全文获取类型
收费全文 | 126413篇 |
免费 | 5991篇 |
国内免费 | 91篇 |
专业分类
林业 | 5649篇 |
农学 | 3638篇 |
基础科学 | 741篇 |
12934篇 | |
综合类 | 27445篇 |
农作物 | 5097篇 |
水产渔业 | 5329篇 |
畜牧兽医 | 62889篇 |
园艺 | 1442篇 |
植物保护 | 7331篇 |
出版年
2018年 | 1278篇 |
2017年 | 1363篇 |
2016年 | 1277篇 |
2015年 | 1165篇 |
2014年 | 1388篇 |
2013年 | 4116篇 |
2012年 | 2662篇 |
2011年 | 3279篇 |
2010年 | 2137篇 |
2009年 | 2018篇 |
2008年 | 3203篇 |
2007年 | 3225篇 |
2006年 | 3026篇 |
2005年 | 2973篇 |
2004年 | 2841篇 |
2003年 | 2920篇 |
2002年 | 2759篇 |
2001年 | 3337篇 |
2000年 | 3304篇 |
1999年 | 2764篇 |
1997年 | 1131篇 |
1995年 | 1282篇 |
1993年 | 1138篇 |
1992年 | 2510篇 |
1991年 | 2637篇 |
1990年 | 2771篇 |
1989年 | 2795篇 |
1988年 | 2632篇 |
1987年 | 2546篇 |
1986年 | 2597篇 |
1985年 | 2607篇 |
1984年 | 2159篇 |
1983年 | 1928篇 |
1982年 | 1352篇 |
1981年 | 1286篇 |
1980年 | 1193篇 |
1979年 | 2133篇 |
1978年 | 1723篇 |
1977年 | 1526篇 |
1976年 | 1426篇 |
1975年 | 1605篇 |
1974年 | 2082篇 |
1973年 | 2080篇 |
1972年 | 2121篇 |
1971年 | 2040篇 |
1970年 | 1903篇 |
1969年 | 1669篇 |
1968年 | 1430篇 |
1967年 | 1573篇 |
1966年 | 1393篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
L G Rickard G L Zimmerman E P Hoberg P W Lockwood D W Weber R Miller 《Veterinary parasitology》1989,33(2):125-133
The effectiveness of the morantel sustained release trilaminate (MSRT) in controlling gastrointestinal nematodes through a grazing season was evaluated using 60 yearling beef stocker calves randomly divided into 2 groups of 30 animals each. In April 1985, the calves comprising the treatment group each received an MSRT designed to release morantel tartrate continuously for 90 days while those of the control group remained unmedicated. All animals were weighed and samples of rectal feces were taken at 14-day intervals, beginning on Day 0, until trial termination (Day 168). At trial termination, 10 control and 10 treated calves were necropsied for recovery of gastrointestinal nematodes. Three sets of parasite-na?ve tracer calves were utilized to evaluate the initial, interim and final levels of pasture contamination by nematode larvae. Overall, the use of the MSRT resulted in a 75.5% reduction (P less than 0.001) in output of nematode eggs from the principals, an 81.8% reduction (P less than 0.001) in numbers of gastrointestinal nematodes in principals (at trial termination), and a 96.9% reduction (P less than 0.05) of pasture larval nematode contamination (as indirectly indicated by parasite burdens in tracer calves). The mean weight advantage of treated calves was 16.6 kg per head (P less than 0.001). 相似文献
142.
Germinating seeds and young plants of winter rape var. Górczañski were vernalized for 56–63 days under conditions of 9-hour day, at the temperature 2 and 5 °C and in continuous darkness at the temperature 2 °C. After vernalization the plants grew under conditions enabling to complete vernalization: in a glass-house at the temperature day/night 15/10 °C and in semi natural conditions of open vegetation hall in the period from June till August. After sub-optimal vernalization further growth of the plants at lowered temperature increased its effectiveness (completion of vernalization). Depending on the degree of the vernalization of the plants the completion of their vernalization was both obligatory, i.e. conditioning the acquisition of the ability of generative development, and facultative i.e. accelerating this development. It has been demonstrated that the population of plants of the examined variety is strongly differentiated not only with respect of vernalization requirements in the particular plants, but also what regards the effectiveness of vernalization completion. New observations have been made indicating that the mechanisms controlling the successive phases of generative development, i.e. phase of forming flower buds and the flowering phase are not identical which may be interpreted as indicating that the "flowering factor" is polymorphous. 相似文献
143.
