全文获取类型
收费全文 | 21176篇 |
免费 | 5990篇 |
国内免费 | 326篇 |
专业分类
林业 | 3110篇 |
农学 | 3411篇 |
基础科学 | 1943篇 |
4305篇 | |
综合类 | 6705篇 |
农作物 | 1321篇 |
水产渔业 | 891篇 |
畜牧兽医 | 3329篇 |
园艺 | 714篇 |
植物保护 | 1763篇 |
出版年
2025年 | 20篇 |
2024年 | 299篇 |
2023年 | 317篇 |
2022年 | 557篇 |
2021年 | 903篇 |
2020年 | 896篇 |
2019年 | 805篇 |
2018年 | 577篇 |
2017年 | 805篇 |
2016年 | 777篇 |
2015年 | 1022篇 |
2014年 | 939篇 |
2013年 | 1183篇 |
2012年 | 1386篇 |
2011年 | 1446篇 |
2010年 | 1434篇 |
2009年 | 1349篇 |
2008年 | 1258篇 |
2007年 | 1384篇 |
2006年 | 1284篇 |
2005年 | 1094篇 |
2004年 | 536篇 |
2003年 | 496篇 |
2002年 | 408篇 |
2001年 | 432篇 |
2000年 | 544篇 |
1999年 | 683篇 |
1998年 | 610篇 |
1997年 | 521篇 |
1996年 | 513篇 |
1995年 | 504篇 |
1994年 | 454篇 |
1993年 | 405篇 |
1992年 | 371篇 |
1991年 | 293篇 |
1990年 | 240篇 |
1989年 | 204篇 |
1988年 | 162篇 |
1987年 | 97篇 |
1986年 | 69篇 |
1985年 | 35篇 |
1984年 | 20篇 |
1983年 | 36篇 |
1982年 | 21篇 |
1981年 | 24篇 |
1980年 | 15篇 |
1979年 | 8篇 |
1974年 | 9篇 |
1964年 | 6篇 |
1963年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 612 毫秒
901.
A hydroponic experiment was carried out to study effects of chromium (Cr) stress on the subcellular distribution and chemical form of Ca, Mg, Fe, and Zn in two rice genotypes differing in Cr accumulation. The results showed that Ca, Mg, Fe, and Zn ions were mainly located in cell walls and vacuoles in roots. However, large amounts of metal ions were transferred from the vacuole to the nucleus and to other functional organelles in shoots. Chromium concentrations in the nutrient solution of 50 μM and above significantly decreased Ca concentrations in the chloroplast/trophoplast, the nucleus, and in mitochondria. It further increased Mg concentrations in the nucleus and in mitochondria, as well as Zn and Fe concentrations in the chloroplast/trophoplast. These Cr‐induced changes in ion concentrations were associated with a significant reduction in plant biomass. It is suggested that Cr stress interferes with the functions of mineral nutrients in rice plants, thus causing a serious inhibition of plant growth. The chemical forms of the four nutrients were determined by successive extraction. Except for Ca, which was mainly chelated with insoluble phosphate and oxalic acid, Mg, Zn, and Fe were extractable by 80% ethanol, d‐H2O, and 1μM NaCl. The results indicated that these low–molecular weight compounds, such as organic acids and amino acids, may play an important role in deposition and translocation of Mg, Zn, and Fe in the xylem system of rice plants. 相似文献
902.
X. Wu R. Zhao L. Liu S. Bean P. A. Seib J. McLaren R. Madl M. Tuinstra M. Lenz D. Wang 《Cereal Chemistry》2008,85(4):495-501
Nine sorghum cultivars (five inbred lines and four hybrids) were grown in 2006 in three locations (Mount Hope, KS, Halstead, KS, and Plainview, TX) under different irrigation conditions and were evaluated for composition and ethanol fermentation efficiency. The objective was to study, in one growing season, the effects of genotype, growing location, and irrigation on the physical and chemical properties and fermentation efficiencies of grain sorghum. Genotype had a significant effect on chemical composition, physical properties, and ethanol yield. The cultivars showed a large variation in starch (61.0–74.8%), protein (7.56–16.35%), crude fat (2.79–4.77%), crude fiber (0.58–2.57%), ash (1.25–2.26%), kernel weight (20.0–35.9 mg), kernel hardness (49.6–97.5), and kernel size (1.9–2.7 mm) and were the most important factors affecting ethanol fermentation efficiency (87.5–93.9%). Starch and protein contents were significantly affected by growing location but not by irrigation. Environment had a significant effect on ethanol yields. Unexpectedly, irrigation somewhat reduced fermentation efficiency. 相似文献
903.
