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   112篇
  免费   4篇
  国内免费   2篇
林业   8篇
农学   8篇
  27篇
综合类   6篇
农作物   8篇
水产渔业   8篇
畜牧兽医   32篇
园艺   4篇
植物保护   17篇
  2022年   2篇
  2021年   5篇
  2020年   2篇
  2019年   2篇
  2018年   6篇
  2017年   4篇
  2016年   4篇
  2015年   1篇
  2014年   2篇
  2013年   12篇
  2012年   12篇
  2011年   5篇
  2010年   9篇
  2009年   6篇
  2008年   7篇
  2007年   2篇
  2006年   1篇
  2005年   3篇
  2004年   6篇
  2003年   4篇
  2002年   5篇
  2000年   1篇
  1999年   1篇
  1998年   2篇
  1996年   1篇
  1995年   1篇
  1989年   2篇
  1988年   1篇
  1987年   1篇
  1983年   1篇
  1981年   1篇
  1980年   1篇
  1975年   1篇
  1974年   2篇
  1973年   2篇
排序方式: 共有118条查询结果,搜索用时 46 毫秒
71.
OBJECTIVE: To determine whether plasma concentrations of tumor necrosis factor-alpha (TNF-alpha) are increased in cats with congestive heart failure (CHF) secondary to cardiomyopathy. ANIMALS: 26 adult cats with CHF and cardiomyopathy and 9 healthy control cats. PROCEDURE: Plasma concentrations of TNF-alpha were measured in cats with CHF and cardiomyopathy. Tumor necrosis factor-alpha was measured by quantifying cytotoxic effects of TNF-alpha on L929 murine fibrosarcoma cells. RESULTS: Concentrations of TNF-alpha were increased (0.13 to 3.6 U/ml) in 10 of 26 cats with CHF but were undetectable in the other 16 cats with CHF and all control cats. In 20 of 26 cats with CHF right-sided heart failure (RHF) was evident; TNF-alpha concentrations were increased in 9 of these 20 cats. The remaining 6 cats had left-sided heart failure (LHF); TNF-alpha concentrations were increased in only 1 of these cats. Age of cats with LHF (mean +/- SD, 12.1+/-6.2 years) was not significantly different from age of the cohort with RHF (10.5+/-5.2 years). Body weight of cats with increased TNFalpha concentrations (5.4+/-1.8 kg) was not significantly different from body weight of cats with CHF that did not have measurable concentrations of TNF-alpha (4.7+/-1.6 kg). CONCLUSIONS AND CLINICAL RELEVANCE: Concentrations of TNF-alpha were increased in many cats with CHF. Cats with RHF were most likely to have increased TNF-alpha concentrations. Increased plasma concentrations of TNF-alpha in cats with CHF may offer insights into the pathophysiologic mechanisms of heart failure and provide targets for therapeutic interventions.  相似文献   
72.
Ovaries of two goats with persistent corpus luteum were studied by histochemical methods. Lutein cells showed moderate alkaline phosphatase and acid phosphatase activity associated with strong delta 5-3β-hydroxysteroid dehydrogenase and succinic tetrazolium reductase activity. The results are interpreted as an indication that the corpus luteum was functioning.  相似文献   
73.
The aim of this study was to evaluate the effect of rosemary essential oils (REO) and the forage nature on ewes' performances, immune response and lambs' growth and mortality. Forty‐eight dairy ewes (Sicilo‐Sarde) were fed oat‐hay or oat‐silage supplemented with 400 g of concentrate during pregnancy and 600 g during postpartum. The experimental concentrate contained the same mixture as the control (barley, soybean meal and mineral vitamin supplement) more 0.6 g/kg of REO. Two groups were obtained with each forage (Hay groups: H‐C and H‐REO; Silage groups: S‐C and S‐REO). REO increased the dry matter (DM) intake, the nitrogen intake and retention being higher with the silage groups (P < 0.05). REO increased solid non‐fat (P = 0.004) and fat contents of colostrum which was higher with hay (P = 0.002). REO decreased lamb mortality (P < 0.05) which averaged 21% for control groups and 6% for H‐REO, while no mortality was recorded with S‐REO. REO dietary supply improved forage intake and tended to ameliorate colostrum production; it could be a natural additive to improve ewes' performances.  相似文献   
74.
