全文获取类型
收费全文 | 101627篇 |
免费 | 5627篇 |
国内免费 | 68篇 |
专业分类
林业 | 3905篇 |
农学 | 3257篇 |
基础科学 | 531篇 |
11688篇 | |
综合类 | 17122篇 |
农作物 | 3444篇 |
水产渔业 | 5127篇 |
畜牧兽医 | 54814篇 |
园艺 | 1210篇 |
植物保护 | 6224篇 |
出版年
2018年 | 1525篇 |
2017年 | 1572篇 |
2016年 | 1424篇 |
2015年 | 1278篇 |
2014年 | 1451篇 |
2013年 | 4015篇 |
2012年 | 2764篇 |
2011年 | 3381篇 |
2010年 | 2236篇 |
2009年 | 2161篇 |
2008年 | 3251篇 |
2007年 | 3156篇 |
2006年 | 3004篇 |
2005年 | 2675篇 |
2004年 | 2656篇 |
2003年 | 2685篇 |
2002年 | 2463篇 |
2001年 | 3441篇 |
2000年 | 3469篇 |
1999年 | 2746篇 |
1998年 | 1118篇 |
1997年 | 1033篇 |
1996年 | 941篇 |
1995年 | 1149篇 |
1994年 | 1043篇 |
1993年 | 961篇 |
1992年 | 2220篇 |
1991年 | 2394篇 |
1990年 | 2259篇 |
1989年 | 2185篇 |
1988年 | 2061篇 |
1987年 | 2069篇 |
1986年 | 2057篇 |
1985年 | 1999篇 |
1984年 | 1664篇 |
1983年 | 1471篇 |
1982年 | 942篇 |
1979年 | 1435篇 |
1978年 | 1135篇 |
1977年 | 1068篇 |
1976年 | 1044篇 |
1975年 | 1103篇 |
1974年 | 1316篇 |
1973年 | 1264篇 |
1972年 | 1266篇 |
1971年 | 1112篇 |
1970年 | 1130篇 |
1969年 | 1121篇 |
1968年 | 954篇 |
1967年 | 975篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
23.
24.
B J Culliton 《Science (New York, N.Y.)》1989,245(4919):697-698
25.
T Sekizaki Y Nakasato I Nonomura 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1992,54(3):493-499
Chicken pathogenic Escherichia coli strains were found to autoagglutinate in a static culture of trypticase soy broth (TSB). One strain, designated PDI-386, was further studied for its autoagglutinating property. Acidity in the cultured medium caused by glucose degradation induced the autoagglutination. The bacterial cells grown in a glucose-free L-broth could be aggregated by adding acid, which suggests a potentiality of autoagglutination of the strain grown in the L-broth. The autoagglutinating parent (Agg) formed small colonies with irregular edges like rough colonies on the TS agar, whereas its non-autoagglutinating variant (Nag) formed larger smooth colonies with a perfectly round edge. The Nag colony was easily generated from the Agg colony on the TS agar. The autoagglutinating property was very unstable when the bacteria was passed in the TSB, but rather stable in the L-broth. Under electron microscope, the Agg were found to possess pili of more than 20 microns in length. However, the phenotypic expression of autoagglutination did not correlate with that of mannose-sensitive hemagglutination against guinea pig erythrocytes. Incubation of the Nag in the L-broth at room temperature for more than 10 days provoked the reversion of the autoagglutination. There was no difference between the Agg and the Nag in terms of surface hydrophobicity, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns of membrane proteins and LPS, and plasmid profiles. The virulence of the Agg was higher than that of the Nag. The autoagglutination property is, however, so unstable that the pathogenicity of E. coli isolates from chickens should be carefully evaluated. 相似文献
26.
J B Herrick 《Journal of the American Veterinary Medical Association》1992,201(12):1854-1855
27.
