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   186篇
  免费   15篇
林业   11篇
农学   17篇
基础科学   5篇
  39篇
综合类   12篇
农作物   9篇
水产渔业   3篇
畜牧兽医   84篇
园艺   4篇
植物保护   17篇
  2023年   2篇
  2022年   3篇
  2021年   7篇
  2020年   11篇
  2019年   8篇
  2018年   11篇
  2017年   8篇
  2016年   9篇
  2015年   7篇
  2014年   5篇
  2013年   18篇
  2012年   7篇
  2011年   9篇
  2010年   12篇
  2009年   7篇
  2008年   14篇
  2007年   9篇
  2006年   6篇
  2005年   5篇
  2004年   5篇
  2003年   3篇
  2002年   1篇
  2001年   2篇
  2000年   4篇
  1998年   1篇
  1996年   1篇
  1995年   1篇
  1992年   2篇
  1991年   3篇
  1990年   1篇
  1988年   3篇
  1987年   2篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1979年   2篇
  1978年   4篇
  1977年   1篇
  1975年   2篇
  1974年   1篇
  1972年   1篇
排序方式: 共有201条查询结果,搜索用时 15 毫秒
31.
Boron (B) deficiency is potentially an important nutrient constraint in calcareous soils. We determined B deficiency incidence and spatial distribution in rainfed wheat (Triticum aestivum L.) in 1.82 Mha Pothohar plateau in Pakistan, its relationship with soil types, crop responses to B, and internal B requirement and B fertilizer use efficiency of wheat. Plant and soil analyses indicated deficiency in 64% of the 61 sampled fields; geostatistics-aided contour maps delineated B deficient areas. In rainfed field experiments, B use increased wheat yields up to 11%. Fertilizer requirement was 1.2 kg B ha?1; critical B concentration (mg kg?1) ranges were: young whole shoots, 4–6; flag leaves, 5–7. Boron uptake by wheat was 0.14–0.58% of applied dosage, leaving substantial residual impact. Highly cost-effective B use or B-efficient genotype adoption can enhance wheat productivity and grower-income. Such effective nutrient assessment and management approaches can be beneficially adopted elsewhere as well.  相似文献   
32.
Gesunde Pflanzen - Biochar (BC) is known to enhance plant growth and may activate plant resistance to various soil borne pathogens. In this experiment, the rice husk (RH) BC was combined with...  相似文献   
33.
两个试验旨在评价肉牛日粮中紫花苜蓿替代禾本科干草的消化动力学。试验1:要测试的饲草组合分别为:100%大须芒草,25%苜蓿和75%大须芒草,50%苜蓿和50%大须芒草,100%苜蓿。采用非线性回归测定即刻可溶性分数A,潜在的可降解分数B,不降解分数C,干物质和中性洗剂纤维消失率。随着苜蓿添加量的增加,干物质分数A线性升高(P=0.03),干物质和中性洗剂纤维分数B线性降低(P=0.01),干物质和中性洗剂纤维消失率线性升高(P≤0.02)。试验2:采用2×2因子设计,测试苜蓿替代鸭茅干草和采食水平的影响。苜蓿添加水平为不添加或含25%(作为饲喂基础),采食水平为每天限制在体重的1%(以干物质为基础)或自由采食。限饲组肉牛营养素摄入量最低(P≤0.05),自由采食鸭茅干草的肉牛营养素摄入量居中,自由采食鸭茅干草和苜蓿的肉牛营养素摄入量最高。采食水平和饲草来源对除蛋白质外的所有营养素的总消化道表观消化率没有影响(P≥0.23)。与单独饲喂鸭茅饲草的肉牛相比,采食鸭茅干草和苜蓿的肉牛蛋白质总消化道表观消化率显著提高33%(P=0.01)。干物质和中性洗剂纤维消失的延迟时间不受苜蓿或采食水平影响(P≥0.20)。限制日粮组和自由采食组,与单独采食鸭茅饲草的肉牛相比,采食鸭茅饲草和苜蓿的肉牛对鸭茅饲草干物质和中性洗剂纤维的消失率更快(P≤0.01)。与限饲组肉牛相比,自由采食组肉牛对鸭茅饲草大、小颗粒的平均贮留时间有缩短的趋势(P≤0.06)。在自由采食和添加苜蓿的条件下,小颗粒鸭茅饲草通过率趋向于更快(P=0.09)。自由采食与鸭茅饲草平均贮留时间缩短和小颗粒鸭茅饲草通过率加快相关;然而添加苜蓿能提高小颗粒鸭茅饲草通过率,干物质和中性洗剂纤维消失率。  相似文献   
34.
