全文获取类型
收费全文 | 10205篇 |
免费 | 609篇 |
国内免费 | 746篇 |
专业分类
林业 | 932篇 |
农学 | 698篇 |
基础科学 | 236篇 |
2754篇 | |
综合类 | 4172篇 |
农作物 | 592篇 |
水产渔业 | 328篇 |
畜牧兽医 | 1212篇 |
园艺 | 310篇 |
植物保护 | 326篇 |
出版年
2024年 | 55篇 |
2023年 | 205篇 |
2022年 | 332篇 |
2021年 | 409篇 |
2020年 | 384篇 |
2019年 | 488篇 |
2018年 | 392篇 |
2017年 | 576篇 |
2016年 | 656篇 |
2015年 | 477篇 |
2014年 | 563篇 |
2013年 | 809篇 |
2012年 | 960篇 |
2011年 | 688篇 |
2010年 | 563篇 |
2009年 | 506篇 |
2008年 | 444篇 |
2007年 | 503篇 |
2006年 | 403篇 |
2005年 | 371篇 |
2004年 | 261篇 |
2003年 | 212篇 |
2002年 | 166篇 |
2001年 | 141篇 |
2000年 | 137篇 |
1999年 | 130篇 |
1998年 | 85篇 |
1997年 | 85篇 |
1996年 | 70篇 |
1995年 | 108篇 |
1994年 | 68篇 |
1993年 | 66篇 |
1992年 | 46篇 |
1991年 | 49篇 |
1990年 | 39篇 |
1989年 | 48篇 |
1988年 | 22篇 |
1987年 | 16篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1956年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
161.
KU Daping Bernie DELL. Research Institute of Tropical Forestry CAF Guangzhou China . Murdoch University. Perth. Australia 《中国林业科技(英文版)》2002,(1)
Eucalypts are very popular for revegetation in many parts of south China because of their capacity to tolerate degraded sites and unfertile soils,and their fast growth potential to coppice. This paper reviews a decade of field trials in china, undertaken as part of several bilateral researchprograms in plantation forestry, concerning the use of fertilizers, harvest residue management and inoculation with ectomycorrhizal fungi. One of the key questions addressed is whether the productivity of plantation eucalypts in south China can be increased to the world average by nutrient management across a rotation. 相似文献
162.
Nitrogen fixing and non-N2 fixing legumes such as Gliricidia speium and Senna siamea have been used in alley cropping systems for soil improvement and source of N for food crops. However their
establishments could be limited by P and moisture deficiencies in degraded soils. Vesicular-arbuscular mycorrhizal fungi can
help to overcome these deficiencies. We examined the effects of a vesicular-arbuscular mycorrhizal (VAM) fungus, Glomus deserticola, on the performance of sole hedgerow trees of Gliricidia sepium and Senna siamea and their mixtures (interplanted) in a fallowed alley cropping experiment on a degraded Alfisol in southwestern Nigeria.
Percentage root infection by VAM fungi was higher in inoculated plants than in uninoculated ones irrespective of whether they
were interplanted or non-interplanted. Inoculation with G. deserticola increased dry matter accumulation and nutrient uptake (N. P, Mg and K) but there was no significant interaction between mycorrhizal
inoculation and interplanting for growth and nutrient uptake except for the uptake of P, Mg and K in G. sepium. Inoculation with G. deserticola reduced leaf shedding of G. sepium by 50% but did not have the same effect for S. siamea. For both tree species inoculated plants extracted more water from 0–30 cm depth than the uninoculated ones. 相似文献
163.
164.
R. Lal 《Agroforestry Systems》1989,8(2):97-111
Field runoff plots, 70 x 10 m each, were established on a tropical Alifisol in southwestern Nigeria to monitor water runoff,
soil erosion and nutrient loss in water runoff. The non-agroforestry control treatment (A) was established at two levels:
plow-till and no-till systems of seedbed preparation. There were two agroforestry systems based on contour hedgerows of (B)
Leucaena leucocephala and (C) Gliricidia sepium established at 4-m and 2-m spacings. Field plots were established in 1982 and hydrological measurements were made for uniform
maize-cowpea rotation for 12 consecutive growing seasons from 1982 through 1987.
Once established hedgerows of Leucaena at 2-m spacing were extremely effective in reducing water runoff and controlling erosion. Runoff, erosion and nutrient losses
were generally more from maize grown in the first season than from cowpea grown in the second. Mean seasonal erosion from
maize was 4.3, 0.10, 0.57, 0.10, 0.64 and 0.60 t/ha for plow-till, no-till, Leucaena-4m, Leucaena-2m, Gliricidia-2m treatments, respectively. Mean runoff in the first season from treatments listed in the order above was 17.0, 1.3, 4.9,
3.3, 4.3, and 2.4 percent of the rainfall received. There were high losses of Ca and K in water runoff from the plow-till
treatment. In contrast to runoff and erosion, losses of bases in water runoff from agroforestry treatments were relatively
high, high concentration of bases in runoff was probably due to nutrient recycling by the deep-rooted perennials. 相似文献
165.
