首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1528篇
  免费   74篇
  国内免费   1篇
林业   143篇
农学   221篇
基础科学   24篇
  316篇
综合类   48篇
农作物   91篇
水产渔业   46篇
畜牧兽医   513篇
园艺   68篇
植物保护   133篇
  2023年   10篇
  2022年   24篇
  2021年   33篇
  2020年   31篇
  2019年   24篇
  2018年   67篇
  2017年   57篇
  2016年   69篇
  2015年   38篇
  2014年   42篇
  2013年   122篇
  2012年   57篇
  2011年   81篇
  2010年   58篇
  2009年   48篇
  2008年   69篇
  2007年   55篇
  2006年   47篇
  2005年   40篇
  2004年   34篇
  2003年   39篇
  2002年   43篇
  2001年   28篇
  2000年   26篇
  1999年   29篇
  1998年   13篇
  1997年   9篇
  1996年   15篇
  1995年   11篇
  1994年   10篇
  1993年   12篇
  1992年   18篇
  1991年   20篇
  1990年   30篇
  1989年   21篇
  1988年   15篇
  1987年   20篇
  1986年   17篇
  1985年   17篇
  1984年   11篇
  1983年   12篇
  1982年   14篇
  1981年   17篇
  1980年   14篇
  1979年   21篇
  1978年   15篇
  1977年   11篇
  1970年   8篇
  1969年   14篇
  1968年   12篇
排序方式: 共有1603条查询结果,搜索用时 15 毫秒
991.
Laboratory indices (KCl extraction, thermal fractionation, pepsin extraction, C:N ratio and N mineralization) of organic materials were compared with plant availability of mineral-N produced from organic-N in a greenhouse experiment. Six types of organic materials [farmyard manure (FYM), pig manure (PG), poultry manure (PL), sewage sludge (SS), pressmud (PM) and compost (CP)] were compared with urea as a chemical reference fertilizer. Relative effectiveness of organic N (REo) was used to compare the fraction of N extracted with different N availability laboratory indices. REo values of organic materials ranged from 0.14 to 0.77 and decreased in the following order: PL > PG > SS > PM > CP > FYM. The KCl-extracted inorganic N, pepsin-extracted organic N and N mineralized during 42 days gave a positive relationship with REo, and the C:N ratio a negative relationship with REo. Among the different N availability laboratory indices, pepsin extraction of organic N, C:N ratio and N mineralization can be recommended for determining mineralizable organic N in organic materials. KCl-extracted inorganic N proved to be a useful index for organic materials having a low inorganic N fraction. Thermal fractionation did not provide a suitable index of plant-available N in organic materials.  相似文献   
992.
Salt-affected soils in arid and semi-arid tracts of the Indian Punjab are prone to deficiency of micronutrients. Nine profiles from alluvial terraces, sand dunes and palaeochannels in the southwestern Punjab were investigated for total and diethylenetriamine-penta-acetic acid (DTPA) extractable Zn, Cu, Mn and Fe. Soil physiography exerted significant influence on the spatial distribution of micronutrients. Total contents varied from 20–78 for Zn, 8–32 for Cu, and 88–466 mg kg?1 for Mn and 0.82–2.53% for Fe. DTPA-extractable contents varied from 0.10–0.98 for Zn, 0.14–1.02 for Cu, 0.54–13.02 for Fe and 0.82–9.4 mg kg?1 for Mn. Total contents were higher in fine-textured soil than in coarse-textured soils. Concentration of micronutrients in the surface layer was low and there occurred more accumulation in the Cambic horizon. Organic carbon, pH, clay, silt and calcium carbonate exerted strong influence on the distribution of micronutrients. DTPA extractable Zn, Cu, Mn and Fe increased with increasing organic carbon but decreased with increase in pH and calcium carbonate content. Total micronutrient contents increased with increase in clay, silt and calcium carbonate contents and decreased with increase in sand content.  相似文献   
993.
