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   286篇
  免费   4篇
林业   94篇
农学   4篇
  91篇
综合类   26篇
农作物   8篇
水产渔业   2篇
畜牧兽医   39篇
园艺   4篇
植物保护   22篇
  2020年   3篇
  2015年   2篇
  2014年   3篇
  2013年   15篇
  2012年   11篇
  2011年   14篇
  2010年   3篇
  2009年   9篇
  2008年   15篇
  2007年   14篇
  2006年   9篇
  2005年   8篇
  2004年   10篇
  2003年   13篇
  2002年   8篇
  2001年   3篇
  1999年   5篇
  1998年   2篇
  1993年   2篇
  1992年   2篇
  1990年   3篇
  1989年   3篇
  1988年   3篇
  1986年   3篇
  1985年   2篇
  1981年   3篇
  1976年   3篇
  1973年   2篇
  1968年   3篇
  1967年   2篇
  1965年   2篇
  1959年   3篇
  1958年   2篇
  1957年   2篇
  1956年   2篇
  1955年   2篇
  1954年   2篇
  1942年   2篇
  1938年   8篇
  1936年   6篇
  1935年   4篇
  1931年   5篇
  1930年   6篇
  1929年   5篇
  1928年   5篇
  1927年   5篇
  1926年   10篇
  1925年   4篇
  1907年   2篇
  1895年   4篇
排序方式: 共有290条查询结果,搜索用时 15 毫秒
51.
Acrylamide exposure was investigated in subgroups of the EPIC study population (510 subjects from 9 European countries, randomly selected and stratified by age, gender, and smoking status) using hemoglobin adducts of acrylamide (HbAA) and its primary metabolite glycidamide (HbGA). Blood samples were analyzed for HbAA and HbGA by HPLC/MS/MS. Statistical models for HbAA and HbGA were developed including body mass index (BMI), educational level, and physical activity. A large variability in acrylamide exposure and metabolism between individuals and country groups was observed with HbAA and HbGA values ranging between 15-623 and 8-377 pmol/g of Hb, respectively. Both adducts differed significantly by country, sex, and smoking status. HbGA values were significantly lower in high alcohol consumers than in moderate consumers. With increasing BMI, HbGA in nonsmokers and HbAA in smokers decreased significantly. In the assessment of potential health effects related to acrylamide exposure, country of origin, BMI, alcohol consumption, sex, and smoking status should be considered.  相似文献   
52.
53.
West Nile virus lineage 2 (WNV‐2) was detected in the brain of 17 goshawks (Accipiter gentilis) that succumbed to neuroinvasive disease in the Czech Republic during 2018: twelve birds were captive and five wild. Furthermore, two wild sparrowhawks (Accipiter nisus) and three other captive birds of prey (golden eagle Aquila chrysaetos, hybrid saker falcon Falco cherrug × F. rusticolus and Harris's hawk Parabuteo unicinctus) also died due to WNV encephalitis. The 2018 outbreak in Czech raptors clearly reflects a new epidemiological situation and indicates an increasing risk of both raptor and human infection with WNV‐2 in the country.  相似文献   
54.
Radiata pine sapwood and heartwood were dried using high-temperature, conventional-temperature, and air drying schedules with and without pre-steaming. They were then impregnated by vacuum treatment with double-distilled water, toluidine blue, and fluorescein dye. For sapwood, there were only minor differences in uptake between drying methods and when pre-steaming was used. Using microscopy, the primary flow pathways in sapwood were found to be the resin canal network and ray parenchyma cells, which provided conduction without large resistance. In heartwood, uptake was strongly influenced by pre-steaming the green lumber. After pre-steaming heart-wood, there was an increase in uptake from all surfaces but especially from the radial surfaces. Lower extractive contents, disruption of epithelial and ray parenchyma cells, and alteration of the condition of bordered pits were also associated with pre-steaming. It was therefore possible to classify flow paths in radiata pine heartwood five ways, according to uptake values and wood anatomical features.This research was presented in part at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998.  相似文献   
55.
56.
