全文获取类型
收费全文 | 265983篇 |
免费 | 16724篇 |
国内免费 | 8187篇 |
专业分类
林业 | 31198篇 |
农学 | 25265篇 |
基础科学 | 9625篇 |
49719篇 | |
综合类 | 28707篇 |
农作物 | 19812篇 |
水产渔业 | 17581篇 |
畜牧兽医 | 74705篇 |
园艺 | 8047篇 |
植物保护 | 26235篇 |
出版年
2022年 | 2484篇 |
2021年 | 4740篇 |
2020年 | 5180篇 |
2019年 | 5707篇 |
2018年 | 5075篇 |
2017年 | 6134篇 |
2016年 | 6757篇 |
2015年 | 7133篇 |
2014年 | 8286篇 |
2013年 | 19509篇 |
2012年 | 8905篇 |
2011年 | 10845篇 |
2010年 | 11042篇 |
2009年 | 11529篇 |
2008年 | 9759篇 |
2007年 | 8688篇 |
2006年 | 9453篇 |
2005年 | 8255篇 |
2004年 | 6303篇 |
2003年 | 5908篇 |
2002年 | 4723篇 |
2001年 | 4985篇 |
2000年 | 4916篇 |
1999年 | 5384篇 |
1998年 | 5429篇 |
1997年 | 5167篇 |
1996年 | 4920篇 |
1995年 | 5497篇 |
1994年 | 4726篇 |
1993年 | 4353篇 |
1992年 | 3924篇 |
1991年 | 3927篇 |
1990年 | 3483篇 |
1989年 | 3374篇 |
1988年 | 2896篇 |
1987年 | 2762篇 |
1986年 | 2539篇 |
1985年 | 2893篇 |
1984年 | 2889篇 |
1983年 | 2816篇 |
1982年 | 2522篇 |
1981年 | 2483篇 |
1980年 | 2474篇 |
1979年 | 2358篇 |
1978年 | 2263篇 |
1977年 | 2171篇 |
1976年 | 2015篇 |
1975年 | 1757篇 |
1974年 | 1758篇 |
1973年 | 1699篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Halyomorpha halys, commonly known as the brown marmorated stink bug, has been recorded for the first time from the Maltese Islands. The record is currently based on the capture of a single specimen. Information is provided on the distribution range of this polyphagous species which was accidentally introduced into Europe (Switzerland) in 2007 and since then has invaded many European countries. Morphological details are also included to aid in the discrimination of this species from similar species occurring in the Mediterranean region. Notes are provided on the feeding strategies used by this insect and the type of damage incurred on agricultural commodities, which are often rendered unsaleable. 相似文献
102.
In May 2017 and 2018, Planococcus vovae (Nasonov) (Hemiptera: Pseudococcidae) was collected in Hammam Sousse (Tunisia) on the ornamental plant Cupressus macrocarpa (Cupressaceae). The infestation was observed on needles which showed symptoms of desiccation and chlorosis. This is the first record of P. vovae in Tunisia and in North Africa. 相似文献
103.
Peterman William E. Winiarski Kristopher J. Moore Chloe E. Carvalho Carolina da Silva Gilbert Anthony L. Spear Stephen F. 《Landscape Ecology》2019,34(9):2197-2208
Landscape Ecology - Landscape resistance surfaces are often used to address questions related to movement, dispersal, or population connectivity. However, modeling landscape resistance is... 相似文献
104.
Huanglongbing (HLB), associated with a non-culturable bacterium ‘Candidatus Liberibacter asiaticus’ (CLas), is a highly destructive citrus disease with a long but poorly documented history in China. No effective treatment for HLB is available. The identification of new prophages in abundant CLas genomic sequence data provides new insights into both the diversity of CLas strains and HLB management. In this study, CLas populations from nine provinces were surveyed for the presence of prophage. Two major prophage typing groups (PTGs) were discovered to be associated with two different altitude regions: strains of CLas in PTG1 from high altitude regions (HAR) mainly contained prophage Type 1 only or Types 1 and 3, whereas strains of CLas in PTG2 from low altitude regions (LAR) mainly contained prophage Type 2. The discovery of these CLas population patterns provides evidence for independent origins of HLB in HAR and LAR. Guangdong province is the generally recognized domestic region of origin for HLB and is primarily responsible for the dissemination of HLB in LAR through transport of seedlings. Both Yunnan and Sichuan provinces are the probable regions of origin for HLB in HAR. PTG2 was further divided into two subgroups: PTG2-1, found in Guangdong, Fujian and Guangxi and PTG2-2, found in Jiangxi, Zhejiang and Hunan. These regions and prophage types are correlated with early and late introductions of HLB in LAR. These molecular analyses were supported by studying the history of the dissemination of HLB in historical documents. 相似文献
105.
