全文获取类型
收费全文 | 11386篇 |
免费 | 248篇 |
国内免费 | 16篇 |
专业分类
林业 | 1001篇 |
农学 | 382篇 |
基础科学 | 62篇 |
1958篇 | |
综合类 | 525篇 |
农作物 | 805篇 |
水产渔业 | 893篇 |
畜牧兽医 | 4943篇 |
园艺 | 279篇 |
植物保护 | 802篇 |
出版年
2023年 | 40篇 |
2022年 | 87篇 |
2021年 | 175篇 |
2020年 | 167篇 |
2019年 | 215篇 |
2018年 | 275篇 |
2017年 | 352篇 |
2016年 | 321篇 |
2015年 | 347篇 |
2014年 | 371篇 |
2013年 | 420篇 |
2012年 | 756篇 |
2011年 | 603篇 |
2010年 | 292篇 |
2009年 | 232篇 |
2008年 | 331篇 |
2007年 | 320篇 |
2006年 | 227篇 |
2005年 | 921篇 |
2004年 | 783篇 |
2003年 | 573篇 |
2002年 | 239篇 |
2001年 | 150篇 |
2000年 | 52篇 |
1999年 | 165篇 |
1992年 | 123篇 |
1991年 | 149篇 |
1990年 | 177篇 |
1989年 | 158篇 |
1988年 | 178篇 |
1987年 | 121篇 |
1986年 | 149篇 |
1985年 | 123篇 |
1984年 | 101篇 |
1983年 | 85篇 |
1979年 | 134篇 |
1978年 | 97篇 |
1977年 | 94篇 |
1976年 | 77篇 |
1975年 | 138篇 |
1974年 | 130篇 |
1973年 | 119篇 |
1972年 | 140篇 |
1971年 | 118篇 |
1970年 | 88篇 |
1969年 | 105篇 |
1968年 | 114篇 |
1967年 | 125篇 |
1966年 | 106篇 |
1965年 | 71篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
本试验通过在饲粮中添加不同剂量的甜菜碱研究其对热应激肉鸡生长性能、十二指肠消化酶活性及盲肠微生物区系的影响。选取270只14日龄爱拔益加(AA)肉鸡随机分成6组:常温组、热应激组,常温+0.1%甜菜碱组、热应激+0.1%甜菜碱组、热应激+0.2%甜菜碱、热应激+0.4%甜菜碱组。热应激肉鸡饲养在(32±1)℃的高温环境中。每组3个重复,每个重复15只。预试期7 d,正试期21 d。结果表明:1)饲粮添加甜菜碱可极显著增加28~42日龄热应激肉鸡的体重(P<0.01),极显著降低22~35日龄肉鸡料重比(P<0.01);2)除添加0.1%和0.2%甜菜碱饲粮对28日龄热应激肉鸡胰蛋白酶活性无显著影响(P>0.05)和添加0.1%甜菜碱对35日龄热应激肉鸡淀粉酶活性无显著影响(P>0.05)外,不同浓度的甜菜碱均能显著或极显著增加28、35、42日龄热应激肉鸡十二指肠胰蛋白酶、淀粉酶和胰脂肪酶活性(P<0.05或P<0.01);3)饲粮添加甜菜碱极显著提高了28、35、42日龄热应激肉鸡盲肠内乳酸杆菌的数量(P<0.01),极显著降低了产气荚膜梭菌的数量(P<0.01)。由此可见,热应激状态下,在基础饲粮中添加甜菜碱可改善AA肉鸡生长性能,提高十二指肠消化酶的活性,维持盲肠内微生物区系平衡,从而减轻热应激对肉鸡的危害。 相似文献
82.
Liliana R. Leite-Martins Maria I.M. Mahú Ana L. Costa Ângelo Mendes Elisabete Lopes Denisa M.V. Mendonça João J.R. Niza-Ribeiro Augusto J.F. de Matos Paulo Martins da Costa 《Preventive veterinary medicine》2014
Antimicrobial resistance (AMR) is a growing global public health problem, which is caused by the use of antimicrobials in both human and animal medical practice. The objectives of the present cross-sectional study were as follows: (1) to determine the prevalence of resistance in Escherichia coli isolated from the feces of pets from the Porto region of Portugal against 19 antimicrobial agents and (2) to assess the individual, clinical and environmental characteristics associated with each pet as risk markers for the AMR of the E. coli isolates. 相似文献
83.
