全文获取类型
收费全文 | 3285篇 |
免费 | 141篇 |
国内免费 | 3篇 |
专业分类
林业 | 235篇 |
农学 | 464篇 |
基础科学 | 87篇 |
854篇 | |
综合类 | 83篇 |
农作物 | 273篇 |
水产渔业 | 70篇 |
畜牧兽医 | 981篇 |
园艺 | 98篇 |
植物保护 | 284篇 |
出版年
2023年 | 22篇 |
2022年 | 38篇 |
2021年 | 50篇 |
2020年 | 86篇 |
2019年 | 87篇 |
2018年 | 119篇 |
2017年 | 136篇 |
2016年 | 108篇 |
2015年 | 83篇 |
2014年 | 94篇 |
2013年 | 296篇 |
2012年 | 140篇 |
2011年 | 158篇 |
2010年 | 125篇 |
2009年 | 113篇 |
2008年 | 112篇 |
2007年 | 138篇 |
2006年 | 143篇 |
2005年 | 110篇 |
2004年 | 71篇 |
2003年 | 77篇 |
2002年 | 72篇 |
2001年 | 58篇 |
2000年 | 52篇 |
1999年 | 53篇 |
1998年 | 41篇 |
1997年 | 43篇 |
1996年 | 34篇 |
1995年 | 34篇 |
1994年 | 29篇 |
1993年 | 28篇 |
1992年 | 30篇 |
1991年 | 36篇 |
1990年 | 31篇 |
1989年 | 38篇 |
1988年 | 46篇 |
1987年 | 35篇 |
1986年 | 29篇 |
1985年 | 24篇 |
1984年 | 26篇 |
1983年 | 26篇 |
1982年 | 22篇 |
1980年 | 34篇 |
1979年 | 37篇 |
1978年 | 20篇 |
1976年 | 20篇 |
1971年 | 20篇 |
1970年 | 37篇 |
1969年 | 24篇 |
1968年 | 23篇 |
排序方式: 共有3429条查询结果,搜索用时 15 毫秒
971.
Kanika Singh Hitesh B. Vasava Didier Snoeck Bhabani S. Das David Yinil Damien Field Todd Sanderson Chris Fidelis Israr Majeed Niranjan Panigrahi 《Soil Use and Management》2019,35(3):492-502
In this study, diffuse reflectance spectroscopy (DRS) approach was examined for making input recommendations in the smallholder cocoa farms of Papua New Guinea (PNG). Soil samples were collected from four provinces of PNG. Soil samples from four different depths (0–10, 10–30, 30–60 and 60–90 cm) of 32 profiles in each of these site were used to create a database of soil chemical and physical properties. Spectral reflectance values at 1 nm interval covering visible to shortwave‐infrared (350–2,500 nm) were collected for each of these soil samples to develop partial least squares regression models. Soil textural fractions, soil organic carbon contents and available N were well predicted by the DRS approach with R2 values larger than 0.75. Moderate to poor estimation efficiencies were observed for remaining parameters. Nevertheless, the estimated soil attributes and their corresponding measured soil parameters were used as inputs to an input recommendation model of soil diagnosis to create input recommendation for a targeted cocoa yield of 1,000 kg dry cocoa beans ha‐1 Resulting input recommendations were similar for both of these input sources (measured and DRS‐estimated) suggesting that the DRS approach may provide an easy way to create input recommendations. 相似文献
972.
Poplars are affected by a large number of foliar pathogens in nurseries and in the field, which result in biomass reductions. Management of these diseases is essential to minimise losses. During field surveys between 2008 and 12, an unrecognized leaf spot disease was observed on several commercial clones of P. deltoides (G‐48, Udai, WSL‐22 & WSL‐39). The pathogen was identified as Curvularia eragrostidis. Pathogenicity was proven on all host clones. This paper is the first report of the pathogen affecting poplars. 相似文献
973.
Tahir Hussain Awan Pompe C. Sta Cruz Bhagirath Singh Chauhan 《Journal of pest science》2015,88(2):427-438
974.
