全文获取类型
收费全文 | 20465篇 |
免费 | 893篇 |
国内免费 | 2155篇 |
专业分类
林业 | 2018篇 |
农学 | 1918篇 |
基础科学 | 2421篇 |
3054篇 | |
综合类 | 8721篇 |
农作物 | 1161篇 |
水产渔业 | 704篇 |
畜牧兽医 | 2244篇 |
园艺 | 512篇 |
植物保护 | 760篇 |
出版年
2024年 | 142篇 |
2023年 | 361篇 |
2022年 | 661篇 |
2021年 | 781篇 |
2020年 | 762篇 |
2019年 | 823篇 |
2018年 | 530篇 |
2017年 | 838篇 |
2016年 | 974篇 |
2015年 | 794篇 |
2014年 | 1208篇 |
2013年 | 1198篇 |
2012年 | 1736篇 |
2011年 | 1640篇 |
2010年 | 1243篇 |
2009年 | 1186篇 |
2008年 | 1078篇 |
2007年 | 1254篇 |
2006年 | 1140篇 |
2005年 | 933篇 |
2004年 | 758篇 |
2003年 | 624篇 |
2002年 | 450篇 |
2001年 | 401篇 |
2000年 | 350篇 |
1999年 | 265篇 |
1998年 | 227篇 |
1997年 | 161篇 |
1996年 | 163篇 |
1995年 | 125篇 |
1994年 | 109篇 |
1993年 | 136篇 |
1992年 | 92篇 |
1991年 | 89篇 |
1990年 | 75篇 |
1989年 | 64篇 |
1988年 | 38篇 |
1987年 | 37篇 |
1986年 | 18篇 |
1985年 | 16篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1963年 | 1篇 |
1962年 | 3篇 |
1956年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
竹类资源在我国石漠化防治中的应用研究 总被引:1,自引:1,他引:1
石漠化问题是岩溶地区首要生态问题, 严重制约着区域社会经济可持续发展。因石漠化土地具有双层水文结构、缺土少水、富钙(镁)、偏碱性的特性, 物种选择受限; 而岩溶地区竹类种质资源丰富, 其生态与经济效益俱佳, 是实现治"石"与致富的有效物种, 推广意义重大。文中介绍了我国石漠化土地现状和生态特征、我国竹类资源分布状况及主要特性, 分析了竹类在石漠化防治中的可行性, 阐述了石漠化治理中竹类品种选择要求以及石漠化治理中主要丛生竹品种和主要特性, 并提出石漠化治理中竹类栽培与抚育管理的关键技术与要点, 以期为我国在全面推进石漠化综合治理工程中加强竹类资源广泛应用提供参考。 相似文献
942.
研究了引种观赏竹对低温的生理响应,综合评价其抗寒能力,以期为竹资源在北方的推广提供科学指导。以山东省聊城市百竹园的金镶玉竹(Phyllostachys aureosulcata 'Spectabilis’)、黄纹竹(Ph. vivax 'Huanwenzhu’)、紫竹(Ph. nigra)3种引种观赏竹为研究对象,研究了3种引种观赏竹的出笋率及电导率、超氧化物歧化酶(SOD)活性、可溶性糖、可溶性蛋白、游离脯氨酸、丙二醛(MDA)含量等6个抗寒生理指标,采用熵权TOPSIS法进行抗寒性综合评价。结果表明:出笋率从高到低依次为金镶玉竹、黄纹竹、紫竹。人工低温处理下,随低温胁迫的加剧,3种竹叶的电导率均呈上升趋势,金镶玉竹的电导率最高;MDA含量表现为先降低后上升;金镶玉竹叶片中渗透物质含量高于黄纹竹和紫竹,可溶性糖、可溶性蛋白质、游离脯氨酸的含量升高;金镶玉竹叶片SOD酶活性显著高于其他2个竹种;基于熵权法进行抗寒性综合评价,可溶性蛋白质含量在抗寒指标中占的权重最大(23.69%),其次为游离脯氨酸(22.56%)和可溶性糖(15.40%);TOPSIS评价得出金镶玉竹抗寒能力最强,其次为黄纹竹、紫竹。 相似文献
943.
