全文获取类型
收费全文 | 1733篇 |
免费 | 149篇 |
专业分类
林业 | 157篇 |
农学 | 87篇 |
基础科学 | 4篇 |
430篇 | |
综合类 | 52篇 |
农作物 | 86篇 |
水产渔业 | 212篇 |
畜牧兽医 | 655篇 |
园艺 | 18篇 |
植物保护 | 181篇 |
出版年
2024年 | 2篇 |
2023年 | 27篇 |
2022年 | 29篇 |
2021年 | 61篇 |
2020年 | 57篇 |
2019年 | 49篇 |
2018年 | 118篇 |
2017年 | 101篇 |
2016年 | 88篇 |
2015年 | 69篇 |
2014年 | 98篇 |
2013年 | 140篇 |
2012年 | 162篇 |
2011年 | 126篇 |
2010年 | 72篇 |
2009年 | 61篇 |
2008年 | 92篇 |
2007年 | 79篇 |
2006年 | 76篇 |
2005年 | 67篇 |
2004年 | 63篇 |
2003年 | 49篇 |
2002年 | 54篇 |
2001年 | 32篇 |
2000年 | 16篇 |
1999年 | 14篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 6篇 |
1972年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1961年 | 2篇 |
排序方式: 共有1882条查询结果,搜索用时 15 毫秒
71.
Higher feeding diets effects on age and liveweight gain at puberty in crossbred Nelore × Hereford heifers 总被引:1,自引:1,他引:0
Júlio Otávio Jardim Barcellos Gabriel Ribas Pereira Eduardo Antunes Dias Concepta McManus Leonardo Canellas Mari Lourdes Bernardi Adriana Tarouco Ênio Rosa Prates 《Tropical animal health and production》2014,46(6):953-960
This study was conducted to determine the age and liveweight at puberty of 120 crossbred beef heifers submitted to four diets to achieve predetermined weight gains (kg/day): 0.5 (G500; n?=?32), 0.75 (G750; n?=?32), 1.0 (G1000; n?=?29), and 1.25 (G1250; n?=?27). Animals were classified depending on their level of crossing between Nelore (N) and Hereford (H): 25%N-75%H, 37.5%N-63.5%H, 43.7%N-56.7%H, 50%N-50%H, and 75%N-25%H. Reproductive evaluation was performed at the beginning and at the end of the experimental period by ultrasonography and hormone analysis. The average age and liveweight at puberty were 388.0?±?1.9 days and 331.4?±?1.3 kg, respectively. Animals from the 25%N-75%H group reached puberty earlier than heifers from other genetic groups supplemented with G1250 diet (P?<?0.05). Heifers with higher degree of Nelore (75%N-25%H) fed with G1000 diet showed estrus 42 days prior to mating, but only 57 % reached puberty at mating (P?<?0.05). Heifers with follicles of higher diameter reached puberty (P?<?0.05) earlier. Higher average daily weight gain showed a positive effect on follicular diameter and IGF-I level at puberty (P?<?0.01). Concentrations of GH were lower in heifers fed G1250 compared to G1000 diet (P?<?0.05). There was a significant interaction between nutritional level and insulin levels at puberty (P?<?0.01). We demonstrated the relationship between IGF-I and average daily gain on the onset of puberty in heifers. In conclusion, heifers submitted to the higher feeding level showed a higher follicular diameter and were younger at puberty. 相似文献
72.
