全文获取类型
收费全文 | 3132篇 |
免费 | 238篇 |
国内免费 | 1篇 |
专业分类
林业 | 351篇 |
农学 | 111篇 |
基础科学 | 11篇 |
688篇 | |
综合类 | 284篇 |
农作物 | 143篇 |
水产渔业 | 169篇 |
畜牧兽医 | 1198篇 |
园艺 | 69篇 |
植物保护 | 347篇 |
出版年
2023年 | 22篇 |
2022年 | 35篇 |
2021年 | 55篇 |
2020年 | 73篇 |
2019年 | 54篇 |
2018年 | 98篇 |
2017年 | 115篇 |
2016年 | 113篇 |
2015年 | 92篇 |
2014年 | 110篇 |
2013年 | 169篇 |
2012年 | 219篇 |
2011年 | 253篇 |
2010年 | 134篇 |
2009年 | 134篇 |
2008年 | 219篇 |
2007年 | 194篇 |
2006年 | 157篇 |
2005年 | 167篇 |
2004年 | 140篇 |
2003年 | 127篇 |
2002年 | 123篇 |
2001年 | 55篇 |
2000年 | 47篇 |
1999年 | 48篇 |
1998年 | 30篇 |
1997年 | 18篇 |
1996年 | 16篇 |
1995年 | 24篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 25篇 |
1991年 | 15篇 |
1990年 | 19篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1987年 | 20篇 |
1986年 | 8篇 |
1985年 | 16篇 |
1983年 | 10篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1976年 | 10篇 |
1974年 | 7篇 |
1973年 | 10篇 |
1972年 | 7篇 |
1970年 | 8篇 |
1969年 | 12篇 |
1968年 | 7篇 |
1958年 | 7篇 |
排序方式: 共有3371条查询结果,搜索用时 15 毫秒
1.
Twelve different mating types among the Hampshire and Landrace breeds were used to determine direct, maternal, heterosis, and recombination effects for performance and carcass traits. Mating types used were two purebred, two F1, two F2, two F3, and four backcross. Carcass data were collected on 238 barrows and 262 gilts over four replications. Traits measured were length (LENG), 10th rib off midline backfat (BF10), longissimus muscle area (LMA), and dressing percentage (DRS%). Average backfat (AVBF) was calculated as the mean of three midline fat depths measured opposite the first rib, last rib, and last lumbar vertebra. The model used to evaluate the carcass traits included main effects of mating type, farrowing season, and sex and included slaughter weight as a covariate. The performance traits of ADG, feed efficiency (FE), daily feed consumption (DFC), lean gain per day (LNGN), and lean efficiency (LNEF) were measured on a pen basis. Comparisons of reciprocal F1 crosses showed that carcasses from pigs sired by Hampshire boars were leaner and had more LMA than those sired by Landrace boars. Heterosis percentages were significant for AVBF (7.2%; P less than .01), BF10 (8.8%; P less than .01), DRS% (1.5%; P less than .01), ADG (11.5%; P less than .01), DFC (10.2%; P less than .01), LNGN (10.6%; P less than .01), and LNEF (6.0%; P less than .05). Epistatic recombination losses in the offspring were significant for LENG (3.6 cm; P less than .05) and approached significance for BF10 (6.1 mm; P less than .10). 相似文献
2.
Abstract. Experiments were conducted for one year on two different soil types. On a clay soil straw was either (a) burnt, (b) baled leaving the stubble, or (c) chopped and spread. The soil was tine cultivated to depths of 5, 10 or 15 cm or ploughed to 20 or 30 cm before winter wheat was sown conventionally. In addition, a direct-drilled crop was sown after each straw treatment. On a silt loam soil the direct-drilled, tine cultivated to 15 cm and ploughed to 30 cm treatments following burning or chopping and spreading straw were repeated.
Tine cultivation incorporated less straw than ploughing, decreased plant establishment and early growth but did not decrease yield. Direct-drilling through chopped straw decreased yield on the silt loam but not on the clay soil. Short straw (< 5 cm) was easier to incorporate than longer straw. Ploughing was the most efficient method of straw incorporation because it inverts soil. Early effects on crop growth and nutrient uptake following straw incorporation were transient and associated with large amounts of straw in the seeded layer of soil. 相似文献
Tine cultivation incorporated less straw than ploughing, decreased plant establishment and early growth but did not decrease yield. Direct-drilling through chopped straw decreased yield on the silt loam but not on the clay soil. Short straw (< 5 cm) was easier to incorporate than longer straw. Ploughing was the most efficient method of straw incorporation because it inverts soil. Early effects on crop growth and nutrient uptake following straw incorporation were transient and associated with large amounts of straw in the seeded layer of soil. 相似文献
3.
Christian Walzer Anna Kübber-Heiss Nadia Robert 《Journal of veterinary diagnostic investigation》2002,14(1):76-79
Removal of the spinal cord is considered time consuming and difficult. A delay in the necropsy procedure, especially in the central nervous system, can result in significant tissue autolysis and subsequent diagnostic difficulties. In the field, where many necropsies are performed, suitable electric saws are mostly unavailable. A technically simple and rapid method for spinal cord removal, requiring only a straightforward tool, has been devised. No necropsy-induced structural damage has been noted on histopathologic examination. 相似文献
4.
Expression of β2-integrin on monocytes and blood polymorphonuclear leukocytes in the periparturient period in dairy cows
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)
Araceli Diez-Fraile Luc Duchateau Evelyne Meyer Christian Burvenich 《Canadian journal of veterinary research》2003,67(3):235-238
The hypothesis that an altered expression of CD11/CD18 on bovine circulating monocytes, polymorphonuclear leukocytes (PMN), or both, contributes to an increased mastitis susceptibility in periparturient cows was tested. Expression of CD18 and CD11a, -b, -c on bovine monocytes and PMN were assessed in 8 Friesian-Holstein cows by flow cytometry from 2 wk before calving to 5 wk after calving. Minor changes in adhesion molecule expression levels were detected throughout the experimental period. Compared with PMN, monocytes exhibited an expression level that was similar for CD18, higher for CD11a and CD11c, but lower for CD11b. Differences in density may reflect the relative importance of these adhesion molecules on both leukocyte types. In this study, the decreased number of milk resident macrophages and PMN observed during the periparturient period could not be attributed to changes of CD11/CD18 levels on circulating leukocytes. 相似文献
5.
6.
7.
8.
Evaluation of a Killed Vaccine Against Porcine Pleuropneumonia Due to Haemophilus pleuropneumoniae 总被引:20,自引:2,他引:18
Higgins R Larivière S Mittal KR Martineau GP Rousseau P Cameron J 《The Canadian veterinary journal. La revue veterinaire canadienne》1985,26(2):86-89
A bacterin containing serotypes 1 and 5 of Haemophilus pleuropneumoniae was developed for the prevention and the control of porcine pleuropneumonia. It was injected intramuscularly into three groups of ten piglets, the first group with one dose, the second one with two doses and the third one with three doses at two-week intervals. Another group of ten piglets did not receive the vaccine. All the piglets were then challenged by an aerosol of mixed suspensions of H. pleuropneumoniae serotypes 1 and 5. Two and three injections of vaccine completely prevented mortality, whereas half of the control piglets and of those receiving only one dose of vaccine died. All surviving piglets, both control and vaccinated, had severe signs of respiratory disease for at least 36 hours after exposure to challenge. Moreover, vaccination did not induce the production of antibodies at high titers. Local reactions were not noted after vaccination and at postmortem; ten weeks after the challenge, there were no signs of abscess formation or induration. 相似文献
9.
10.