The purpose of this study was to characterize the land use, vegetation structure, and diversity in the Barnowpara Sanctuary, Raipur district, Chhattisgarh, India through the use of satellite remote sensing and GIS. Land cover and vegetation were spatially analyzed by digitally classifying IRS 1D LISS III satellite data using a maximum likelihood algorithm. Later, the variations in structure and diversity in different forest types and classes were quantified by adopting quadratic sampling procedures. Nine land-cover types were delineated: teak forest, dense mixed forest, degraded mixed forest, Sal mixed forest, open mixed forest, young teak plantation, grasslands, agriculture, habitation, and water bodies. The classification accuracy for different land-use classes ranged from 71.23% to 100%. The highest accuracy was observed in water bodies and grassland, followed by habitation and agriculture, teak forest, degraded mixed forest, and dense mixed forest. The accuracy was lower in open mixed forest, and sal mixed forest. Results revealed that density of different forest types varied from 324 to 733 trees ha-1, basal area from 8.13 to 28.87 m2·ha-1 and number of species from 20 to 40. Similarly, the diversity ranged from 1.36 to 2.98, concentration of dominance from 0.06 to 0.49, species richness from 3.88 to 6.86, and beta diversity from 1.29 to 2.21. The sal mixed forest type recorded the highest basal area, diversity was highest in the dense mixed forest, and the teak forest recorded maximum density, which was poor in degraded mixed forests. The study also showed that Normalized Difference Vegetation Index(NDVI) was strongly correlated to with the Shannon Index and species richness. 相似文献
975.
Hassan Bashiru Shelukindo Balthazar Msanya Ernest Semu Sibaway Mwango Bal Ram Singh Pantaleo Munishi 《农业科学与技术》2014,(3):224-234
Despite the fact that miombo woodland soils have significant implications in global climate change processes, few studies have been done to characterize and classify the soils of the miombo woodland ecosystem of Tanzania. The current study was carried out to map and classify soils of Kitonga Forest Reserve, which is a typical miombo woodland ecosystem, in order to generate relevant information for their use and management. A representative study area of 52 km2 was selected and mapped at a scale of 1:50,000 on the basis of relief. Ten representative soil profiles were excavated and described using standard methods. Soil samples were taken from genetic soil horizons and analyzed in the laboratory for physico-chemical characteristics using standard methods. Using field and laboratory analytical data, the soils were classified according to the FAO-World Reference Base (FAO-WRB) for Soil Resources system as Cambisols, Leptosols and Fluvisols. In the USDA-NRCS Soil Taxonomy system the soils were classified as Inceptisols and Entisols. Topographical features played an important role in soil formation. The different soil types differed in physico-chemical properties, hence exhibit differences in their potentials, constraints and need specific management strategies. Texture varied from sandy to different loams; pH from 5.1 to 5.9; organic carbon from 0.9 g/kg to 20 g/kg; and CEC from 3 cmol/(+)kg to 24 cmol/(+)kg. Sustainable management of miombo woodlands ecosystem soils requires reduced deforestation and reduced land degradation. 相似文献
976.
Lucinda van Stee Sarah Boston Ameet Singh Fiona Park Danielle Richardson Anthony Abrams-Ogg Andrew Vince 《The Canadian veterinary journal. La revue veterinaire canadienne》2014,55(9):849-856
We describe 3 cases of cats that were presented with a sudden onset of monoparesis as a result of arterial thromboembolism without evidence of cardiovascular disease that were subsequently diagnosed with a primary pulmonary carcinoma. Arterial tumor thromboemboli due to pulmonary carcinoma should be considered as a differential diagnosis in cases of lameness or paresis in older cats. We theorize that large tumor emboli may obstruct peripheral arteries leading to acute monoparesis. 相似文献
977.
