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   214篇
  免费   13篇
林业   46篇
农学   15篇
  41篇
综合类   6篇
农作物   17篇
水产渔业   30篇
畜牧兽医   42篇
园艺   8篇
植物保护   22篇
  2024年   1篇
  2023年   1篇
  2022年   6篇
  2021年   2篇
  2020年   6篇
  2019年   2篇
  2018年   13篇
  2017年   7篇
  2016年   9篇
  2015年   7篇
  2014年   6篇
  2013年   23篇
  2012年   17篇
  2011年   15篇
  2010年   10篇
  2009年   8篇
  2008年   16篇
  2007年   10篇
  2006年   7篇
  2005年   6篇
  2004年   6篇
  2003年   3篇
  2002年   4篇
  2001年   3篇
  2000年   4篇
  1999年   5篇
  1998年   1篇
  1997年   4篇
  1995年   6篇
  1994年   1篇
  1993年   1篇
  1992年   2篇
  1989年   1篇
  1988年   3篇
  1987年   1篇
  1986年   1篇
  1982年   1篇
  1979年   1篇
  1977年   1篇
  1976年   1篇
  1974年   1篇
  1973年   3篇
  1971年   1篇
排序方式: 共有227条查询结果,搜索用时 15 毫秒
51.
Sweet cherry (Prunus avium L.) is a self-incompatible species. Determination of the S-genotypes of cherry cultivars is crucial for breeding and to select appropriate cultivars for cross-fertilisation and fruit set. In this study, we characterised the S-genotypes of 25 sweet cherry cultivars, some of which had being bred at the Research and Breeding Institute of Pomology (RBIP), Holovousy, Czech Republic, and others were European cultivars in the RBIP collection. S-genotyping was carried out by polymerase chain reaction using consensus primers for the S-RNase and SFB genes, and capillary electrophoresis. Nine different known S-haplotypes (S1, S2, S3, S4, S5, S6, S9, S13, and S16) were identified and the cultivars were assigned to 12 incompatibility groups. One local cultivar, ‘Pta?ka z Plzně’, originated from a wild forest seedling and used as a pollinator, was assigned to Group 0 of universal donors. The pedigree of some cultivars was confirmed by their S-genotype. This study represents the ?rst comprehensive S-genotype screening of sweet cherry genetic resources in the Czech Republic and will be useful for the design of crossing programmes and orchard management of these sweet cherry cultivars.  相似文献   
52.
本文论述了孟加拉国吉大港大学校园里,不同年龄(5、10、20年)的羯布罗香(Dipterocarpus turbinatus Gaertn. F)人工林内,距树木基部不同距离(1、2、3、4米)处,外生侵染菌根的水平分布状况.在山的3个部位(顶部、中部和下部)对各人工林外生侵染菌根的侵染进行了测定.在不同水平分布距离处的树下采集了1000cm3的根际土壤样本,不同距离和山高处的外生侵染菌根浸染率差异显著.在5年和10年林龄的人工林内,浸染率随着距树的距离的增加而快速下降,而在20年林龄的人工林内,浸染率随着距树基部距离的增加而急剧增加.山下部20年生人工林内距树4m处的浸染率最高(81.3%),山顶部5年生人工林内距树4m处的浸染率最低(55.33%).图6参32.  相似文献   
53.
Status of organic carbon (C), total nitrogen (N), available potassium (K), calcium (Ca) and phosphorus (P) in three different depths (0-5 cm, 5-15 cm and 15-30 cm) on two hill slopes of 35% and 55% in orange orchard cultivated by the Mro tribe of Chittagong Hill. Tracts (CHTs) were evaluated and compared with those in degraded bush forests, through digging three profiles in each land use. The content of all the five nutrients was found to be higher in the soil of orange orchard than in the soil of forest. But the variation was not consistent for both the slopes. The content varied depth wise also, having the highest value in surface soil in case of both the land uses on both the slopes. A mean available K content was significantly higher in orange orchard than in forest on 55% slope, while it was lower on 35% slope. Surface soil contained the nutrients of K and Ca with the amount of 0.2905-mg·g^-1 soil and 3.025-mg·g^-1 soil respectively in the orchard, while 0.1934-mg·g^-1 soil and 1.6083-mg·g^-1 soil were respectively in the forest. Organic carbon and total nitrogen were found more or less similar in surface soil on both the land uses showing a slight difference. Available P was found only in orange orchard, and in forest it was too little in amount to detect by the spectrophotometer. The degraded forests were poor in nutrient content due to high rate of soil erosion, which would be possible to be improved by bringing it under tree cover as proved by the adaptation of orange orchard there.  相似文献   
54.
