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   745篇
  免费   54篇
  国内免费   50篇
林业   73篇
农学   31篇
基础科学   15篇
  62篇
综合类   252篇
农作物   44篇
水产渔业   111篇
畜牧兽医   182篇
园艺   30篇
植物保护   49篇
  2024年   5篇
  2023年   8篇
  2022年   21篇
  2021年   33篇
  2020年   22篇
  2019年   42篇
  2018年   40篇
  2017年   36篇
  2016年   52篇
  2015年   32篇
  2014年   32篇
  2013年   51篇
  2012年   49篇
  2011年   51篇
  2010年   43篇
  2009年   45篇
  2008年   31篇
  2007年   18篇
  2006年   30篇
  2005年   24篇
  2004年   10篇
  2003年   26篇
  2002年   24篇
  2001年   18篇
  2000年   11篇
  1999年   15篇
  1998年   12篇
  1997年   4篇
  1996年   8篇
  1995年   4篇
  1994年   6篇
  1993年   7篇
  1992年   4篇
  1991年   4篇
  1990年   4篇
  1989年   3篇
  1988年   5篇
  1987年   3篇
  1986年   1篇
  1984年   3篇
  1983年   1篇
  1982年   6篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
  1975年   1篇
  1974年   1篇
排序方式: 共有849条查询结果,搜索用时 437 毫秒
41.
Pome fruits are poor in nitrogenous compounds and the addition of nitrogen can improve colonisation of the fruits by antagonists. Twenty-two nitrogenous compounds were evaluated for their effect on Candida sake (CPA-1) growth in vitro. Ten compounds that induced greater growth were applied with the antagonist to wounded fruits to evaluate their effect on enhancing control of Penicillium expansum. Calcium chloride and 2-deoxy-D-glucose were also tested. L-serine and L-aspartic acid enhanced biocontrol by C. sake against P. expansum on apples. On apples and pears, ammonium molybdate, calcium chloride and 2-deoxy-D-glucose improved the capacity of the antagonist to control P. expansum. The addition of ammonium molybdate at 1 mM allowed C. sake to be used on apples and pears at a lower concentration without diminishing control. Similar results were observed with the addition of calcium chloride to the antagonist. 2-deoxy-D-glucose at 6 and 18 mM enhanced biocontrol on pears by over 81%, but on apples the improvement of biocontrol was observed only at 6 mM. In cold storage, the combination of ammonium molybdate and C. sake completely eliminated the incidence of blue mould on pears, and reduced its severity and incidence by more than 80% on apples.  相似文献   
42.
The occurrence of trichostrongylid nematodes in young cattle was studied in relation to climate and geographical location, by examination of herbage and faecal samples from 8 farms in 7 different regions in Norway, during 3 consecutive summers. Species of Ostertagia and Cooperia were dominant. Infective larvae, especially those of Ostertagia, were able to survive the winter in the pasture to a great extent in all the areas studied. The spring larval counts varied considerably from place to place, and from year to year, but were often at fairly high levels. This confirms previous findings that the larvae which overwinter on the pasture may be a major cause of losses. Overt clinical disease, however, was only seen at 1 farm during this investigation.The large number of larvae often seen in the autumn seems to be of less significance as a cause of disease, due to the late appearance, but is of major importance as a source of the larvae which survive the winter in the pasture and infect young cattle the following spring.There was no obvious correlation between pasture larval counts and the climate, except that there seemed to be higher counts in the warmer parts of the country, where the grazing season is also longer. The only place were both faecal egg counts and larval counts in the herbage were consistently low, was in the very far north.  相似文献   
43.
In evaluating radiographs of the limb joints and head, students encounter difficulty where superimposition occurs. By replacing calcium with silver salts in the bone, enhanced radiopacity can be produced. In this study, silver impregnation was used to increase the radiopacity of individual carpal and tarsal bones, selected bones of the skull and the sinuses, and guttural pouch of the horse. This provides an interpretation aid for teaching radiographic anatomy of these regions.  相似文献   
44.
大白菜游离小孢子培养胚胎发生中的加倍机制   总被引:6,自引:0,他引:6  
 利用Leica体视显微镜, DAPI荧光染色观察比较大白菜小孢子正常发育为成熟花粉粒与游离小孢子培养胚胎发生细胞核的分裂方式, 探讨大白菜游离小孢子培养胚胎发生及其自然加倍的机理。观察结果显示以B途径为主要发育途径的大白菜小孢子, 胚胎发生的启动机制是热激诱导下单倍体小孢子体积膨大, 染色体发生自然加倍, 从而激发小孢子进入孢子体发育途径; 大白菜小孢子胚再生植株具有较高的自然加倍率, 这与小孢子培养热激诱导激发小孢子单核自然加倍为二倍体密切相关。  相似文献   
45.
