全文获取类型
收费全文 | 1629篇 |
免费 | 23篇 |
专业分类
林业 | 158篇 |
农学 | 71篇 |
基础科学 | 48篇 |
384篇 | |
综合类 | 48篇 |
农作物 | 301篇 |
水产渔业 | 239篇 |
畜牧兽医 | 300篇 |
园艺 | 19篇 |
植物保护 | 84篇 |
出版年
2024年 | 38篇 |
2023年 | 33篇 |
2022年 | 55篇 |
2021年 | 73篇 |
2020年 | 81篇 |
2019年 | 94篇 |
2018年 | 106篇 |
2017年 | 112篇 |
2016年 | 106篇 |
2015年 | 52篇 |
2014年 | 89篇 |
2013年 | 173篇 |
2012年 | 108篇 |
2011年 | 104篇 |
2010年 | 92篇 |
2009年 | 68篇 |
2008年 | 90篇 |
2007年 | 55篇 |
2006年 | 30篇 |
2005年 | 17篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 9篇 |
2001年 | 4篇 |
2000年 | 10篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1972年 | 1篇 |
1939年 | 1篇 |
排序方式: 共有1652条查询结果,搜索用时 17 毫秒
71.
Marjan?Jannatdoust Reza?DarvishzadehEmail author Roghayyeh?Ziaeifard Mohammad?Ali?Ebrahimi Hamid?Hatami?Maleki Esmaeel?Gholinezhad Ali?Asghar?Hatamnia 《Journal of Crop Science and Biotechnology》2016,19(1):37-44
Genetic diversity within and among 50 populations of confectionery sunflower (Helianthus annuus L.) collected from different geographical areas of Iran was evaluated by using microsatellite and retrotransposon markers. The number of alleles (Na) in SSR loci ranged from 2 to 3 with an average of 2.1. The polymorphic bands in retrotransposon markers ranged from 7 in locus CR-UR1 to 15 in locus CR-816 with a mean value of 11.33. Herarchical clustering of individuals (50 × 5 = 250) by neighbor joining method in DARwin5 software subdivided them into three groups. Using Bayesian method in the software pakage of Structure, the studied individuals were subdivided into two sub-populations. Principal coordinate analysis revelaed that the two first components explaine 7.86 and 6.16% of the total variance, respectively. Analysis of molecular variance revealed a higher level of genetic variation within (70%) than between (30%) populations. High molecular variation among individuals within population possibly is due to high allogamy nature of the sunflower plant. Low genetic variation observed between populations could be considered as a consequence of genetic equilibrium that has occurred over the long period of cultivation of confectionery sunflower in this area as well as seed exchange among regions. The traditional assumption that selecting genotypes of different geographical origin will maximize the diversity available to a breeding project does not hold in confectionery sunflower. 相似文献
72.
Keyvan Karami Saeed Zerehdaran Ali Javadmanesh Mohammad Mahdi Shariati Hossien Fallahi 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2019,136(3):205-216
Imprinted genes display biased expression of paternal and maternal alleles in mammals. They are marked through epigenetic process during gametogenesis. Characterization of imprinted genes has expanded our understanding of the regulation and function of genes. In the current study, 22 experimentally validated imprinted genes in bovine (Bos Taurus) were analysed. Several supervised machine learning algorithms and attribute weighting methods were used to find characteristics of different types of imprinted genes and suggest a classification method for finding maternally and paternally expressed genes in bovine. For assessing the best model and comparing attributes in other organisms, we have also conducted a comparative analysis for human and sheep imprinted genes. According to the results of the present study, GC contents 10 and 100 kb upstream, Gly and Gln amino acids, Ile/ATC codon usage, LINE and SINE in 100kbup and length of first intron were significantly different between the maternal and paternal genes in cattle. Considering all species together, we found that GC content 100 kb up, LINE 100 kb up and the frequency of amino acids like Gly, Gln and Met were the most important attributes for identifying the paternal and maternal imprinted genes. These findings could imply conservation pattern in the attributes among these species. 相似文献
73.
