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   454篇
  免费   36篇
  国内免费   2篇
林业   19篇
农学   26篇
基础科学   5篇
  80篇
综合类   65篇
农作物   36篇
水产渔业   27篇
畜牧兽医   189篇
园艺   5篇
植物保护   40篇
  2023年   3篇
  2022年   10篇
  2021年   17篇
  2020年   15篇
  2019年   19篇
  2018年   17篇
  2017年   15篇
  2016年   17篇
  2015年   16篇
  2014年   20篇
  2013年   56篇
  2012年   11篇
  2011年   30篇
  2010年   18篇
  2009年   16篇
  2008年   15篇
  2007年   23篇
  2006年   11篇
  2005年   20篇
  2004年   13篇
  2003年   2篇
  2002年   7篇
  2001年   9篇
  2000年   7篇
  1999年   4篇
  1998年   10篇
  1997年   6篇
  1996年   4篇
  1995年   6篇
  1994年   3篇
  1993年   10篇
  1992年   4篇
  1991年   3篇
  1990年   8篇
  1989年   2篇
  1988年   2篇
  1987年   6篇
  1986年   4篇
  1985年   6篇
  1984年   7篇
  1983年   3篇
  1980年   3篇
  1979年   2篇
  1976年   2篇
  1971年   1篇
  1970年   1篇
  1968年   1篇
  1967年   1篇
  1963年   1篇
  1962年   1篇
排序方式: 共有492条查询结果,搜索用时 15 毫秒
481.
Leaf protein concentrate (LPC) fortified dishes were compared with isoproteinous and isocaloric amounts of milk for the supplementation of the normal diets of the children of a local slum: 40 children were fed LPC-fortified dishes as a supplement and 40 other children were fed milk as a supplement; 20 children who were not given any supplements served as a control group. Data on increases in height and weight and on haemoglobin and red blood cell status confirmed that the LPC-fortified dishes were comparable to milk as a supplement to provide protein, minerals and vitamins to nutritionally inadequate local diets.  相似文献   
482.
Recognition of peatlands as a key natural store of terrestrial carbon has led to new initiatives to protect and restore them. Some afforested bogs are being clear-felled and restored (forest-to-bog restoration) to recover pre-afforestation ecosystem function. However, little is known about differences in the peat properties between intact, afforested and restored bogs. A stratified random sampling procedure was used to take 122 peat cores from three separate microforms associated with intact (hollows; hummocks; lawns), afforested and restored bogs (furrows; original surface; ridges) at two raised and two blanket bog locations in Scotland. Common physical and chemical peat properties at eight depths were measured in the laboratory. Differences in bulk density, moisture and carbon content between the afforested (mean = 0.103 g cm−3, 87.8% and 50.9%, respectively), intact (mean = 0.091 g cm−3, 90.3% and 51.3%, respectively) and restored bogs (mean = 0.095 g cm−3, 89.7% and 51.1%, respectively) were small despite their statistical significance. The pH was significantly lower in the afforested (mean = 4.26) and restored bogs (mean = 4.29) than the intact bogs (mean = 4.39), whereas electrical conductivity was significantly higher (mean: afforested = 34.2, restored = 38.0, intact = 25.3 μS cm−1). While significant differences were found between treatments, effect sizes were mainly small, and greater differences in pH, electrical conductivity, specific yield and hydraulic conductivity existed between the different intact bogs. Therefore, interactions between geographic location and land management need to be considered when interpreting the impacts of land-use change on peatland properties and functioning.  相似文献   
483.
The magnitude of damage to buffalo spermatozoa during incubation with different levels of H2O2 was assessed. A total number of 24 ejaculates from four Murrah buffalo bulls were analysed in the study. Each ejaculate was split into two parts (part I and II). Part I was extended in Tris–egg yolk–citrate extender (20% egg yolk:7% glycerol), equilibrated (4 h at 5°C) and cryopreserved in 0.5‐ml French straws and stored in liquid nitrogen. The other part was utilized for fresh semen studies. The sperm in fresh, equilibrated and frozen–thawed semen was separated by centrifugation (1500 g ; 15 min) and were washed with sperm TALP. The sperm cells were re‐suspended in incubation TALP at the rate of 108 sperm cells per millilitre and incubated with 0, 10, 25, and 50 μm H2O2 per ml at 37°C. Sperm motility, viability and intact acrosome percentages were assessed at 15‐min intervals up to 60 min of incubation. Lipid peroxidation levels of sperm were assessed at 0 and 60 min of incubation. The results of the experiment revealed that sperm motility decreased drastically during incubation with H2O2. Among the different levels of H2O2, the 50‐μm H2O2‐incorporated group had significantly (p < 0.05) higher malonaldehyde (MDA) level than the other groups. In the 50‐μm H2O2‐incorporated group, the MDA levels in fresh, equilibrated and frozen–thawed semen after incubation for 60 min were 961.6 ± 12.7, 991.8 ± 10.3 and 1234.9 ± 9.6 nm per 109 spermatozoa respectively. An inverse relationship was observed between sperm motility, viability, intact acrosome percentages and concentration of H2O2 and duration of incubation. The decrease in sperm functions with duration of incubation and concentration of H2O2 was significantly (p < 0.05) higher in frozen–thawed than fresh and equilibrated spermatozoa.  相似文献   
484.