The inherent properties of rayon fibre have been changed with additional properties through graft copolymerization of acrylamide, AAm, by chemical method using ceric ammonium nitrate/nitric acid, (CAN/HNO3), as a redox initiator and γ-radiation induced mutual method. Reaction conditions such as monomer and initiator concentration, liquor ratio, temperature and time of reaction, amount of radiation dose have been optimized with respect to percentage of grafting. Maximum percentage of grafting (Pg), (40 %) using CAN/HNO3 was obtained at [CAN]=31.92×10?3 moles/l, [HNO3]=79.36×10?2 moles/l, [AAm]=14.07×102 moles/l in 20 ml of H2O at 45 °C within 120 min while in case of radiation induced method, maximum Pg (30 %) was obtained at higher monomer concentration (28.14×10?2 moles/l) and time (180 min) in 10 ml of H2O at room temperature with total dose exposure of 11.178 kGy. The graft copolymers were characterized by FTIR, thermogravimetric and scanning electron micrographic analysis. Swelling behaviour in water, methanol, ethanol, acetone and DMF and dyeing and flame retarding properties of rayon fibre and grafted rayon fibre were investigated. Percent dye uptake (71.8 %) was found to be higher than that observed for the pristine fibre (57.4 %) and the grafted fibre after post phosphorylation reaction showed excellent flame retarding properties.  相似文献   
994.
An investigation was undertaken using a combination of microbiological and DNA-based approaches to evaluate combinations of two/three/four cyanobacterial strains (BF1 Anabaena torulosa; BF2, Nostoc carneum; BF3, Nostoc piscinale; BF4, Anabaena doliolum), using a novel vermicompost-based carrier, for their promise as inoculants in rice crop. The crop was maintained under 60% WHC through intermittent irrigation. Selected combinations (BF1 + 2 + 3; BF1 + 2 + 4; BF1 + 3 + 4) showed a consistent trend regarding their superiority over other treatments in terms of plant growth promotion and soil microbiological parameters. Microscopic examination of soil enrichment cultures raised from the treatments revealed their comparative abundance over native flora. A significant enhancement in terms of soil microbial biomass carbon and humus content was also recorded in these treatments. The soil enzymatic profile of the inoculated treatments involving FDA, dehydrogenase, acid phosphates, alkaline phosphatase, aryl esterase and β-glucosidase also revealed the promise of the inoculated strains. 16SrDNA sequencing, followed by BLAST analyses provided valuable information regarding the establishment of Anabaena strains. RFLP analyses of the 16SrDNA sequences of soil DNA and phylogenetic analyses vis a vis sequences of the inoculated cyanobacterial strains revealed the promise of treatments ?BF1 + 2 + 3, BF1 + 2 + 4 and BF1 + 3 + 4. Panicle weight (yield attribute) was statistically at par with the fertilizer controls 1/2N + PK and significantly higher than 1/3N + PK. To our knowledge, this represents a first report on evaluating the establishment of cyanobacterial inoculants in rice crop grown under non-flooded conditions (or intermittent irrigation) using a combination of agronomic, microbiological and soil DNA related attributes.  相似文献   
995.
A survey of potato fields located in the south-eastern region of Himachal Pradesh (India) was carried out in order to find out the natural pathogens infecting the white grub, Brahmina coriacea. About 88 % population of the infected grubs were found to exhibit symptoms of natural bacterial infection during the years 2007–2008. Hence, we attempted to isolate and characterize the most potent bacteria for the management of B. coriacea and tested their insecticidal activity. In this study, ten different bacterial isolates belonging to genera Bacillus, Psychrobacter, Paracoccus, Paenibacillus, Mycobacterium, Staphylococcus and Novosphingobium were isolated from B. coriacea. Bacterial species were identified based on morphology, biochemical tests and homologies of 16S rRNA gene sequences. Pathogenicity tests for all isolated bacteria at 1.0 × 108 cfu/ml of broth were performed on late first instar grubs. Among the bacteria tested, Bacillus cereus induced highest mortality level of 51.85 % within 7 days of treatment followed by Psychrobacter pulmonis (33.33 %), Bacillus psychrodurans (25.93 %), Bacillus pumilus (25.93 %), Paenibacillus tylopili (22.22 %) and Novosphingobium capsulatum (18.52 %). Mortality levels were further increased up to 100 % by B. cereus followed by 88.89 % by P. pulmonis after 30 days of treatment. Our results indicate that B. cereus, P. pulmonis, B. psychrodurans, B. pumilus, P. tylopili and N. capsulatum may be valuable biological control agents for white grubs, B. coriacea.  相似文献   
996.
