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   166篇
  免费   5篇
林业   27篇
农学   4篇
  52篇
综合类   9篇
农作物   4篇
水产渔业   4篇
畜牧兽医   48篇
园艺   16篇
植物保护   7篇
  2023年   1篇
  2022年   2篇
  2021年   2篇
  2019年   5篇
  2018年   13篇
  2017年   10篇
  2016年   6篇
  2015年   2篇
  2014年   5篇
  2013年   16篇
  2012年   10篇
  2011年   13篇
  2010年   4篇
  2009年   4篇
  2008年   8篇
  2007年   6篇
  2006年   9篇
  2005年   5篇
  2004年   5篇
  2003年   8篇
  2002年   2篇
  2001年   1篇
  2000年   1篇
  1999年   3篇
  1998年   1篇
  1996年   1篇
  1995年   1篇
  1994年   1篇
  1993年   2篇
  1992年   2篇
  1989年   1篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1983年   2篇
  1980年   1篇
  1973年   2篇
  1972年   2篇
  1970年   1篇
  1969年   1篇
  1968年   1篇
  1967年   1篇
  1963年   1篇
  1918年   1篇
  1917年   3篇
  1916年   2篇
排序方式: 共有171条查询结果,搜索用时 227 毫秒
91.
92.
The effect of application of omega-3 polyunsaturated fatty acids (omega-3 PUFA) on intestinal colonization by Lactobacillus paracasei and on cellular immunity has been investigated in gnotobiotic pigs. The administration of polyunsaturated fatty acids positively affected the adhesion of Lactobacillus paracasei to the jejunal mucosa of gnotobiotic piglets. When compared to the control group, the number of Lactobacillus paracasei adhering to the jejunal mucosa was by 12% higher in piglets of the experimental group (5.10 log 10/cm2 vs. 4.55 log 10/cm2). The respective counts of Lactobacillus paracasei adhering to the ileal and colonic mucosa of 28 day old gnotobiotic piglets reached 4.45 and 5.05 log 10/cm2 in group C and 4.44 and 4.95 log 10/cm2 in group E. Omega-3 PUFA supplementation increased the phagocytic activity of neutrophils by almost 100% on day 28 of life as well as the subpopulations of lymphocytes (CD8) in the peripheral blood of germ-free piglets on day 21 of life. Our results indicate that the action of probiotics in the gut may be modulated by dietary PUFA. The stimulatory effect of PUFA upon adhesion of lactobacilli could be used for enhancing the effectiveness of probiotics in inhibiting digestive tract pathogens.  相似文献   
93.
Localization of the sheep FcRn in the mammary gland   总被引:5,自引:0,他引:5  
Among the multiple functions, which have been identified for the neonatal Fc receptor (FcRn), we study its role in the IgG transport in the mammary gland during the colostrum formation. For this reason, we have obtained several mammary gland biopsies from a pregnant sheep around parturition. The presence of the FcRn heavy chain mRNA was detected exclusively in the acinar and ductal epithelial cell by in situ hybridization (ISH). We detected strong signal in samples harvested 24 and 10 days prepartum; however, in samples we collected postpartum was barely detectable. Immunohistochemistry confirmed our ISH data. The cytoplasm of the epithelial cells of the acini and ducts in the mammary gland biopsies stained homogeneously before parturition, although a remarkable difference was observed in the pattern after lambing. The signal indicated uneven distribution of the FcRn alpha chain in the epithelial cells 1 and 5 days postpartum, since the apical sides of the epithelial cells were highlighted. The presence of the FcRn in the acinar and ductal epithelial cells and the obvious change of its distribution before and after parturition suggest that FcRn plays an important role in the IgG transport during colostrum formation. FcRn expression was also found in the lamb duodenal crypt epithelial cells, which have been previously demonstrated to secrete IgG1 in newborn ruminants, suggesting secretory role of the FcRn in ruminant epithelial cells.  相似文献   
94.
Biological invasions of insects, plants, and fungal pest species often cause substantial disturbance to forest ecosystems and as well as severe socioeconomic impacts. Central Europe acts as a ‘bridge’ between Western and Eastern Europe both ecologically and as an important transit corridor for people. Human activity, including the movement of material goods, increases the risk of invasions. Some species introduced in the past have been established, becoming common and causing serious problems (such as Dreyfusia nordmannianae or Hyphantria cunea). The status, importance and spatial distribution in Slovakia of seven different forest pests recently introduced into Slovak forest ecosystems (Cameraria ohridella, Coleotechnites piceaella, Cryphonectria parasitica, Dothistroma septospora, Ips duplicatus, Parectopa robiniella, Phyllonorycter robiniellus) as well as two others not yet recorded in Slovakia (Anoplophora glabripennis, Phytophthora spp.) is discussed.  相似文献   
95.
Saponins from Chenopodium album   总被引:3,自引:0,他引:3  
Lavaud C  Voutquenne L  Bal P  Pouny I 《Fitoterapia》2000,71(3):338-340
The isolation and spectral data of three saponins from the roots of Chenopodium album L. are reported. One of them is a seco-glycoside analogous to compounds that were previously found in species belonging to Caryophyllales.  相似文献   
96.