The baobab tree (Adansonia digitata L.) is a valued savannah tree. Although variation in fruit characteristics of this tree have been studied, no studies to our knowledge have been carried out on variation of leaf morphology which can be linked to drought adaptation mechanisms. Accessions of baobab from different ecosystems in Benin were characterised for leaf size and thickness, stomata size and density on the abaxial surface of leaves. Significant variation was found in leaf size and stomata characteristics. Trees from northern study sites had higher stomata density and smaller guard cell length than those from southern study sites. The results show that pruning has a significant effect on leaf size, but not on stomatal characteristics. Trees from northern study sites showed more xerophytic characteristics than those from the south. It seems that genetic and physiological effects may play a role in baobab drought adaptation.  相似文献   
35.
The response of different wheat cultivars to drought imposed after three and six weeks of seedling emergence was evaluated in the wire house. The seeds of recommended local wheat cultivars were sown in plastic pots. The drought stress decreased the water relation, nutrient uptake and grain yield of all the wheat cultivars. The early drought stress significantly reduced the nitrogen (N) uptake by 38% while late drought stress decreased nitrogen uptake by 46%. The phosphorus (P) and potassium (K) uptake were decreased by 49% and 37% under early drought stress, respectively while their uptake was decreased by 51% each under late drought stress. Grain yield was reduced by 24% under early drought stress while it was reduced by 60% under late drought stress. Water deficit at early growth stages reduced grain weight by 10% while it was reduced by 35% under water deficit at later stages of growth.  相似文献   
36.
The effects of soil amendments [i.e., control, gypsum, farmyard manure (FYM), and gypsum?+?FYM] and seed priming (i.e., unprimed, seed soaked in water for 10?hr prior to sowing, and seed soaked in 0.4% gypsum solution for 10?hr prior to sowing) were assessed on growth and yield of wheat (Triticum aestivum L.) crop in alkali soil in northwestern Pakistan. A split plot design was used, keeping priming methods in main plots and soil amendments in sub-plots. The results showed that the effects of soil amendments and seed priming on grain yield, straw yield, harvest index and number of spikes were significant but their interactive effect was non-significant. The highest crop yields and yield index were obtained with gypsum?+?FYM amendments, and seed priming with gypsum solution. The effect on seed emergence, plant height and number of grains per spike was, however, not significant. Grain yield increased by 104% in gypsum?+?FYM treatment over control and by 16.8% with seed primed in water, followed by 8.5% with priming in gypsum solution, as compared to non-priming. The weight of 1000 grains was significantly increased by 35% in gypsum?+?FYM treatment and by 15.8% in gypsum priming. The phosphorus (P) and potassium (K) content increased with soil amendments. Soil pH and gypsum requirement reduced significantly with soil amendments. The blend of gypsum and FYM has improved the properties of salt-affected soil and enhanced fertility for optimum production of wheat in addition to the beneficial effect of seed priming in gypsum solution on crop yield. Using these amendments could be ameliorative in removing the adverse effect of the salt-affected soils, rendering the soil a good medium for plant growth.  相似文献   
37.
