全文获取类型
收费全文 | 14002篇 |
免费 | 630篇 |
国内免费 | 1619篇 |
专业分类
林业 | 1579篇 |
农学 | 2372篇 |
基础科学 | 1183篇 |
2220篇 | |
综合类 | 4186篇 |
农作物 | 871篇 |
水产渔业 | 464篇 |
畜牧兽医 | 1957篇 |
园艺 | 486篇 |
植物保护 | 933篇 |
出版年
2024年 | 41篇 |
2023年 | 143篇 |
2022年 | 386篇 |
2021年 | 524篇 |
2020年 | 531篇 |
2019年 | 490篇 |
2018年 | 365篇 |
2017年 | 482篇 |
2016年 | 506篇 |
2015年 | 636篇 |
2014年 | 582篇 |
2013年 | 706篇 |
2012年 | 826篇 |
2011年 | 898篇 |
2010年 | 838篇 |
2009年 | 775篇 |
2008年 | 730篇 |
2007年 | 800篇 |
2006年 | 722篇 |
2005年 | 699篇 |
2004年 | 341篇 |
2003年 | 416篇 |
2002年 | 486篇 |
2001年 | 462篇 |
2000年 | 379篇 |
1999年 | 413篇 |
1998年 | 314篇 |
1997年 | 273篇 |
1996年 | 215篇 |
1995年 | 213篇 |
1994年 | 213篇 |
1993年 | 176篇 |
1992年 | 167篇 |
1991年 | 115篇 |
1990年 | 95篇 |
1989年 | 106篇 |
1988年 | 79篇 |
1987年 | 39篇 |
1986年 | 19篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1966年 | 1篇 |
1965年 | 2篇 |
1964年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
In this paper, the influence of melamine polyphosphate (MPP) and aluminum hypophosphite (AHP) on mechanical properties, flame retardancy and thermal degradation of high-density polyethylene/wood flour composites (HDPE/WF) was investigated. The synergistic effect of MPP and AHP was investigated. Polyethylene grafted with maleic anhydride (PE-g-MAH) was used as coupling agent. The experimental data demonstrated that the HDPE/WF composites with 35 wt% MPP/AHP (3:2) could achieve a LOI value of 29.6 % and UL-94 V-0 rating. In addition, the cone value also revealed that the heat release rate and the smoke production rate were clearly reduced. SEM results showed that the synergistic system (MPP/AHP = 3:2) could form a dense and thick char layer and good adhesion between wood flour and HDPE matrix, which prevented the transfer of heat flux and fuel gases. Incorporation of MPP and AHP improved the thermal stability of HDPE/wood flour as observed from the thermogravimetric analysis results and also enhanced the thermal resistance of char layer at high temperature based on scanning electron microscopy observation. 相似文献
993.
针叶树幼树移栽与容器大苗造林试验 总被引:2,自引:0,他引:2
为了提高半干旱地区针叶树造林的成活率,在内蒙古奈曼旗兴隆沼林场开展了针叶树幼树带土坨移植试验与塑料容器大苗造林试验。结果表明,8年生境子松幼树移植成活率达88% ̄98%;4年生不同树种容器苗造林成话率达76% ̄87%。樟子松容器苗成活率比裸根苗高53%;流动风沙土造林地比生草风沙土造林地高45%。 相似文献
994.
桤木人工林林分胸径与树高的威布尔分布拟合 总被引:3,自引:0,他引:3
根据桤木人工林 8个年龄段样地资料 ,分别对胸径与树高的样数分布进行威布尔拟合 ,经统计检验 ,全部属于左偏的威布尔分布 相似文献
995.
杉木种源选择的投影寻踪法应用 总被引:1,自引:0,他引:1
改进的投影寻踪法是一种新方法,这种方法把每一个种源的多指标投影成一维的指标值,根据投影值的大小就可直接进行排序.以福建农林大学莘口教学林场杉木种源试验为例,采用改进的投影寻踪法开展杉木优良种源选择研究.结果表明;从生长快、生长量大、材性好的角度考虑,福建南平是最好的种源;闽北地区杉木种源的调拨以南平种源为佳,其次为湖南会同种源.这与实际试验结论相符,也与应用层次分析法所得的结论基本一致,应用改进投影寻踪法开展林木种源选择是可行的、科学的. 相似文献
996.
997.
998.
The 18 species of bird studied originally are known to belong to muscicapids, robins and sylviids of passerines, but some dis- putations are always present in their classification systems. In this experiment, phylogenetic relationships of 18 species of passerines were studied using Adenylate Kinase lntron 5 (AKS) sequences and DNA techniques. Through sequences analysis in comparison with each other, phylogenetic tree figures of 18 species of passerines were constructed using Neighbor-Joining (N J) and Maximum-Parsimony (MP) meth- ods . The results showed that sylviids should be listed as an independent family, while robins and flycatchers should be listed into Musci- capidae. Since the phylogenetic relationships between long-tailed tits and old world warblers are closer than that between long-tailed tits and parids, the long-tailed tits should be independent of paridae and be categorized into aegithalidae. Muscicapidae and Paridae are known to be two monophylitic families, but Sylviidae is not a monophyletic group. AK5 sequences had better efficacy in resolving close relationships of interspecies among intrageneric groups. 相似文献
999.
温度对大叶桃花心木(Swietenia macrophylla King)幼苗叶片的光合影响 总被引:2,自引:0,他引:2
本文研究了大叶桃花心木(Swietenia macrophylla King)一年生幼苗在经过夜温处理后的光响应曲线和在饱和光强下的CO2反应曲线.结果表明:在大气CO2浓度下,叶片的最佳光合作用温度在25-31℃之间,而在饱和CO2浓度下为31-35℃.在25℃以下光合速率开始降低,主要是由于羧化效率的降低,而当温度超过31℃时,光合速率下降,是因为羧化效率的降低和呼吸速率的增加.CO2浓度对光合的促进作用在低温下受到抑制,这意味着未来在CO2浓度增高的情况下,高浓度的CO2对热带常绿植物光合的促进在冬天低温情况下表现不十分明显.图4参23. 相似文献
1000.
Water relation parameters of bare-root seedlings of Chinese fir (Cunninghamia lanceolata Hook.)and Masson pine (Pinus massoniana Lamb.)were measured and changes of root growth potential as well as field survival rate of both species were studied after the bare-root seedlings were exposed in a sunny field condition.the results showed that masson pine had a lower osmotic potential(-2.07Mpa) at turgor loss point and at full turgor(-1.29Mpa),compared with Chinese fir(-1.80Mpa and -1.08Mpa respectively).The parameter Vp/Vo(63.27%) of Masson pine was higher than that of chinese fir (58.03%).This means that Masson pine has a stronger ability to tolerate desiccation,compared to Chinese fir according to analysis of above water relation parameters.Root growth potential and field survival rate decreased with prolonging duration of exposure.The field survival rate of both species was reduced to less than 40% after the seedling being exposed only two hours.Water potentials of -1.60 Mpa and -1.70 Mpa were suggested to be critical values for Chinese fir and Masson pine respectively in successful reforestation. 相似文献