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   395篇
  免费   45篇
林业   65篇
农学   18篇
基础科学   12篇
  114篇
综合类   13篇
农作物   19篇
水产渔业   52篇
畜牧兽医   97篇
园艺   9篇
植物保护   41篇
  2023年   3篇
  2022年   5篇
  2021年   12篇
  2020年   12篇
  2019年   21篇
  2018年   34篇
  2017年   23篇
  2016年   40篇
  2015年   18篇
  2014年   27篇
  2013年   42篇
  2012年   24篇
  2011年   23篇
  2010年   17篇
  2009年   15篇
  2008年   14篇
  2007年   8篇
  2006年   11篇
  2005年   13篇
  2004年   4篇
  2003年   6篇
  2002年   4篇
  2001年   1篇
  2000年   8篇
  1999年   7篇
  1998年   1篇
  1997年   2篇
  1995年   2篇
  1994年   1篇
  1992年   1篇
  1991年   2篇
  1990年   5篇
  1989年   2篇
  1988年   1篇
  1985年   3篇
  1983年   4篇
  1982年   2篇
  1980年   2篇
  1979年   2篇
  1978年   1篇
  1977年   3篇
  1976年   3篇
  1973年   1篇
  1972年   3篇
  1970年   2篇
  1969年   3篇
  1962年   1篇
  1961年   1篇
排序方式: 共有440条查询结果,搜索用时 500 毫秒
91.
Background: In order to discover new strategies to replace antibiotics in the post-antibiotic era in meat-type chicken production, two new synbiotics were tested:(Lactobacillus salivarius IBB3154 plus galactooligosaccharide(Syn1) and Lactobacillus plantarum IBB3036 plus raffinose family oligosaccharides(Syn2).Methods: The synbiotics were administered via syringe, using a special automatic system, into the egg air chamber of Cobb 500 broiler chicks on the 12 thday of egg incubation(2 mg of prebiotics + 105 cfu bacteria per egg).Hatched roosters(total 2,400) were reared on an experimental farm, kept in pens(75 animals per pen), with free access to feed and water. After 42 d animals were slaughtered. Blood serum, pancreas, duodenum and duodenum content were collected.Results: Syn2 increased trypsin activity by 2.5-fold in the pancreas and 1.5-fold in the duodenal content. In the duodenum content, Syn2 resulted in ca 30% elevation in lipase activity and 70% reduction in amylase activity.Syn1 and Syn2 strongly decreased expression of m RNA for GLP-1 and GIP in the duodenum and for GLP-1 receptors in the pancreas. Simultaneously, concentrations of the incretins significantly diminished in the blood serum(P 0.05). The decreased expression of incretins coincides with changed activity of digestive enzymes in the pancreas and in the duodenal content. The results indicate that incretins are involved in the action of Syn1 and Syn2 or that they may even be their target. No changes were observed in key hormones regulating metabolism(insulin, glucagon, corticosterone, thyroid hormones, and leptin) or in metabolic indices(glucose,NEFA, triglycerides, cholesterol). Additionally, synbiotics did not cause significant changes in the activities of alanine and aspartate aminotransferases in broiler chickens. Simultaneously, the activity of alkaline phosphatase and gamma glutamyl transferase diminished after Syn2 and Syn1, respectively.Conclusion: The selected synbiotics may be used as in ovo additives for broiler chickens, and Syn2 seems to improve their potential digestive proteolytic and lipolytic ability. Our results suggest that synbiotics can be directly or indirectly involved in incretin secretion and reception.  相似文献   
92.
