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   263篇
  免费   17篇
  国内免费   2篇
林业   23篇
农学   13篇
基础科学   2篇
  84篇
综合类   26篇
农作物   22篇
水产渔业   30篇
畜牧兽医   56篇
园艺   9篇
植物保护   17篇
  2023年   6篇
  2022年   11篇
  2021年   10篇
  2020年   7篇
  2019年   16篇
  2018年   24篇
  2017年   14篇
  2016年   8篇
  2015年   8篇
  2014年   8篇
  2013年   21篇
  2012年   15篇
  2011年   16篇
  2010年   16篇
  2009年   7篇
  2008年   10篇
  2007年   4篇
  2006年   6篇
  2005年   9篇
  2004年   7篇
  2003年   3篇
  2002年   5篇
  1997年   2篇
  1996年   2篇
  1995年   2篇
  1994年   2篇
  1993年   1篇
  1992年   2篇
  1990年   2篇
  1989年   2篇
  1988年   3篇
  1987年   1篇
  1986年   3篇
  1985年   2篇
  1984年   1篇
  1983年   3篇
  1982年   3篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1974年   1篇
  1972年   2篇
  1971年   2篇
  1970年   1篇
  1967年   1篇
  1966年   1篇
  1945年   1篇
排序方式: 共有282条查询结果,搜索用时 15 毫秒
71.
Abstract

Soil acidity is one of the main factors that limit profitable and sustained agricultural production. Oil palm (Elaeis guineensis Jacq.) is mainly planted in acidic soils. In the last years, there has been a stagnated yield and increases in disease incidence and severity worldwide that could be attributed in some extent to soil acidity. This study was conducted to determine the effects of soil acidity alleviation on oil palm seedlings. The effects of ground magnesium limestone or dolomite and magnesium carbonate (0, 1.1, 2.2, 3.3 and 4.4 t ha?1) applied to an Ultisol dominated by kaolinite (pH in water 4.4) were evaluated on selected morphological, physiological and nutritional characteristics of hybrid (Deli dura × AVROS pisifera) and clonal (clone 366) oil palm progenies under nursery conditions for 8 months. Increasing rates of ground magnesium limestone and magnesium carbonate showed a significant effect on improving soil pH and lowering exchangeable aluminium. The hybrid oil palm showed significant either linear or quadratic trends for most of the parameters evaluated, indicating that the best responses for morphological and physiological traits were achieved from 2.5 to 4.23 t ha?1 with ground magnesium limestone and 2.87 to 3.45 t ha?1 with magnesium carbonate. Positive effects of increasing rates of ground magnesium limestone and magnesium carbonate were observed on nitrogen and magnesium uptake. Aluminium concentration in the third frond decreased significantly with increasing ground magnesium limestone rate. A significant reduction of manganese uptake was also observed with increasing rates of both ameliorants. The clonal oil palm progeny exhibited a better performance on un-amended treatment. This may be explained by the significant higher root growth of this progeny. Soil acidity alleviation improved the oil palm seedling growth. These results are important for the oil palm industry and could be applied in the nursery stage as well as extended to the immature stage.  相似文献   
72.
The accrual of cancer mutation data and related functional and clinical associations have revolutionised human oncology, enabling the advancement of precision medicine and biomarker-guided clinical management. The catalogue of cancer mutations is also growing in canine cancers. However, without direct high-powered functional data in dogs, it remains challenging to interpret and utilise them in research and clinical settings. It is well-recognised that canine and human cancers share genetic, molecular and phenotypic similarities. Therefore, leveraging the massive wealth of human mutation data may help advance canine oncology. Here, we present a structured analysis of sequence conservation and conversion of human mutations to the canine genome through a ‘caninisation’ process. We applied this analysis to COSMIC, the Catalogue of Somatic Mutations in Cancer, the most prominent human cancer mutation database. For the project's initial phase, we focused on the subset of the COSMIC data corresponding to Cancer Gene Census (CGC) genes. A total of 670 canine orthologs were found for 721 CGC genes. In these genes, 365 K unique mutations across 160 tumour types were converted successfully to canine coordinates. We identified shared putative cancer-driving mutations, including pathogenic and hotspot mutations and mutations bearing similar biomarker associations with diagnostic, prognostic and therapeutic utility. Thus, this structured caninisation of human cancer mutations facilitates the interpretation and annotation of canine mutations and helps bridge the knowledge gap to enable canine precision medicine.  相似文献   
73.