Seeing the fact that farm managers in Germany feed anionic salts to transition cows once daily, this study set out to evaluate whether the effects on the acid–base status (ABS) and calcium excretion in urine would persist throughout the entire day beyond this feeding practice. Eleven non-lactating, non-pregnant, Holstein–Friesian-cows with a rumen fistula were administered 2Eq of calcium chloride (CaCl2/five cows) or calcium sulfate (CaSO4/six cows) once daily for a period of 1 week. At day 7, blood and urine samples were taken every 4 h starting at 06:00 a.m. before feeding the anionic salts, and then ending at the same time the next day. Feeding anionic salts to the cows induced metabolic acidosis in both of the groups. The changes tended to be greater in CaCl2-cows. After 12 h, the acidosis lessened and the initial values were reached after 24 h. The CaCl2-cows, however, still showed signs of compensated metabolic acidosis. The results of the present study showed that feeding anionic salts once daily confined the risk of an interrupted effect of the anionic salts on the acid–base status as well as calcium metabolism after 12 h.  相似文献   
57.
To improve sorghum grain protein nutritional quality, improved sorghum lines were transformed to suppress the synthesis of different kafirin sub-classes, or backcrossed into transgenic lines with improved protein quality. Co-suppression of the alpha-, gamma- and delta-kafirin sub-classes and removal of the tannin trait resulted in transgenic sorghum lines with high cooked protein digestibility (±80%), improved Amino Acid Score (0.8) and Protein Digestibility Corrected Amino Acid Score (0.7) compared to the non-transgenic null controls (±50%, 0.4 and 0.2, respectively). These high protein quality lines had a floury endosperm. They also had modified protein body structure, where the protein bodies were irregular shaped with few to numerous invaginations and were less densely packed, with a dense protein matrix visible around the protein bodies. When fewer sub-classes were suppressed, i.e. gamma 1 and delta 2, the endosperm was corneous with normal protein body structure but the improvement in cooked protein digestibility appeared to be less. Apparently, co-suppression of several kafirin sub-classes is required to obtain high protein nutritional quality sorghum lines, but this seems to result in floury-type grain endosperm texture.  相似文献   
58.
59.
Since 1993, Rhizoctonia crown and root rot (Rhizoctonia solani AG 2–2 IIIB) has represented an increasing problem for sugar beet production in Germany. Up to now, the outbreak of the infection and the spread of the disease within a field cannot be predicted and effective countermeasures are not available. Although little is known about the living conditions of R. solani in soils, abiotic soil properties are likely to influence the disease occurrence. Investigations were carried out based on 60 pairwise comparisons, each consisting of a disease‐affected and an adjacent nonaffected patch on farmers' fields in 2002 and 2003. Soil samples from the top soil layer (0–30 cm) were collected before harvest, and eight of the most frequently mentioned soil properties potentially influencing Rhizoctonia crown and root rot infection were examined: bulk density, texture, carbonate carbon, potassium, phosphorus, organic carbon, total nitrogen, and pH. The occurrence of the disease was significantly related to the soil C : N ratio, indicating the influence of soil organic matter on the disease occurrence. Examinations of soil thin sections showed that organic‐matter particles in the soil serve as a substrate for R. solani. All other soil physical and chemical properties examined did not differ between the disease‐affected and nonaffected patches and seem to be of minor importance.  相似文献   
60.
In this pilot study, we tested whether a soft mat (foam covered with a heat-sealed thermoplastic) reduces alterations and injuries at the skin and the leg joints.The soft mat in the lying area of partly slatted pens was compared to a lying area consisting of either bare or slightly littered (100 g straw per pig and day) concrete flooring. In this study we focused on skin lesions on the legs of finishing pigs as indicators of impaired welfare. Pigs were kept in 19 groups of 8-10 individuals and were examined for skin lesions around the carpal and tarsal joints either at a weight of <35 kg, or at close to 100 kg. The likelihood of hairless patches and wounds at the tarsal joints was significantly lower in pens with the soft lying mat than in pens with a bare concrete floor. Pens with a littered concrete floor did not differ compared to pens with a bare concrete floor. The soft lying mat thus improved floor quality in the lying area in terms of preventing skin lesions compared to bare and slightly littered concrete flooring. Such soft lying mats have thus the potential to improve lying comfort and welfare of finishing pigs.  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