Paulo Ricardo Dell'Armelina Rocha Andrea Bertuglia Elena Biasibetti Michela Bullone Alfonso Rosamilia Loretta Masoero Maria Teresa Capucchio 《Journal of Equine Veterinary Science》2014
Choroid plexus papilloma (CPP) is a rare, benign, intracranial neoplasm. The present report described a choroid plexus papilloma of the fourth ventricle with unusual proliferative reaction of ependymal/subependymal cells in a stallion. A single, soft neoformation, red-gray in color, with an irregular surface, resembling a cauliflower, expanding from the fourth ventricle to the cerebellar peduncles was observed. Microscopically, the neoformation was composed of a single layer of simple cuboidal to columnar epithelium with a well-vascularized papillary-arboriform pattern. Multifocal subependymal aggregates forming rosettes were observed near the mesencephalic aqueduct (MA). Glial-fibrillary-acidic-protein (GFAP) was markedly positive only in the neuropil adjacent to the proliferative areas of the MA. Ependymal/subependymal reactions secondary to CPP have never been described in equine or human neuropathology. The capabilities of ependymal cells to regenerate and eventually proliferate are controversial and unclear and, thus, require additional investigation to understand the adaptive mechanisms of this rare pathogenic condition. 相似文献
84.
Carmen Lucia de Souza Rech José Luiz Rech Vivian Fischer Mabel Mascarenhas Wiegand Heden Luiz Marques Moreira Maria Teresa Moreira Osório Frank Siewerdt 《Tropical animal health and production》2014,46(1):191-195
The objective of this trial was to evaluate the effect of whole rice meal (WRM) inclusion in the concentrate upon body development, carcass traits, and meat quality of lambs. Twenty-four castrated lambs with an average initial body weight of 17.90?±?2.72 kg were randomly blocked according to two genetic groups (Corriedale and Texel by Corriedale crossbreds). Three isocaloric (11.3 MJ/kg of metabolizable energy) and isonitrogenous (17 % crude protein) diets were offered to the animals for 74 days. Diets consisted of 40 % forage and 60 % concentrate diet, on a dry matter basis, with 0, 15, or 30 % of WRM inclusion into the concentrate. Body growth (after slaughter), carcass, and meat traits were evaluated on each animal. Results obtained indicated that genotype did not affect body growth, carcass, and meat traits except for yellowness. No significant interaction between diet and genotype were detected. Inclusion of up to 30 % WRM did not significantly (P?>?0.05) affect body growth, carcass, and meat traits, except for meat color. Meat luminosity progressively increased (36.32?+?0.055X) while redness (15.13???0.03X) decreased with the inclusion of WRM in the diet, but still remained within acceptable values. The study indicates that WRM may be included up to 30 % in the concentrate replacing corn without adverse effects upon body development, carcass traits, and meat quality of lambs. 相似文献
85.
86.
将36 头盘江黄牛及其杂交牛分成12 组,采用不同的日粮,进行两期育肥试验,得到不同的增重水平和实际营养物质摄入量。用各组实际采食的干物质( DM) 、粗蛋白(CP) 、综合净能(NEmf) 与我国试行的《肉牛饲养标准》进行比较。结果表明,除干物质与标准相差较多( - 6 .3 % ) 外,粗蛋白和综合净能与标准相当接近( 仅相差- 1 .5 % 和2 .8 % ) ,说明盘江黄牛及其杂交牛在育肥中的营养需要基本与标准相符,在配制日粮时,可以参考我国的《肉牛饲养标准》。 相似文献
87.