Sonali Prusty Madhu Mohini Shivlal Singh Kundu Ajay Kumar Chander Datt 《Tropical animal health and production》2014,46(1):65-70
Fifteen male Murrah buffalo calves (15–18 months, 227.98?±?4.44 kg body weight) were distributed randomly in to three equal groups and fed solely on either berseem (G1), oats (G2), or chicory fodder (G3). A digestibility trial followed by methane measurement using SF6 tracer technique was conducted. No significant difference was observed in nutrient intake; however, crude protein (CP) intake was lower in G2 (0.35 kg) than G1 (0.7) and in G3 (0.71) and non-fibrous carbohydrates (NFC), and neutral detergent insoluble CP (NDICP) intake was significantly (p?<?0.05) higher in G3 (1.54 and 0.31 kg) followed by G2 (1.27 and 0.2 kg) and G1 (1.06 and 0.18 kg). The digestible dry matter, organic matter, neutral detergent fiber, and ether extract intake was similar in all the groups, whereas the digestible CP and NFC intake was lower in G2 compared to G1 and G3. Chicory- and berseem-fed groups emitted 12.2 and 5.2 % less methane than oats-fed group. However, no significant difference was observed in the absolute methane loss and methane loss as percentage of energy intake (p?>?0.05) among the groups. There was positive correlation between nutrient intake and total methane production. However, an inverse relationship was observed between total digestible carbohydrate intake and methane production (g/kg dry matter intake). The following regression equations were developed to estimate methane production: methane (g/kg BW) = 128.8553 + (167.7456 × dNDFI) + (216.32 × dCPI) ? (40.3313 × dNFCI) and methane (g/d) = ?1.7494 + (41.42 × NDFI) + (39.8686 × CPI) + (0.5197 × NFCI). 相似文献
978.
Uttarani Maibam Sohan Vir Singh Anil Kumar Singh Suresh Kumar Ramesh Chandra Upadhyay 《Tropical animal health and production》2014,46(7):1155-1160
To evaluate difference in the expression of skin color genes (melanocortin 1 receptor (MC1R) and premelanosome (PMEL)) in lymphocytes during winter and summer season and their correlation with tyrosinase enzyme and cortisol, ten Karan-Fries heifers were selected from National Dairy Research Institute (NDRI) cattle farm. Blood samples were collected from the animals during winter (THI?=?60) and summer (THI?=?83) season at weekly intervals. Relative MC1R and PMEL messenger RNA (mRNA) expression of Karan Fries cattle was found to be significantly (P?0.01) higher during winter than summer. Similarly, tyrosinase activity during winter was found to be significantly (P?0.01) higher than summer season. However, plasma cortisol level was significantly (P?0.01) higher during summer than winter. Thus, expression of the skin color genes showed positive correlation with tyrosinase enzyme, but negative correlation with cortisol level. Expression of MC1R and PMEL in lymphocytes and tyrosinase activity of Karan Fries cattle was highly reduced during summer. The present study showed that the ability of Karan Fries cattle to protect themselves from the harmful radiation of sunlight by melanization decreased with increased heat stress on them. 相似文献
979.
Economic losses due to cystic echinococcosis in India: Need for urgent action to control the disease
Balbir B. Singh Navneet K. Dhand Sandeep Ghatak Jatinder P.S. Gill 《Preventive veterinary medicine》2014
Cystic ehinococcosis (CE) caused by Echinococcus granulosus remains a neglected zoonotic disease despite its considerable human and animal health concerns. This is the first systematic analysis of the livestock and human related economic losses due to cystic echinococcosis in India. 相似文献
980.
Viruses alter the structure and the function of mitochondria for survival. Electron microscopy analysis of the cells infected with bovine adenovirus 3 revealed extensive damage to the inner mitochondrial membrane characterized by dissolution of the cristae and amorphous appearance of mitochondrial matrix with little or no damage to the outer mitochondrial membrane. There were fewer cristae with altered morphology. Potential patches of protein synthesis machinary around mitochondria could be observed at 12 hours post infection (hpi). At 24 hpi, the multi vascular bodies were evident throughout the infected cell. ATP production, mitochondrial Ca2+ and mitochondrial membrane potential (MMP) peaked at 18 hpi but decreased significantly at 24 hpi. This decrease coincided with the increased production of superoxide (SO) and reactive oxygen species (ROS), at 24 hpi indicating acute oxidative stress in the cells and suggesting a complete failure of the cellular homeostatic machinary. The results reveal an intericate relationship between Ca2+ homeostasis, the ATP generation ability of cells, SO and ROS production, and regulation of MMP following infection by bovine adenovirus 3. 相似文献