We studied the effects of two types of selective thinning on beech stands formed by a shelterwood cut in 1910 — with lower number of crop trees and higher thinning intensity (T1) and higher number of crop trees with lower thinning intensity (T2). The stands were thinned in 1980, 1991 and 2001. Despite a lower stand density after thinning, the annual basal area increments of thinned stands in both thinning periods (1980–1991 and 1991–2002) were around 20% higher compared to those of the control (unthinned) stands. The mean annual basal area increment of dominant trees was 30–56% larger in the thinned plots compared to the control plots. Of 176 initial crop trees in the T1, 72% were chosen again during the last thinning. In the T2, 258 crop trees were chosen in the first thinning, and only 62% of these trees were chosen again during the last thinning. Only crown suppression and diameter classes of crop trees significantly influenced their basal area increment when diameter classes, crown size, crown suppression, and social status were tested. In the thinned stands, the dominant trees are more uniformly distributed if compared to the dominant trees in the control plots. Finally, the herbaceous cover and the species diversity were higher in the thinned plots.  相似文献   
97.
Antioxidant properties of marjoram (Origanum majorana L.) herb and extracts obtained with ethanol, n-hexane, and supercritical CO2 extraction are presented. Individual antioxidants, ursolic acid, carnosic acid, and carnosol, were quantified with high-performance liquid chromatography. The effects of different parameters (temperature and pressure) of high-pressure extraction on the yield of carnosol were studied. Furthermore, two marjoram herbs from Hungary and Egypt were compared measuring hydrogen-donating abilities with 1,1-diphenyl-2-picrylhydrazyl by spectrophotometric and the total scavenger capacities by chemiluminometric methods from the aqueous extracts of the herbs. The antioxidant activities of the solvent extracts were performed using the Rancimat method. The Egyptian herb and its extracts possessed better antioxidant activities than Hungarian ones. Applying supercritical CO2 extraction, the highest value of carnosol was obtained at 400 bar and 60 degrees C.  相似文献   
98.
The thick loess–paleosol-sequences in Tadzhikistan, which indirectly record the environmental changes from the Upper Pliocene to the present-day, have been extensively described from a chronostratigraphical and archaeological point of view. The genesis of the soil-sedimentary complexes and their implications for palaeoenvironmental reconstruction in Tadzhikistan, however, have been considered only relatively recently [Bronger, A., Winter, R., Derevjanko, O., Aldag, S., 1993. Loess–paleosol sequences in Tadjikistan as a palaeoclimatic record of the Quaternary in Central Asia. Quaternary Proceedings 4, 69–81; Lomov, S.P., Tursina, T.V., Zhou, L.P., 1996. Magnetic susceptibility of soils: Micromorphology and possible reconstructions of climate. In: Soil micromorphology. Studies in Soil Diversity, Diagnostics, Dynamics, 10th International Working Meeting on Soil Micromorphology. Moscow, Russia, July 8–13, 1996, p. 145]. The pedocomplex of Last Interglacial and Early Glacial age (Oxygen Isotope Stage 5) in the Tagidjar and Darai Kalon sections near the town of Khovaling is represented by three major stages of soil formation. The soil characteristics have been micromorphologically analysed. The distinction between primary and secondary carbonates is of major importance to understand the soil forming processes. The relative distribution of needle fibre calcite (NFC), micritic infillings (M), hypocoatings (CHC), coarse calcitic grains (CCG) and calcified root cells (CRC) provides detailed insights into the environmental conditions prior, during and following pedogenesis. The abundance of coprolitic aggregates (CA) and pupal chambers gives a clear indication of the rate of biological activity which prevailed during the last two soil forming stages. Void pseudomorphs after gypsum crystals (gypsum pseudomorphs) are frequently observed beneath the Cca horizons of the paleosols. Using the present-day climate and soilscape as a reference base, the obtained pedosedimentary events detected in the Tadzhikistan sections provide a detailed palaeoenvironmental record. Indeed, glacial and interglacial climates and soils respond to contemporaneous climatic schemes and soil forming processes, which are still active in the region today. The amount and the seasonal variability of precipitation, mostly, are at the origin of the variable soils formed during glacial and interglacial ages.  相似文献   
99.
Oedaleus senegalensis is a serious pest of millet in the Sahel, but the correlation to crop loss remains largely unknown. Therefore, the correlation between densities of O. senegalensis, defoliation level and millet yields was investigated in Niger in 2008, and a simple model to foresee the yield based on these parameters was developed. The yield was significantly correlated to both the density of O. senegalensis and the defoliation level on 17 September. The best model to foresee millet yield involved grasshopper density and cumulated rainfall and may be regarded a tentative method in O. senegalensis control.  相似文献   
100.
Precise field experiments were established on two sites with winter wheat under different soil-climatic conditions in the Czech Republic. Four treatments were fertilized with same dose of nitrogen (200 kg N ha?1) and increasing dose of sulphur (0, 10, 20 and 40 kg S ha?1) using nitrogen–sulphur (N–S) fertilizer with calcium sulphate form. Soil and plant aboveground biomass samples were taken in the stages of development BBCH 26–28; 30–32; 37–39; 49–51. The winter wheat grain yield ranged between 7.20 and 10.86 t ha?1 and had an increasing trend with increasing sulphur dose. Although the differences were usually not statistically significant, there were found increasing tendencies of bioavailable sulphur content in soil with increasing S split doses. Soil S content decreased with time probably due to plant uptake. Sulphur dose did not influence the S content in plant aboveground biomass. The total S contents in grain after harvest ranged between 0.09% and 0.14% and were not significantly influenced with the fertilizing treatment. The same statement is valid for the S content in straw, which ranged between 0.03% and 0.11%. Both, S content in winter wheat seeds and straw were strongly influenced by the site conditions.  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