全文获取类型
收费全文 | 2583篇 |
免费 | 124篇 |
国内免费 | 415篇 |
专业分类
林业 | 79篇 |
农学 | 223篇 |
基础科学 | 36篇 |
358篇 | |
综合类 | 831篇 |
农作物 | 584篇 |
水产渔业 | 27篇 |
畜牧兽医 | 821篇 |
园艺 | 68篇 |
植物保护 | 95篇 |
出版年
2024年 | 20篇 |
2023年 | 43篇 |
2022年 | 86篇 |
2021年 | 93篇 |
2020年 | 96篇 |
2019年 | 121篇 |
2018年 | 109篇 |
2017年 | 130篇 |
2016年 | 143篇 |
2015年 | 114篇 |
2014年 | 148篇 |
2013年 | 192篇 |
2012年 | 148篇 |
2011年 | 161篇 |
2010年 | 129篇 |
2009年 | 147篇 |
2008年 | 172篇 |
2007年 | 131篇 |
2006年 | 114篇 |
2005年 | 126篇 |
2004年 | 80篇 |
2003年 | 95篇 |
2002年 | 46篇 |
2001年 | 71篇 |
2000年 | 76篇 |
1999年 | 38篇 |
1998年 | 45篇 |
1997年 | 40篇 |
1996年 | 41篇 |
1995年 | 35篇 |
1994年 | 20篇 |
1993年 | 28篇 |
1992年 | 26篇 |
1991年 | 18篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 13篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有3122条查询结果,搜索用时 15 毫秒
101.
102.
《African Journal of Range and Forage Science》2013,30(3):181-183
Pteronia paniculata is an indigenous, unpalatable shrub that invades mismanaged Karooveld, resulting in degraded rangelands with low species diversity and grazing potential. We conducted a series of trials in the Succulent Karoo Randteveld near Barrydale to determine if the uniform defoliation of P. paniculata dominated vegetation at two heights (0.05 m and 0.20 m above ground level) using a brush-cutter and, in one trial, application of a second cut will improve the plant species composition, productivity and grazing capacity of the veld. Brush-cutting treatments and the uncut control all resulted in a change in species composition towards greater species diversity and more palatable species and an average increase of 540 kg ha?1 (28%) in above-ground biomass over four years. It appears that there was a pervasive improvement in species composition associated with a general decline in the cover and abundance of P. paniculata over the time-scale of the present study that was not influenced by the defoliation treatments, except for the 1996-cut treatment where the cover of P. paniculata increased. The absence of propagules of palatable species in the soil seed bank and competition from P. paniculata (a long-lived, perennial shrub) are assumed to be among the main reasons for the lack of response of the vegetation community to the defoliation treatments. Brush-cutting (in the absence of reseeding), aimed at reducing the dominance of unpalatable karoo shrubs, was more costly but not significantly better than long-term resting in improving veld composition or forage production. 相似文献
103.
104.
本次研究选用莫斯模型法(Moss)对额济纳旗宜牧土地生产力进行了研究,在此基础上估算出载畜量,为该旗的牧业可持续发展和生态环境保护提供理论依据。 相似文献
105.
Agroforestry systems in North America 总被引:2,自引:0,他引:2
Agroforestry systems in North America vary widely in terms of components (tree, forb, graminoid, and shrub species) and outputs. Most of the agroforestry systems used in North America have emphasized wood and livestock production. The objective of each system has been to produce annual and long term economic returns and sustainable yields. Inputs such as fossil fuels, fertilizers, herbicides and pesticides are relatively low compared to those used in conventional agriculture.Major agroforestry system types in each of eight North American regions are described. The major species used as vegetational components in each system are enumerated by region. The numerous variations in how these components are mixed have created an almost endless number of actual systems. Management problems and solutions, economic concerns, and system comparisons have also been addressed for each region. 相似文献
106.
以东农253为试验材料,在玉米6叶期喷施吨田宝(DTB)、DCPTA和ETH复配剂(KP)两种化控剂,对照为清水。结果表明,DTB和KP均可提高春玉米根系伤流量,特别是生育后期的流量,分别比对照提高了72.34%和129.78%;提高了伤流液中矿质元素的流量,氨基酸的总流量也得到相应的提高,特别是丝氨酸的流量。内源激素IAA、CTK和ABA流量在各时期均有增加;GA流量在乳熟期得到显著提高,拔节期、抽雄吐丝期和灌浆初期均低于对照,之后得到显著提高。对内源激素比值均有不同程度的影响,改变了激素间的平衡水平;提高了行粒数和百粒重,产量分别比对照提高了13.89%和21.06%。相关性分析表明,玉米根系伤流量及其组分与产量密切相关,表明化控剂具有调控根系伤流量、矿质元素和内源激素流量的作用,对促进地上部生长发育和产量的形成有重要作用。 相似文献
107.
试验表明春油菜的胚长、子叶长宽、胚轴长宽的变化基本同步,都呈现S形曲线,增长峰值出现在花后第14—15天,接近最大值的时间在花后第22—25天。胚干重在花后第28天增加最快,日增量达0.24mg.胚细胞数在花后第22天不再增加,此时胚干重仅为其最终胚重的1/5左右,而胚长已接近最大值,施用氮肥能使胚早期发育延缓,同时能防止胚珠退化,增加粒数,提高粒重。 相似文献
108.
Bonginkosi C Gumbi Julie T Shapiro Themba Mahlaba Robert McCleery Duncan MacFadyen 《African Zoology》2018,53(1):23-29
Grazing by large mammals alters vegetation physiognomy, consequently changing habitat suitability for small mammal communities. We investigated the response of terrestrial small mammals to grazing by wild and domesticated ungulates at the boundary of a protected area (Telperion Nature Reserve) and surrounding cattle ranches in Mpumalanga, South Africa over two seasons. Fifteen paired grids were set on either side of the boundary fence at which small mammals were trapped in Sherman live traps placed flat on the ground. A total of 11 760 trap nights resulted in the capture of 187 animals belonging to 14 species (11 rodents, two shrews and one elephant shrew). The small mammal communities in grasslands grazed by domesticated or wild ungulates were similar in abundance, species richness, diversity and demographic parameters, likely due to the fact that vegetation structure of the two grazing systems was also similar. We used generalised linear models to show that rock and grass cover were plausible predictors of small mammal abundance in this system. Rock cover showed a positive relationship with small mammal abundance whilst grass cover showed a negative relationship. Our observations suggest that at the scale of our study and with the current stocking densities, wild and domesticated ungulates have similar impacts on the small mammal community. 相似文献
109.
110.
壮丰安对冬小麦春生叶生理功能的调控效应初步研究 总被引:8,自引:0,他引:8
试验以京冬6号和京冬8号为材料,研究了新型植物生长调节剂-壮丰安对冬小麦春生叶片生理功能的调控作用,结果表明:壮丰安处理使春生1-5片叶长度,宽度及叶面积减少,控制了冬小麦前期旺长;使旗叶长度,宽度及叶面积增加;使叶片叶绿素总量及可溶性蛋白质含量增加;使叶片过氧化物酶,过氧化氢酶及超氧化物歧化酶活性提高,使叶片综合性状得到改善,促进灌浆,提高产量。 相似文献