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   519篇
  免费   56篇
  国内免费   29篇
林业   33篇
农学   6篇
基础科学   3篇
  45篇
综合类   112篇
农作物   20篇
水产渔业   33篇
畜牧兽医   293篇
园艺   18篇
植物保护   41篇
  2023年   9篇
  2022年   14篇
  2021年   9篇
  2020年   10篇
  2019年   20篇
  2018年   21篇
  2017年   32篇
  2016年   21篇
  2015年   17篇
  2014年   11篇
  2013年   35篇
  2012年   17篇
  2011年   9篇
  2010年   12篇
  2009年   20篇
  2008年   20篇
  2007年   32篇
  2006年   23篇
  2005年   29篇
  2004年   19篇
  2003年   26篇
  2002年   22篇
  2001年   16篇
  2000年   11篇
  1999年   8篇
  1998年   12篇
  1997年   8篇
  1996年   5篇
  1995年   3篇
  1994年   4篇
  1993年   4篇
  1992年   9篇
  1991年   5篇
  1990年   10篇
  1989年   4篇
  1988年   10篇
  1987年   5篇
  1986年   10篇
  1985年   3篇
  1984年   4篇
  1983年   2篇
  1981年   2篇
  1979年   5篇
  1977年   2篇
  1976年   4篇
  1973年   4篇
  1971年   4篇
  1900年   4篇
  1893年   1篇
  1890年   1篇
排序方式: 共有604条查询结果,搜索用时 15 毫秒
111.
通过放牧梯度试验,研究放牧对内蒙古典型草原5种优势植物在个体、种群和群落水平上的影响,探讨大针茅(Stip grandis)对放牧生态系统植物群落地上生物量的调控作用。结果表明:个体水平,中轻度放牧对以大针茅和糙隐子草(Cleistogenes squarrosa)为代表的丛生禾草株高影响较小,对以羊草(Leymus chinensis)、黄囊苔草(Carex korshinskyi)和米氏冰草(Agropyron michnoi)为代表的根茎型禾草株高影响较大,植物株高的降低与个体地上生物量减少呈显著正相关。种群水平,大针茅种群生物量对放牧的响应迟缓,羊草、米氏冰草、糙隐子草和黄囊苔草种群生物量的减少与多度减少呈显著正相关。群落水平,大针茅的耐牧性使其成为资源重配的获益者,轻中度放牧干扰下,其地上生物量的补偿生长缓冲了放牧对群落的影响,对维持群落生产力与功能稳定性起重要的调控作用。  相似文献   
112.
玉米秸秆低温降解复合菌系的筛选   总被引:7,自引:0,他引:7  
【目的】为加快北方高寒地区玉米秸秆降解速度,筛选低温条件下具有良好降解玉米秸秆的复合菌系。【方法】以富含纤维素的腐烂物为菌源,通过滤纸崩解初筛、酶活和秸秆降解率为指标复筛进行玉米秸秆降解菌系的筛选,并对其成分进行分析。【结果】从腐烂的树叶和高原锯末中筛选到两组玉米秸秆降解复合菌系1号和8号。1号和8号复合菌系在玉米秸秆培养基中,15℃培养15 d,玉米秸秆分解率分别达到30.21%和32.21%;1号复合菌系包含木霉和多种细菌,8号复合菌系含青霉和多种细菌;两组复合菌系优势细菌均为梭菌属和芽孢杆菌属菌种。【结论】筛选到的菌系在低温(15℃)实验室条件下能降解玉米秸秆,菌系主要组成是木霉、青霉、梭菌属(Clostridium sp.)、芽孢杆菌属(Bacillus sp.)和草螺菌属(Herbaspirillum sp.)的细菌。  相似文献   
113.
