全文获取类型
收费全文 | 2131篇 |
免费 | 70篇 |
国内免费 | 226篇 |
专业分类
林业 | 18篇 |
农学 | 51篇 |
基础科学 | 7篇 |
84篇 | |
综合类 | 777篇 |
农作物 | 27篇 |
水产渔业 | 31篇 |
畜牧兽医 | 1397篇 |
园艺 | 11篇 |
植物保护 | 24篇 |
出版年
2024年 | 7篇 |
2023年 | 21篇 |
2022年 | 53篇 |
2021年 | 94篇 |
2020年 | 73篇 |
2019年 | 87篇 |
2018年 | 47篇 |
2017年 | 102篇 |
2016年 | 90篇 |
2015年 | 90篇 |
2014年 | 111篇 |
2013年 | 90篇 |
2012年 | 179篇 |
2011年 | 162篇 |
2010年 | 134篇 |
2009年 | 146篇 |
2008年 | 126篇 |
2007年 | 135篇 |
2006年 | 108篇 |
2005年 | 86篇 |
2004年 | 93篇 |
2003年 | 75篇 |
2002年 | 56篇 |
2001年 | 35篇 |
2000年 | 48篇 |
1999年 | 35篇 |
1998年 | 30篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有2427条查询结果,搜索用时 15 毫秒
91.
92.
为研究大肠杆菌不耐热肠毒素(LT)对小鼠胚胎稳定性的影响,运用大肠杆菌表达系统制备了具有生物活性的重组大肠杆菌LT,用重组LT通过腹腔注射处理妊娠小鼠,分析了LT对小鼠胚胎稳定性的影响。首先采用PCR方法从产毒大肠杆菌菌株44815基因组中扩增LT的A、B亚基基因,将其插入到pET-20b(+)原核表达载体pelB信号肽的下游,分别构建成LTA和LTB分泌型表达载体;将载体分别转化大肠杆菌BL21(DE3)pLysS,在IPTG的诱导下进行表达,利用Ni-NTA琼脂糖凝胶从细菌周质释放液中提取和纯化重组LTA和LTB蛋白;利用细胞毒性试验检测重组蛋白的生物活性。然后用制备的重组LT注射妊娠6d的小鼠,连续注射3d后,统计小鼠的胚胎存活率。同时用ELISA方法检测小鼠血清中与胚胎稳定性密切相关的Th1型细胞因子(IFN-γ、IL-2)和Th2型细胞因子(IL-4、IL-10)及IL-β的表达水平。结果表明,采用分泌性表达策略实现了重组LT在大肠杆菌中的高效分泌表达,LTA和LTB的表达量分别达68、62mg/L。表达的重组LT具有明显的细胞毒性作用;用LT处理妊娠小鼠,胚胎的存活率为32%,明显低于对照组;小鼠血清中Th1型细胞因子IFN-γ和IL-2的含量明显高于对照组(P〈0.01),分别为对照组的2、3倍。同时细胞因子IL-1β为对照组的2倍(P〈0.01),而稳定胚胎发育的Th2型细胞因子IL-4、IL-10没有明显变化(P〉0.05)。据此推测,LT可能与大肠杆菌性肠炎引起妊娠家畜流产有关,LT对胚胎稳定性的影响除与LT的直接毒性有关外,可能还与LT介导的免疫调节异常有关。 相似文献
93.
94.
通过对某养鹅专业户病死产蛋鹅的病原分离,革兰氏染色镜检,生化试验,药敏实验。结果表明:分离菌为大肠杆菌,对头孢噻肟、阿米卡星、壮观霉素等高度敏感,对青霉素、四环素等产生耐药。分离菌制成蜂胶灭活苗免疫该专业户产蛋鹅后,发病率和死亡率明显下降,具有较好的免疫效果。 相似文献
95.
近年来,从华东地区患腹泻仔猪中分离到一些表达K88菌毛的大肠杆菌,这些菌株只与K88a因子单抗反应,而不与b、c、d因子单抗反应。通过K88常规血清交叉吸收试验、SDS-PAGE、Western印迹,表明这些菌株不仅与K88ac参考菌株C83907制备的c因子血清反应,而且与以分离株SEC586制备且经K88ab、K88ac、K88ad参考菌株吸收后的血清也反应。对分离株SEC586、SEC464的K88主要亚单位结构基因faeG的克隆、测序,发现该基因由846对核苷酸组成,编码菌毛主要亚单位的262个氨基酸及21个氨基酸的信号肽,比国外报道的K88ac FaeG亚单位(263个氨基酸)少了1个氨基酸,比K88ab、K88ad(265个氨基酸)少了3个氨基酸。SEC586、SEC464菌株的FaeG亚单位氨基酸序列的同源性为97.7%,它们与K88ac的同源性为94.7%和96.2%;与K88ab的同源性为90.1%和91.2%;与K88ad的同源性为87.0%和88,6%。结果表明,新分离的K88ac大肠杆菌黏附素主要亚单位已发生了部分变异。 相似文献
96.
