全文获取类型
| 收费全文 | 92806篇 |
| 免费 | 5843篇 |
| 国内免费 | 49篇 |
专业分类
| 林业 | 3939篇 |
| 农学 | 3568篇 |
| 基础科学 | 661篇 |
| 11835篇 | |
| 综合类 | 13754篇 |
| 农作物 | 3445篇 |
| 水产渔业 | 5329篇 |
| 畜牧兽医 | 49096篇 |
| 园艺 | 1240篇 |
| 植物保护 | 5831篇 |
出版年
| 2020年 | 791篇 |
| 2019年 | 1020篇 |
| 2018年 | 1658篇 |
| 2017年 | 1923篇 |
| 2016年 | 1752篇 |
| 2015年 | 1476篇 |
| 2014年 | 1798篇 |
| 2013年 | 3963篇 |
| 2012年 | 3107篇 |
| 2011年 | 3801篇 |
| 2010年 | 2458篇 |
| 2009年 | 2420篇 |
| 2008年 | 3650篇 |
| 2007年 | 3395篇 |
| 2006年 | 3309篇 |
| 2005年 | 2822篇 |
| 2004年 | 2725篇 |
| 2003年 | 2730篇 |
| 2002年 | 2502篇 |
| 2001年 | 3468篇 |
| 2000年 | 3375篇 |
| 1999年 | 2604篇 |
| 1998年 | 1008篇 |
| 1997年 | 1081篇 |
| 1996年 | 909篇 |
| 1995年 | 1055篇 |
| 1994年 | 918篇 |
| 1993年 | 923篇 |
| 1992年 | 1886篇 |
| 1991年 | 1947篇 |
| 1990年 | 1880篇 |
| 1989年 | 1885篇 |
| 1988年 | 1643篇 |
| 1987年 | 1613篇 |
| 1986年 | 1649篇 |
| 1985年 | 1555篇 |
| 1984年 | 1251篇 |
| 1983年 | 1055篇 |
| 1982年 | 729篇 |
| 1979年 | 1081篇 |
| 1978年 | 837篇 |
| 1975年 | 837篇 |
| 1974年 | 920篇 |
| 1973年 | 881篇 |
| 1972年 | 813篇 |
| 1971年 | 812篇 |
| 1970年 | 812篇 |
| 1969年 | 798篇 |
| 1968年 | 716篇 |
| 1967年 | 749篇 |
排序方式： 共有10000条查询结果，搜索用时 31 毫秒
41.
S T Grubbs S A Kania L N Potgieter 《Journal of veterinary diagnostic investigation》2001,13(2):128-132
Subgroup-specific peptide-based enzyme-linked immunosorbent assays from the G-protein of the ovine and bovine respiratory syncytial virus (RSV), respectively, were used to determine the prevalence of the ovine and bovine subgroup strains of RSV infections in cattle. A total of 1,102 bovine serum samples were obtained from 6 diagnostic laboratories located in the northwestern and the southeastern USA and were tested for antibody to either the bovine or ovine subgroups of RSV. Antibody to viruses from each subgroup was present in samples from each region and all states tested. The Southeast had a higher prevalence of the bovine subgroup strains (69.5%). Then did the Northwest (40.9%). The prevalence of the ovine strain was similar for the two regions (16.7% in the southeast, 14.9% in the northwest). The overall prevalence was 56.6% for the bovine strain and 15.9% for the ovine strain. These results suggest members of the ovine subgroup of RSV circulate in the cattle population but with less frequency than those viruses of the bovine subgroup. 相似文献
42.
van Miert AS 《The Veterinary quarterly》1985,7(3):200-216
Summary Acute febrile diseases are characterized by specific and non-specific symptoms. The non-specific responses are presented under the headings: fever, inflammation and pain, experimental models for investigating febrile reactions, haematologic changes, blood biochemical changes, cardiovascular effects, changes in gastric function, and the effects of fever upon pharmacokinetics of drugs. It was the purpose of this review to describe present concepts of thermoregulation and fever, the associated reactions produced by bacterial pyrogens and the mechanisms of these reactions. The available data illustrate, that many questions have not yet been clearly answered. However, the entire field of research involving endogenous substances, such as interleukin-1, is now moving ahead with great speed. Furthermore, there is some evidence which suggests that fever and the associated lower plasma zinc and iron levels act together as a co-ordinated non-specific host defence mechanism. Since experimental fever has a distinct effect upon the pharmacokinetics of drugs, more attention should be given to this aspect. 相似文献
43.
Dogs vaccinated with a Leptospira interrogans vaccine containing serogroups Canicola and Icterohaemorrhagiae and prepared from cultures grown in a protein-free medium resisted challenge with heterologous representatives of these serogroups. In contrast, control dogs were pyrexic and leptospires were isolated from the blood for nine days following Canicola challenge and six days after Icterohaemorrhagiae challenge. Leptospires were isolated from the urine of controls throughout the post challenge period and from kidneys at post mortem examination of six out of six and four out of six Canicola and Icterohaemorrhagiae challenged controls, respectively. There have been no reports of hypersensitivity reactions to this vaccine since its introduction in 1980. 相似文献
44.
Traditional forest economics deals with regularly-ordered activities.For many reasons, however, choices must often be made amongconflicting operational priorities. In these circumstances,maximizing net discounted revenue per hectare does not maximizeglobal profit. Priorities for action should be chosen in orderof urgency index ratio, defined as the cost of delaying an operationdivided by the units of limited resource needed to undertakethe operation. Forest managers tend to use informal and sometimesconflicting rules to assign priorities among uses of limitedresources. These priorities often differ from those indicatedby urgency index ratio. Urgency index ratio can be determinedby simple calculations based on readily-available data. Theconcept can be extended to include multiple constraints. 相似文献
45.
46.
47.
48.
Woodworth RS 《Science (New York, N.Y.)》1941,94(2438):265-270
49.
50.