全文获取类型
收费全文 | 1567篇 |
免费 | 96篇 |
国内免费 | 98篇 |
专业分类
林业 | 58篇 |
农学 | 99篇 |
基础科学 | 12篇 |
331篇 | |
综合类 | 629篇 |
农作物 | 115篇 |
水产渔业 | 174篇 |
畜牧兽医 | 231篇 |
园艺 | 50篇 |
植物保护 | 62篇 |
出版年
2024年 | 10篇 |
2023年 | 9篇 |
2022年 | 26篇 |
2021年 | 39篇 |
2020年 | 39篇 |
2019年 | 41篇 |
2018年 | 26篇 |
2017年 | 59篇 |
2016年 | 60篇 |
2015年 | 59篇 |
2014年 | 69篇 |
2013年 | 80篇 |
2012年 | 149篇 |
2011年 | 126篇 |
2010年 | 125篇 |
2009年 | 112篇 |
2008年 | 82篇 |
2007年 | 112篇 |
2006年 | 101篇 |
2005年 | 60篇 |
2004年 | 49篇 |
2003年 | 48篇 |
2002年 | 32篇 |
2001年 | 33篇 |
2000年 | 41篇 |
1999年 | 20篇 |
1998年 | 17篇 |
1997年 | 17篇 |
1996年 | 23篇 |
1995年 | 24篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1990年 | 12篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1974年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1761条查询结果,搜索用时 31 毫秒
141.
鸭肝蛋白酶的分离纯化及其部分性质研究 总被引:1,自引:1,他引:1
经Tris-HCl缓冲液抽提、硫酸铵分级沉淀、DEAE-Sepharose Fast Flow离子交换层析、Sephacryl S-200凝胶过滤层析,得到鸭肝蛋白酶电泳纯制品.纯化倍数为650.16倍,回收率为19.23%.经SDS-PAGE和凝胶过滤测得该酶的分子量为35kD.该酶在pH6.0~11.0,温度低于25℃稳定,当温度上升到55℃时活性迅速下降.该酶在pH10和60℃时达到最高活性.进一步研究得知:Cu^2+离子对该酶有明显促进作用,而Mn^2+却使酶几乎失活.以酪蛋白为底物,在pH10.0、37℃时测得米氏常数Km值为1.33%. 相似文献
142.
水相酶法提取蛋黄油工艺的响应面分析法研究 总被引:6,自引:0,他引:6
采用蛋白酶水解鲜鸡蛋蛋黄提取蛋黄油,通过响应曲面分析法建立蛋黄油提取率的二次多项数学模型,并考察酶添加比例、底物质量浓度和反应时间对蛋黄油提取率的影响,优化出蛋黄油提取率达到56.81%的工艺参数:酶添加比例为2.04%,底物质量浓度为20.28%,反应时间为14 h。 相似文献
143.
喹诺酮类(吡哌酸、诺氟沙星)药物的热分解特性研究 总被引:3,自引:0,他引:3
分别采用差示扫描量热法(DSC)、热重法(TG)和微分热重法(DTG),研究了喹诺酮类(吡哌酸、诺氟沙星)抗菌药的热分解动力学过程,计算了其热分解动力学参数——活化能(E),分析了其热分解机理,并剖析了喹诺酮类药物有机结构上的差异。 相似文献
144.
考察不同溶剂、物料比、反应时间、反应温度对酸值的影响,通过正交实验优化出两种酸酐合成的最佳工艺分别为:①桐油:顺丁稀二酸酐=20:5.5 ,反应时间90min,反应温度115℃,不加溶剂;②桐酸:顺丁稀二酸酐=10:2.6,反应时间90min,反应温度140℃,不加溶剂.用红外光谱比较两者的结构.用不同酸值的两种酸酐固化环氧树脂,测试胶化时间,结果为酸值越大,胶化时间越短;游离酸值越小,胶化时间越短. 相似文献
145.
146.
将起源于黄色菌(Flavobacteriumsp.KI72)的6─氨基己酸二聚体水解酶(EⅡ)基因以质粒pTS1209为载体,转入假单孢菌PseudomonasputidaNT1126中,得到具有EⅡ高表达活性转基因株,表明以假单胞菌为宿主进行EⅡ酶分子育种的可行性,并为EⅡ酶尚处于进化中的推论提供了旁证。 相似文献
147.
