首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   14047篇
  免费   463篇
  国内免费   939篇
林业   1163篇
农学   1002篇
基础科学   1123篇
  1060篇
综合类   5112篇
农作物   751篇
水产渔业   339篇
畜牧兽医   2186篇
园艺   2185篇
植物保护   528篇
  2024年   86篇
  2023年   230篇
  2022年   408篇
  2021年   460篇
  2020年   523篇
  2019年   513篇
  2018年   414篇
  2017年   593篇
  2016年   785篇
  2015年   701篇
  2014年   896篇
  2013年   810篇
  2012年   1270篇
  2011年   1079篇
  2010年   878篇
  2009年   779篇
  2008年   641篇
  2007年   622篇
  2006年   586篇
  2005年   408篇
  2004年   353篇
  2003年   279篇
  2002年   232篇
  2001年   240篇
  2000年   197篇
  1999年   204篇
  1998年   171篇
  1997年   148篇
  1996年   117篇
  1995年   119篇
  1994年   123篇
  1993年   91篇
  1992年   97篇
  1991年   83篇
  1990年   69篇
  1989年   63篇
  1988年   64篇
  1987年   32篇
  1986年   19篇
  1985年   8篇
  1984年   17篇
  1983年   4篇
  1982年   5篇
  1981年   5篇
  1980年   4篇
  1979年   7篇
  1978年   3篇
  1977年   6篇
  1973年   2篇
  1955年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
从宁夏部分奶牛场(牧场、养殖小区)采集94份临床型乳房炎乳样、70份隐性乳房炎乳样,并分离鉴定出4株非脱羧勒克菌,其中临床型乳房炎分离出1株、隐性乳房炎分离出3株。药敏试验结果表明,4株非脱羧勒克菌均对链霉素、氨基糖苷类、喹诺酮类、头孢类药物敏感;对磺胺类、林可胺类药物则产生不同程度的耐药性。  相似文献   
22.
Reasons for performing study: Type 2 diabetes mellitus (T2DM) is diagnosed rarely in equine practice although it may be under‐recognised. A greater awareness of the condition and therapeutic considerations would be to the benefit of such cases presenting in practice. More investigation into the pharmacological management of these cases is needed. Objectives: Three cases of diabetes mellitus were investigated using a specific test for insulin sensitivity and pancreatic β cell function in order to define accurately and characterise the existence of T2DM in all 3 subjects. Methods: The insulin‐modified frequently sampled i.v. glucose tolerance test was performed in each case and the data so obtained were subject to minimal model analysis of insulin‐glucose dynamics. Cases were then monitored following treatment using a combination of dietary modification, metformin, glibenclamide and pergolide. Results: Marked insulin resistance was identified in each case and, furthermore, severe pancreatic β cell dysfunction was present therefore classifying each case as end stage T2DM. Treatment was nevertheless associated with restoration of normoglycaemia in all cases. Conclusions: T2DM in horses may be more common than generally considered. In some cases individuals may respond to therapy aimed at restoring insulin sensitivity and pancreatic function. Drugs used in other species for the treatment of T2DM have not yet been adequately tested in horses. Potential relevance: T2DM should be considered as an important differential diagnosis in mature to elderly horses and ponies suffering from weight loss, polydipsia and polyuria. Clinicians should be encouraged to offer treatment and management advice when such cases are encountered.  相似文献   
23.
The aim of this study was to compare blood copy, haematological and glucose values between cats experimentally infected with either Mycoplasma haemofelis (Group HF: 10 cats), ‘Candidatus M. haemominutum’ (Group HM: 3 cats) or ‘Candidatus M. turicensis’ (Group TU: 3 cats). Blood samples were collected regularly up to 85 days post-infection (DPI) for haemoplasma real-time quantitative PCR, haematology, Coombs’ testing and blood glucose measurement. Statistical analysis was performed using a general linear model (ANOVA) appropriate for a repeated measures experiment with significance set as P < 0.05. Cats in Group TU had significantly lower blood copy numbers than cats in Group HF (P < 0.001) and HM (P < 0.001). All Group HF cats developed anaemia (often severe), macrocytosis and evidence of erythrocyte-bound antibodies whereas Groups HM and TU cats did not. Group HF had significantly lower PCVs, haemoglobin concentrations and red blood cell counts, and significantly higher mean cell volumes, than Groups HM and TU. In Group HF, erythrocyte-bound antibodies reactive at 4 °C (both IgM and IgG) appeared between 8 and 22 DPI and persisted for two to four weeks, whereas those reactive at 37 °C (primarily IgG) appeared between 22 and 29 DPI and persisted for one to five weeks. In most cats antibodies appeared after the fall in haemoglobin started. Although Group TU had significantly lower glucose concentrations than Groups HF (P = 0.006) and HM (P = 0.027), mean blood glucose concentrations remained within the reference range in all groups. This study demonstrates that M. haemofelis infection, in contrast to ‘Candidatus M. haemominutum’ and ‘Candidatus M. turicensis’ infection, can result in a severe macrocytic anaemia and the development of cold and warm reactive erythrocyte-bound antibodies.  相似文献   
24.
