全文获取类型
收费全文 | 78787篇 |
免费 | 4247篇 |
国内免费 | 93篇 |
专业分类
林业 | 3185篇 |
农学 | 2045篇 |
基础科学 | 462篇 |
8556篇 | |
综合类 | 15393篇 |
农作物 | 3127篇 |
水产渔业 | 3414篇 |
畜牧兽医 | 41663篇 |
园艺 | 844篇 |
植物保护 | 4438篇 |
出版年
2019年 | 718篇 |
2018年 | 1091篇 |
2017年 | 1211篇 |
2016年 | 1046篇 |
2015年 | 903篇 |
2014年 | 1189篇 |
2013年 | 2618篇 |
2012年 | 2110篇 |
2011年 | 2570篇 |
2010年 | 1614篇 |
2009年 | 1726篇 |
2008年 | 2595篇 |
2007年 | 2402篇 |
2006年 | 2282篇 |
2005年 | 2133篇 |
2004年 | 2075篇 |
2003年 | 2135篇 |
2002年 | 1921篇 |
2001年 | 2384篇 |
2000年 | 2438篇 |
1999年 | 1868篇 |
1998年 | 720篇 |
1997年 | 711篇 |
1996年 | 711篇 |
1995年 | 805篇 |
1993年 | 740篇 |
1992年 | 1553篇 |
1991年 | 1750篇 |
1990年 | 1634篇 |
1989年 | 1646篇 |
1988年 | 1472篇 |
1987年 | 1534篇 |
1986年 | 1596篇 |
1985年 | 1547篇 |
1984年 | 1184篇 |
1983年 | 1057篇 |
1982年 | 704篇 |
1979年 | 1152篇 |
1978年 | 894篇 |
1977年 | 755篇 |
1975年 | 774篇 |
1974年 | 1024篇 |
1973年 | 1024篇 |
1972年 | 1043篇 |
1971年 | 993篇 |
1970年 | 987篇 |
1969年 | 903篇 |
1968年 | 810篇 |
1967年 | 799篇 |
1966年 | 732篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Five groups of eight fattening pigs were vaccinated and then infected with Aujeszky's disease virus. Viral excretion was evaluated by two means: deep nasal swabbing and air sampling. It appeared that infectious airborne virus could be recovered from day 1 to day 6 after infection in the isolated units where control animals were raised. In vaccinated animals, airborne particles were also detected but the amount and duration varied in relation to their immune status at the day of virulent challenge: viral excretion was significantly lower in pigs presenting a high antibody level (1/16 to 1/64) just before infection. Results obtained with nasal swabs and with air samples were closely related. Despite its low sensitivity, the air sampling procedure could be considered as an efficient tool for reflecting infectious viral pressure in a confined atmosphere. 相似文献
172.
173.
Summary Plants of tetraploid Festuca pratensis var. apennina (2n=28) collected from Switserland and Northern Italy produced few inflorescences when grown in the field and under glasshouse conditions. The effects of winter and spring treatments upon reproductive growth were investigated and it was concluded that exposure to low winter temperatures and the control of tiller density in the spring were two important factors controlling the production of inflorescences. A procedure for the production of seed is suggested which will allow breeders to obtain efficient multiplication of collected plant material. 相似文献
174.
Ice towers, probably formed by recent fumarolic activity, have been found around the summit calderas of two volcanoes in Marie Byrd Land. These active (?) volcanoes lie within a broad belt of Mesozoic intrusion and late Cenozoic extrusion that appears to be part of the circum-Pacific orogenic province. 相似文献
175.
176.
177.
B. Martínez-López B. Ivorra E. Fernández-Carrión A.M. Perez A. Medel-Herrero F. Sánchez-Vizcaíno C. Gortázar A.M. Ramos J.M. Sánchez-Vizcaíno 《Preventive veterinary medicine》2014
This study presents a multi-disciplinary decision-support tool, which integrates geo-statistics, social network analysis (SNA), spatial-stochastic spread model, economic analysis and mapping/visualization capabilities for the evaluation of the sanitary and socio-economic impact of livestock diseases under diverse epidemiologic scenarios. We illustrate the applicability of this tool using foot-and-mouth disease (FMD) in Peru as an example. The approach consisted on a flexible, multistep process that may be easily adapted based on data availability. The first module (mI) uses a geo-statistical approach for the estimation (if needed) of the distribution and abundance of susceptible population (in the example here, cattle, swine, sheep, goats, and camelids) at farm-level in the region or country of interest (Peru). The second module (mII) applies SNA for evaluating the farm-to-farm contact patterns and for exploring the structure and frequency of between-farm animal movements as a proxy for potential disease introduction or spread. The third module (mIII) integrates mI–II outputs into a spatial-stochastic model that simulates within- and between-farm FMD-transmission. The economic module (mIV) connects outputs from mI–III to provide an estimate of associated direct and indirect costs. A visualization module (mV) is also implemented to graph and map the outputs of module I–IV. After 1000 simulated epidemics, the mean (95% probability interval) number of outbreaks, infected animals, epidemic duration, and direct costs were 37 (1, 1164), 2152 (1, 13, 250), 63 days (0, 442), and US$ 1.2 million (1072, 9.5 million), respectively. Spread of disease was primarily local (<4.5 km), but geolocation and type of index farm strongly influenced the extent and spatial patterns of an epidemic. The approach is intended to support decisions in the last phase of the FMD eradication program in Peru, in particular to inform and support the implementation of risk-based surveillance and livestock insurance systems that may help to prevent and control potential FMD virus incursions into Peru. 相似文献
178.
179.
180.
The genetic diversity of 283 Mycobacterium bovis (M. bovis) and 10 Mycobacterium caprae (M. caprae) strains, isolated between 2002 and 2007 from cattle, goat, red deer and wild boar from six different geographical regions of Portugal was investigated by spoligotyping. The technique showed a good discriminatory power (Hunter-Gaston Index, h=0.9) for the strains, revealing 29 different patterns. One pattern (SB0121) was clearly predominant, accounting for 26.3% of the isolates; ten patterns, representing 20.7% of the isolates, had never been reported previously. Multiple spoligotypes were detected in thirteen cattle and one goat herd, most of which were found in beef cattle and extensive management regions, suggesting different infection sources. With the exception of two spoligotypes, those in wildlife species were also found in domestic species. 相似文献