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   871篇
  免费   71篇
  国内免费   42篇
林业   141篇
农学   92篇
基础科学   15篇
  44篇
综合类   385篇
农作物   41篇
水产渔业   95篇
畜牧兽医   93篇
园艺   41篇
植物保护   37篇
  2024年   4篇
  2023年   14篇
  2022年   21篇
  2021年   30篇
  2020年   38篇
  2019年   44篇
  2018年   33篇
  2017年   27篇
  2016年   47篇
  2015年   28篇
  2014年   50篇
  2013年   59篇
  2012年   56篇
  2011年   50篇
  2010年   41篇
  2009年   46篇
  2008年   38篇
  2007年   50篇
  2006年   48篇
  2005年   49篇
  2004年   33篇
  2003年   20篇
  2002年   21篇
  2001年   25篇
  2000年   14篇
  1999年   17篇
  1998年   11篇
  1997年   12篇
  1996年   6篇
  1995年   9篇
  1994年   15篇
  1993年   5篇
  1992年   8篇
  1991年   3篇
  1990年   3篇
  1989年   2篇
  1988年   4篇
  1987年   2篇
  1986年   1篇
排序方式: 共有984条查询结果,搜索用时 875 毫秒
91.
苗青  赵夙铭  赵丽英 《油气储运》2005,24(11):13-16
根据东北管网原油输量下降后管网的结蜡情况,制定未来东北管网安全经济运行方案,利用东北管网大庆原油结蜡规律的研究成果,对东北管网未来的结蜡情况进行了预测和分析,得到了有价值的结论.  相似文献   
92.
In order to understand the cuticular wax properties of Asian pear fruits (cv. Pingguoli), a series of assays was conducted on extraction, fractionation and determination of composition. The results showed that the maximum yield of wax from the fruit was obtained by chloroform/methanol (3:1), and then by chloroform extraction. Polar and low polar fractions occupied 64.3% and 26.9% of total crude wax by column chromatography. 54 and 22 components were identified in polar and low polar fractions by GC/MS, respectively. Long-chain fatty acids and triterpenoids predominated in polar fraction and n-alkanes were predominant in low polar fraction. In vitro tests indicated that polar fraction, low polar fraction and total crude wax inhibited spore germination and mycelial growth of Alternaria alternata, which is a causal agent of Alternaria rot of pears, and the maximum inhibition was obtained by polar fraction. These findings indicated that n-alkanes in low polar fraction and triterpenoids, fatty acid in polar fraction might have contributed to the antifungal properties of pear fruit cuticular waxes.  相似文献   
93.
以乔木白蜡为试验品种,通过对不同时期土壤和植物叶片取样的养分检测及对植物生长量的监测,探讨不同施肥处理,特别是施用磷肥对白蜡生长量的影响。结果表明:合理使用有机肥和无机肥,特别是磷肥的合理使用,增加了植物对氮肥的吸收,促进了土壤氮素释放。说明了磷肥在白蜡生长过程中所起的重要作用,打破了园林苗木生长过程中主要以氮肥为主要肥料施用的观念,阐述了磷肥在白蜡生长过程中对其生长量所产生的显著影响。  相似文献   
94.
Conidial germination and differentiation, the so‐called prepenetration processes, of the barley powdery mildew fungus (Blumeria graminis f.sp. hordei) are triggered in vitro by very‐long‐chain aldehydes, minor constituents of barley leaf wax. However, until now it has not been demonstrated that these cuticle‐derived molecules also play a significant role in the initiation and promotion of the fungal prepenetration processes in vivo, on the surface of a living plant leaf. In the maize (Zea mays) wax mutant glossy11, which is completely devoid of cuticular very‐long‐chain aldehydes, germination and appressorial differentiation of B. graminis were strongly impeded. Spraying the mutant leaf surface with aldehyde‐containing wild‐type wax or pure n‐hexacosanal (C26‐aldehyde) fully restored fungal prepenetration, whereas maize wild‐type leaf surfaces coated with n‐docosanoic acid exhibited reduced conidial germination rates of 23%, and only 5% of the conidia differentiated infection structures. In vitro studies were performed to further corroborate the extensive prevention of fungal germination and differentiation in response to artificial surfaces coated with aldehyde‐deficient maize wax. Because of its phenotype affecting the B. graminis prepenetration processes, the glossy11 mutation of maize may become a valuable molecular target and genetic tool that could provide a means of developing basal powdery mildew resistance in the globally important crops wheat and barley.  相似文献   
95.