Florfenicol (FF) is a broad-spectrum antibiotic used increasingly in aquaculture, livestock, and poultry to treat diseases. To avoid using labor-intensive instrumental methods to detect residues of FF in food and food products, a simple and convenient indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) method for florfenicol's major metabolite, florfenicol amine (FFA), was developed using a polyclonal antibody prepared in this study. FFA was covalently attached to carrier protein as immunogen by using the glutaraldehyde method. The antibodies obtained were characterized by an ELISA method and showed excellent specificity and sensitivity with the 50% inhibition values (IC 50) of 3.34 microg/L for FFA in PBS buffer. In the ELISA, sample extractions were performed by ethyl acetate/ammonium hydroxide (90 + 10, v/v) following combined acid hydrolysis of FF and its known metabolites. The limits of detection (LOD) calculated from the analysis of 20 known negative swine muscle, chicken muscle, and fish samples were 3.08, 3.3, and 3.86 microg/kg (mean + 3 SD), respectively. Recoveries of FFA fortified at the levels of 5, 50, 100, and 300 microg/kg ranged from 64.6 to 124.7%, with coefficients of variation of 11.3-25.8% over the range of FFA concentrations studied. Validation of the ELISA method with FFA-fortified swine muscle at the levels of 10, 50, 100, and 200 microg/kg was carried out using GC, resulting in a similar correlation in swine muscle ( r = 0.97). The results suggest that this ELISA is a specific, accurate, and sensitive method, which is suitable for use as a screening method to detect residues of FFA in animal edible tissues. 相似文献
904.
905.
906.
907.
果蝇是为害杨梅果实的主要害虫,目前主要依靠乙基多杀菌素防控,成本较高,急需研究替代药剂,短稳杆菌(Empedobacter brevi)是一种新型细菌杀虫剂,为了明确短稳杆菌的防控效果和对果实品质的影响,本试验在杨梅转色成熟期喷雾,设5个处理,1.00×107、1.25×107和1.67×107短稳杆菌以及30和40 mg/L乙基多杀菌素,清水喷雾做对照。结果表明,与对照相比,5个处理药后7 d的果蝇防效为91.92%-96.76%,各处理间虫果率差异不显著,用药后13 d防效在82.76%-88.27%之间,1.67×107短稳杆菌处理虫果率最低;5个处理的果实可溶性固形物含量提高5.41%-7.21%,其中1.67×107短稳杆菌处理的提高幅度最大,果实硬度显著提高33.21%-46.42%,落果率显著下降37.57%-42.86%,硬度和落果率各处理间差异不显著。综合果蝇防控效果和果实品质等因素,短稳杆菌是防治杨梅果蝇乙基多杀菌素的理想替代药剂,值得在产业上大力推广。 相似文献
908.
909.
910.
为客观定量评价天气气候对怀化冰糖橙可溶性固形物(SSC)的影响,应用怀化地区麻阳和洪江2015年到2022年连续8年冰糖橙SSC资料,采用逐步回归、多元线性回归、聚类分析等统计方法,构建冰糖橙SSC综合气候品质指数(Iocq)模型,划分冰糖橙SSC 的Iocq等级。得到 7月中旬~9月中旬日较差、06月中旬~10月上旬降水量和8月中旬~9月中旬日照时数为影响冰糖橙SSC含量的关键气象因子,因子影响权重系数分别为0.46、0.34、0.20。参照湖南冰糖橙品质等级标准,得到Iocq≥2.4为特优果,2.4>Iocq≥1.6为优等果,1.6>Iocq≥0.6为一等果,0.6>Iocq为二等果。该SSC综合气候品质评价模型回代检验准确率为93.8%,实测检验2019~2021年中方县桐木镇冰糖橙SSC综合气候品质等级结果完全正确,该模型可应用于冰糖橙SSC品质评价实践。 相似文献