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   123篇
  免费   2篇
林业   4篇
农学   7篇
  36篇
综合类   17篇
农作物   13篇
水产渔业   10篇
畜牧兽医   25篇
园艺   6篇
植物保护   7篇
  2021年   1篇
  2020年   4篇
  2019年   2篇
  2018年   7篇
  2017年   1篇
  2016年   5篇
  2015年   2篇
  2014年   3篇
  2013年   13篇
  2012年   3篇
  2011年   5篇
  2010年   4篇
  2009年   3篇
  2008年   6篇
  2007年   3篇
  2006年   8篇
  2005年   2篇
  2004年   3篇
  2003年   5篇
  2002年   3篇
  2001年   3篇
  2000年   2篇
  1999年   2篇
  1998年   1篇
  1996年   1篇
  1992年   2篇
  1991年   3篇
  1989年   1篇
  1988年   2篇
  1987年   2篇
  1985年   3篇
  1983年   2篇
  1982年   1篇
  1981年   1篇
  1979年   1篇
  1977年   2篇
  1976年   2篇
  1975年   1篇
  1973年   2篇
  1971年   1篇
  1969年   3篇
  1967年   1篇
  1966年   1篇
  1965年   1篇
  1964年   1篇
排序方式: 共有125条查询结果,搜索用时 15 毫秒
11.
A safe and simple thin layer chromatographic method has been developed for the estimation of niacin and niacinamide in pharmaceutical preparations containing other vitamins, enzymes, herbs, antiamoebic drugs, etc. The method involves removal of excipients from the preparation by ethanol precipitation and isolation of niacin or niacinamide from other ingredients by TLC on silica gel with water as developing solvent, followed by extraction in 0.1N HCl, and spectrophotometric estimation of the vitamin at 262 nm. The percent recoveries for niacin and niacinamide were 100.1 +/- 1.9 and 100.2 +/- 1.5, respectively.  相似文献   
12.
Teeth of a North American ictidosaur, Pachygenelus milleri, n. sp., found in the Upper Triassic Dockum Group of Texas, indicate that it is very similar to Pachygenelus monus of South Africa and Chaliminia musteloides of South America. The presence of a Gondwana element in the Northern Hemisphere attests to the ease of dispersal of the Late Triassic vertebrates through Pangea. Ictidosaurs are small, highly advanced, carnivorous cynodonts that display a mosaic of reptilian and mammalian features in the masticatory apparatus. They were contemporaneous with early mammals and probably closely related to them.  相似文献   
13.
14.
A greenhouse pot experiment was conducted to study the effect of application of three levels of phosphorus (0, 50 and 100 ppm) and three levels of zinc (0, 5 and 10 ppm) in all possible combinations on yield and tissue concentrations of zinc, copper, iron and manganese by rice at two different growth stages (35 and 90 days after transplantation). The results showed that application of both phosphorus and zinc increased the dry matter yield of shoot and root at both the growth stages. Phosphorus or zinc application was found to influence the concentration of zinc, copper, iron and manganese in shoot and in root but these influences varied with the growth stages of the plant as well as with the level of zinc and phosphorus application. The results further showed that phosphorus or zinc application influenced the absorption of zinc/phosphorus, iron, manganese and copper by rice plants and their translocation from root to shoot. Such effects were found to be more prominent at early growth stage than at late growth stage of the plants.  相似文献   
15.
Of 200 genotypes of cauliflower screened for their reaction to blackrot disease (Xanthomonas campestris (Pam.) Dowson) ‘MGS-2⊕-3⊕’, ‘Pua Kea’ and ‘SN 445’, derived from Indian cauliflower cultivars, possessed a high degree of resistance. Neither ‘Snowball’ nor its relatives ‘Erfurt’ and ‘Alpha’ showed any resistance. For the plant breeder, soaking the seed in a bacterial suspension is the most useful screening-technique; less useful were the spraying of whole plants with a suspension and the severing of a leaf-tip beneath a suspension. There were positive and highly significant correlations between seed soaking and seedling reaction, seed soaking and adult plant reaction, and seedling reaction and adult plant reaction.  相似文献   
16.