Field and pot experiments were conducted to evaluate the effect of co-cultivation and crop rotation on the growth and corm rot disease of gladiolus (Gladiolus grandiflorus sect. Blandus) cv. Aarti caused by Fusarium oxysporum f.sp. gladioli (Massey) Snyd. and Hans. In the field experiment, gladiolus was co-cultivated with 10 agricultural/horticultural crops viz. Allium cepa L., Brassica campestris L., Capsicum annuum L., Eruca sativa Mill., Helianthus annuus L., Tagetes erectus L., Zea mays L., Vinca rosea L. and Rosa indica L., in a soil infested with F. oxysporum. All the crops except V. rosea and R. indica reduced disease incidence. The effect of H. annuus and T. erectus was significant and more pronounced than other co-cultivated crops. In general, root and shoot dry biomass, corm fresh weight, number of cormlets and number of flowers per spike decreased as compared to the un-inoculated monoculture gladiolus treatment (negative control) but these parameters enhanced as compared to the F. oxysporum inoculated monoculture gladiolus treatment (positive control). In a pot experiment, all the crops of the field experiment except V. rosea and R. indica were sown in rotation with gladiolus. Pot grown plants of different species were harvested at maturity and the soil was inoculated with F. oxysporum. Gladiolus was cultivated 1 week after inoculation. Disease incidence was significantly suppressed in all the treatments ranging from 29% to 53%. The highest suppression of disease incidence was recorded in T. erectus (53%) followed by B. campestris (49%). The effect of preceding crops on various vegetative parameters was similar in the pot experiment to that of the field experiment. The present study suggests that corm rot disease of gladiolus can be managed by mixed cropping of H. annuus and T. erectus or cultivation of T. erectus and B. campestris in rotation.  相似文献   
38.
Asian bears face major threats due to the impact of human activities as well as a critical lack of knowledge about their status, distribution and needs for survival. Once abundant in northern Pakistan, the Himalayan brown bear (Ursus arctos isabellinus) has been exterminated in most of its former distribution range. It presently occurs sparsely, in small populations, the Deosai National Park supporting the largest isolate. This decline might imply a reduction in genetic diversity, compromising the survival of the population. Using a combination of fecal DNA analysis and field data, our study aimed at assessing the size and genetic status of the Deosai population and give guidelines for its conservation and management. Using fecal genetic analysis, we estimated the population to be 40-50 bears, which compares well with the field census of 38 bears. The northern Pakistani brown bear population may have undergone an approximate 200-300-fold decrease during the last thousand years, probably due to glaciations and the influence of growing human population. However, in spite of the presence of a bottleneck genetic signature, the Deosai population has a moderate level of genetic diversity and is not at immediate risk of inbreeding depression. Gene flow might exist with adjacent populations. We recommend careful monitoring of this population in the future both with field observations and genetic analyses, including sampling of adjacent populations to assess incoming gene flow. The connectivity with adjacent populations in Pakistan and India will be of prime importance for the long-term survival of Deosai bears.  相似文献   
39.
Simultaneous measurement of the renal clearance of endogenous creatinine and exogenous inulin in eight sheep showed similar mean +/- SD (n = 32) values of 13.8 +/- 1.3 and 13.2 +/- 2.0 ml min-1 (10 kg)-1 bodyweight respectively. These results demonstrate that the renal clearance of endogenous creatinine is a satisfactory measure of glomerular filtration rate (GFR) in sheep. The plasma concentrations of endogenous creatinine and urea were significantly higher because of haemoconcentration during summer, resulting in lower GFR than in winter. Besides glomerular filtration and back diffusion, the renal handling of urea in sheep seems to involve mechanisms analogous to active tubular secretion.  相似文献   
40.
1. Two experiments were conducted to examine time of oviposition for hens exposed to continuous dim lighting, to dim lighting alternating with bright lighting in a 24 h cycle or to a mixed system using bright light, dim light and darkness. 2. Under continuous dim lighting (0.3 lux), the pattern of ovipositions was the same as that reported previously for constant darkness, more eggs being laid around midnight than around noon. 3. With alternating bright and dim phases, mean time of lay was approximately 16 h after the transition from bright to dim lighting, which was 3 h earlier than under the corresponding cycle of light and dark. This phase advance was the same whether the bright:dim ratio was 16:1 or 160:1. 4. Dim lighting (1.25 lux) preceded by a period of normal lighting (5 lux or 50 lux) and followed by 8 h darkness was treated as part of the photoperiod. 5. It is concluded that, when there is no darkness, a period of dim lighting is treated as darkness, provided the contrast between bright and dim phases is sufficient. However, when darkness, dim light and bright light are all included in a cycle, the dim light is treated as part of the photoperiod, even though there may be a contrast between the brightly lit and dimly lit phases which, in the absence of darkness, would cause the dim phase to be treated as dark.  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