全文获取类型
收费全文 | 1144篇 |
免费 | 57篇 |
国内免费 | 2篇 |
专业分类
林业 | 16篇 |
农学 | 2篇 |
112篇 | |
综合类 | 281篇 |
农作物 | 12篇 |
水产渔业 | 20篇 |
畜牧兽医 | 726篇 |
园艺 | 1篇 |
植物保护 | 33篇 |
出版年
2012年 | 86篇 |
2011年 | 100篇 |
2010年 | 15篇 |
2009年 | 11篇 |
2008年 | 96篇 |
2007年 | 91篇 |
2006年 | 71篇 |
2005年 | 69篇 |
2004年 | 74篇 |
2003年 | 90篇 |
2002年 | 59篇 |
2001年 | 47篇 |
2000年 | 72篇 |
1999年 | 35篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 16篇 |
1992年 | 15篇 |
1991年 | 19篇 |
1990年 | 23篇 |
1989年 | 39篇 |
1988年 | 12篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1971年 | 5篇 |
1966年 | 3篇 |
1959年 | 3篇 |
1958年 | 3篇 |
1957年 | 9篇 |
1947年 | 3篇 |
1946年 | 2篇 |
1945年 | 2篇 |
1944年 | 2篇 |
1941年 | 3篇 |
1936年 | 2篇 |
1932年 | 2篇 |
1931年 | 3篇 |
1923年 | 2篇 |
1893年 | 2篇 |
1891年 | 2篇 |
1889年 | 2篇 |
排序方式: 共有1203条查询结果,搜索用时 0 毫秒
1.
2.
3.
Sample surveys provide data for academic research, government policy-making, the media, and business. Statistical research aims to improve survey data by reducing extraneous sources of variability and thus increasing accuracy. Researchers have begun to use paradigms adapted from the cognitive sciences to study those sources of variability associated with the processes that the respondent undertakes in understanding questions, remembering, judging and estimating, and formulating answers. To generalize laboratory-based findings, researchers must begin to embed designed experiments that vary the questionnaire content into sample surveys of broad population. Issues associated with the design of and statistical inference from such embedded experiments are examined and illustrated with an example on the effects of context questions on responses in attitude surveys. 相似文献
4.
5.
6.
7.
8.
9.
10.
Long MT Gibbs EP Mellencamp MW Zhang S Barnett DC Seino KK Beachboard SE Humphrey PP 《Equine veterinary journal》2007,39(6):486-490
REASON FOR PERFORMING STUDY: West Nile virus (WNV) infection is endemic and able to cause disease in naive hosts. It is necessary therefore to evaluate the safety of new vaccines. OBJECTIVES: To establish: 1) the safety of a modified live Flavivirus/West Nile virus (WN-FV) chimera by administration of an overdose and testing for shed of vaccine virus and spread to uninoculated sentinel horses; 2) that this vaccine did not become pathogenic once passaged in horses; and 3) vaccine safety under field conditions. METHODS: There were 3 protocols: 1) In the overdose/shed and spread study, horses were vaccinated with a 100x immunogenicity overdose of WN-FV chimera vaccine and housed with sentinel horses. 2) A reversion to virulence study, where horses were vaccinated with a 20x immunogenicity overdose of WN-FV chimera vaccine. Horses in both studies were evaluated for abnormal health conditions and samples obtained to detect virus, seroconversion and dissemination into tissues. 3) In a field safety test 919 healthy horses of various ages, breeds and sex were used. RESULTS: Vaccination did not result in site or systemic reactions in either experimental or field-injected horses. There was no shed of vaccine virus, no detection of vaccine virus into tissue and no reversion to virulence with passage. CONCLUSIONS: WN-FV chimera vaccine is safe to use in horses with no evidence of ill effects from very high doses of vaccine. There was no evidence of reversion to virulence. In addition, administration of this vaccine to several hundred horses that may have been previously exposed to WNV or WNV vaccine resulted in no untoward reactions. POTENTIAL RELEVANCE: These studies establish that this live attenuated Flavivirus chimera is safe to use for immunoprophylaxis against WNV disease in horses. 相似文献