全文获取类型
收费全文 | 186383篇 |
免费 | 9184篇 |
国内免费 | 14718篇 |
专业分类
林业 | 20070篇 |
农学 | 14638篇 |
基础科学 | 9792篇 |
25809篇 | |
综合类 | 88988篇 |
农作物 | 13168篇 |
水产渔业 | 5627篇 |
畜牧兽医 | 17337篇 |
园艺 | 5090篇 |
植物保护 | 9766篇 |
出版年
2024年 | 1223篇 |
2023年 | 3113篇 |
2022年 | 4877篇 |
2021年 | 5550篇 |
2020年 | 5496篇 |
2019年 | 6495篇 |
2018年 | 3802篇 |
2017年 | 6378篇 |
2016年 | 8127篇 |
2015年 | 6775篇 |
2014年 | 9735篇 |
2013年 | 9966篇 |
2012年 | 14115篇 |
2011年 | 13997篇 |
2010年 | 11305篇 |
2009年 | 11457篇 |
2008年 | 10355篇 |
2007年 | 12051篇 |
2006年 | 10328篇 |
2005年 | 8480篇 |
2004年 | 6731篇 |
2003年 | 5801篇 |
2002年 | 4486篇 |
2001年 | 4040篇 |
2000年 | 3648篇 |
1999年 | 2914篇 |
1998年 | 2505篇 |
1997年 | 2209篇 |
1996年 | 2096篇 |
1995年 | 2099篇 |
1994年 | 1873篇 |
1993年 | 1602篇 |
1992年 | 1416篇 |
1991年 | 1223篇 |
1990年 | 1104篇 |
1989年 | 951篇 |
1988年 | 683篇 |
1987年 | 499篇 |
1986年 | 270篇 |
1985年 | 95篇 |
1984年 | 63篇 |
1983年 | 35篇 |
1982年 | 47篇 |
1981年 | 58篇 |
1980年 | 43篇 |
1979年 | 34篇 |
1978年 | 28篇 |
1977年 | 18篇 |
1976年 | 22篇 |
1962年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
国内外养羊业发展特点与趋势 总被引:11,自引:0,他引:11
当前肉羊业在大洋洲、美洲、欧洲和一些非洲国家得到迅猛发展,世界羊肉,特别是羔羊肉的生产和消费显著增长。肉羊产业具有周转快、投资少、效益高等特点,已成为我国在资源短缺、畜禽产品需求日益增加的背景下,保持畜牧业可持续发展的重要途径之一。本文还仔细分析我国肉羊生产存在的不足和发展的优势,并结合国内外养羊业发展的趋势提出了及时调整养羊业的生产方向和产品结构,研究和推广先进实用的养羊综合配套技术等发展我国养羊业的建议。 相似文献
82.
以从美国威斯康星大学引进的叶用芥菜胞质雄性不育系叶用4-4为母本,以泰国清迈大学选育出的8个优良叶用芥菜品种为转育父本,杂交后连续回交4代(BC4),再将BC4与优良叶用芥菜品种40R2-3-4配制8个杂交组合,其中2个组合(4-4 × 19-H-12)×40R2-3-4和(4-4 × 2R2)×40R2-3-4结球率为100%,产量比商用品种分别高34%和13%,比其亲本分别高25%和5%。 相似文献
83.
84.
根据北京地区资料分析了沙尘的年代变化、月变化,春季是沙尘天气的高发期并以浮尘和扬沙为主。造成沙尘天气的冷空气主要有三条路径,它与蒙古气旋、冷锋、高空急流等大尺度天气系统紧密相连。 相似文献
85.
