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   221篇
  免费   14篇
林业   36篇
农学   11篇
基础科学   6篇
  48篇
综合类   11篇
农作物   10篇
水产渔业   31篇
畜牧兽医   56篇
园艺   8篇
植物保护   18篇
  2023年   2篇
  2022年   4篇
  2021年   9篇
  2020年   9篇
  2019年   16篇
  2018年   18篇
  2017年   11篇
  2016年   12篇
  2015年   7篇
  2014年   15篇
  2013年   11篇
  2012年   12篇
  2011年   18篇
  2010年   8篇
  2009年   9篇
  2008年   8篇
  2007年   7篇
  2006年   7篇
  2005年   12篇
  2004年   1篇
  2003年   4篇
  2002年   2篇
  2001年   1篇
  2000年   3篇
  1999年   4篇
  1995年   1篇
  1994年   2篇
  1992年   1篇
  1991年   1篇
  1990年   4篇
  1989年   1篇
  1988年   1篇
  1985年   2篇
  1982年   3篇
  1980年   1篇
  1979年   1篇
  1977年   2篇
  1970年   1篇
  1969年   3篇
  1962年   1篇
排序方式: 共有235条查询结果,搜索用时 15 毫秒
231.
232.
The aim of this work was to evaluate the antioxidant potential of teas prepared from twenty-four commercially available berries and flowers of Sambucus nigra L. in relation to their phenolic profile, as reflected by the most representative phenolic acids (caffeic, chlorogenic, p-coumaric, ferulic, gallic and syringic acids); flavonols (quercetin, kaempferol, myricetin and rutin); and total phenolic (TPC), phenolic acid (TAC) and flavonoid (TFC) contents. The infusions prepared from elderflowers contained more abundant phenolic compounds than the elderberry infusions. The TPC of these infusions ranged from 19.81 to 23.90 mg of gallic acid equivalents/g dry weight of sample (GAE/g DW) for elderberries and from 15.23 to 35.57 mg GAE/g DW for elderflowers, whereas the TFC ranged from 2.60 to 4.49 mg of rutin equivalents/g dry weight of sample (RUTE/g DW) in elderberry infusions and from 5.27 to 13.19 mg RUTE/g DW in elderflower infusions. Among the phenolic compounds quantified in this study, quercetin (2.07–9.48 mg/g DW) and myricetin (1.17–9.62 mg/g DW) had the highest concentrations in the teas prepared from berries and flowers, respectively. Moreover, the antioxidant potential of elder infusions assessed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and ferric reducing antioxidant power (FRAP) assays revealed that the teas prepared from flowers had higher mean DPPH and FRAP activities than the teas prepared from berries. Therefore, elder beverages could be important dietary sources of natural antioxidants that contribute to the prevention of diseases caused by oxidative stress.  相似文献   
233.
The Russian sturgeon is a highly prized species reared in aquaculture. The process of gonad development in this critically endangered species is poorly understood. The aim of this study was to describe the localization of Sox9 protein during gonad development of the Russian sturgeon from the day of hatching to the 1440 day post hatching (dph). The larvae at age 1, 10, 25 dph and prepared gonads of 300, 720, 1440 dph individuals were immunohistochemistry‐stained for Sox9 detection. Sox9‐positive regions were detected in larvae in primordial germ cells cytoplasm. Analysis of 300 dph sturgeon gonads revealed the presence of the Sox9 protein in cytoplasm of some oocytes in the chromatin nucleus stage. In testes at 720 dph, Sox9 was observed in the cytoplasm of type A and early B spermatogonias. In the ovaries, Sox9 was observed in the cytoplasm of diplotene oocytes and prefollicular cells. In testes of 1440 dph sturgeon, Sox9 was present in the nucleus of the spermatocytes and in types A and B spermatogonias cytoplasm. Analysis of ovaries at 1440 dph reveals multiple diplotene oocytes with a Sox9‐positive cytoplasm. Furthermore, in 720 and 1440 dph, sturgeon presence of intersexual gonads was detected. In intersex gonads, Sox9 was observed in the cytoplasm of diplotene oocytes and type A spermatogonias. This study may be the first attempt to determine Sox9 protein localization during ontogenesis of the Russian sturgeon. Localization of Sox9 protein may become a useful marker of the maturation level in testis of the Russian sturgeon.  相似文献   
234.