Rostral and caudal rhinoscopy in dogs and cats facilitates the investigation of the nasal cavity and accurate biopsy. Rostral rhinoscopy can be performed by rigid endoscopes; caudal rhinoscopy requires flexible endoscopes. Deep anaesthesia or additional analgesia with local anaesthesia is necessary. The nasal cavity is assessed by its form, colour, surface of the mucous membrane, hyperemia, plaques, lesions, and the secretion is assessed by its quantity, colour and viscosity. Foreign bodies and neoplasia must also be looked for. Case reports with abnormal findings are described. 相似文献
28.
A S Waldvogel G A Anderson D L Phillips B I Osburn 《Comparative immunology, microbiology and infectious diseases》1992,15(1):53-63
Bluetongue virus infection in sheep and cattle during fetal development causes neuropathology. Two strains of bluetongue virus serotype 11 designated as UC-2 and UC-8 have different virulence patterns in newborn mice. These viruses have distinctly different electropherotype patterns on polyacrylamide gel electrophoresis indicating a genetic difference in these two viruses of the same serotype. Four bovine fetuses each were inoculated intramuscularly with either UC-2 or UC-8, and one fetus was inoculated with placebo. The inoculation was made intramuscularly through the uterine wall at 120 days' gestation, and the bovine fetuses were recovered by cesarean section 12 or 20 days after inoculation. Fetal blood was collected for virus isolation and serology. Virus was reisolated from brain, blood, lung and liver. Both strains, UC-2 and UC-8, cause severe lesions in the 120 day fetuses. The encephalomalacic lesions occurred earlier and were more severe in fetuses inoculated with UC-8 as compared to those inoculated with UC-2. The subtle differences observed in the fetuses inoculated with the two different strains suggest that there is a difference in pathogenic potential of the two viruses. These differences do not appear to be completely dependent upon the host species. 相似文献
29.
J W McBride R E Corstvet D B Paulsen J R McClure F M Enright 《American journal of veterinary research》1992,53(10):1889-1894
Systemic and pulmonary antibody responses of calves to Pasteurella haemolytica were evaluated by measuring immunoglobulin production in blood for 9 days and in pulmonary lavage fluid for 7 days after intrapulmonary inoculation. Clinical signs, pulmonary lesions, pulmonary and systemic inflammatory response, and amount of antigen in lavage fluid were used to evaluate the response of calves to challenge with P haemolytica. The pulmonary response consisted of production of IgG, IgE, and IgM antibodies to P haemolytica antigens and a 17- to 68-fold increase of cells in lavage fluid 8 hours after inoculation, with a gradual decrease toward normal. Antibodies of the IgM isotype to P haemolytica were demonstrated as early as 8 hours through 7 days after inoculation in 3 of 3 calves. Of the anti-P haemolytica isotypes, IgM was found in the highest concentration. In all of the inoculated calves, IgE was found 1 to 2 days after inoculation, and IgG was found in 2 of 3 inoculated calves from day 1 through 7 after inoculation. Detection of IgG correlated with smaller pulmonary lesions. Immunoglobulin A was not detected in lavage fluid. Serum was evaluated for IgG and IgM antibody response to P haemolytica. Specific IgM was detectable 5 days after inoculation, and IgG was detectable 7 days after inoculation. Pasteurella haemolytica antigens were not detected in serum or plasma. A transient increase in neutrophil count was found 8 hours after inoculation, with return to baseline values by 24 hours after inoculation.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
30.
The pyrimidine analog 5-bromodeoxyuridine (BUdR) competes with thymidine for incorporation into DNA. Substitution of BUdR for thymidine does not significantly affect cell viability but does block cell differentiation in many different lineages. BUdR substitution in a mouse myoblast line blocked myogenic differentiation and extinguished the expression of the myogenic determination gene MyoD1. Forced expression of MyoD1 from a transfected expression vector in a BUdR-substituted myoblast overcame the block to differentiation imposed by BUdR. Activation of BUdR-substituted muscle structural genes and apparently normal differentiation were observed in transfected myoblasts. This shows that BUdR blocks myogenesis at the level of a myogenic regulatory gene, possibly MyoD1, not by directly inhibiting the activation of muscle structural genes. It is consistent with the idea that BUdR selectively blocks a class of regulatory genes, each member of which is important for the development of a different cell lineage. 相似文献