我国著名土壤和国土整治学家中科院学部委员朱显谟教授   总被引:24,自引:2,他引:24  
  相似文献   
96.
采用紫花芒、桂香芒、红象牙和印度1号芒果的果实,通过扫描电子显微镜观察,发现果实皮孔少,开口小,蜡质密度大的紫花芒果实耐贮藏。分泌腔多的桂香芒和印度1号果实芳香味浓。果肉薄壁细胞中淀粉粒增多,果实愈趋近成热。薄壁细胞中淀粉粒多的桂香芒,果实后熟后含糖量高。  相似文献   
97.
In-house composting has the potential to improve the viability of the high-rise house for commercial egg production by producing a value-added product from the manure without requiring a separate composting facility. The feasibility of in-house composting depends in part on having the ability to handle the manure mass that accumulates over an extended period. This field study showed that in-house composting is possible for the length of an egg production cycle. Beginning with windrows of a carbon source, fresh pine sawdust or shredded yard waste, upon which manure fell from the cage rows above, compost volume grew rapidly in the first few weeks, but slowed after composting activity peaked, as indicated by compost temperatures. In cold weather, when ventilation rates were low, compost remixing temporarily produced high ammonia levels in the house, but ammonia levels at other times were comparable to or lower than those in an undisturbed house. The final compost was friable and nutrient-rich, although the handling quality of the yard waste compost was reduced by persistence of elongated woody pieces of the original carbon source. The ability to access the manure storage area of a high-rise house over a cycle of production gives potential to deliver manure amendments to improve nitrogen retention in the compost, which would have the effect of improving its fertilizer value and reducing ammonia emission from the house.  相似文献   
98.
原油输送管道内涂层防结蜡问题研究   总被引:4,自引:0,他引:4  
管道内涂层可以减少原油中的蜡在管壁上的沉积量,利用自行设计的原油动态结蜡模拟装置,对比研究了不同涂层的防蜡率,以及在不同搅拌转速和不同的油温及壁温下管壁内涂层对防蜡率的影响。结果表明,涂层的防蜡率随着时间的增长有下降的趋势;搅拌速度越大,防蜡效果越好;壁温和油温对防蜡效果影响不大。  相似文献   
99.
The ability of two commercial rapid identification systems, API 20E and BBL Crystal E/NF, to reliably identify bacterial isolates from the internal organs of reared sea bass were compared. The tests gave different results: API 20E identified bacteria as Pseudomonas spp. with 37% accuracy, while BBL Crystal E/NF identified them as Flavobacterium odoratum with 99% accuracy. Although F. odoratum is not a marine fish pathogen, conventional tests conducted with the same isolates were more indicative of them being Flavobacterium spp. than Pseudomonas spp., suggesting that BBL Crystal E/NF was more reliable in this identification. Both systems were found to be applicable for diagnostics of marine fish pathogens, but should be used with caution because of possible misinterpretation.  相似文献   
100.
无机肥与有机肥配施对烟株农艺性状及烟叶产质量的影响   总被引:4,自引:0,他引:4  
为了解无机肥与商品牛粪配施对烟叶产质量的影响,采用田间试验方法,研究了商品牛粪与无机肥配合施用对烤烟植株农艺性状及烟叶产值量的影响。结果表明:商品牛粪与无机肥不同用量配合施用对烟株农艺性状的影响不明显,无机肥750kg/hm2+商品牛粪2 250kg/hm2能获得较好的经济效益,无机肥750kg/hm2+商品牛粪1 500kg/hm2对上部烟叶化学品质有一定的改善作用。烤烟大田生产中施用无机肥750kg/hm2配施商品牛粪1 500~2 250kg/hm2有利于提高烟叶的产质量和经济效益。  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