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   168篇
  免费   7篇
林业   33篇
基础科学   1篇
  31篇
综合类   23篇
农作物   1篇
水产渔业   18篇
畜牧兽医   62篇
园艺   3篇
植物保护   3篇
  2022年   1篇
  2021年   2篇
  2020年   7篇
  2019年   10篇
  2018年   7篇
  2017年   3篇
  2016年   5篇
  2015年   1篇
  2013年   11篇
  2012年   8篇
  2011年   7篇
  2010年   9篇
  2009年   15篇
  2008年   11篇
  2007年   12篇
  2006年   8篇
  2005年   8篇
  2004年   9篇
  2003年   5篇
  2002年   4篇
  2001年   2篇
  2000年   2篇
  1999年   4篇
  1998年   3篇
  1997年   2篇
  1995年   1篇
  1992年   1篇
  1991年   2篇
  1987年   1篇
  1986年   1篇
  1985年   2篇
  1982年   1篇
  1977年   1篇
  1924年   1篇
  1916年   3篇
  1915年   2篇
  1914年   2篇
  1905年   1篇
排序方式: 共有175条查询结果,搜索用时 15 毫秒
41.
42.
INTRODUCTIONEllca{opIusmicrolhccaF.MucII.(coolibal1)l1asawidegeographicrangemainly``-itl1intl1caridandscl11i-aridzonesofAustralia(Bola11dctal.l984).Tl1erangcoflatitlldeisl4-33Su-itl1analtitudinalrangeofJustabovesealeveIto7oom.Tl1crcislcssvariationincli-ma…  相似文献   
43.
A field-based study was carried out to broaden our knowledge of fully mechanized cut-to-length harvesting productivity in naturally grown forests in the northern European part of Russia (NEPR). The recorded data comprised 38 midsized single-grip harvesters (JD 1270D) in clear-cutting operations in the Karelia, Komi, Vologda, Leningrad, Tver, and Kirov regions in NEPR, 4.3 million felled trees, and 1.4 million m3 u.b. (under bark) of processed timber. Harvesting operations were conducted in forest stands composed of spruce (48% on average), pine (19%), birch (22%), and aspen (11%), with an average stem volume 0.31 m3 u.b. The cut-to-length harvesters produced from 4.3 to 14.9 m3 u.b./productive machine hour (PMH) and 16.0–49.5 m3 u.b./stem processing machine hour (S proc MH). A machine evaluation analysis and a regression analysis were used to formulate models for predicting cutting productivity of modern single-grip harvester. The regression models were developed to estimate the productivity of the harvesters in the regions taking into account two significant factors influencing the productivity: the stem volume and tree species of the felled trees. Productivity/cubic meter u.b. of processed timber/PMH was calculated according to stem volume and tree species distributions in most forest-covered NEPR regions. Further research is suggested to improve the developed productivity models and to allow prediction of system performance over a broad range of stand and site conditions.  相似文献   
44.
在内蒙古阿尔山的田间诱捕试验中,落叶松八齿小蠹引诱剂1共诱集到16头落叶松八齿小蠹和1319头天敌红胸郭公虫,而落叶松八齿小蠹引诱剂2诱集到24104头落叶松八齿小蠹和776头红胸郭公虫。室内的触角电位试验结果表明:落叶松八齿小蠹对引诱剂2的触角反应(雌虫2.139mV±0.678mV,雄虫2.169mV±0.473mV)大于引诱剂1(雌虫0.440mV±0.232mV,雄虫0.297mV±0.142mV),对引诱剂1的反应值和对照差不多;而红胸郭公虫对引诱剂1的触角反应(雌虫4.618mV±1.106mV,雄虫4.534mV±1.087mV)明显大于引诱剂2(雌虫2.209mV±0.680mV,雄虫1.953mV±0.601mV),对引诱剂2也有一定的反应值。触角电位试验与田间诱捕试验结果相符合。GC-MS分析结果表明:引诱剂1的主要成分为3.06%的cis-geraniol,1.98%的Ipsenol,80.36%的(S)-cis-verbenol和1.03%的1-verbenone;结合卖方公司提供的数据,引诱剂1的主要成分为4.78%的2-methyl-3-buten-2-ol,63.71%的Ipsenol(纯度为96.9%),1.46%的Cedrene和22.42%的Isocaryophillene。结合以上数据分析得出:不同成分引诱剂对落叶松八齿小蠹及天敌红胸郭公虫引诱能力显著不同,Ipsenol对诱集落叶松八齿小蠹起重要作用,而(S)-cis-verbenol则对诱集天敌红胸郭公虫起重要作用。  相似文献   
45.
46.
A 6-month-old female alpaca was presented for stranguria. Based on the history, physical examination findings, and radiographic studies, the alpaca was diagnosed with bladder outlet obstruction, secondary to pelvic displacement of the bladder, a condition previously unreported in camelids. Cystopexy was performed and the alpaca recovered unremarkably.  相似文献   
47.
