全文获取类型
收费全文 | 85662篇 |
免费 | 19167篇 |
国内免费 | 29181篇 |
专业分类
林业 | 9590篇 |
农学 | 9277篇 |
基础科学 | 9458篇 |
35742篇 | |
综合类 | 35693篇 |
农作物 | 7061篇 |
水产渔业 | 6500篇 |
畜牧兽医 | 10281篇 |
园艺 | 3267篇 |
植物保护 | 7141篇 |
出版年
2024年 | 920篇 |
2023年 | 1248篇 |
2022年 | 1819篇 |
2021年 | 1847篇 |
2020年 | 3425篇 |
2019年 | 6805篇 |
2018年 | 6345篇 |
2017年 | 7310篇 |
2016年 | 7999篇 |
2015年 | 8257篇 |
2014年 | 7360篇 |
2013年 | 7857篇 |
2012年 | 7847篇 |
2011年 | 7035篇 |
2010年 | 5941篇 |
2009年 | 5404篇 |
2008年 | 4286篇 |
2007年 | 4442篇 |
2006年 | 3938篇 |
2005年 | 3439篇 |
2004年 | 2967篇 |
2003年 | 2710篇 |
2002年 | 2493篇 |
2001年 | 2094篇 |
2000年 | 1798篇 |
1999年 | 1730篇 |
1998年 | 1598篇 |
1997年 | 1507篇 |
1996年 | 1371篇 |
1995年 | 1439篇 |
1994年 | 1371篇 |
1993年 | 1114篇 |
1992年 | 1097篇 |
1991年 | 884篇 |
1990年 | 720篇 |
1989年 | 703篇 |
1988年 | 610篇 |
1987年 | 432篇 |
1986年 | 423篇 |
1985年 | 221篇 |
1984年 | 202篇 |
1983年 | 191篇 |
1982年 | 194篇 |
1981年 | 238篇 |
1980年 | 193篇 |
1979年 | 154篇 |
1978年 | 131篇 |
1975年 | 109篇 |
1965年 | 139篇 |
1964年 | 142篇 |
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
121.
122.
123.
Epidemiological study of enzootic pneumonia in dairy calves in Saskatchewan. 总被引:4,自引:0,他引:4
下载免费PDF全文
![点击此处可从《Canadian journal of veterinary research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
J Van Donkersgoed C S Ribble L G Boyer H G Townsend 《Canadian journal of veterinary research》1993,57(4):247-254
A field study involving 325 calves from 17 dairy herds in Saskatchewan was conducted to determine the risk of enzootic pneumonia and to assess its association with a number of factors. Two different case definitions of pneumonia were used in the analyses: the first was based on producers' treatment risk (CASE1) and the second was based on semimonthly clinical examinations of calves by the research veterinarian (CASE2). The risk of pneumonia based on CASE1 was 39% and on CASE2 was 29%. The measure of agreement between CASE1 and CASE2 at the calf level of analysis was poor (kappa = 0.24, SE = 0.02) and at the herd level of analysis was moderate (kappa = 0.40, SE = 0.12). The mortality risk from pneumonia was 1.8% and a variety of infectious organisms were isolated from pneumonic lungs. Twenty-seven percent of the calves had inadequate (total IgG < or = 800 mg/dL) levels of passively acquired antibodies as measured by radial immunodiffusion. The proportion of seropositive titers in calves within the first two weeks of age was 94% to parainfluenza 3 virus (PI3V) and bovine respiratory syncytial virus (BRSV), 73% to Pasteurella haemolytica (Ph), 68% to bovine viral diarrhea virus (BVDV), 67% to infectious bovine rhinotracheitis virus (IBRV), 46% to Mycoplasma dispar (Md), 44% to Haemophilus somnus (Hs), and 21% to Mycoplasma bovis (Mb). At the calf level of analysis and after adjusting for clustering, there was a negative association (p = 0.10) between the diagnosis of pneumonia based on CASE2 and total IgG levels and Ph titers (rPh).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
124.
125.
