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   142篇
  免费   0篇
林业   14篇
农学   2篇
基础科学   1篇
  61篇
综合类   10篇
农作物   2篇
水产渔业   3篇
畜牧兽医   37篇
园艺   5篇
植物保护   7篇
  2021年   2篇
  2016年   1篇
  2015年   1篇
  2014年   3篇
  2013年   7篇
  2012年   5篇
  2011年   4篇
  2010年   2篇
  2009年   4篇
  2008年   3篇
  2007年   6篇
  2006年   5篇
  2005年   6篇
  2004年   7篇
  2003年   1篇
  2002年   8篇
  2001年   8篇
  2000年   9篇
  1999年   7篇
  1998年   3篇
  1997年   10篇
  1995年   6篇
  1994年   1篇
  1992年   1篇
  1991年   3篇
  1989年   2篇
  1988年   1篇
  1986年   1篇
  1983年   1篇
  1981年   1篇
  1980年   2篇
  1979年   2篇
  1978年   2篇
  1976年   3篇
  1975年   1篇
  1974年   8篇
  1973年   4篇
  1966年   1篇
排序方式: 共有142条查询结果,搜索用时 15 毫秒
71.
72.
Abstract

Six plant protection products (esfenvalerate, diflufenican, isoproturon, terbutylazine, chlorsulphuron, and metsulphuron-methyl) were added to pig and bovine liquid manure, and the degradation of the compounds was followed over a period of 57 &lparlsulphonylureas)(sulphonylureas) or 77 (other compounds) weeks. After 57 weeks more than 50% of the sulphonylureas remained in the bovine liquid manure, while 25% remained in the pig liquid manure. After 77 weeks >90% terbutylazine, 50–60% enfenvalerate, and 10–40% diflufenican and isoproturon had been degraded in both bovine and pig liquid manure. With exception of terbutylazine, the examined plant protection products were neither quickly nor extensively degraded. The practice to add unused spraying liquid or rinse-water containing plant protection products to liquid manure constitutes a risk that unwanted compunds are inadvertently added to the fields when the liquid manure is used as fertilizer, and this may cause crop damage.  相似文献   
73.
Forestry in Sweden as well as in other European countries is characterised by intense and increasing international competition resulting in decreasing roundwood prices in real terms. This is especially the situation in the mountainous region of Sweden with long transportation distances between the felling site and the processing industries located at the coast. The question arises whether forestry must be run more extensively than at present to achieve the optimal rate of silvicultural activities compared with the amount of timber cut. With this in mind, optimising economic analyses have been performed at the stand level as well as at the level of forest estates. Results of the analyses reveal that more intensive thinning (more frequent operations) and shorter rotation periods would increase profit and offset continuously decreasing roundwood prices. Intensive pre-commercial thinning (cleaning) is especially important for profitability of the subsequent thinnings and the final cut. The large number of cuts during the rotation will increase logging costs. However, this will be more than offset by the increasing production of economically matured dimensions of timber, an effect that will be still more pronounced when using new harvesting technology. Moreover, frequent high thinning operations (thinning ‘from above’ or removal of dominant trees) will result in more dense wood close to the pith, more evenly distributed year rings, and fewer and smaller knots in the lower part of the stem — in other words more valuable roundwood which will justify high transportation costs. Several biological and technical aspects of these treatment programs are discussed in the paper.  相似文献   
74.

Background

There is a growing interest in beef cattle breeding in Sweden. The majority of the females are bred naturally, which is why it is important to choose healthy fertile bulls to obtain good reproduction and profitability. The breeding soundness evaluation includes measurement of scrotal circumference (SC). Our aim was to analyze if the SC of performance tested beef bulls has changed over the years. In total, 1332 bulls (Angus, Charolais, Hereford and Simmental) from 13 batches (1997-2010) were included in the study. Case book entries from final evaluation of the bulls, 11-13 months old, were compiled and analyzed.

Results

An overall mean SC of 34.7 cm independent of breed and age was found which is above the set minimum level. Only eleven bulls did not reach the minimum level. An increase in SC of 0.06-0.07 cm/year was shown for all breeds. In all (1997-2010), the increase of the average SC (independent of breed and age) was approximately 1 cm. The positive trend was apparent for all breeds but only statistically significant for the Charolais breed.

