全文获取类型
收费全文 | 1802篇 |
免费 | 88篇 |
国内免费 | 174篇 |
专业分类
林业 | 236篇 |
农学 | 236篇 |
基础科学 | 145篇 |
300篇 | |
综合类 | 589篇 |
农作物 | 80篇 |
水产渔业 | 52篇 |
畜牧兽医 | 239篇 |
园艺 | 48篇 |
植物保护 | 139篇 |
出版年
2024年 | 8篇 |
2023年 | 20篇 |
2022年 | 50篇 |
2021年 | 61篇 |
2020年 | 78篇 |
2019年 | 57篇 |
2018年 | 35篇 |
2017年 | 70篇 |
2016年 | 52篇 |
2015年 | 81篇 |
2014年 | 63篇 |
2013年 | 98篇 |
2012年 | 109篇 |
2011年 | 149篇 |
2010年 | 123篇 |
2009年 | 88篇 |
2008年 | 93篇 |
2007年 | 104篇 |
2006年 | 90篇 |
2005年 | 87篇 |
2004年 | 36篇 |
2003年 | 52篇 |
2002年 | 68篇 |
2001年 | 57篇 |
2000年 | 45篇 |
1999年 | 49篇 |
1998年 | 34篇 |
1997年 | 25篇 |
1996年 | 27篇 |
1995年 | 31篇 |
1994年 | 21篇 |
1993年 | 25篇 |
1992年 | 22篇 |
1991年 | 12篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有2064条查询结果,搜索用时 718 毫秒
71.
滇西北高山针叶林区主要林型下外生菌根真菌的分布 总被引:11,自引:1,他引:11
1985年和1986年,我们在云南西北部高山针叶林内,采用标准地调查和路线踏查相结合的方法,在杜鹃-冷杉林等7个主要林型中进行了外生菌根真菌调查。经对采集标本的鉴定,计有33个属约140余种外生菌根真菌。它们在各种林型下的分布有着一定的规律。其种类组成和分布的多度与林木的组成、土壤和地形条件,如海拔高度、坡向、坡度等有密切的关系。 相似文献
72.
麻疯树不同地理种源种子性状及苗期生长初报 总被引:14,自引:1,他引:14
麻疯树种子性状及育苗试验表明:参试的麻疯树不同地理种源的种子外观差异不大,长度、宽度、侧径变异系数分别为2.9%、4.6%和3.3%;千粒重差异相对较大,变异系数达到7.7%,千粒重表现比较好的种源有6号、12号、17号、20号,千粒重可作为麻疯树优良材料选择的指标;不同种源苗木生长差异较大,综合地径和苗高生长情况,总体生长表现比较好的种源有2号、4号、10号、13号、14号、19号,地径平均值为0.89~1.13 cm,苗高平均值为8.9~10.6 cm;6号、7号种源苗期个体分化比较大;苗高和地径之间相关关系符合幂函数方程y=9.595x0.3134(R=0.642 4);不同地理种源苗期耐寒性差异显著,耐寒性最强的为11号、13号和14号种源;其次为1~5号、10号、12号、20号种源;为了防止冻害,育苗地点应选在福建南部没有霜冻或霜冻时间比较短的地方,播种时间宜在5~8月。 相似文献
73.
塔拉提取物化学利用的研究进展 总被引:20,自引:4,他引:20
塔拉是富含没食子单宁的主要植物资料之一。本文从其自然资源、塔拉提了化学及其加工利用等几方面的研究进展作了综述。指出塔拉的工业开发利用将会有进一步的发展。 相似文献
74.
Zane Kalvīte Zane Lībiete Ivars Kļaviņš Arta Bārdule Kārlis Bičkovskis 《Scandinavian Journal of Forest Research》2021,36(1):1-14
ABSTRACT Despite near-extinction in the nineteenth century, after efficient restoration measures the population of Eurasian beaver (Castor fiber L.) in Latvia currently is viable and growing. While the ecological effect of the species on water quality and biodiversity is generally positive, the high number of animals in production forests often creates challenges for management. Drainage ditches are among the most favoured habitats of beavers resulting in flooded stands, reduced tree growth and economical losses. The aim of the study was to evaluate the chemical properties of water in forest drainage ditches, affected by beaver activity, and their changes after the dam removal. Chemical composition of surface water in ditches was analysed in sampling points above dam, below dam and in the ditch itself after removal of the dam; results compared to pristine beaver site nearby on a small stream. Results did not show significant differences between concentrations above and below dams. After removal of the dams, significant increase in DOC, N-NO3 -, N-NH4 + and TSS concentrations and significant decrease in TP concentrations were observed in some of the sites. Observed concentrations of all measured parameters were significantly lower in pristine beaver site than in beaver sites on drainage ditches. 相似文献
75.
