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   501篇
  免费   23篇
  国内免费   2篇
林业   28篇
农学   22篇
基础科学   8篇
  103篇
综合类   67篇
农作物   34篇
水产渔业   26篇
畜牧兽医   170篇
园艺   18篇
植物保护   50篇
  2023年   3篇
  2022年   9篇
  2021年   17篇
  2020年   13篇
  2019年   14篇
  2018年   10篇
  2017年   19篇
  2016年   14篇
  2015年   16篇
  2014年   18篇
  2013年   27篇
  2012年   31篇
  2011年   32篇
  2010年   17篇
  2009年   24篇
  2008年   36篇
  2007年   23篇
  2006年   26篇
  2005年   19篇
  2004年   16篇
  2003年   14篇
  2002年   14篇
  2001年   9篇
  2000年   8篇
  1999年   6篇
  1998年   10篇
  1997年   3篇
  1996年   5篇
  1995年   3篇
  1994年   4篇
  1993年   3篇
  1992年   2篇
  1991年   5篇
  1990年   5篇
  1989年   5篇
  1988年   3篇
  1987年   3篇
  1986年   5篇
  1985年   5篇
  1983年   2篇
  1982年   3篇
  1981年   3篇
  1980年   2篇
  1978年   6篇
  1973年   2篇
  1970年   1篇
  1967年   1篇
  1953年   2篇
  1936年   2篇
  1930年   1篇
排序方式: 共有526条查询结果,搜索用时 31 毫秒
1.
Serum concentrations of glucose, cholesterol, triglycerides, and serum alkaline phosphatase activity were measured over different periods of time of food deprivation in male rats. Thirty percent of non-fasted rat's sera was found to be lipemic. At 16 hours of fasting, glucose levels dropped by 30% compared to the level of the non-fasting control group, and remained at a relatively constant level for up to 48 hours of fasting. Triglyceride concentrations decreased at 16 hours after fasting. Serum cholesterol levels were not changed at any of the fasting periods compared to the non-fasted control group. Alkaline phosphatase activity was decreased at 8 hours of fasting, with further declines in activity of the serum enzyme seen at 16, 24, and 48 hours of fasting. It was concluded that at 16 to 18 hours fasting, a non-absorptive state had been reached in male rats.  相似文献   
2.
3.
4.
Fracture-related infections remain a leading cause of morbidity and mortality. We aimed to establish a simple contaminated radial osteotomy model to assess the efficacy of a biodegradable polymer poly(sebacic-co-ricinoleic acid) [p(SA-RA)] containing 20% w/w gentamicin. A unilateral transverse osteotomy was induced in Sprague-Dawley (SD) rats, followed by application of Staphylococcus aureus suspension over the fracture. After successfully establishing the contaminated open fracture model, we treated the rats either systemically (intraperitoneal cefuroxime), locally with p(SA-RA) containing gentamicin, or both. Control groups included non-contaminated group and contaminated groups that were either untreated or treated with the polymer alone. After 4 weeks, the bones were subjected to micro-CT scanning and microbiological and histopathology evaluations. Micro-CT analysis revealed similar changes in the group subjected to both local and systemic treatment as in the non-contaminated control group. Lack of detectable bacterial growth was noted in most animals of the group subjected to both local and systemic treatment, and all samples were negative for S. aureus. Histopathological evaluation revealed that all treatment modalities containing antibiotics were highly effective in reducing infection and promoting callus repair, resulting in early bone healing. While p(SA-RA) containing gentamicin treatment showed better results than cefuroxime, the combination of local and systemic treatment displayed the highest therapeutic potential in this model.  相似文献   
5.
Undermixing or overmixing the dough results in varied experimental loaf volumes. Bread preparation requires a trained baker to evaluate dough development and determine the stop points of the mixer. Instrumentation and electronic control of the dough mixer would allow for automatic mixing. This study used a 200 g mixer that provided an output signal during dough mixing to evaluate potential mixing stop points. The effect of varied mixing time on the baked loaf volume was tested by using three flours with protein contents of 10.6, 12.4, and 13.8%. Dough samples were undermixed, mixed to peak, and overmixed. Overmixing by 0.6 min reduced the loaf volume in all flours tested, by 16–50 cm3 at 90 rpm and by 29–68 cm3 at 118 rpm. When the high‐protein flour sample was undermixed, the largest baked loaves were produced, with an average volume of 922 cm3. A second objective studied the similarities and differences between a 200 g mixer and a 35 g mixograph. The same flours were mixed on both units. The mixing peaks for the 200 g mixer were normalized with the 35 g mixograph peaks. When flour and water were used, the mixing times for the 200 g mixer averaged 0.7, 1.2, and 1.6 min shorter than the 35 g mixograph, at 90, 104, and 118 rpm, respectively. Although both the 200 g mixer and the 35 g mixograph system look mechanically similar, they both have unique mechanical motion, speeds, and sample sizes. Their results may show similar trends, but their measured values are usually different. However, when other baking ingredients were included in the 200 g mixer at 90 rpm, the mixing times were within 0.2 min of the 35 g mixograph times for three of four flours.  相似文献   
6.
