全文获取类型
收费全文 | 20494篇 |
免费 | 1479篇 |
国内免费 | 136篇 |
专业分类
林业 | 2041篇 |
农学 | 810篇 |
基础科学 | 141篇 |
4849篇 | |
综合类 | 1235篇 |
农作物 | 963篇 |
水产渔业 | 1821篇 |
畜牧兽医 | 7906篇 |
园艺 | 469篇 |
植物保护 | 1874篇 |
出版年
2023年 | 168篇 |
2022年 | 258篇 |
2021年 | 471篇 |
2020年 | 508篇 |
2019年 | 429篇 |
2018年 | 912篇 |
2017年 | 932篇 |
2016年 | 910篇 |
2015年 | 703篇 |
2014年 | 809篇 |
2013年 | 1238篇 |
2012年 | 1613篇 |
2011年 | 1464篇 |
2010年 | 902篇 |
2009年 | 718篇 |
2008年 | 1198篇 |
2007年 | 1134篇 |
2006年 | 944篇 |
2005年 | 947篇 |
2004年 | 822篇 |
2003年 | 777篇 |
2002年 | 637篇 |
2001年 | 460篇 |
2000年 | 437篇 |
1999年 | 376篇 |
1998年 | 113篇 |
1997年 | 111篇 |
1996年 | 82篇 |
1995年 | 96篇 |
1994年 | 59篇 |
1993年 | 53篇 |
1992年 | 129篇 |
1991年 | 108篇 |
1990年 | 109篇 |
1989年 | 108篇 |
1988年 | 94篇 |
1987年 | 87篇 |
1986年 | 97篇 |
1985年 | 99篇 |
1984年 | 80篇 |
1983年 | 69篇 |
1982年 | 37篇 |
1979年 | 72篇 |
1978年 | 55篇 |
1977年 | 40篇 |
1974年 | 52篇 |
1973年 | 67篇 |
1972年 | 54篇 |
1971年 | 51篇 |
1969年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
David R Bayne David Dunseth Cecilio García Ramirios 《Aquaculture (Amsterdam, Netherlands)》1976,7(2):133-146
A supplementary feed containing 30% coffee pulp was evaluated for use in the culture of Tilapia aurea in El Salvador, Central America. A comparison of the coffee pulp feed with a feed containing all of the same ingredients except coffee pulp was made with T. aurea raised in 1.0-m3 cages suspended in a fertilized earthen pond. Survival was high in all treatments and there was no significant difference in average weight gain between groups of fish receiving the two experimental feeds. Production trials were conducted in 100-m2 fish pens and in 0.05-ha earthen ponds. Pen-raised fish receiving coffee pulp feed grew faster throughout the experiment, and total production was approximately twice that in control treatments. Highest production in pens was 1.25 kg/m2 per year. Results of production pond trials using T. aurea at 9 000/ha and stocked with the piscivorous Cichlasoma managuense yielded an estimated 3 392 kg/ha per year in fed treatments and 2 049 kg/ha per year in controls. Low feed conversion (1.92) and low feed cost resulted in an increase in net annual earnings of $251.00/ha. 相似文献
992.
Patrícia Castro Monteiro Maria Inês Braga de Oliveira Franmir Rodrigues Brando Caio Francisco Santana Farias Cludia Majolo Francisco Clio Maia Chaves Humberto Ribeiro Bizzo Fernanda Loureiro de Almeida OSullivan Maurício Latera Martins Edsandra Campos Chagas 《Aquaculture Research》2022,53(1):265-275
This study evaluated the effect of short-term baths with the essential oils (EOs) of Lippia sidoides, Ocimum gratissimum and Zingiber officinale on the survival, haematological, biochemical and histopathological parameters of native fish tambaqui (Colossoma macropomum), challenged with Aeromonas hydrophila. After challenge, the fish infected with A. hydrophila received therapeutic baths of 60 min, for five consecutive days. Treatments were as follows: challenged and not treated; challenged and treated with 10 mg L?1 of gentamicin; challenged and treated with EO of L. sidoides (2.5 and 5.0 mg L?1); challenged and treated with EO of O. gratissimum (5.0 and 10.0 mg L?1); challenged and treated with Z. officinale EO (5.0 and 10.0 mg L?1). The highest survival rates were 89.5% (fish treated with 5.0 mg L?1 of O. gratissimum EO) and 75.0% (fish treated with 5.0 mg L?1 of L. sidoides EO). Reductions in the haematocrit percentage, haemoglobin and erythrocyte number were observed in fish treated with L. sidoides and Z. officinale EOs compared with control fish. Mild to moderate damage to the liver tissue of fish after challenge and EO treatments were observed. It is suggested that baths containing O. gratissimum and L. sidoides EOs consist in a viable treatment to increase survival rates of C. macropomum infected with A. hydrophila. 相似文献
993.