Conclusions

In conclusion, our results indicated an increase in the SC over time, which improves the possibilities to obtain performance tested beef sires in Sweden with the potential for achieving better fertility results.  相似文献   
75.
The present investigation provides a new method for the nixtamalization process wherein corn endosperm fractions (corn meal) are treated in an alkaline solution that yields quality masa or instant masa flour like traditional nixtamalization process (alkaline cooking of corn with lime). The objective of this work was to determine the best combination of nixtamalization process variables for producing nixtamalized instant flour (NIF) from corn meal. Nixtamalization conditions were selected from factorial combinations of process variables including nixtamalization time (NT 8–22 min) and cooking temperature (CT 78–88°C). A central composite rotable experimental design was chosen. Lime concentration was 1% (10 g of Ca(OH)2/L of water) and ratio of corn meal to cooking medium was 1:4. At the end of each cooking, each treatment was steeped for 5 hr at room temperature (25°C). Nixtamalized corn meal was dried (55°C/12 hr) and milled to pass through 80 U.S. mesh to obtain NIF. Response surface methodology (RSM) was applied as an optimization technique over four response variables: masa firmness (MF), masa adhesiveness (MA), tortilla cutting force (CF), and tortilla tensile strength (TS). Predictive models for response variables were developed as a function of process variables. Conventional graphic methods were applied to obtain response variable values similar to the control (MASECA). Contour plots of each response variable applied superposition surface methodology to obtain a contour plot for observation and for selecting the best combination of nixtamalization time (NT 15 min) and cooking temperature (CT 83°C) for producing an optimized NIF from corn meal. Values of MF, MA, CF, and TS obtained from the predictive models were compared with those derived from experimental tests; a close agreement (coefficient of variance < 10%) between both values was observed.  相似文献   
76.
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   
77.
78.
Twenty-seven weaned pigs with a wasting appearance were investigated. From a morphological point of view the pigs were divided into three groups. In the group of pigs with macro-scopical signs of regional ileitis, affected tissue showed substantial epithelial proliferation, and electron microscopic studies revealed the presence of microorganisms within the cytoplasm of the epithelial cells. There was a loss of, or only faint, enzymatic activity of alkaline phosphatase in the mucosal epithelium. In another group of five pigs there was no, or only slight, light microscopical signs of regional ileitis but presence of intracellular microorganisms. The enzymatic activity of the ileal epithelium was low. Low enzymatic activity of the ileal epithelium was observed in a third group of wasting pigs, which had no histological or electron microscopical signs of regional ileitis.  相似文献   
79.
The possibility of using the Iosipescu shear test device to study the combined shear and compression behavior of anisotropic materials was examined. Measurements were made using both an original (Wyoming version) and an in-house modified Iosipescu shear and compression fixture. Numerical simulation of the combined shear and compression test was carried out to verify the reliability of the modified device. The numerical results were compared with data from experiments on a medium-density fiberboard. The numerical results show good agreement with the experimental results for the shear test in all the three material directions tested. The shapes as well as the values of the strain fields were similar in the numerical and experimental results. Different rotations of the combined shear and compression device were studied using the finite element method to find the combinations that gave reliable results in shear and compression. It was found that the 45° rotation gave the most uniform strain fields in the section between the notches. This rotation was tested on the fiberboard.  相似文献   
80.
In order to investigate the way in which fibre properties affect the mechano-sorptive creep phenomenon in paper, single wood fibres were exposed to tensile stresses at a constant humidity of 80% relative humidity (RH) and in a cyclic humidity environment varying between 80 and 30% RH. Contrary to earlier claims, it was demonstrated that single wood fibres exposed to a cyclic RH show a considerably higher creep than that corresponding to the highest RH experienced in the cycle, i.e., a mechano-sorptive behaviour. The creep strain rate at cyclic humidity was shown to be a function of the creep rate at constant climate, and to be an apparent linear function of the applied stress.  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