2006年2月18~23日位于祁连山南麓天峻县的生格乡地区,先后有20多只岩羊突然死亡。通过对捕获岩羊的临床检查、栖息地调查和对其周围牧户的访问结果表明:岩羊在短时间大量死亡是多种病原体和作为应激源气候因子(大雪、大风和强烈的太阳光直接照射和雪地反射)的联合作用导致岩羊患传染性角膜结膜炎病失明而从悬崖处摔死的结果,而人类活动导致的生境破碎化加剧了本病的发生、流行和患病动物的死亡。  相似文献   
46.
陆生固氮蓝藻对土壤环境的影响   总被引:8,自引:2,他引:6  
我们于1988-1990-年通过野外调查和室外试验,探讨了陆生固氮蓝藻对土壤环境的影响。试验证明,陆生固氮蓝藻可以利用空气中的分子态氮合成氮素化合物,不断地加富土壤中的氮化物。同时,由于它们大量的繁殖和死亡腐解也增加了土壤中的有机物质使土肿微生物的生长和活动更加旺盛,土  相似文献   
47.
Abstract

Two laboratory-scale, upflow anaerobic reactors were constructed to treat blue crab (Callinectes sapidus) cooking wastewater for determination of the volume and composition of the resulting bio-gas. Both systems (A and B) consisted of two 4-liter (L) upflow anaerobic reactors and one 8-L aerobic reactor in series. The first anaerobic reactor of System A contained 240,12.7 mm foam cubes, while the first anaerobic reactor of System B contained 180 foam pieces (25.4 ×25.4 ×12.7 mm). Biogas production rates for System A ranged from 6.6 L gas/L feed to 10.0 L gas/L feed. Mean values for System B ranged from 7.1 L gas/L feed to 11.9 L gas/L feed. Methane and carbon dioxide comprised 68% and 28%, respectively, of the gas from both systems. Hydrogen sulfide averaged 1.5% and 1.4% for systems A and B, respectively. A pilot-scale biogas collection and utilization system was also constructed and successfully demonstrated. Details of the pilot-scale system design are provided in the paper to help processors better understand how the technology might be applied.  相似文献   
48.
49.
氧化石墨烯(Graphene Oxide,GO)拥有较大的比表面积和较高的稳定性,可用来吸附水体中的多种污染物,其潜在功能稳定性具有规模化应用前景。考虑到GO在高级氧化体系中结构和形貌会发生改变,探究了经UV/H2O2和UV/过硫酸盐(Persulfate, PS)产生强氧化性自由基的体系处理后所得GOs对亚甲基蓝(Methylene Blue, MB)的吸附性能。氧化性自由基体系光源为300 W中压汞灯,30 mL GO储备液(1 mg/mL)在2种氧化体系下反应1、2、4 h后制得GOs。实验考察了不同反应条件对GOs吸附动力学的影响,傅里叶变换红外光谱(FTIR)研究了GOs氧化前后表面官能团的变化。结果显示,经UV/H2O2, UV/PS氧化1 h后,GOs表面的含氧官能团数量开始明显减少;吸附动力学过程更符合准二级动力学模型(R2>0.999);吸附热力学过程更符合Langmuir模型,MB饱和吸附量(经UV/H2O2和UV/PS氧化1、2、4 h后分别记G1-1, G1-2, G1-3, G2-1, G2-2, G2-3)依次为580.26, 591.80, 598.63, 521.77, 554.91, 568.00 mg/g。研究表明,GO可以快速吸附较大浓度范围内的MB,且对低浓度染料表现出更好的去除效果;GO对MB的吸附量随着pH值的增加逐渐增大,且在碱性条件下的增加得更明显;经氧化处理后,GOs的吸附性能随着氧化时间的增长,性能减弱,尤其在UV/PS体系中更为显著。  相似文献   
50.
美式家具仿古涂饰工艺技术   总被引:2,自引:0,他引:2  
研究美式家具仿古涂装中的木材着色剂和涂装工艺技术.通过对着色材料成分、着色方法和机理的分析,说明不同的着色剂的作用和适用环境,并介绍仿古做旧的具体工艺程序和操作要点.  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