三株芽孢杆菌抑菌活性分析及对肉鸡舍空气微生物的影响   总被引:1,自引:0,他引:1  
【目的】分析2株解淀粉芽孢杆菌(Bacillus amyloliquefaciens)和1株苏云金芽孢杆菌(Bacillus thuringiensis)的基本特性以及对大肠埃希氏菌(Escherichia.coli,CVCC1570)的抑制活性;分析3株芽孢杆菌复合制剂对肉鸡舍空气大肠杆菌和金黄色葡萄球菌的抑制作用,为改善畜舍环境提供基础数据。【方法】对3株芽孢杆菌进行形态学观察、镜检和生长曲线测定,以大肠埃希氏菌(CVCC1570)为指示菌株,采用琼脂扩散法对单一菌株的抑菌特性进行测定,筛选出适宜的抑菌浓度;利用三因子三水平的正交试验设计,筛选出最佳抑菌效果的复合芽孢杆菌组合;鸡舍喷洒试验采用单因子设计,分为3个处理组,每个处理设3个重复,分别为空白对照组,化学消毒剂阳性对照组(苯扎氯铵),喷洒复合芽孢杆菌菌剂处理组。在肉鸡不同日龄检测鸡舍内大肠杆菌和金黄色葡萄球菌的变化规律。【结果】3株芽孢杆菌为革兰氏阳性需氧菌。芽孢杆菌SKN01和芽孢杆菌SKN02生长曲线相近,在培养2h开始进入对数生长期。芽孢杆菌SKN03生长较缓慢,进入对数生长期的时间相对较长。单一菌株对大肠埃希氏菌有效抑菌浓度均为108CFU•mL-1。经正交试验测定,3株芽孢杆菌复合菌液最佳抑菌组合为4×108 CFU•mL-1、4×108 CFU•mL-1、6×108 CFU•mL-1。最佳组合复合芽孢杆菌喷洒鸡舍,能够有效抑制大肠杆菌和金黄色葡萄球菌的生长,在肉鸡生长后期复合制剂的抑菌效果明显。【结论】3株芽孢杆菌能够有效抑制大肠埃希氏菌,同时复合菌液能够有效减少鸡舍有害微生物的数量,起到改善鸡舍环境的作用。  相似文献   
114.
以薏米和枸杞为主要原料制成一种保健饮品。通过正交试验,确定最佳生产配比为:蔗糖5%,柠檬酸0.2%,薏米、枸杞的比例为3∶1。对饮料的可溶性固形物、酸度、还原糖、金属元素、氨基酸含量等指标进行测定。结果为:可溶性固形物5.76%;pH值5.42;还原糖含量17.9mg·L-1。Zn、Mg、Na、Fe、Mn、Ca、K等7种金属元素的含量分别为0.0045,4.7855,35.1020,0.0169,0.0060,4.7429,22.3690g·L-1。Cd、Pb、Cr、Cu、Co等均未测出,且含有16种氨基酸,总量为22.79μg·L-1。  相似文献   
115.
The results from two trials with Cox’s Orange Pippin concerned with the development of primary branches are reported. The first trial, with newly planted one-year-old trees, compared the use of feathers as primary branches with trees where these were removed and new shoots selected as branches. Where feathers were retained the trees had larger girths, more shoots, greater total shoot growth, and the final tree weights were heavier. The crotch angles of all three primary branches were wider where feathers were utilized. On feathered trees there was no advantage in leaving the central leader uncut for the first year. The second trial, in the nursery, showed that by removal of incipient feathers up to 70 cm. from the ground, more and longer feathers were secured in the region where primary branches are required. Trunk renewal, involving the drastic cutting back of the maiden tree to within 5 cm. of the bud union, did not increase the number and length of feathers the following year in this trial.  相似文献   
116.
The field performance of 27 apple rootstock clones, including M.XXV and all the Malling-Merton ones is reviewed over a fifteen-year period. Three scion varieties were used, Cox’s Orange Pippin, Jonathan and Ellison’s Orange, and the trials were planted both on loam and on sand soil types.

None of the new clones made trees as small as those on M.IX, their vigour ranging from that of M.VII to that of M.XVI. MM.106 made trees similar in size and cropping to those on M.VII on the loam soil, but on the sand they were smaller. MM.I06, unlike M.VII, was free from the suckering habit. Trees on MM.III and M.Il were similar in size but Cox on MM.III yielded 20% more fruit over the whole period of the trial and during the years 11 to 15. Trees on MM.I04 were heavy-bearing and larger than those on M.Il and MM.III. In the very vigorous group, MM.Iog cropped heavily but was poorly anchored. Trees on M.XXV were superior in this respect and cropped more heavily than those on M.XVI. Cox and Ellison were unthrifty on 829, but the Jonathan trees behaved normally. Jonathan on MM.102 showed severe interveinalleaf scorch symptoms of magnesium deficiency and cropping was poor.