桃果皮毛、果肉颜色对果实糖与酸含量的影响及相关性研究 总被引:8,自引:0,他引:8
对山桃和栽培桃品种杂交后代 10 7个个体 (分成 2 2个毛桃和 85个油桃 ,或 75个白肉桃和 3 2个黄肉桃 )的果实糖酸含量遗传规律进行了研究。结果表明 ,桃果实中的可溶性糖和酸主要是蔗糖和苹果酸 ,分别占总可溶性糖的 65%左右和总酸含量的 50 %。油桃各基因型的蔗糖、果糖、山梨糖醇、总糖、可溶性固形物及奎宁酸平均含量均显著高于毛桃 ,而毛桃和油桃基因型之间的苹果酸、柠檬酸、总酸平均含量及糖酸比没有显著差异。所有毛桃和油桃基因型的莽草酸含量都很低 ,为 0 .0 11~ 0 .0 46meq·10 0g- 1FW。果实内葡萄糖和果糖含量呈正相关 (r =0 .63 ) ,蔗糖、葡萄糖、果糖分别与山梨糖醇呈显著或极显著直线正相关 ,且苹果酸与蔗糖、山梨糖醇、总糖和可溶性固形物呈显著正相关。毛桃的平均单果重显著大于油桃 ,且可溶性固形物和总酸含量与果实的大小呈显著直线负相关。此外 ,盛花后果实发育天数影响果实内糖酸含量 相似文献
148.
Paula Aguilera Fernando Borie Alex Seguel Pablo Cornejo 《Soil biology & biochemistry》2011,43(12):2427-2431
Arbuscular mycorrhizal spores and glomalin-related soil protein (GRSP) isolated from acid soils were analyzed using confocal laser scanning microscopy (CLSM) for Al detection. Mycorrhizal structures of Glomus intraradices produced under in vitro conditions as well as spores and GRSP from neutral and Cu-polluted soils were used as contrasting criteria. Spores and GRSP from soils with 7 and 70% Al saturation showed autofluorescence which increased especially at the highest soil Al level and when Al3+ solution was added. G.intraradices spores showed fluorescence only when exogenous Al3+ was added. On the contrary, spores and GRSP from neutral and Cu-polluted soils showed little or no significant fluorescence. This fluorescence shown by fungal structures and GRSP when subjected to high Al (of endogenous or exogenous origin) suggest a high capacity for Al immobilization, which could be an effective way to reduce Al activity and phytotoxicity in acid soils. 相似文献
149.
Eklou A. Somado Kanwar L. Sahrawat Ronald F. Kuehne 《Biology and Fertility of Soils》2006,43(1):124-130
Experiments were conducted during 1996–1998 in screen house and in the field in the humid forest zone of Côte d’Ivoire, to evaluate the effects of phosphorus (P) from phosphate rock (PR) on the performance of the root nodulating legume Crotalaria micans grown for 8 weeks. The experimental soils were acid Ultisols with <4 mg/kg extractable Bray-1 P. Tilemsi PR from Mali and triple superphosphate (TSP) were applied at 60 kg P ha?1 (screen house) and 90 kg P ha?1 (field) to the legume. Legume N-fixed (BNF) was estimated by the 15N-isotope dilution and δ 15N natural abundance methods, using Cassia obtusifolia L. as a non-fixing legume reference plant. Without P supply, and under the field conditions, C. micans produced less than 1 tonne of biomass and accumulated 29 kg N/ha. The application of PR-P enhanced legume N by about fourfold over the unfertilised control. There was no significant difference between the effects of TSP and PR. Phosphorus application mainly affected the total amount of N accumulated rather than the percentage derived from the atmosphere (%N dfa) per se. Furthermore, the cumulative effects of PR-P on the performance of C. micans greatly improved with time in the screen house. This study confirms that Tilemsi PR is an agronomically effective source of P for short-duration legume green manure (GM) even in the first year of its application to acid P-deficient soils in the West African humid zone. 相似文献
150.
Microbiological processes in soil organic phosphorus transformations in conventional and biological cropping systems 总被引:5,自引:0,他引:5
We studied microbiological processes in organic P transformations in soils cultivated with conventional and biological farming systems during the 13th and 14th year of different cropping systems. The treatments included control, biodynamic, bioorganic, and conventional plots and a mineral fertilization treatment. Different P fractions were investigated using a sequential fractionation method. Labile organic P, extracted by 0.5 M NaHCO3, was not affected by the farming systems. However, residual organic P remaining in the soil at the end of the sequential fractionation procedure showed that the biodynamic treatment, in particular, led to a modification of the composition of organic P. Labile organic P, organic P extractable in 0.1 M NaOH, and total residual P all showed temporal fluctuations. As total residual P consists of more than 70% organic P, it can be assumed that residual organic P contributed to these variations. This result indicates that chemically resistant organic P participates in short-term accumulation and mineralization processes. All biological soil parameters tested in this study showed significant temporal fluctuations, mainly attributed to differences in climatic conditions between years, but possibly also related to the growth cycle of the crop. The higher values of the biological soil parameters in the biodynamic and bioorganic treatments were explained by the greater importance of manure and the different plant protection strategies. The level of phosphatase activity and mineralization of organic C indicated a higher turnover of organic substrates, and thus of organic P, in the biodynamic and bioorganic treatments. Biological parameters were shown to be critical for assessing the significance of organic P in the soil P turnover. 相似文献