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   305篇
  免费   12篇
  国内免费   1篇
林业   24篇
农学   6篇
  65篇
综合类   30篇
农作物   11篇
水产渔业   27篇
畜牧兽医   131篇
园艺   11篇
植物保护   13篇
  2023年   4篇
  2022年   10篇
  2021年   15篇
  2020年   4篇
  2019年   11篇
  2018年   15篇
  2017年   12篇
  2016年   7篇
  2015年   7篇
  2014年   7篇
  2013年   17篇
  2012年   22篇
  2011年   22篇
  2010年   12篇
  2009年   17篇
  2008年   21篇
  2007年   20篇
  2006年   15篇
  2005年   15篇
  2004年   16篇
  2003年   13篇
  2002年   8篇
  2001年   4篇
  2000年   1篇
  1999年   2篇
  1998年   1篇
  1995年   1篇
  1994年   1篇
  1993年   4篇
  1991年   2篇
  1989年   2篇
  1988年   1篇
  1984年   1篇
  1979年   1篇
  1978年   1篇
  1950年   1篇
  1948年   1篇
  1933年   1篇
  1932年   1篇
  1931年   1篇
  1930年   1篇
排序方式: 共有318条查询结果,搜索用时 15 毫秒
91.
In order to enhance the removal of heavy metals such as Ni, Cu, Zn and Cd from wastewater, different cow dung/sewage sludge ratios were tested to assess the effect of these metals on the adaptability of Eisenia fetida earthworms to the treatment process carried out in a typical plant located in Tamaulipas, Mexico. Two experimental water treatment setups were proposed. The first set of experiments was planned to determine the adequate sewage sludge/cow dung ratio(s), whereas the second arrangement was designed to evaluate the growth performance and fecundity of the earthworms under high heavy metal concentrations. To achieve the objectives, the experiments were conducted for 90 days under controlled environmental conditions. Maximum worm biomass and growth rates were attained in samples containing 25 wt.% of sewage sludge. Weight and mortality of worms were significantly affected by the high levels of heavy metals, making difficult the metal accumulation in the worm tissues.  相似文献   
92.
Abstract

The humus composition was analyzed and the humic acid characterized by UV and visible absorption spectroscopy in order to investigate the rotting and maturing process of city refuse compost according to the method of Kumada et al. During the composting process, the following findings were obtained: (1) the HT value was almost constant, but the HE/HT ratio varied somewhat, (2) HA increased with decrease in FA, and the PQ value so increased clearly, (3) the shoulder-like absorption at a wavelength near 270 nm weakened, and (4) the RF value of humic acid increased, whereas the Δ log K value seldom varied.

The IR spectrum of humic acid gradually changed as follows: (1) the absorption band in the 1700-1600 cm-1 region and in the 1550-1500 cm-1 region increased slightly, (2) the band in the 1100-1000 cm-1 region decreased, and (3) the bands at 835 and 710 cm-1 com pletely disappeared. On the whole, the shape of the IR spectrum of the city refuse compost became featureless. These changes were probably due to the oxidation which occurred in the composting process.  相似文献   
93.
94.
Root-knot nematodes (RKN) are obligate parasite species of the genus Meloidogyne that cause great losses in Arabica coffee (Coffea arabica L.) plantations. Identification of resistant genotypes would facilitate the improvement of coffee varieties aiming at an environmental friendly and costless nematode control. In this work, the C. arabica genotype ‘UFV 408-28’ was found to be resistant to the most destructive RKN species M. incognita. Pathogenicity assays indicated that the highly aggressive populations of M. incognita races 1, 2 and 3 were not able to successfully reproduce on ‘UFV 408-28’ roots and displayed a low gall index (GI = 2). An average reduction of 87% reduction of the M. incognita population was observed on ‘UFV 408-28’ when compared to the susceptible cultivar ‘IAC 15’. By contrast, ‘UFV 408-28’ was susceptible to the related species M. exigua and M. paranaensis (GI = 5 and 4, respectively). Histological observations performed on sections of UFV408-28 roots infected with M. incognita race 1 showed that nematode infection could be blocked right after penetration or during migration and establishment stages, at 6 days, 7 days and 8 days after infection (DAI). Fluorescence and bright field microscopy observations showed that root cells surrounding the nematodes exhibited HR-like features such as accumulation of phenolic compounds and a necrotic cell aspect. In the susceptible ‘IAC 15’ roots, 6 DAI, feeding sites contained giant cells with a dense cytoplasm. Necrotic cells were never observed throughout the entire infection cycle. The HR-like phenotype observed in the ‘UFV 408-28’—M. incognita interaction suggests that the coffee resistance may be mediated by a R-gene based immunity system and may therefore provide new insights for understanding the molecular basis of RKN resistance in perennial crops.  相似文献   
95.
