significant differences in the predictive performance of the SDM and four of the experts, although the SDM performed slightly better than the other two experts. Our results point to the suitability of the proposed species distribution modeling approach to obtain fast and cost effective recommendations for species selection in forest restoration projects. 相似文献
88.
Digestive enzyme activity during early larval development of the Cuban gar Atractosteus tristoechus 总被引:1,自引:0,他引:1
Y. Comabella R. Mendoza C. Aguilera O. Carrillo A. Hurtado T. García-Galano 《Fish physiology and biochemistry》2006,32(2):147-157
The ontogenesis of digestive enzymes (proteases, amylases, lipases, and phosphatases) in Cuban gar Atractosteus tristoechus was determined in larvae between 5 and 18 days after hatching (DAH). Variations in specific activities of most enzymes were related to the transition from endogenous to exogenous feeding and to the transition from the larval to the juvenile stage. Alkaline protease activity was not detected until 8 DAH in contrast to acid protease activity, which was quantifiable at 5 DAH. Acid protease activity was consistently higher than alkaline protease activity, indicating the presence of a functional stomach in the early stages of larval development. The acid protease activities of larvae and adults were compared by means of zymogram analysis. Four acid protease bands were found in adults (two more than in larvae). This result is the first time that more than one band of acid proteolytic activity has been found in Lepisosteidae. High lipase activity indicated the importance of lipid utilization, particularly during yolk-sac absorption. In contrast to the other enzymes studied, amylase activity was consistently low, probably due to the strictly carnivorous diet of gar larvae and their low capacity for carbohydrate digestion. High activities of aminopeptidase and acid and alkaline phosphatases suggest intestinal absorption. This result, together with the existence of a short gut and a lower proteolytic activity in the intestine than in the stomach, suggest that most of the proteolytic activity takes place in the stomach, while the primary function of the intestine is nutrient uptake. 相似文献
89.
Santos Y García-Marquez S Pereira PG Pazos F Riaza A Silva R El Morabit A Ubeira FM 《Journal of fish diseases》2005,28(3):165-172
The commercial furunculosis vaccine Aquavac Furovac 5 and an autogenous vaccine, based on the challenge strain, induced immune protection in turbot, Scophthalmus maximus (L.), as shown in challenge tests 120 days post-immunization by injection (relative percentage of survival, RPS = 72-99%). This protective effect lasted for at least 6 months post-immunization at appreciable levels (RPS = 50-52%). Neither the autogenous vaccine nor the commercial vaccine was able to induce significant levels of protection against Aeromonas salmonicida in turbot when administered by immersion. Antibody levels were high or moderate in fish vaccinated by injection with the different vaccines and very low in fish vaccinated by immersion. The field results show that delivering an oral boost after the primary vaccination by injection did not enhance protection of turbot against furunculosis and that water-based (autogenous vaccine) and oil adjuvanted (Alpha Ject 1200) vaccines administered by injection conferred similar levels of protection (RPS > 80%) in turbot. 相似文献
90.
A nested polymerase chain reaction (PCR) system was developed for the detection of Flexibacter maritimus from fish tissue. The total procedure for the diagnosis of marine flexibacteriosis, from the point of DNA extraction to the electrophoretic analysis, can be performed in < 4 h. This was achieved by the combination of a short thermal cycling programme with a rapid DNA extraction procedure. The assay was extremely sensitive, capable of detecting as few as 75 cfu mg(-1) fish tissue. The accuracy of the nested PCR was confirmed under field conditions using tissue samples recovered during 1993-2002 from fish suffering marine flexibacteriosis. The nested PCR method proved to be efficient for the rapid and sensitive detection of F. maritimus from fish tissues and can be used for routine diagnosis of the disease caused by this pathogen. 相似文献