全文获取类型
收费全文 | 88131篇 |
免费 | 4947篇 |
国内免费 | 92篇 |
专业分类
林业 | 3987篇 |
农学 | 2412篇 |
基础科学 | 496篇 |
10598篇 | |
综合类 | 15678篇 |
农作物 | 3479篇 |
水产渔业 | 4268篇 |
畜牧兽医 | 45866篇 |
园艺 | 991篇 |
植物保护 | 5395篇 |
出版年
2020年 | 757篇 |
2019年 | 829篇 |
2018年 | 1484篇 |
2017年 | 1641篇 |
2016年 | 1470篇 |
2015年 | 1218篇 |
2014年 | 1578篇 |
2013年 | 3169篇 |
2012年 | 2786篇 |
2011年 | 3153篇 |
2010年 | 1924篇 |
2009年 | 2026篇 |
2008年 | 3065篇 |
2007年 | 2832篇 |
2006年 | 2633篇 |
2005年 | 2509篇 |
2004年 | 2377篇 |
2003年 | 2436篇 |
2002年 | 2159篇 |
2001年 | 2573篇 |
2000年 | 2615篇 |
1999年 | 2029篇 |
1998年 | 754篇 |
1996年 | 755篇 |
1995年 | 830篇 |
1993年 | 759篇 |
1992年 | 1662篇 |
1991年 | 1848篇 |
1990年 | 1726篇 |
1989年 | 1756篇 |
1988年 | 1577篇 |
1987年 | 1638篇 |
1986年 | 1692篇 |
1985年 | 1635篇 |
1984年 | 1253篇 |
1983年 | 1120篇 |
1981年 | 744篇 |
1979年 | 1246篇 |
1978年 | 972篇 |
1977年 | 829篇 |
1975年 | 809篇 |
1974年 | 1104篇 |
1973年 | 1084篇 |
1972年 | 1127篇 |
1971年 | 1065篇 |
1970年 | 1007篇 |
1969年 | 929篇 |
1968年 | 832篇 |
1967年 | 826篇 |
1966年 | 758篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
Serum samples collected from 687 indigenous chickens located in small scattered groups in four states of Nigeria were examined for antibodies to infectious bursal disease (IBD) virus by the agar-gel precipitation (AGPT) and counterimmunoelectrophoresis (CIEOP) tests. 51 of the positive samples were further titrated by each of the two techniques. CIEOP detected more positive reactors (74.59%) than AGPT (58.95%). CIEOP also detected higher antibody levels among the reactors [geometric mean titre (GMT) of 51 samples was 23.02] when compared to AGPT. GMT of the same 51 samples was 21.8. The prevalence of antibodies to IBD virus in the indigenous chickens ranged from 64.7 to 77.7% CIEOP reactors between states. Since reports of IBD outbreaks among these chickens are rare unlike the situation among commercial poultry flocks, it was concluded that local chickens probably act as carriers of IBD virus. 相似文献
102.
103.
J. E. Reubranb 《European Journal of Forest Research》1870,14(1):137-139
Ohne Zusammenfassung 相似文献
104.
105.
106.
Shorr E 《Science (New York, N.Y.)》1940,91(2361):321-322
107.
E M Aburto A Cribb I C Fuentealba B O Ikede F S Kibenge F Markham 《Canadian journal of veterinary research》2001,65(2):104-110
This study evaluates the ability of selenium (Se) supplementation to prevent experimental copper (Cu)-induced hepatocellular damage. Weanling male Fischer 344 rats were randomly assigned to groups of 15, 3 groups (A,B,C) were fed Cu-loaded diets (containing 2000 microg/g copper, added as CuSO4) and different levels of Se (added as Na2SeO3 x 5H2O) as follows: A) Cu-loaded/Se adequate diet (0.4 microg/g Se, fed basis); B) Cu-loaded/Se-supplemented diet (2 microg/g Se); and C) Cu-loaded/Se-deficient diet (< 0.2 microg/g). Three additional groups (D,E,F) were fed diets containing adequate levels of Cu (14 microg/g Cu, fed basis) and different levels of Se as follows: D) Cu-adequate/Se-adequate diet; E) Cu-adequate/Se-supplemented diet (2 microg/g Se); and F) Cu-adequate/Se-deficient (< 0.2 microg/g) diet. After 4, 8, and 12 weeks on the experimental diets, liver samples were processed for histology, histochemistry, metal analysis, glutathione peroxidase (GSH-Px) measurement, and quantification of malondialdehyde (MDA). Morphologic changes characteristic of Cu-associated hepatitis, without an increase in hepatic MDA levels, were seen in all Cu-loaded rats in each sampling. Similar changes occurred in rats fed Se-adequate, Se-supplemented and Se-deficient diets. This study demonstrates that Fischer 344 rats fed 2000 microg/g Cu develop morphologic changes due to Cu toxicity without evidence of lipid peroxidation. Furthermore, Se supplementation does not result in protection against Cu-induced liver injury. 相似文献
108.
109.
E C?té 《Veterinary Clinics of North America: Small Animal Practice》2001,31(6):1129-45, v
Severe heart disease may cause hypotension and hypoperfusion, and ultimately circulation may cease altogether. These two clinical syndromes are cardiogenic shock and cardiac arrest, respectively. This review summarizes the causes and clinical features of each, and describes the treatment options available to clinicians managing patients in cardiogenic shock. 相似文献
110.
M E Kehrli K A Weigel A E Freeman J R Thurston D H Kelley 《Veterinary immunology and immunopathology》1991,27(4):303-319
Blood neutrophil functions, lymphocyte blastogenic responses, serum complement, and serum conglutinin activity of 98 lactating Holstein cows from two genetic lines were evaluated. The genetic lines were produced in a selection experiment that created and perpetuated genetic differences in milk production for up to seven generations. No significant differences between the two genetic lines of cows were found for neutrophil function, lymphocyte blastogenic responses, serum complement levels, or serum conglutinin levels. Significant differences between sire progeny groups within lines were found for unstimulated and mitogen-stimulated lymphocyte blastogenesis (P less than 0.0001), and almost all neutrophil functions (antibody independent neutrophil cytotoxicity, antibody dependent neutrophil cytotoxicity, ingestion of bacteria, iodination, chemiluminescence, chemokinesis, and chemotaxis (P less than or equal to 0.05)). Sire progeny group differences (P less than or equal to 0.0001) within lines for serum complement and conglutinin activity were also found. Neutrophil chemiluminescence activity (positive relationship; P less than or equal to 0.001), concanavalin A-stimulated lymphocyte blastogenesis (positive relationship; P less than or equal to 0.004), and serum conglutinin activity levels (negative relationship; P less than or equal to 0.01) each had small but significant associations with the total milk somatic cell count. Cows seropositive for bovine leukosis virus had increased resting and mitogen-stimulated lymphocyte blastogenic activity and were associated with increased in vitro neutrophil random migration and production of superoxide anion. Estimates of genetic parameters of various immune cell functions, of serum complement and of conglutinin levels for daughters of 11 sires with 4-6 daughters in the data set were determined. In this report, genetic variation was demonstrated for nonspecific humoral and cellular immunity. 相似文献