Pedro Soler-Lloréns Yolanda Gil-Ramírez Ana Zabalza-Baranguá Maite Iriarte Raquel Conde-álvarez Amaia Zú?iga-Ripa Beatriz San Román Michel S Zygmunt Nieves Vizcaíno Axel Cloeckaert María-Jesús Grilló Ignacio Moriyón Ignacio López-Go?i 《Veterinary research》2014,45(1):72
Brucella spp. are Gram-negative bacteria that behave as facultative intracellular parasites of a variety of mammals. This genus includes smooth (S) and rough (R) species that carry S and R lipopolysaccharides (LPS), respectively. S-LPS is a virulence factor, and mutants affected in the S-LPS O-polysaccharide (R mutants), core oligosaccharide or both show attenuation. However, B. ovis is naturally R and is virulent in sheep. We studied the role of B. ovis LPS in virulence by mutating the orthologues of wadA, wadB and wadC, three genes known to encode LPS core glycosyltransferases in S brucellae. When mapped with antibodies to outer membrane proteins (Omps) and R-LPS, wadB and wadC mutants displayed defects in LPS structure and outer membrane topology but inactivation of wadA had little or no effect. Consistent with these observations, the wadB and wadC but not the wadA mutants were attenuated in mice. When tested as vaccines, the wadB and wadC mutants protected mice against B. ovis challenge. The results demonstrate that the LPS core is a structure essential for survival in vivo not only of S brucellae but also of a naturally R Brucella pathogenic species, and they confirm our previous hypothesis that the Brucella LPS core is a target for vaccine development. Since vaccine B. melitensis Rev 1 is S and thus interferes in serological testing for S brucellae, wadB mutant represents a candidate vaccine to be evaluated against B. ovis infection of sheep suitable for areas free of B. melitensis. 相似文献
73.
A. C. O. Dearo G. de Moraes Marcondes J. C. O. Araújo C. E. S. Grumadas P. C. Marino W. T. Teixeira G. de La Penha Chiacchio Fernandes 《Equine Veterinary Education》2014,26(12):640-644
Strangulating obstruction of the small intestine by anomalous mesenteric bands is an uncommon cause of colic in horses. The most commonly reported bands are mesodiverticular bands that are embryological remnants of the vitelline arteries. Despite the congenital nature of the anomaly, a wide age range of horses can be affected. This report describes a case of small intestinal strangulating obstruction caused by an unusual, anomalous congenital band attached to the ileocaecal fold in a yearling colt. Information including case background, history, clinical, laboratory, surgical and pathological findings is described. 相似文献
74.
Carmen Murcia Laura Coello Rogelio Fernández María Jesús Martín Fernando Reyes Andrés Francesch Simon Munt Carmen Cuevas 《Marine drugs》2014,12(2):1116-1130
Tanjungides A (1) (Z isomer) and B (2) (E isomer), two novel dibrominated indole enamides, have been isolated from the tunicate Diazona cf formosa. Their structures were determined by spectroscopic methods including HRMS, and extensive 1D and 2D NMR. The stereochemistry of the cyclised cystine present in both compounds was determined by Marfey’s analysis after chemical degradation and hydrolysis. We also report the first total synthesis of these compounds using methyl 1H-indole-3-carboxylate as starting material and a linear sequence of 11 chemical steps. Tanjungides A and B exhibit significant cytotoxicity against human tumor cell lines. 相似文献
75.
Ana Bartual Néstor Arandia-Gorostidi Andrés Cózar Soledad Morillo-García María Jesús Ortega Montserrat Vidal Ana María Cabello Juan Ignacio González-Gordillo Fidel Echevarría 《Marine drugs》2014,12(2):682-699
Polyunsaturated aldehydes (PUAs) are organic compounds mainly produced by diatoms, after cell wounding. These compounds are increasingly reported as teratogenic for species of grazers and deleterious for phytoplanktonic species, but there is still scarce information regarding concentration ranges and the composition of PUAs in the open ocean. In this study, we analyzed the spatial distribution and the type of aldehydes produced by the large-sized (>10 μm) phytoplankton in the Atlantic Ocean surface. Analyses were conducted on PUAs released after mechanical disruption of the phytoplankton cells, referred to here as potential PUAs (pPUAs). Results show the ubiquitous presence of pPUA in the open ocean, including upwelling areas, as well as oligotrophic gyres. Total pPUA concentrations ranged from zero to 4.18 pmol from cells in 1 L. Identified PUAs were heptadienal, octadienal and decadienal, with heptadienal being the most common (79% of total stations). PUA amount and composition across the Atlantic Ocean was mainly related to the nitrogen:phosphorus ratio, suggesting nutrient-driven mechanisms of PUA production. Extending the range of trophic conditions considered by adding data reported for productive coastal waters, we found a pattern of PUA variation in relation to trophic status. 相似文献
76.