G. Singh 《Agroforestry Systems》1995,29(1):61-75
High salt concentration in the soil is a serious problem in vast areas of otherwise productive agricultural lands in India. Establishment of salt tolerant vegetation could be an effective way of ameliorating this problem. In an 8-year field trial on an alkali soil, growth and biomass production ofProsopis juliflora was greater in sole stand than when interplanted with the grassLeptochloa fusca, but soil improvement was greater for the mixed tree-grass treatment.Prosopis accumulated substantially more biomass nutrients when in sole stand, but total nutrient recycling was similar with and without grass. Less salt tolerant but more palatable fodder crops such asTrifolium resupinatum, T. alexandrium andMelilotus denticulata were successfully grown withProsopis after removingL. fusca in theProsopis plus grass treatment 50 months after commencement. Tentative economic analysis suggests theProsopis plus grass system gives higher returns. TheProsopis-Leptochloa system combines production with biological reclamation, and is an appropriate form of reclamation agroforestry for alkali lands. 相似文献
166.
苦竹各器官主要营养元素分布及采伐的养分输出 总被引:3,自引:0,他引:3
本文根据四川长宁苦竹(Pleioblastus amarus)各器官生物量以及其主要营养元素含量和储量,研究了苦竹采伐的养分输出问题。结果表明:苦竹各器官中N、P、K、Si、Ca、Mg等6种营养元素以代谢旺盛的竹叶和竹鞭中含量最高;6种养分元素在各器官贮存量(单位:kg.hm-2)从大至小的排序为:叶(510.8)>竹根(230.62)>杆(182.14)>枝(163.77>竹鞭(59.19)>竹蔸(41.16)。苦竹采伐的养分年输出量(单位:kg.hm-2)从大至小的排序为:Si(50.23)>K(38.77)>N(35.58)>Mg(4.55)>P(3.86)>Ca(3.31)。对比该地区的降雨输入,苦竹林地养分以Si失衡最为严重;其次为K、N。若采伐时将竹叶带出竹林,6种元素的养分输出总量将增加1.48倍。可见,竹叶归还林地对维持地力具有极其重要的作用。 相似文献
167.
对20个杉木不同家系的苗木进行磷素营养要求试验,1年生苗木盆栽试验结果表明:杉木不同家系苗木对磷素营养反应敏感,2g磷处理使苗高、地径分别增益3.7%—96.5%、7.4%—61.1%,4g磷处理使苗高、地径分别增益2.1%—83.1%、3.7%—57.9%,杉木苗期需要磷素营养。三明38、三明67、三明48、三明58四个家系生长比较理想,在0g磷处理下,1年生平均苗高13.0—15.99cm,平均地径0.23—0.27cm,这4个家系具有更大的生长潜力,20个家系间对磷素营养要求方面不存在显著的差异。 相似文献
168.
169.
秦岭松栎林带生物量及其营养元素分布特征 总被引:22,自引:2,他引:22
秦岭脱齿栎林、油松林和华山林(包括0-60cm土层)营养元素总贮量达29.2500-390.1739t.hm^-2,其大小为锐齿栎林>华山松>油松林,土壤中营养现贮量占系统总量的93.10%-99.39%,植被层和凋落物层仅占0.57%-3.00%和0.10%-1.99%;3林分乔木层生物量、木材蓄积量和营养元素积累量平均值分别为120.483t.hm^-2,129.384m^3.hm^-2和1226.9kg.hm^-2,锐齿栎林>油松林>华山松林。3林分林下植被层生物量现存量和营养元素积累量平均值分别为1.553t.hm^-2和53.1kg.hm^-2,锐齿栎林最大,华山松林最小。林下凋落物现存量和营养元素积量平均值分别为17.475t.hm^-2和502.5kg.hm^-2,3林分凋落物现存量、营养元素含量及其积累量都存在明显的差异。锐齿栎林、油松林和华山松林营养元素年吸收量、归还量、存留量和平均归还率分别为33.4、147.2和264.3,195.6、66.9和84.1,138.8、80.4和180.2kg.hm^-2和0.585、0454和0.318,3林分各营养元素的年吸收量,归还量和存留量也存在一定的差异,锐齿栎林干和皮中Ca和Mg含量远远高于油松林和华山松林的,锐齿栎林多代连作势必导致营养元素的大量流失,特别是Ca和Mg,会破坏土壤原有离子动态平衡,引起林地土壤理化性质改变,林地生产潜力逐渐下降。 相似文献
170.
1983—1987年对湖北省武昌、宜昌、当阳县和陕西省城固县油橄榄中试园土壤与营养状况进行了研究。结果表明:油橄榄生长较好的(一类树下)土壤条件是pH7—8,CaCO_3>5%,有机质>1.8%,速效N>74.4—87.4mg/kg土,速效P>40mg/kg土,速效K>200mg/kg土,交换性Ca103—181mmol/kg土,交换性Mg24—34mmol/kg土。生长结实好的一类树叶片营养指标为N2.0—2.5%,P_2O_5 0.14%,K_2O 1.5%,CaO 4.0%,MgO 0.8%。通过分析建立了预测产量和施肥控制的回归方程。 相似文献