Chlamydomonas reinhardtii is a unicellular green alga whose lineage diverged from land plants over 1 billion years ago. It is a model system for studying chloroplast-based photosynthesis, as well as the structure, assembly, and function of eukaryotic flagella (cilia), which were inherited from the common ancestor of plants and animals, but lost in land plants. We sequenced the approximately 120-megabase nuclear genome of Chlamydomonas and performed comparative phylogenomic analyses, identifying genes encoding uncharacterized proteins that are likely associated with the function and biogenesis of chloroplasts or eukaryotic flagella. Analyses of the Chlamydomonas genome advance our understanding of the ancestral eukaryotic cell, reveal previously unknown genes associated with photosynthetic and flagellar functions, and establish links between ciliopathy and the composition and function of flagella.  相似文献   
96.
Schistosomiasis is a parasitic disease that affects more than 250 million people. The treatment is limited to praziquantel and the control of the intermediate host with the highly toxic molluscicidal niclosamide. Marine algae are a poorly explored and promising alternative that can provide lead compounds, and the use of multivariate analysis could contribute to quicker discovery. As part of our search for new natural compounds with which to control schistosomiasis, we screened 45 crude extracts obtained from 37 Brazilian seaweed species for their molluscicidal activity against Biomphalaria glabrata embryos and schistosomicidal activities against Schistosoma mansoni. Two sets of extracts were taxonomically grouped for metabolomic analysis. The extracts were analyzed by GC–MS, and the data were subjected to Pattern Hunter and Pearson correlation tests. Overall, 22 species (60%) showed activity in at least one of the two models. Multivariate analysis pointed towards 3 hits against B. glabrata veliger embryos in the Laurencia/Laurenciella set, 5 hits against B. glabrata blastula embryos, and 31 against S. mansoni in the Ochrophyta set. Preliminary annotations suggested some compounds such as triquinane alcohols, prenylated guaianes, dichotomanes, and xenianes. Despite the putative identification, this work presents potential candidates and can guide future isolation and identification.  相似文献   
97.
Chondracanthus chamissoi is an important source of carrageenan in Chile. Presently, all the production is harvested from wild populations. This study reports the first attempt to cultivate C. chamissoi. Experiments were conducted with female gametophytic and sporophytic thalli by inserting them among braids of a 7 mm polypropylene rope. Inoculated ropes were placed at 1, 3 and 5 m depths in two sheltered bays in northern Chile. The fronds adapted well to cultivation and grew at all the depths tested, although the greatest increase in biomass was observed at 1 m depth. On a yearly cycle, higher biomass increases were observed in autumn and winter months compared with the spring and summer. We believe that by adapting the cultivation methodology, this species could be cultivated year round.  相似文献   
98.
To examine the hormonal and nutritional regulation of insulin-like growth factor I (IGF-I) mRNA expression, a sequence-specific solution hybridization/RNase protection assay for coho salmon IGF-I mRNA was developed. This assay is both rapid and sensitive and has low inter- (less than 15%) and intra-assay variations (less than 5%). Using this assay, the tissue distribution of IGF-I mRNA and effects of growth hormone (GH), prolactin (PRL) and somatolactin (SL) on hepatic IGF-I mRNA expression in coho salmon were examined in vivo. Liver had the highest IGF-I mRNA level of 16 pg/μg DNA. Significant amounts of IGF-I mRNA were also found in all other tissues examined (intestine 4.1, kidney 3.8, gill arch 2.4, brain 2.4, ovary 2.3, muscle 2.1, spleen 1.7 and fat 1.1 pg/μg DNA). Injection of coho salmon GH at doses of 0.1 and 1 μg/g body weight significantly increased the hepatic IGF-I mRNA levels in a dose-dependent manner. Injection of coho salmon SL, a recently discovered member of the GH/PRL family, stimulated the IGF-I mRNA expression at the higher dose (1 μg/g), whereas coho salmon PRL had no effect at either dose. Concentration-dependent stimulation by coho salmon GH was also obtained in vitro in primary culture of salmon hepatocytes in concentrations ranging from 0.01 to 1 μg/ml. These results indicate that IGF-I mRNA expression occurs in a variety of tissues in coho salmon, and that at least the hepatic expression is under the regulation of GH and possibly other hormones. The sequence-specific assay established in the present study can be used for accurate quantitation of IGF-I mRNA in salmonid species, and can contribute to a better understanding of the physiology of IGF-I in salmonids.