Background: Interleukin-1β(IL-1β) is important mediator of inflammatory-induced suppression of reproductive axis at the hypothalamic level. At the beginning of inflammation, the main source of cytokines in the cerebrospinal fluid(CSF) is peripheral circulation, while over time, cytokines produced in the brain are more important. Melatonin has been shown to decrease pro-inflammatory cytokines concentration in the brain. In ewes, melatonin is used to advance the onset of a breading season. Little is known about CSF concentration of IL-1β in ewes and its correlation with plasma during inflammation as well as melatonin action on the concentration of IL-1β in blood plasma and the CSF, and brain barriers permeability in early stage of lipopolysaccharide(LPS)-induced inflammation.Methods: Systemic inflammation was induced through LPS administration in melatonin-and sham-implanted ewes. Blood and CSF samples were collected before and after LPS administration and IL-1β and albumin concentration were measured. To assess the functions of brain barriers albumin quotient(QAlb) was used.Expression of IL-1β(Il1B) and its receptor type Ⅰ(Il1r1) and type Ⅱ(Il1r2) and matrix metalloproteinase(Mmp) 3 and 9 was evaluated in the choroid plexus(CP).Results: Before LPS administration, IL-1β was on the level of 62.0 ± 29.7 pg/mL and 66.4 ± 32.1 pg/mL in plasma and 26.2 ± 5.4 pg/mL and 21.3 ± 8.7 pg/mL in the CSF in sham-and melatonin-implanted group, respectively.Following LPS it increased to 159.3 ± 53.1 pg/mL and 197.8 ± 42.8 pg/mL in plasma and 129.8 ± 54.2 pg/mL and139.6 ± 51.5 pg/mL in the CSF. No correlations was found between plasma and CSF IL-1β concentration after LPS in both groups. The QAlb calculated before LPS and 6 h after was similar in all groups. Melatonin did not affected m RNA expression of Il1B, Il1r1 and Il1r2 in the CP. The m RNA expression of Mmp3 and Mmp9 was not detected.Conclusions: The lack of correlation between plasma and CSF IL-1β concentration indicates that at the beginning of inflammation the local synthesis of IL-1β in the CP is an important source of IL-1β in the CSF. Melatonin from slow-release implants does not affect IL-1β concentration in plasma and CSF in early stage of systemic inflammation.  相似文献   
93.
94.
Flavescence dorée phytoplasma (FDp) is a quarantine pathogen associated with a severe and epidemic grapevine yellows disease representing a great threat for grapevine cultivation in Europe. An increase in disease spread prompted efforts to identify FDp strains in Croatia. Over 800 samples of grapevine together with presumed reservoir plants and almost 400 samples of Scaphoideus titanus and other potential vectors were collected countrywide and analysed. FDp isolates were characterized by multilocus sequence typing (MLST) of map, secY and uvrB-degV genes in order to determine genetic diversity and structure of FDp populations, and to trace transmission pathways. FD-related phytoplasmas were found in Croatia for the first time in alder, the invasive tree species Ailanthus altissima and leafhopper Phlogotettix cyclops. Phylogenetic analysis revealed the presence of three mapFD strain clusters: mapFD1, mapFD2 and mapFD3, and for the first time in Croatia a case of Palatinate grapevine yellows strain A (PGY-A). In total, 7 different map, 10 secY and 11 uvrB-degV genotypes were detected. The identification of 15 comprehensive FDp genotypes based on MLST suggests separate routes for disease introduction and propagation origins in Croatia. Moreover, high genetic variability of Croatian isolates indicates a complex ecological cycle of FDp involving various hosts.  相似文献   
95.
Selected engineering properties of seeds of four red clover varieties were studied. The seeds of diploid and tetraploid forms were statistically different in terms of true and bulk density, porosity, volume, 1000 seed weight, equivalent diameter and yellowness index. The volume, 1000 seed weight and equivalent diameter were found to be statistically higher for tetraploid than for diploid forms. The accuracy of varietal classification based on the physical properties of seeds was found to be most satisfactory. Varieties of Bona and Jubilatka were identified with 100% accuracy based on the physical properties of seeds. Bona was the most conducive variety for the classification of red clover seeds based on four groups of engineering properties. The relationships between groups of properties described by total redundancy did not exceed 50% for any of variable pairs.  相似文献   
96.
97.
Bugs parasiting on boats burdensome in panel houses The troublesome occurrence ofCimex dissimilis (Horvath 1910) in tow new housing estates built of panel houses is recorded. The bugs parasiting on bats (Nyctalus noctula (Schreber)) seating in gaps on the southern and southwestern sides of the house crawled in the rooms bit men, soiled the bed linen, and were troublesome by their number.  相似文献   
98.