The influence of 50 and 100 μm Ni on membrane integrity, hydrogen peroxide content, lipid peroxidation as well as total fatty acid composition was studied in shoots and roots of wheat seedlings. In both organs, treatment with Ni led to significant increase in electrolyte leakage reflecting the metal‐induced enhancement of membrane permeability. In the shoots, it was accompanied by significant increase in lipid peroxidation. Accumulation of hydrogen peroxide, more pronounced in the shoots, was also found in Ni‐treated wheat. Exposure of wheat seedlings to Ni altered the total fatty acid composition, leading to decrease in their unsaturation, which was indicated by reduction in double bond index. In both organs, a significant decrease in linolenic acid (C18 : 3) content was observed. It was accompanied by increased linoleic (C18 : 2) and oleic (C18 : 1) acid contents in shoots and roots, respectively. In the shoots, parallel increase in palmitic acid (C16 : 0) and decrease in palmitoleic acid (C16 : 1) were found at the end of the experiment. Our results suggest that modification of fatty acid profile in Ni‐treated wheat seedlings is partly related to lipid peroxidation and increased electrolyte leakage and may reflect damage of cells caused by the metal.  相似文献   
55.
Understanding individual movements in heterogeneous environments is central to predicting how landscape changes affect animal populations. An important but poorly understood phenomenon is behavioural response to habitat boundaries and the way animals cross inhospitable matrix surrounding habitat patches. Here, we analyze movement decisions, flight behaviour, and activity of the endangered scarce large blue Phengaris (Maculinea) teleius, focusing on the differences among the patterns observed in patch interior, at patch boundaries and within matrix. The probability of crossing an external patch boundary, regardless of the land use in the adjacent area, was considerably lower than crossing a ‘control line’ within patch interior. Movement distances, flight durations and net squared displacement were largest in matrix, while similarly smaller at patch boundaries and in patch interior. The distribution of angles between successive movements was clearly clustered around 0° (indicating flight in a straight line) in matrix and at patch boundaries, but not in patch interior. There were no differences in time spent on foraging, resting and ovipositing between patch interior and boundaries, but the first two activities rarely, and oviposition never, happened in matrix. Our results suggest that although P. teleius adults do not avoid using the resources located in the boundaries of habitat patches, they often return to the interior of the patches when crossing their boundaries. However, having entered the matrix the butterflies perform relatively long and straight flights. The estimated probability of emigration and net squared distance implies that the dispersal between local populations is common in this species in the studied area.  相似文献   
56.
In this study, the effects of seven pure plant secondary metabolites (PSM s) on rumen fermentation, methane (CH4) production and rumen bacterial community composition were determined. Two in vitro trials were conducted. In trial 1, nine concentrations of 8‐hydroxyquinoline, αterpineol, camphor, bornyl acetate, αpinene, thymoquinone and thymol were incubated on separate days using in vitro 24‐hr batch incubations. All compounds tested demonstrated the ability to alter rumen fermentation parameters and decrease CH4 production. However, effective concentrations differed among individual PSM s. The lowest concentrations that reduced (<  .05) CH4 production were as follows: 8 mg/L of 8‐hydroxyquinoline, 120 mg/L of thymoquinone, 240 mg/L of thymol and 480 mg/L of αterpineol, camphor, bornyl acetate and αpinene. These concentrations were selected for use in trial 2. In trial 2, PSM s were incubated in one run. Methane was decreased (<  .05) by all PSM s at selected concentrations. However, only 8‐hydroxyquinoline, bornyl acetate and thymoquinone decreased (<  .05) CH4 relative to volatile fatty acids (VFA s). Based on denaturing gradient gel electrophoresis analysis, different PSM s changed the composition of bacterial communities to different extents. As revealed by Ion Torrent sequencing, the effects of PSM s on relative abundance were most pronounced in the predominant families, especially in Lachnospiraceae , Succinivibrionaceae , Prevotellaceae , unclassified Clostridiales and Ruminococcaceae . The CH 4 production was correlated negatively (?.72; <  .05) with relative abundance of Succinivibrionaceae and positively with relative abundance of Ruminococcaceae (.86; <  .05). In summary, this study identified three pure PSM s (8hydroxyquinoline, bornyl acetate and thymoquinone) with potentially promising effects on rumen CH4 production. The PSM s tested in this study demonstrated considerable impact on rumen bacterial communities even at the lowest concentrations that decreased CH4 production. The findings from this study may help to elucidate how PSM s affect rumen bacterial fermentation.  相似文献   
57.