7.
Rain-fed agriculture is widespread in Inner Mongolia, northern China, where wind erosion of farmland is very common because of sandy soil and dry, windy weather. However, very little is known about the effects of wind erosion on soil physical and chemical properties in this region. A field experiment was conducted in sandy farmland, where erosional and depositional gradients were established to evaluate the effects of wind erosion and leeward sand accumulation on soil texture, nutrient content, soil water, and soil temperature. The research showed that long term wind erosion could result in significant soil coarseness, infertility and dryness. Severe erosion reduced clay by 59.6%, organic C by 71.2%, total N by 67.4%, total P by 31.4%, available N by 64.5%, available P by 38.8%, and average soil water content by 51.8%, compared with non-eroded farmland in the study region. The sand fraction (particles > 0.05 mm), pH and ground-surface temperature increased by 6.2%, 3.7%, and 2.2 °C, respectively. Accumulated sand also caused a decrease in nutrients and soil water content. Under severe sand accumulation, clay was reduced by 2.0%, organic C by 19.3%, total N by 21.7%, total P by 13.7%, available N by 52.5%, and average soil water content by 26.6%. The sand fraction, pH, available P, and ground-surface temperature increased by 0.2%, 0.9%, 5.8% and 2.8 °C, respectively.  相似文献   
8.
The antioxidative phytochemicals in various fruits and vegetables are widely recognized for their role in scavenging free radicals, which are involved in the etiology of many chronic diseases. Colored fruits are especially considered a quality trait that correlates with their nutritional values and health benefits. The specific aim of this study was to investigate the antioxidants in the juice and freeze-dried flesh and peel of red pummelo and their ability to scavenge free radicals and compare them with those in white pummelo juice. The total phenolic content of red pummelo juice extracted by methanol (8.3 mg/mL) was found to be significantly higher than that of white pummelo juice (5.6 mg/mL). The carotenoid content of red pummelo juice was also significantly higher than that in white pummelo juice. The contents of vitamin C and delta-tocopherol in red pummelo juice were 472 and 0.35 mug/mL, respectively. The ability of the antioxidants found in red pummelo juice to scavenge radicals were found by methanol extraction to approximate that of BHA and vitamin C with a rapid rate in a kinetic model. The ability of methanol extracts of freeze-dried peel and flesh from red pummelo to scavenge these radicals was 20-40% that of BHA and vitamin C effects. Fresh red pummelo juice is an excellent source of antioxidant compounds and exhibited great efficiency in scavenging different forms of free radicals including DPPH, superoxide anion, and hydrogen peroxide radicals.  相似文献   
9.
Applying a combination of classical and geostatistical methods, we identified soil properties and their spatial variation in a 5-year grazed sand dune (GSD5) and a 20-year recovered sand dune (RSD20) in Horqin Sandy Land, northern China. The paper assesses the effect of grazing, topography and vegetation restoration on spatial heterogeneity of soil properties. The results showed that soil organic carbon, total nitrogen, very fine sand (0.1–0.05 mm) content and their coefficients of variation were lower in GSD5 than in RSD20, while soil water contents (0–20 cm and 20–40 cm depths) were higher in GSD5 than in RSD20. Geostatistical analysis revealed that the spatial structured variance accounted for the largest proportion of total sample variance in soil properties at the measured scale under grazing and restoration. The spatial autocorrelation ranges were 66.30 m for soil organic carbon and 50.80 m for total nitrogen in GSD5 less than those in RSD20 (70.00 m and 76.10 m, respectively), while the spatial autocorrelation ranges of soil particle size fractions and soil water contents in RSD20 were less than those in GSD5. Kriging-interpolated maps also showed that the heterogeneity of soil organic carbon and total nitrogen and their degree of patch fragmentation were higher in GSD5 than in RSD20. These results suggested that continuous grazing resulted in an increase in spatial variability of soil nutrient and a decrease in spatial variability of soil particle size fractions and soil water content. Soil organic carbon and total nitrogen of sand dunes are associated closely with soil particle size fractions, relative height of sampling site and vegetation cover. Spatial patterns of soil properties are most strongly related to grazing, topography and plant-induced heterogeneity in sand dune ecosystems prone to wind erosion.  相似文献   
10.
Rinderpest had been reported in most parts of Ethiopia when the Pan African Rinderpest Campaign (PARC) was launched. As a result of intensive disease investigation and strategic vaccination, most parts of the country are now considered provisionally free, and widespread vaccination has been replaced by clinical and serological surveillance. Details of any episodes of disease are recorded and followed up after laboratory confirmation of suspected cass using antigen-capture ELISA. This paper is based on observations on the performance of the antigen detection ELISA compared to the agar gel immunodiffusion (AGID) test, which also differentiates rinderpest from peste des petits ruminants (PPR). The stability of the specific viral antigen was monitored for 4 days, and rinderpest and PPR antigens were still detected, depending on the type of specimen. Antigen capture ELISA is more rapid, sensitive and virus specific than the AGID. Even if the cold chain of the specimen is compromised for a day or two during sample collection and submission, the specimen may still be suitable for testing by ELISA.  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