从实际工程的角度出发,对电路电测方法进行了论述。在微通信工程中,需要获得障碍物的位置和高度,最合理的天线高度组合和障碍物绕射损耗等参数,为此论述了微波电路电测方法及技术要求。在大庆-秦皇岛输油管道通信工程中采用了A,B测试法进行测试,得到高度-损耗曲线。这种曲线给出相对自由空间接收电平与收,发天线高度之间的关系。在测试所得的高度-损耗曲线与断面图相结合的基础上,由绕射损耗计算公式推出了几种常见障碍 相似文献
126.
本文研究了光子消灭算符α的任κ次幂算符α~κ的正交归一本征态的高阶压缩特性。研究结果表明:光子消灭算符α的偶数次幂α~κ的正交归一本征态一定不存在N<κ,但N≠κ/2的第2N阶压缩,只可能存在第κ阶压缩和N≥κ的第2N阶压缩;光子消灭算符α的奇数次幂α~κ的正交归一本征态一定不存在N<κ的第2N阶压缩,只可能存在N≥κ的第2N阶压缩。 相似文献
127.
Alkaline phosphatase isoenzymes in feline serum using an agarose gel alkaline phosphatase kit method. 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Canadian journal of veterinary research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
B S Horney A J Farmer A MacKensie D J Honor S Buczkowski 《Canadian journal of veterinary research》1992,56(4):373-375
Total serum alkaline phosphatase (ALP) activity is the product of the combined activity of isoenzymes from a number of tissue sources. In this study, a commercially available kit for electrophoretic separation of ALP isoenzymes in an agarose gel was used to separate ALP isoenzymes in feline tissue extracts and serum. Five separate bands of ALP activity were identified. These bands were numbered 1 to 5 with band 1 having the most anodal migration. The tissue of origin corresponding to the migration position of the isoenzymes are as follows: Band 3 was the liver isoenzyme, band 4 was the bone isoenzyme and ALP isoenzymes of both intestine and kidney migrate in the position labelled band 5. Band 1 appears to be related to albumin and does not represent true ALP activity. The tissue source of band 2 (a and b) was not identified. Serum ALP activity of mature, healthy cats is primarily of liver origin. Immature cats (< 1 year of age) have a greater proportion of the bone isoenzyme in the serum. 相似文献
128.
129.
本文对大岛樱中国引种点危害较严重的4种病害和2种害虫进行观测和种类鉴定,指出了各病虫害的危害症状和发生发展规律等,并试验或介绍了相应的防治措施。 相似文献
130.
Nephrotoxicity of amphotericin B in dogs: a comparison of two methods of administration. 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Canadian journal of veterinary research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
S I Rubin D R Krawiec H Gelberg R D Shanks 《Canadian journal of veterinary research》1989,53(1):23-28
Two methods of administration of amphotericin B were compared for their ability to produce nephrotoxicity in 12 dogs. Six dogs received six alternate day doses of amphotericin B: 1 mg/kg administered as a rapid bolus in 25 mL 5% dextrose in water. Another six dogs received alternate day treatments of the same dose of amphotericin B in 1 L 5% dextrose in water over 5 h. Both treatment groups experienced significant reductions in glomerular filtration rate, as measured by inulin clearance, 24 h endogenous creatinine clearance, serum creatinine and serum urea. This reduction in glomerular filtration rate was most marked in the group receiving the drug as a rapid bolus. The inulin clearances decreased from 3.54 +/- 0.30 mL/min/kg (means +/- SEM) on day 0 to 1.15 +/- 0.25 mL/min/kg on day 12 in the slow infusion group and from 3.24 +/- 0.25 mL/min/kg on day 0 to 0.46 +/- 0.11 mL/min/kg on day 12 in the rapid bolus group. Renal lesions characteristic of amphotericin B administration were observed in all dogs tested. The dogs which received amphotericin B as a rapid bolus had a significantly greater number of tubular lesions than the slow infusion group. Systemic side effects, such as vomiting, diarrhea and weight loss, were observed in both treatment groups but were most severe in the rapid bolus group.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献