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   212篇
  免费   18篇
林业   12篇
农学   3篇
  9篇
综合类   18篇
农作物   3篇
水产渔业   5篇
畜牧兽医   171篇
园艺   3篇
植物保护   6篇
  2023年   3篇
  2022年   1篇
  2021年   7篇
  2020年   7篇
  2019年   4篇
  2018年   10篇
  2017年   7篇
  2016年   6篇
  2015年   12篇
  2014年   9篇
  2013年   11篇
  2012年   20篇
  2011年   9篇
  2010年   6篇
  2009年   7篇
  2008年   11篇
  2007年   19篇
  2006年   6篇
  2005年   8篇
  2004年   4篇
  2003年   5篇
  2001年   3篇
  2000年   6篇
  1999年   5篇
  1998年   2篇
  1997年   1篇
  1995年   1篇
  1994年   1篇
  1991年   1篇
  1990年   2篇
  1989年   4篇
  1988年   4篇
  1987年   1篇
  1985年   3篇
  1984年   2篇
  1983年   4篇
  1981年   1篇
  1978年   3篇
  1977年   1篇
  1974年   2篇
  1973年   1篇
  1972年   2篇
  1971年   2篇
  1970年   3篇
  1969年   1篇
  1944年   1篇
  1908年   1篇
排序方式: 共有230条查询结果,搜索用时 15 毫秒
11.
12.
In a 2 × 2 factorial arrangement, 16 groups of 12 pigs were assigned to one of two housing systems (straw bedding, S vs. Barren, B) and to one of two starch types (native, N vs. pregelatinized potato starch, P, each included at 35%) to study effects on apparent faecal digestible nutrient intakes. Intake of straw from bedding material was estimated, using several markers, and results are discussed. Straw intake of the S-pigs was estimated between 143 and 234 g DM/d for P-pigs and between 96 and 156 g DM/d for N-pigs, depending on the method used. Nutrient digestibility was reduced in N-pigs when compared with P-pigs. Intake of digestible dry matter, energy, starch and ADF was increased in S-pigs, but the intake of digestible protein was reduced. Despite greatly reduced nutrient digestibility in S-pigs, additional digestible nutrient intake due to housing on a straw bedding can be considerable.  相似文献   
13.
A non-ambulatory dog with tetraparesis following a pain episode that had evolved over 2 months was submitted for medical treatment and diagnosed with intervertebral disk disease at C3-C4 and dorsal extradural compression at C1-C2 and C3-C4 using myelography and computed tomography. The dog experienced ambulation recovery after 15 days of treatment with only electroacupuncture and Chinese herbal medicine, with marked improvement occurring after only 10 treatments. Six months of follow-up demonstrated that the dog was stable and had no recurrence of symptoms. Therefore, it was concluded that the combination of electroacupuncture and Chinese herbal medicine was responsible for motor rehabilitation.  相似文献   
14.
A factorial field experiment, located near Chalk River, Ontario, Canada, was used to test the effects of brush competition, fertility, and soil temperature on first and second-season growth of planted white pine and white spruce. Soil temperature, soil moisture tension, and photosynthetically active radiation were continuously monitored to quantify treatment effects. Foliar nutrition was assessed on nursery stock pre-planting and on current and previous foliage age classes after one growing-season. Measurement of biomass components and leaf surface area was carried out after one growing-season. Increasing soil temperature improved the net photosynthetic rate (Pn) of both species in the first growing-season. Relative growth rate (Gr) of both species was positively affected by the soil temperature treatments but, because of changes in carbon partitioning and foliage morphology, was not directly related to Pn. Fertilization and brush control treatments caused compensating adjustments in morphology and biomass allocation that did not affect Gr in the first season. In the second season, environmental conditions changed and brush competition increasingly influenced growth. Despite the changes in environmental conditions during the plantation establishment period, the ability of trees to successfully adjust to environmental stress increased from the first growing-season to the second.  相似文献   
15.
We present a new, rapid method for high-resolution online determination of delta13C in tree rings, combining laser ablation (LA), combustion (C), gas chromatography (GC) and isotope ratio mass spectrometry (IRMS) (LA-C-GC-IRMS). Sample material was extracted every 6 min with a UV-laser from a tree core, leaving 40-microm-wide holes. Ablated wood dust was combusted to CO2 at 700 degrees C, separated from other gases on a GC column and injected into an isotope ratio mass spectrometer after removal of water vapor. The measurements were calibrated against an internal and an external standard. The tree core remained intact and could be used for subsequent dendrochronological and dendrochemical analyses. Cores from two Scots pine trees (Pinus sylvestris spp. sibirica Lebed.) from central Siberia were sampled. Inter- and intra-annual patterns of delta13C in whole-wood and lignin-extracted cores were indistinguishable apart from a constant offset, suggesting that lignin extraction is unnecessary for our method. Comparison with the conventional method (microtome slicing, elemental analysis and IRMS) indicated high accuracy of the LA-C-GC-IRMS measurements. Patterns of delta13C along three parallel ablation lines on the same core showed high congruence. A conservative estimate of the precision was +/- 0.24 per thousand. Isotopic patterns of the two Scots pine trees were broadly similar, indicating a signal related to the forest stand's climate history. The maximum variation in delta13C over 22 years was about 5 per thousand, ranging from -27 to -22.3 per thousand. The most obvious pattern was a sharp decline in delta13C during latewood formation and a rapid increase with spring early growth. We conclude that the LA-C-GC-IRMS method will be useful in elucidating short-term climate effects on the delta13C signal in tree rings.  相似文献   
16.