The metabolic consequences of the isoenergetic replacement of dietaryprotein by carbohydrates (CHO) were compared in studies of European eel andrainbow trout. Diets with 45/20, 37/30, 29/40 and 21/50 percentprotein/carbohydrate were assessed during a 12-week experiment. The CHO sourcewas pre-gelatinized corn starch. Fish of initial average weight 45gwere fed to satiation twice daily. Weight-gain and feed-efficiency data weregenerally better in trout than in eel, presumably because trout digestibilitycoefficients for protein and energy were higher than in eel. In both species,regardless of physiological differences in digestion and absorption, feedintakeand nutrient digestibility were lower when dietary CHO was higher, but theinter-species differences decreased with increasing dietary CHO.Pyruvate kinase activity (PK) in trout was not affected by dietary CHO content,while blood-glucose and liver-glycogen levels significantly rose withincreasingdietary CHO. In contrast, blood-glucose levels appeared to be regulated ineels,perhaps by an accelerated glycolysis rate, revealed by changes in PK.Gluconeogenic activity was inhibited in trout fed a diet containing20–30%CHO, while in eels this activity was not inhibited by dietary replacement ofprotein by carbohydrate. Liver glucose 6-phosphate dehydrogenase activity(G6PDH) was inhibited in trout fed increasing dietary CHO, whereas in eelsG6PDHoperated at a high rate regardless of dietary composition. These results mayindicate that eels have a better capacity for metabolising high-CHO/low-proteindiets than do trout. 相似文献
994.
J.N. Gutiérrez N.J. Duncan N. García-Aguilar P.V. Estañol A. García-Gasca 《Fish physiology and biochemistry》2003,28(1-4):341-342
A fragment of a glycoprotein hormone receptor (GpHR) gene was isolated from the ovary of the bullseye puffer. This cDNA fragment showed similarity to the thyrotropin (TSH) and gonadotropin (LH and FSH) receptors. GpHR mRNA expression in the ovary gradually increased during oocyte maturation. 相似文献
995.
Adriana Vella Sinéad Murphy Joan Giménez Renaud de Stephanis Barbara Mussi Joseph G. Vella Kamel Larbi Doukara Daniela Silvia Pace 《水产资源保护:海洋与淡水生态系统》2021,31(Z1):110-136
- Preservation of endangered species is now recognized as a relevant component of regional and global conservation actions achieved through the maintenance of the remaining populations in a favourable conservation status. The Mediterranean common dolphin (Delphinus delphis) is listed as an Endangered subpopulation in the International Union for Conservation of Nature Red List, with declining numbers in some of the areas where it has been studied for numerous years. Prey depletion, fisheries bycatch, pollution, health risks, and climate change are among the recognized threats that the species is facing in the region.
- The existing national, regional, and international legislation pertinent to Mediterranean countries should aid greater science–policy–management integration and support innovative research and monitoring towards effective conservation. The challenges inherent in studying the pelagic D. delphis should not preclude the use of long-term, year-round, multiplatform surveys, side by side with the latest molecular tools, which aid our understanding of its populations' genetic diversity, resistance to diseases, and resilience in a semi-enclosed fast-changing sea.
- Addressing the multiplicity of problems confronting the species requires collaborative effort at all levels to share and merge resources, data, and expertise more efficiently. In this review, we provide an overview of the current knowledge on the Mediterranean common dolphin, the main threats, and knowledge gaps that are priorities for addressing its conservation, while providing clear recommendations for effectively safeguarding the species and its habitat at both local and regional levels.
996.