S Chikamatsu H K Zhao N Kikuchi T Hiramune 《Nippon juigaku zasshi. The Japanese journal of veterinary science》1989,51(5):887-891
Sera from 1186 apparently healthy sheep in Hokkaido were examined by enzyme-linked immunosorbent assay (ELISA) and immunodiffusion (ID) for the presence of antibodies against Corynebacterium pseudotuberculosis. ELISA-positives were 466 (39.3%) while ID-positives were 330 (27.8%). Spread of caseous lymphadenitis in sheep in Hokkaido was thus clarified. Although ID was less sensitive than ELISA in detecting the antibodies against C. pseudotuberculosis it did not give any non-specific reaction. From the results and in view of the simplicity of the test procedure, ID was found to be of practical diagnostic value. Distribution by age group of anti-C. pseudotuberculosis antibodies in 758 sheep in a herd detected by both tests showed that the ratio of positives was low in sheep aged less than 1 year, and the ratio increased significantly in those aged 1 year and continued to increase with age until it reached a plateau at the age of 4-5 years. 相似文献
144.
Spraying in so-called space cultures (orchards, vineyards) is determined by two main aims which require contrary technical measures for their realization: (1) optimal even distribution of droplet deposition on the target. This generally requires sufficient air assistance of droplet transportation and penetration in order to bridge the distance between the nozzle outlet and the target; (2) the surplus energy which normally exists should be minimized in order to avoid any droplet flow outside the target. Several possibilities exist to approach these requirements: (1) optimal blower design and correct adjustment for each specific purpose; (2) catching and recycling of misdirected droplets by recycling units; (3) sensoring of gaps in the canopy and activation of a nozzle shut-off. The legal requirements of the BBA are given, together with the results of experiments on drift and ground deposition of chemicals from air-assisted sprayers, with special attention to recycling units and sensored sprayers. 相似文献
145.
A field experiment was conducted during the winter seasons of 1992–93 and 1993–94 at Anand to study the effect of FYM, nitrogen and source of fertilizer on growth and yield of mustard [ Brassica juncea (L.) Czernj & Cosson]. The results showed significant variation in leaf area index (LAI), crop growth rate (CGR), dry matter production and seed yield. The direct effect of farmyard manure (FYM) was conspicuous in improving the growth of mustard. FYM application at 10 tonnes ha−1 significantly increased the LAI, CGR and dry matter accumulation per plant at almost all the stages during first year study (1992–93) and in pooled analysis. Similarly, nitrogen application registered maximum LAI, CGR at 75 kg level and RGR and NAR at 50 kg level at almost all the during both years. Sulphur carrying source (Ammonium sulphate plus single super phosphate) increased all stages growth characters. Maximum dry matter accumulation per plant and seed yield were recorded with highest levels of FYM (20 tonnes ha−1 ), N (75 kg ha−1 ) and source having S. Seed yield was strongly associated with LAI and dry matter accumulation per plant at all the stages. 相似文献
146.
147.
Canine liposarcoma 总被引:1,自引:0,他引:1
148.
149.
The determination of differentiation and transplantation antigens will be of growing importance in immune diagnosis for individual animals as well as for breeding purposes in populations. Differentiation antigens characterize subsets of cell populations and indicate their functional capacity while transplantation antigens represent markers of individuals of a species. Occurrence and significance of these antigenic systems are briefly reviewed. 相似文献
150.
There is only limited information on sheep interferon available. Recent publications have reported on: 1. an interferon (IFN) alpha subtype, which is secreted by the fetal trophectoderm into the lumen of the uterus between the 10th and 21st day of gestation. It was therefore named ovine trophoblast protein (oTP-1), and is responsible for signalling pregnancy to the ewe via high affinity receptors in the endometrium. It is thought that oTP-1 acts by directly influencing prostaglandin metabolism. 2. the role of lentivirus-induced interferon (LV-IFN) in the pathogenesis of Maedi/Visna. The results indicate that LV-IFN limits viral replication and therefore contributes to virus persistence and is also responsible for a chronic inflammatory process. 3. the mitogen- or antigen-dependent induction of ovine interferon gamma (IFN gamma) and its characterization. 相似文献