Evaluation of irrigation and drainage systems can help managers find problems and deliver water in the system more efficiently. Adequacy, efficiency, equity and dependability are important indicators for evaluation of management in irrigation and drainage systems. Evaluation of overall performance based on the above‐mentioned four indicators can be useful for more accurate judgement about system performance. In this paper, a new simple overall water delivery performance indicator (OPI) and a general form (OWDPI) are defined based on the combination of the four previously mentioned indicators, adequacy, efficiency, equity and dependability. Three performance classes were also defined to represent standard values. The overall performance indicator was used for evaluation of the Doroodzan Irrigation Network (DIN) in south‐western Iran. Results showed that although adequacy in 2001 and efficiency in 2015 were good for DIN, the overall delivery performance indicator was poor and equal to 0.70 and 0.72 in the 2 years of study. The developed overall performance indicator may be a suitable tool for better evaluation and comparison of DIN and other similar irrigation and drainage systems around the world. © 2019 John Wiley & Sons, Ltd. 相似文献
74.
Fatemeh Kiumarsi;Meghdad Jourgholami;Mohammad Jafari;Angela Lo Monaco;Rachele Venanzi;Rodolfo Picchio; 《Land Degradation u0026amp; Development》2024,35(6):2084-2096
Among the various species of trees, black alder (Alnus glutinosa (L.) Gaertn.) is one of the most commonly used trees for the reforestation and restoration programs of degraded forestlands in the Hyrcanian forest, particularly in the skid trails. The effects of reforestation with black alder on the recovery of litter (thickness, C, N, C/N) and soil physicochemical, biochemical, biological, and microbial properties in the skid trails with three levels of compactions were examined over a 27-year period. Results showed that the litter characteristics such as thickness, carbon (C), nitrogen (N), and C/N were at the highest level in low intensity traffic as compared to those of medium and frequent intensities. Results showed that the values of total porosity, macroporosity, aggregate stability, silt, and clay were at the lowest level in the natural stand. The highest values of soil pH, C, C/N ratio, and C storage were recorded under the skid trail with frequent machine passages. The restoration values of soil physical and chemical properties were significantly higher in the low level of machine traffic after a period of 27 years where black alder reforestation was performed on the skid trails, as compared to the medium and frequent machine traffic levels, as well as the undisturbed area. Black alder litter affected soil nitrogen and the maximum amounts of earthworm density and dry mass. This also includes fine root biomass. These data were recorded in the trails with low machine traffic as compared to those of medium and frequent traffic. The results clearly showed that black alder is effective in reaching the objectives of restoration programs, given that it promotes soil organic matter, builds up soil structure via root-soil feedback, and improves the soil by creating a major source of nitrogen through enhancing the nitrogen cycle. 相似文献
75.
Traditional systems of medicine have become a topic of global importance recently. Increased commercialization of economically
important medicinal plants has resulted in overharvesting, threatening their survival. The present study was carried out to
document the indigenous uses of medicinal plants by the local communities in and around Rema-Kalenga Wildlife Sanctuary, Bangladesh.
Data collection was predominantly qualitative recording the species use, identifying their relative importance (RI) and assessing
the informants’ consensus factor (Fic) on associated knowledge. We interviewed 140 households of the local community and 5 local herbal practitioners. A total
of 44 plant species were in use to treat 33 ailments under 10 broad disease categories. Five species were found to have high
use versatility (RI > 1), Emblica officinale L. being the most versatile. Respiratory problems scored the highest Fic value (0.56) involving the use of 30% of the species recorded. Terminalia bellerica Roxb., Sterculia villosa Roxb., Dillenia pentagyna Roxb. and Terminalia arjuna Bedd. were being harvested commercially. Use by the community, particularly for subsistence consumption, seemed to be sustainable,
but commercial extraction of some species appeared unsustainable. Buffer zone-based commercial farming of medicinal plants
with a commercial value could serve a dual purpose of assuring sustainable alternative income generation for local communities
as well as conserving the natural resources in protected areas. 相似文献
76.
77.