The contamination of lettuce, spinach and basil with pathogenic E. coli has caused numerous illnesses over the past decade. E. coli O157:H7, E. coli O104:H4 and avian pathogenic E. coli (APECstx‐ and APECstx+) were inoculated on basil plants and in promix substrate using drip and overhead irrigation. When overhead inoculated with 7 log CFU/ml of each strain, E. coli populations were significantly (= 0.03) higher on overhead‐irrigated plants than on drip‐irrigated plants. APECstx‐, E. coli O104:H4 and APECstx+ populations were recovered on plants at 3.6, 2.3 and 3.1 log CFU/g at 10 dpi (days post‐inoculation), respectively. E. coli O157:H7 was not detected on basil after 4 dpi. The persistence of E. coli O157:H7 and APECstx‐ were similar when co‐inoculated on lettuce and spinach plants. On spinach and lettuce, E. coli O157:H7 and APEC populations declined from 5.7 to 6.1 log CFU/g and 4.5 log CFU/g, to undetectable at 3 dpi and 0.6–1.6 log CFU/g at 7 dpi, respectively. The detection of low populations of APEC and E. coli O104:H4 strains 10 dpi indicates these strains may be more adapted to environmental conditions than E. coli O157:H7. This is the first reported study of E. coli O104:H4 on a produce commodity.  相似文献   
997.
Summary

The effect of three arbuscular mycorrhizal (AM) inocula at four available levels of phosphorus (8.41, 12.53, 13.63 and 14.6 ppm) in non-disinfected soil was studied on the growth, flowering, P uptake and root colonization in micropropagated bulblets of Lilium sp. (Asiatic hybrid ‘Gran Paradiso’). The inoculated bulblets fared significantly better than the uninoculated ones in terms of all the growth variables, namely size, weight, shoot length, number of leaves and leaf area, and in P uptake. However, bulblets inoculated with different AM inocula had optimum growth at different P levels. Bulblets inoculated with indigenous mixed vesicular-arbuscular mycorrhiza species (VAM I) and Glomus intraradices isolate 2 (VAM III) showed the best growth and early flowering at available soil P of 13.6 ppm, whereas those inoculated with Glomus intraradices isolate 1 (VAM II) showed higher growth at 2.5 ppm available soil P. Amongst the three tested inocula, VAM I promoted maximum shoot length, bulblet size, and weight at 13.6 ppm P. The bulblets under this treatment also flowered earlier, nearly a month before the uninoculated control ones.  相似文献   
998.