Javier Fernández Laura Marín Raquel álvarez-Alonso Saúl Redondo Juan Carvajal Germán Villamizar Claudio J. Villar Felipe Lombó 《Marine drugs》2014,12(5):2668-2699
Diverse actinomycetes produce a family of structurally and biosynthetically related non-ribosomal peptide compounds which belong to the chromodepsipeptide family. These compounds act as bisintercalators into the DNA helix. They give rise to antitumor, antiparasitic, antibacterial and antiviral bioactivities. These compounds show a high degree of conserved modularity (chromophores, number and type of amino acids). This modularity and their high sequence similarities at the genetic level imply a common biosynthetic origin for these pathways. Here, we describe insights about rules governing this modular biosynthesis, taking advantage of the fact that nowadays five of these gene clusters have been made public (thiocoraline, triostin, SW-163 and echinomycin/quinomycin). This modularity has potential application for designing and producing novel genetic engineered derivatives, as well as for developing new chemical synthesis strategies. These would facilitate their clinical development. 相似文献
77.
Lima Daniel Jadson Noronha Menezes Rosemberg F. Araújo Fabiana Oliveira 《Journal of Soils and Sediments》2022,22(3):982-993
Journal of Soils and Sediments - We quantified the phosphorus (P) fractions and oxide content in the sediment of eight tropical semiarid reservoirs to assess how water-level decreases affect the... 相似文献
78.
79.
The anthelmintic efficacy of ivermectin (IVM), piperazine citrate (PPZ) and fenbendazole (FBZ) alone, and combinations of FBZ with varying dosages of PPZ, was evaluated for the control of strongyles of Mangalarga equids. In all cases of positive strongly egg counts per gram of faeces (EPG) before and after treatment, pure populations of cyathostome larvae with eight gut cells were consistently observed in faecal cultures. The faecal egg count reductions (FECR) were evaluated between Day 7 and Day 56 post-treatment. Significant differences (P less than or equal to 0.05) were found between Day 7 and Day 49 when comparing the mean EPG values of IVM with those of the other anthelmintics. PPZ alone and the combination of FBZ (7.5 mg kg-1) and PPZ (55 mg base kg-1) did not show significant differences during the trial; both groups exhibiting an FECR of greater than 90% between Day 7 and Day 30. Horses treated with the combinations of FBZ (7.5 mg kg-1) and PPZ at either 40 or 25 mg base kg-1, and with FBZ alone at either 7.5 or 15 mg kg-1, showed an FECR of less than 90% 2 weeks after treatment. The emergence of a degree of resistance of strongyles to FBZ and PPZ in a segment of the cyathostomes in this population is suggested. 相似文献
80.
Janaina O Luna Manoel A A Santos Edison L Durigon Jo?o P Araújo Júnior José M B Duarte 《Journal of zoo and wildlife medicine》2003,34(4):414-415
Esophageal-pharyngeal fluids from 53 free-ranging marsh deer (Blastocerus dichotomus) captured for a research program in the state of Mato Grosso do Sul, Brazil, were assayed for tuberculosis. Total DNA was extracted. amplified by polymerase chain reaction using specific primers for Mycobacterium tuberculosis complex (M. tuberculosis, M. bovis, M. microti, and M. africanum), and observed by agarose gel electrophoresis stained with ethidium bromide. All samples were negative. This, along with necropsy and histopathology data, suggests that these animals are not shedding and probably do not have active disease. 相似文献