Mohammad Jafar Bahrani Foroud Salehi Sayed Abdolreza Kazemeini 《Archives of Agronomy and Soil Science》2013,59(2):179-187
Crop residues are beneficial substances affecting crop production and soil properties. A field experiment was carried out to evaluate the effects of wheat (Triticum aestivum L.) residue rates (0, 25, 50 and 75%) combined with N levels (0, 34.5, 69, 103.5 kg ha?1) on yield and yield components of two red common bean (Phaseolus vulgaris L.) cultivars and to monitor chemical soil parameters. The experiment was conducted at Research Center, College of Agriculture, Shiraz University, Shiraz, Iran for two years (2008–2009). The experiment was conducted as a split–split plot arranged in a randomized complete blocks design with three replications. The highest seed yield was obtained when 25–50% of residues were incorporated. The highest seed yield, seed weight per plant, 100-seed weight and seed number per pod were obtained with 103.5 kg N ha?1 with no significant difference to 69 kg N ha?1. Residue incorporation significantly increased soil organic carbon (SOC) as well as available K and P content. It is possible to sow red common bean as a double cropping by soil incorporation of 25–50% wheat residues with application of 69 kg N ha?1. 相似文献
78.
The beneficial effects of a Glomus deserticola strain isolated from the rhizosphere of grasses (belonging to Poaceae family) growing along the industrial waste from a distillery were investigated under stress conditions. The study was conducted to assess the efficacy of the arbuscular mycorrhizal (AM) fungal ecotype in salinity and heavy metal (HM) tolerance of eggplant (Solanum melongena L.) in soils amended with various stress levels of NaCl, zinc and cadmium. Mycorrhizal (M) seedlings produced a significantly (p < 0.05) greater growth response and were more tolerant to salt and HM stresses than nonmycorrhizal (NM) seedlings in all treatments. The HM contents in the plant tissues were significantly higher in M than NM eggplants. Furthermore, when the efficacy was compared with other AM isolates in HM-polluted soils with Sudan grass (Sorghum sudanese Staph.) as a test plant, the AM ecotype responded best to these soils, as evident from the significantly greater growth response and its aggressiveness in colonizing roots in all soil types tested. These results suggest that this G. deserticola ecotype can be used as an effective tool to alleviate the adverse effects of excessive salinity and HM toxicity on plant growth. Finally, the isolate may have potential in the bioremediation of polluted soils. 相似文献
79.
Houshang Ghamarnia Mohammad Amin Parandyn Issa Arji Vahid Rezvani 《Archives of Agronomy and Soil Science》2013,59(5):733-751
A field study was conducted over two years on maize at Islam Abad Research Station at 34°7′42′′N and 46°27′23′′E and elevation of 1348 m a.s.l in Kermanshah Province, western Iran in order to compare the effects of different irrigation methods and treatments on irrigation water use efficiency, crop yield, yield response factor, pan and seasonal crop coefficients, and other maize parameters. The experiment was a complete randomized block design with three replicates. During the study, irrigation water was applied at 40, 60, 80 and 100% of the maize seasonal water requirement for different surface drip tape (SDT) treatments, and 100% only for conventional furrow irrigation treatments with and without soil and water monitoring. The results showed that by using the above-mentioned different drip tape and surface treatments with soil and water monitoring, maize seasonal irrigation water use savings of 81, 71, 61, 52 and 36% were achieved compared with local conventional furrow irrigation without any soil, water and root monitoring, respectively. The yield response factor (K y), seasonal crop (K c) and pan coefficient (K p) for maize were 0.80, 0.76 and 0.97, respectively. 相似文献
80.
Khosro Mohammadi Yousef Sohrabi Ali Mokhtassi-Bidgoli Mohammad Tahsin Karimi Nezhad 《Archives of Agronomy and Soil Science》2013,59(6):793-798
This experiment was conducted in split plots based on randomized complete block design with three replications. Three crop sequences: (R1): chickpea, sunflower, wheat, and canola; (R2): green manure, chickpea, green manure, wheat, green manure, and canola; (R3): canola, wheat, and canola were used as main plots. Sub plots consisted of six methods of fertilization: (N1): farmyard manure; (N2): compost; (N3): chemical fertilizers; (N4): farmyard manure + compost; (N5): farmyard manure + compost + chemical fertilizers; and (N6): control. Results showed that the enzyme activities were higher in the N4 treatment. The highest amount of acid phosphatase, protease, dehydrogenase activity, and grain yield was observed in R2 sequence. The highest urease activity (58.6 µg g?1 h?1) was obtained in R2N4 treatment. In R2N4 treatment using in-farm inputs, a non chemical fertilizer system can be carried out to improve soil biological activity. 相似文献