LC/MS analysis of cyclohexanedione oxime herbicides in water   总被引:1,自引:0,他引:1  
A multiresidue method for the determination of alloxydim (methyl 2, 2-dimethyl-4, 6-dioxo-5-[1-[2-propenyloxy)amino]butylidene]cyclohexanec arb oxylate), clethodim (E, E)-(+/-)-2-[1-[[3-chloro-2-propenyl)oxy]imino]propyl]-5-[2-(ethylthio )propyl]-3-hydroxy-2-cyclohexen-1-one), sethoxydim ((+/-)-2-[1-(ethoxyimino)butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2 -cy clohexen-1-one), and two metabolites, clethodim sulfoxide ((E, E)-(+/-)-2-[1-[[3-chloro-2-propenyl)oxy]imino]propyl]-5-[2-(ethylsulf inyl)propyl]-3-hydroxy-2-cyclohexen-1-one) and sethoxydim sulfoxide ((+/-)-2-[1-(ethoxyimino)butyl]-5-[2-ethylsulfinyl)propyl]-3 -hydroxy- 2-cyclohexen-1-one), in water by high-performance liquid chromatography/electrospray/mass spectrometry (LC/ES/MS) is reported. River water and distilled water were spiked at 0.08 and 0.8 microgram L(-1) with all three herbicides, which were then extracted from the water by C(18)-SPE (SPE = solid-phase extraction). The herbicides and metabolites were quantified and confirmed using selected ion monitoring. The percent recoveries of the herbicides from water spiked at 0.8 microgram L(-1) were as follows: alloxydim, 117 +/- 11%; clethodim, 96 +/- 14%; sethoxydim, 89 +/- 13%. There was no evidence of oxidation of clethodim and sethoxydim during the extraction to their respective sulfoxides. The limit of quantitation was <0.1 microgram L(-1). We have shown that we can analyze and confirm three cyclohexanedione oxime herbicides and two metabolites in water by LC/ES/MS. This multiresidue method should also be appropriate for other cyclohexanedione oximes.  相似文献   
235.
The effect of arable field margin composition on invertebrate biodiversity   总被引:1,自引:0,他引:1  
A replicated field experiment designed to compare five types of field margin in terms of their invertebrate biodiversity was established in North Yorkshire, UK. Four replicate margins on arable land each contained five treatment plots 72 m long by 6 m wide. The treatments were: (1) cropped to the edge; (2) sown ‘tussocky’ grass mix; (3) sown ‘grass and wildflower’ mix; (4) Split margin (3 m ‘tussocky’ grass adjacent to hedge and 3 m ‘grass and wildflower’ next to crop); and (5) natural regeneration. Invertebrates were sampled by pitfall trapping, sweep netting, and butterfly and bumblebee transects, and identified to species level. The use of different flower species by foraging bumblebees was also examined.Despite all treatments containing a flush of annual weeds early in the establishment year, the five margin types were distinct in their vegetation composition by their first mid-summer. Where statistically significant results were obtained for invertebrates, avoidance of the ‘cropped’ treatment was by far the commonest observed response. This tendency could be clearly demonstrated amongst the carabids, spiders, butterflies, bumblebees, millipedes and harvestmen, with margins often containing double or more the number of invertebrates of similar areas cropped to the edge. Having avoided the crop, preferences for other margin types were mixed, but there was a marked tendency by many nectar and/or pollen-feeding, flying insects towards greater abundance on those margins containing sown ‘wildflowers’ (e.g. butterflies Meadow Brown and Ringlet, Bumblebees, Pollen Beetle Meligethes sp.) or flowers either sown or unsown (Soldier Beetle Rhagonycha fulva). There was a less strong tendency for predatory species occurring in the vegetation canopy and depending on small, especially flying insects for food, to also prefer the flowery treatments (e.g. total spiders caught by sweeping, seven-spot ladybird). Harvestmen in autumn reject natural regeneration in favour of any sown treatment. Only one species, the carabid Nebria brevicollis, was trapped in higher numbers in the cropped treatment than on any sown margin, and then only in autumn. Of the six common bumblebee species, the two longest-tongued species showed different patterns of flower visitation from the remaining four.These results clearly demonstrate that sown field margins can rapidly produce substantial biodiversity benefits on arable land, with the resulting fauna influenced by the type of field margin created.  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