在金融危机的背景下,能源价格的上涨给家禽生产带来了巨大的压力.在育雏的过程中,要根据鸡舍的状况,雏鸡数量的多少,通风换气过程中的散热等因素匹配育雏器的数量,以最大限度地降低能源的消耗.在通风的过程中,必须合理地选择风扇,同时对不同位置的进气口进行正确地操作,以降低能耗.此外,应加强对风扇的日常维护以改善性能,提高效率.  相似文献   
485.
The study examined chemical composition and rheological and sensory properties of probiotic soy yogurt during 28 day storage at 4 degrees C. Soymilk supplemented with 2% (w/v) inulin or 1% (w/v) each of raffinose and glucose was used as a base for soy yogurt manufacture. Viability of probiotic organisms and their metabolic activity measured as production of organic acids and aldehyde content responsible for beany flavor, as well as rheological and sensory properties of soy yogurt, were examined. Inulin or raffinose/glucose supplementation in soymilk increased the bacterial population by one log cycle and the amount of lactic acid. Probiotic bacteria metabolized more aldehyde than yogurt culture and substantially reduced the beaniness in soy yogurt as determined by sensory evaluation. The probiotic soy yogurts showed more viscous and pseudoplastic properties than the control soy yogurts, but the sensory evaluation results showed preference for the control soy yogurts which were slightly less viscous. Control soy yogurt provided better mouth feel than probiotic soy yogurts.  相似文献   
486.
The transmission of Stagonospora nodorum from four naturally infected winter wheat seedlots was quantified in controlled environment germination chambers at 9, 13, 17, 21, and 25 °C. Seedlings were harvested when the second leaf began to emerge. Coleoptiles and first seedling leaves were examined for the presence of lesions caused by S. nodorum. First leaves were incubated on Bannon's medium for 2 weeks, after which they were examined for pycnidia of S. nodorum. Transmission to the coleoptile occurred at all temperatures, but decreased from 100% to 72% as temperature increased from 9 to 25 °C. Transmission to the first leaf was less, dropping from 37% to 2% as temperature increased from 9 to 25 °C. At least 44% of infected first leaves were symptomless at all temperatures, with 96% of infected leaves showing no symptoms at 25 °C. Transmission to seedling leaves occurred over a broad temperature range. Under the high densities at which wheat is sown, a significant number of infected seedlings per unit area may originate from relatively low initial seed infection levels and transmission efficiencies.  相似文献   
487.
488.
Electrochemical methods were combined with redox-active surfactants to actively control the motions and positions of aqueous and organic liquids on millimeter and smaller scales. Surfactant species generated at one electrode and consumed at another were used to manipulate the magnitude and direction of spatial gradients in surface tension and guide droplets of organic liquids through simple fluidic networks. Solid microparticles could be transported across unconfined surfaces. Electrochemical control of the position of surface-active species within aqueous films of liquid supported on homogeneous surfaces was used to direct these films into periodic arrays of droplets with deterministic shapes and sizes.  相似文献   
489.
490.
Tetravalent uranium in calcite   总被引:1,自引:0,他引:1  
X-ray absorption spectroscopy and x-ray fluorescence microprobe studies of 35-million-year-old calcite from a Mississippi Valley-type zinc ore deposit indicate substitution of tetravalent uranium for divalent calcium. Thus, tetravalent uranium has a stable location in calcite deposited under reducing conditions. This result validates uranium-series dating methods (including uranium/lead dating) for ancient calcite and shows that calcite provides a sink for uranium in deep groundwater aquifers and anoxic lacustrine and marine basins.  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