在马铃薯原种生产中,播种密度和播种期对原种繁育的产量、种薯大小等有着明显的影响。选用当地主栽品种大西洋,于2017-2018年在山丹县冷凉区域,同一地点开展不同播期和密度试验。播种选择4月25日、5月5日、5月15日、5月25日和6月5日,种植密度设置60 000、90 000、120 000、150 000和180 000粒/hm 2 5个水平。结果表明,在当地的栽培模式大垄双行覆膜种植下,4月25日-5月15日播种,播种密度为120 000、150 000粒/hm 2,产量在45 285~46 770kg/hm 2,中种薯率在75.3%~79.6%,合格种薯多,均为最高,且此范围产量差异不显著。考虑到节约原原种投入降低成本,生产中优选120 000粒/hm 2的播种密度,在4月25日-5月15日种植,是大西洋原种繁育的最佳选择方案。 相似文献
106.
Sonia Czarnes Pierre-Edouard Mercier Damien G. Lemoine Jihane Hamzaoui Laurent Legendre 《Journal of Agronomy and Crop Science》2020,206(5):505-516
Members of the bacterial genus Azospirillum are root-associated bacteria that increase yield in cereals by promoting growth and alleviating drought stress. How plants integrate the many bacterium-derived growth-promoting stimuli with other environmental factors to generate a coordinated response remains unresolved. Using a commercial Azospirillum strain, A. lipoferum CRT1 and two host maize cultivars, it was observed that bacterization reduced the drought-induced increase in lateral root growth and enhanced the flood-induced increase in lateral root growth in the more drought- and flood-sensitive cultivar. In the other one, A. lipoferum CRT1 only elicited a moderate root growth response under low soil water potential. The photosynthetic potential and activity were increased in the earlier cultivar and decreased in the later one, irrespective of the soil water content. No impact of the bacterium was seen on the growth of the leaves of both cultivars under both stresses until the third leaf stage, therefore suggesting that it is a consequence of multiple primary adaptations to biotic and abiotic stresses. It is suggested that host–bacteria recognition leads to a stress-specific modulation of the root response and a differential stress-independent effect on photosynthesis. This is the first report of the impact of Azospirillum under flood conditions. 相似文献
107.
108.
成都平原不同作物种植模式生产效率及其影响因素研究—以成都市郫都区为例 总被引:1,自引:0,他引:1
为研究成都平原不同种植模式的农田生产效率,基于2017年对成都市郫都区13个乡镇92户农户调查数据,运用DEA-Tobit模型分析了郫都区主要的水旱轮作和旱作种植模式的农田经营效率及影响因素。研究结果表明:不同种植模式平均农田生产效率为0.793,不同模式农田生产效率排序依次为蔬菜连作或轮作(0.957)、水稻-大蒜(0.847)、水稻-油菜(0.782)、韭菜连作(0.759)、水稻-蔬菜(0.722)、水稻-圆根萝卜(0.689),农田生产效率未达到有效值1的原因主要是规模效益较低;同时,各模式均存在资金和劳动力投入冗余,水稻-蔬菜、水稻-油菜模式还存在产出不足问题;影响6种模式生产效率的因素均不相同,政策因素对农田生产效率的影响相对较大。为进一步提高郫都区农田生产效率,建议适度推广农田规模化经营,加强农村富余劳动力转移,完善各类农业政策措施。 相似文献
109.
ABSTRACT This study deals with the influence of electron beam irradiation (EBI) on the wettability of Norway spruce surface samples. To evaluate this possible effect in detail, the changes in chemistry and wood structure were analysed using the methods of IR spectroscopy and Scanning Electron Microscopy (SEM). The surface wettability was determined by the contact angle measurement method. The results of infrared spectra show decreased relative numbers of available hydrophilic groups (e.g. hydroxyl and carbonyl groups) in the wood surfaces due to the electron beam irradiation. This behaviour is consistent with the values from the surface wettability measurements. Structural differences of the wood surfaces after electron beam irradiation were not detectable. Based on these findings pre-treatment of wood surfaces for industrial usages can be a potential field of application of this technology. 相似文献
110.