全文获取类型
收费全文 | 78660篇 |
免费 | 3987篇 |
国内免费 | 52篇 |
专业分类
林业 | 3805篇 |
农学 | 2423篇 |
基础科学 | 400篇 |
8573篇 | |
综合类 | 15599篇 |
农作物 | 3195篇 |
水产渔业 | 3667篇 |
畜牧兽医 | 39336篇 |
园艺 | 943篇 |
植物保护 | 4758篇 |
出版年
2018年 | 962篇 |
2017年 | 1051篇 |
2016年 | 966篇 |
2015年 | 869篇 |
2014年 | 1049篇 |
2013年 | 2771篇 |
2012年 | 1838篇 |
2011年 | 2260篇 |
2010年 | 1472篇 |
2009年 | 1365篇 |
2008年 | 2197篇 |
2007年 | 2204篇 |
2006年 | 2000篇 |
2005年 | 1943篇 |
2004年 | 1840篇 |
2003年 | 1881篇 |
2002年 | 1780篇 |
2001年 | 2288篇 |
2000年 | 2278篇 |
1999年 | 1881篇 |
1998年 | 714篇 |
1997年 | 710篇 |
1995年 | 822篇 |
1993年 | 705篇 |
1992年 | 1492篇 |
1991年 | 1554篇 |
1990年 | 1673篇 |
1989年 | 1654篇 |
1988年 | 1528篇 |
1987年 | 1479篇 |
1986年 | 1528篇 |
1985年 | 1518篇 |
1984年 | 1253篇 |
1983年 | 1147篇 |
1982年 | 772篇 |
1981年 | 717篇 |
1979年 | 1249篇 |
1978年 | 979篇 |
1977年 | 850篇 |
1976年 | 803篇 |
1975年 | 913篇 |
1974年 | 1201篇 |
1973年 | 1240篇 |
1972年 | 1255篇 |
1971年 | 1183篇 |
1970年 | 1103篇 |
1969年 | 1004篇 |
1968年 | 863篇 |
1967年 | 907篇 |
1966年 | 837篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
The effects of offspring sex, weight, age, and level of interaction with the dam on responses to weaning were examined to assist in the development of a weaning protocol for alpacas. In the first study, preand post-weaning activities, and weight change over Days -12-0,0-7 and 7-16 with respect to weaning, were recorded for 20 dam-offspring (hembra-cria) pairs aged 81-200 days. Pre-weaning changes in dam and offspring weights were positively related (P<0.05). Although heavier crias tended to be found closer to their dams than lighter crias (P<0.05) no additional effect of age on the dam-offspring relationship was found. Following weaning, cria growth rates were low over Days 0-7 but improved over Days 7-16, and hembra weight change followed the same pattern. Over Days 0-2, grazing and sitting activities of hembras and crias were replaced by standing and walking along paddock fencelines, although by Day 2 fenceline activities had decreased (P<0.05). Crias which were more frequently observed at fencelines had lower post-weaning growth rates (P<0.05). In the second study, pre-weaning sucking behaviour, and weight change over Days -30-0, 0-8 and 8-16 with respect to weaning, were recorded for 19 hembra-cria pairs aged 124-160 days. During 10 hours of observation on Days -5 and -4, the total duration of sucking by individual crias varied from 0-18 minutes, and the mean +/- SEM duration of sucking was 1.94 +/- 0.113 minutes. Cria sucking behaviour was positively related to growth rate prior to and weight at weaning (P<0.05). As in the first study, pre-weaning changes in dam and offspring weights were positively related (P<0.05). Following weaning, growth rates of the crias were depressed and the hembras lost weight over Days 0-8 and 8-16. The changes in growth rate and behaviour in Studies 1 and 2 indicated that weaning can be stressful for hembras and crias. However, there was no evidence from either study that pre-weaning behavioural or physical characteristics were related to the changes. 相似文献
162.
163.
Abstract Extract A 15-year-old pony mare developed firm irregular bony swellings on all four legs. These were most severe around the carpal and fetlock joints of the forelegs, restricting both flexion and extension. Over about 6 months the horse had periodic bouts of coughing. She showed moderate weight loss and a depressed demeanour. 相似文献
164.
E H Bohl 《Journal of the American Veterinary Medical Association》1979,174(6):613-615
Rotavirus is a name given to a group of viruses that have similar characteristics and are generally capable of causing diarrhea in the young. Infection of pigs with porcine rotavirus is common and widespread and can result in diarrhea, especially in 1- to 4-week-old pigs. This virus is frequently associated with a diarrheal syndrome popularity known as "white scours," "milk scours," or "3-week-old scours." Pigs less than 1 week old are infrequently infected, presumably because of adequate passive immunity. The infection resembles enzootic transmissible gastroenteritis. Diagnosis can be made by immunofluorescent staining of mucosal scrappings from the small intestines. 相似文献
165.
L F Woodard H W Renshaw D Burger C S McCain R B Wilson 《American journal of veterinary research》1979,40(5):636-644
166.
167.
168.
169.
H. A. Vanhoof 《European journal of plant pathology / European Foundation for Plant Pathology》1979,85(1):31-37
Potato virus YN (PVYN) infection was determined by the tobacco test in Swifterbant (Eastern Flevoland). In plots with beet, wheat and seed potatoes the infection exhibited an identical course. No differences were found either between PVYN infection in the border and that in the middle of a field planted with ware potatoes, although infection pressure was clearly higher here than in the plot with seed potatoes. A barrier crop of 10 rows of wheat did not decrease the infection pressure of the virus.From August onwards, the spread of PVYN in Lienden (Betuwe) was followed. Here virus transmission was found continuously, even until mid-November.Potato volunteers outside as well as in potato fields are serious infection sources. In 1976 and in 1977 virus spread was detected before the flight ofMyzus persicae, as determined with yellow Moericke traps. Infection pressure can be measured more efficiently by the tobacco test than by aphid trapping. The effect of rogueing at the time of virus spread should be reconsidered.If infection pressures in different areas or successive years are to be compared, the tobacco test should be standardized. A proposal to this effect is made.Samenvatting In Swifterbant (Oostelijk Flevoland) werd de infectie met het aardappel-YN-virus (PVYN) bepaald met behulp van de tabakstoests. In percelen met bieten, tarwe en pootaardappelen bleek de infectie hetzelfde verloop te hebben. Tussen het infectieverloop van PVYN in de rand en in het midden van een veld consumptieaardappelen werd eveneens geen verschil gevonden. Wel was de infectiedruk hier duidelijk hoger dan in het pootgoedperceel. Een barrier crop van 10 rijen tarwe verminderde de infectiedruk niet.De volgende conclusies kunnen worden getrokken. Aardappelopslag buiten en in aardappelvelden vormt een zeer belangrijke infectiebron. Zowel in 1976 als in 1977 vond de virusverspreiding plaats vóór de vlucht vanMyzus persicae begon, zoals deze werd bepaald met behulp van de gele Moericke vangbakken. Het effect van opzuiveren ten tijde van de virusverspreiding dient aan een nader onderzoek te worden onderworpen. De infectiedruk kan met de tabakstoets op meer directe wijze worden vastgesteld dan met bladluisvangsten mogelijk is.Wil men overgaan tot het vergelijken van de infectiedruk in verschillende gebieden of in verschillende jaren, dan dient de tabakstoets te worden gestandaardiseerd. Een voorstel hiertoe wordt gedaan. 相似文献
170.