A Dam 《Acta veterinaria Scandinavica》1973,14(5):691-699
Experiments have been carried out with vaccination of pregnant mice against E. coli, followed by i.p. challenge of the offspring at one week of age.With a septicaemic strain the results were highly significant, and the method is therefore recommendable for testing of vaccines against such strains of E. coli.Results were less clear-cut with enteropathogenic strains of E. coli. However, with mortality rates of 40 to 45 % in baby mice born by non-vaccinated mothers and less than 15 % in baby mice born by vaccinated mothers, the difference in percentage mortality seems sufficient to warrant the use of the method also in the control of vaccines against enteropathogenic E. coli strains. 相似文献
97.
98.
A risk-factor study was performed in eight dairy herds found to excrete verocytotoxin-producing Escherichia coli (VTEC) O157 in a former prevalence study. Associations between excretion of VTEC O157 and management factors such as housing and feeding were analysed in a generalised linear mixed model. The animals were stratified in three age groups and sampled four times during 1 year. The risk of excreting VTEC O157 was higher among weaned calves than non-weaned calves. Among the calves aged 1–4 months, the risk was reduced if the calf had suckled colostrum from the mother or if the calf had stayed >2 days with the mother after calving. Calves aged 5–24 months that had been moved within the last 2 weeks had a higher risk, but risk was reduced if fed barley silage. Cows fed grain or molasses had a higher risk of excreting VTEC O157. 相似文献
99.
Infections of chickens with Escherichia coli serotypeO78 can be treated with the antibiotic sarafloxacin. Three experiments were conducted on the administration of this drug to chickens that had been experimentally infected with E. coli. The birds were monitored for 10 days after infection for their average daily gain (ADG) and feed conversion ratio (FCR), and the post-mortem pathology was assessed. In the first experiment, sarafloxacin (20 mg/L, equivalent to 5 mg/kg live weight per day), given in the drinking water for 3 days after infection, led to a reduction in the mortality from 75% to 27%, but the ADG of the treated birds was still less than that of the uninfected controls. In the second experiment, when the sarafloxacin was administered at the same dose in the water but over only 2 h, there was also a considerable reduction in mortality, and the ADG and the FCR also improved significantly. In the third experiment, the dose dependence of the drug was tested. The birds were given 5 and 10 mg/kg per day sarafloxacin in each group, starting within 2 h after infection. This rapid administration of the drug completely prevented mortality, while the ADG and FCR were similar to those of the uninfected controls. 相似文献
100.
Brajesh C. Varshney N.M. Ponnanna Pranati A. Sarkar Pragna Rehman Jigar H. Shah 《Journal of veterinary science (Suw?n-si, Korea)》2007,8(1):57-64
Escherichia coli (E. coli) strains were collected from young diarrheic calves in farms and field. Strains that expressed the K99 (F5) antigen were identified by agglutination tests using reference antibodies to K99 antigen and electron microscopy. The K99 antigen from a selected field strain (SAR-14) was heat-extracted and fractionated on a Sepharose CL-4B column. Further purification was carried out by sodium deoxycholate treatment and/or ion-exchange chromatography. Monoclonal antibodies to purified K99 antigen were produced by the hybridoma technique, and a specific clone, NEK99-5.6.12, was selected for propagation in tissue culture. The antibodies, thus obtained, were affinity-purified, characterized and coated onto Giemsa-stained Cowan-I strain of Staphylococcus aureus (S. aureus). The antibody-coated S. aureus were used in a co-agglutination test to detect K99+ E. coli isolated from feces of diarrheic calves. The specificity of the test was validated against reference monoclonal antibodies used in co-agglutination tests, as well as in ELISA. Specificity of the monoclonal antibodies was also tested against various Gram negative bacteria. The developed antibodies specifically detected purified K99 antigen in immunoblots, as well as K99+ E. coli in ELISA and co-agglutination tests. The co-agglutination test was specific and convenient for large-scale screening of K99+ E. coli isolates. 相似文献