During a staying at Berlin (West) in 1977/80 studies were conducted on the host-searching, oviposition and host-specificity ofEudorylas subterminalis, a parasitic fly species of Pipunculidae. The visual orientation of the female fly plays undoubtedly a dominant role in searching the host. The female fly usually selects for oviposition only second, third and fourth instar nymphs of the cicadellid hosts. The first instar nymph is rarely attacked, while fifth instar is not accepted at all. The female oviposits within the haemocoel between fourth and fifth tergital region of the host. The fly is unspecific and attacks species of leafhoppers belonging to the family Cicadellidae. The records of Pipunculidae and their hosts in Berlin (West) have also been stated.  相似文献   
74.
A heat expansion process similar to that used for expanded bead polystyrene was used to expand starch-based compositions. Foam beads made by solvent extraction had the appearance of polystyrene beads but did not expand when heated due to an open-cell structure. Nonporous beads, pellets, or particles were made by extrusion or by drying and milling cooked starch slurries. The samples expanded into a low-density foam by heating 190-210 degrees C for more than 20 s at ambient pressures. Formulations containing starch (50-85%), sorbitol (5-15%), glycerol (4-12%), ethylene vinyl alcohol (EVAL, 5-15%), and water (10-20%) were studied. The bulk density was negatively correlated to sorbitol, glycerol, and water content. Increasing the EVAL content increased the bulk density, especially at concentrations higher than 15%. Poly(vinyl alcohol) (PVAL) increased the bulk density more than EVAL. The bulk density was lowest in samples made of wheat and potato starch as compared to corn starch. The expansion temperature for the starch pellets decreased more than 20 degrees C as the moisture content was increased from 10 to 25%. The addition of EVAL in the formulations decreased the equilibrium moisture content of the foam and reduced the water absorption during a 1 h soaking period.  相似文献   
75.
During the past decade, Fascioloides magna, the large American liver fluke, has spread within free-living deer in wetlands of the Danube in Lower Austria. The aim of this study was to determine the current infection rates with F. magna and other digenean parasites in the intermediate host snail Galba truncatula from risk areas in Lower Austria. A total of 3444 G. truncatula were collected and examined microscopically for the presence of digenean trematodes. A set of randomly selected snails and isolated trematode stages were also investigated molecular biologically by PCR and sequencing. Digenean parasites were detected with a prevalence of 2.41% (1.83% Paramphistomoidea; 0.46% Echinostomatoidea; 0.09% Strigeida; 0.06% Plagiorchiida). F. magna was found with an overall prevalence of 0.23%, which may indicate a recovery of the parasite population in spite of an ongoing triclabendazole treatment programme. Moreover, high risk areas and a seasonality of infections were observed.  相似文献   
76.
The ethylacetate and n-butanol fractions of ethanolic extract of Platanus orientalis leaves led to the isolation of new acylated flavonol glycoside as 3',5,7-trihydroxy-4'-methoxyflavonol 3-[O-2-O-(2,4-Dihydroxy)-E-cinnamoyl-α-L-rhamnopyranosyl-(1→6)-β-D-glucopyranosyl (1→2)]-β-D-glucopyranoside, along with seven known compounds. All the compounds were characterized by NMR including 2D NMR techniques. The isolates were evaluated for NF-κB, nitric oxide (NO), aromatase and QR2 chemoprevention activities and some of them appeared to be modestly active.  相似文献   
77.