Many of the new rootstocks fell into similar vigour groups. It is suggested that, in other apple-growing areas of the world, other rootstocks besides MM.104, MM.106, MM.III and M.XXV, which were selected .for English conditions, should be tried experimentally. The data presented suggest MM.1O1, MM.103, MM.110, MM.115 and MM.116 as worthy of local study in addition to the four others.  相似文献   
117.
In experiments during 1967 and 1968 three French bean cultivars, Processor, Meteor and Tenderlong, were harvested twice-weekly as the crop matured. Field and laboratory tests, viz. alcohol-insoluble-solids (AIS), dry matter (DM), seed percentage, seed length and shear press values, were assessed as indices of maturity.

Seed percentage and seed length increased with successive harvests but proved subject to variation with cultivar and with season. Shear values obtained using 100-g samples did not increase significantly with successive harvests. Both AIS and DM were good indices of maturity and were highly correlated (r > 0.99) with each other in both seasons.  相似文献   
118.
119.
Dakota Pearl (ND2676-10) is a medium-maturing chipping cultivar with uniform, round, bright white-skinned tubers with shallow eyes. Dakota Pearl has the ability to produce commercially acceptable chips following long-term storage at 5.5 C without the need for reconditioning. It yields well under both dryland and irrigated trial conditions in North Dakota. North Central Regional Potato Variety Trial and Snack Food Association Trial results indicate it has wide adaptability. Yield and specific gravity under dryland conditions are similar to Norchip; Dakota Pearl has a low percentage of external defects. Average set is 12 to 14 tubers per hill. Dakota Pearl demonstrates wide consumer appeal as a tablestock cultivar due to attractive tuber appearance and bright-white skin. Sensory evaluation scores for baking, boiling, and microwaving are comparable to those of standard chip cvs Atlantic, NorValley, and Snowden. The specific gravity of Dakota Pearl is similar to cvs Norchip and NorValley, lower than for Atlantic or Snowden. Total glycoalkaloid levels are low, at 1.5 mg/100 g fresh tuber tissue. The North Dakota Agricultural Experiment Station released Dakota Pearl on 23 April 1999.  相似文献   
120.
Snow cover is an important water source for vegetation growth in arid and semi-arid areas,and grassland phenology provides valuable information on the response of terrestrial ecosystems to climate change.The Mongolian Plateau features both abundant snow cover resources and typical grassland ecosystems.In recent years,with the intensification of global climate change,the snow cover on the Mongolian Plateau has changed correspondingly,with resulting effects on vegetation growth.In this study,using MOD10A1 snow cover data and MOD13A1 Normalized Difference Vegetation Index(NDVI)data combined with remote sensing(RS)and geographic information system(GIS)techniques,we analyzed the spatiotemporal changes in snow cover and grassland phenology on the Mongolian Plateau from 2001 to 2018.The correlation analysis and grey relation analysis were used to determine the influence of snow cover parameters(snow cover fraction(SCF),snow cover duration(SCD),snow cover onset date(SCOD),and snow cover end date(SCED))on different types of grassland vegetation.The results showed wide snow cover areas,an early start time,a late end time,and a long duration of snow cover over the northern Mongolian Plateau.Additionally,a late start,an early end,and a short duration were observed for grassland phenology,but the southern area showed the opposite trend.The SCF decreased at an annual rate of 0.33%.The SCD was shortened at an annual rate of 0.57 d.The SCOD and SCED in more than half of the study area advanced at annual rates of 5.33 and 5.74 DOY(day of year),respectively.For grassland phenology,the start of the growing season(SOS)advanced at an annual rate of 0.03 DOY,the end of the growing season(EOS)was delayed at an annual rate of 0.14 DOY,and the length of the growing season(LOS)was prolonged at an annual rate of 0.17 d.The SCF,SCD,and SCED in the snow season were significantly positively correlated with the SOS and negatively correlated with the EOS and LOS.The SCOD was significantly negatively correlated with the SOS and positively correlated with the EOS and LOS.The SCD and SCF can directly affect the SOS of grassland vegetation,while the EOS and LOS were obviously influenced by the SCOD and SCED.This study provides a scientific basis for exploring the response trends of alpine vegetation to global climate change.  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