全文获取类型
收费全文 | 83730篇 |
免费 | 4700篇 |
国内免费 | 51篇 |
专业分类
林业 | 2909篇 |
农学 | 2276篇 |
基础科学 | 568篇 |
9212篇 | |
综合类 | 14868篇 |
农作物 | 3082篇 |
水产渔业 | 3921篇 |
畜牧兽医 | 45704篇 |
园艺 | 879篇 |
植物保护 | 5062篇 |
出版年
2018年 | 1032篇 |
2017年 | 1170篇 |
2016年 | 1084篇 |
2015年 | 935篇 |
2014年 | 1172篇 |
2013年 | 3052篇 |
2012年 | 2119篇 |
2011年 | 2695篇 |
2010年 | 1648篇 |
2009年 | 1754篇 |
2008年 | 2587篇 |
2007年 | 2402篇 |
2006年 | 2403篇 |
2005年 | 2126篇 |
2004年 | 2087篇 |
2003年 | 2076篇 |
2002年 | 1969篇 |
2001年 | 2700篇 |
2000年 | 2803篇 |
1999年 | 2131篇 |
1998年 | 813篇 |
1997年 | 823篇 |
1996年 | 807篇 |
1995年 | 1017篇 |
1994年 | 888篇 |
1993年 | 841篇 |
1992年 | 1930篇 |
1991年 | 2080篇 |
1990年 | 1923篇 |
1989年 | 1934篇 |
1988年 | 1824篇 |
1987年 | 1929篇 |
1986年 | 1975篇 |
1985年 | 1872篇 |
1984年 | 1481篇 |
1983年 | 1298篇 |
1982年 | 880篇 |
1979年 | 1366篇 |
1978年 | 1122篇 |
1977年 | 973篇 |
1976年 | 937篇 |
1975年 | 983篇 |
1974年 | 1272篇 |
1973年 | 1298篇 |
1972年 | 1234篇 |
1971年 | 1147篇 |
1970年 | 1088篇 |
1969年 | 964篇 |
1968年 | 832篇 |
1967年 | 869篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
J.F.D. Frazer 《Biological conservation》1973,5(4):271-276
While various experimental methods may show the number of butterflies in a given area, this, of itself, is no pointer either to general scarcity or to the reverse. Even less can it be taken as being the result of a particular set of outside influences. However, low levels in certain (otherwise plentiful) species may be taken as indicating unsuitable management trends. 相似文献
82.
83.
84.
85.
In a survey of fungi causing seedling diseases of sugar beet using a soil bioassay, Aphanomyces cochlioides and Pythium spp. were found to occur in 39% and 31%, respectively, of 341 sugar-beet fields selected in a stratified random sample in England, The frequency of A. cochlioides-infested soils varied widely in the different sugar-beet growing areas of the country. Soil pH was the single factor most strongly associated with the distribution of the pathogen, but regression models applied to combinations of factors indicated that soil texture and the interval between sugar-beet crops were also relevant to its frequency. It was detected less often in soils of high pH (≥ 75). heavy texture and where the interval between sugar-beet crops exceeded 5 years. No significant associations were found between the proportion of soils with Pythium spp. and soil or cropping factors. 相似文献
86.
87.
The sciatic nerve was surgically transected in 6 dogs. The resulting dysfunction and the positive effects of a transfer of the tendon of the vastus lateralis muscle to the long digital extensor muscle were evaluated, alone and in combination with a talocrural arthrodesis. Two dogs that received both arthrodesis and tendon transfer showed the greatest improvement in gait. 相似文献
88.
All the poultry in each of four distinct Moroccan villages were vaccinated against Newcastle disease using Hitchner B1 and inactivated vaccines. Poultry in a fifth village were monitored as controls. Mortality in the poultry was followed for 20 weeks after the first vaccination and blood samples were taken every 4 weeks from chickens for estimation of antibodies against Newcastle disease virus. Sixty-three percent of the chicken population and 60% of the turkey population in the control village died during the 20 weeks of observation. Necropsied birds showed lesions consistent with Newcastle disease. Mortality did not exceed 22% in the vaccinated villages. 相似文献
89.
Phytoparasitica - The effect of foliar urea treatments on the persistence of synthetic pyrethroid residues on tomato was studied. Fenvalerate was found to persist more and deltamethrin less than... 相似文献
90.