The use of polymerase chain reaction for determination of virulence factors of Escherichia coli strains isolated from pigs in Poland. 总被引:5,自引:0,他引:5
J Osek P Gallien M Truszczy?ski D Protz 《Comparative immunology, microbiology and infectious diseases》1999,22(3):163-174
E. coli strains isolated from pigs with postweaning diarrhea or edema disease were tested by phenotypic and genotypic methods for the presence of virulence antigens and genes, respectively. The slide agglutination and ELISA analyses were used for determination of F4, F5, F6, F17, and F41 fimbriae whereas the prevalence of fimbrial fedA and toxin eltI, estI, estII, stx1, stx2 and stx2e genes were recorded by the means of PCR. Only F4 antigen (ac variant) was found in strains of the serogroup O149:K91 isolated from pigs with diarrhea. PCR analyses showed that the fedA gene encoding F18 fimbriae was present in 61.9% of strains isolated from pigs with diarrhea and in 84.2% of strains isolated from pigs with edema disease. The eltI genes encoding heat-labile toxin I (LTI) were present only in 9 out of 21 strains recovered from pigs with diarrhea. Shiga toxin 2 variant (stx2e) genes were found in six isolates from edema disease and also in one strain from diarrhea. The PCR test used in the study was a sensitive and valuable method for determination of virulence factors of E. coli strains. 相似文献
88.
We have studied the cellular alterations, after in vitro adherence, of purified K88ab fimbriae to membranes of porcine enterocytes. Effects on enzymatic activities as disaccharydases and alkaline phosphatase show low changes. While cAMP levels were decreased (44%), guanylyl cyclase was increased (up to 200%), and levels of cGMP were in consequence significantly affected. This study support the role of cyclic GMP as intracellular mediator for adherence, and suggest their implication in disease, affecting a membrane-mediated mechanisms for guanylate cyclase activation, that is unique in the intestine. 相似文献
89.
Cezinande Meira Valsair Matos Pessoa Jo?o Carlos Pinheiro Ferreira Gustavo Henrique M. Araujo Marilu M. Gioso Sony Dimas Bicudo Eunice Oba Cassia Orlandi 《Journal of veterinary science (Suw?n-si, Korea)》2006,7(4):387-390
The present study was conducted in order to verify the efficacy of lower doses and alternative routes of a prostaglandin F2α analogue, luprostiol (PGF), for the induction of luteolysis and the precipitation of estrus in nonlactating Nelore cows (Bos taurus indicus). A conventional dose (15 mg) of PGF was compared to doses lower than the conventional dose, which ranges from 10 to 50%, that were administered intramuscularly (IM), intravulvosubmucosally (IVSM), or in the Bai-hui acupuncture site located within the lumbosacral area. The cows were administered PGF 8 day after estrus in the presence of a corpus luteum, and randomly assigned to the following groups: G1 (positive control), 15 mg, IM (n = 23); G2, 7.5 mg, IM (n = 23); G3, 3.75 mg, IM (n = 24); G4, 7.5 mg, IVSM (n = 25); G5, 3.75 mg, Bai-hui acupoint (n = 24); and G6, 1.5 mg, Bai-hui acupoint (n = 25). The results indicated that 50% of a conventional dose of PGF (7.5 mg) resulted in a complete luteal regression (plasma progesterone <1 ng/ml) at Hour 48, and hastened estrus, regardless of whether or not PGF was administered IM or IVSM. Comparatively, 10 or 25% of the conventional dose, even when administered to the Bai-hui acupoint, resulted in an initial reduction in the concentration of progesterone at Hour 24, followed by an increase observed at Hour 48. In conclusion, 25% of a conventional PGF dose administered via the Bai-hui acupoint proved inadequate to induce a complete luteal regression, whereas 50% of a conventional dose administered IM or IVSM was found to be the minimal dose required to induce effectively a complete luteal regression, and to precipitate the onset of estrus in nonlactating Nelore cows. 相似文献
90.
Felipe Nogueira Soares Maria Emilia Franco Oliveira Luciana Cristina Padilha-Nakaghi Luís Guilherme de Oliveira Marcus Antônio Rossi Feliciano Felipe Brener Bezerra de Oliveira Pedro Paulo Maia Teixeira Wilter Ricardo Russiano Vicente Cristian Faturi Luiz Fernando de Souza Rodrigues 《Tropical animal health and production》2015,47(8):1465-1471