944.
围绕农作物秸秆在人造板生产中的综合利用,结合我国稻秸秆人造板生产和应用的实际情况,就稻秸秆的原料资源、原料的特性和改性、专用胶黏剂、稻秸秆人造板产品模式、稻秸秆板生产工艺难点、稻秸秆板的性能、稻秸秆板的用途和稻秸秆人造板产业的形成与发展等八个问题发表了意见与建议。 相似文献
945.
能源林收获机方案设计 总被引:1,自引:0,他引:1
介绍了作业环境及作业工艺对能源林收获机技术性能的要求,应用系统分析设计法拟定了多个待选方案,并用模糊综合评判法对其进行对比,得出最佳方案。 相似文献
946.
Summary In vitro pollen germination at 10°C, 14°C and 22°C of four groups of two pure line tomato varieties was compared with their plant growth at 19°C D/10°C N under controlled environmental conditions. Generally, pollen germination was slow at 10°C but after 6 h the percentage of germination was similar to that at 22°C. Maximum germination was obtained at 14°C already after 4 h. The longest pollen tubes occurred at 22°C. The two varieties within each group differed significantly from each other for percentage of pollen germination. For one group, this difference was greater at 10°C than at 22°C. The varieties in two groups also differed significantly for pollen tube growth. These differences in pollen tube growth rate were greater at 22°C than at 10°C. There was no clear relationship between pollen germination, pollen tube growth and plant growth in any of the four pairs of varieties. The results are discussed with regard to the possibility of pollen selection at low temperature in order to improve the efficiency of breeding for growth at low temperature. 相似文献
947.
948.
Bai Shaoliang Zhu Xijun 《保鲜与加工》1990,(1)
In this pager, four full-scale corner joint assemblies of reinforced concrete frame beam and column with different detail structure are tested under low cycle loading, The process of damage development and the characteristics of break of the assemblies in the course of alternately increasing positive and negative bending deformation are learned Strength, stiffness and ductility of assemblies and the various regulations of energy consumption are also studied. Compared with these properties, the anti-seismic behavior is tentatively commented. Besides, the test results of the strain distribution of beam and column longitudinal bars and stress state of joint stirrups are analyzed. 相似文献
949.
Summary Diallel crosses were made between 15 tomato genotypes with varying performance under a low energy regime. It appeared that differences between genotypes for 11 vegetative and generative plant characters are determined mainly by additive genetic variation. For breeding cultivars adapted to low energy conditions, crossing genotypes with a high GCA for weight of trusses and fruits (WTF) and genotypes with a high GCA for weight of vegetative plant parts (WVP) seems most promising. Complications may arise from the negative correlation between GCA values for WTF and WVP, and the strong positive correlation between GCA values for fruit number and WTF, causing small fruits. 相似文献
950.
Summary When Asiatic lilies are forced during the winter period, additional light is needed to prevent flower bud abscission and flower bud blasting. Growth room experiments showed considerable differences among eight lily cultivars in their response to low light. Among these cultivars, Connecticut King and Enchantment appeared to be the most sensitive to low light conditions while Uncle Sam and Scout were the least sensitive.Analysis of an incomplete diallel cross between nine cultivars showed significant differences in general combining ability (GCA) for flower bud abortion, number of buds, forcing time, plant height and leaf scorch under winter greenhouse conditions. Enchantment had the highest positive GCA for bud abortion, indicating a high sensitivity to low light conditions. Uncle Sam had the lowest GCA. Pirate and Scout appeared to have a high GCA for sensitivity to leaf scorch. Connecticut King was found to be a probable source of cytoplasmic male sterility. The data suggest that male sterility is associated with better response to low light conditions. 相似文献