果寡糖对猪粪便细菌群作用下L-色氨酸代谢的影响 总被引:3,自引:0,他引:3
本试验研究了果寡糖对猪粪便细菌群作用下L -色氨酸代谢的影响。将 10 % (W/V)粪水厌氧分装于无菌瓶中 ,分成 4组 :1组 (对照 )添加 2 5 0 μmol/LL -色氨酸 ;2~ 4组 :分别在对照组的基础上添加 0 .5 % ,1.0 %和 1.5 %果寡糖。 38℃、厌氧培养。在培养期的不同时间点 (0 ,2 ,4 ,6 ,8,12 ,18,2 4h)分别从各瓶中取 1mL培养液 ,分析各培养液中吲哚类物质含量。培养 2 4h后 ,分析各培养液中细菌学指标和pH。结果表明 :含L -色氨酸的体外培养液中添加 0 .5 % ,1.0 %和 1.5 %果寡糖 ,培养 2 4h后 ,使粪臭素浓度、吲哚 - 3-乙酸峰值和pH值均显著降低。添加1.0 %和 1.5 %果寡糖显著降低色氨酸降解率和粪臭素相对产率 ,显著提高吲哚相对产率 ,显著降低梭菌和大肠杆菌数 ,显著增加双歧杆菌和总厌氧菌数。 相似文献
86.
Six cats with an advanced stage squamous cell carcinoma (SCC) of the nasal planum were treated with a combination of superficial radiotherapy and intralesional carboplatin therapy. This multimodality protocol was well tolerated by the majority of cats and resulted in complete responses in all cats (100%). Median follow‐up for all cats is 268 days, and the median time‐to‐recurrence, time‐to‐progression and overall survival have not yet been reached. Our study, although limited in number of animals and with a relatively short median follow‐up compared to other studies for this disease, suggests that a combination of radiotherapy and intralesional carboplatin is a useful treatment option for an advanced stage SCC of the nasal planum in cats and warrants further application of the multimodality approach presented here. 相似文献
87.
88.
通过对重庆近郊的沙坪坝区、北碚区、九龙坡区、永川市、璧山县、铜梁县的7个养鸭场病死鸭的病原分离,分离到三株细菌,经染色镜检、生化鉴定、动物回归实验,确诊为鸭里氏杆菌。药敏试验结果显示对庆大霉素、青霉素、链霉素、土霉素等高度敏感。在临床上交替使用这些药物,收到较好治疗效果。将分离菌制成灭活苗免疫1周龄的健康鸭,20日龄时用分离菌进行攻毒,平均保护率达83.3%。 相似文献
89.
90.
Michael R. Bedford 《British poultry science》2018,59(5):486-493
ABSTRACT1. Enzymes have been used commercially for nearly 40 years and save significant costs through sparing of expensive nutrients but the mechanism by which this is achieved is still debated.2. The research focused on non-starch polysaccharidase (NSPase) enzymes is used as an example of where greater progress could have been made if the details of the work had been described more fully and the analysis of the data generated had been broader in scope and more critical.3. Lack of standardisation of the details presented in the materials and methods has been identified as a significant barrier to meaningful retrospective analysis and thus limits advances in the understanding of the mode of action of these enzymes.4. The identity of the enzyme employed and its activity is often lacking, and more importantly the purity is rarely disclosed. Contaminant activities which are neither listed nor assayed could play a significant role in the responses observed.5. The dose optimum of most enzymes is often considerably higher than that employed in most studies. Thus studies claiming synergy between two ‘activities’ should ensure that the response is not related to each enzyme simply augmenting the dose of just one activity in the finished feed. This is a common problem, and coupled with the lack of factorial experiments to justify the presence of each enzyme in a multi-enzyme product, it is not surprising that there is still debate as to whether single or multi-enzymes are best suited poultry rations.6. The three proposed mechanisms for NSPases (viscosity, cell wall and prebiotic) are discussed, and along with their strengths and weaknesses it is suggested that a re-evaluation of each is needed. Viscosity may have to be re-evaluated as being a function not only of the cereal being fed, but of the age of the animal as well. The cell wall theory as described is poorly modelled in vitro and hence the validity of these data is questioned. The prebiotic theory may need significant modification as it appears that the quantities of oligomers produced are insufficient to generate the additional volatile fatty acids (VFA)’s reported. It is likely that all three mechanisms play a role in the responses observed, but the prebiotic mechanism probably plays by far the most important part in low viscosity diets.7. Future research would be improved if it considered all potential mechanisms when designing a trial. Significant failings are apparent as a result of adherence to tenets in explanation of the results. Most importantly, it should be emphasised that a hypothesis is there to be tested, not defended. 相似文献