17.
ABSTRACT Sweet pepper-Leveillula taurica microclimate relations were studied under controlled conditions and in commercial greenhouses. Conidial germination occurred at 10 to 37 degrees C and was optimal at 20 degrees C. Conidial viability declined as temperatures increased to 40 degrees C for 6 h. Leaf colonization was optimal at 15 to 25 degrees C. Severe leaf infections occurred at 15 to 20 degrees C and conidiation was suppressed at 20 to 25 degrees C. Highest germination rates were observed at 75 to 85% relative humidity (RH). Severity of leaf coverage by symptoms was high for plants which were subjected to longer periods of temperatures between 10 to 15 degrees C and daytime RH between 85 to 95%, and positively correlated with nighttime RH. Disease severity was negatively correlated with lengthy periods of temperatures >25 degrees C, day and night average temperatures, and average daytime RH. Conversely, leaf shedding was relatively high under conditions characterized by long periods of temperatures >20 degrees C and <13 degrees C, and positively correlated with average daytime temperatures and periods of RH <75%. Increasing nighttime temperatures by heating and daytime temperatures by closing the greenhouse side walls reduced disease in two commercial greenhouse experiments. A midseason shift from a cooler greenhouse climate to warm daytime climate halted epidemic development. Flower number and yield were reduced in infected crops.  相似文献   
18.
This study evaluated the effects of the mode of transportation on weight and metabolism of young bulls, which are generally transported by two systems: droving and truck. This experiment consisted of two phases: transportation and refeeding and involved transportation by droving and truck. Fifty young Nellore bulls were separated in equal numbers in both groups, droving group and truck group. In the transportation phase, animals were moved, in a 640-km journey. The refeeding phase consisted of 84 days and commenced after the animals arrived at the fattening farm. The effect of the transportation system on animals’ weight, metabolic hormones, and serum biochemistry was assessed after 28, 56, and 84 days. During the transportation phase, animals in the droving group lost 10.11 kg and animals in the truck group gained 13.1 kg. The truck group showed 20.5 kg of weight gain at the end of the refeeding phase. The highest triiodothyronine (T3) and thyroxine (T4) concentrations were observed on days 0 and 60 in the transportation phase in both droving and truck groups. The serum cortisol concentration was higher in the droving group than in the truck group on day 56 of the refeeding phase. The IGF-I concentrations were higher during the refeeding phase in the droving group than in the truck group. Our results showed that transportation by droving leads to increased weight loss and reduced further weight gain compared to transportation by truck and that serum concentrations of T4, cortisol, and insulin-like growth factor (IGF-I) hormones are altered by the transportation system.  相似文献   
19.
Plasmin is a protease in milk, which concentration is increased during mastitis. The aim of the study was design and characterize short, tailor made fluorogenic substrates for plasmin to see differences in plasmin activity in healthy milk compared to mastitic milk. According to the specificity matrix of plasmin, containing 125 currently known plasmin substrates, six novel plasmin specific substrates were designed and characterized. Eight other substrates were insensitive for plasmin, which was in line with our expectations. The plasmin-sensitive substrates showed no cross-reactivity with proteases from mastitogenic bacteria in vitro. A proof of concept to distinguish healthy milk from mastitic milk is described. Potentially, these substrates present a rapid alternative to the currently established methodologies to detect mastitis in milk.  相似文献   
20.
A 2.5‐year‐old intact male Roborovski hamster (Phodopus roborovskii) was presented with a large subcutaneous mass overlying the abdomen, affecting the animal's ambulation and access to different compartments of the cage through narrow tubing. Ultrasound examination delineated a well‐circumscribed mass in the subcutis of the caudoventral abdominal region. The mass was surgically excised and on cytologic examination showed, in a background of blood, a small population of individually arranged oval to spindle‐shaped cells that exhibited a moderate degree of anisokaryosis, coarsely stippled chromatin, one or more prominent nucleoli, and lightly basophilic well‐defined cytoplasmic processes. Histologically, the mass was composed of interlacing streams and bundles of pleomorphic spindle cells (ganglion‐like cells) with variable amounts of collagenous stroma. The neoplastic cells exhibited moderate features of malignancy. These cells stained intensely with vimentin, but not with any other markers, including antibodies to cytokeratin AE1/AE3, S100 protein, desmin, smooth muscle actin, synaptophysin, neurofilament, and androgen receptor. Based on histologic features, the mass was diagnosed as an atypical fibrosarcoma. This is the first report of an atypical fibrosarcoma in a Roborovski hamster and one of few reports of atypical fibrosarcoma in domesticated hamsters overall.  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