Summary

Experiments were conducted to observe the effect of different concentrations of 1-methylcyclopropene (1-MCP) on the post-harvest life and quality of ‘Allison’ kiwifruit (Actinidia deliciosa). Fruit were treated with 1-MCP at 0.5 µl l–1, 1.0 µl l–1, or 2.0 µl l–1, un-treated fruit served as controls. Each 1-MCP treatment was applied for 24 h at 20°C. After treatment, fruit were transferred to ambient temperature storage (22º ± 4ºC; 65 – 70% relative humidity) for 18 d, during which time observations on various physical, physiological, and biochemical parameters were recorded at 3 d intervals. Our results indicated that 2.0 µl l–1 1-MCP was the most effective treatment to delay softening and ripening in ‘Allison’ kiwifruit, as such fruit showed the lowest mean weight loss (9.8 ± 0.2%), the highest mean fruit firmness value (32.7 ± 0.2 N), and began to ripen only after 12 d in storage, whereas untreated fruit started ripening on day-6 of storage. The activities of fruit softening enzymes such as polygalacturonase (PG; 58.5 ± 0.3 µg galacturonic acid g–1 FW h–1), and lipoxygenase (LOX; 3.96 ± 1.3 µmoles linoleic acid oxidised min–1 g–1 FW h–1) were lower, and total phenolics (TP) contents (24.3 ± 0.3 mg 100 g–1) and anti-oxidant (AOX) activities (12.5 ± 0.03 µmol Trolox g–1 FW h–1) were higher in 1-MCP-treated fruit than in untreated fruit (PG, 98.3 ± 0.5 µg galacturonic acid g–1 FW h–1; LOX, 4.39 ± 1.0 µmoles min–1 g–1 FW h–1; TP, 5.3 ± 0.6 mg 100 g–1; AOX, 4.7 ± 0.02 µmol Trolox g–1 FW h–1, respectively). In addition, 1-MCP-treated fruit exhibited lower rates of respiration (48.3 ± 0.4 ml CO2 kg–1 h–1) and ethylene production (30.2 ± 0.02 µl kg–1 FW h–1) than untreated fruit (58.9 ± 0.6 ml CO2 kg–1 h–1; 38.7 ± 0.04 µl kg–1 FW h–1, respectively). Similarly, 1-MCP-treated fruit had higher titratable acidity (TA; 1.33 ± 0.3%) and ascorbic acid (AA) contents (115.9 ± 2.6 mg 100 g–1 pulp) and lower soluble solids contents (SSC; 8.33º ± 0.2º Brix) than untreated kiwifruit (TA, 1.0 ± 0.2 %; AA, 105.3 ± 2.2 mg 100 g–1 pulp; SSC, 13.7º ± 0.3º Brix, respectively). Thus, 2.0 µl l–1 1-MCP can be used for the post-harvest treatment of ‘Allison’ kiwifruit to enhance its shelf-life and marketability by approx. 6 d.  相似文献   
999.
Rice, one of the most important staple food crops of the world, suffers a major setback nutritionally, because it is deficient in bioavailable zinc. In an attempt to answer this problem a field study was performed for two years during 2010 and 2011. Rice plants were treated with selected plant growth promoting rhizobacteria (PGPR; P. putida, P. fluorescens, A. lipoferum, B 15, B 17, B 19, BN 17, and BN 30) and plant growth, zinc (Zn) content in different plant parts and grains was analyzed. The data obtained showed enhancement in rice growth and hence, increased rice yield in response to PGPR application. All isolates resulted in almost 1.5- to 2-fold increase in Zn content in roots, shoots as well as grains in comparison to the control. The bacterial isolates B 17, B 19, and BN 17 were of particular interest as they induced the movement of Zn from roots to shoots as well as from husk to the grains, thus making grains enriched in Zn (around 25% higher Zn content). Therefore, it can be concluded that application of PGPR strains is an important strategy to combat the problem of zinc deficiency in rice and consecutively in human masses.  相似文献   
1000.
One hundred and twenty school girls in the age group of 13–15 years from four Government schools of Ludhiana city were selected for the study. On the basis of their family income they were divided into three experimental groups i.e. income group I (IgI), income group II (IgII) and income group III (IgIII). The results showed that the intake was low for all the foods. However, the consumption of fruits, milk and milk-products, sugar and jaggery, fats and oils by the subjects of IgII and IgIII was significantly higher (p<0.05) than IgI. The mean daily intake of energy, protein, iron, calcium, vitamin A & vitamin C was inadequate while the intake of fibre was adequate by the subjects as compared to ICMR recommendations. There was no significant difference in energy, protein and iron intakes among the subjects of three groups. However, the fibre intake by the subjects of IgI was significantly higher (p<0.05) than the subjects of IgIII, whereas the intake of calcium, vitamin A and ascorbic acid by the subjects of IgII & IgIII was significantly higher (p<0.05) than those of IgI. The average body weights and heights of the subjects were normal. The haemoglobin (Hb) level of the subjects ranged from 8.5–12.5 g/dl with a mean value of 10.73+0.07 and reported that only 23 percent of the subjects had acceptable level.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号