Two experiments were conducted to investigate the effects of 1,25(OH)2D3 to stimulate Na+-dependent phosphate uptake in Caco-2 cells, and the effects of dietary vitamin D supplementation to vitamin D-deficient nursery pigs on Na+-dependent nutrient uptake and mRNA expression of NaPi-IIb cotransporter and calbindin D9k in the jejunum. In Exp. 1, 250,000 Caco-2 cells were seeded on Costar 12 mm Snapwell inserts with a 0.40 µm polycarbonate filter and a seeding density of 0.25 × 106 and studied at 15 d postconfluence. Cells were treated with 10 nM of either 1,25(OH)2D3 or vehicle for 48 h and then mounted in modified Ussing chambers for transepithelial measurements. In Exp. 2, pigs (n = 32) were removed from sows at 3 d of age, placed on a vitamin D-deficient milk replacer diet and housed in a room devoid of sunlight and UV light in the range of 280 to 300 nm. On day 28, serum 25(OH)D3 concentrations were measured to verify low vitamin D status. Pigs (BW 10.10 ± 0.38 kg) were then individually housed day 28 postweaning and allotted to 1 of 2 dietary treatments. Dietary treatments consisted of corn-soybean-based diets with vitamin D supplementations of 0 or 1,500 IU/kg diet for 12 d. Blood samples were taken from the brachiocephalic vein on the initial (day 0) and final day (day 10, 11, or 12) of the study for analysis of serum 25(OH)D3, P, and Ca. Pigs were euthanized and jejunal segments were harvested and used in modified Ussing chambers and for RNA isolation and subsequent quantitative RT-PCR analysis. In Exp. 1, treating Caco-2 cells with 10 nM 1,25(OH)2D3 resulted in a 52% increase (P < 0.005) in Na+-dependent phosphate uptake compared with cells treated with a vehicle. In Exp. 2, Na+-dependent phosphate and glucose transport did not differ (P > 0.10) among treatment groups. Additionally, NaPi-IIb and calbindin D9k mRNA expression were not different (P > 0.10) between treatment groups. No differences (P > 0.10) were detected in final serum P or 25(OH)D3 concentrations between treatments. However, serum Ca linearly increased (P < 0.05) as the concentration of supplemental vitamin D increased in the diet. Overall, while 1,25(OH)2D3 stimulated Na+-dependent phosphate uptake in Caco-2 cells, supplementing diets with 1,500 IU/kg vitamin D3 from cholecalciferol did not increase jejunal Na+-dependent phosphate uptake or NaPi-IIb mRNA expression over that of pigs fed diets with no supplemental cholecalciferol.  相似文献   
48.
不同药剂处理对库尔勒香梨枝条抗冻性的影响   总被引:1,自引:0,他引:1  
以库尔勒香梨为试验材料,秋季落叶前2周进行水杨酸(SA)0.5,1.0,2.0 mmol/L,腐胺(Put)1.0,5.0,10.0 mmol/L,亚精胺(Spd)0.5,1.0,2.0 mmol/L等3个药剂、9个不同处理,取样后在人工低温处理条件下分析库尔勒香梨的抗冻性。试验结果表明,相对电导率、脯氨酸、MDA、SOD的累积贡献率达到94.1%,可作为库尔勒香梨主要的抗寒性鉴定指标,其中,相对电导率贡献率为71.6%,可单独作为库尔勒香梨抗寒性的鉴定指标。3种药剂处理后枝条的抗冻强弱顺序为1.0 mmol/L SA〉2.0 mmol/L SA〉5.0 mmol/L Put〉1.0 mmol/L Spd〉0.5 mmol/L Spd〉对照。在生产实践中,可根据实际情况于果实采收后喷施浓度1.0-2.0 mmol/L的水杨酸,以提高库尔勒香梨在越冬期的抗冻性。  相似文献   
49.
Compliance with a 10-day course of oral antibacterial drugs in dogs being treated as outpatients at a veterinary clinic was assessed by use of pill count data obtained by telephone interview. The association between compliance and several possible determinants of compliance was investigated. Ninety-five animal owners were included in the study, with 44 per cent reporting 100 per cent compliance with the treatment regimen and as many as 88 per cent reporting a compliance level of 80 per cent or more. The compliance level was significantly higher (P < 0.002) when the animal owners felt that the veterinarians spent enough time on the consultation. Moreover, compliance was significantly higher (P < 0.05) for dogs being treated for gastrointestinal infections compared with those being treated for other diseases.  相似文献   
50.
Applied-field Mössbauer spectra are reported for selected synthetic samples of α-Fe1-xAlxOOH, γ-Fe1-xAlxOOH, δ-FeOOH, α-(Fe1-xAlx)2O3 and γ-Fe2O3. Field strengths of up to 90 kOe were used at temperatures of mostly 4.2 K. The effects of the Al substitution and/or the crystallinity are discussed. Specific characteristics of the spectra are enlightened which might serve as complimentary sources of information for the characterization of soil oxides and oxyhydroxides. It is pointed out that several questions remain unanswered to date and that further systematic research is justified.  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