全文获取类型
收费全文 | 25823篇 |
免费 | 1272篇 |
国内免费 | 2556篇 |
专业分类
林业 | 2239篇 |
农学 | 2253篇 |
基础科学 | 961篇 |
5686篇 | |
综合类 | 10223篇 |
农作物 | 1690篇 |
水产渔业 | 1365篇 |
畜牧兽医 | 3390篇 |
园艺 | 832篇 |
植物保护 | 1012篇 |
出版年
2024年 | 114篇 |
2023年 | 382篇 |
2022年 | 639篇 |
2021年 | 809篇 |
2020年 | 827篇 |
2019年 | 944篇 |
2018年 | 609篇 |
2017年 | 1139篇 |
2016年 | 1362篇 |
2015年 | 1160篇 |
2014年 | 1402篇 |
2013年 | 1758篇 |
2012年 | 2051篇 |
2011年 | 2046篇 |
2010年 | 1632篇 |
2009年 | 1600篇 |
2008年 | 1341篇 |
2007年 | 1537篇 |
2006年 | 1313篇 |
2005年 | 1014篇 |
2004年 | 814篇 |
2003年 | 700篇 |
2002年 | 509篇 |
2001年 | 471篇 |
2000年 | 441篇 |
1999年 | 381篇 |
1998年 | 364篇 |
1997年 | 323篇 |
1996年 | 297篇 |
1995年 | 288篇 |
1994年 | 246篇 |
1993年 | 257篇 |
1992年 | 210篇 |
1991年 | 161篇 |
1990年 | 146篇 |
1989年 | 123篇 |
1988年 | 83篇 |
1987年 | 64篇 |
1986年 | 34篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1962年 | 3篇 |
1956年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
71.
72.
73.
The effect of take-all root lesions on nitrate uptake of wheat was investigated in two experiments under controlled conditions. Plants were supplied with a nutrient solution labelled with 15 N during stem elongation and flowering to assess the distribution of the isotopic tracer in the different plant organs, and particularly in root segments located on both sides of take-all lesions. The 15 N atom percentage excess measured in root segments located below lesions longer than 1 cm was reduced on average by half compared with that in healthy roots and root segments above lesions, reflecting a reduction in nitrogen uptake by these root segments. This reduction probably resulted from the invasion and breakdown of phloem vessels by the fungus hyphae, interrupting energy supply and thus the uptake process. Severely infected plants showed an increase in the uptake rate per unit of efficient root, which appeared to be a compensatory response to reduction of efficient root biomass in order to satisfy shoot nitrogen demand. However, this compensatory response was insufficient to ensure nitrogen accumulation equivalent to that of healthy plants, as reductions in nitrogen accumulated in roots and aerial parts at flowering were up to 56 and 49%, respectively, for plants with more than 50% of the root system below lesions longer than 1 cm. 相似文献
74.
J Petersen 《Weed Research》2003,43(1):33-39
Summary The experiments were carried out in the two spring barley fields of the organic six-course cattle:crop rotation at Foulumgaard, Denmark. The weed density was 300 and 1800 plants m−2 respectively. Pig slurry was applied by hand in microplots by four methods: broadcasting followed by incorporation, or injected in bands to depths of 5, 10 or 15 cm. Spring barley and weeds were sampled separately six times during the tillering and elongation phase of the spring barley. The effect of application method on dry-matter (d.m.) production, nitrogen uptake and recovery of applied nitrogen in the spring barley and the weeds is reported. Slurry banding halved the weed d.m. and weed N uptake compared with broadcasting, irrespective of weed density. Weeds recovered up to 12% of the applied nitrogen, which made them a significant competitor when the slurry was broadcast and incorporated. Banding by direct injection reduced the slurry:soil contact and the weed:crop competition balance for applied nitrogen moved in favour of the crop. Thus, the crop recovery of applied nitrogen at the end of the sampling period was increased from approximately 45% for broadcast and incorporated to approximately 50% for injected slurry, and coincidental weed recovery was reduced to a maximum of 5%. As the nitrogen supply normally affects plant d.m. production, banding of slurry might well improve crop competitiveness and its tolerance to mechanical weed control. 相似文献
75.
稀土对刺槐苗木生理特性影响的研究 总被引:9,自引:1,他引:9
稀土对刺槐苗木生理特性影响的研究赵兰勇,梁玉堂(山东农业大学林学院泰安271018)王九龄(北京林业大学北京100083)关键词稀土,刺槐,光合速率,叶绿素含量,水分利用效率,矿质元素含量近年来,稀土元素在农业上的应用研究越来越受到人们的重视,并且已... 相似文献
76.
77.
优质牦牛肉肉质的综合评价 总被引:8,自引:0,他引:8
冶成君 《青海畜牧兽医杂志》2004,34(4):18-19
2000-2002年对大通牛场40头6月龄不同性别的全哺乳牦牛的肉质进行了综合评价。对供试牦牛肌肉pH、嫩度、肌纤维细度、系水率、肉的贮存损失、肉的煮熟时间、熟肉率和烹饪损失率及肉色等进行了评价,分析了肌肉的化学成分,氨基酸及微量元素含量。结果表明该牦牛肉系水率强,肉的煮熟时间短,肉的贮存损失及烹饪损失较小,肌纤维较细,肉色深红。并具有蛋白质含量高,脂肪含量低及富含各种氨基酸的特点。 相似文献
78.
79.
80.