We investigated the composition of plant communities to quantify their relationships with environmental parameters in the Chitral Hindukush range of Pakistan. We sampled tree vegetation using the Point Centered Quarter (PCQ) method while understory vegetation was sampled in 1.5-m circular quadrats. Cedrus deodara is the national symbol of Pakistan and was dominant in the sampled communities. Because environmental variables determine vegetation types, we analyzed and evaluated edaphic and topographic factors. DCA-Ordination showed the major gradient as an amalgam of elevation (p<0.05) and slope (p<0.01) as the topographic factors correlated with species distribution. Soil variables were the factors of environmental significance along DCA axes. However, among these factors, Mg2+ , K + and N2+ contributed not more than 0.054% 0.20% and 0.073%, respectively, to variation along the first ordination axis. We conclude that the principal reason for weak or no correlation with many edaphic variables was the anthropogenic disturbance of vegetation. The understory vegetation was composed of perennial herbs in most communities and was most dense under the tree canopy. The understory vegetation strongly regulates tree seedling growth and regeneration patterns. We recommend further study of the understory vegetation using permanent plots to aid development of forest regeneration strategies.  相似文献   
78.
Species that belong to the genus Triticum L. and the genetically related Aegilops L. genus are important genetic and economic resources because they have an evolutionary relationship with the two main agricultural crops T. aestivum (bread wheat) and T. durum (durum wheat). Therefore, it is important to understand the genetic relationships among the cultivated wheat species and their wild relatives. The latter have a great role in the improvement of cultivated wheat. Molecular markers are the best choice and most reliable means to study these relationships accurately. In this study, we compared the efficiency of the biochemical methods A–PAGE and SDS–PAGE on seed storage proteins and the molecular methods RAPDs and ISSRs to explore the genetic relationships among seven species of Triticum and 20 Aegilops species. Three phylogenetic trees obtained in this study were compared with available classifications and phylogenetic trees constructed earlier for these species. It was noted that the tree based on ISSRs data was the most congruent with those classification and trees. This may be attributed to the fact that ISSRs is more specific, and therefore more reliable. This study is the first to study genetic relationships among all species studied here using biochemical and molecular techniques.  相似文献   
79.
Present study was designed to investigate the prevalence and mortality (%) caused by Peste des Petitis Ruminant (PPR) and its possible association with abortion in goat flocks at different areas of Pakistan. A total of 140 animals were samples in the population of 650 which was having 185 deaths (Mortality rate = 28 %) from three different regions of the country. There were 58 abortions in the 140 pregnant goats of above said population One hundred & ten (110) serum samples from diseased, recovered and apparently healthy animals were tested for the presence of PPR antibodies by competitive ELISA (c ELISA). Eighty-four (84) animals were positive for PPR antibodies whereas in apparently healthy adult goats in the same flock, no PPR antibodies were detected. Twenty-four (24) tissue samples collected from the dead animals and six samples from aborted fetus were tested for the presence of PPR antigen by Immuno-capture ELISA (Ic ELISA). Nineteen (19) out of thirty (30) organ samples mainly from lung, spleen, lymph node were found positive for PPR antigen but negative from lungs of aborted fetus. There was a high rate of abortions (28–45 %) in each of the outbreak and it was highest in the outbreak of Golra Sharif, Islamabad (No. = 21 in total population of 100). As the serum samples from the aborted dams were found positive for PPR antibodies so the study provides the possible association of mortality and prevalence of PPR disease with high rate of abortions in goat.  相似文献   
80.
Sweet and sour are the most important taste of blueberries, and they are produced by sugar and acid, respectively. Their contributions to the taste depend not only on the levels of sugar and acid, but also on the types and relative proportions of sugar and acid. Therefore, it is very important to evaluate the composition and levels of sugar and acid in blueberries. Regional differences and variety diversity also affect the sugar and acid characteristics of fruits. Therefore, this study selected two main producing regions in northern China(Weihai and Yingkou) to examine the sugar and acid characteristics of 11 common blueberry cultivars. The indexes measured included soluble sugars, organic acids, soluble solid content and titratable acidity. The results showed that glucose and fructose were the major sugars, and citric acid and quinic acid were the major organic acids. Correlation analysis showed that glucose, fructose, and sucrose were positively correlated with total sugar content; the citric acid content was positively correlated with the titratable acidity and total organic acids. Titratable acidity, glucose, fructose, sucrose, total sugar content, citric acid, shikimic acid and total acid content of the blueberries varied significantly between regions(P0.05). In general, compared with Weihai blueberries, Yingkou blueberries had higher sugar content and lower acid content. The results of this study may provide useful references for the evaluation of sweet and sour flavors and cultivar selection of blueberries.  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