Abstract

A study of simulated rat damage was done to determine the loss of wheat yield when O (control). 10, 30 and 50% ot the wheat stems were cut at tillering, booting, dough and mature crop stages. The yields at harvest from each of 128 1‐m2 plots were compared by analysis of variance and least significant difference tests. Yield at the tillering stages was not significantly different from the controls but yields at all other stages differed significantly. Yield losses in tillering and booting stages were not significant for the different damage levels except for 50% stem cutting at the booting stage. The yields from dough and mature crop stages at all damage levels were significantly lower than yields from controls. No significant differences in yield at all growth stages were observed between control plots and those receiving 10% damage, but 30 and 50% damage gave significant losses.  相似文献   
58.
Cancer is a leading cause of death worldwide. There are a lot of cancer causing agents which are divided as physical carcinogens, chemical carcinogens and biological carcinogens. But most of the carcinogens or causes of cancer are related to our lifestyle like diet, habit, occupation, radiation and some infection, etc. Chemoprevention is highly necessary to prevent cancer related preterm death. For this besides avoiding the causes of cancer we should concentrate ourselves on our diet. Because, numerous phytochemicals derived from edible plants have been reported to interfere with a specific stage of the carcinogenic process. Many mechanisms have been shown to account for the anticarcinogenic actions of dietary constituents and recently attention has been focused on intracellular-signalling cascades as common molecular targets for various chemopreventive phytochemicals. In this study, we tried to describe lifestyle related causes of cancer and the molecular basis of cancer prevention through the phytochemicals.  相似文献   
59.
Many benzimidazoles are known inducers of cytochromes P4501A (CYP1A) in laboratory animals and cell lines. As flubendazole and mebendazole are benzimidazole anthelmintics often used in a pheasant, in the present study an effect of these drugs in primary cultures of pheasant (Phasianus colchicus) hepatocytes was investigated. After 48 h incubation of the hepatocytes with the benzimidazoles (0.2-5 microM), CYP1A activities -- ethoxyresorufin O-deethylation (EROD) and methoxyresorufin O-demethylation (MROD) activities were measured and the CYP1A protein levels were determined by Western blotting. None of the tested benzimidazoles influenced the CYP1A protein content. No pharmacologically significant enhancement of CYP1A after exposure of the hepatocytes to flubendazole and mebendazole was found. Inhibition of the EROD/MROD activities caused by both tested substances was observed only at the highest concentration (5 microM). From a point of view of CYP1A induction or inhibition, the treatment of pheasants by both anthelmintics tested seems to be safe. Our study demonstrates the inter-species differences in CYP1A inducibility and the importance of induction/inhibition studies on target animals.  相似文献   
60.
Light and shelter are very important ecological factors that can affect many traits of fish. Therefore, a study was conducted to explore the effect of light and shelter on some phenotypic traits of stinging catfish (Heteropneustes fossilis Bloch, 1794). During experiment, equal‐sized juveniles (mean ± SE: 9.04 ± 0.09 cm) were collected and reared in aquariums dividing into four treatment groups, such as T1 (0L:24D without pipe), T2 (0L:24D with pipe), T3 (12L:12D without pipe) and T4 (12L:12D with pipe). Each treatment had 36 fish, which were randomly distributed into three replications. The fish were kept up to 120 days, and then, the growth performance and skin colour were analysed. The results showed that both lighting and shelter conditions as well as their interactions had significant effects on some traits expression. The analyses revealed that lighting condition significantly influenced body area, head width and skin coloration, while shelter condition significantly affected total and standard length, body area, and their interaction showed significant effects on body area, head width and anal fin length. Thus, this study indicates that stinging catfish show better growth performance and colour patterns especially in dark and sheltered conditions which could be recommended for the successive production of this highly priced fish species.  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