采用试管凝集反应对海晏县的牦牛进行了布氏杆菌病的血清学检测,共检测177份血清样品,结果检出阳性血清9份,阳性率为5.08%。  相似文献   
25.
Six Swedish Red and White dairy cows, producing 20-39 kg of 4% fat-corrected milk were given a ration balanced in energy and protein. They had access to feed from 05.15 to 09.00 and from 13.00 to 16.30 and were milked at 06.15 and 15.30. The milk was analysed for urea with a FIA technique.There was a significant diurnal variation in milk urea. The highest values were found 3–5 h after the beginning of the morning feeding and the lowest values (down to 60% of the max. values) during late night. Within 1 h after the start of the morning feeding the urea values had increased significantly, but they had decreased within the same time after the start of the afternoon feeding. Since there was a pronounced diurnal variation in the milk fat content, the urea concentration was also recalculated to concentration in the water phase of the milk. It was higher in that phase, but the pattern of the diurnal variation was not changed significantly. However, analyses on milk with a very high fat content may give misleading results.There were no important differences in the milk urea concentration of different udder quarters. When calculated as concentration in the water phase of the milk, no differences in urea concentration were found between the beginning and the end of milking. The analytical method had a good precision (coefficient of variation max. 3%). The milk urea concentration was not changed significantly after storage during 10 days at 4°C when no preservative was added; but after 17 days the milk had turned sour and the urea value had increased. When a preservative (bronopole) was added the urea concentration remained unchanged during 17 days. Deepfreezing did not influence the urea concentration.  相似文献   
26.
从138份血清样品的比较试验结果显示,快速凝集试验(RCA)比补体结合试验(CF)检测边缘无浆体感染的敏感性高(88.9%:81.5%),假阴性率低(11.1%:18.5%),两者都具有良好的特异性和预测性,检测阳性符合率高,快速凝集试验对一次感染牛的持续检出阳性时间更长久(303天:92天)  相似文献   
27.
The aim of this study was to investigate the microbial protein yield of different pure carbohydrates to contribute to a more precise prediction of the microbial protein formed in the rumen. In a first experiment, sucrose, wheat starch, microcrystalline cellulose and citrus pectin were incubated for 8 and 24 hr in the modified Hohenheim gas test (HGT) system (3 runs × 2 syringes) including gas production, ammonia and short‐chain fatty acid concentration measurements. Ammonia values were used for estimation of the microbial protein formation. In a second experiment, the same substrates were incubated for 96 hr in the HGT system (2 runs × 3 syringes) and gas production was measured after 2, 4, 6, 8, 12, 16, 24, 30, 36, 48, 60, 72 and 96 hr of incubation to obtain the fermentation kinetics and the time of half‐maximal gas production (t1/2) of the substrates. The substrates differed considerably in their fermentation kinetics, and therefore, comparison on the basis of t1/2 was chosen as the most meaningful. At t1/2, microbial protein yield [g/kg dry matter] was higher for cellulose than for sucrose and pectin and higher for starch than for sucrose. The microbial protein expressed in g/L gas production was higher for starch and cellulose than for sucrose and pectin at t1/2. Effects of carbohydrates related to ruminal pH may remain undetected in in vitro trials.  相似文献   
28.
研究蚕桑产业经济中蚕茧价格(CAP)、蚕种饲养量(简称发种量,SSQ)、蚕药用量(SMQ)3个变量之间的关系,有助于科学预测蚕桑产业经济的发展变化规律。选取1991-2009年江苏省海安县蚕桑生产的年度数据,应用格兰杰因果关系检验(Granger causality test)方法,对上述3个变量进行平稳性检验、变量的一阶差分与单位根检验和格兰杰因果关系检验。结果表明,蚕茧价格与发种量、发种量与蚕药用量之间存在格兰杰因果关系,蚕茧价格与蚕药用量之间不存在格兰杰因果关系,即:蚕茧价格增长能引起发种量的增加,但发种量增加却不是蚕茧价格增长的原因,蚕茧价格对发种量的影响滞后期为2年,到第3年影响程度已逐渐弱化;发种量增加能引起蚕药用量的增加,但影响滞后期只有1年,超过1年后的影响不显著;蚕茧价格与蚕药用量之间从实际趋势看有一定的关联性,但相互之间的影响关系不是直接的,难以建立函数关系。研究结果与蚕桑产业发展变化的实际情况基本相符,认为格兰杰因果关系检验方法可应用于蚕桑产业经济相关因素的发展变化规律研究。  相似文献   
29.
青脚白羽鸡测交羽色效应研究   总被引:1,自引:1,他引:1  
青脚白羽鸡是近年来选育出的新品种,为了利用好该鸡种优良的种质特性,试验中用其他优良鸡种与其测交,以期使更多的优良性状组合在一起,甚至超过双亲,将杂交优势在生产中加以利用。目前的试验结果表明,以青脚白羽鸡作母本、川东大黑鸡作父本的测交组合经济性状效果最好,其测交的羽色遗传效应较复杂,认真研究该遗传效应,对于丰富遗传育种理论和指导育种实践有着重要的意义。  相似文献   
30.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号