1. Despite the importance of Llangorse Lake as the largest natural body of fresh water in South Wales, no long‐term limnological project has ever been planned for the lake. 2. A mass of data is available from sampling carried out at intervals since 1961, but these visits were for various reasons and used widely differing levels of expertise. However, from these data some indications of seasonal variations, effects of climate and human interference on the lake system over 30 years have been inferred. 3. Depth soundings revealed the general shallowness of the lake with two deeper basins. Wind action oxygenated the water and stirred up sediments releasing nutrients and resting algal stages into the water column. Periods of thermal stratification were transient in summer. Secchi disc and light readings showed greatest light penetration in April/May. The lake water remained alkaline throughout. Dissolved ammonia values were low in the 1960s, increased in the 1970s and decreased again in the 1980s. Nitrite‐ and nitrate‐nitrogen showed a converse pattern over the years. Phosphate (PO4 P) and silica (SiO2) values were highest in the 1960s, showed a decrease in the 1970s and early‐1980s, and rose again towards the end of the decade, as did the chloride values. Seasonal fluctuations of all nutrients were observed. 4. Diatoms dominated the phytoplankton, with highest production in summer and early autumn. The Cyanobacteria (blue–green algae) produced blooms in the 1960s and 1970s, but Chlorophyta (green algae) increased over the years and dominated in the 1980s after a diversion of sewage from the lake. Diatom production followed a vernal and late summer periodicity common in temperate lakes. Results from diatom stratigraphy of the deep sediment cores indicated a change from epiphytic to planktonic species related to land‐use change and a subsequent increase in soil erosion and turbidity. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   
75.
Journal of Plant Diseases and Protection - In Mexico, okra (Abelmoschus esculentus L.) is grown mainly for export, but its production is affected by various pests and diseases. Plants with mosaic...  相似文献   
76.
狗蔷薇不定根可被噻苯隆(TDZ)高效诱导形成类原球茎,深入探讨其诱导阶段的分子生物学机制,有利于指导切花月季建立类似高效再生和遗传转化体系.快速、准确克隆和筛选狗蔷薇类原球茎发生的关键基因是进行分子生物学水平研究的一个重要前提.利用苹果(Malus×domestica)、桃(Prunus persica)和草莓(Fragaria vesca)高同源性基因5'UTR(非翻译区)的相对保守性,在其内保守区域设计上游简并引物,以M-MLV逆转录酶反转录合成cDNA为模板,直接扩增蔷薇科植物狗蔷薇(Rosa canina)RcPIN1(pin-formed)和RcPLT(plethora)基因5’末端,大大减少了获取众多目的基因全长的时间及成本.结果显示,在狗蔷薇RcPIN1和RcPLT基因与其对应苹果、桃和草莓高同源性基因的5'UTR内,很多区域表现出较高保守性,表明在5'UTR相对保守区域设计上游简并引物扩增目的基因5’末端的合理性.与常规5'CDNA末端快速扩增技术(5’RACE)相比,本方法无需对cDNA模板5’末端加尾同聚物和引入锚定引物,即不必使用昂贵的5’RACE试剂盒,具有快捷、节约等优点,是一种获取蔷薇科植物基因5'末端的可行途径.  相似文献   
77.
78.
79.
Ilex paraguariensis A. St.-Hil. is used to prepare a traditional tealike beverage widely appreciated in Argentina, Paraguay, Uruguay, and southern Brazil. In these countries, the tea is popularly known as mate or chimarr?o. The aim of this work is to characterize the elemental composition of commercial Ilex paraguariensis and determine the portion of each element present in the leaves that is eluted in the water during the infusion process and consequently ingested by the drinker. Using the particle-induced X-ray emission technique, we verified the presence of Mg, Al, Si, P, S, Cl, K, Ca, Ti, Mn, Fe, Cu, Zn, and Rb at different concentrations, which accounts for about 3.4% of the total mass. The results show a loss of about 90% of K and Cl, 50% of Mg and P, and 20% of Mn, Fe, Cu, Zn, and Rb by the leaves after the infusion. The volume of water used in the infusion affects only the concentration of elements such as Cl, P, K, and Mg until the first 600 mL of water, where a steep decrease in the concentration of these elements was observed in brewed leaves. Furthermore, higher water temperatures (typical temperatures used in infusions, between 80 and 100 degrees C) favor the extraction of K and Cl into the infusion, while the concentration of other elements remains practically constant as a function of temperature.  相似文献   
80.
Oxazolidine E, an aldehydic cross-linking agent, is used to impart hydrothermal stability to collagen. The purpose of this study was to investigate the exact nature of oxazolidine E induced cross-links with collagen by using synthetic peptides having sequence homology with collagen type I. Tandem mass spectrometry revealed the formation of methylol and Schiff-base adducts upon reaction of oxazolidine E with the peptides. This was confirmed by allowing the reaction to proceed under reducing conditions using cyanoborohydride. Mass spectrometry (MS)-MS analysis clearly showed interaction of tryptophan and lysine residues with oxazolidine E and demonstrated that arginine could be cross-linked with glycine in the presence of oxazolidine E through the formation of a methylene bridge. Collagen fibrils regenerated from monomers in the presence and absence of oxazolidine E were studied using atomic force microscopy to investigate morphological alterations. Regenerated fibrils showing the typical 65 nm D-banding pattern were obtained from those formed both in the presence and absence of oxazolidine E, and there was no evidence of a change in the D-periodicity of these fibrils. This indicated that oxazolidine E does not hinder collagen molecules from correctly aligning to form the quarter-stagger structure.  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