76.
77.
利用Hyperion影像及盐碱地分布端元提取了鲁西北典型盐碱地光谱数据并对其特性进行了探析,以证实光谱信息对于该区盐碱地研究的可用性。利用生成的原始及包络线去除的光谱曲线,分别从土壤电导率、土壤盐分含量及一系列诊断性指标入手,借助诊断性吸收波段对本区盐碱地特性进行了分析。结果表明:该区盐碱地兼具其他地点盐碱地光谱吸收共性及自身特性,证实了基于遥感光谱信息的盐碱地特性分析是可行的,可用于区域盐碱地遥感监测。 相似文献
78.
Chen L Huang Z Wang Q Shang J Huang R Bi F 《Journal of agricultural and food chemistry》2007,55(7):2659-2663
New propesticides with two effects of both benzoylphenylureas and carbamates were designed and synthesized by the key intermediate N-chlorosulfenyl-N-methylcarbamate, which was prepared for the first time. These benzoylphenylurea-S-carbamates were identified by 1H NMR spectroscopy and elemental analyses. The bioactivities of the new compounds were evaluated. These benzoylphenylurea-S-carbamates exhibited excellent larvicidal activities against Oriental armyworm, some of which were good as compared to the parent benzoylphenylureas. Toxicity assays indicated that these benzoylphenylurea-S-carbamates had knockdown activities of carbamates at higher concentrations and insect growth regulator activities of benzoylphenylureas at lower concentrations. We found that the title compounds exhibited good systemic larvicidal activities against Oriental armyworm, which were especially advantageous when combating sucking pests. Some of these title compounds can kill aphids and mosquitoes as well. 相似文献
79.
Wang X Li K Shi D Xiong N Jin X Yi J Bi D 《Journal of agricultural and food chemistry》2007,55(6):2072-2078
A rapid immunochromatographic lateral-flow test strip was developed in the competitive reaction format for the detection of sulfonamides in eggs and chicken muscle. A monoclonal antibody against the common structure of sulfonamides was conjugated to colloidal gold particles as the detection reagent and an N-sulfanilyl-4-aminobenzoic acid (SUL)-bovine serum albumin (BSA) conjugate was immobilized to a nitrocellulose membrane as the capture reagent to prepare the test strip. With this method, it required only 15 min to accomplish the semiquantitative or quantitative detection of sulfonamides. The sensitivity to sulfonamides (sulfamonomethoxine, sulfamethoxydiazine, sulfadimethoxine, and sulfadiazine) was at least 10 ng/mL, as determined with an optical density scanner. By eye measurement, the sensitivity was 20 ng/mL for sulfamonomethoxine, sulfamethoxydiazine, and sulfadimethoxine and 40 ng/mL for sulfadiazine. On the basis of a sulfamonomethoxine standard curve, recoveries were from 89.5 to 95.6% for sulfamonomethoxine, from 89.5 to 95.1% for sulfamethoxydiazine, from 85.0 to 95.6% for sulfadimethoxine, and from 44.8 to 60.9% for sulfadiazine in egg and chicken muscle samples. A parallel analysis of 27 egg samples and 28 chicken muscle samples from the animal experiment showed that the differences between test strips and high-performance liquid chromatography (HPLC) were from 0.8 to 11.2% for egg samples and from 2.2 to 34% for chicken muscle samples for the quantitative detection, and the agreement rates between test strips and HPLC were 100%, based on the maximum allowed residue level of sulfadiazine (100 ng/g) established by the European Union and China. In conclusion, the method is rapid and accurate for the detection of sulfonamides in eggs and chicken muscles. 相似文献
80.
浙江遂昌毛竹产业发展的困境与对策 总被引:1,自引:1,他引:0
为促进浙江遂昌毛竹产业可持续发展,深入分析了遂昌县毛竹产业发展的现状、存在的问题。结果表明:毛竹一产春笋、竹材价格下降,生产成本上升,劳动力缺乏;二产规模企业不足,环保问题未能有效破解,产业链不完整,初加工废料和毛竹采伐剩余物竹枝、竹叶绝大部分还未充分利用;三产毛竹产业文创产品和旅游产品开发相对滞后。为此,摆脱毛竹产业的困境,必须通过体制机制创新,主体培育壮大,生产要素集聚,落实“主攻二产、发展三产、提升一产”的措施,实现一二三产融合发展。 相似文献