Résumé Afin d'étudier les régulations homronales et nutritionnelles de l'expression des ARNm de l'IGF-I (insulin-like growth factor I), un dosage spécifique par hybridation en solution des ARNm d'IGF-I de saumon coho et protégé des RNases, a été développé. Ce dosage, à la fois rapide et sensible, présente un faible coefficient de variation inter- (< 15%) et intra- (< 5%) dosage. L'étude de la distribution tissulaire des ARNm de l'IGF-I et des effets de l'hormone de croissance (GH), de la prolactine (Prl) et de la somatolactine (SI) sur l'expression hépatique des ARNm de l'IGF-I, a été entreprise in vivo chez le saumon coho en utilisant ce dosage. Le foie présente les plus grandes quantités d'ARNm d'IGF-I (16 pg/μg d'ADN). Des quantités significatives d'ARNm d'IGF-I ont été également détectées dans tous les autres tissus étudiés (intestin 4,1; rein 3,8; branchie 2,4; ovaire 2,3; muscle 2,1; rate 1,7 et graisse 1,1 pg/μg d'ADN). L'injection à des saumons coho, de GH à des doses de 0,1 et 1 μg/g de poids vif, augmente significativement et de manière dose dépendante les niveaux hépatiques d'ARNm d'IGF-I. L'injection de SI de saumon coho, un membre récemment découvert de la famille GH/Prl, stimule avec la plus haute dose utilisée, l'expression des ARNm d'IGF-I alors que la Prl n'a aucun effet. La GH augmente de manière dose dépendante (0,01–1 μg/ml) l'expression in vitro des ARNm d'IGF-I par des ARNm d'IGF-I par des hépatocytes de saumon coho en culture. Ces résultats indiquent que, chez le saumon coho, l'expression des ARNm d'IGF-I est présente dans le nombreaux tissus et que, l'expression hépatique est, au moins en partie, régulée par la GH et peut-être par d'autres hormones. Le dosage par séquence spécifique mise au point dans le présent travail, peut-être utilisé pour la quantification précise des ARNm, d'IGF-I de salmonidés et devrait permettre une meilleure connaissance de la physiologie de L'IGF-I chez les salmonidés.
  相似文献   
99.
Gossip is a form of affective information about who is friend and who is foe. We show that gossip does not influence only how a face is evaluated--it affects whether a face is seen in the first place. In two experiments, neutral faces were paired with negative, positive, or neutral gossip and were then presented alone in a binocular rivalry paradigm (faces were presented to one eye, houses to the other). In both studies, faces previously paired with negative (but not positive or neutral) gossip dominated longer in visual consciousness. These findings demonstrate that gossip, as a potent form of social affective learning, can influence vision in a completely top-down manner, independent of the basic structural features of a face.  相似文献   
100.
In this study, fecal Escherichia coli isolates (n=188) from 34 dog-owner pairs and 26 healthy control humans (2 isolates per individual) were tested for susceptibility to 6 antimicrobials and screened for virulence genes. Genetic diversity between canine and owner isolates was evaluated by pulsed-field gel electrophoresis (PFGE). Canine isolates exhibited significantly different rates of resistance to four and two antimicrobials, compared to control and owner isolates, respectively. Of the genes examined, the prevalence of sfa, hly, and cnf genes in canine isolates were higher than in control isolates, but not than in owner isolates. These results suggest that characteristics of owner isolates are somewhat similar to canine isolates, compared to isolates from non-dog owners. In addition, PFGE analysis revealed that transfer of E. coli between owners and their dogs had occurred within 3/34 (8.8%) households. Considering the effects of dog ownership on the population of E. coli isolates from owners, further epidemiological studies are required.  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