全文获取类型
收费全文 | 18379篇 |
免费 | 924篇 |
国内免费 | 1760篇 |
专业分类
林业 | 644篇 |
农学 | 1625篇 |
基础科学 | 631篇 |
5781篇 | |
综合类 | 8205篇 |
农作物 | 1591篇 |
水产渔业 | 151篇 |
畜牧兽医 | 1227篇 |
园艺 | 682篇 |
植物保护 | 526篇 |
出版年
2024年 | 156篇 |
2023年 | 418篇 |
2022年 | 628篇 |
2021年 | 745篇 |
2020年 | 698篇 |
2019年 | 750篇 |
2018年 | 524篇 |
2017年 | 896篇 |
2016年 | 1121篇 |
2015年 | 890篇 |
2014年 | 999篇 |
2013年 | 1300篇 |
2012年 | 1512篇 |
2011年 | 1344篇 |
2010年 | 1075篇 |
2009年 | 1013篇 |
2008年 | 881篇 |
2007年 | 1051篇 |
2006年 | 939篇 |
2005年 | 712篇 |
2004年 | 499篇 |
2003年 | 435篇 |
2002年 | 319篇 |
2001年 | 263篇 |
2000年 | 285篇 |
1999年 | 174篇 |
1998年 | 180篇 |
1997年 | 184篇 |
1996年 | 186篇 |
1995年 | 146篇 |
1994年 | 114篇 |
1993年 | 115篇 |
1992年 | 117篇 |
1991年 | 89篇 |
1990年 | 79篇 |
1989年 | 79篇 |
1988年 | 48篇 |
1987年 | 42篇 |
1986年 | 24篇 |
1985年 | 9篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1963年 | 1篇 |
1962年 | 4篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
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
35.
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
36.
37.
38.
在陕西省关中土娄土区布置线辣椒、甘蓝、白菜、芹菜钾肥大田试验,研究不同蔬菜对钾肥的肥效反应。结果表明,增施钾肥可使蔬菜硝态氮含量降低11.8%~116.0%,维生素C含量增加0.4~147.4mg/kg;产量增加9.3%~33.8%;明显促进营养生长和生殖生长;400cm深土壤剖面硝态氮累积量减少22.7~48.0kg/hm2,尤其在80~220cm剖面减少最为明显。 相似文献
39.
不同地域环境对枸杞蛋白质和药用氨基酸含量的影响 总被引:12,自引:0,他引:12
根据2000~2001年我国北方六省(区)多点枸杞采样资料和田间试验资料,利用K-均值聚类方法和非线性回归方法,对比分析了宁杞1号枸杞蛋白质和9种药用氨基酸含量的差异和特点,以及生态因子对它们的影响。分析结果表明,不同地域栽种的宁杞1号枸杞蛋白质和9种药用氨基酸含量的变异系数分别为16.58%和16.22%,除品种因子的决定作用以外,环境条件对枸杞蛋白质含量有一定作用,其中土壤水解氮含量对蛋白质和氨基酸合成有一定作用,二者呈对数关系。 相似文献
40.
脂蛋白LPPQ是丝状霉形体丝状亚种SC型(MmmSC)非洲株、欧洲株和疫苗株所特有的。LPPQ N末端域具有良好的免疫原性,在牛体内可诱导产生强大、特异、早期、持续的免疫反应。本研究根据已发表的LPPQ基因序列设计引物,用Pyrobest^TM高保真DNA聚合酶从MmmSC HVRI X株中扩增出了LPPQ N末端基因序列,并进行了克隆与序列测定。核苷酸序列比较结果显示,HVRI X株的LPPQ N末端基因序列与国外发表的序列同源性为99.7%,由其推导的氨基酸序列同源性为99,1%,为脂蛋白LPPQ N末端基因体外表达奠定了基础。 相似文献