Application of nitrification inhibitor has potential to increase soil nitrogen (N) retention throughout the growing season and finally increase corn (Zea mays L.) yield. During the 2012–2014 growing seasons, on-farm field trials were conducted to determine the effects of nitrapyrin (Instinct) with two N sources, urea and urea ammonium nitrate, at two rates, 85% and 100% of recommended N, and side-dress on grain yield and soil inorganic N availability in the Red River Valley of the North Dakota. Preplant urea N at 100% recorded the greatest yield in 2 out of 3 years. At late sampling, the greatest soil inorganic N was observed with side-dress urea ammonium nitrate at 100% within 0–30 cm (last 2 years). For spring fertilizer N management, addition of nitrapyrin had no effect on yield and inconsistent effect on soil N availability. Our results suggest that fertilizer N management should be evaluated on a local scale and consider annual variability in weather.  相似文献   
17.
Two experiments, one short-term and one long-term, were conducted to elucidate the acute and chronic effects, respectively, of endosulfan exposure on the haemato-immunological and histopathological responses of Channa puncatatus. In the short-term study, fish were exposed to sublethal endosulfan (8.1 μg l−1) for 12, 24, 36, 48, 72 and 96 h. In the long-term study, fish were fed with normal diet and simultaneously either exposed to endosulfan (1.2 μg l−1) for 90 days or not. Results showed that the ascorbic acid levels in both the liver and the muscle decreased significantly (P < 0.05) by acute and chronic endosulfan exposure. The haemoglobin (Hb) level reduced significantly (P < 0.05) by 15.5% within 12 h of acute endosulfan exposure, further decreased by 25.8% after 24 h of exposure, however, thereafter the values increased and at the end of 72 h returned to normal levels. Almost similar trend was observed for the erythrocyte (RBC) count. The WBC count and the nitroblue tetrazolium (NBT) value showed a general increasing trend with increase in the duration of acute endosulfan exposure. The chronic exposure of C. punctatus to endosulfan significantly (P < 0.05) lowered the Hb level, RBC and WBC counts, NBT reduction value and the plasma parameters such as plasma protein, albumin (A) and globulin (G) compared with that of the control (except for A/G ratio). Endosulfan exposure also severely altered the liver histological structure. Overall results indicated that both short-term acute and long-term chronic endosulfan exposure had a significant impact on the haemato-immunological parameters and tissue histopathology of C. punctatus.  相似文献   
18.
Summary

Cauliflower (Brassica oleracea L. var. botrytis) was grown in refined sand at low (0.0011 mg l?1), normal (0.55 mg l?1) and excess (5.5 mg l?1) Mn, each at three levels of B, deficient (0.0033 mg l?1), normal (0.33 mg H) and excess (3.3 mg l?1). In Mn deficient cauliflowers a deficiency of B accentuated visible symptoms of Mn deficiency and aggravated the Mn deficiency effects i.e. a decrease in dry matter, leaf Mn, sugars, starch, chlorophyll, Hill reaction and specific activity of aldolase and an increase in the concentrations of proline and inorganic phosphorus. In cauliflowers exhibiting B toxicity symptoms under conditions of excess B, excess Mn increased leaf Mn, sugars, nucleic acids, protein P, nucleic acid P, acid-labile P and leaf B. Excess Mn decreased the concentrations of DNA, protein nitrogen, chlorophyll and activities of peroxidase, aldolase and leaf B, leaf Mn in boron deficient cauliflowers.  相似文献   
19.
Summary In the mild and short winter of the Ganges plains, the yield contributing characters such as number of shoots/plant, plant height, leaflet size, tuber yield/plant and tuber number/plant were studied for fifty varieties of potato. From the simple, partial and genotypic and phenotypic correlation studies it was observed that leaflet size, number of tubers/plant and plant height were closely connected with the yield of potato tubers. A multiple regression equation was also prepared and it was found that the leaflet size had the maximum influence on yield followed by number of tubers/plant and plant height.  相似文献   
20.
The need for scientific composting methods for effective utilization of organic waste is increasing day by day. In this respect, a new process called the Novcom composting method is being increasingly adopted by the organic tea planters of Assam and Darjeeling (India) for large-scale composting. Study of the biodegradation process under this method and quality evaluation of the end product was carried out at Maud tea estate (Assam) during 2008–2009 and 2009–2010. Generation of high temperatures (>65°C) within the compost heap during the biodegradation process provided an indication regarding the destruction of pathogens and weed seeds in the composted material. Samples collected on day 0, 7, 14, 21 and 30 of composting, were analyzed for physicochemical properties, nutrient status, microbial population, stability and phytotoxicity parameters. The most significant finding was the high microbial population (in the order of 1016 cfu g?1) in the final product, which was generated naturally during biodegradation. Assessment of the maturity and stability parameters of the compost indicated that biodegradation was complete in ~3 weeks. The study provided an indication of the potential of the Novcom composting method for the production of good quality, stable and mature compost, within a short period.  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