全文获取类型
收费全文 | 123804篇 |
免费 | 6857篇 |
国内免费 | 88篇 |
专业分类
林业 | 5233篇 |
农学 | 3545篇 |
基础科学 | 724篇 |
13949篇 | |
综合类 | 23273篇 |
农作物 | 4679篇 |
水产渔业 | 5743篇 |
畜牧兽医 | 64687篇 |
园艺 | 1370篇 |
植物保护 | 7546篇 |
出版年
2018年 | 1578篇 |
2017年 | 1787篇 |
2016年 | 1624篇 |
2015年 | 1445篇 |
2014年 | 1774篇 |
2013年 | 4464篇 |
2012年 | 3258篇 |
2011年 | 3964篇 |
2010年 | 2476篇 |
2009年 | 2663篇 |
2008年 | 3847篇 |
2007年 | 3699篇 |
2006年 | 3581篇 |
2005年 | 3257篇 |
2004年 | 3170篇 |
2003年 | 3153篇 |
2002年 | 2995篇 |
2001年 | 3889篇 |
2000年 | 3888篇 |
1999年 | 3053篇 |
1998年 | 1169篇 |
1997年 | 1203篇 |
1996年 | 1173篇 |
1995年 | 1411篇 |
1994年 | 1260篇 |
1993年 | 1234篇 |
1992年 | 2617篇 |
1991年 | 2749篇 |
1990年 | 2553篇 |
1989年 | 2591篇 |
1988年 | 2464篇 |
1987年 | 2593篇 |
1986年 | 2611篇 |
1985年 | 2524篇 |
1984年 | 2018篇 |
1983年 | 1785篇 |
1982年 | 1226篇 |
1979年 | 1859篇 |
1978年 | 1533篇 |
1977年 | 1321篇 |
1976年 | 1319篇 |
1975年 | 1367篇 |
1974年 | 1806篇 |
1973年 | 1765篇 |
1972年 | 1777篇 |
1971年 | 1682篇 |
1970年 | 1550篇 |
1969年 | 1448篇 |
1968年 | 1206篇 |
1967年 | 1291篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
D J Larson L G Morehouse R F Solorzano D A Kinden 《American journal of veterinary research》1979,40(4):477-486
Fourteen neonatal dogs (4 through 11 days of age) were exposed orally to the Purdue strain of transmissible gastroenteritis (TGE) virus, and six dogs of similar age were noninoculated controls. Clinical signs of enteric disease did not develop. Both exposed and control dogs had normal fecal passages and appetite throughout the experiment. Jejunal epithelium from dogs euthanatized at 12, 24, 48, and 96 hours and at 10 days after exposure did not exhibit morphologic alterations detectable by light microscopy. Electron microscopic examination indicated that jejunal epithelial cells contained TGE viral particles as early as 12 hours after dogs were exposed. There were no apparent morphologic alterations or signs of desquamation of virus-infected cells, however. Results of pig transmission studies indicated that viable TGE virus was in jejunal tissue of the dogs as early as 12 hours and as late as 10 days after exposure to the virus. 相似文献
993.
J M Kaneene P Nicoletti R K Anderson C C Muscoplat D W Johnson 《American journal of veterinary research》1979,40(11):1503-1509
Cell-mediated immune responses in cattle adult-vaccinated with Brucella abortus strain 19, cattle infected with B abortus field strain, and nonexposed cattle were studied by an in vitro lumphocyte-stimulation test (LST). Lymphocytes were prepared from peripheral bovine blood by the Ficoll-diatrizoate technique, and results were assayed for [3H]thymidine incorporation into DNA by liquid scintillation spectrometry. Serotests and bacteriologic isolation attempts were conducted simultaneously with LST. Lymphocytes from cattle infected with field strains had significantly (P = 0.01) higher specific lymphocyte-stimulation inexposed controls. The LST, the serum standard-tube agglutination test (STT), the Rivanol (RIV) test, and the complement-fixation (CF) test correctly classified cattle from which field strains and strain 19 of B abortus were isolated. The LST was negative in cattle vaccinated with B abortus strain 19 (nonshedding), but the three serotests had many false-positive reactions. The CF test had the least false-positive reaction, followed by the RIV test, and the STT was the least specific. Well before the three serotests became positive, the LST was positive in samples from some cattle during the incubation period of the infection. There was little or no correlation between cell-mediated immune responses (as measured by LST) and serum antibody responses (as measured by STT, RIV test, and CF test) in vaccinated but culture-negative cattle and in some nonvaccinated cattle during the incubation period. 相似文献
994.
Naturally acquired Brucella abortus infections were studied during consecutive pregnancies in eight sheep and in their lambs over a period of 40 months to evaluate epizootiologic aspects of natural infection in sheep. Brucella abortus was isolated from the ewes following 16 of 26 natural terminations of pregnancy: from 5 of 6 ewes in the first year, from six of eight ewes in the second year, from two of six ewes in the third year, and from three of six ewes in the fourth year. Vaginal swab samples and milk samples were the most consistent source of the brucella organisms. Brucella abortus was isolated from three ewes when standard tube test seroagglutination titers were less than 1:100. In contrast, results of supplemental tests (card, 2-mercaptoethanol, complement-fixation, and Rivanol) remained positive during the study. During the 40 months, B abortus was isolated from 4 of 4 aborted fetuses, 2 of 5 stillborn lambs, 10 of 37 living lambs, and as an indicator of continuing infection, from 6 of 12 lambs born during the fourth year. Although B abortus has a definite host preference for cattle, this study demonstrated that under appropriate management conditions, sheep may be naturally infected and may remain infected for more than 40 months. Epizootiologic evaluation of all factors, including husbandry practices and exposure potential, should be utilized in determining the need to test other species that may have been exposed to cattle infected with B abortus. 相似文献
995.
996.
Hartline FF 《Science (New York, N.Y.)》1979,204(4395):823-824
997.
998.
999.
L F Woodard H W Renshaw D Burger C S McCain R B Wilson 《American journal of veterinary research》1979,40(5):636-644
1000.
T L Huber M C Peed R C Wilson D D Goetsch 《American journal of veterinary research》1979,40(6):792-794
Absorption of endotoxin from the gastrointestinal tract was evaluated in hay-fed and lactic acidotic sheep duodenally infused with 10 mg of Escherichia coli endotoxin, and in lactic acidotic sheep not infused. The effect of abomasal fluid on biological activity of endotoxin was also evaluated. Leukopenia was the criterion used for detecting endotoxemia. Absorption of endotoxin from the gastrointestinal tract was not detected in either hay-fed or lactic acidotic sheep. Endotoxin appeared to maintain its activity after incubation with abomasal fluid, and the presence of endogenous endotoxin in abomasal contents was indicated. The results indicate that endotoxin of alimentary origin may not be involved in the lactic acidosis syndrome in ruminants. 相似文献