Zusammenfassung Das Material der Arbeit bilden die Beobachtungsergebnisse von fünf Dauerversuchsreihen (DVR), die in 30–40j?hrigen ungepflegten Buchen-Reinbest?nden in der Slowakei (CSSR) angelegt wurden. Die Arbeit umfa?t eine waldbauliche Analyse der ersten zwei in Form einer freien Hochdurchforstung erfolgten Eingriffe. Das Durchforstungsintervall betrug 4 Jahre. Die freie Hochdurchforstung, die an den DVR der Forschungsanstalt für Forstwirtschaft in Zvolen angewandt wurde, soll folgende Arten der Phytotechnik miteinander verbinden: die positive Oberstandauslese, die positive Unterstandauslese, die negative, die Sanit?r- und die relative Reifeauslese. Hauptgegenstand der waldbaulichen Pflege stellen die sog. Erwartungs- bzw. Zielb?ume dar. Für die Auswahl wurden in der Arbeit Qualit?ts-, Dimensions- und Abstandskriterien herangezogen. In den ursprünglich ungepflegten Buchenstangenh?lzern überwog, was das Volumen betrifft, in den gesunden Best?nden bei beiden Eingriffen die positive Oberstandauslese. Durch sie werden die Erwartungsb?ume gef?rdert. Sie kommt in den gesunden Best?nden an erster Stelle zur Geltung. In den stark erkrankten Best?nden tritt bei der Auszeichnung der Durchforstung dagegen die sanit?re Auslese in den Vordergrund. Erst dann folgt die positive Oberstandauslese. In ungepflegten Stangenh?lzern bietet bei der Hochdurchforstung die versp?tete S?uberung keine Vorteile gegenüber der positiven Oberstandauslese.
Summary The author discusses the results of thinning experiments in pure beech stands in the CSSR. This article deals with an evaluation of experimental results in 5 series of permanent sample plots, which were established in 30 to 40 year-old stands. The thinning interval in these experiments was invariably 4 years. The method being a free selection thinning involved the following operations: a positive selection thinning in the upper storey, a positive selection thinning in the understorey, a negative sanitary thinning and the relative maturity selection. The most important objective in thinnings is to promote the growth of those trees which are selected to be retained until the end of the rotation. In untended beech stands priority was given to positive selection in the upper storey, whereas sanitary selection played an important part in diseased stands. This sanitary selection thinning is subsequently followed by a positive selection thinning in the upper storey.
  相似文献   
99.
In order to increase the effect of the biopreparation Thuricide HP, we mixed it with pyrethroid Ambusch, a substance highly effective against insects possessing satisfactory parameters as regards toxic residua. Using aerial application, we tested Thuricide HP as a 0.5% suspension in a dose of 1 kg in 200 l water per one ha, the same dose of the preparation combined with a sublethal dose of Ambusch (8 ml/ha, i. e., 2 g of effective substance), and Ambusch in a dose of 120 ml/ha, i. e., 30 g of effective substance/1 ha. The mortality of larvae ofO. brumata andT. viridana attained 61% after the application of Thuricide HP, 83% after Thuricide HP combined with Ambusch, 96% after treatment with Ambusch. As indicated by our results, the biopreparation killed only larvae of Lepidoptera, while pyrethroid effected the entire spectrum of insect species colonizing the crowns of the treated stand. A combination of the biopreparation with a sublethal dose of pyrethroid was sufficiently effective against the pest, with a decreased effect on the remaining insect species.  相似文献   
100.
Abstract

Two wood plastic composite (WPC) boards, one experimental and one commercial, were exposed to exterior conditions and evaluated non-destructively using a clinical magnetic resonance imaging (MRI) unit for moisture content (MC) and distribution. The experimental board was exposed in Vancouver, British Columbia, for more than 8 years, and the commercial board was exposed near Hilo, Hawaii, for 2 years. Both boards were characterized in terms of wood content, density, water uptake properties and voids content. The experimental board was additionally destructively analysed for water absorption of the WPC and MC calculated based on the wood content for verification of MRI results. MRI detected the presence of free water and its distribution in both of the WPC boards. Fibre saturation in the experimental board was found to be about 22–24%, in comparison to 25–30% present in most wood species. There was good correlation between the detection of free water by MRI and by destructive testing. Magnetic resonance images showed various major points of water entry in the WPC boards such as the support area, the cut ends, the dripping edge and the sides of the boards. For the experimental board, significant water entry also occurred at the upper exposed surface.  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