为探究池塘中间培育不同月龄文蛤(Meretrix meretrix)的生长特性, 测定了 10、15、20 月龄文蛤的壳长(SL)、 壳宽(SW)、壳高(SH)和活体重量(BW)等参数, 运用相关分析、通径分析和多元回归分析等方法, 探讨了形态性状对活体重量的作用效果。结果显示, 10、15 月龄文蛤活体重量相关系数最高的形态性状为壳长(SL), 20 月龄文蛤活体重量相关系数最高的形态性状为壳宽(SW); 通径分析结果显示, 对 10、15 和 20 月龄文蛤活体重量直接影响最大的分别为壳长(SL)、壳高(SH)和壳宽(SW)。各月龄活体重量(BW)与形态性状建立的多元回归方程分别为 BW10=?2.976+ 0.100SL+0.140SW+0.101SH (R2 =0.969); BW15=?12.176+0.085SL+0.441SW+0.415SH (R2 =0.957); BW20= ?21.506+0.255SL+ 1.098SW+0.152SH (R2 =0.920)。异速生长方程显示不同月龄文蛤具有不同的生长规律, 10 月龄文蛤为正异速生长, 15 月龄文蛤为等速生长, 而 20 月龄文蛤为负异速生长。结果表明, 在池塘中间培育期间, 影响文蛤活体重量的形态性状随文蛤龄期而变化, 10 月龄及 15 月龄对活体重量影响最大的分别为壳长和壳高, 但随着龄期的增加, 壳宽对活体重量的影响程度增加, 是 20 月龄时对活体重量影响最大的数量性状指标, 研究结果可为文蛤中间培育和选育提供理论参考。 相似文献
997.
Marie-Pier Poirier-Guay Marie-Claude Bélanger Diane Frank 《The Canadian veterinary journal. La revue veterinaire canadienne》2014,55(11):1079-1082
A Yorkshire terrier dog was presented for episodes of “star gazing” behavior expressed as upward raising of the head and neck extension with subsequent staring at the ceiling or sky. Erosive gastritis with reflux esophagitis was diagnosed. Treatment of these conditions was associated with resolution of the behavior, suggesting a causal link. 相似文献
998.
Javier Bezos Sergio Marqués Julio Álvarez Carmen Casal Beatriz Romero Ana Grau Olga Mínguez Lucas Domínguez Lucía de Juan 《Research in veterinary science》2014
Goats can act as reservoirs for tuberculosis (TB) infection. The main etiological agents of TB in goats are Mycobacterium caprae and Mycobacterium bovis and they infect also a wide range of domestic and wild animals and humans. Control programmes based mainly on the application of single and comparative intradermal tuberculin (SIT and SCIT respectively) tests are being implemented in certain regions of Spain with a high density of caprine flocks as Castilla y León, including goats with epidemiological relationship with cattle. The aim of this study was to evaluate the performance of the intradermal tests in naturally TB-infected caprine flocks from this region. The study was performed using data from 17,450 goats in 54 different flocks that were classified as TB-infected in the control programmes executed in 2010 and 2011. Data from 1237 goats from 7 dairy flocks depopulated after the first intradermal testing were used to estimate the sensitivity (Se) using bacteriology as the gold-standard. Overall Se of the SIT test using the severe interpretation was 43.9% (CI 95%, 40.4–47.4) and decreased to 38.8% (CI 95%, 35.5–42.3) using the standard interpretation. Overall Se of the SCIT test ranged between 21.3% (CI 95%, 17.6–25.4) and 7% (CI 95%, 4.9–9.8) depending of the interpretation criteria. A significant weak positive correlation was found between age and skin fold thickness (Spearman’s test p < 0.05). Results from this study yielded, in general, low Se values probably due the systematic detection and slaughter of reactors as a consequence of the eradication programme in previous years or the presence of factors that may interfere in the diagnosis. Therefore, these results suggest the necessity of including ancillary diagnostic tools and/or strict interpretation criteria to maximize detection of positive animals in infected settings. 相似文献
999.
1000.
Anne Muckle Alfonso López Marcelo Gottschalk Carlos López-Méndez Jan Giles Lorraine Lund Matthew Saab 《The Canadian veterinary journal. La revue veterinaire canadienne》2014,55(10):946-949
Streptococcus suis was isolated postmortem from 2 lambs with a history of lameness. Identity of S. suis was confirmed by species-specific polymerase chain reaction (PCR) and by 16S rRNA gene sequencing. One isolate was untypable by serotyping and non-encapsulated, while the other isolate was serotype 33. The lambs had come from the same farm, and there was no evidence of contact between the lambs and pigs. Although the natural niche for S. suis is considered to be the pig, a wide range of host species may be affected by this pathogen. 相似文献